Bias‐Free Solar‐To‐Hydrogen Peroxide Production Using Nanoporous BiVO 4 ‐Based Photoanode With Atomic Layer Deposited SnO 2

ABSTRACT Hydrogen peroxide (H 2 O 2 ) is a green oxidant with an energy density comparable to that of compressed hydrogen, making it a promising candidate for chemical energy storage. Converting renewable energy into H 2 O 2 via the photoelectrochemical water oxidation reaction offers a sustainable pathway, yet the competing oxygen evolution reaction limits the solar‐to‐chemical conversion (SCC) efficiency. Here, we develop a BiVO 4 based photoanode combined with a conformal SnO 2 passivation layer. A built‐in electric field is established at the SnO 2 /BiVO 4 heterojunction, which facilitates charge separation and promoting hole transport toward the SnO 2 surface. The valence band edge of SnO 2 is also thermodynamically favorable for H 2 O 2 production. To further improve H 2 O 2 production, a CaSnO 3 cocatalyst is integrated on the photoanode, enabling enhanced reaction kinetics and selectivity toward 2e − water oxidation pathway. The resulting CaSnO 3 /SnO 2 /BiVO 4 photoanode achieves an average Faradaic efficiency of 90% over wide potential range of 0.6–2.1 V RHE , with a H 2 O 2 generation rate of 0.838 µmol cm −2 min −1 and a photocurrent density of 5.44 mA·cm −2 at 1.23 V RHE . Photoelectrochemical device composed of CaSnO 3 /SnO 2 /BiVO 4 photoanode and perovskite/Si photovoltaic simultaneously produce H 2 O 2 and H 2 without applied bias, which achieving SCC efficiency of 1.12%, the highest record to date for bias‐free H 2 O 2 production at a single photoanode.