Intraphase Switching of Hollow CoCuFe Nanocubes for Efficient Electrochemical Nitrite Reduction to Ammonia

This study addresses the urgent need to focus on the nitrite reduction reaction (NO₂^-RR) to ammonia (NH₃). A ternary-metal Prussian blue analogue (CoCuFe-PBA) was utilized as the template material, leveraging its tunable electronic properties to synthesize CoCuFe oxide (CoCuFe-O) through controlled calcination. Subsequently, a CoCuFe alloy (CoCuFe-A) was obtained via pulsed laser irradiation in liquids. The electrochemical properties of CoCuFe-O, derived from the PBA crystal structure, demonstrated a high yield of NH₄⁺ at a rate of 555.84 μmol h^-1 cm^-2, with the highest Faradaic efficiency of 91.8% and a selectivity of 97.3% during a 1-h NO₂^-RR under an optimized potential of -1.0 V vs. Ag/AgCl. In situ Raman spectroscopy revealed the collaborative role of redox pairs (Co³⁺/Co²⁺ and Fe³⁺/Fe²⁺) as proton (H⁺) suppliers, with Cu centers serving as NO₂^- binders, thereby enhancing the reaction rate. Additionally, theoretical studies confirmed that Fe and Co atoms are more reactive than Cu toward intermediates playing crucial roles in hydrogenation, while Cu primarily activates NO owing to hydrogenation by the Fe and Co atoms and a high kinetic barrier in H₂O* adsorption. This comprehensive investigation provides valuable insights into the electrochemical NO₂^-RR, establishing a foundation for efficient and sustainable NH₃ synthesis strategies.