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ChemComm
DOI: 10.1039/C5CC06730H
COMMUNICATION
Journal Name
19
chalcogenides such as NiSe are reported to decrease as a function Pd Se shows very good electrocatalytic activity and this opens up
4
of cycling while the palladium selenides are found to be very stable. ways of reducing the noble metal content in catalysts of interest.
The phase purity of the selenides after cycling for 3000 cycles is Notes and references
confirmed using SEM and XRD analyses (Figure S14,S15) and there
is no significant change observed and the compositions of the
phases remain unaltered after three thousand cycles of HER. The
stability in alkaline conditions (1M KOH and 1M NaOH) has also
been tested by cycling the electrode and checking the XRD patterns
before and after the voltammetry studies. It is found that the phase
purity is retained even after 1000 continuous cycles (Fig. S19). The
XPS data confirm these observations on the stability of palladium
selenide phases (Fig. S21). It is clear that any local, interfacial pH
change that may occur during HER does not degrade the material.
The activities of electrocatalysts also depend on the number of
active sites for H-adsorption which in-turn depends on the
electrochemical surface area of the material. The active surface
areas of the three phases are determined using underpotential
1
2
3
4
N. S. Lewis and D. G. Nocera, Proc. Natl. Acad. Sci. U. S. A., 2006,
103, 15729.
N. R. Udengaard, Prepr. Pap.-Am. Chem. Soc. Div. Fuel Chem.,
2
004, 49, 906.
J. O. M. Bockris, I. A. Ammar and A. K. M. S. Huq, J. Phys. Chem.,
957, 61, 879.
(a) V. Ritleng, C. Sirlin and M. Pfeffer, Chem. Rev., 2002, 102,
731; (b) B. Lim, M. Jiang, P. H. Camargo, E. C. Cho, J. Tao, X. Lu,
1
1
Y. Zhu and Y. Xia, Science, 2009, 324, 1302; (c) A. Kudo and Y.
Miseki, Chem. Soc. Rev., 2009, 38, 253.
(a) L.-L. Long, A.-Y. Zhang, Y.-X. Huang, X. Zhanga and H.-Q. Yu,
J. Mater. Chem. A, 2015, 3, 4301; (b) Q. Chen, C. Suo, S. Zhang
and Y. Wang, Int. J. Photoenergy, 2013, 2013, 1.
(a) X. Jiang, B. Mayers, Y. Wang, B. Cattle and Y. Xia, Chem.
Phys. Lett., 2004, 385, 472; (b) Madhu and R. N. Singh, Int. J.
Hyd. Energy, 2011, 36, 10006; (c) S. Geller, Acta Crystallogr.,
1962, 15, 713; (d) M. Afzaal, M. A. Malik and P. O’Brien, J.
Mater. Chem., 2010, 20, 4031.
5
6
deposition of copper. The electrochemical surface areas of Pd17Se15
Pd Se and Pd Se phases are found to be 0.048, 0.72 and 1 m /g
7 4 4
,
2
respectively (Fig. S16).To understand and compare the activities of
different phases of palladium selenides, density functional theory
7
P. L. Musetha, N. Revaprasadu, G. A. Kolawole, R. V. S. R.
Pullabhotla, K. Ramasamy and P. O'Brien, Thin Solid Films, 2010,
2
0,21
(DFT) calculations are carried out
and the details are given in
5
19, 197.
the supporting information. The availability of d-band density of
states (DOS) at the Fermi level is generally correlated with the
electrocatalytic acivity . It is found that the Pd d-band DOS are
found to be higher and placed exactly above the fermi level in the
8
9
L. B. Kumbhare, V. K. Jain, P. P. Phadnis and M. Nethaji, J.
Organomet. Chem., 2007, 692, 1546.
(a) H. Joshi, K. N. Sharma, A. K. Sharma, Om Prakash and A. K.
Singh, Chem. Commun., 2013, 49, 7483; (b) K.Suresh, S N
Karthick and S Sampath, J.Mater.Chem A., 2015, DOI:
22
case of Pd
The selenium contribution at the Fermi level is found to be very
small for Pd Se while it becomes fairly considerable in the case of
the other two phases. Additionally, the positive charge on Pd (as
given in XPS data earlier) is smaller in the case of Pd Se as
4
Se while in the other two cases, it is not (Figs. S17, S18).
1
0.1039/c5ta04956c
1
0 H. R. Naren, A. Tamizhavel and S. Ramakrishan, J. Phys.: Conf.
Ser., 2011, 273, 012074.
