Maximizing Surface Single-Ni Sites on Hollow Carbon Sphere for Efficient CO2 Electroreduction

Single-atom catalysts show great application potential due to their high catalytic efficiency but suffer from insufficient active site density and utilization. Herein, a robust single-atomic Ni catalyst anchored on porous hollow carbon spheres (Ni–N–HCS) was successfully synthesized via a pyrolysis approach employing SiO₂-templated HCS, dicyandiamide, and Ni(CH₃COO)₂·4H₂O as raw materials. Profiting from the abundant (3.47 wt %) and accessible single-Ni active sites and the robust hollow carbon architecture, this catalyst showed superior performance for electrochemical CO₂ reduction reaction in an H-type cell. A prominent Faradaic efficiency for CO (95.04%) can be achieved at a −0.70 V vs a reversible hydrogen electrode (RHE) and the value can even be kept at >80% over a broad voltage range (−0.62 to −0.87 V vs RHE) with a desirable CO current density (10.88 mA·cm^–2). In addition, the FE_CO was kept almost unchanged during continuous electrolysis for 40 h. Significantly, Ni–N–HCS also exhibits an excellent CO selectivity of >95% over the whole investigated potential window in the flow cell. We believe this work will provide a new possibility to build single-atom catalysts with maximized utilization for improving electrochemical performance.