Probing the Function of a Li-CO₂ Battery with a MXene/Graphene Oxide Composite Cathode Electrocatalyst

We systematically diagnose here the various phases formed at the electrodes in a Li-CO₂ battery. The CO₂ cathode comprises a mixture of two-dimensional electrocatalysts, MXene and graphene oxide (MXene/GO), configured on Ni foam. The observed overpotential for MXene/GO (2.4 V) is lower than that for GO (2.8 V). MXene/GO also outperforms GO in terms of battery stability and performance. The overall battery reaction (Li₂CO₃ ↔ Li + CO₂) is more efficient in the case of MXene/GO than in the case of GO. This is convincingly demonstrated using ex situ high-resolution synchrotron X-ray diffraction and Raman scattering spectroscopy, which strongly indicates that the MXene/GO composite is more capable than GO in converting Li₂CO₃ to Li and CO₂. When the Li anode is probed, CO₂ crossover is evident via the observation of the formation of LiOH/Li₂CO₃ phases, the proportions of which change during successive cycles.