The　direct　hybridization　of　Pt　and　g-C3N4　generally　forms　a　Schottky　barrier　between　the　two　components,　which　unavoidably　hinders　the　migration　of　photogenerated　electrons　from　g-C3N4　to　the　Pt　cocatalyst.　Herein,　we　report　the　first　efficient　allochroic　Pt/g-C3N4　photocatalyst　that　can　form　an　ohmic　contact　through　photoconversion　of　semiconducting　g-C3N4　to　metalloid,　accompanied　with　the　charge　carrier　storage　and　photocatalyst　color　change,　which　is　proved　experimentally　and　theoretically.　Through　intermittent　exposure　of　Pt/g-C3N4　photocatalyst　to　air　for　a　few　minutes　during　photocatalysis,　the　photocatalyst　shows　the　highest　hydrogen　evolution　performances.　The　ohmic　contacts　greatly　promote　the　electron　transfer　from　the　semiconducting　g-C3N4　to　the　Pt　cocatalyst　driven　by　the　built-in　electric　field.　In　addition,　the　mechanism　for　the　photocatalyst　deactivation　and　activation　is　presented.　The　compositional　tuning　of　the　allochroic　g-C3N4　through　light　irradiation　and　exposure　to　air　can　control　over　the　photocatalytic　activity　and　long-term　stability　for　hydrogen　evolution.　This　report　for　the　first　time　unveils　the　deactivation　and　regeneration　mechanisms　of　SCN.　©　2023　The　Author(s)