Bias‐Free Solar Water Splitting by Tetragonal Zircon BiVO4 Nanocrystal Photocathode and Monoclinic Scheelite BiVO4 Nanoporous Photoanode

Abstract p‐type tetragonal zircon BiVO 4 nanocrystal photocathodes (P‐BVO) and n‐type monoclinic scheelite BiVO 4 nanoporous photoanodes (N‐BVO) are prepared by a hydrothermal method and an electrochemical synthesis method, respectively. Pt nanoparticles and cobalt‐phosphate (Co‐Pi) as co‐catalysts are loaded by an electrodeposition way to improve the photoelectrochemical (PEC) performance of BiVO 4 (BVO) electrodes. After modification, a monochromatic incident photon‐to‐current conversion efficiency (IPCE) of P‐BVO/Pt at 360 nm is improved by 2.2 times, and the highest IPCE of N‐BVO/Co‐Pi at 440 nm is increased by 1.7 times. The calculated electron‐hole separation yield and the charge carrier injection yield of N‐BVO/Co‐Pi at 1.23 V RHE are further improved to 80% and 86%, respectively. The surface modification also results in the latest ≈0.2% half‐cell solar‐to‐hydrogen energy conversion efficiency (HC‐STH) for a P‐BVO/Pt photocathode and a higher ≈1.16% half‐cell applied bias photon‐to‐current conversion efficiency (ABPE) for an N‐BVO/Co‐Pi photoanode. Furthermore, the prepared photoelectrodes are proved to have excellent stability for water splitting. Above all, a tandem‐type PEC cell containing the newly developed P‐BVO/Pt photocathode and an N‐BVO/Co‐Pi photoanode is built for the first time, which evolves H 2 and O 2 at a stoichiometric ratio of 2:1 with a bias‐free STH of 0.14%.