Boosting Ammonia Oxidation Kinetics via Amorphous Structural Engineering and Cu Incorporation in Ni-Based Catalysts

The electrochemical ammonia oxidation reaction (AOR) has attracted increasing attention as a sustainable anodic reaction for hydrogen production, owing to its lower theoretical potential compared to the oxygen evolution reaction. Despite this thermodynamic advantage, the multi-electron nature of AOR leads to sluggish kinetics, resulting in the need for highly active electrocatalyst. Under alkaline conditions, Ni catalysts are electrochemically converted to NiOOH, which provides a suitable electronic structure to facilitate ammonia adsorption and dehydrogenation, making Ni a promising catalyst for AOR. Nonetheless, their intrinsically low activity still needs further structural and compositional modification. In this work, amorphous NiCu hydroxide catalysts were synthesized via a facile precipitation–metal nitrate deposition method. The amorphous structure provides a high density of coordinatively unsaturated sites, enhancing reactant accessibility, while the incorporation of Cu stabilizes Ni³⁺ species and promotes active site regeneration. As a result, the optimized NiCu 5:1 catalyst achieved nearly complete ammonia removal efficiency (~100 %), with an ammonia removal rate of 691.7 μmol∙h -1 ∙cm -2 and accelerated the paired hydrogen evolution on a Pt cathode, yielding a hydrogen production rate of 2.45 mmol∙h -1 ∙cm -2 . These findings demonstrate that combining amorphous structural engineering with compositional modification can effectively overcome the intrinsic kinetic limitations of Ni-based catalysts, thereby accelerating AOR and consequently enhancing the paired HER, contributing to sustainable hydrogen production.