High-Density Atomically Dispersed Metals Activate Adjacent Nitrogen/Carbon Sites for Efficient Ammonia Electrosynthesis from Nitrate.

While electrocatalytic reduction of nitrate to ammonia presents a sustainable solution for addressing both the environmental and energy issues within the nitrogen cycle, it remains a great challenge to achieve high selectivity and activity due to undesired side reactions and sluggish reaction kinetics. Here, we fabricate a series of metal-N-C catalysts that feature hierarchically ordered porous structure and high-density atomically dispersed metals (HD M 1 /PNC). Specifically, the as-prepared HD Fe 1 /PNC catalyst achieves an ammonia production rate of 21.55 mol g cat -1 h -1 that is at least 1 order of magnitude enhancement compared with that of the reported metal-N-C catalysts, while maintaining a 92.5% Faradaic efficiency when run at 500 mA cm -2 for 300 h. In addition to abundant active sites, such high performance benefits from the fact that the high-density Fe can more significantly activate the adjacent N/C sites through charge redistribution for improved water adsorption/dissociation, providing sufficient active hydrogen to Fe sites for nitrate ammoniation, compared with the low-density counterpart. This finding deepens the understanding of high-density metal-N-C materials at the atomic scale and may further be used for designing other catalysts.