- Oxysulfide photocatalyst for visible-light-driven overall water splitting
-
Oxysulfide semiconductors have narrow bandgaps suitable for water splitting under visible-light irradiation, because the electronegative sulfide ions negatively shift the valence band edges of the corresponding oxides1,2. However, the instability of sulfide ions during the water oxidation is a critical obstacle to simultaneous evolution of hydrogen and oxygen3. Here, we demonstrate the activation and stabilization of Y2Ti2O5S2, with a bandgap of 1.9 eV, as a photocatalyst for overall water splitting. On loading of IrO2 and Rh/Cr2O3 as oxygen and hydrogen evolution co-catalysts, respectively, and fine-tuning of the reaction conditions, simultaneous production of stoichiometric amounts of hydrogen and oxygen was achieved on Y2Ti2O5S2 during a 20 h reaction. The discovery of the overall water splitting capabilities of Y2Ti2O5S2 extends the range of promising materials for solar hydrogen production.
- Wang, Qian,Nakabayashi, Mamiko,Hisatomi, Takashi,Sun, Song,Akiyama, Seiji,Wang, Zheng,Pan, Zhenhua,Xiao, Xiong,Watanabe, Tomoaki,Yamada, Taro,Shibata, Naoya,Takata, Tsuyoshi,Domen, Kazunari
-
-
Read Online
- An artificial model of photosynthetic photosystem II: Visible-light-derived O2 production from water by a di-μ-oxo-bridged manganese dimer as an oxygen evolving center
-
Visible-light-derived O2 production was yielded by conjugating water oxidation catalysis by [(OH2)(terpy)Mn(μ-O) 2Mn(terpy)(OH2)]3+ as an oxygen evolving center model and photo-sensitization of [Ru(bpy)3]2+ as a photoexcitation center model at an interlayer of mica.
- Yagi, Masayuki,Toda, Mayuu,Yamada, Satoshi,Yamazaki, Hirosato
-
-
Read Online
- Photoinduced catalytic reaction by a fluorescent active cryptand containing an anthracene fragment
-
Tripping the light fantastic: A fluorescently active cryptand containing an anthracene fragment catalyzes the photoinduced reduction of CuII to CuI with simultaneous oxidation of water to oxygen (see scheme).
- Hao, Hong-Guo,Zheng, Xiao-Dan,Lu, Tong-Bu
-
-
Read Online
- 3d-4f {CoII3Ln(OR)4} Cubanes as Bio-Inspired Water Oxidation Catalysts
-
Although the {CaMn4O5} oxygen evolving complex (OEC) of photosystem II is a major paradigm for water oxidation catalyst (WOC) development, the comprehensive translation of its key features into active molecular WOCs remains challenging. The [CoII3Ln(hmp)4(OAc)5H2O] ({CoII3Ln(OR)4}; Ln = Ho-Yb, hmp = 2-(hydroxymethyl)pyridine) cubane WOC series is introduced as a new springboard to address crucial design parameters, ranging from nuclearity and redox-inactive promoters to operational stability and ligand exchange properties. The {CoII3Ln(OR)4} cubanes promote bioinspired WOC design by newly combining Ln3+ centers as redox-inactive Ca2+ analogues with flexible aqua-/acetate ligands into active and stable WOCs (max. TON/TOF values of 211/9 s-1). Furthermore, they open up the important family of 3d-4f complexes for photocatalytic applications. The stability of the {CoII3Ln(OR)4} WOCs under photocatalytic conditions is demonstrated with a comprehensive analytical strategy including trace metal analyses and solution-based X-ray absorption spectroscopy (XAS) investigations. The productive influence of the Ln3+ centers is linked to favorable ligand mobility, and the experimental trends are substantiated with Born-Oppenheimer molecular dynamics studies. (Chemical Equation Presented).
- Evangelisti, Fabio,Moré, René,Hodel, Florian,Luber, Sandra,Patzke, Greta Ricarda
-
-
Read Online
- Oxygen Vacancy Structure Associated Photocatalytic Water Oxidation of BiOCl
-
A central issue in understanding photocatalytic water splitting on a stoichiometric or defective nanostructured oxide surface is its adsorption mode and related reactivity. More than just improving the adsorption of water on oxide surfaces, we demonstrate in this work that surface oxygen vacancies (OVs) also offer a possibility of activating water toward thermodynamically enhanced photocatalytic water oxidation, while the water activation state, as reflected by its capability to trap holes, strongly depends on the structures of OVs. Utilizing well-ordered BiOCl single-crystalline surfaces, we reveal that dissociatively adsorbed water on the OV of the (010) surface exhibits higher tendency to be oxidized than the molecularly adsorbed water on the OV of the (001) surface. Analysis of the geometric atom arrangement shows that the OV of the BiOCl (010) surface can facilitate barrierless O-H bond breaking in the first proton removal reaction, which is sterically hindered on the OV of the BiOCl (001) surface, and also allow more localized electrons transfer from the OV to the dissociatively adsorbed water, leading to its higher water activation level for hole trapping. These findings highlight the indispensable role of crystalline surface structure on water oxidation and may open up avenues for the rational design of highly efficient photocatalysts via surface engineering. (Chemical Equation Presented).
- Li, Hao,Shang, Jian,Zhu, Huijun,Yang, Zhiping,Ai, Zhihui,Zhang, Lizhi
-
-
Read Online
- Catalytic water oxidation based on Ag(i)-substituted Keggin polyoxotungstophosphate
-
A 1D chain-like Ag(i)-substituted Keggin polyoxotungstophosphate, K3[H3AgIPW11O39]·12H2O, has been synthesized in a high yield and characterized by single-crystal X-ray diffraction, XRD, IR, TG/DTA and elemental analysis. When the polyoxotungstophosphate is dissolved in aqueous solutions, 31P NMR, MS and conductivity analyses indicate that a Ag(i) anion-complex formulated as [H3AgI(H2O)PW11O39]3- is formed and is stable in a solution of pH 3.5-7.0. The oxidation of [H3AgI(H2O)PW11O39]3- by S2O82- has been studied by ESR, UV-Visible spectroscopy, 31P NMR and UV-Raman spectroscopy. It was found that [H3AgI(H2O)PW11O39]3- can be oxidized to dominantly generate a dark green Ag(ii) anion-complex [H3AgII(H2O)PW11O39]2- and a small amount of Ag(iii) complex [H3AgIIIOPW11O39]3-, simultaneously evolving O2. Compared with [AgI(2,2′-bpy)NO3] and AgNO3, [H3AgI(H2O)PW11O39]3- has the higher activity in chemical water oxidation. This illustrates that the [PW11O39]7- ligand plays important roles in both the transmission of electrons and protons, and in the improvement of the redox performance of silver ions. The rate of O2 evolution is a first-order law with respect to the concentrations of [H3AgI(H2O)PW11O39]3- and S2O82-, respectively. A possible catalytic water oxidation mechanism of [H3AgI(H2O)PW11O39]3- is proposed, in which the [H3AgII(H2O)PW11O39]2- and [H3AgIIIOPW11O39]3- intermediates are determined and the rate-determining step is [H3AgIIIOPW11O39]3- oxidizing water into H2O2. This journal is
- Cui, Ying,Shi, Lei,Yang, Yanyi,You, Wansheng,Zhang, Lancui,Zhu, Zaiming,Liu, Meiying,Sun, Licheng
-
-
Read Online
- Mechanisms of water oxidation catalyzed by the cis,cis-[(bpy) 2Ru(OH2)]2O4+ ion
-
The cis,cis-[(bpy)2RuIII(OH2)] 2O4+ μ-oxo dimeric coordination complex is an efficient catalyst for water oxidation by strong oxidants that proceeds via intermediary formation of cis,cis-[(bpy)2RuV(O)]2O 4+ (hereafter, {5,5}). Repetitive mass spectrometric measurement of the isotopic distribution of O2 formed in reactions catalyzed by 18O-labeled catalyst established the existence of two reaction pathways characterized by products containing either one atom each from a ruthenyl O and solvent H2O or both O atoms from solvent molecules. The apparent activation parameters for μ-oxo ion-catalyzed water oxidation by Ce4+ and for {5,5} decay were nearly identical, with ΔH? = 7.6 (±1.2) kcal/mol, ΔS? = -43 (±4) cal/deg mol (23 °C) and ΔH? = 7.9 (±1.1) kcal/mol, ΔS? = -44 (±4) cal/deg mol, respectively, in 0.5 M CF3SO3H. An apparent solvent deuterium kinetic isotope effect (KIE) of 1.7 was measured for O2 evolution at 23 °C; the corresponding KIE for {5,5} decay was 1.6. The 32O2/ 34O2 isotope distribution was also insensitive to solvent deuteration. On the basis of these results and previously established chemical properties of this class of compounds, mechanisms are proposed that feature as critical reaction steps H2O addition to the complex to form covalent hydrates. For the first pathway, the elements of H2O are added as OH and H to the adjacent terminal ruthenyl O atoms, and for the second pathway, OH is added to a bipyridine ring and H is added to one of the ruthenyl O atoms.
- Yamada, Hiroshi,Siems, William F.,Koike, Tohru,Hurst, James K.
