Demand-side flexibility enables cost savings in a reversible pH-swing electrochemical process for oceanic CO2 removal

Summary Oceans absorb 40% of all carbon dioxide (CO₂) emissions, making CO₂ removal from seawater as critical as from the air. A reversible pH-shifting seawater process uses hydrogen and redox salt to extract CO₂, generating and consuming power during acidification and basification, respectively. An equivalent circuit model predicts performance dependent on key transport and thermodynamic parameters. The need to overcome mass-transport limitations, particularly liquid boundary-layer diffusion, is crucial for industrial current densities. Energy-intensity calculations indicate this process is competitive with prior oceanic CO₂ removal processes and even with direct air capture, when pumping energy cost is eliminated. Utilizing variable electricity pricing enables up to $65 (USD) savings per ton of CO₂, which is 17% of oceanic and 52% of atmospheric CO₂ capture costs. At the present largest desalination plant, 100 kilotons of CO₂ can be captured per year, resulting in $6.5 million operational cost savings.