Quantifying capital-energy trade-offs in bipolar membrane electrodialysis for atmospheric and oceanic carbon removal

[Geoengineering News]

https://www.cell.com/joule/abstract/S2542-4351(26)00108-X

Authors: Hussain M. Almajed, Bri-Mathias Hodge, Wilson A. Smith

10 April 2026

Context & scale

Deploying carbon dioxide removal (CDR) technologies has become an important pillar in achieving net-zero CO2 emissions targets. Recent estimates suggest that we need to remove around 1 billion metric tonnes of CO2 annually to reach the net-zero point by 2050. At this large scale, engineered CDR technologies, such as direct air capture (DAC) and direct ocean capture (DOC), will be necessary to preserve land while capturing enormous amounts of CO2 from the atmosphere. DAC can absorb CO2 using alkaline solutions, whereas DOC relies on the natural air-ocean equilibrium that absorbs around 30% of anthropogenic CO2 emissions annually. Once CO2 is captured, it is usually regenerated before its storage or utilization. However, the CO2 regeneration step consumes a high amount of energy, which is typically supplied by heat from natural gas combustion at high temperatures. Electrifying this step to use low-carbon electricity offers a promising strategy to manage the carbon balance of engineered CDR processes. Bipolar membrane electrodialysis (BPMED) presents a suitable solution that uses electricity to generate acidic and basic streams, which are then used to regenerate CO2 at ambient temperatures.

The integration of DAC and DOC with BPMED presents electrified engineered CDR pathways that enable flexible dynamic operation, which could benefit from hourly variable wholesale electricity prices. When participating in wholesale electricity markets, dynamic CDR plants could turn off during hours of extremely high wholesale electricity prices and stay on during hours when wholesale electricity prices do not cause an increase in the levelized cost of CO2 capture. Optimizing this flexibility using process and techno-economic models while considering design and operational trade-offs would inform the design of policy incentives, technology development, and technology comparisons. This work builds an understanding of the integration of BPMED in atmospheric and oceanic CO2 capture applications.

Highlights

• Electrodialysis uses electricity to regenerate CO2 from (bi)carbonate solutions

• Dynamic operation of grid-powered direct air capture plants reduces CO2 capture costs

• Electrodialysis capital costs dominate the CO2 capture costs in direct ocean capture

• Decarbonized grid electricity is necessary to reach a high carbon removal efficiency

Summary

Coupling bipolar membrane electrodialysis (BPMED) with direct air capture (DAC) and direct ocean capture (DOC) presents promising carbon removal pathways. We develop, validate, and integrate process and techno-economic models to assess this integration under variable power scenarios. We find that differences in dissolved inorganic carbon content introduce an energy-size trade-off, leading to smaller BPMED areas via DAC, compared with DOC-BPMED, at the expense of 100-fold higher current densities. Consequently, DAC-BPMED is more sensitive to operational costs, whereas DOC-BPMED is more sensitive to capital costs. Estimated grid-connected capture cost ranges are US$304–US$1,281/t-CO2 and US$535–US$2,220/t-CO2 for DAC-BPMED and DOC-BPMED, respectively. Selling excess NaOH and concentrating the CO2 feedstock could potentially alleviate some CO2 capture costs via DOC-BPMED, while off-grid renewable power integration increases capture costs in both routes. These findings offer novel insights into BPMED-based carbon removal and motivate further research that advances performance while improving cost-effectiveness.

Source: CellPress