Highly Active Hydrogen Evolution Electrodes via Co-deposition of ...
Supporting Information for
Highly Active Hydrogen Evolution Electrodes via Co-deposition of Platinum and Polyoxometalates Chao Zhang,† Yahui Hong,† Ruihan Dai,† Xinping Lin,† La-Sheng Long,† Cheng Wang,*,† and Wenbin Lin*,†,§ †
Collaborative Innovation Center of Chemistry for Energy Materials, State Key Laboratory of Physical Chemistry of Solid Surfaces, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, P.R. China § Department of Chemistry, University of Chicago, 929 E 57th Street, Chicago, IL 60637, USA.
Email: *Wenbin Lin, [email protected] *Cheng Wang, [email protected]
S1
Experimental Chemicals and reagents α-K8SiW11O39·xH2O (SiW11) and α-K6P2W18O62·xH2O (P2W18) were synthesized according to the literature procedures1 and characterized by cyclic voltammetry and IR spectra. H4SiW12O40·xH2O (SiW12) and H2SO4 (98%) were purchased from Sinopharm Chemical Reagent Co.,Ltd (SCRC) without further purification. The 0.5M H2SO4 electrolyte was obtained by diluting H2SO4 (98%) with ultrapure water (18.2 MΩ cm @ 25 oC). Unless otherwise stated, all electrochemical solutions were degassed thoroughly with pure N2 and kept under positive pressure of N2 during experiments.
Physical methods Three-electrode electrochemical studies were performed using a CH Instrument-660e electrochemical workstation in simple single-compartment cells. Unless otherwise stated, three-electrode electrochemistry was performed using a 5 mm diameter(S = 0.196 cm2) glassy carbon (GC) disc working electrode with a platinum wire (d = 1mm, L = 1cm) counter electrode or a graphite counter electrode. Before each experiment, the GC was polished to a mirror finish with alumina paste of decreasing grain sizes from 0.5µm to 50nm. The electrode then underwent an ultrasonic washing in ethanol for several minutes and was finally rinsed with distilled water twice. The reference electrode was Ag/AgCl (3.5M KCl) electrode and had been calibrated (+0.2046 V) against a normal hydrogen electrode (NHE) in 0.5M H2SO4 (E(NHE) = E(Ag/AgCl) + 0.2046V). The uncompensated cell resistance was determined from a single-point high-frequency impedance measurement and was compensated by the built-in positive-feedback software. All electrochemistry experiments were conducted at 20-25 oC. GC measurement was conducted on a Techcomp GC7900 with a TCD detector and a 5Å molecular sieves packed column with Ar as a carrier gas. Scanning Electron Microscope (SEM) images were obtained on Hitachi S-4800 and the Zeiss Sigma SEM system. Transmission Electron Microscope (TEM) images were obtained on the JEM 1400 system. XPS analysis was performed on a PHI Quantum 2000 Scanning ESCA Microprobe with a monochromatised microfocused Al X-ray source.
General procedure for the preparation of active working electrodes The preparation of active working electrodes (involving SiW11 or not) was accomplished by applying a constant potential (e.g., -1.0V vs. NHE) S2
to a newly polished GC working electrode for a certain duration (e.g., 2 hours). The counter electrodes were a Pt wire or a graphite rod as described in the article. Unless otherwise stated, 0.5M H2SO4 electrolyte (50 mL in each electrochemical experiment) was stirred and deaerated by purging with N2. After the electrolysis, the modified GCs were washed by ultrapure water. All LSV curves of the modified GCs were obtained in 0.5M H2SO4 unless otherwise stated. The key parameters in electrode modification are the concentration of SiW11 and electrolysis duration. These details are discussed in the article. The potential of the Ag/AgCl reference electrode was checked before and after the electrolysis in order to ensure its proper operations. The XPS and SEM experiments were performed with a detachable GC working electrode. Other modified conditions were the same as mentioned above. Table S1. A summary of electrode modification conditions and their abbreviations Electrolyte solution
