Origin of the enhancement of electrocatalytic activity and durability of PtRu alloy prepared from a hetero bi-nuclear Pt–Ru complex for methanol oxidation reactions

PtRu alloy, prepared by pyrolysis of hetero bi-nuclear Pt–Ru complexes, showed a higher electrocatalytic activity and durability in the methanol oxidation reaction (MOR) than PtRu alloy prepared by pyrolysis of a mixture of K2PtCl4 and RuCl3. The origin of this activity enhancement was investigated by XPS and Ru K edge XAFS measurements. Although both alloys were composed of metallic Pt and RuO2, the RuO2 in the PtRu alloy prepared from the Pt–Ru complex had greater oxygen deficiency than that in the PtRu alloy prepared from the mixture of K2PtCl4 and RuCl3. XAFS measurements showed that the Ru–O distance of the former was longer than that of the latter, suggesting the presence of the weakly coordinated oxygen species, i.e., H2O, in the PtRu alloy prepared from the Pt–Ru complex. The H2O coordinated to Ru can become an active oxidant, i.e., surface Ru–OH, under electrochemical conditions and enhance MOR activity and durability.