The　charge　transfer　between　hydrogen　evolution　photocatalysts　(HEPs)　and　oxygen　evolution　photocatalysts　(OEPs)　is　the　rate-determining　step　that　controls　the　overall　performance　of　a　Z-scheme　water-splitting　system.　Here,　we　carefully　design　reduced　graphene　oxide　(RGO)　nanosheets　for　use　as　solid-state　mediators　to　accelerate　the　charge　carrier　transfer　between　HEPs　(e.g.,　polymeric　carbon　nitride　(PCN))　and　OEPs　(e.g.,　Fe2O3),　thus　achieving　efficient　overall　water　splitting.　The　important　role　of　RGO　could　also　be　further　proven　in　other　PCN-based　Z-systems　(BiVO4/RGO/PCN　and　WO3/RGO/PCN),　illustrating　the　universality　of　this　strategy.　©　2019　Wiley-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim