Demand-side flexibility enables cost savings in a reversible pH-swing electrochemical process for oceanic CO<inf>2</inf> removal

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.