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

Electrocatalytic reduction of waste nitrates (NO(3)(−)) enables the synthesis of ammonia (NH(3)) 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(3)(−) reduction to NH(3) in neutral media, with a specific focus on deciphering the role of the NO(2)(−) intermediate in the reaction cascade, reveals strong correlations (R=0.9) between the NO(2)(−) reduction activity and NO(3)(−) reduction selectivity for NH(3). Moreover, theoretical computations reveal the associative/dissociative adsorption pathways for NO(2)(−) evolution, over the normal M-N(4) sites and their oxo-form (O-M-N(4)) for oxyphilic metals. This work provides a platform for designing multi-element NO(3)RR cascades with single-atom sites or their hybridization with extended catalytic surfaces.