Both　the　hydrogen　evolution　reaction　(HER)　and　the　oxygen　evolution　reaction　(OER)　are　crucial　to　water　splitting,　but　require　alternative　active　sites.　Now,　a　general　pi-electron-assisted　strategy　to　anchor　single-atom　sites　(M=Ir,　Pt,　Ru,　Pd,　Fe,　Ni)　on　a　heterogeneous　support　is　reported.　The　M　atoms　can　simultaneously　anchor　on　two　distinct　domains　of　the　hybrid　support,　four-fold　N/C　atoms　(M@NC),　and　centers　of　Co　octahedra　(M@Co),　which　are　expected　to　serve　as　bifunctional　electrocatalysts　towards　the　HER　and　the　OER.　The　Ir　catalyst　exhibits　the　best　water-splitting　performance,　showing　a　low　applied　potential　of　1.603　V　to　achieve　10　mA　cm(-2)　in　1.0　m　KOH　solution　with　cycling　over　5　h.　DFT　calculations　indicate　that　the　Ir@Co　(Ir)　sites　can　accelerate　the　OER,　while　the　Ir@NC3　sites　are　responsible　for　the　enhanced　HER,　clarifying　the　unprecedented　performance　of　this　bifunctional　catalyst　towards　full　water　splitting.