-
-
Read Online
- Cerium(IV)-driven water oxidation catalyzed by a manganese(V)-nitrido complex
-
The study of manganese complexes as water-oxidation catalysts (WOCs) is of great interest because they can serve as models for the oxygen-evolving complex of photosystem II. In most of the reported Mn-based WOCs, manganese exists in the oxidation states III or IV, and the catalysts generally give low turnovers, especially with one-electron oxidants such as CeIV. Now, a different class of Mn-based catalysts, namely manganese(V)-nitrido complexes, were explored. The complex [MnV(N)(CN)4]2- turned out to be an active homogeneous WOC using (NH4)2[Ce(NO3)6] as the terminal oxidant, with a turnover number of higher than 180 and a maximum turnover frequency of 6 min-1. The study suggests that active WOCs may be constructed based on the MnV(N) platform. High turnover: The study of manganese complexes as catalysts for the oxidation of water is of great interest as they can serve as models for the oxygen-evolving complex of photosystem II. The manganese(V)-nitrido complex [Mn(N)(CN)4]2- was now shown to catalyze the oxidation of water by cerium(IV) with a turnover number (TON) of higher than 180.
- Ma, Li,Wang, Qian,Man, Wai-Lun,Kwong, Hoi-Ki,Ko, Chi-Chiu,Lau, Tai-Chu
-
-
Read Online
- Mechanistic interpretation of CO oxidation turnover rates on supported Au clusters
-
Kinetic and isotopic data are used to interpret the mechanistic role of gaseous H2O molecules and of non-reducible (Al2O 3) and reducible (TiO2, Fe2O3) supports on CO oxidation turnovers catalyzed by small Au clusters (2O acts as a co-catalyst essential for O2 activation and for catalyst stability in CO oxidation at near-ambient temperatures, but also inhibits rates via competitive adsorption at higher H2O pressures. The effects of CO, O2, and H2O pressures on CO oxidation turnover rates, the absence of 16O2/18O 2 and 16O2/H218O exchange, and the small H2O/D2O kinetic isotope effects are consistent with quasi-equilibrated molecular adsorption of CO, O 2, and H2O on Au clusters with the kinetic relevance of H2O-mediated O2 activation via the formation of hydroperoxy intermediates (OOH), which account for the remarkable reactivity and H2O effects on Au clusters. These elementary steps proceed on Au clusters without detectable requirements for support interface sites, which are no longer required when H2O is present and mediates O2 activation steps. Rate enhancements by H2O were also observed for CO oxidation on Pt clusters (1.3 nm), which is also limited by O2 activation steps, suggesting H2O-aided O2 activation and OOH species in oxidations involving kinetically-relevant O2 activation. These intermediates have also been proposed to account for the ability of O2/H2O mixtures to act as reactants in alkene epoxidation on Au-based catalysts.
- Ojeda, Manuel,Zhan, Bi-Zeng,Iglesia, Enrique
-
-
Read Online
- Mechanistic studies of the oxygen evolution reaction by a cobalt-phosphate catalyst at neutral pH
-
The mechanism of the oxygen evolution reaction (OER) by catalysts prepared by electrodepositions from Co2+ solutions in phosphate electrolytes (Co-Pi) was studied at neutral pH by electrokinetic and 18O isotope experiments. Low-potential electrodepositions enabled the controlled preparation of ultrathin Co-Pi catalyst films (III-OH and CoIV-O in which a phosphate species is the proton acceptor, followed by a chemical turnover-limiting process involving oxygen-oxygen bond coupling.
- Surendranath, Yogesh,Kanan, Matthew W.,Nocera, Daniel G.
-
-
Read Online
- Dual function photocatalysis of cyano-bridged heteronuclear metal complexes for water oxidation and two-electron reduction of dioxygen to produce hydrogen peroxide as a solar fuel
-
The photocatalytic production of hydrogen peroxide from water and dioxygen under visible light irradiation was made possible by using polymeric cyano-bridged heteronuclear metal complexes (MII[RuII(CN)4(bpy)]; MII = NiII, FeII and MnII), where the photocatalytic two-electron reduction of O2 and water oxidation were catalysed by the Ru and MII moieties, respectively.
- Aratani, Yusuke,Suenobu, Tomoyoshi,Ohkubo, Kei,Yamada, Yusuke,Fukuzumi, Shunichi
-
-
Read Online
- An Oxofluoride Catalyst Comprised of Transition Metals and a Metalloid for Application in Water Oxidation
-
The application of the recently discovered oxofluoride solid solution (CoxNi1-x)3Sb4O6F6 as a catalyst for water oxidation is demonstrated. The phase exhibits a cubic arrangement of the active metal that forms oxo bridges to the metalloid with possible catalytic participation. The Co3Sb4O6F6 compound proved to be capable of catalyzing 2H2O→O2+4H++4e- at 0.33V electrochemical and ≤0.39V chemical overpotential with a TOF of 4.4 10-3, whereas Ni3Sb4O6F6 needs a higher overpotential. Relatively large crystal cubes (0.3-0.5mm) are easily synthesized and readily handled as they demonstrate both chemical resistance to wear after repeated insitu tests under experimental conditions, and have a mechanical hardness of 270V0.1 using Vickers indentation. The combined properties of this compound offer a potential technical advantage for incorporation to a catalytic interface in future sustainable fuel production.
- Svengren, Henrik,Hu, Shichao,Athanassiadis, Ioannis,Laine, Tanja M.,Johnsson, Mats
-
-
Read Online
- Structure-function relationships for electrocatalytic water oxidation by molecular [Mn12O12] clusters
-
A series of Mn12O12(OAc)16-xLx(H2O)4 molecular clusters (L = acetate, benzoate, benzenesulfonate, diphenylphosphonate, dichloroacetate) were electrocatalytically investigated as water oxidation electrocatalysts on a fluorine-doped tin oxide glass electrode. Four of the [Mn12O12] compounds demonstrated water oxidation activity at pH 7.0 at varying overpotentials (640-820 mV at 0.2 mA/cm2) and with high Faradaic efficiency (85-93%). For the most active complex, more than 200 turnovers were observed after 5 min. Two structure-function relationships for these complexes were developed. First, these complexes must undergo at least one-electron oxidation to become active catalysts, and complexes that cannot be oxidized in this potential window were inactive. Second, a greater degree of distortion at Mn1 and Mn3 centers correlated with higher catalytic activity. From this distortion analysis, either or both of these two Mn centers are proposed to be the catalytically active site.
- Yan, Yong,Lee, John S.,Ruddy, Daniel A.
-
-
Read Online
- Rate-Limiting O-O Bond Formation Pathways for Water Oxidation on Hematite Photoanode
-
Photoelectrochemical (PEC) water oxidation has attracted heightened interest in solar fuel production. It is well accepted that water oxidation on hematite is mediated by surface trapped holes, characterized to be the high valent -Fea?O species. However, the mechanism of the subsequent rate-limiting O-O bond formation step is still a missing piece. Herein we investigate the reaction order of interfacial hole transfer by rate law analysis based on electrochemical impedance spectroscopy (EIS) measurement and probe the reaction intermediates by operando Fourier-transform infrared (FT-IR) spectroscopy. Distinct reaction orders of ~1 and ~2 were observed in near-neutral and highly alkaline environments, respectively. The unity rate law in near-neutral pH regions suggests a mechanism of water nucleophilic attack (WNA) to -Fea?O to form the O-O bond. Operando observation of a surface superoxide species that hydrogen bonded to the adjacent hydroxyl group by FT-IR further confirmed this pathway. In highly alkaline regions, coupling of adjacent surface trapped holes (I2M) becomes the dominant mechanism. While both are operable at intermediate pHs, mechanism switch from I2M to WNA induced by local pH decrease was observed at high photocurrent level. Our results highlight the significant impact of surface protonation on O-O bond formation pathways and oxygen evolution kinetics on hematite surfaces.
- Zhang, Yuchao,Zhang, Hongna,Liu, Anan,Chen, Chuncheng,Song, Wenjing,Zhao, Jincai
-
-
Read Online
- Characterization of the O2-evolving reaction catalyzed by [(terpy)(H2O)MnIII(O)2MnIV (OH2(terpy)](NO3)3 (terpy = 2,2′:6,2″-terpyridine)
-
The complex [(terpy)(H2O)MnIII(O)2MnlV (OH2)(terpy)](NO3)3 (terpy = 2,2′:6,2″-terpyridine) (1) catalyzes O2 evolution from either KHSO5 (potassium oxone) or NaOC1. The reactions follow Michaelis-Menten kinetics where Vmax = 2420 ± 490 mol O2 (mol 1)-1 hr-1 and Km = 53 ± 5 mM for oxone ([1] = 7.5 μM), and Vmax = 6.5 ± 0.3 mol O2 (mol 1)-1 hr-1 and KM = 39 ± 4 mM for hypochlorite ([1] = 70 μM), with first-order kinetics observed in 1 for both oxidants. A mechanism is proposed having a preequilibrium between 1 and HSO5- or OCI-, supported by the isolation and structural characterization of [(terpy)-(SO4)MnIV(O)2MnlV (O4S)(terpy)] (2). Isotope-labeling studies using H218O and KHS16O5 show that O2 evolution proceeds via an intermediate that can exchange with water, where Raman spectroscopy has been used to confirm that the active oxygen of HSO5- is nonexchanging (t1/2 ? 1 h). The amount of label incorporated into O2 is dependent on the relative concentrations of oxone and 1.32O2:34O2:36 O2 is 91.9 ± 0.3:7.6 ± 0.3:0.51 ± 0.48, when [HSO5-] = 50 mM (0.5 mM 1), and 49 ± 21:39 ± 15:12 ± 6 when [HSO5-] = 15 mM (0.75 mM 1). The rate-limiting step of O2 evolution is proposed to be formation of a formally MnV=O moiety which could then competitively react with either oxone or water/hydroxide to produce O2. These results show that 1 serves as a functional model for photosynthetic water oxidation.
