Dynamic evolution of Co species and morphological reconstruction on Co-N-C during the nitrate reduction reaction in neutral solution

The electrochemical nitrate reduction reaction (eNO₃⁻RR) is considered an effective approach for converting nitrate-containing wastewater to ammonia. The adsorption and activation of NO₃⁻ is the critical step for many materials and the high energy barrier inhibits the continuation of the reduction reaction. The Co nanoparticles encapsulated in the carbon layer we prepared spontaneously react with NO₃⁻ and the resulting Co²⁺ is then reduced by electroreduction to Co⁰, which circulates continuously. This resulted in overcoming the energy input required for NO₃⁻ adsorption and conversion, thereby increasing the catalytic activity. At the same time, the morphology of the catalyst reconstructed from a dodecahedron to an interwoven nanosheet structure and the increased surface area also gives it better properties. The obtained Co(OH)₂@Co-N-C has an excellent eNO₃⁻RR of 2774.7 μg·h⁻¹·cm⁻² with a Faraday efficiency of 81.4% in neutral solution. At the same time, the material-modified electrode can run stably for more than 100 h. Our work provides a new idea for the design of Co-based catalysts for eNO₃⁻RR.