CuCo₂O₄/CuO Heterostructure with Oxygen Vacancies Induced by Plasma for Electrocatalytic Nitrate Reduction to Ammonia

Electrochemical nitrate reduction (NO₃RR) to ammonia production is regarded as one of the potential alternatives for replacing the Haber-Bosch technology for realizing artificial ammonia synthesis. In this study, a CuCo₂O₄/CuO-Ar heterostructure in the shape of dandelion nanospheres formed by nanoarrays has been successfully constructed, demonstrating excellent NO₃RR performance. Experimental results indicate that Ar plasma etching of CuCo₂O₄/CuO-Ar significantly increases the content of oxygen vacancies compared to the sample of CuCo₂O₄/CuO-Air etched by air plasma, resulting in improved NO₃RR performance. Density functional theory calculations further confirm that the existence of more oxygen vacancies effectively decreases the energy barrier of nitrate adsorption, which is due to the generation of more oxygen vacancies facilitating nitrate adsorption and weakening the N-O bonds of nitrate after plasma treatment. As a result, CuCo₂O₄/CuO-Ar exhibits a high NH₃ yield of 0.55 mmol h^-1 cm^-2 and a Faraday efficiency of 95.07% at the optimal potential of -0.9 V (vs RHE) in a neutral medium. Importantly, CuCo₂O₄/CuO-Ar also showcases excellent electrocatalytic stability. This study presents new views on the design and structure regulation of NO₃RR electrocatalysts and their potential applications in the future.