Microwave-assisted fabrication of self-supported graphene-based high-entropy alloy electrode for efficient and stable electrocatalytic nitrate reduction to ammonia

Abstract

Direct electrochemical nitrate reduction for ammonia (NRA) synthesis is an efficient and environmentally friendly production technology. However, the development of highly selective electrocatalysts is still a challenge due to its nine-proton and eight-electron reaction. High-entropy alloys (HEAs) have a wide range of elements and adjustable properties, giving them excellent application potential in multi-step reactions. In this work, we skillfully use the local high temperature and excellent thermal conductivity generated at the reduced graphene oxide (rGO) defect in the microwave process to achieve a rapid quenching process in 10 seconds. This approach overcomes element immiscibility and results in a self-supported, single-phase, non-precious metal and uniform FeCoNiCuSn alloy electrode. The HEA reaches a remarkable NH3 yield of 883.7±11.2 μg h^-1 cm^-2, the maximum Faradaic efficiency (FE) of 94.5±1.4%, and the highest NH3 selectivity of 90.4±2.7%. Experimental and theoretical calculations reveal that the presence of multiple adjacent elements in HEA triggers a synergistic catalytic effect, while the excellent mass and charge transfer properties of rGO jointly encourage the performance of electrochemical NRA. In particular, NO₃⁻ favors vertical adsorption at Fe-Fe sites, and the desorption of NH3 is identified as the rate-determining step (RDS) with a extremely small ΔG of 0.7eV.