Key Laboratory for Green Chemical Technology of the Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin300072, China.
School of Chemistry and Chemical Engineering, Southeast University, Nanjing211189, China.
ACS Appl Mater Interfaces. 2023 Jan 11;15(1):838-847. doi: 10.1021/acsami.2c15467. Epub 2022 Dec 22.
The controllable synthesis of specific defective carbon catalysts is crucial for two-electron oxygen reduction reaction (2e ORR) to generate HO due to the great potential applications. Herein, the defective carbon catalysts (Mo-CDC-ns) were prepared by an electrochemical activation (ECA) method with MoC/C as a parent. Electrochemical cyclic voltammetry curves, X-ray photoelectron spectroscopy, inductively coupled plasma-mass spectrometry, scanning electron microscopy, and high-resolution transmission electron microscopy confirm the evolution process of a defective carbon structure from the MoC phase in which Mo species are first oxidized to Mo species and then the latter are dissolved into the solution and defective carbon is simultaneously formed. Raman and electron paramagnetic resonance spectra reveal that the defect types in Mo-CDC-ns are the edge defect and vacancy defect sites. Compared with the parent MoC/C, Mo-CDC-ns exhibit gradually increased kinetic current density and selectivity for HO generation with an extension of activation cycles from 10 (Mo-CDC-10) to 30 (Mo-CDC-30). Over Mo-CDC-30, a kinetic current density of 19.4 mA cm and a selectivity close to 90% in 0.1 M KOH solution were achieved, as well as good stability for HO production in an extended test up to 12 h in an H-cell. Graphene planes and Stone Wales 5757-carbon were constructed as basic models for density functional theory calculations. It revealed that the obtained defective structure after the removal of Mo atoms contains the double vacancy at the edge of graphene (Edge-DVC) and the topological defect on the plane of 5757-carbon (5757C-D), which show more moderate reaction free energy for forming *OOH and smaller energy barrier of 2e ORR.
可控合成具有特定缺陷的碳催化剂对于二电子氧还原反应（2e ORR）生成 HO 至关重要，因为其具有巨大的潜在应用价值。在此，采用电化学活化（ECA）法以 MoC/C 为前驱体制备了缺陷碳催化剂（Mo-CDC-ns）。电化学循环伏安曲线、X 射线光电子能谱、电感耦合等离子体质谱、扫描电子显微镜和高分辨率透射电子显微镜证实了从 MoC 相中演变出缺陷碳结构的过程，其中 Mo 物种首先被氧化为 Mo 物种，然后后者溶解在溶液中，同时形成缺陷碳。拉曼和电子顺磁共振光谱表明，Mo-CDC-ns 中的缺陷类型为边缘缺陷和空位缺陷位。与母体 MoC/C 相比，Mo-CDC-ns 在活化循环从 10 次（Mo-CDC-10）延长至 30 次（Mo-CDC-30）时，表现出逐渐增加的动力学电流密度和对 HO 生成的选择性。在 Mo-CDC-30 以上，在 0.1 M KOH 溶液中获得了 19.4 mA cm 的动力学电流密度和接近 90%的选择性，并且在 H 池中的延长测试中，HO 生成的稳定性长达 12 h。构建了石墨烯平面和 Stone Wales 5757-碳作为密度泛函理论计算的基本模型。结果表明，去除 Mo 原子后得到的缺陷结构包含石墨烯边缘的双空位（Edge-DVC）和 5757-碳平面上的拓扑缺陷（5757C-D），它们对形成*OOH 的反应自由能更适中，并且 2e ORR 的能量势垒更小。
