The　development　of　photocatalysts　enabling　stable　and　highly　efficient　water　splitting　hydrogen　production　remains　an　open　challenge　in　the　field　of　energy　photocatalysis.　Herein,　Ni2P/γ-Ga2O3　nanosheets　have　been　reported　as　excellent　water　splitting　photocatalysts.　Ni2P　particles　and　γ-Ga2O3　nanosheets　were　synthesized　by　a　facile　hydrothermal　process.　The　Ni2P/γ-Ga2O3　samples　were　prepared　by　an　electrostatic　self-assembly　method　with　Ni2P　particles　and　γ-Ga2O3　nanosheets　as　precursors.　The　0.5　wt%　Ni2P/γ-Ga2O3　sample　shows　a　photocatalytic　H2-production　activity　as　high　as　2.7　mmol　g−1　h−1　in　pure　water　and　12　mmol　g−1　h−1　in　an　aqueous　methanol　solution　under　a　125　W　high　pressure　mercury　lamp,　respectively,　which　are　much　higher　than　those　of　pure　γ-Ga2O3　and　Pt/γ-Ga2O3　nanosheets　modified　with　a　comparable　Pt　content.　The　Ni2P　component　plays　a　role　as　an　electron　collector　that　promotes　efficient　separation　of　photogenerated　electrons　and　holes,　and　thereby　improves　the　efficiency　of　photocatalytic　hydrogen　production.　The　effects　of　inorganic　and　organic　sacrificial　reagents　on　the　reaction　efficiency　and　stability　were　observed　and　discussed.　This　work　shows　that　Ni2P　as　a　cocatalyst　substituting　noble　metals　can　greatly　improve　the　photocatalytic　hydrogen　production　efficiency　of　γ-Ga2O3　compared　to　that　in　pure　water　and　a　methanol-water　solution.　©　2022　The　Royal　Society　of　Chemistry.