Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
Center for Water and Ecology, State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China.
Proc Natl Acad Sci U S A. 2023 Jan 17;120(3):e2209979120. doi: 10.1073/pnas.2209979120. Epub 2023 Jan 10.
The electrolysis of nitrate reduction to ammonia (NRA) is promising for obtaining value-added chemicals and mitigating environmental concerns. Recently, catalysts with high-performance ammonia synthesis from nitrate has been achieved under alkaline or acidic conditions. However, NRA in neutral solution still suffers from the low yield rate and selectivity of ammonia due to the low binding affinity and nucleophilicity of NO. Here, we confirmed that the in-situ-generated Fe(II) ions existed as specifically adsorbed cations in the inner Helmholtz plane (IHP) with a low redox potential. Inspired by this, a strategy (Fe-IHP strategy) was proposed to enhance NRA activity by tuning the affinity of the electrode-electrolyte interface. The specifically adsorbed Fe(II) ions [SA-Fe(II)] greatly alleviated the electrostatic repulsion around the interfaceresulting in a 10-fold lower in the adsorption-free energy of NO when compared to the case without SA-Fe(II). Meanwhile, the modulated interface accelerated the kinetic mass transfer process by 25 folds compared to the control. Under neutral conditions, a Faraday efficiency of 99.6%, a selectivity of 99%, and an extremely high NH yield rate of 485.8 mmol h g were achieved. Theoretical calculations and in-situ Raman spectroscopy confirmed the electron-rich state of the SA-Fe(II) donated to orbitals of N atom and favored the hydrogenation of *NO to *NOH for promoting the formation of high-selectivity ammonia. In sum, these findings complement the textbook on the specific adsorption of cations and provide insights into the design of low-cost NRA catalysts with efficient ammonia synthesis.
硝酸盐还原氨（NRA）的电解在获得增值化学品和减轻环境问题方面具有广阔的前景。最近，在碱性或酸性条件下，已经实现了具有高性能氨合成的硝酸盐催化剂。然而，由于 NO 的结合亲和力和亲核性较低，中性溶液中的 NRA 仍然存在氨产率和选择性低的问题。在这里，我们证实了原位生成的 Fe(II)离子以低氧化还原电位存在于内亥姆霍兹平面（IHP）中作为特定吸附的阳离子。受此启发，提出了一种通过调节电极-电解质界面亲和力来增强 NRA 活性的策略（Fe-IHP 策略）。特定吸附的 Fe(II)离子 [SA-Fe(II)] 极大地减轻了界面周围的静电排斥，与没有 SA-Fe(II)的情况相比，NO 的吸附自由能降低了 10 倍。同时，与对照相比，调制后的界面加速了动力学质量转移过程 25 倍。在中性条件下，实现了 99.6%的法拉第效率、99%的选择性和高达 485.8mmol h g 的极高 NH 产率。理论计算和原位拉曼光谱证实了 SA-Fe(II)向 N 原子的轨道提供的富电子状态，并有利于NO 向*NOH 的加氢，从而促进高选择性氨的形成。总之，这些发现补充了关于阳离子特定吸附的教科书内容，并为设计具有高效氨合成的低成本 NRA 催化剂提供了思路。
