Hollow Mesoporous Carbon Sphere Loaded Ni-N₄ Single-Atom: Support Structure Study for CO₂ Electrocatalytic Reduction...

Single-atom catalysts have become a hot spot because of the high atom utilization efficiency and excellent activity. However, the effect of the support structure in the single-atom catalyst is often unnoticed in the catalytic process. Herein, a series of carbon spheres supported Ni-N₄ single-atom catalysts with different support structures are successfully synthesized by the fine adjustment of synthetic conditions. The hollow mesoporous carbon spheres supported Ni-N₄ catalyst (Ni/HMCS-3-800) exhibits superior catalytic activity toward the electrocatalytic CO₂ reduction reaction (CO₂ RR). The Faradaic efficiency toward CO is high to 95% at the potential range from -0.7 to -1.1 V versus reversible hydrogen electrode and the turnover frequency value is high up to 15 608 h^-1 . More importantly, the effect of the geometrical structures of carbon support on the CO₂ RR performance is studied intensively. The shell thickness and compactness of carbon spheres regulate the chemical environment of the doped-N species in the carbon skeleton effectively and promote CO₂ molecule activation. Additionally, the optimized mesopore size is beneficial to improve diffusion and overflow of the substance, which enhances the CO₂ adsorption capacity greatly. This work provides a new consideration for promoting the catalytic performance of single-atom catalysts.