Tandem Electrocatalytic Nitrate Reduction to Ammonia on MBenes.

We demonstrate the great feasibility of MBenes as a new class of tandem catalysts for electrocatalytic nitrate reduction to ammonia (NO RR). As a proof of concept, FeB is first employed as a model MBene catalyst for the NO RR, showing a maximum NH -Faradaic efficiency of 96.8 % with a corresponding NH yield of 25.5 mg h  cm at -0.6 V vs. RHE. Mechanistic studies reveal that the exceptional NO RR activity of FeB arises from the tandem catalysis mechanism, that is, B sites activate NO to form intermediates, while Fe sites dissociate H O and increase *H supply on B sites to promote the intermediate hydrogenation and enhance the NO -to-NH conversion.