Li Peng, Jiao Yuzhou, Ruan Yaner, Fei Houguo, Men Yana, Guo Cunlan, Wu Yuen, Chen Shengli
Hubei Key Laboratory of Electrochemical Power Sources, College of Chemistry and Molecular Sciences, Wuhan University, Wuhan, 430072, China.
School of Chemistry and Materials Science, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), University of Science and Technology of China, Hefei, 230026, China.
Nat Commun. 2023 Oct 31;14(1):6936. doi: 10.1038/s41467-023-42749-7.
A standing puzzle in electrochemistry is that why the metal-nitrogen-carbon catalysts generally exhibit dramatic activity drop for oxygen reduction when traversing from alkaline to acid. Here, taking FeCo-N-C double-atom catalyst as a model system and combining the ab initio molecular dynamics simulation and in situ surface-enhanced infrared absorption spectroscopy, we show that it is the significantly distinct interfacial double-layer structures, rather than the energetics of multiple reaction steps, that cause the pH-dependent oxygen reduction activity on metal-nitrogen-carbon catalysts. Specifically, the greatly disparate charge densities on electrode surfaces render different orientations of interfacial water under alkaline and acid oxygen reduction conditions, thereby affecting the formation of hydrogen bonds between the surface oxygenated intermediates and the interfacial water molecules, eventually controlling the kinetics of the proton-coupled electron transfer steps. The present findings may open new and feasible avenues for the design of advanced metal-nitrogen-carbon catalysts for proton exchange membrane fuel cells.
电化学领域长期存在的一个谜题是，为何金属-氮-碳催化剂在从碱性环境转变为酸性环境时，通常会出现氧还原活性的急剧下降。在此，以FeCo-N-C双原子催化剂作为模型体系，并结合从头算分子动力学模拟和原位表面增强红外吸收光谱，我们表明，导致金属-氮-碳催化剂上氧还原活性依赖于pH值的原因，是显著不同的界面双层结构，而非多个反应步骤的能量学。具体而言，电极表面上截然不同的电荷密度，使得在碱性和酸性氧还原条件下界面水具有不同的取向，从而影响表面氧化中间体与界面水分子之间氢键的形成，最终控制质子耦合电子转移步骤的动力学。本研究结果可能为设计用于质子交换膜燃料电池的先进金属-氮-碳催化剂开辟新的可行途径。
