Exploring the Charge Dynamics in a Synergistically Modified BiVO₄ Photoanode with La Doping and Cobalt-Based Phytate Compound Cocatalyst for Photoelectrochemical Water Oxidation

Bismuth vanadate (BiVO₄) is a potential photoelectrode for photoelectrochemical (PEC) applications. Nevertheless, the rapid charge recombination and sluggish water oxidation kinetics greatly limit the PEC activity. To address these drawbacks, this study developed a cooperative modification strategy with simultaneous La doping and amorphous cobalt-phytate compound (Co-phy) as a cocatalyst on BiVO₄ to raise the PEC performance. La doping increased the donor density, and the decoration of the Co-phy cocatalyst expedited water oxidation kinetics and further improved the utilization efficiency of charge carriers. As a result, the constructed hybrid photoelectrode (La-BVO/Co-phy) generated a photocurrent of 2.12 mA·cm^-2 at 1.23 V vs RHE, about 4.8 times that of the pristine BiVO₄ photoelectrode (0.44 mA·cm^-2). Moreover, a significant reduction in onset potential and prominent improvement in conversion efficiency, stability, and charge separation efficiency were achieved for the synergistically modified photoanode. Furthermore, a profound exploration on the charge dynamics disclosed increased carrier density, decreased charge recombination, and enhanced charge transfer kinetics as a consequence of the synchronized effect of La doping and Co-phy cocatalyst, which greatly contributed to the elevated PEC activity. This work introduces a practical route to fabricating BiVO₄-based photoelectrodes for solar water splitting applications.