Annealing temperature effects on photoelectrochemical performance of bismuth vanadate thin film photoelectrodes

The effects of annealing treatment between 400 degrees C and 540 degrees C on crystallization behavior, grain size, electrochemical (EC) and photoelectrochemical (PEC) oxygen evolution reaction (OER) performances of bismuth vanadate (BiVO4) thin films are investigated in this work. The results show that higher temperature leads to larger grain size, improved crystallinity, and better crystal orientation for the BiVO4 thin film electrodes. Under air-mass 1.5 global (AM 1.5) solar light illumination, the BiVO4 thin film prepared at a higher annealing temperature (500-540 degrees C) shows better PEC OER performance. Also, the OER photocurrent density increased from 0.25 mA cm(-2) to 1.27 mA cm(-2) and that of the oxidation of sulfite, a hole scavenger, increased from 1.39 to 2.53 mA cm(-2) for the samples prepared from 400 degrees C to 540 degrees C. Open-circuit photovoltage decay (OCPVD) measurement indicates that BiVO4 samples prepared at the higher annealing temperature have less charge recombination and longer electron lifetime. However, the BiVO4 samples prepared at lower annealing temperature have better EC performance in the absence of light illumination and more electrochemically active surface sites, which are negatively related to electrochemical double-layer capacitance (C-dl). C-dl was 0.0074 mF cm(-2) at 400 degrees C and it decreased to 0.0006 mF cm(-2) at 540 degrees C. The OER and sulfide oxidation are carefully compared and these show that the efficiency of charge transport in the bulk ((bulk)) and on the surface ((surface)) of the BiVO4 thin film electrode are improved with the increase in the annealing temperature. The mechanism behind the light-condition-dependent role of the annealing treatment is also discussed.