- Limburg,Vrettos,Chen,De Paula,Crabtree,Brudvig
-
-
Read Online
- UV-enhanced exchange of O2 with H2O adsorbed on TiO2
-
Ultraviolet light dramatically increases the rate of isotope exchange between gas-phase O2 and water adsorbed on TiO2 at room temperature, but it does not affect the rate of CO2-water exchange. Both ethanol and acetaldehyde, when coadsorbed with H218O, dramatically decrease the rate of O2 exchange, but not CO2 exchange, with adsorbed H218O. This decrease is attributed to a combination of competition for adsorbed oxygen between exchange and photocatalytic oxidation of the adsorbed organic and blocking of the oxygen adsorption sites by the organic. The same oxygen species participate in O2-H218O exchange and photocatalytic oxidation.
- Muggli, Darrin S.,Falconer, John L.
-
-
Read Online
- Sustained water oxidation photocatalysis by a bioinspired manganese cluster
-
(Chemical Equation Presented) The generation game: A manganese-oxo complex with a cubic {Mn4O4}7+ core catalyzes the electrooxidation of water when suspended within the aqueous channels of a Nafion membrane (see picture). Illumination with visible light under an applied potential of 1.0 V (vs Ag/AgCl) generates current over one thousand turnovers. The catalytically active species arises from photolysis and subsequent dissociation of the manganese complex.
- Brimblecombe, Robin,Swiegers, Gerhard F.,Dismukes, G. Charles,Spiccia, Leone
-
-
Read Online
- Visible light water oxidation using a Co-catalyst loaded anatase-structured Ti1-(5 x /4)NbxO2-y-δNy compound
-
The photocatalytic activity of anatase-structured Ti 1-(5x/4)NbxO2-y-δNy (x = 0.25, y = 0.02; NbN-25) was examined for water oxidation under UV and visible light irradiation. The semiconductor was prepared by sol-gel processing followed by nitridation in flowing ammonia and exhibits an indirect optical gap of 2.2 eV. Ti1-(5x/4)NbxO2-y-δNy was loaded with RuO2 by an impregnation technique, and optimized conditions reveal that 1 wt % RuO2 generates 16 μmol O2 from water with concomitant IO3- reduction after 3 h of illumination under simulated solar radiation at a flux of 600 mW/cm2 illumination, which corresponds to 6-sun AM1.5G illumination (compared to no detectible O2 without the RuO2 cocatalyst). A series of cut-on filters shows that the catalyst-loaded semiconductor evolves O 2 for λ ≤ 515 nm, and a gas-phase mass spectrometry isotope labeling experiment shows that irradiating an iodate solution in H 218O in the presence of 1 wt % RuO2 loaded on NbN-25 gives rise to catalytic water oxidation: both 36O2 and 34O2 are observed. It is unclear whether 16O arises from IO3- or surface reconstruction on the photocatalyst, but ICP-AES analysis of the postirradiated solution shows no dissolved metal ions.
- Breault, Tanya M.,Brancho, James J.,Guo, Ping,Bartlett, Bart M.
-
-
Read Online
- Unveiling the role of tetragonal BiVO4 as a mediator for dual phase BiVO4/g-C3N4 composite photocatalysts enabling highly efficient water oxidation: Via Z -scheme charge transfer
-
Monoclinic scheelite BiVO4 (BVO-M) based materials are of great interest as photocatalysts for water oxidation essential to produce value-added chemical fuels, but their slow charge transfer and low activity are yet to be resolved. As a solution to overcome this challenge, we report Z-scheme photocatalyst fabricated by integrating the dual phase structure of monoclinic scheelite and tetragonal zircon-type BiVO4 (BVO-T) moieties with graphitic carbon nitride (g-C3N4) having π-conjugated two dimensional layers suited to visible light-induced charge transfer. Moreover, V K-edge and Bi L3-edge X-ray absorption near-edge structure (XANES) and Fourier transformed extended X-ray absorption fine structure (EXAFS) spectra demonstrate that the tetragonal zircon-type BiVO4 structures in a Z-scheme catalyst form a bridge between BVO-M and g-C3N4 structures so that it acts as an electron mediator to accelerate charge transfer, in agreement with the zeta-potential analysis and the band structure revealed by UV-vis spectroscopy and ultraviolet photoelectron spectroscopy analyses. Furthermore, a Z-scheme photocatalyst is exhibited to show a 3-fold longer charge carrier lifetime than BVO-M, thereby enabling the greater than three-fold enhancement in photocatalytic water oxidation activity. Additionally, isotope 18O-labelling experiments reveal that evolved oxygen molecules result from water through photocatalytic water oxidation.
- Kong, Hyung Jun,Kim, Keon-Han,Kim, Sangjun,Kang, Jeung Ku,Lee, Heebin,Kang, Jeung Ku
-
-
Read Online
- Morphology-Controlled Self-Assembly and Nanostructured NiO: An Efficient and Robust Photocatalytic Water-Oxidation Catalyst
-
Three α-NiO nanocompounds of different morphology, with nanorods, nanowires, and nanoplates, were synthesized by controlling the ratio of reactants and temperature. The shape and structure of the nanocompounds were confirmed by SEM, XRD, FTIR, Raman spectroscopy, energy-dispersive X-ray spectroscopy, BET, and X-ray photoelectron spectroscopy (XPS) analysis. These compounds were examined as catalysts in photocatalytic water oxidation with [Ru(2,2′-bipyridine)3]2+ and S2O82- as a photosensitizer and a sacrificial oxidant, respectively. All of the samples exhibit high turnover frequencies and perfect stability in slightly alkaline conditions. A characteristic peak at around E=0.95 V versus Ag/AgCl assigned to a Ni3+ species was detected by cyclic voltammetry, which suggests that a high-valent nickel species may be responsible for water oxidation. The surface properties of the α-NiO nanorods also remain unchanged after examination by XPS before and after the photocatalytic reaction.
- Du, Xiaoqiang,Ding, Yong,Li, Chengqiang
-
-
Read Online
- Water oxidation by mononuclear ruthenium complexes with TPA-based ligands
-
The synthesis, characterization, and water oxidation activity of mononuclear ruthenium complexes with tris(2-pyridylmethyl)amine (TPA), tris(6-methyl-2-pyridylmethyl)amine (Me3TPA), and a new pentadentate ligand N,N-bis(2-pyridinylmethyl)-2,2′-bipyridine-6-methanamine (DPA-Bpy) have been described. The electrochemical properties of these mononuclear Ru complexes have been investigated by both experimental and computational methods. Using CeIV as oxidant, stoichiometric oxidation of water by [Ru(TPA)(H2O)2]2+ was observed, while Ru(Me3TPA)(H2O)2]2+ has much less activity for water oxidation. Compared to [Ru(TPA)(H2O) 2]2+ and [Ru(Me3TPA)(H2O) 2]2+, [Ru(DPA-Bpy)(H2O)]2+ exhibited 20 times higher activity for water oxidation. This study demonstrates a new type of ligand scaffold to support water oxidation by mononuclear Ru complexes.
- Radaram, Bhasker,Ivie, Jeffrey A.,Singh, Wangkheimayum Marjit,Grudzien, Rafal M.,Reibenspies, Joseph H.,Webster, Charles Edwin,Zhao, Xuan
-
-
Read Online
- Characterization of a Dinuclear MnV=O Complex and Its Efficient Evolution of O2 in the Presence of Water
-
A high valent MnV=O porphyrin dimer is prepared by peracid oxidation or an MnIII dimer under basic conditions at room temperature (see scheme; mCPBA = m-chloroperbenzoic acid). The addition of an acid to a solution of the MnV=O complex results in quantitative dioxygen evolution. Water and/or hydroxide ions are the sources of both the oxo ligand and the evolved dioxygen.
