Balancing N₂ and H adsorption for electrochemical ammonia synthesis: Mechanisms, operando insights, and design strategies

Direct conversion of N₂ to NH₃ via electrocatalysis driven by renewably generated electricity provides a promising route to enhance energy sustainability and enable carbon-neutral ammonia production. However, the competing hydrogen evolution reaction in aqueous solutions substantially limits the selectivity toward ammonia formation. Another issue that needs to be addressed is the insufficient adsorption and activation of N₂ molecules on catalyst surfaces. In this review, we establish a unified perspective on balancing N₂ and H adsorption as a central design principle to regulate reaction pathways and kinetics for optimized NH₃ production. We first summarize the fundamental NRR mechanisms together with rigorous experimental protocols to ensure reliable evaluation. State-of-the-art in situ and operando characterization techniques are critically discussed to provide mechanistic insights into reaction intermediates, interfacial processes, and their dynamic evolution. Based on these insights, strategies for rationally tuning the adsorption balance of N₂ and H species are systematically analyzed, linking catalyst structure to activity and selectivity. Finally, key challenges in achieving reliable benchmarking, suppressing HER, and translating mechanistic understanding into catalyst design are outlined, along with future research directions. This review provides a mechanistically informed framework and practical guidelines for the rational design of advanced electrocatalysts for efficient ammonia synthesis.