Capture and conversion of CO₂ from oceanwater can lead to net-negative emissions and can provide carbon source for synthetic fuels and chemical feedstocks at the gigaton per year scale. Here, we report a direct coupled, proof-of-concept electrochemical system that uses a bipolar membrane electrodialysis (BPMED) cell and a vapor-fed CO₂ reduction (CO₂R) cell to capture and convert CO₂ from oceanwater. The BPMED cell replaces the commonly used water-splitting reaction with one-electron, reversible redox couples at the electrodes and demonstrates the ability to capture CO₂ at an electrochemical energy consumption of 155.4 kJ mol⁻¹ or 0.98 kWh kg⁻¹ of CO₂ and a CO₂ capture efficiency of 71%. The direct coupled, vapor-fed CO₂R cell yields a total Faradaic efficiency of up to 95% for electrochemical CO₂ reduction to CO. The proof-of-concept system provides a unique technological pathway for CO₂ capture and conversion from oceanwater with only electrochemical processes.

The widespread application of aqueous rechargeable zinc ion batteries (ARZIBs) is limited by issues from both electrodes, including poor reversibility of the zinc anode and low capacity of the cathode. Here, we report the application of a Zn²⁺ substituted Nafion separator (Zn-Nafion) in ARZIBs which improves the performance of both the cathode and anode. On the anode side, the Zn-Nafion separator creates a uniform electrical and Zn²⁺ concentration field near the zinc anode surface, resulting in limited zinc dendrite growth. Therefore, a Zn symmetric cell with a Zn-Nafion separator shows a lower polarization and longer cycle life than those applying a traditional glass fiber separator. On the cathode side, the Zn-Nafion separator increases the contribution of the H⁺ reaction in the H⁺/Zn²⁺ co-insertion process, and causes the randomly distributed byproducts, Zn₄SO₄(OH)₆·nH₂O platelets, to transform into a dense solid-electrolyte-interphase layer, which protects the cathode from dissolving into the electrolyte. Thus, the energy density and capacity retention of both zinc full cells (applying commercial V₂O₅ or α-MnO₂ nanowires as the cathode) are dramatically improved by the Zn-Nafion separator. Notably, the Zn//Zn-Nafion//V₂O₅ cell delivers a high specific capacity of 495.8 mA h g⁻¹ (374.4 W h kg⁻¹) with a low cathode cost (39.23 US$ W h kg⁻¹). Moreover, the Zn-Nafion separator can be recycled at least ten times without performance degradation, which significantly reduces the cost of the battery. The present work can provide a novel insight into cost-effective and high-performance battery technologies.