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

Metal–CO 2 batteries have received significant attention. Specifically, Zn–CO 2 batteries have attracted interest because of their ability to produce value-added chemicals from CO 2 . However, owing to the low driving force of Zn (high redox potential, E Zn(OH) 4 2– /Zn of −1.2 V vs SHE), they exhibit low energy density and face challenges in the production of high-value C 2 chemicals requiring high energy barriers. In this study, we designed hybrid Na–CO 2 batteries which utilize the high driving force of Na (low redox potential, E Na + /Na of −2.7 V vs SHE) to achieve high energy density and produce C 2 chemicals. This system produced CO, formate, and C 2 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–CO 2 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.