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

During the electrocatalytic NO 3 - reduction reaction (NO 3 - RR) under neutral condition, the activation of H 2 O 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 H 2 O 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 NH 3 production by NO 3 - 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 NO 3 - RR electrocatalysts.