Investigation of copper-based catalysts for the electroreduction of nitrate to ammonia

Abstract

The Haber-Bosch process is one of the most important chemical processes in use today and remains the primary method for producing ammonia—a compound essential for fertilizers, pharmaceuticals, textiles, and with potential as a hydrogen carrier.1–3 While vital to modern industry, this process consumes nearly 2% of global energy and emits around 450 million tons of CO2 annually.2,4 Electrochemical ammonia synthesis offers a greener alternative by converting nitrate (NO3-) pollutants into ammonia (NH3), simultaneously enabling sustainable ammonia production and water remediation.1,5 The electroreduction of nitrate was investigated using copper and CuxM100–x nanoparticles (M = Ni, Fe, or Co) synthesized by pulsed laser ablation in liquids (PLAL), a surfactant-free technique that produces clean, high–surface-area catalysts through laser ablation of metal targets in liquid media.6,7 The resulting nanoparticles were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), and microwave plasma atomic emission spectroscopy (MP-AES), and their electrocatalytic performance toward NO3- reduction was evaluated by cyclic voltammetry (CV) and chronoamperometry (CA). Among the catalysts studied, CuxCo100-x alloys exhibited the highest selectivity toward ammonia.8 The best performance was achieved with Cu50Co50 catalysts spray-coated onto Toray carbon paper at −1.3 V vs. Ag/AgCl, reaching a Faradaic efficiency (FE) of ~90%; this catalyst was therefore examined in greater detail.8 Batch electrolysis optimization studies investigated the effects of applied potential, catalyst composition, catalyst loading, carbon-to-catalyst ratio, and binder content on FE for the CuxCo100–x catalysts. Building on these optimized conditions, flow-cell electrolysis was subsequently employed to evaluate long-term operation and identify operating parameters that maximize both catalytic efficiency and durability.