- Shimazaki, Yuichi,Nagano, Taro,Takesue, Hironori,Ye, Bao-Hui,Tani, Fumito,Naruta, Yoshinori
-
-
Read Online
- Water oxidation catalysed by iron complex of N,N′-dimethyl-2,11-diaza[3,3](2,6)pyridinophane. Spectroscopy of iron-oxo intermediates and density functional theory calculations
-
The macrocyclic [FeIII(L1)Cl2]+ (1, L1 = N,N′-dimethyl-2,11-diaza[3,3](2,6)pyridinophane) complex is an active catalyst for the oxidation of water to oxygen using [NH4]2[CeIV(NO3)6] (CAN), NaIO4, or Oxone as the oxidant. The mechanism of 1-catalysed water oxidation was examined by spectroscopic methods and by 18O-labelling experiments, revealing that FeIVO and/or FeVO species are likely to be involved in the reaction. The redox behaviour of 1 and these high-valent FeO species of L1 has been examined by both cyclic voltammetry and density functional theory (DFT) calculations. In aqueous solutions, the cyclic voltammograms of 1 at different pH show a pH-dependent reversible couple (E1/2 = +0.46 V vs. SCE at pH 1) and an irreversible anodic wave (Epa = +1.18 V vs. SCE at pH 1) assigned to the FeIII/FeII couple and the FeIII to FeIV oxidation, respectively. DFT calculations showed that the E value of the half reaction involving [FeV(L1)(O)(OH)]2+/[FeIV(L1)(O)(OH2)]2+ is +1.42 V vs. SCE at pH 1. Using CAN as the oxidant at pH 1, the formation of an FeIVO reaction intermediate was suggested by ESI-MS and UV-vis absorption spectroscopic measurements, and the rate of oxygen evolution was linearly dependent on the concentrations of both 1 and CAN. Using NaIO4 or Oxone as the oxidant at pH 1, the rate of oxygen evolution was linearly dependent on the concentration of 1, and a reactive FeVO species with formula [FeV(L1)(O)2]+ generated by oxidation with NaIO4 or Oxone was suggested by ESI-MS measurements. DFT calculations revealed that [FeV(L1)(O)2]+ is capable of oxidizing water to oxygen with a reaction barrier of 15.7 kcal mol-1.
- To, Wai-Pong,Wai-Shan Chow, Toby,Tse, Chun-Wai,Guan, Xiangguo,Huang, Jie-Sheng,Che, Chi-Ming
-
-
Read Online
- Resonance Raman evidence for the interconversion between an [Fe(III)-η1-OOH]2+ and [Fe(III)-η2-O2]+ species and mechanistic implications thereof
-
The deprotonation of [Fe(III)(N4Py)(η1-OOH)]2+ 1 gives [Fe(III)(N4Py)(η2-OO)]+ 2, as unequivocally demonstrated by resonance Raman spectroscopy, and leads to the loss of alkane hydroxylation activity by 1.
- Ho, Raymond Y. N.,Roelfes, Gerard,Hermant, Roel,Hage, Ronald,Feringa, Ben L.,Que Jr., Lawrence
-
-
Read Online
- Half-sandwich iridium complexes for homogeneous water-oxidation catalysis
-
Iridium half-sandwich complexes of the types Cp*Ir(N-C)X, [Cp*Ir(N-N)X]X, and [CpIr(N-N)X]X are catalyst precursors for the homogeneous oxidation of water to dioxygen. Kinetic studies with cerium(IV) ammonium nitrate as primary oxidant show that oxygen evolution is rapid and continues over many hours. In addition, [Cp*Ir(H2O) 3]SO4 and [(Cp*Ir)2(μ-OH) 3]OH can show even higher turnover frequencies (up to 20 min -1 at pH 0.89). Aqueous electrochemical studies on the cationic complexes having chelate ligands show catalytic oxidation at pH > 7; conversely, at low pH, there are no oxidation waves up to 1.5 V vs NHE for the complexes. H218O isotope incorporation studies demonstrate that water is the source of oxygen atoms during cerium(IV)-driven catalysis. DFT calculations and kinetic experiments, including kinetic-isotope-effect studies, suggest a mechanism for homogeneous iridium-catalyzed water oxidation and contribute to the determination of the rate-determining step. The kinetic experiments also help distinguish the active homogeneous catalyst from heterogeneous nanoparticulate iridium dioxide.
- Blakemore, James D.,Schley, Nathan D.,Balcells, David,Hull, Jonathan F.,Olack, Gerard W.,Incarvito, Christopher D.,Eisenstein, Odile,Brudvig, Gary W.,Crabtree, Robert H.
-
-
Read Online
- Pathways of water oxidation catalyzed by ruthenium "blue dimers" characterized by18O-lsotopic labeling
-
Earlier 18O-H2O labeling studies had indicated that two concurrent pathways may exist for water oxidation catalyzed by [Ru(bpy) 2(OH2)]2O4+, aμ-oxo bridged diruthenium complex known colloqu
- Cape, Jonathan L.,Siems, William F.,Hurst, James K.
-
-
Read Online
- Mechanistic Investigations of Water Oxidation by a Molecular Cobalt Oxide Analogue: Evidence for a Highly Oxidized Intermediate and Exclusive Terminal Oxo Participation
-
Artificial photosynthesis (AP) promises to replace societys dependence on fossil energy resources via conversion of sunlight into sustainable, carbon-neutral fuels. However, large-scale AP implementation remains impeded by a dearth of cheap, efficient catalysts for the oxygen evolution reaction (OER). Cobalt oxide materials can catalyze the OER and are potentially scalable due to the abundance of cobalt in the Earths crust; unfortunately, the activity of these materials is insufficient for practical AP implementation. Attempts to improve cobalt oxides activity have been stymied by limited mechanistic understanding that stems from the inherent difficulty of characterizing structure and reactivity at surfaces of heterogeneous materials. While previous studies on cobalt oxide revealed the intermediacy of the unusual Co(IV) oxidation state, much remains unknown, including whether bridging or terminal oxo ligands form O2 and what the relevant oxidation states are. We have addressed these issues by employing a homogeneous model for cobalt oxide, the [Co(III)4] cubane (Co4O4(OAc)4py4, py = pyridine, OAc = acetate), that can be oxidized to the [Co(IV)Co(III)3] state. Upon addition of 1 equiv of sodium hydroxide, the [Co(III)4] cubane is regenerated with stoichiometric formation of O2. Oxygen isotopic labeling experiments demonstrate that the cubane core remains intact during this stoichiometric OER, implying that terminal oxo ligands are responsible for forming O2. The OER is also examined with stopped-flow UV-visible spectroscopy, and its kinetic behavior is modeled, to surprisingly reveal that O2 formation requires disproportionation of the [Co(IV)Co(III)3] state to generate an even higher oxidation state, formally [Co(V)Co(III)3] or [Co(IV)2Co(III)2]. The mechanistic understanding provided by these results should accelerate the development of OER catalysts leading to increasingly efficient AP systems.
- Nguyen, Andy I.,Ziegler, Micah S.,O?a-Burgos, Pascual,Sturzbecher-Hohne, Manuel,Kim, Wooyul,Bellone, Donatela E.,Tilley, T. Don
-
-
Read Online
- Evidence of Mars-Van-Krevelen Mechanism in the Electrochemical Oxygen Evolution on Ni-Based Catalysts
-
Water oxidation is a crucial reaction for renewable energy conversion and storage. Among the alkaline oxygen evolution reaction (OER) catalysts, NiFe based oxyhydroxides show the highest catalytic activity. However, the details of their OER mechanism are still unclear, due to the elusive nature of the OER intermediates. Here, using a novel differential electrochemical mass spectrometry (DEMS) cell interface, we performed isotope-labelling experiments in 18O-labelled aqueous alkaline electrolyte on Ni(OH)2 and NiFe layered double hydroxide nanocatalysts. Our experiments confirm the occurrence of Mars-van-Krevelen lattice oxygen evolution reaction mechanism in both catalysts to various degrees, which involves the coupling of oxygen atoms from the catalyst and the electrolyte. The quantitative charge analysis suggests that the participating lattice oxygen atoms belong exclusively to the catalyst surface, confirming DFT computational hypotheses. Also, DEMS data suggest a fundamental correlation between the magnitude of the lattice oxygen mechanism and the faradaic efficiency of oxygen controlled by pseudocapacitive oxidative metal redox charges.
- Dionigi, Fabio,Ferreira de Araújo, Jorge,Merzdorf, Thomas,Oh, Hyung-Suk,Strasser, Peter
-
-
Read Online
- Light induced carbon dioxide reduction by water at binuclear ZrOCo II unit coupled to ir oxide nanocluster catalyst
-
An all-inorganic polynuclear unit consisting of an oxo-bridged binuclear ZrOCoII group coupled to an iridium oxide nanocluster (IrO x) was assembled on an SBA-15 silica mesopore surface. A photodeposition method was developed that affords coupling of the IrO x water oxidation catalyst with the Co donor center. The approach consists of excitation of the ZrOCoII metal-to-metal charge-transfer (MMCT) chromophore with visible light in the presence of [Ir(acac)3] (acac: acetylacetonate) precursor followed by calcination under mild conditions, with each step monitored by optical and infrared spectroscopy. Illumination of the MMCT chromophore of the resulting ZrOCoII-IrOx units in the SBA-15 pores loaded with a mixture of 13CO2 and H2O vapor resulted in the formation of 13CO and O 2 monitored by FT-IR and mass spectroscopy, respectively. Use of 18O labeled water resulted in the formation of 18O 2 product. This is the first example of a closed photosynthetic cycle of carbon dioxide reduction by water using an all-inorganic polynuclear cluster featuring a molecularly defined light absorber. The observed activity implies successful competition of electron transfer between the IrOx catalyst cluster and the transient oxidized Co donor center with back electron transfer of the ZrOCo light absorber, and is further aided by the instant desorption of the CO and O2 product from the silica pores.
