The two-dimensional graphitic carbon nitride (g-CN) is a promising support for electrochemistry catalysts owing to its stability and controllable chemical composition. Here, by density functional theory (DFT) a serial of transition metal single-atom catalysts (SAC) supported on the g-CN with vacancy (denoted as TM/CN, TM=Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ir and Pt) were studied for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The non-noble Ni and Co single atom exhibited relatively strong binding energies over the defective g-CN support. The d-band center of TM performed a good descriptor for adsorption free energies of intermediates. For OER, the overpotential of non-noble Co/CN was as low as 0.30 V, comparable to Rh/CN. For ORR, both Co/CN and Rh/CN displayed excellent performance with overpotentials of around 0.50 V. The volcano plot revealed that the proper binding strength of O* and OH* on Co/CN rendered it an excellent bifunctional catalyst for both OER and ORR. Considering the superior performance of Co SAC over g-CN than not only g-CN but also defective graphene, we postulate that there could exist an optimized C/N ratio of carbon-rich g-CN support for improving the non-noble Co SAC activity on oxygen electrode.

中文翻译：

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用于析氧和还原反应的 g-C2N2 双功能单原子催化剂的理论设计

二维石墨氮化碳（g-CN）由于其稳定性和化学组成可控，是一种很有前景的电化学催化剂载体。这里，根据密度泛函理论（DFT），一系列过渡金属单原子催化剂（SAC）负载在空位的g-CN上（表示为TM/CN，TM=Mn，Fe，Co，Ni，Cu，Ru，研究了 Rh、Pd、Ir 和 Pt）的析氧反应（OER）和氧还原反应（ORR）。非贵重的 Ni 和 Co 单原子在有缺陷的 g-CN 载体上表现出相对较强的结合能。 TM 的 d 带中心对中间体的吸附自由能起到了良好的描述作用。对于 OER，非贵金属 Co/CN 的过电势低至 0.30 V，与 Rh/CN 相当。对于 ORR，Co/CN 和 Rh/CN 均表现出优异的性能，过电势约为 0.50 V。火山图显示，Co/CN 上 O* 和 OH* 的适当结合强度使其成为 OER 和 OER 的出色双功能催化剂。 ORR。考虑到Co SAC不仅比g-CN而且比有缺陷的石墨烯都优于g-CN，我们假设可能存在富碳g-CN载体的优化C/N比来改善非贵金属Co SAC氧电极上的活性。