1 J. Muller and A. Terfort, Inorg. Chim. Acta, 2006, 359, 4821.
2 N.S. John, G.U. Kulkarni, A. Datta, S.K. Pati, F. Komori, G.
Kavitha, C. Narayana and M.K. Sanyal, J. Phys. Chem. C, 2007,
4
1
1
4
compared to the other two, based on the shift in binding energy
values (Table S2). The binding energy value for Pd (0) is 335.1 eV
1
11, 1868.
while the values are 335.3 eV for Pd
the other two phases. This is in parallel to the observation based on
charge density analysis performed on the three selenides. The 14 (a) A. B. Volynski, A. Yu. Stakheev, N. S. Telegina, V. G. Senin, L.
M. Kustov and R. Wennrich, Spectrochim. Acta Part B, 2001, 56,
387; (b) V. V. Singh, U. Kumar, S. N. Tripathi and A. K. Singh,
4
Se and 336.3 and 336.7 eV for 13 G. K. Rao, A. Kumar, B. Kumar and A. K. Singh, Dalton Trans.,
2012, 41, 4306.
average charge on Pd is smaller in the case of Pd
4
Se (0.05) and
1
increases when the phases are Pd Se (0.12) and subsequently
7
4
Dalton Trans., 2014, 43, 12555; (c) J. Zhang, Y. Xu and B.
Zhang, Chem. Commun., 2014, 50, 13451.
Pd17Se15 (0.17) (Table S5). It should be noted that there are Pd
atoms with different environment in the structures of the palladium
2
3
15 (a) X. J. Bian, J. Zhu, L. Liao, M. D. Scanlon, P. Y. Ge, C. Ji, H. H.
Girault and B. H. Liu, Electrochem. Commun., 2012, 22, 128; (b)
V. Kiran, D. Mukherjee, R. N. Jenjeti and S. Sampath, Nanoscale,
selenides and hence an average charge is given for comparative
purposes. As a consequence, the oxidation state of Pd in Pd Se is
smaller than that of the other two phases. This possibly will help in
the effective adsorption of protons on Pd Se as compared to the 16 Y. Li, H. Wang, L. Xie, Y. Liang, G. Hong and H. Dai, J. Am. Chem.
Pd Se and Pd17Se15. Of course, this is true when the adsorption Soc., 2011, 133, 7296.
sites are composed only of palladium. It is likely so since palladium 17 (a) Y. Takasu, Y. Fujii, K. Yasuda, Y. Iwanaga and Y.
4
2
014, 6, 12856.
4
7
4
Matsuda, Electrochim. Acta, 1989, 34, 453; (b) T. F. Jaramillo, K.
P. Jorgensen, J. Bonde, J. H. Nielsen, S. Horch and I.
Chorkendorff, Science, 2007, 317, 100.
(
0) is a known hydrogen adsorption material. Additionally, the
structural analysis reveals that the palladium sites are relatively
open in the case of Pd Se and it is crowded as the composition
becomes Pd Se and Pd17Se15. All the above arguments lead to the
fact that Pd Se is a better electrocatalyst than the other two
members studied, Pd Se and Pd17Se15. Low Tafel slope and charge
transfer resistance and high exchange current density and
electrochemical surface area makes Pd Se an excellent
4
1
1
8 (a) D. Merki, S. Fierro, H. Vrubel, X. Hu, Chemi. Sci., 2011, 2,
7
4
1
262; (b) J. D. Benck, Z. Chen, L.Y. Kuritzky, A.J. Forman, T.F.
4
Jaramillo, ACS Catal., 2012, 2, 1916.
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4
9 (a) Z. Zhang, B. Lu, J. Hao, W. Yang and J. Tang, Chem.
Commun., 2014, 50, 11554; (b) C. He and J. Tao, Chem.
Commun., 2015, 51, 8323; (c) E. J. Popczun, J. R. McKone, C. G.
Read, A. J. Biacchi, A. M. Wiltrout, N. S. Lewis and R. E. Schaak,
J. Am. Chem. Soc., 2013, 135, 9267.
0 G. Kresse and J. Furthmüller, Phys. Rev. B, 1996, 54, 11169.
1 G. Kresse and D. Joubert, Phys. Rev. B, 1999, 59, 1758.
2 A. Hamidani and B. Bennecer, Comput. Mater. Sci., 2010, 48,
4
electrocatalyst as compared to the other two phases. An important
point to highlight is the fact the adsorption / desorption peaks
associated with of H atoms, before the onset of hydrogen gas
evolution as observed on pure Pt and Pd phases is not observed in
the case of palladium selenides. This requires further investigation.
In Summary, three different palladium selenide phases
2
2
2
1
15.
2
3 (a) T. Matkovic and K. Schubert, J. Less-Common Met., 1978,
Pd17Se15, Pd
7
Se
4 4
and Pd Se are prepared by thermolysis of different
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9, 57; (b) F. Gronvold and E. Rost, Acta. Crsytallogr., 1962, 15,
palladium organoselenolate complexes. Among the three phases,
1
1.
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| J. Name., 2012, 00, 1-3
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