Multifunctional Noble Metal Phosphide Electrocatalysts for the Organic Molecule Electro-Oxidation

Abstract

The small organic molecule electro-oxidation (OMEO) is the important anodic reaction occurring in direct liquid fuel cells (DLFCs), whose kinetics are largely hindered by the low activity and poor stability of electrocatalysts. Noble metals (e.g. Pt, Pd) are currently the state-of-the-art catalysts for the OMEO; however, for practical applications their electrocatalytic performance needs to be improved. Herein, we demonstrate that a simple phosphorization treatment at different temperatures is able to convert commercially available supported noble metal catalysts (PdNi, Pd) into multifunctional metal phosphide (PdNiP) or phosphide-metal heterostructures (PdP2-Pd/C), which exhibit substantially enhanced electrocatalytic performance toward a number of OMEO model reactions including the formic acid oxidation reaction (FAOR), methanol oxidation reaction (MOR), ethanol oxidation reaction (EOR), and ethylene glycol oxidation reaction (EGOR), in terms of not only apparent activity, but also of specific and mass activities, poisoning tolerance and catalytic stability. The improved performance and stability results from the modification of electronic structure by the introduced phosphor and synergy between of multinary structure (PdP and NiP, PdP2 and Pd), 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. The simple phosphorization approach reported here allows for mass production of highly-active electrocatalytic performance toward multiple OMEO reactions, holding substantial promise for their large-scale application in DLFCs.