- Kim, Wooyul,Yuan, Guangbi,McClure, Beth Anne,Frei, Heinz
-
-
Read Online
- Room Temperature Aerobic Peroxidation of Organic Substrates Catalyzed by Cobalt(III) Alkylperoxo Complexes
-
Room temperature aerobic oxidation of hydrocarbons is highly desirable and remains a great challenge. Here we report a series of highly electrophilic cobalt(III) alkylperoxo complexes, CoIII(qpy)OOR supported by a planar tetradentate quaterpyridine ligand that can directly abstract H atoms from hydrocarbons (R′H) at ambient conditions (CoIII(qpy)OOR + R′H → CoII(qpy) + R′?+ ROOH). The resulting alkyl radical (R′?) reacts rapidly with O2to form alkylperoxy radical (R′OO?), which is efficiently scavenged by CoII(qpy) to give CoIII(qpy)OOR′ (CoII(qpy) + R′OO?→ CoIII(qpy)OOR′). This unique reactivity enables CoIII(qpy)OOR to function as efficient catalysts for aerobic peroxidation of hydrocarbons (R′H + O2→ R′OOH) under 1 atm air and at room temperature.
- Chen, Yunzhou,Shi, Huatian,Lee, Chi-Sing,Yiu, Shek-Man,Man, Wai-Lun,Lau, Tai-Chu
-
supporting information
p. 14445 - 14450
(2021/09/18)
-
- A Novel Porous Ti-Squarate as Efficient Photocatalyst in the Overall Water Splitting Reaction under Simulated Sunlight Irradiation
-
A new porous titanium(IV) squarate metal–organic framework (MOF), denoted as IEF-11, having a never reported titanium secondary building unit, is successfully synthesized and fully characterized. IEF-11 not only exhibits a permanent porosity but also an outstanding chemical stability. Further, as a consequence of combining the photoactive Ti(IV) and the electroactive squarate, IEF-11 presents relevant optoelectronic properties, applied here to the photocatalytic overall water splitting reaction. Remarkably, IEF-11 as a photocatalyst is able to produce record H2 amounts for MOF-based materials under simulated sunlight (up to 672 μmol gcatalyst in 22 h) without any activity loss during at least 10 d.
- Salcedo-Abraira, Pablo,Babaryk, Artem A.,Montero-Lanzuela, Eva,Contreras-Almengor, Oscar R.,Cabrero-Antonino, María,Grape, Erik Svensson,Willhammar, Tom,Navalón, Sergio,Elk?im, Erik,García, Hermenegildo,Horcajada, Patricia
-
-
- Cobalt-Based Metal-Organic Cages for Visible-Light-Driven Water Oxidation
-
Water oxidation to molecular oxygen is indispensable but a challenge for splitting H2O. In this work, a series of Co-based metal-organic cages (MOCs) for photoinduced water oxidation were prepared. MOC-1 with both bis(μ-oxo) bridged dicobalt and Co-O (O from H2O) displays catalytic activity with an initial oxygen evolution rate of 80.4 mmol/g/h and a TOF of 7.49 × 10-3 s-1 in 10 min. In contrast, MOC-2 containing only Co-O (O from H2O) in the structure results in a lower oxygen evolution rate (40.8 mmol/g/h, 4.78 × 10-3 s-1), while the amount of oxygen evolved from the solution of MOC-4 without both active sites is undetectable. Isotope experiments with or without H218O as the reactant successfully demonstrate that the molecular oxygen was produced from water oxidation. Photophysical and electrochemical studies reveal that photoinduced water oxidation initializes via electron transfer from the excited [Ru(bpy)3]2+? to Na2S2O8, and then, the cobalt active sites further donate electrons to the oxidized [Ru(bpy)3]3+ to drive water oxidation. This proof-of-concept study indicates that MOCs can work as potential efficient catalysts for photoinduced water oxidation.
- Chen, Zi-Ye,Li, Dan,Long, Zi-Hao,Wang, Xu-Sheng,Wang, Xue-Zhi,Zhou, Jie-Yi,Zhou, Xiao-Ping
-
p. 10380 - 10386
(2021/07/21)
-
- A Metal-Free Donor–Acceptor Covalent Organic Framework Photocatalyst for Visible-Light-Driven Reduction of CO2 with H2O
-
Visible-light-driven CO2 reduction to valuable chemicals without sacrificial agents and cocatalysts remains challenging, especially for metal-free photocatalytic systems. Herein, a novel donor–acceptor (D–A) covalent organic framework (CT-COF) was constructed by the Schiff-base reaction of carbazole-triazine based D–A monomers and possessed a suitable energy band structure, strong visible-light-harvesting, and abundant nitrogen sites. CT-COF as a metal-free photocatalyst could reduce CO2 with gaseous H2O to CO as the main carbonaceous product with approximately stoichiometric O2 evolution under visible-light irradiation and without cocatalyst. The CO evolution rate (102.7 μmol g?1 h?1) was 68.5 times that of g-C3N4 under the same conditions. In situ Fourier-transform (FT)IR analysis indicated that CT-COF could adsorb and activate the CO2 and H2O molecules and that COOH* species may be a key intermediate. DFT calculations suggested that nitrogen atoms in the triazine rings may be photocatalytically active sites.
- Lei, Kai,Wang, Di,Ye, Liqun,Kou, Mingpu,Deng, Yu,Ma, Zhaoyu,Wang, Li,Kong, Yan
-
p. 1725 - 1729
(2020/03/11)
-
- Role of Lattice Oxygen in the Oxygen Evolution Reaction on Co3O4: Isotope Exchange Determined Using a Small-Volume Differential Electrochemical Mass Spectrometry Cell Design
-
This work demonstrates the role of lattice oxygen of metal oxide catalysts in the oxygen evolution reaction (OER) as evidenced by isotope labeling together with the differential electrochemical mass spectrometry (DEMS) method. Our recent report assessed this role for Co3O4 using a flow-through DEMS cell, which requires a large volume of electrolyte. Herein, we extend this procedure to different Co3O4 catalyst loadings and particle sizes as well as the mixed Ag + Co3O4 catalyst. We introduce, for the first time, a novel small-volume DEMS cell design capable of using disc electrodes and only 3O4 catalyst is higher than that on the single Co3O4 catalyst, which illustrates the improved electrocatalytic activity previously reported on this mixed catalyst. Furthermore, the real surface area of the catalysts is estimated using different methods (namely, the ball model, double layer capacitance, isotope exchange, and redox peak methods). The surface areas estimated from the Brunauer-Emmett-Teller (BET) and ball models are comparable but roughly three times higher than that of the redox peak method. Our method represents an alternative approach for probing the mechanism and real surface area of catalysts.
- Amin, Hatem M. A.,K?nigshoven, Peter,Hegemann, Martina,Baltruschat, Helmut
-
p. 12653 - 12660
(2019/10/11)
-
- Encapsulating Perovskite Quantum Dots in Iron-Based Metal–Organic Frameworks (MOFs) for Efficient Photocatalytic CO2 Reduction
-
Improving the stability of lead halide perovskite quantum dots (QDs) in a system containing water is the key for their practical application in artificial photosynthesis. Herein, we encapsulate low-cost CH3NH3PbI3 (MAPbI3) perovskite QDs in the pores of earth-abundant Fe-porphyrin based metal organic framework (MOF) PCN-221(Fex) by a sequential deposition route, to construct a series of composite photocatalysts of MAPbI3?PCN-221(Fex) (x=0–1). Protected by the MOF the composite photocatalysts exhibit much improved stability in reaction systems containing water. The close contact of QDs to the Fe catalytic site in the MOF, allows the photogenerated electrons in the QDs to transfer rapidly the Fe catalytic sites to enhance the photocatalytic activity for CO2 reduction. Using water as an electron source, MAPbI3?PCN-221(Fe0.2) exhibits a record-high total yield of 1559 μmol g?1 for photocatalytic CO2 reduction to CO (34 %) and CH4 (66 %), 38 times higher than that of PCN-221(Fe0.2) in the absence of perovskite QDs.
- Wu, Li-Yuan,Mu, Yan-Fei,Guo, Xiao-Xuan,Zhang, Wen,Zhang, Zhi-Ming,Zhang, Min,Lu, Tong-Bu
-
supporting information
p. 9491 - 9495
(2019/06/24)
-
- Engineering a CsPbBr3-based nanocomposite for efficient photocatalytic CO2 reduction: Improved charge separation concomitant with increased activity sites
-
Metal-halide perovskite nanocrystals have emerged as one of the promising photocatalysts in the photocatalysis field owing to their low-cost and excellent optoelectronic properties. However, this type of nanocrystals generally displays low activity in photocatalytic CO2 reduction owing to the lack of intrinsic catalytic sites and insufficient charge separation. Herein, we functionalized CsPbBr3 nanocrystals with graphitic carbon nitride, containing titanium-oxide species (TiO-CN) to develop an efficient composite catalyst system for photocatalytic CO2 reduction using water as the electron source. Compared to its congener with pristine CsPbBr3, the introduction of TiO-CN could not only increase the number of active sites, but also led to a swift interfacial charge separation between CsPbBr3 and TiO-CN due to their favorable energy-offsets and strong chemical bonding behaviors, which endowed this composite system with an obviously enhanced photocatalytic activity in the reduction of CO2 to CO with water as the sacrificial reductant. Over 3-fold and 6-fold higher activities than those of pristine CsPbBr3 nanocrystals and TiO-CN nanosheets, respectively, were observed under visible light irradiation. Our study provides an effective strategy for improving the photocatalytic activity of metal-halide perovskite nanocrystals, thus promoting their photocatalytic application in the field of artificial photosynthesis.
