An overview on the evolution of metal-CO₂ batteries: Focus on aqueous Zn–CO₂ batteries

Metal–CO₂ batteries bring a new dimension to the field of carbon capture utilization and storage technology as it can simultaneously store surplus electricity and also reduce greenhouse gas CO₂. This technology gains further importance when CO₂ conversion becomes flexible and tunable to specific value-added CO₂ reduction products with a high degree of selectivity, as it becomes a cheap and controllable way to maximize electricity utilization. Metal–CO₂ batteries having nonaqueous electrolytes showed high discharge voltage and capacity but a limited number of CO₂ reduction products due to the absence of protons. However, aqueous Zn–CO₂ batteries enjoy the benefit of proton-coupled electron transfer that eventually assists flexible CO₂ electrochemistry with more value-added products. In this review, we have discussed about the evolution of metal-CO₂ batteries inspired from the developments of metal-air batteries, in the presence of CO₂ gas as impurities. This review sheds light on the device construction and mechanistic details of electrocatalytic CO₂ reduction in nonaqueous medium taking Li–CO₂ batteries as an example. A comparative analysis of CO₂ electrochemistry in nonaqueous and aqueous electrolytes highlighting the advantages of aqueous electrolytes, which assist proton-coupled electron transfer, has been reported in this article. Aimed to counter the problem of limited value-added CO₂ reduction products in nonaqueous metal–CO₂ batteries, development of aqueous Zn–CO₂ batteries has been elucidated. As the practical application and advancement of these aqueous Zn-CO₂ batteries largely depend on the designing of efficient cathode materials, we have highlighted the recent developments of carbonaceous and transition metal-based cathodes used in aqueous Zn-CO₂ batteries.