Probing the Function of a Li-CO 2 Battery with a MXene/Graphene Oxide Composite Cathode Electrocatalyst.

We systematically diagnose here the various phases formed at the electrodes in a Li-CO 2 battery. The CO 2 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 (Li 2 CO 3 ↔ Li + CO 2 ) 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 Li 2 CO 3 to Li and CO 2 . When the Li anode is probed, CO 2 crossover is evident via the observation of the formation of LiOH/Li 2 CO 3 phases, the proportions of which change during successive cycles.