- Guo, Xiao-Xuan,Tang, Shang-Feng,Mu, Yan-Fei,Wu, Li-Yuan,Dong, Guang-Xing,Zhang, Min
-
p. 34342 - 34348
(2019/11/11)
-
- Rational Design of Crystalline Covalent Organic Frameworks for Efficient CO2 Photoreduction with H2O
-
Solar energy-driven conversion of CO2 into fuels with H2O as a sacrificial agent is a challenging research field in photosynthesis. Herein, a series of crystalline porphyrin-tetrathiafulvalene covalent organic frameworks (COFs) are synthesized and used as photocatalysts for reducing CO2 with H2O, in the absence of additional photosensitizer, sacrificial agents, and noble metal co-catalysts. The effective photogenerated electrons transfer from tetrathiafulvalene to porphyrin by covalent bonding, resulting in the separated electrons and holes, respectively, for CO2 reduction and H2O oxidation. By adjusting the band structures of TTCOFs, TTCOF-Zn achieved the highest photocatalytic CO production of 12.33 μmol with circa 100 % selectivity, along with H2O oxidation to O2. Furthermore, DFT calculations combined with a crystal structure model confirmed the structure–function relationship. Our work provides a new sight for designing more efficient artificial crystalline photocatalysts.
- Lu, Meng,Liu, Jiang,Li, Qiang,Zhang, Mi,Liu, Ming,Wang, Jin-Lan,Yuan, Da-Qiang,Lan, Ya-Qian
-
supporting information
p. 12392 - 12397
(2019/08/16)
-
- Role of water oxidation in the photoreduction of graphene oxide
-
By means of a H218O labeling experiment in combination with mass spectrometry tracking, we studied GO photoreduction. Observation of 18O labeled O2 provides direct evidence to confirm that water oxidation occurs during GO photoreduction. In combination with DFT calculations, we propose a mechanism for O2 and CO2 evolution in the photoreduction of GO.
- Li, Hongjiang,Song, Xuedan,Shi, Yantao,Gao, Yan,Si, Duanhui,Hao, Ce
-
p. 1837 - 1840
(2019/02/12)
-
- Artificial Photosynthesis of Methanol by Mn:CdS and CdSeTe Quantum Dot Cosensitized Titania Photocathode in Imine-Based Ionic Liquid Aqueous Solution
-
The artificial photosynthesis (APS) of carbon-based chemicals from CO2 and water is a promising strategy for solar energy conversion and storage. A new Mn-doped CdS and CdSeTe quantum dot cosensitized TiO2 photocathode was fabricated and applied to CO2 reduction in an APS cell with modified BiVO4 as the counter electrode. The 3 D structure of the photocathode constructed by Mn:CdS and CdSeTe quantum dots showed a high efficiency for light harvesting and electron transfer in this system to yield methanol at a rate of 90 μm h?1 cm?2 at ?0.9 V versus the saturated calomel electrode under 200 mW cm?2 irradiation. Methanol could also be produced by a two-electrode system under the same conditions. 13CO2-labeling experiments were performed to show that the carbon-based products are derived from CO2. A mechanism for CO2 reduction in this new APS cell was proposed based on the experimental results. In addition, headspace GC was used to quantify the products by an external standard method.
- Nie, Rong,Ma, Wenjie,Dong, Yapeng,Xu, Yanjie,Wang, Jinyuan,Wang, Jianguo,Jing, Huanwang
-
p. 3342 - 3350
(2018/08/24)
-
- Photoelectrochemical Reduction of CO2 Coupled to Water Oxidation Using a Photocathode with a Ru(II)-Re(I) Complex Photocatalyst and a CoOx/TaON Photoanode
-
Photoelectrochemical CO2 reduction activity of a hybrid photocathode, based on a Ru(II)-Re(I) supramolecular metal complex photocatalyst immobilized on a NiO electrode (NiO-RuRe), was confirmed in an aqueous electrolyte solution. Under half-reaction conditions, the NiO-RuRe photocathode generated CO with high selectivity, and its turnover number for CO formation reached 32 based on the amount of immobilized RuRe. A photoelectrochemical cell comprising a NiO-RuRe photocathode and a CoOx/TaON photoanode showed activity for visible-light-driven CO2 reduction using water as a reductant to generate CO and O2, with the assistance of an external electrical (0.3 V) and chemical (0.10 V) bias produced by a pH difference. This is the first example of a molecular and semiconductor photocatalyst hybrid-constructed photoelectrochemical cell for visible-light-driven CO2 reduction using water as a reductant.
- Sahara, Go,Kumagai, Hiromu,Maeda, Kazuhiko,Kaeffer, Nicolas,Artero, Vincent,Higashi, Masanobu,Abe, Ryu,Ishitani, Osamu
-
supporting information
p. 14152 - 14158
(2016/11/06)
-
- Kagóme Cobalt(II)-Organic Layers as Robust Scaffolds for Highly Efficient Photocatalytic Oxygen Evolution
-
Two Kagóme cobalt(II)-organic layers of [Co3(μ3-OH)2(bdc)2]n (1) and [Co3(μ3-OH)2(chdc)2]n (2) (bdc=o-benzenedicarboxylate and chdc=1,2-cyclohexanedicarboxylate) that bear bridging OH- ligands were explored as water oxidation catalysts (WOCs) for photocatalytic O2 production. The activities of 1 and 2 towards H2O oxidation were assessed by monitoring the in situ O2 concentration versus time in the reaction medium by utilizing a Clark-type oxygen electrode under photochemical conditions. The oxygen evolution rate (RO2) was 24.3 μmol s-1 g-1 for 1 and 48.8 μmol s-1 g-1 for 2 at pH 8.0. Photocatalytic reaction studies show that 1 and 2 exhibit enhanced activities toward the oxidation of water compared to commercial nanosized Co3O4. In scaled-up photoreactions, the pH value of the reaction medium decreased from 8.0 to around 7.0 after 20 min and the O2 production ceased. Based on the amounts of the sacrificial oxidant (K2S2O8) used, the yield of O2 produced is 49.6 % for 2 and 29.8 % for 1. However, the catalyst can be recycled without a significant loss of catalytic activity. Spectroscopic studies suggest that the structure and composition of recycled 1 and 2 are maintained. In isotope-labeling H218O (97 % enriched) experiments, the distribution of 16O16O/16O18O/18O18O detected was 0:7.55:92.45, which is comparable to the theoretical values of 0.09:5.82:94.09. This work not only provides new catalysts that resemble ligand-protected cobalt oxide materials but also establishes the significance of the existence of OH- (or H2O) binding sites at the metal center in WOCs. Water splitting: Two assembled cobalt(II)-carboxylate layers that bear bridging OH- ligands are explored as water oxidation catalysts for photocatalytic O2 production. Their activities towards H2O oxidation are assessed by monitoring the in situ O2 concentration versus time in the reaction medium by utilizing a Clark-type oxygen electrode under photochemical conditions.
- Xu, Jiaheng,Wang, Zhi,Yu, Wenguang,Sun, Di,Zhang, Qing,Tung, Chen-Ho,Wang, Wenguang
-
p. 1146 - 1152
(2016/06/01)
-
- An IrSi oxide film as a highly active water-oxidation catalyst in acidic media
-
We report an acid-stable Si oxide-doped Ir oxide film (IrSi oxide film), made by metal organic chemical vapour deposition (MOCVD) of an IrV complex for electrochemical water-oxidation. This is a successful improvement of catalytic ability and stability depending upon the pH of Ir oxide by doping of Si oxide. The turnover frequency (TOF) of the electrochemical water-oxidation by the IrSi oxide film is the highest of any Si oxide-doped Ir oxide materials and higher even than that of Ir oxide in acidic media.
- Tran, Viet-Ha,Yatabe, Takeshi,Matsumoto, Takahiro,Nakai, Hidetaka,Suzuki, Kazuharu,Enomoto, Takao,Hibino, Takashi,Kaneko, Kenji,Ogo, Seiji
-
p. 12589 - 12592
(2015/08/06)
-
- Efficient photocatalytic water oxidation catalyzed by polyoxometalate [Fe11(H2O)14(OH)2(W3O10)2(α-SbW9O33)6]27- based on abundant metals
-
An eleven iron-containing nanoscale inorganic polyanionic oxide cluster was reported as the first example for exceptional photocatalytic water oxidation. Under optimal conditions, a remarkable turn-over number (TON) of 1815 ± 50 and a turn-over frequency (TOFinitial) of 6.3 s-1 over 1 were achieved for water oxidation.
- Du, Xiaoqiang,Ding, Yong,Song, Fangyuan,Ma, Baochun,Zhao, Junwei,Song, Jie
-
p. 13925 - 13928
(2015/09/07)
-
- Catalytic oxidation of water and alcohols by a robust iron(III) complex bearing a cross-bridged cyclam ligand
-
An iron(III) complex bearing a cross-bridged cyclam ligand (4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane) is an efficient catalyst for the oxidation of both water and alcohols using sodium periodate as the oxidant. In catalytic water oxidation a maximum turnover number (TON) of 1030 is achieved, while in catalytic alcohol oxidation >95% conversions and yields can be obtained.
