Metal-free surface-microporous graphene electrocatalysts from CO2 for rechargeable all-solid-state zinc–air batteries

Abstract

Novel surface-microporous graphene (SMG), which was synthesized directly from CO₂via its reaction with a Na/K liquid alloy, was demonstrated as a robust metal-free electrocatalyst for the air cathode of ZABs. The SMG-based ZAB (SMG-ZAB) exhibited an excellent peak power density of 65 mW cm⁻² at a current density of 83 mA cm⁻², which is comparable to that of the ZAB with a commercial 20% Pt/C cathode (65 mW cm⁻² at 84 mA cm⁻²). Furthermore, the SMG-ZAB delivered an unprecedented small charge–discharge voltage gap of 0.25 V at 2 mA cm⁻² with excellent durability, which is not only superior to that (0.75 V) of the 20% Pt/C-based ZAB, but also better than any reported values of all-solid-state ZABs. The excellent performance of the SMG electrocatalyst can be attributed to the synergistic effect of its defects and oxygen-containing surface functional groups as well as its unique pore structure of interconnected macropores and surface micropores. This provides a promising route to develop excellent metal-free air cathodes for secondary metal–air batteries from a greenhouse gas.