In　this　work,　protonated　poly(heptazine　imide)　(H-PHI)　was　obtained　by　adding　acid　to　the　suspension　of　potassium　PHI　(K-PHI)　in　ethanol.　It　was　established　that　the　obtained　H-PHI　demonstrates　very　high　photocatalytic　activity　in　the　reaction　of　hydrogen　formation　from　ethanol　in　the　presence　of　Pt　nanoparticles　under　visible　light　irradiation　in　comparison　with　K-PHI.　This　enhancement　can　be　attributed　to　improved　efficiency　of　photogenerated　charge　transfer　to　the　photocatalyst’s　surface,　where　redox　processes　occur.　Various　factors　influencing　the　system’s　activity　were　evaluated.　Notably,　it　was　discovered　that　the　conditions　of　acid　introduction　into　the　system　can　significantly　affect　the　size　of　Pt　(cocatalyst　metal)　deposition　on　the　H-PHI　surface,　thereby　enhancing　the　photocatalytic　system’s　stability　in　producing　molecular　hydrogen.　It　was　established　that　the　system　can　operate　efficiently　in　the　presence　of　air　without　additional　components　on　the　photocatalyst　surface　to　block　air　access.　Under　optimal　conditions,　the　apparent　quantum　yield　of　molecular　hydrogen　production　at　410　nm　is　around　73%,　the　highest　reported　value　for　carbon　nitride　materials　to　date.　The　addition　of　acid　not　only　increases　the　activity　of　the　reduction　part　of　the　system　but　also　leads　to　the　formation　of　a　value-added　product　from　ethanol-1,1-diethoxyethane　(acetal)　with　high　selectivity.　©　2024　The　Authors.　Published　by　American　Chemical　Society.