- Tan, Peng,Kwong, Hoi-Ki,Lau, Tai-Chu
-
supporting information
p. 12189 - 12192
(2015/07/27)
-
- Hexagonal nanoplates of NiO/CoO/Fe2O3 composite acting as an efficient photocatalytic and electrocatalytic water oxidation catalyst
-
A unique hexagonal sheet-shaped NiO/CoO/Fe2O3 composite with irregularly shaped nanoparticles was fabricated for the first time through a simple co-precipitation and hydrothermal method. The NiO/CoO/Fe2O3 composite was characterized by numerous techniques (TEM, HRTEM, PXRD, EDX, ICP-AES, BET, and XPS) to confirm its structure and composition. This structure of the NiO/CoO/Fe2O3 composite may enhance the photocatalytic and electrocatalytic performance for water oxidation. Compared with NiO, CoO and Fe2O3, the NiO/CoO/Fe2O3 composite exhibits a lower overpotential and a much smaller Tafel slope of 49 mV dec-1 for water oxidation. At the same time, the composite possesses beneficial ferromagnetic properties and superior stability; thus, it can be used repeatedly without any loss in activity.
- Zhao, Yukun,Zhang, Yan,Ding, Yong,Chen, Mindong
-
p. 15628 - 15635
(2015/09/07)
-
- Water Oxidation by Mononuclear Ruthenium Complex with a Pentadentate Isoquinoline-Bipyridyl Ligand
-
Mononuclear ruthenium complexes with a pentadentate ligand, N,N-bis[(isoquinolin-1-yl)methyl][6-(pyridin-2-yl)pyridin-2-yl]methanamine (DIQ-Bpy), were synthesized and characterized by 1H NMR spectroscopy, elemental analysis, electrochemistry, and theoretical calculations. The oxidation of water by [Ru(DIQ-Bpy)(H2O)]2+ was observed in the presence of excess amounts of CeIV. Relative to [Ru(DPA-Bpy)(H2O)]2+ [DPA-Bpy = N,N-bis(2-pyridinylmethyl) -2,2-bipyridine-6-methanamine], the substitution of pyridine groups in DPA-Bpy with electron-withdrawing isoquinolines results in higher redox potential and lower activity for the oxidation of water by [Ru(DIQ-Bpy)(H2O)] 2+. A kinetic study of water oxidation by [Ru(DPA-Bpy)(H 2O)]2+ suggests a mononuclear pathway for the oxidation of water. The noncovalent interaction between isoquinoline groups in [Ru(DIQ-Bpy)(H2O)]2+, which favors the formation of dinuclear species, might account for the lower activity for water oxidation by [Ru(DIQ-Bpy)(H2O)]2+. Mononuclear Ru complexes with a pentadentate ligand, N,N-bis[(isoquinolin-1-yl)methyl][6-(pyridin-2-yl)pyridin- 2-yl]methanamine (DIQ-Bpy), were synthesized and characterized. The effects of isoquinoline groups on the electrochemistry and the activity of [Ru(DIQ-Bpy)(H2O)]2+ on water oxidation are discussed. Copyright
- Vennampalli, Manohar,Liang, Guangchao,Webster, Charles Edwin,Zhao, Xuan
-
supporting information
p. 715 - 721
(2014/03/21)
-
- Hexagonal assembly of Co3V2O8 nanoparticles acting as an efficient catalyst for visible light-driven water oxidation
-
Co3V2O8, a uniform hexagonal sheet-shaped morphology, for the first time acted as a robust catalyst for water oxidation. Under optimal photocatalytic conditions (photoirradiation at λ ≥ 420 nm, Ru(bpy)3Cl2 as the photosensitizer, Na2S2O8 as the oxidant in borate buffer at pH = 8.5), the optimum apparent TOF of 10.9 μmol s-1 m-2 and O2 initial evolution rate of 31.7 μmol s-1 g-1 were achieved, which, to our best knowledge, are the highest values reported for heterogeneous photocatalytic water oxidation to date. Variables of the photocatalytic reaction, including catalyst concentrations, pH, dye concentrations and oxidant concentrations, were systemically studied. The oxygen atoms of the evolved oxygen came from water, as confirmed by isotope-labeled experiments. The stability of Co3V2O8 was tested and confirmed with multiple experiments (FT-IR, XRD, XPS), which indicated that Co3V2O8 is a stable catalyst under water oxidation. In addition, a mechanism of Co3V2O8 for the process of water oxidation was proposed.
- Zhao, Yukun,Liu, Yongdong,Du, Xiaoqiang,Han, Ruixin,Ding, Yong
-
p. 19308 - 19314
(2015/02/18)
-
- Water oxidation by mononuclear ruthenium complex with a pentadentate isoquinoline-bipyridyl ligand
-
Mononuclear ruthenium complexes with a pentadentate ligand, N,N-bis[(isoquinolin-1-yl)methyl][6-(pyridin-2-yl)pyridin-2-yl]methanamine (DIQ-Bpy), were synthesized and characterized by 1H NMR spectroscopy, elemental analysis, electrochemistry, and theoretical calculations. The oxidation of water by [Ru(DIQ-Bpy)(H2O)]2+ was observed in the presence of excess amounts of CeIV. Relative to [Ru(DPA-Bpy)(H2O)]2+ [DPA-Bpy = N,N-bis(2-pyridinylmethyl)-2,2-bipyridine-6-methanamine], the substitution of pyridine groups in DPA-Bpy with electron-withdrawing isoquinolines results in higher redox potential and lower activity for the oxidation of water by [Ru(DIQ-Bpy)(H2O)]2+. A kinetic study of water oxidation by [Ru(DPA-Bpy)(H2O)]2+ suggests a mononuclear pathway for the oxidation of water. The noncovalent interaction between isoquinoline groups in [Ru(DIQ-Bpy)(H2O)]2+, which favors the formation of dinuclear species, might account for the lower activity for water oxidation by [Ru(DIQ-Bpy)(H2O)]2+.
- Vennampalli, Manohar,Liang, Guangchao,Webster, Charles Edwin,Zhao, Xuan
-
p. 715 - 721
(2015/04/27)
-
- Light-harvesting photocatalysis for water oxidation using mesoporous organosilica
-
An organic-based photocatalysis system for water oxidation, with visible-light harvesting antennae, was constructed using periodic mesoporous organosilica (PMO). PMO containing acridone groups in the framework (Acd-PMO), a visible-light harvesting antenna, was supported with [RuII(bpy) 32+] complex (bpy=2,2'-bipyridyl) coupled with iridium oxide (IrOx) particles in the mesochannels as photosensitizer and catalyst, respectively. Acd-PMO absorbed visible light and funneled the light energy into the Ru complex in the mesochannels through excitation energy transfer. The excited state of Ru complex is oxidatively quenched by a sacrificial oxidant (Na2S2O8) to form Ru 3+ species. The Ru3+ species extracts an electron from IrOx to oxidize water for oxygen production. The reaction quantum yield was 0.34 %, which was improved to 0.68 or 1.2 % by the modifications of PMO. A unique sequence of reactions mimicking natural photosystem II, 1) light-harvesting, 2) charge separation, and 3) oxygen generation, were realized for the first time by using the light-harvesting PMO. The lining's on the wall: A photocatalysis system for water oxidation linked with a solid light-harvesting antenna was constructed using periodic mesoporous organosilica (PMO), mimicking photosystem II. The acridone-containing PMO absorbed visible light and funneled the light energy into [Ru(bpy)3]2+ complex fixed in the mesochannels. Oxygen was evolved on IrOx nanoparticles deposited on the pore surface (see figure; bpy=2,2'-bipyridine).
- Takeda, Hiroyuki,Ohashi, Masataka,Goto, Yasutomo,Ohsuna, Tetsu,Tani, Takao,Inagaki, Shinji
-
supporting information
p. 9130 - 9136
(2014/07/22)
-
- Water oxidation catalysis with nonheme iron complexes under acidic and basic conditions: Homogeneous or heterogeneous?
-
Thermal water oxidation by cerium(IV) ammonium nitrate (CAN) was catalyzed by nonheme iron complexes, such as Fe(BQEN)(OTf)2 (1) and Fe(BQCN)(OTf)2 (2) (BQEN = N,N′-dimethyl-N,N′-bis(8- quinolyl)ethane-1,2-diamine, BQCN = N,N′-dimethyl-N,N′-bis(8- quinolyl)cyclohexanediamine, OTf = CF3SO3-) in a nonbuffered aqueous solution; turnover numbers of 80 ± 10 and 20 ± 5 were obtained in the O2 evolution reaction by 1 and 2, respectively. The ligand dissociation of the iron complexes was observed under acidic conditions, and the dissociated ligands were oxidized by CAN to yield CO2. We also observed that 1 was converted to an iron(IV)-oxo complex during the water oxidation in competition with the ligand oxidation. In addition, oxygen exchange between the iron(IV)-oxo complex and H 218O was found to occur at a much faster rate than the oxygen evolution. These results indicate that the iron complexes act as the true homogeneous catalyst for water oxidation by CAN at low pHs. In contrast, light-driven water oxidation using [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine) as a photosensitizer and S2O8 2- as a sacrificial electron acceptor was catalyzed by iron hydroxide nanoparticles derived from the iron complexes under basic conditions as the result of the ligand dissociation. In a buffer solution (initial pH 9.0) formation of the iron hydroxide nanoparticles with a size of around 100 nm at the end of the reaction was monitored by dynamic light scattering (DLS) in situ and characterized by X-ray photoelectron spectra (XPS) and transmission electron microscope (TEM) measurements. We thus conclude that the water oxidation by CAN was catalyzed by short-lived homogeneous iron complexes under acidic conditions, whereas iron hydroxide nanoparticles derived from iron complexes act as a heterogeneous catalyst in the light-driven water oxidation reaction under basic conditions.
