Polymeric　carbon　nitride　modified　with　selected　heteroatom　dopants　was　prepared　and　used　as　a　model　photocatalyst　to　identify　and　understand　the　key　mechanisms　required　for　efficient　photoproduction　of　H2O2　via　selective　oxygen　reduction　reaction　(ORR).　The　photochemical　production　of　H2O2　was　achieved　at　a　millimolar　level　per　hour　under　visible-light　irradiation　along　with　100　%　apparent　quantum　yield　(in　360–450　nm　region)　and　96　%　selectivity　in　an　electrochemical　system　(0.1　V　vs.　RHE).　Spectroscopic　analysis　in　spatiotemporal　resolution　and　theoretical　calculations　revealed　that　the　synergistic　association　of　alkali　and　sulfur　dopants　in　the　polymeric　matrix　promoted　the　interlayer　charge　separation　and　polarization　of　trapped　electrons　for　preferable　oxygen　capture　and　reduction　in　ORR　kinetics.　This　work　highlights　the　key　features　that　are　responsible　for　controlling　the　photocatalytic　activity　and　selectivity　toward　the　two-electron　ORR,　which　should　be　the　basis　of　further　development　of　solar　H2O2　production.　©　2020　Wiley-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim