Pd–Cu alloy catalyst synthesized by citric acid-assisted galvanic displacement reaction for N2O reduction

Abstract

In this study, the composition-optimized Pd–Cu catalyst for electrochemical N2O reduction in highly alkaline solution was prepared by a galvanic displacement method. The atomic ratio of Pd to Cu in Pd–Cu bimetallic catalyst, which has been known to be hardly controlled using galvanic displacement, was tailored by varying the concentration of citric acid in galvanic displacement bath. With increasing citric acid concentration, the decreased grain size, characterized by X-ray diffraction, and the increased amount of carbon in Pd–Cu catalyst, measured by energy-dispersive X-ray spectrometry, revealed the incorporation of citric acid into the catalyst, which was attributed to the tunable catalyst composition. The incorporation of citric acid into Pd–Cu deposit restrained the diffusion of Cu from Cu substrate to deposit, leading to decrease in the Cu content in Pd–Cu. The electrocatalytic activity for N2O reduction was strongly dependent on the Pd/Cu composition in Pd–Cu catalysts. Among the investigated Pd–Cu catalysts with different compositions, the highest electrocatalytic activity was obtained with Pd60Cu40 with a Tafel slope of 0.096 V dec−1. Moreover, the Pd60Cu40 catalyst showed remarkably enhanced mass-specific activity for N2O reduction, compared with a commercial Pd/C. The density functional theory (DFT) calculations revealed that the highest N2O reduction activity of Pd60Cu40 could be attributed to the facilitation of an adsorption/desorption balance for N2O reduction, resulting from the appropriately lowered d-band center of catalyst.