From Kernel Rearrangement to Surface Oxygen Vacancy Enrichment: Boosting Ammonia Electrosynthesis on 3D Urchin-like Cu-Co Oxides.

Abstract

Nitrate-to-ammonia electroreduction represents an environmentally friendly pathway for both ammonia synthesis and nitrogen source recovery. However, its efficiency is still limited by insufficient active sites to adsorb nitrate and activate H₂O simultaneously. Herein, a kernel structure rearrangement strategy is proposed to construct a rapid electron transfer channel inside an urchin-like Cu-Co oxide using Pluronic@F127 as a template, which is beneficial for increasing the surface oxygen vacancy coverage after electrochemical in situ reconstruction. An ammonia production rate exceeding 0.25 mmol cm^-2 h^-1 and 100% Faraday efficiency (-0.2 V (RHE)) are achieved in neutral medium, superior to other reported three-dimensional materials. Density functional theory calculations and in situ characterizations reveal that the nitrate spatial hindrance caused by the increase of oxygen vacancy coverage makes it easier for the adjacent oxygen vacancy to adsorb H₂O and produce active hydrogen. The rapid migration of active hydrogen between adjacent oxygen vacancies is beneficial for the reduction of the Gibbs free energy of *NO₂ hydrogenation, minimizing the formation of the byproduct nitrite and thus promoting the energy utilization in both ammonia synthesis and Cl^--mediated total nitrogen removal. The spatially hindered strategy proposed in this work provides a way to improve three-dimensional materials' electrochemical hydrogenation performances.