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

ABSTRACT

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-Nx 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.