Qian Sheng-Jie, Cao Hao, Lv Xin-Mao, Li Jun, Wang Yang-Gang
State Key Laboratory of Quantum Functional Materials and Department of Chemistry, Southern University of Science and Technology, Shenzhen, Guangdong 518055, China.
Department of Chemistry and Engineering Research Center of Advanced Rare-Earth Materials of Ministry of Education, Tsinghua University, Beijing 100084, China.
J Am Chem Soc. 2025 Jun 18;147(24):21032-21040. doi: 10.1021/jacs.5c05728. Epub 2025 Jun 3.
The persistent paradox in electrochemical nitrate reduction (NORR)─the requirement of high overpotentials despite its highly exothermic nature─remains a critical roadblock for efficient ammonia electrosynthesis. Here, we resolve this conundrum by identifying a high-valent anionic intermediate as kinetic gatekeepers during the nitrate reduction on a single-atom catalyst by using AIMD simulations under explicit solvation and electrode potentials. Employing our self-developed constant-potential thermodynamic integration method, we reveal a stark kinetic barrier dichotomy: while the reaction is thermodynamically favorable governed by the N-O break, the protonation to oxygen at a low anionic state necessitates substantial activation energy. Mechanistic analysis uncovers that electrode polarization preactivates *NO into a metastable high-valent *NO intermediate, which serves as the key step to the following protonation process. Crucially, this intermediate's stabilization requires a highly negative potential, directly linking its formation to the observed overpotential. Furthermore, molecular dynamics simulations also demonstrate that K cations play a key role in electrostatically stabilizing the adsorption of negatively charged NO onto the negatively polarized cathode. This work calls for the urgent reconsideration of conventional nitrate reduction mechanisms and the exigency of refined interface design principles for improved nitrate electrocatalysis.
电化学硝酸盐还原（NORR）中持续存在的悖论——尽管其具有高度放热的性质，但仍需要高过电位——仍然是高效氨电合成的关键障碍。在这里，我们通过在明确的溶剂化和电极电位下使用AIMD模拟，确定了一种高价阴离子中间体作为单原子催化剂上硝酸盐还原过程中的动力学守门人，从而解决了这一难题。采用我们自行开发的恒电位热力学积分方法，我们揭示了一个明显的动力学势垒二分法：虽然反应在热力学上有利于N-O键的断裂，但在低阴离子状态下向氧的质子化需要大量的活化能。机理分析发现，电极极化将NO预激活为亚稳态的高价NO中间体，这是随后质子化过程的关键步骤。至关重要的是，这种中间体的稳定需要高度负的电位，直接将其形成与观察到的过电位联系起来。此外，分子动力学模拟还表明，K阳离子在静电稳定带负电荷的NO在带负电的极化阴极上的吸附方面起着关键作用。这项工作呼吁紧急重新考虑传统的硝酸盐还原机制，以及为改进硝酸盐电催化而精心设计界面设计原则的紧迫性。
