Photocatalytic　hydrogen　peroxide　synthesis　is　a　green　approach　to　produce　this　widely-used　chemical　and　potential　energy　carrier,　yet　performance　is　often　poor.　A　porphyrin-based　photocatalyst　is　now　shown　to　produce　hydrogen　peroxide　by　an　unusual　mechanism　involving　both　photoexcited　electrons　and　holes　with　promising　efficiency.