Counter electrode
Applied Potential (vs. NHE)
Electrolysis duration
Abbreviation
1mM SiW11, 0.5M H2SO4
Pt wire
-0.7V
2 hours
-0.7V-1mM-2h-Pt
1mM SiW11, 0.5M H2SO4
Pt wire
-0.7V
12 hours
-0.7V-1mM-12h-Pt
1mM SiW11, 0.5M H2SO4
Pt wire
-1.0V
8 hours
-1.0V-1mM-8h-Pt
10mM SiW11, 0.5M H2SO4
graphite
-1.0V
2 hours
-1.0V-10mM-2h-G
Pt wire
-1.0V
2 hours
-1.0V-10mM-2h-Pt
Graphite
-1.0V
2 hours
-1.0V-10mM-2h-G-K2PtCl6
0.5M H2SO4
Pt wire
-1.0V
2 hours
-1.0V-0mM-2h-Pt
0.5M H2SO4
Graphite
-1.0V
2 hours
1.0V-0mM-2h-G
1 µMK2PtCl6 and 0.5M H2SO4
Graphite
-1.0V
2 hours
-1.0V-0mM-2h-G-K2PtCl6
10mM SiW11, 0.5M H2SO4
Pt wire
-1.0V
12 hours
-1.0V-10mM-12h-Pt
10mM SiW11, 0.5M H2SO4 1 µMK2PtCl6, 10mM SiW11 and 0.5M H2SO4
S3
Figure S1 Polarization curves of modified GCs obtained at different electrolysis potential (vs. NHE) with different electrolysis durations. All electrolysis processes were conducted with 1mM SiW11 in 0.5M H2SO4 solutions. The LSV curves were obtained in 0.5M H2SO4. Scan rate: 5mV/s.
Figure S2. Polarization curves of modified GCs in 0.5M H2SO4 solutions. Modification conditions: black curve: -1.0V-0mM-2h-G-K2PtCl6; red curve:-1.0V-10mM-2h-G; blue curve:-1.0V-10mM-2h-Pt; green curve: -1.0V-10mM-2h-G-K2PtCl6. Scan rate: 5 mV/s. From Figure S2 we can conclude that 1µM K2PtCl6 and 10mM SiW11 (50 mL 0.5M H2SO4 as electrolyte) co-modified GC has identical HER behaviors to the Pt working electrode. On the contrary, the GC modified by 1µM K2PtCl6 alone demonstrated a poorer HER activity. S4
Figure S3. Polarization curves of stepwise modified GCs. a) step 1: modified in 1 µM K2PtCl6 (black, 1); step 2: modified in 10 mM SiW11 after the first step (red, 2). b) Step 1: modified in 10 mM SiW11 (black, 1); step 2: modified in 1 µM K2PtCl6 after the first step (red, 2). Blue curves (3) in a) & b) is obtained by electrodeposition in 1 µM K2PtCl6 and 10 mM SiW11 together. Scan rate: 5 mV/s. In order to figure out the effects of Pt and SiW11on the electrode modification, we modified GCs with Pt and SiW11 separately. FigureS3 demonstrates polarization curves of stepwise modified GCs in 0.5M H2SO4. The newly polished GC was first electrolyzed in 50 mL 0.5M H2SO4 with 1µM K2PtCl6 at -1.0V vs. NHE for 1 hour (all the electrochemical experiments mentioned in Figure S3 used graphite rods as the counter electrodes). The modified GC was then washed with ultrapure water and placed in 0.5M H2SO4 and tested in a LSV scan (FigureS3a black curve). After that, the modified GC was washed with ultrapure water again and placed in 50 mL 0.5M H2SO4 with 10mM SiW11 for another hour of electrolysis (-1.0V vs. NHE). Red curve in FigureS3a was obtained in 0.5M H2SO4 after the second step of electrolysis. The reverse modification procedures were also performed and the LSV curves of the modified GCs in 0.5M H2SO4 were shown in FigureS3b. Blue curves in FigureS3 a&b were obtained in 0.5M H2SO4 after 1 hour of electrolysis with 1µM K2PtCl6 and 10mM SiW11 together in 50mL 0.5M H2SO4 (applied potential: -1.0V vs. NHE).
S5
Figure S4. A comparison of CV in 0.5M H2SO4 for the Pt disk working electrode and the modified GCs. Scan rate: 1000 mV/s.
Figure S5. TEM image of Pt particles in the sample -1.0V-10mM-12h-Pt.
S6
Figure S6. XPS spectra of the modified GCs. Sample: -1.0V-10mM-2h-Pt.
