The rising importance of transport electrification has promoted the increasing need for large-scale energy storage with high energy density. Compared with conventional lithium ion batteries, lithium-air (Li-air) batteries have a much higher theoretical energy density, attracting increasing attention and research effort. The calculated mass-specific energy density of Li-air batteries is 3458 Wh kg-1, making itself a potential power source for electrical vehicle (EV). However, for the purpose of meeting the requirements for EV application, many issues for Li-air batteries need to be considered, such as exploring stable electrolytes, designing efficient catalysts, suppressing lithium dendrite formation, as well as preventing the contamination of CO2 and H2O in the ambient air, etc. These issues are derived from the reaction chemistry of Li-air batteries, which is different from the intercalation chemistry of Li-ion batteries. To bring Li-air batteries closer to practical reality, understanding reaction chemistry related to electrolyte, electrode and contaminant is of great importance. In this thesis, the catalytic reaction of molybdenum carbide which occur during both discharge and charge under pure CO2, pure O2, CO2/O2 mixture, and ambient air are studied in detail. A trend is identified between the observed overpotential during charge and the decomposition of different discharge products. Additionally, plausible mechanistic pathways under both CO2 and O2 for carbon-based and non-carbon-based electrodes are proposed, along with the potential catalyst design for practical Li-air batteries
