Fabrication of Nickel Single Atoms with Ionic Liquids by Only One-Step Pyrolysis for CO2 Electroreduction.

Single-atom catalysts (SACs) are appealing for carbon dioxide (CO2) electroreduction with the utmost advantages; however, their preparation is still challenging because of the complicated procedure. Here, a novel Ni-based single-atom catalyst (Ni-BB-BD) is constructed from raw materials, [BMIM]BF4, [BMIM]DCN, and NiCl2·6H2O, directly without any precursor by only one-step pyrolysis. Ni-BB-BD achieves a maximum carbon monoxide Faradaic efficiency (FECO) of 96.5% at -0.8 V vs RHE, as well as long-term stability over 16 h. High current density up to -170.6 mA cm-2 at -1.0 V vs RHE is achieved in the flow cell along with a CO selectivity of 97.7%. It is identified that [BMIM]BF4 is the nitrogen source, while [BMIM]DCN is mainly taken as the carbon source. Theoretical studies have revealed that the rich nitrogen content, especially for the uncoordinated nitrogen, plays a critical role in lowering rate-limiting barrier height. This work develops a facile and effective strategy to prepare the SACs.

Liquid Nitrogen Sources Assisting Gram-Scale Production of Single-Atom Catalysts for Electrochemical Carbon Dioxide Reduction.

Developing metal-nitrogen-carbon (M-N-C)-based single-atom electrocatalysts for carbon dioxide reduction reaction (CO2 RR) have captured widespread interest because of their outstanding activity and selectivity. Yet, the loss of nitrogen sources during the synthetic process hinders their further development. Herein, an effective strategy using 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4 ]) as a liquid nitrogen source to construct a nickel single-atom electrocatalyst (Ni-SA) with well-defined Ni-N4 sites on a carbon support (denoted as Ni-SA-BB/C) is reported. This is shown to deliver a carbon monoxide faradaic efficiency of >95% over a potential of -0.7 to -1.1 V (vs reversible hydrogen electrode) with excellent durability. Furthermore, the obtained Ni-SA-BB/C catalyst possesses higher nitrogen content than the Ni-SA catalyst prepared by conventional nitrogen sources. Importantly, only thimbleful Ni nanoparticles (Ni-NP) are contained in the large-scale-prepared Ni-SA-BB/C catalyst without acid leaching, and with only a slight decrease in the catalytic activity. Density functional theory calculations indicate a salient difference between Ni-SA and Ni-NP in the catalytic performance toward CO2 RR. This work introduces a simple and amenable manufacturing strategy to large-scale fabrication of nickel single-atom electrocatalysts for CO2 -to-CO conversion.