Both Hole Transfer and Cocatalysis Exhibited by Organometallic Complexes for Enhancing Water-Splitting Performance of the Photoreducing BiVO4 Photoanode

Abstract

BiVO₄ is recognized as a promising water-splitting photoanode candidate; however, the inherent properties of short carrier diffusion length, poor electron mobility, and slow surface reaction still impede its application. In response, an incorporated BiVO₄-based photoelectrode has been designed by oxygen vacancy (O_v) fabrication and organometallic complexes decoration. The O_v produced by photoassisted self-reduction dramatically improves the carrier density and conductivity of BiVO₄ and restrains the photogenerated electron–hole recombination. Furthermore, the organometallic complex coating constructed by tannic acid (TA) and single metal (Fe, Co, or Ni) ions plays a positive role in increasing the electrochemically active surface area and accelerating the reaction kinetics. Particularly, the TA-Co decoration can be treated as both a hole transfer and cocatalyst layer. It can quickly extract carriers to reach the electrode surface, simultaneously reduce interface charge transfer resistance, and provide plentiful active sites for the oxygen evolution reaction (OER). The results show that the photocurrent density of the O_V-BiVO₄/TA-Co photoanode attains 3.8 mA cm^–2 at 1.23 V vs RHE, 5.28 times enhanced than that of bare BiVO₄. It also displays good photocorrosion resistance and stability. This work offers a specific path to design the highly active composite photoanode and enables efficient extraction and utilization of photogenerated holes to optimize PEC water-splitting performance.