Mesoporous platinum as a catalyst for oxygen electroreduction and methanol electrooxidation

A mesoporous platinum catalyst (H_I-Pt) containing pores of diameter 34 Å has been examined as a potential catalytic material for both the electrochemical reduction of oxygen and the electrochemical oxidation of methanol. The material has been characterized in sulfuric acid at room temperature by voltammetry and chronoamperometry as an abrasively deposited microelectrode. About one-quarter of the internal pore surface area appears to be electrochemically accessible. The material shows good activity towards the reduction of dissolved dioxygen molecules, with an exchange current density and Tafel slope close to that seen for conventional dispersed platinum catalysts. The mass activity towards the oxygen reduction in 0.5 mol dm^-3 H₂SO₄ reaction is quite low, at 1.1 A g^-1, and the specific activity is also quite low at 7.4 μA cm^-2, both at 900 mV (RHE). Both these low values may be due to the relatively poor surface area to volume ratio of this particular catalyst formulation. In comparison, the methanol oxidation activity seems to be significantly improved compared to normal dispersed platinum catalysts in 0.5 mol dm^-3H₂SO₄ and 1 mol dm^-3 CH₃OH with values of 20 A g^-1, and 42 mA cm^-2 at 0.55 V (RHE) and 65 °C. A discussion of the unique features of this catalyst and how the structural morphology of the mesoporous phase may affect the electrocatalytic activity of the catalyst is given.