Seawater Electrolysis Enables Multipathway Climate Change Mitigation through Atmospheric Carbon Dioxide Removal,...

Thermodynamically favorable ("downhill") reactions that convert carbon dioxide (CO2) into stable solid and dissolved carbonates via reaction with alkaline materials offer a promising route to immobilize gigatonnes of CO2 drawn from dilute sources such as the atmosphere, oceans, and low-concentration flue gases. While subsurface geological CO2 mineralization is technically viable, it depends on specific geological conditions, water availability, and, critically, the availability of unbuilt infrastructure (e.g., pipelines, monitoring stations) and access to concentrated CO2, whose separation from dilute sources is both energy- and cost-intensive. Considering the dual need to remove CO2 from the atmosphere and to decarbonize emission-intensive industries, this perspective highlights electrolysis-driven pH-swing approaches that (a) accelerate CO2 removal from air or flue gases, with overall economics strengthened by the coproduction of hydrogen (H2), and (b) enable low-carbon cement (and hence, concrete) production. First, we present a seawater electrolysis strategy that enables atmospheric carbon dioxide removal (CDR) and produces (Ca,Mg) carbonates/hydroxides and H2 for a gross energy intensity (gEI) of ∼2 MWh per tonne of CO2 (MWh/tCO2). Here, key considerations include acid management and the mitigation of chlorine evolution at scale. Second, we highlight electrochemical methods to synthesize portlandite (Ca(OH)2) and H2 at ambient temperature and pressure from calcium-rich minerals and industrial residues, at ∼2 MWh per tonne Ca(OH)2. We discuss efficient means for calcium extraction and electrolytic Ca(OH)2 precipitation as critical aspects of this pathway. Collectively, these electrolysis-based methods offer scalable, energy-efficient solutions for gigatonne-scale CDR and "hard-to-abate" industrial sectors, particularly when powered by renewable energy.