ARTICLE IN PRESS
JID: CCLET
[m5G;May 30, 2021;16:44]
Q. Zhang, Y. Wang, Y. Wang et al.
Chinese Chemical Letters xxx (xxxx) xxx
Fig. 2. (a) SEM images of blank CC. (b, c) SEM images of Co-1-P@CC. (d-f) Corre-
sponding elemental mapping of Co-1-P@CC.
clearly confirmed the electrodeposition and uniform distribution of
Co porphyrins on the surfaces of CC electrode. Moreover, the XPS
analysis of Co-1-P@CC showed signals attributed to Co 2p (796.8
and 780.6 eV), which is identical to that of Co-1-P molecular com-
plex, further confirming the presence of Co-1-P on CC electrode
(Fig. S17 in Supporting information). For Co-2-P, Co-1-P and Co-
2-C, XPS (Figs. S18–20 in Supporting information) and EDX ele-
mental mapping (Figs. S21–23 in Supporting information) results
clearly showed signals of Co, N and C, further confirming the pres-
ence of these Co porphyrins and corroles in their electrodeposited
films. Moreover, Co-1-P, Co-2-P, Co-1-C and Co-2-C were analyzed
by Raman. Comparing to the simply adsorbed monomeric Co por-
phyrin and Co corrole on CC electrodes, electropolymerized films
displayed the decrease of the ID/IG ratio (Figs. S24–27 in Support-
ing information). This result indicates that polymerization reaction
occurred between the molecules.
Fig. 1. Structure diagram of (a) Co-1-P, (b) Co-2-P, (c) Co-1-C, (d) Co-2-C.
Herein, we report the electropolymerization of Co porphyrins and
corroles on conductive carbon cloth (CC) electrode for OER.
Four monomeric cobalt porphyrins and corroles with differ-
ent functional groups were designed and used for polymeriza-
tion. Metal-free porphyrins, tetrakis(p-N-pyrrolylphenyl)porphyrin
(1-P) [54], tetrakis(thien-3-yl)-porphyrin (2-P) [55], 5,10,15-tris(4-
aminophenyl)corrole (1-C) [52,56] and 5,10,15-tris(3-thienyl)corrole
(2-C) [57,58] were synthesized by using literature methods, and
their purity was verified by mass spectrometry (Figs. S3, S5, S8, S10
in Supporting information). The reaction of porphyrin and corrole
ligands with Co salts afforded Co-1-P, Co-2-P, Co-1-C and Co-2-C,
respectively (Fig. 1). The purity of the bulk samples of Co-1-P, Co-
2-P, Co-1-C and Co-2-C was confirmed by mass spectrometry (Figs.
S4, S6, S9, S11 in Supporting information). The cyclic voltammo-
grams (CVs) of these Co complexes were recorded in dry acetoni-
trile solution containing 0.1 mol/L Bu4NPF6. In general, Co-1-P, Co-
2-P and Co-1-C showed two redox events, while Co-2-C showed
three redox events (Figs. S12–S15 in Supporting information). This
result also proved the purity of these four complexes.
A three-electrode system was selected to test the OER prop-
erty of electropolymerized samples in 0.1 mol/L KOH solutions. As
shown in Fig. 3a, the blank CC exhibited very poor catalytic cur-
rent of OER. The linear sweep voltammetry (LSV) of Co-1-P@CC
displayed a significant catalytic current with the onset potential
of 1.61 V versus RHE (reversible hydrogen electrode, all potentials
recorded in aqueous solutions are referenced to RHE unless oth-
erwise noted). This value corresponds to an onset overpotential
of 380 mV, which is smaller than those of Co-2-P@CC (409 mV),
Co-1-C@CC (430 mV) and Co-2-C@CC (405 mV). Particularly, Co-
1-P@CC revealed the highest current density under the same ap-
plied potentials (i.e., 1.75 V). Encouraged by the above results, we
also studied the effects of electroplating times on catalytic perfor-
mance. As shown in Fig. 3b, the catalytic current increased with
the increase of the electrodeposition CV cycle numbers. However,
Co-1-P is easily fallen away from the CC electrode after more than
60-cycle CV. Thus, CC electrodes electroplymerized through 60-
cycle CV were used for the following measurements. In addition,
we normalized the activity with the amount of Co contents on CC
electrode. The Co contents of four samples were determined by the
inductively coupled plasma mass spectrometry (ICP-MS, Table S1 in
Supporting information). As shown in Fig. 3c, Co-1-P@CC still dis-
played the highest catalytic performance. Tafel slope of Co-1-P@CC
(70.8 mV/dec) is smaller than that of Co-2-P@CC (85.5 mV/dec),
Co-1-C@CC (96.9 mV/dec) and Co-2-C@CC (156.3 mV/dec), indicat-
ing good kinetics during OER (Fig. 3d).
Electropolymerization was conducted by using a CC electrode as
the working electrode. The CC electrode was dipped into an ace-
tonitrile solution containing 0.1 mol/L Bu4NPF6 and a specific Co
complex (1 mmol/L) with the use of a carbon rod as the auxiliary
electrode and Ag/AgNO3 as the reference electrode [59,60]. After
60 cycles scanning between 0 V and 1.7 V (vs. ferrocene) under
N2, the working electrode was gently rinsed with dichloromethane
and ethanol, and then was finally dried at room temperature under
dark.
After electropolymerization, the resulted hybrids were analyzed
by X-ray photoelectron spectroscopy (XPS), scanning electron mi-
croscopy (SEM) and energy dispersive X-ray (EDX) element map-
ping, showing the absence of irregular particles of metal por-
phyrins and corroles (Fig. 2 and Fig. S16 in Supporting informa-
tion). As shown in Fig. 2, comparing to bare CC electrodes (Fig. 2a),
Co-1-P@CC exhibited significant complex loading (Fig. 2b). The
SEM image of Co-1-P@CC (Fig. 2c) and the corresponding EDX ele-
Controlled potential electrolysis (CPE) for OER in 0.1 mol/L KOH
solutions was performed to examine the catalyst stability. The cur-
rents of Co-1-P@CC were constant in 10 h electrolysis (Fig. 4a). The
2