Figure S7. Time course of the catalytic current during an electrolysis experiment using a Pt/SiW11-modified GC (modification conditions:-1.0V-10mM-2h-Pt). Applied HER potential: -100 mV vs. NHE; electrolyte solution: 0.5M H2SO4. An electrolysis experiment was conducted using a modified (-1.0V-10mM-2h-Pt) GC (Figure S7). The current density decreased sharply at the beginning of the electrolysis and after 8hours of electrolysis, the current density gradually stabilized at 10% of its original value. S7
Table S2. ICP-MS results of modified GCs before and after stability test Sample
Pt (ng/cm2)
-1.0V-0mM-2h-Pt -1.0V-0mM-2h-Pt, after 100 LSV runs
(6.0±2.4)×101
-1.0V-10mM-2h-Pt -1.0V-10mM-2h-Pt, after 100 LSV runs
(7.6±2.5)×101
9.7±1.5 (7.8±2.4)×101
Figure S8. Comparisons of polarization data in 0.5M H2SO4 for GCs co-deposited with SiW11/Pt, SiW12/Pt and P2W18/Pt. Scan rate: 5 mV/s. All POM concentrations were 10 mM during the modification and the GCs were kept at -1.0V vs. NHE for 2 hours.
Figure S9. Polarization curves of 1mM SiW11 in 0.5M H2SO4 solution. With the increase of scanning times, HER overpotential decreases gradually. Scan rate: 5 mV/s. S8
Polarization curves in Figure S9 were obtained in 1mM SiW11(0.161g) in 0.5M H2SO4 solution (50 mL). After each sweep, the GC was washed by ultrapure water several times. With more and more scan times, the HER overpotential decreased gradually and finally reached around -0.74V vs. NHE at -20 mA/cm2. The HER overpotential did not continue to decrease with more LSV scans.
Figure S10. Polarization curves of the Pt working electrode and modified GCs with different electrolysis times and potentials.
Figure S10 demonstrates the polarization curves of the modified GCs with different electrolysis times and potentials (black, red and green curves).These modified GCs are all obtained by electrolyzing in 10mM SiW11(1.61g) in 50 mL 0.5M H2SO4 (Pt counter electrodes were used). After the deposition, the GC was washed with ultrapure water and tested with a LSV scan in 0.5M H2SO4.The blue curve is the LSV curve of the Pt working electrode in 0.5M H2SO4. Scan rate: 5 mV/s.
S9
Figure S11. Polarization curves of GCs modified by electrolysis for different times and potentials in 0.5 M H2SO4 without POMs. The counter electrodes were Pt wires in the electrolysis processes. Scan rate: 5 mV/s.
The GCs were modified by electrolyzing at -1.0V and -0.7V vs. NHE in 0.5M H2SO4 for different times (NO SiW11 was added in electrolyte). As shown in Figure S11, lower electrolytic potential led to a higher HER activity. This may be due to the fact that lower potential on the working electrode could lead to higher current which drives up the potential on the counter electrode and thus dissolves more Pt from the anode and deposit them on the GC surface. However, when the electrolysis time was extended to 12 hours, such an influence from the anodic potential disappeared. Based on this information, we conclude that the GC surface is saturated with Pt after such a long electrolysis time, and more Pt loading will not further improve the HER catalytic activity.
S10
Figure S12. Polarization curves of GCs modified with different electrolysis times, potentials and concentrations of SiW11 in 0.5 M H2SO4. The counter electrodes were graphite in the electrolysis processes. Scan rate: 5 mV/s.
Figure S12 shows LSV curves of modified GCs in 0.5M H2SO4. The GCs were modified with different electrolysis times, potential and concentrations of SiW11 in 0.5 M H2SO4. The counter electrodes were graphite rods in the electrolysis processes. These results confirm that GC modified by POM alone also have HER activity and the main influence factors here is electrolysis duration.
S11
Figure S13. EDS results of modified GCs in SEM (left) and TEM (right).
Table S3. EDS results of modified GC in SEM and TEM. EDS analysis (at. %) W Pt
Pt source SEM
TEM
Pt Wire as counter
1.3
-
1µM K2PtCl6
0.5
0.13
electrolysis duration
particle diameter
EDS analysis (at. %) W Pt 1.57 -
2h
3-5 nm
4h
10-20 nm
2.13
3.53
8h
35-50 nm
1.7
7.68
S12
Figure S14. Cyclic Voltammograms of 1mM SiW12 and 1mM SiW11 in 0.5M H2SO4.
