Ethanol-tolerant polyethyleneimine functionalized palladium nanowires in alkaline media: the “molecular window gauze” induced the selectivity for the oxygen reduction reaction

Abstract

Owing to the alcohol crossover problem, improving the selectivity of cathodic electrocatalysts for the oxygen reduction reaction (ORR) is one of the key challenges for the commercial viability of direct alcohol fuel cells. Pd is a highly efficient Pt-alternative electrocatalyst for the ORR in alkaline media and it is also highly active for the alcohol oxidation reaction (AOR) in alkaline media. In this work, we demonstrate an efficient water-based synthesis of Pd nanowires (Pd-NWs) in the presence of polyethyleneimine (PEI) with a branched structure. Experimental results show that the formation of Pd-NWs originates from the oriented attachment. During the synthesis, Pd-NWs are simultaneously functionalized by PEI due to the strong Pd–N interaction, which is confirmed by molecular dynamics simulation and various physical characterizations. PEI layers on Pd-NWs efficiently serve as a “molecular window gauze” to physically block the access of alcohol molecules to Pd sites but allow the access of oxygen molecules owing to their difference in molecular size, resulting in excellent alcohol tolerance of Pd-NWs for the ORR in alkaline media. Our results provide a new strategy for the design of ethanol-tolerant noble metal electrocatalysts.