Gelatin-Induced Synthesis of Strain-Engineered Spherical CuO Nanoparticles for Efficient Nitrate Reduction to Ammonia.

The electrochemical reduction of nitrate to ammonia offers an environmentally sustainable pathway for nitrogen fixation. However, achieving both efficiency and selectivity in nitrate reduction presents a formidable challenge, due to the involvement of sluggish multielectron transfer processes. Herein, the successful synthesis of spherical Cu₂O nanoparticles (s-Cu₂O) exhibiting significant compressive strain effects, achieved through a one-pot method using gelatin as a structural modifier, is reported. The s-Cu₂O catalyst demonstrates exceptional electrochemical performance for nitrate reduction reaction (NORR), achieving a Faradaic efficiency (FE) of 95.07%, ammonia selectivity of 92.03%, a nitrate conversion rate of 97.77%, and a yield rate of 284.83 µmol h⁻¹ cm⁻ at -0.8 V versus reversible hydrogen electrode (vs. RHE) for ammonia production. Structural characterization and density functional theory calculations reveal that compressive strain plays a critical role in modulating the electronic structure of the catalyst, thereby activating the *NO intermediate in the potential determining step and effectively suppressing the hydrogen evolution reaction. Furthermore, it is implemented in a Zn-NO battery, and the test results indicate that the battery achieved a peak power density of 3.95 mW cm at a potential of 0.129 V (vs Zn/Zn⁺), illustrating its excellent electrochemical and functional efficacy. This work introduces a novel strategy for the rational design of high-performance electrocatalysts through strain engineering, offering broad implications for energy-efficient ammonia synthesis, and sustainable nitrogen cycling.