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キーワード:
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要旨:
The electrochemical reduction of nitrates (NO<sub>3</sub><sup>−</sup>) enables a pathway for the carbon neutral synthesis of ammonia (NH<sub>3</sub>), via the nitrate reduction reaction (NO<sub>3</sub>RR), which has been demonstrated at high selectivity. However, to make NH<sub>3</sub> synthesis cost-competitive with current technologies, high NH3 partial current densities (j<sub>NH3</sub>) must be achieved to reduce the levelized cost of NH<sub>3</sub>. Here, the high NO<sub>3</sub>RR activity of Fe-based materials is leveraged to synthesize a novel active particle-active support system with Fe<sub>2</sub>O</sub>3 nanoparticles supported on atomically dispersed Fe–N–C. The optimized 3×Fe<sub>2</sub>O<sub>3</sub>/Fe–N–C catalyst demonstrates an ultrahigh NO<sub>3</sub>RR activity, reaching a maximum j<sub>NH3</sub> of 1.95 A cm<sup>−2</sup> at a Faradaic efficiency (FE) for NH<sub>3</sub> of 100% and an NH<sub>3</sub> yield rate over 9 mmol hr<sup>−1</sup> cm<sup>−2</sup>. Operando XANES and post-mortem XPS reveal the importance of a pre-reduction activation step, reducing the surface Fe<sub>2</sub>O<sub>3</sub> (Fe<sup>3+</sup>) to highly active Fe<sup>0</sup> sites, which are maintained during electrolysis. Durability studies demonstrate the robustness of both the Fe<sub>2</sub>O<sub>3</sub> particles and Fe–N<sub>x</sub> sites at highly cathodic potentials, maintaining a current of −1.3 A cm<sup>−2</sup> over 24 hours. This work exhibits an effective and durable active particle-active support system enhancing the performance of the NO<sub>3</sub>RR, enabling industrially relevant current densities and near 100% selectivity.
