南方科技大学王阳刚团队揭示了单原子催化剂上氧还原反应电位依赖的速率决定步骤。相关研究成果发表在2025年1月14日出版的《美国化学会杂志》。

单原子催化剂（SACs）因其在实现高效氧还原反应（ORR）方面取代铂基催化剂的潜力而引起了广泛关注，但由于其难以捉摸的反应机制，SACs的合理优化仍然具有挑战性。

该文中，通过采用从头计算分子动力学模拟和热力学积分方法，构建了分散在氮掺杂石墨烯（Fe-N4/C）上的单个铁原子催化剂上的ORR的势能依赖自由能，并将这些参数进一步积分到微观动力学模型中。研究证明，SACs上ORR的速率决定步骤（RDS）在操作电位范围内是电位依赖的，而不是不变的。

具体来说，在电荷中性条件下，RDS被计算为具有最高势垒的水解吸，而随着电势的增加，它逐渐转变为*OH物种、O₂*物种和O*物种的质子化，而不管*OH物种的质质子化是电势决定步骤。此外，研究揭示了轴向吸附水的动态吸附在促进单原子位点释放方面的关键作用，从而提高了ORR率。

该工作解决了长期以来关于SACs上ORR的RDS的争议，并表明放热率最低的步骤并不总是RDS的同义词，这突显了在现实潜在条件下检查动力学势垒，对于理解电催化性能的重要性。

附：英文原文

Title: Revealing the Potential-Dependent Rate-Determining Step of Oxygen Reduction Reaction on Single-Atom Catalysts

Author: Hui-Min Yan, Gang Wang, Xin-Mao Lv, Hao Cao, Gang-Qiang Qin, Yang-Gang Wang

Issue&Volume: January 14, 2025

Abstract: Single-atom catalysts (SACs) have attracted widespread attention due to their potential to replace platinum-based catalysts in achieving efficient oxygen reduction reaction (ORR), yet the rational optimization of SACs remains challenging due to their elusive reaction mechanisms. Herein, by employing ab initio molecular dynamics simulations and a thermodynamic integration method, we have constructed the potential-dependent free energetics of ORR on a single iron atom catalyst dispersed on nitrogen-doped graphene (Fe–N4/C) and further integrated these parameters into a microkinetic model. We demonstrate that the rate-determining step (RDS) of the ORR on SACs is potential-dependent rather than invariant within the operative potential range. Specifically, under the charge-neutral condition, the RDS is calculated to be water desorption with the highest barrier, while as the potential increases, it gradually transitions to the protonation of *OH species, O2* species, and O* species, regardless of the protonation of *OH species as the potential-determining step. Moreover, we reveal the critical role of the dynamic adsorption of axially adsorbed water in facilitating the release of the single-atom site, thus enhancing the ORR rate. Our work has resolved the long-standing controversies over the RDS of ORR on SACs and implies that the step with the lowest exothermicity is not always synonymous with the RDS, highlighting the importance of examining the kinetic barriers under realistic potential conditions for understanding the electrocatalytic performance.

DOI: 10.1021/jacs.4c16098

Source: https://pubs.acs.org/doi/abs/10.1021/jacs.4c16098