Molten Salt Assisted Synthesis of Single-Atom Nickel Catalysts for Electroreduction of Co2 with Nearly 100% Co Selectivity

Abstract

The synthesis of single-atom catalysts (SACs) with target architecture owning ultrathin layered morphology, high surface area and exposed metal active sites is still a great challenge. Herein, we chose 2D bimetallic ZIF-L as precursor combined with molten salt assisted method realizing the aimed synthesis of single-atom Ni imbedded in porous and ultrathin N-doped carbon nanosheets for efficient electrochemical CO2 reduction. Molten salt assisted method avoids the collapse, agglomeration, and shrinkage of ZIF-L nanosheets in synthetic process, and benefits the formation of porous structure of nitrogen-doped carbon nanosheets with exposed single-atom Ni active sites. The as-synthesized MS-L-Ni-NC exhibits remarkable electrocatalytic CO2-to-CO performance with the faradaic efficiency over 95.9% in a wide potential range from -0.7 to -1.0 V vs. RHE in H-type cell. An optimal FECO of 98.7% at -0.8 V vs. RHE and a large current density of 20.6 mA·cm-2 at -1.0 V are observed for the MS-L-Ni-NC, which are much higher than those of D-L-Ni-NC without molten-salt assistance and MS-Ni-NC with 3D ZIF as precursor. DFT calculations reveal that the coordinatively unsaturated pyridine Ni-N sites are the active centers for ECO2RR.

Keywords: CO2 electroreduction, Single-atom catalysts, Molten salt method, Zeolite imidazolate framework, N-doped carbon nanosheets