Photoelectrochemical Water Splitting System—A Study of Interfacial Charge Transfer with Scanning Electrochemical Microscopy

Abstract

Fast charge transfer kinetics at the photoelectrode/electrolyte interface is critical for efficient photoelectrochemical (PEC) water splitting system. Thus, far, a measurement of kinetics constants for such processes is limited. In this study, scanning electrochemical microscopy (SECM) is employed to investigate the charge transfer kinetics at the photoelectrode/electrolyte interface in the feedback mode in order to simulate the oxygen evolution process in PEC system. The popular photocatalysts BiVO4 and Mo doped BiVO4 (labeled as Mo:BiVO4) are selected as photoanodes and the common redox couple [Fe(CN)6](3-)/[Fe(CN)6](4-) as molecular probe. SECM characterization can directly reveal the surface catalytic reaction kinetics constant of 9.30 × 10(7) mol(-1) cm(3) s(-1) for the BiVO4. Furthermore, we find that after excitation, the ratio of rate constant for photogenerated hole to electron via Mo:BiVO4 reacting with mediator at the electrode/electrolyte interface is about 30 times larger than that of BiVO4. This suggests that introduction of Mo(6+) ion into BiVO4 can possibly facilitate solar to oxygen evolution (hole involved process) and suppress the interfacial back reaction (electron involved process) at photoanode/electrolyte interface. Therefore, the SECM measurement allows us to make a comprehensive analysis of interfacial charge transfer kinetics in PEC system.

A Novel Charge Transfer Channel to Simultaneously Enhance Photocatalytic Water Splitting Activity and Stability of CdS

“…To further confirm that a novel charge transfer channel can accelerate the photogenerated holes transfer, scanning photo‐electrochemical microscopy (SPECM) is treated as a powerful technique in situ exploration of “fast” and “slow” dynamics through probe molecules (e.g., Fe(CN) 6 ) 3+ /Fe(CN) 6 ) 2+ , FcMeOH, and MV 2+ /MV + ) using ultra‐microelectrodes in the feedback mode (Figure b) . As shown in Figure b and Figure S12 (Supporting Information), different samples show the different probe approach curves (PACs).…”

Metallic Bi Nanocrystal‐Modified Defective BiVO4 Photoanodes with Exposed (040) Facets for Photoelectrochemical Water Splitting

“…To investigate the photoelectrochemical performances of BiVO 4 photoanodes, the linear sweep voltammogram (LSV) in a three‐electrode electrochemical system, are run from −0.6 to +1.0 V vs. SCE with or without visible light irradiation, as shown in Figure . The onset potential and the current density at 1.23 V vs. RHE are taken as main parameters to evaluate the performances of water splitting . The dark current density at first glance is close to zero, indicating that the natural surface of BiVO 4 photoanodes cannot realize water oxidation reaction without applying high enough overpotential, as shown in Figure (a).…”

Insight into the PEC and interfacial charge transfer kinetics at the Mo doped BiVO4photoanodes

“…Therefore, the hole transfer from a valence band of BiVO 4 to [Fe(CN) 6 ] 4À is kinetically more favorable by DG $ À0.4 eV than the water oxidation. 106 The cathodic potential at the probe is tuned to the reduction potential of [Fe(CN) 6 ] 3À to [Fe(CN) 6 ] 4À so that there is no side reaction such as oxygen reduction take place. Therefore, feedback current can be assumed mainly from the reduction of [Fe(CN) 6 ] 3À .…”