Interfacial　water　and　its　dissociated　species　play　key　roles　in　aqueous　electrocatalysis.　Here,　the　authors　study　the　ethanol　electrooxidation　on　platinum　electrodes　at　potentials　up　to　1.5　V　vs.　RHE　and　find　that　the　oxygen　species　stemming　from　water,　PtOHads,　and　alpha-PtO2　act　as　catalytic　centers.　Water　and　its　dissociated　species　at　the　solid-liquid　interface　play　critical　roles　in　catalytic　science;　e.g.,　functions　of　oxygen　species　from　water　dissociation　are　gradually　being　recognized.　Herein,　the　relationship　between　oxide　identity　(PtOHads,　PtOads,　and　PtO2)　and　electrocatalytic　activity　of　platinum　for　ethanol　electrooxidation　was　obtained　in　perchlorate　acidic　solution　over　a　wide　potential　range　with　an　upper　potential　of　1.5　V　(reversible　hydrogen　electrode,　RHE).　PtOHads　and　alpha-PtO2,　rather　than　PtOads,　act　as　catalytic　centers　promoting　ethanol　electrooxidation.　This　relationship　was　corroborated　on　Pt(111),　Pt(110),　and　Pt(100)　electrodes,　respectively.　A　reaction　mechanism　of　ethanol　electrooxidation　was　developed　with　DFT　calculations,　in　which　platinum　oxides-mediated　dehydrogenation　and　hydrated　reaction　intermediate,　geminal　diol,　can　perfectly　explain　experimental　results,　including　pH　dependence　of　product　selectivity　and　more　active　alpha-PtO2　than　PtOHads.　This　work　can　be　generalized　to　the　oxidation　of　other　substances　on　other　metal/alloy　electrodes　in　energy　conversion　and　electrochemical　syntheses.