Electrocatalytic nitrate (NO3 -) reduction to ammonia (NH3) represents a sustainable pathway for resource recovery and wastewater treatment. However, its application in neutral media typical of real wastewater sources is constrained by weak NO3 - adsorption and proton scarcity, which necessitate high overpotentials that promote the competing hydrogen evolution reaction (HER) and lower selectivity. Here, we overcome this dilemma through a dynamic phase-transition strategy using a defect-engineered Co3O4-x catalyst, which achieves ∼100% Faradaic efficiency with a high NH3 yield rate of 11.6 mg h-1 cm-2 at -0.5 V versus RHE in neutral electrolyte. Operando spectroscopy and theoretical calculations reveal an electrochemically reversible phase transition, wherein cathodic potential reduces Co3+ to Co2+, forming a Co(OH)2 intermediate that spontaneously reverts upon potential removal. This dynamic restructuring spatiotemporally decouples NO3 - adsorption and hydrogenation: the Co3+-rich phase captures NO3 -, while the transient Co(OH)2 activates water to supply active hydrogen for hydrogenation steps. This self-adaptive process suppresses HER and ensures remarkable stability during 300 h of operation. The catalyst further demonstrates robust performance across diverse real wastewaters without supporting electrolytes and enables efficient NH3 recovery. This work establishes dynamic phase engineering as a transformative design paradigm for adaptive electrocatalysts, paving the way for practical sustainable nitrogen management.
Xu et al. (Wed,) studied this question.
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