Elucidating electrochemical nitrate and nitrite reduction over atomically-dispersed transition metal sites.

Electrocatalytic reduction of waste nitrates (NO) enables the synthesis of ammonia (NH) in a carbon neutral and decentralized manner. Atomically dispersed metal-nitrogen-carbon (M-N-C) catalysts demonstrate a high catalytic activity and uniquely favor mono-nitrogen products. However, the reaction fundamentals remain largely underexplored. Herein, we report a set of 14; 3d-, 4d-, 5d- and f-block M-N-C catalysts. The selectivity and activity of NO reduction to NH in neutral media, with a specific focus on deciphering the role of the NO intermediate in the reaction cascade, reveals strong correlations (R=0.9) between the NO reduction activity and NO reduction selectivity for NH. Moreover, theoretical computations reveal the associative/dissociative adsorption pathways for NO evolution, over the normal M-N sites and their oxo-form (O-M-N) for oxyphilic metals. This work provides a platform for designing multi-element NORR cascades with single-atom sites or their hybridization with extended catalytic surfaces.