Phase Engineering of High-Entropy Alloy for Enhanced Electrocatalytic Nitrate Reduction to Ammonia

Abstract

Directly electrochemical conversion of nitrate (NO<inf>3</inf>⁻) is an efficient and environmentally friendly technology for ammonia (NH<inf>3</inf>) production but is challenged by highly selective electrocatalysts. High-entropy alloys (HEAs) with unique properties are attractive materials in catalysis, particularly for multi-step reactions. Herein, we first reported the application of HEA (FeCoNiAlTi) for electrocatalytic NO<inf>3</inf>⁻ reduction to NH<inf>3</inf> (NRA). The bulk HEA is active for NRA but limited by the unsatisfied NH<inf>3</inf> yield of 0.36 mg h⁻¹ cm⁻² and Faradaic efficiency (FE) of 82.66 %. Through an effective phase engineering strategy, uniform intermetallic nanoparticles are introduced on the bulk HEA to increase electrochemical active surface area and charge transfer efficiency. The resulting nanostructured HEA (n-HEA) delivers enhanced electrochemical NRA performance in terms of NH<inf>3</inf> yield (0.52 mg h⁻¹ cm⁻²) and FE (95.23 %). Further experimental and theoretical investigations reveal that the multi-active sites (Fe, Co, and Ni) dominated electrocatalysis for NRA over the n-HEA. Notably, the typical Co sites exhibit the lowest energy barrier for NRA with *NH<inf>2</inf> to *NH<inf>3</inf>as the rate-determining step.