High-Density\nAtomically Dispersed Metals Activate\nAdjacent Nitrogen/Carbon Sites for Efficient Ammonia Electrosynthesis\nfrom Nitrate

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