Nanoporous PtCo surface alloy architecture with enhanced properties for methanol electrooxidation

Abstract

By selectively dealloying a PtCoAl ternary alloy, a novel nanoporous PtCo (np-PtCo) alloy with a three-dimensional bicontinuous pore-ligament structure is successfully fabricated. X-ray diffraction and electron microscopic characterizations demonstrate the single-crystal nature of the alloy ligament with a ligament size down to 3 nm. After a mild electrochemical dealloying process, a nanoporous near-surface alloy structure with a Pt-rich surface and a PtCo alloy core is obtained. Electrochemical measurements show that the np-PtCo surface alloy has greatly enhanced catalytic activity and durability toward methanol electrooxidation compared with a state-of-the-art Pt/C catalyst. The peak current density of methanol electrooxidation on a np-PtCo surface alloy is more than 5 times of that on Pt/C. More importantly, continuous potential cycling from 0.6 to 0.9 V (vs RHE) in a 0.5 M H2SO4 aqueous solution demonstrates that a np-PtCo surface alloy has excellent structure stability, with more than 90% of the initial electrochemical active surface area (EASA) retained after 5000 potential cycles. Under the same conditions, the EASA of Pt/C drops to 70%. With evident advantages of facile preparation as well as enhanced electrocatalytic activity and durability, a np-PtCo surface alloy nanomaterial holds great potential as an anode catalyst in direct methanol fuel cells.