Stabilizing the Coordination Environment of Single-Atom Nickel Using Unexposed Nickel Nanoparticles for Enhanced Electrochemical Reduction of CO2

Adding Ni nanoparticles (NPs) is an effective methodology to improve the catalytic activity of Ni single-atom catalysts (SACs) in the electrochemical CO2 reduction reaction (CO2RR). However, the effect of the form in which the Ni NPs exist on the Ni SAs needs further exploration. Herein, the interaction between Ni NPs in different forms of existence and Ni SAs is investigated on g-C3N4-inducing carbon nanosheets. Comparing with the impregnated Ni NPs, the in situ-doped Ni NPs are encapsulated by a graphitic carbon layer to avoid catalyzing the hydrogen evolution reaction (HER) and facilitate the adsorption of CO2. Meanwhile, the graphitic carbon layer boosts the catalytic stability of Ni SAs that are recognized as the active sites. As a result, the maximal FECO reaches 98.1% at −0.83 V (vs RHE). The large amount of Ni SAs increases jCO to 27.5 mA cm–2 at −1.13 V (vs RHE). A density functional theory (DFT) simulation confirms that the graphitic carbon layer covering the Ni NPs can reduce the energy barrier of the CO2RR to increase the selectivity on Ni–N4 sites. The clarification of the reaction mechanism for the graphitic carbon layer induced by Ni NPs paves a new path for the rational design of Ni SA-dominated catalysts for highly efficient CO2 reduction.