Toward an Understanding of the Reversible Li-CO₂ Batteries over Metal-N₄-Functionalized Graphene Electrocatalysts

The lack of low-cost catalysts with high activity leads to the unsatisfactory electrochemical performance of Li-CO₂ batteries. Single-atom catalysts (SACs) with metal-N moieties have great potential to improve battery reaction kinetics and cycling ability. However, how to rationally select and develop highly efficient electrocatalysts remains unclear. Herein, we used density functional theory (DFT) calculations to screen SACs on N-doped graphene (SAMe@NG, Me = Cr, Mn, Fe, Co, Ni, Cu) for CO₂ reduction and evolution reaction. Among them, SACr@NG shows the promising potential as an effective electrocatalyst for the reversible Li-CO₂ batteries. To verify the validity of the DFT calculations, a two-step method has been developed to fabricate SAMe@NG on a porous carbon foam (SAMe@NG/PCF) with similar loading of ∼8 wt %. Consistent with the theoretical calculations, batteries with the SACr@NG/PCF cathodes exhibit a superior rate performance and cycling ability, with a long cycle life and a narrow voltage gap of 1.39 V over 350 cycles at a rate of 100 μA cm^-2. This work not only demonstrates a principle for catalysts selection for the reversible Li-CO₂ batteries but also a controllable synthesis method for single atom catalysts.