Creation of Dopant‐Plasmon Synergism in Double Perovskites for Bias‐free Photoelectrochemical Synthesis of Bromohydrins and Hydrogen Peroxide

Abstract The integration of photoexcited charge carriers into the synthesis of valuable chemicals offers substantial sustainability benefits, particularly by replacing toxic and costly oxidants and reductants typically used in conventional processes. The efficiency of such transformations is fundamentally governed by the ability to optimize light absorption and charge carrier dynamics within photoelectrodes/photocatalysts. Herein, we present a Cu + /Cu 2+ ‐substituted double perovskite Cs 2 AgBiBr 6 photoanode, embedded with plasmonic Ag nanoparticles, for bias‐free photoelectrochemical production of bromohydrins and H 2 O 2 . Spectroscopic analyses, coupled with three‐dimensional finite‐difference time‐domain simulations, demonstrate that the inclusion of Ag nanoparticles significantly enhances electromagnetic energy utilization and improves carrier separation efficiency. The synergistic effect of the Cu 2+ and Ag nanoparticles results in a 7‐fold increase in the yield of 2‐bromo‐1‐phenylethanol, compared to pristine Cs 2 AgBiBr 6 , alongside an impressive H 2 O 2 productivity of 25.8 μmol h −1 cm −2 . Experimental and theoretical investigations reveal that the Cu 2+ substitution strengthens Br − adsorption and oxidation, promoting the bromohydroxylation of alkenes via electrophilic addition in the bulk solution. These findings offer critical insights into the design of advanced metal halide perovskites for sustainable and solar‐driven chemical transformations.