Synergistic bimetallic CuPd oxide alloy electrocatalyst for ammonia production from the electrochemical nitrate reaction

Abstract

The electrochemical nitrate reduction reaction (eNO₃RRs) can produce value-added chemicals such as ammonia (NH₃) via multiple steps. Here, we demonstrate that bimetallic Cu–Pd–O_x alloy electrocatalysts can promote selective NH₃ production from the eNO₃RR, especially at low overpotential, by accelerating the rate-determining hydrogenation of NO₂⁻, a critical intermediate, on the Cu catalyst. The synergistic effect of Cu and Pd affords 14 times higher NH₃ yield (1.41 mg h⁻¹ cm⁻²) at −0.2 V_RHE with an optimum composition (Cu_0.65Pd_0.35O_x) than that obtained using bare CuO_x. The operando near edge X-ray absorption fine structure (NEXAFS) and simulation results support that the high hydrogen affinity of Pd facilitates sequential hydrogenation on metallic Cu active sites, consequently increasing the NH₃ selectivity and production rate. Our study sheds light on the mechanism of the catalytic eNO₃RR and presents a design strategy for more advanced eNO₃RR electrocatalysts.