Self-Supported Defective Cobalt-Based Cathode for Selective Electrochemical Reduction of Nitrate

Discharge of high-concentration nitrate wastewater poses significant environmental threats. Conversion of nitrate into ammonia achieves a win-win strategy by both promoting sustainable nitrogen resource recycling and eliminating nitrate pollution. Further oxidation of the generated ammonia by free chlorine can also provide a method for the denitrification of wastewater. This study introduces a self-supported, defective cobalt-based electrocatalyst (VO-Co3O4@NF) synthesized via the hydrothermal–calcination method. Upon introduction of oxygen vacancies into the Co3O4 spinel structure, its electron transfer efficiency was enhanced, and its electrochemical activity was improved. Electrochemical nitrate reduction reaction (ENRR) tests demonstrate exceptional performance of 99.5% nitrate conversion, 95.4% ammonia selectivity, and 75.2% Faraday efficiency at −0.59 V vs RHE, with a high ammonia yield rate of 3.14 mg cm–2 h–1. Mechanistic studies reveal the dominance of atomic H* mediated *NOH pathway in ENRR process. The introduction of oxygen vacancies improves the ENRR activity, suggesting a superior intrinsic ENRR activity of the VO-Co3O4@NF electrode. The actual coal chemistry industry wastewater treatment confirmed the practicability of the VO-Co3O4@NF. By coupling cathode ENRR and anode chlorine evolution reaction (CER) processes, complete denitrification is realized in wastewater. This work advances defective cobalt-based catalysts for high-efficiency nitrate reduction, offering a cost-effective alternative to traditional methods.