Energy-Efficient Seawater Lithium Extraction via a Reversible Redox-Hydrogen Coupled System

The global surge in lithium demand poses growing challenges for supply security and sustainability, yet vast lithium reserves in seawater remain largely untapped due to extremely low Li⁺ concentrations and high levels of competing ions. Here, we present an integrated electrochemical system coupling direct lithium extraction from seawater with in situ energy storage and hydrogen co-production. A reversible Ni(OH)₂/NiOOH redox electrode replaces conventional anodic seawater electrolysis, storing electrical energy that would otherwise be wasted and enabling its recovery on demand through a Zn-NiOOH battery configuration. Meanwhile, a NiS₂/MoS₂ catalyst lowers the overpotential for hydrogen evolution at the cathode, generating approximately 807 mL of hydrogen gas per gram of lithium extracted. This synergistic design reduces net energy consumption to 6.40 Wh g^-1_Li, upgrades seawater from a low-quality brine (0.183 mg L^-1 Li⁺) to a Li-rich solution (306.2 mg L^-1) and lowers the Mg/Li ratio by seven orders of magnitude without additional reagent. This approach demonstrates a practical, sustainable route to unlock seawater as a viable high-grade lithium resource for a secure energy future.