Figure S15. Cyclic voltammograms of 1mM SiW12 in 0.5M H2SO4 (left) and 0.2mM P2W18 in 0.2M Na2SO4+H2SO4 aqueous solution (right).
The Cyclic Voltammogram curves of 1mM SiW12 and 1mM SiW11 in 0.5M H2SO4 are different. Black curve in Figure S14 represents the first run on the GC with SiW12 in 0.5M H2SO4 solution and shows four reduction waves, located at -0.225V, -0.450V, -0.615V, -0.795V vs. Ag/AgCl. This result is in agreement with other reports on electrochemical S13
behaviors of SiW12.2,3 On the other hand, 1mM SiW11 in 0.5M H2SO4 demonstrates two waves at -0.347V and -0.560V vs. Ag/AgCl. Both SiW12 and SiW11 could keep their polarogram patterns for 12 hours, indicating SiW11 does not change into SiW12 in 0.5M H2SO4 for at least 12 hours. We also investigate the electrochemical behavior of P2W18 in 0.2M Na2SO4+H2SO4 aqueous solution (Figure S15 left). There are four redox couples observed in the CV: The first two redox couples (0.035V and -0.095V vs. Ag/AgCl) correspond to one-electron redox processes, and the last two redox couples correspond to two-electron redox processes.3
Reference (1) Téazéa, A.; Hervéa, G.; Finke, R. G.; Lyon, D. K. In Inorganic Syntheses; Ginsberg, A. P., Ed.; John Wiley & Sons, Inc., 1990; pp 85–96. (2) Keïta, B.; Nadjo, L. Activation of Electrode Surfaces: Application to the Electrocatalysis of the Hydrogen Evolution Reaction. J. Electroanal. Chem. Interfacial Electrochem. 1985, 191 (2), 441–448. (3) Sadakane, M.; Steckhan, E. Electrochemical Properties of Polyoxometalates as Electrocatalysts. Chem. Rev. 1998, 98 (1), 219–237.
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Highly Active Hydrogen Evolution Electrodes via Co-deposition of Platinum and Polyoxometalates Chao Zhang,† Yahui Hong,† Ruihan Dai,† Xinping Lin,† La-Sheng Long,† Cheng Wang,*,† and Wenbin Lin*,†,§ †
Collaborative Innovation Center of Chemistry for Energy Materials, State Key Laboratory of Physical Chemistry of Solid Surfaces, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, P.R. China § Department of Chemistry, University of Chicago, 929 E 57th Street, Chicago, IL 60637, USA.
Email: *Wenbin Lin, [email protected] *Cheng Wang, [email protected]
S1
Experimental Chemicals and reagents α-K8SiW11O39·xH2O (SiW11) and α-K6P2W18O62·xH2O (P2W18) were synthesized according to the literature procedures1 and characterized by cyclic voltammetry and IR spectra. H4SiW12O40·xH2O (SiW12) and H2SO4 (98%) were purchased from Sinopharm Chemical Reagent Co.,Ltd (SCRC) without further purification. The 0.5M H2SO4 electrolyte was obtained by diluting H2SO4 (98%) with ultrapure water (18.2 MΩ cm @ 25 oC). Unless otherwise stated, all electrochemical solutions were degassed thoroughly with pure N2 and kept under positive pressure of N2 during experiments.
Physical methods Three-electrode electrochemical studies were performed using a CH Instrument-660e electrochemical workstation in simple single-compartment cells. Unless otherwise stated, three-electrode electrochemistry was performed using a 5 mm diameter(S = 0.196 cm2) glassy carbon (GC) disc working electrode with a platinum wire (d = 1mm, L = 1cm) counter electrode or a graphite counter electrode. Before each experiment, the GC was polished to a mirror finish with alumina paste of decreasing grain sizes from 0.5µm to 50nm. The electrode then underwent an ultrasonic washing in ethanol for several minutes and was finally rinsed with distilled water twice. The reference electrode was Ag/AgCl (3.5M KCl) electrode and had been calibrated (+0.2046 V) against a normal hydrogen electrode (NHE) in 0.5M H2SO4 (E(NHE) = E(Ag/AgCl) + 0.2046V). The uncompensated cell resistance was determined from a single-point high-frequency impedance measurement and was compensated by the built-in positive-feedback software. All electrochemistry experiments were conducted at 20-25 oC. GC measurement was conducted on a Techcomp GC7900 with a TCD detector and a 5Å molecular sieves packed column with Ar as a carrier gas. Scanning Electron Microscope (SEM) images were obtained on Hitachi S-4800 and the Zeiss Sigma SEM system. Transmission Electron Microscope (TEM) images were obtained on the JEM 1400 system. XPS analysis was performed on a PHI Quantum 2000 Scanning ESCA Microprobe with a monochromatised microfocused Al X-ray source.
