Marked enhancement in electron-hole separation achieved in the low bias region using electrochemically prepared Mo-doped BiVO4 photoanodes

摘要

Mo-doped BiVO4 electrodes were prepared by an electrochemical route for use as photoanodes in a photoelectrochemical celt. The purpose of Mo-doping was to improve the electron transport properties, which in turn can increase the electron-hole separation yield. The poor electron-hole separation yield was known to be one of the main limiting factors for BiVO4-based photoanodes. The electrochemical route provided an effective way of doping BiVO4, and the optimalty doped sample, BiV_(0.97)Mo_(0.03)O4, increased the electron-hole separation yield from 0.23 to 0.57 at 0.6 V vs. RHE, which is a record high separation yield achieved for BiVO4-based photoanodes. As a result, BiV_(0.97)Mo_(0.03)O4 generated impressive photocurrents, for example, 2 mA cm~(-2) at a potential as low as 0.4 V vs. RHE for sulfite oxidation, which has fast oxidation kinetics and, therefore, the loss of holes by surface recombination is negligible. For photooxidation of water, BiV_(0.97)Mo_(0.03)O4 was paired with FeOOH as an oxygen evolution catalyst (OEC) to improve the poor catalytic ability of BiV_(0.97)Mo_(0.03)O4 for water oxidation. The resulting BiV_(0.97)Mo_(0.03)O4/ FeOOH photoanodes generated a significantly improved photocurrent for water oxidation compared to previous reported results, but the photocurrent of BiV_(0.97)Mo_(0.03)O4/FeOOH for water oxidation could not reach the photocurrent of BiV_(0.97)Mo_(0.03)O4 for sulfite oxidation, in order to examine the cause, the effects of Mo-doping on the interaction between BiVO4 and FeOOH and the effects of FeOOH on the electron-hole separation yield of BiV_(0.97)Mo_(0.03)O4 were investigated in detail, which provided new insights into semiconductor-OEC interactions.