Photocatalytic　synthesis　of　hydrogen　peroxide　(H2O2)　over　graphitic　carbon　nitride　(g-C3N4)　has　gained　increasing　attention　due　to　green,　economy,　sustainability　and　safety.　However,　its　activity　is　impeded　by　the　low　oxidizing　ability　of　photoexcited　holes,　sluggish　oxygen　reduction　reaction　(ORR)　kinetics,　and　fast　recombination　of　photoexcited　charge　carriers.　Here,　we　show　an　Ohmic　heterojunction　of　NiS2/g-C3N4　for　photosynthesis　of　H2O2　from　water　and　air　under　visible　light　illumination　without　sacrificial　agents.　In　this　photosynthesis　system,　NiS2　regulated　the　valence　band　of　g-C3N4　and　improved　the　oxidation　capacity　of　photogenerated　holes,　which　can　directly　oxidize　H2O　to　produce　H2O2.　Additionally,　NiS2　and　g-C3N4　form　a　reverse　barrier　layer　(the　internal　electric　field　force　and　the　band　bending　produce　forces　in　the　same　direction　upon　the　photogenerated　electron　transfer),　which　is　conducive　to　the　separation　and　migration　of　photogenerated　charge　carriers.　More　importantly,　the　separated　electrons　and　holes　are　fully　utilized,　respectively　reducing　O2　and　oxidizing　H2O　to　produce　H2O2.　The　activity　of　H2O2　production　by　NiS2/g-C3N4　was　therefore　significantly　improved　(approximately　4.5-fold　activity　enhancement　in　contrast　to　g-C3N4)　when　the　two　pathways　were　carried　out　simultaneously.　This　study　sheds　light　on　the　reverse　barrier　layer　photocatalyst　with　multiple　functions　for　efficient　H2O2　photosynthesis　and　relevant　solar　energy　utilization.　©　2025　Elsevier　B.V.