- Hong, Dachao,Mandal, Sukanta,Yamada, Yusuke,Lee, Yong-Min,Nam, Wonwoo,Llobet, Antoni,Fukuzumi, Shunichi
-
p. 9522 - 9531
(2013/09/12)
-
- Electrochemical water splitting by gold: Evidence for an oxide decomposition mechanism
-
In this paper we study through a multiplicity of experimental and theoretical techniques the electrochemical evolution of oxygen on gold, the metal on which water splitting was initially discovered more than two centuries ago. The evidence obtained with a combination of in situ surface-enhanced Raman spectroscopy, online electrochemical mass spectrometry and density functional theory calculations suggests the existence of several mechanisms for the evolution of O2 on Au electrodes, depending on the electrode potential. Significantly, at approximately 2.0 V vs. RHE the first O2 that is evolved consists of two oxygens from the surface oxide, suggesting an oxide decomposition or oxide disproportionation step. At somewhat higher potentials, O2 is formed by a combination of oxygen from the oxide lattice and oxygen provided by water. The oxide decomposition step implies a more three-dimensional mechanism for oxygen evolution than suggested in previous mechanisms, which involve only surface-adsorbed intermediates.
- Diaz-Morales, Oscar,Calle-Vallejo, Federico,De Munck, Casper,Koper, Marc T.M.
-
p. 2334 - 2343
(2013/07/19)
-
- Investigation of the selective catalytic reduction of nitric oxide with ammonia over Mn/TiO2 catalysts through transient isotopic labeling and in situ FT-IR studies
-
The transient isotopic labeling studies were performed under steady state conditions by using 15N (15NO and 15NH 3) and 18O (18O2) containing species to investigate the reaction
- Ettireddy, Padmanabha Reddy,Ettireddy, Neeraja,Boningari, Thirupathi,Pardemann, Robert,Smirniotis, Panagiotis G.
-
-
- Synthesis of water and molecular oxygen highly enriched in 17O and 18O isotopes from carbon oxides
-
The reaction of carbon oxides and hydrogen in the presence of the Raney nickel catalyst has been used for water synthesis. A procedure has been developed for the recovery and collection of the synthesized water with minimal losses and without deteriorating the 17O or 18O isotope enrichment as compared to the initial CO2 and CO. The recovery of oxygen with high concentrations of 17O and 18O isotopes is based on the reaction of xenon difluoride with water. The yield based on oxygen achieves 99% without reduction of isotope enrichment, which is confirmed by mass-spectral measurements of oxygen isotope concentrations in the initial reagents and final reaction products. Pleiades Publishing, Ltd., 2011.
- Artyukhov,Kravets,Artyukhov,Babichev,Ryzhkov
-
p. 335 - 337
(2011/08/22)
-
- Water oxidation by a mononuclear ruthenium catalyst: Characterization of the intermediates
-
A detailed characterization of intermediates in water oxidation catalyzed by a mononuclear Ru polypyridyl complex [RuII-OH2] 2+ (Ru = Ru complex with one 4-t-butyl-2,6-di-(1′,8′- naphthyrid-2′-yl)-pyridine ligand and two 4-picoline ligands) has been carried out using electrochemistry, UV-vis and resonance Raman spectroscopy, pulse radiolysis, stopped flow, and electrospray ionization mass spectrometry (ESI-MS) with H218O labeling experiments and theoretical calculations. The results reveal a number of intriguing properties of intermediates such as [RuIV=O]2+ and [Ru IV-OO]2+. At pH > 2.9, two consecutive proton-coupled one-electron steps take place at the potential of the [RuIII-OH] 2+/[RuII-OH2]2+ couple, which is equal to or higher than the potential of the [RuIV=O] 2+/[RuIII-OH]2+ couple (i.e., the observation of a two-electron oxidation in cyclic voltammetry). At pH 1, the rate constant of the first one-electron oxidation by Ce(IV) is k1 = 2 × 104 M-1 s-1. While pH-independent oxidation of [RuIV=O]2+ takes place at 1420 mV vs NHE, bulk electrolysis of [RuII-OH2]2+ at 1260 mV vs NHE at pH 1 (0.1 M triflic acid) and 1150 mV at pH 6 (10 mM sodium phosphate) yielded a red colored solution with a Coulomb count corresponding to a net four-electron oxidation. ESI-MS with labeling experiments clearly indicates that this species has an O-O bond. This species required an additional oxidation to liberate an oxygen molecule, and without any additional oxidant it completely decomposed slowly to form [RuII-OOH]+ over 2 weeks. While there remains some conflicting evidence, we have assigned this species as 1[RuIV-·2-OO]2+ based on our electrochemical, spectroscopic, and theoretical observations alongside a previously reported analysis by T. J. Meyer group (J. Am. Chem. Soc. 2010, 132, 1545-1557).
- Polyansky, Dmitry E.,Muckerman, James T.,Rochford, Jonathan,Zong, Ruifa,Thummel, Randolph P.,Fujita, Etsuko
-
p. 14649 - 14665
(2011/10/12)
-
- Oxygen evolution from BF3/MnO4-
-
MnO4- is activated by BF3 to undergo intramolecular coupling of two oxo ligands to generate O2. DFT calculations suggest that there should be a spin intercrossing between the singlet and triplet potential energy surfaces on going from the active intermediate [MnO2(OBF3)2]- to the O...O coupling transition state.
- Yiu, Shek-Man,Man, Wai-Lun,Wang, Xin,Lam, William W. Y.,Ng, Siu-Mui,Kwong, Hoi-Ki,Lau, Kai-Chung,Lau, Tai-Chu
-
p. 4159 - 4161
(2011/06/19)
-
- Electronic modification of the [RuII(tpy)(bpy)(OH 2)]2+ scaffold: Effects on catalytic water oxidation
-
The mechanistic details of the Ce(IV)-driven oxidation of water mediated by a series of structurally related catalysts formulated as [Ru(tpy)(L)(OH 2)]2+ [L = 2,2′-bipyridine (bpy), 1; 4,4′-dimethoxy-2,2′-bipyridine (bpy-OMe), 2; 4,4′-dicarboxy-2, 2′-bipyridine (bpy-CO2H), 3; tpy = 2,2′6″,2″- terpyridine] is reported. Cyclic voltammetry shows that each of these complexes undergo three successive (proton-coupled) electron-transfer reactions to generate the [RuV(tpy)(L)O]3+ ([RuV=O] 3+) motif; the relative positions of each of these redox couples reflects the nature of the electron-donating or withdrawing character of the substituents on the bpy ligands. The first two (proton-coupled) electron-transfer reaction steps (k1 and k2) were determined by stopped-flow spectroscopic techniques to be faster for 3 than 1 and 2. The addition of one (or more) equivalents of the terminal electron-acceptor, (NH4)2[Ce(NO3)6] (CAN), to the [RuIV(tpy)(L)O]2+ ([RuIV=O] 2+) forms of each of the catalysts, however, leads to divergent reaction pathways. The addition of 1 eq of CAN to the [RuIV=O] 2+ form of 2 generates [RuV=O]3+ (k3 = 3.7 M-1 s-1), which, in turn, undergoes slow O-O bond formation with the substrate (kO-O = 3 × 10-5 s -1). The minimal (or negligible) thermodynamic driving force for the reaction between the [RuIV=O]2+ form of 1 or 3 and 1 eq of CAN results in slow reactivity, but the rate-determining step is assigned as the liberation of dioxygen from the [RuIV-OO]2+ level under catalytic conditions for each complex. Complex 2, however, passes through the [RuV-OO]3+ level prior to the rapid loss of dioxygen. Evidence for a competing reaction pathway is provided for 3, where the [Ru V=O]3+ and [RuIII-OH]2+ redox levels can be generated by disproportionation of the [RuIV=O]2+ form of the catalyst (kd = 1.2 M-1 s-1). An auxiliary reaction pathway involving the abstraction of an O-atom from CAN is also implicated during catalysis. The variability of reactivity for 1-3, including the position of the RDS and potential for O-atom transfer from the terminal oxidant, is confirmed to be intimately sensitive to electron density at the metal site through extensive kinetic and isotopic labeling experiments. This study outlines the need to strike a balance between the reactivity of the [Ru=O]z unit and the accessibility of higher redox levels in pursuit of robust and reactive water oxidation catalysts.
- Wasylenko, Derek J.,Ganesamoorthy, Chelladurai,Henderson, Matthew A.,Koivisto, Bryan D.,Osthoff, Hans D.,Berlinguette, Curtis P.
-
p. 16094 - 16106
(2011/02/17)
-