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Recently, electrochemical NO reduction (eNORR) to ammonia has attracted enormous research interests due to the dual benefits in ammonia synthesis and denitrification fields. Herein, taking Ag as a model catalyst, we have developed a microkinetic model to rationalize the general selectivity trend of eNORR with varying potential, which has been observed widely in experiments, but not understood well. The model reproduces experiments well, quantitatively describing the selectivity turnover from N2O to NH3 and from NH3 to H2 with more negative potential. The first turnover of selectivity is due to the thermochemical coupling of two NO* limiting the N2O production. The second turnover is attributed to the larger transfer coefficient (β) of HER than NH3 production. This work reveals how electrode potential regulate the selectivity of eNORR, which is also beneficial to understand the commonly increasing HER selectivity with the decrease of potential in some other electroreduction reactions such as CO2 reduction.

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