Modulating the Surface Concentration and Lifetime of Active Hydrogen in Cu-Based Layered Double Hydroxides for Electrocatalytic Nitrate Reduction to Ammonia

Strategies incorporating heterometals to introduce surface-active hydrogen (*H) have been extensively utilized to enhance the electrocatalytic activity of Cu-based catalysts in the nitrate reduction reaction (NitRR). However, a comprehensive understanding of *H behavior and its specific impact on regulating the NitRR pathway remains elusive, particularly in a quantitative manner. In this study, we prepared a group of layered double hydroxides (LDHs) as model catalysts with diverse *H concentrations and lifetimes. Our findings reveal that the NitRR activity of Cu-based LDHs is highly dependent on the *H species that could be modulated by the incorporated heterometallic sites. Specifically, we conducted in situ analysis of different Cu-based LDH catalysts using time-resolved scanning electrochemical microscopy. The surface concentration and lifetime of *H at various applied potentials were quantified, enabling us to establish the relationship between the *H behavior and NitRR performance. Therefore, optimal NitRR performance was achieved with CuNi-LDHs, exhibiting a faradaic efficiency of 94.6% and yield rate of 2.7 mg h–1 cm–2 because of its appropriate *H surface concentration and lifetime. Additionally, we observe a trend of CuNi > CuCo > Cu > CuRu > CuFe > CuMg in terms of the faradaic efficiency for NH3 production. These results suggest that by effectively utilizing the stable *H produced by the catalyst, one would allow favorable NitRR performance, offering a promising strategy for other electrocatalytic hydrogenation reactions.