Mesoporous PdCo sponge-like nanostructure synthesized by electrodeposition and dealloying for oxygen reduction reaction

A mesoporous PdCo sponge-like nanostructure was successfully synthesized by the combination of electrodeposition and dealloying, and was evaluated as a catalyst for the oxygen reduction reaction of fuel cells. The synthesized film had a sponge-like mesoporosity consisting of 5-30 nm thick ligaments with pores of tens of nanometers. Its porosity was estimated to be ca. 62%, suggesting that the oxygen transport in the film was smooth. The resultant composition was Pd₉₃Co₇, whose crystalline phase was determined to be a solid solution of Pd₉₂Co₈ by X-ray diffractometry. This degree of alloying is known to induce the most desirable lattice contraction into a Pd catalyst for the oxygen reduction reaction. Actually, the mesoporous PdCo catalyst had a higher specific activity than the Pt catalyst in the potential range of <0.85 V vs. SHE, i.e., the potential range of interest for fuel cell operation. This fascinatingly higher catalytic activity was attributable to the preferable reaction mechanism, because the PdCo electrode had a lower Tafel slope (43 mV decade^-1) than a typical Pt electrode (71 mV decade^-1).