Heterogeneous　photoelectrocatalysis　systems　have　recently　seen　significant　growth　in　organic　transformations,　but　are　limited　by　the　inherent　physicochemical　properties　of　electrode　materials.　To　enhance　selectivity　in　these　processes,　we　propose　an　innovative　advancement　in　the　rational　design　of　photoanodes.　Specifically,　we　incorporated　cobalt　porphyrin　co-catalysts　with　confined　Co　sites　onto　bismuth　vanadate　films　as　a　photoanode.　This　photoanode　significantly　enhances　the　efficacy　of　styrene　epoxidation,　achieving　selectivity　and　conversion　rates　of　90　%　and　99　%,　respectively.　Notably,　the　reaction　utilizes　water　as　the　sole　oxygen　source,　operates　at　room　temperature,　and　is　easily　scalable　for　gram-scale　synthesis.　The　developed　photoanode　demonstrates　robust　performance　across　various　alkene　substrates.　Operando　characterizations　reveal　that　during　the　epoxidation　reaction,　the　confined　Co　sites　within　the　porphyrin　structure　catalyze　the　oxidation　of　H2O　to　form　Co−O*,　serving　as　critical　intermediates　that　facilitate　cyclization　reactions　via　one-electron　processes.　This　study　introduces　an　innovative　heterogeneous　photoelectrocatalysis　strategy　with　customizable　active　sites　tailored　for　selective　catalytic　organic　transformations.　©　2024　Wiley-VCH　GmbH.