NOVELTY - Preparing catalyst (I) on a substrate, comprises depositing a thin-film electrocatalyst of a platinum phosphate composite surface onto the substrate through cyclic voltammetry, where the platinum phosphate composite surface is entirely oxygen reductive.    USE - (I) is useful for: preparing substrates for fuel cells; and reducing oxygen and oxidizing methanol (all claimed) for fuel cell devices. (I) is useful as fuel cell cathode.    ADVANTAGE - (I) generates high power density, hence potentially reduces oxygen. (I) enhances oxygen reduction in water as presumably utilizing water as oxygen source and has the potential to reduce water management problem in the proton exchange membrane fuel cell. (I) can increase the power density of fuel cells due to: offering several active catalysts as a composite to reduce oxygen, as well as larger active surfaces to reduce oxygen because the entire platinum surface, not just a portion of it, is engaged in oxygen reduction; minimizing inactive hydroxide and oxide layers of platinum due to incorporation of bound phosphate to platinum(II) and platinum(III) oxidation states; minimizing loss of catalytic activity by preventing oxidation of platinum that takes place at more positive potentials; minimizing hydrogen cross-over problems because the mixed-valence surface minimizes hydrogen adsorption/desorption properties; and enhancing lifetime by minimizing carbon monoxide reduction, with or without additional catalysts.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a method of preparing substrates for fuel cells, comprising depositing a thin-film electrocatalyst of a platinum phosphate composite surface onto at least one substrate of a membrane electrode assembly of a fuel cell through cyclic voltammetry;    (2) a method of reducing oxygen, comprising: depositing the thin-film electrocatalyst of a platinum phosphate composite surface on a substrate cathode; and reducing oxygen by using the entire platinum phosphate composite surface of the thin-film electrocatalyst; and    (3) a method of oxidizing methanol, comprising: depositing the thin-film electrocatalyst of a platinum phosphate composite surface on a substrate cathode; reducing oxygen from air by using the entire platinum phosphate composite surface of the thin-film electrocatalyst; and oxidizing methanol on an anode.