Single-atom catalysts have emerged as an exciting paradigm with intriguing properties different from their nanocrystal counterparts. Here we report Ni single atoms dispersed into graphene nanosheets, without Ni nanoparticles involved, as active sites for the electrocatalytic CO₂ reduction reaction (CO₂RR) to CO. While Ni metal catalyzes the hydrogen evolution reaction (HER) exclusively under CO₂RR conditions, Ni single atomic sites present a high CO selectivity of 95% under an overpotential of 550 mV in water, and an excellent stability over 20 hours’ continuous electrolysis. The current density can be scaled up to more than 50 mA cm⁻² with a CO evolution turnover frequency of 2.1 × 10⁵ h⁻¹ while maintaining 97% CO selectivity using an anion membrane electrode assembly. Different Ni sites in graphene vacancies, with or without neighboring N coordination, were identified by in situ X-ray absorption spectroscopy and density functional theory calculations. Theoretical analysis of Ni and Co sites suggests completely different reaction pathways towards the CO₂RR or HER, in agreement with experimental observations.

中文翻译：

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石墨烯纳米片中的孤立Ni单原子可实现高性能CO ₂还原†

单原子催化剂已经成为令人兴奋的范例，其有趣的性质与其纳米晶体对应物不同。在这里，我们报告分散在石墨烯纳米片中的Ni单原子，其中不包含Ni纳米粒子，作为将电催化CO ₂还原反应（CO ₂ RR）转化为CO的活性位点。而Ni金属仅在CO ₂ RR下催化氢析出反应（HER）在550 mV的超电势下，Ni单原子位点在水中具有95％的高CO选择性，并且在20小时连续电解过程中具有出色的稳定性。电流密度可扩展至超过50 mA cm ^-2，CO释放转换频率为2.1×10 ⁵ h ^-1同时使用阴离子膜电极组件保持97％的CO选择性。通过原位X射线吸收光谱法和密度泛函理论计算确定了石墨烯空位中不同的Ni位点，无论是否具有相邻的N配位。对Ni和Co位点的理论分析表明，与实验观察结果一致，朝向CO ₂ RR或HER的反应途径完全不同。