Implicating the contributions of surface and bulk states on carrier trapping and photocurrent performance of BiVO4 photoanodes.

Monoclinic-scheelite BiVO4 has been widely studied as a promising oxygen evolution reaction (OER) catalyst in artificial photosynthesis. Though significant progress to improve or augment its catalysis performance has been made, fundamental understanding of its relatively poor performance as a bare material is lacking. In this paper, we report the correlation of the surface structure and trap states with charge separation efficiency and OER performance of bare BiVO4 photoanodes via varying the sample thickness. Using X-ray absorption spectroscopy (XAS), we observed a more compacted, symmetric Bi center in the surface state. Using transient absorption (TA) spectroscopy, we show that the structural properties of the surface lead to shallow and deep hole trap states and electron trapping that occurs at the surface of the material. Despite more severe carrier trapping on the surface, our OER measurements demonstrate that a significant bulk structure is required for light absorption but is only beneficial until the carrier mobility becomes the limiting factor in photoelectrochemical cell studies.