Anode-less Hybrid Na-CO₂ Battery with Sodium Harvesting from Seawater for Both Electricity Storage and Various Chemical Production

Metal-CO2 batteries have received significant attention. Specifically, Zn-CO2 batteries have attracted interest because of their ability to produce value-added chemicals from CO2. However, owing to the low driving force of Zn (high redox potential, EZn( OH) d42-/ Zn of -1.2 V vs SHE), they exhibit low energy density and face challenges in the production of highvalue C-2 chemicals requiring high energy barriers. In this study, we designed hybrid Na-CO2 batteries which utilize the high driving force of Na (low redox potential, ENa +/ Na of -2.7 V vs SHE) to achieve high energy density and produce C-2 chemicals. This system produced CO, formate, and C2 chemicals with 97.0%, 70.4%, and 37.6% Faradaic efficiency (FE), generating a high power density (25.0 mW cm(-2)). Furthermore, we constructed an anode-less hybrid Na-CO2 battery that harvests unlimited Na ions from seawater instead of difficult-to-handle Na metal anode, producing CO with an 85.0% FE. This study shows the potential of next-generation sustainable batteries that can address greenhouse gas problems.