Asymmetric Electrosorption in a Bio-Inspired Reactor Enables Energy Efficient Ocean Carbon Removal

Ocean carbon removal represents a promising pathway for mitigating residual anthropogenic carbon dioxide (CO₂), yet existing methods are constrained by high energy demands and potential ecological risks. Here, inspired by the natural calcification process of corals, we present a bio-inspired capacitive decarbonization (CDC) reactor that sequesters dissolved inorganic carbon (DIC) from seawater as CaCO₃ using only seawater-derived Ca²⁺ and renewable electricity. The CDC system integrates a Ca²⁺-selective electrode with a weak electric field to regulate ion transport and disrupt the hydration shell of Ca²⁺, enhancing its reaction with CO₃ ^2-. To address the limited concentration of CO₃ ^2- relative to Ca²⁺ in seawater, we introduce an asymmetric electrosorption strategy to preferentially enrich CO₃ ^2- at the electrode interface, achieving a DIC conversion rate of up to 34% with an ultralow intrinsic electrochemical energy input of 2.5 kJ mol^-1 CO₂ for the CDC reactor. The reactor exhibits stable continuous operation for over 100 h without fouling, enabled by spatially decoupled CaCO₃ precipitation. To mitigate the reduction in seawater alkalinity, we introduce a mineral-assisted re-alkalinization step that effectively restores pH and supports continued CO₂ absorption. A global integrated analysis model shows the CDC technology could remove up to 11-438 million tonnes of CO₂ by 2050-2100. This work demonstrates a scalable and low-energy solution for durable ocean carbon removal.