Multifunctional Noble Metal Phosphide Electrocatalysts for Organic Molecule Electro-Oxidation

Small organic molecule electro-oxidation (OMEO) is the important anodic reaction occurring in direct liquid fuel cells (DLFCs) and requires efficient and durable electrocatalysts to promote the reactivity and operational stability. Noble metals (e.g., Pt and Pd) are currently the state-of-the-art catalysts for OMEO; however, for practical applications, their electrocatalytic performance needs to be improved. Herein, we report a simple and potentially cost-effective approach to the synthesis of noble metal phosphide (MxPy, M = Pd, Pt) catalysts, which is realized by phosphidating commercially available supported noble metal catalysts in red phosphorus vapor at different temperatures. We demonstrate that the derived PdP2–Pd/C heterostructured catalysts show the best electrocatalytic performance toward a number of OMEO model reactions, including the formic acid oxidation reaction, methanol oxidation reaction, ethanol oxidation reaction, and ethylene glycol oxidation reaction, in terms of not only apparent activity but also of specific and mass activities, poisoning tolerance, and catalytic stability, with respect to both the starting Pd/C and other prepared palladium phosphide control catalysts. Similar performance enhancement is also observed for the PtP2–Pt/C heterostructured catalysts for all model reactions. The enhancement may result from the synergy between the noble metal phosphide and the noble metal, where the formed phosphide facilitates the adsorption of hydroxyl species and promotes the oxidation of poisoning intermediates, giving rise to improved activity, poisoning tolerance, and stability. Our work demonstrates an easy way of boosting the electrocatalytic performance of commercial catalysts toward multiple OMEO reactions and shows substantial promise for their usage in DLFCs.