General procedure for the preparation of active working electrodes The preparation of active working electrodes (involving SiW11 or not) was accomplished by applying a constant potential (e.g., -1.0V vs. NHE) S2
to a newly polished GC working electrode for a certain duration (e.g., 2 hours). The counter electrodes were a Pt wire or a graphite rod as described in the article. Unless otherwise stated, 0.5M H2SO4 electrolyte (50 mL in each electrochemical experiment) was stirred and deaerated by purging with N2. After the electrolysis, the modified GCs were washed by ultrapure water. All LSV curves of the modified GCs were obtained in 0.5M H2SO4 unless otherwise stated. The key parameters in electrode modification are the concentration of SiW11 and electrolysis duration. These details are discussed in the article. The potential of the Ag/AgCl reference electrode was checked before and after the electrolysis in order to ensure its proper operations. The XPS and SEM experiments were performed with a detachable GC working electrode. Other modified conditions were the same as mentioned above. Table S1. A summary of electrode modification conditions and their abbreviations Electrolyte solution
Counter electrode
Applied Potential (vs. NHE)
Electrolysis duration
Abbreviation
1mM SiW11, 0.5M H2SO4
Pt wire
-0.7V
2 hours
-0.7V-1mM-2h-Pt
1mM SiW11, 0.5M H2SO4
Pt wire
-0.7V
12 hours
-0.7V-1mM-12h-Pt
1mM SiW11, 0.5M H2SO4
Pt wire
-1.0V
8 hours
-1.0V-1mM-8h-Pt
10mM SiW11, 0.5M H2SO4
graphite
-1.0V
2 hours
-1.0V-10mM-2h-G
Pt wire
-1.0V
2 hours
-1.0V-10mM-2h-Pt
Graphite
-1.0V
2 hours
-1.0V-10mM-2h-G-K2PtCl6
0.5M H2SO4
Pt wire
-1.0V
2 hours
-1.0V-0mM-2h-Pt
0.5M H2SO4
Graphite
-1.0V
2 hours
1.0V-0mM-2h-G
1 µMK2PtCl6 and 0.5M H2SO4
Graphite
-1.0V
2 hours
-1.0V-0mM-2h-G-K2PtCl6
10mM SiW11, 0.5M H2SO4
Pt wire
-1.0V
12 hours
-1.0V-10mM-12h-Pt
10mM SiW11, 0.5M H2SO4 1 µMK2PtCl6, 10mM SiW11 and 0.5M H2SO4
S3
Figure S1 Polarization curves of modified GCs obtained at different electrolysis potential (vs. NHE) with different electrolysis durations. All electrolysis processes were conducted with 1mM SiW11 in 0.5M H2SO4 solutions. The LSV curves were obtained in 0.5M H2SO4. Scan rate: 5mV/s.
