H* Species Regulation by Mn-Co(OH)₂ for Efficient Nitrate Electro-reduction in Neutral Solution

During the electrocatalytic NO₃⁻ reduction reaction (NO₃⁻RR) under neutral condition, the activation of H₂O to generate H* and the inhibition of inter-H* species binding, are critically important but remain challenging for suppressing the non-desirable hydrogen evolution reaction (HER). Here, a Mn-doped Co(OH)₂ (named as Mn-Co(OH)₂) has been synthesized by in situ reconstruction in the electrolyte, which is able to dissociate H₂O molecules but inhibits the binding of H* species between each other owing to the increased interatomic spacing by the Mn-doping. The Mn-Co(OH)₂ electrocatalyst offers a faradaic efficiency (FE) of as high as 98.9±1.7% at −0.6 V vs. the reversible hydrogen electrode (RHE) and an energy efficiency (EE) of 49.90±1.03% for NH₃ production by NO₃⁻RR, which are among the highest of the recently reported state-of-the-art catalysts in neutral electrolyte. Moreover, negligible degradation at −200 mA cm⁻² has been found for at least 500 h, which is the longest catalytic durations ever reported. This work paves a novel approach for the design and synthesis of efficient NO₃⁻RR electrocatalysts.