Platinum-monolayer electrocatalysts: Palladium interlayer on IrCo alloy core improves activity in oxygen-reduction reaction

We describe the synthesis and electrocatalytic properties of a new low-Pt electrocatalyst consisting of an IrCo core, a Pd interlayer, and a surface Pt monolayer, emphasizing the interlayer’s role in improving electrocatalytic activity for the oxygen-reduction reaction on Pt in HClO4 solution. We prepared the IrCo alloys by decomposing, at 800 °C, hexacyanometalate, KCoIr(CN)6, adsorbed on the carbon surfaces. The synthesis of Ir3Co/C involved heating a mix of metal salts and carbon in hydrogen at 500 °C. Thereafter, we placed a palladium and/or platinum monolayer on them via the galvanic displacement of an underpotentially deposited copper monolayer. The electrocatalysts were characterized using structural- and electrochemical-techniques. For PtML/PdML/IrCo/C, we observed a Pt mass activity of 1.18 A/mg(Pt) and the platinum-group-metals’ mass of 0.16 A/mg(Pt, Pd, Ir). In comparison, without a Pd interlayer, i.e., PtML/IrCo/C, the activities of 0.15 A/mg(Pt) and 0.036 A/mg(Pt, Pd, Ir) were considerably lower. We consider that the palladium interlayer plays an essential role in achieving high catalytic activity by adjusting the electronic interaction of the platinum monolayer with the IrCo core, so that it accelerates the kinetics of adsorption and desorption of the intermediates of oxygen reduction. A similar trend was observed for PtML/PdML and PtML deposited on Ir3Co/C alloy core. We used density functional theory to interpret the observed phenomena.