Figure S2. Polarization curves of modified GCs in 0.5M H2SO4 solutions. Modification conditions: black curve: -1.0V-0mM-2h-G-K2PtCl6; red curve:-1.0V-10mM-2h-G; blue curve:-1.0V-10mM-2h-Pt; green curve: -1.0V-10mM-2h-G-K2PtCl6. Scan rate: 5 mV/s. From Figure S2 we can conclude that 1µM K2PtCl6 and 10mM SiW11 (50 mL 0.5M H2SO4 as electrolyte) co-modified GC has identical HER behaviors to the Pt working electrode. On the contrary, the GC modified by 1µM K2PtCl6 alone demonstrated a poorer HER activity. S4
Figure S3. Polarization curves of stepwise modified GCs. a) step 1: modified in 1 µM K2PtCl6 (black, 1); step 2: modified in 10 mM SiW11 after the first step (red, 2). b) Step 1: modified in 10 mM SiW11 (black, 1); step 2: modified in 1 µM K2PtCl6 after the first step (red, 2). Blue curves (3) in a) & b) is obtained by electrodeposition in 1 µM K2PtCl6 and 10 mM SiW11 together. Scan rate: 5 mV/s. In order to figure out the effects of Pt and SiW11on the electrode modification, we modified GCs with Pt and SiW11 separately. FigureS3 demonstrates polarization curves of stepwise modified GCs in 0.5M H2SO4. The newly polished GC was first electrolyzed in 50 mL 0.5M H2SO4 with 1µM K2PtCl6 at -1.0V vs. NHE for 1 hour (all the electrochemical experiments mentioned in Figure S3 used graphite rods as the counter electrodes). The modified GC was then washed with ultrapure water and placed in 0.5M H2SO4 and tested in a LSV scan (FigureS3a black curve). After that, the modified GC was washed with ultrapure water again and placed in 50 mL 0.5M H2SO4 with 10mM SiW11 for another hour of electrolysis (-1.0V vs. NHE). Red curve in FigureS3a was obtained in 0.5M H2SO4 after the second step of electrolysis. The reverse modification procedures were also performed and the LSV curves of the modified GCs in 0.5M H2SO4 were shown in FigureS3b. Blue curves in FigureS3 a&b were obtained in 0.5M H2SO4 after 1 hour of electrolysis with 1µM K2PtCl6 and 10mM SiW11 together in 50mL 0.5M H2SO4 (applied potential: -1.0V vs. NHE).
S5
Figure S4. A comparison of CV in 0.5M H2SO4 for the Pt disk working electrode and the modified GCs. Scan rate: 1000 mV/s.
Figure S5. TEM image of Pt particles in the sample -1.0V-10mM-12h-Pt.
S6
Figure S6. XPS spectra of the modified GCs. Sample: -1.0V-10mM-2h-Pt.
Figure S7. Time course of the catalytic current during an electrolysis experiment using a Pt/SiW11-modified GC (modification conditions:-1.0V-10mM-2h-Pt). Applied HER potential: -100 mV vs. NHE; electrolyte solution: 0.5M H2SO4. An electrolysis experiment was conducted using a modified (-1.0V-10mM-2h-Pt) GC (Figure S7). The current density decreased sharply at the beginning of the electrolysis and after 8hours of electrolysis, the current density gradually stabilized at 10% of its original value. S7
Table S2. ICP-MS results of modified GCs before and after stability test Sample
Pt (ng/cm2)
-1.0V-0mM-2h-Pt -1.0V-0mM-2h-Pt, after 100 LSV runs
(6.0±2.4)×101
-1.0V-10mM-2h-Pt -1.0V-10mM-2h-Pt, after 100 LSV runs
(7.6±2.5)×101
9.7±1.5 (7.8±2.4)×101
Figure S8. Comparisons of polarization data in 0.5M H2SO4 for GCs co-deposited with SiW11/Pt, SiW12/Pt and P2W18/Pt. Scan rate: 5 mV/s. All POM concentrations were 10 mM during the modification and the GCs were kept at -1.0V vs. NHE for 2 hours.
Figure S9. Polarization curves of 1mM SiW11 in 0.5M H2SO4 solution. With the increase of scanning times, HER overpotential decreases gradually. Scan rate: 5 mV/s. S8
Polarization curves in Figure S9 were obtained in 1mM SiW11(0.161g) in 0.5M H2SO4 solution (50 mL). After each sweep, the GC was washed by ultrapure water several times. With more and more scan times, the HER overpotential decreased gradually and finally reached around -0.74V vs. NHE at -20 mA/cm2. The HER overpotential did not continue to decrease with more LSV scans.
Figure S10. Polarization curves of the Pt working electrode and modified GCs with different electrolysis times and potentials.
Figure S10 demonstrates the polarization curves of the modified GCs with different electrolysis times and potentials (black, red and green curves).These modified GCs are all obtained by electrolyzing in 10mM SiW11(1.61g) in 50 mL 0.5M H2SO4 (Pt counter electrodes were used). After the deposition, the GC was washed with ultrapure water and tested with a LSV scan in 0.5M H2SO4.The blue curve is the LSV curve of the Pt working electrode in 0.5M H2SO4. Scan rate: 5 mV/s.
