Interfacial　charge　transfer　and　separation　are　both　critical　to　the　solar　energy　conversion　efficiency,　whereas　it　remains　an　enduring　challenge.　This　work　demonstrates　the　synergetic　enhancement　of　interfacial　charge　transfer　efficiency　and　bulk　charge　separation　by　depositing　p-type　Co3O4　cocatalyst　onto　n-type　TiO2　nanotube　arrays　(TNTAs)　that　are　uniformly　coated　with　an　ultrathin　carbon　layer,　forming　a　p　−　n　Co3O4/TNTAs　heterojunction.　Being　highly　dispersed　on　the　surface　of　photoanodes,　Co3O4　quantum　dots　retard　forming　charge　recombination　centers　at　the　photoanode/cocatalyst　interface,　which　facilitates　hole　transport.　Simultaneously,　ultrathin　intermediate　carbon　layer　boosts　interfacial　electron　transfer　kinetics,　resulting　in　effective　spatial　charge　separation　and　considerably　improved　photoelectrochemical　(PEC)　water　splitting　performances.　©　2022　The　Authors