双原子单团簇催化剂电催化氮还原反应的理论研究

氨（NH3）在维持人口增长和工业生产等方面扮演着重要角色。目前工业合成氨主要依靠传统的 Haber-Bosch 工艺。然而，电催化氮还原反应（NRR）有望通过使用可再生能源实现 NH3 的分散式生产，这与能源密集型的 Haber-Bosch 工艺形成了鲜明的对比。实现这一目标的关键是找到稳定、高效且具有选择性的 NRR 电催化剂。近年来，非均相单团簇催化剂（SCC）由于其原子级精确的活性位点、丰富的活性原子以及原子级可调控性而成为一类具有潜力的电化学反应催化剂。因此，本文通过使用密度泛函理论（DFT）系统地进行了由氮掺杂石墨烯负载同核 3d过渡金属（TM）二聚体组成的双原子 SCC（记作： M2-N6G）催化 NRR 的研究。我们的研究结果表明，金属二聚体捕获 N2 的能力与催化剂的还原性以及 TM-3d 态和 N-2p 态之间的电子相互作用有关。随后，我们发现，与那些通过侧位构型过度结合 N2 的催化剂相比，以端位构型吸附 N2 的 M2-N6G 具有更好的催化性能。此外，我们得到了 *N2H 吸附自由能（∆ads𝐺∗N2H）和 *NH2（∆ads𝐺∗NH2）吸附自由能之间的线性关系。基于这种线性关系，我们提出了一种合理的策略可用于筛选具有高效催化 NRR 活性的双原子 SCC。最后，通过比较各种 M2-N6G SCC 的稳定性、活性和选择性， Cr2-N6G 和 Mn2-N6G 具有较低的 NRR 发生极限电势和抑制析氢反应发生的能力，从而被预测是具有催化 NRR 最优性能的两种 M2-N6G。目前的工作不仅为 NRR 提供了实验上具有可合成性的候选电催化剂，而且还深入了解了双原子 SCC 的催化机理。这对于双原子 SCC 在电催化领域的发展具有一定的帮助。
 

Ammonia (NH3) plays an important role in maintaining population growth and industrial production. At present, industrial ammonia synthesis mainly relies on the traditional Haber-Bosch process. However, the electrocatalytic dinitrogen reduction reaction (NRR) is promising to realize the decentralized production of ammonia by using renewable energies, which contrasts with the energy-intensive Haber-Bosch process. The key to achieve it is to find stable, efficient and selective electrocatalysts. Recently, the heterogeneous single-cluster catalysts (SCC) have emerged as a promising class of catalysts for electrochemical reactions due to their atomically precise active site, abundant active atoms and atomic level controllability. Herein, the NRR catalyzed by the two-atom SCC consisting of homonuclear 3d transition metal dimers over the N-doped graphene, denoted as M2-N6G, are systematically investigated by using density functional theory (DFT). Our results indicate that the ability of metal dimer to capture N2 is related to the reducibility of the catalyst and the electronic interaction between the N-2p states and the TM-3d states.
Subsequently, comparing with those catalysts which overbind N2 through side-on configurations, the M2-N6G SCC with end-on adsorption of N2 work better. Furthermore, we obtain a linear relationship between the adsorption free energies of *N2H (∆ads𝐺∗N2H) and that of *NH2 (∆ads𝐺∗NH2). Based on this scaling relationship, we propose a compromised strategy for screening efficient two-atom SCC for NRR. Finally, by comparing the stability, activity and selectivity of various M2-N6G SCC, the Cr2-N6G and Mn2-N6G are predicted to be most active for NRR with low limiting potential and high suppression to hydrogen evolution reaction (HER). The present work not only provides experimentally synthesizable electrocatalyst candidates for NRR, but also gives insight into the catalytic mechanism of the two-atom SCC, which is beneficial for the development of two-atom SCC in electrocatalysis.
 

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