S9
Figure S11. Polarization curves of GCs modified by electrolysis for different times and potentials in 0.5 M H2SO4 without POMs. The counter electrodes were Pt wires in the electrolysis processes. Scan rate: 5 mV/s.
The GCs were modified by electrolyzing at -1.0V and -0.7V vs. NHE in 0.5M H2SO4 for different times (NO SiW11 was added in electrolyte). As shown in Figure S11, lower electrolytic potential led to a higher HER activity. This may be due to the fact that lower potential on the working electrode could lead to higher current which drives up the potential on the counter electrode and thus dissolves more Pt from the anode and deposit them on the GC surface. However, when the electrolysis time was extended to 12 hours, such an influence from the anodic potential disappeared. Based on this information, we conclude that the GC surface is saturated with Pt after such a long electrolysis time, and more Pt loading will not further improve the HER catalytic activity.
S10
Figure S12. Polarization curves of GCs modified with different electrolysis times, potentials and concentrations of SiW11 in 0.5 M H2SO4. The counter electrodes were graphite in the electrolysis processes. Scan rate: 5 mV/s.
Figure S12 shows LSV curves of modified GCs in 0.5M H2SO4. The GCs were modified with different electrolysis times, potential and concentrations of SiW11 in 0.5 M H2SO4. The counter electrodes were graphite rods in the electrolysis processes. These results confirm that GC modified by POM alone also have HER activity and the main influence factors here is electrolysis duration.
S11
Figure S13. EDS results of modified GCs in SEM (left) and TEM (right).
Table S3. EDS results of modified GC in SEM and TEM. EDS analysis (at. %) W Pt
Pt source SEM
TEM
Pt Wire as counter
1.3
-
1µM K2PtCl6
0.5
0.13
electrolysis duration
particle diameter
EDS analysis (at. %) W Pt 1.57 -
2h
3-5 nm
4h
10-20 nm
2.13
3.53
8h
35-50 nm
1.7
7.68
S12
Figure S14. Cyclic Voltammograms of 1mM SiW12 and 1mM SiW11 in 0.5M H2SO4.
Figure S15. Cyclic voltammograms of 1mM SiW12 in 0.5M H2SO4 (left) and 0.2mM P2W18 in 0.2M Na2SO4+H2SO4 aqueous solution (right).
The Cyclic Voltammogram curves of 1mM SiW12 and 1mM SiW11 in 0.5M H2SO4 are different. Black curve in Figure S14 represents the first run on the GC with SiW12 in 0.5M H2SO4 solution and shows four reduction waves, located at -0.225V, -0.450V, -0.615V, -0.795V vs. Ag/AgCl. This result is in agreement with other reports on electrochemical S13
behaviors of SiW12.2,3 On the other hand, 1mM SiW11 in 0.5M H2SO4 demonstrates two waves at -0.347V and -0.560V vs. Ag/AgCl. Both SiW12 and SiW11 could keep their polarogram patterns for 12 hours, indicating SiW11 does not change into SiW12 in 0.5M H2SO4 for at least 12 hours. We also investigate the electrochemical behavior of P2W18 in 0.2M Na2SO4+H2SO4 aqueous solution (Figure S15 left). There are four redox couples observed in the CV: The first two redox couples (0.035V and -0.095V vs. Ag/AgCl) correspond to one-electron redox processes, and the last two redox couples correspond to two-electron redox processes.3
Reference (1) Téazéa, A.; Hervéa, G.; Finke, R. G.; Lyon, D. K. In Inorganic Syntheses; Ginsberg, A. P., Ed.; John Wiley & Sons, Inc., 1990; pp 85–96. (2) Keïta, B.; Nadjo, L. Activation of Electrode Surfaces: Application to the Electrocatalysis of the Hydrogen Evolution Reaction. J. Electroanal. Chem. Interfacial Electrochem. 1985, 191 (2), 441–448. (3) Sadakane, M.; Steckhan, E. Electrochemical Properties of Polyoxometalates as Electrocatalysts. Chem. Rev. 1998, 98 (1), 219–237.
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