Characterization of Photoactivity of Nanostructured BiVO4 at Polarized Liquid-Liquid Interfaces by Scanning Electrochemical Microscopy

Abstract

Scanning electrochemical microscopy (SECM) has been used for recording the photoinduced charge-transfer reactions at bismuth vanadate (BiVO4) photocatalyst nanostructures arranged at chemically polarized liquid/liquid (L/L) interfaces between an organic butyronitrile electrolyte and an aqueous electrolyte containing perchlorate as common anion. In addition, [Co(bpy)3](PF6)3 soluble in the organic phase was used as a probe of SECM analysis but also as a sacrificial agent, which effectively improves the separation efficiency of photogenerated charge carriers at the BiVO4 modified L/L interface. The nanoassembled layer did not require contact to a current collector. Interfacial polarization effects on the photoinduced charge-transfer reactions have been investigated by recording the regeneration of the reduced form [Co(bpy)3](PF6)2 at the BiVO4 particle layer in organic phase in SECM feedback approach curves. The kinetic parameters of the interfacial photoinduced electron transfer (ET) reaction have been analyzed under chemically controllable galvanic potential difference at the L/L interface. The potential dependence of the photoinduced ET rate constants followed Butler-Volmer theory. The photogenerated oxygen species distribute between the aqueous and organic phases through the porous BiVO4 particle layer. It can be traced by a transient current for O2 reduction at a gold microelectrode positioned close to the particle layer in the organic phase and biased for diffused-controlled O2 reduction. The results represented a new approach to characterize semiconductor photocatalyst systems spontaneously assembled at the L/L interface and their use for water oxidation reaction as a challenging step in overall water splitting process.