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Avalilação PREreview de Integrated Bipolar Membrane Electrodialysis and Electrolysis for CO2 Capture and Conversion

de Rabah Mokhbi
Publicado
DOI
10.5281/zenodo.21418047
Licença
CC BY 4.0

This preprint presents BMEED, a system that integrates bipolar membrane electrodialysis (BMED) with a CO₂ electrolyzer (CO2E) into a single unit for combined bicarbonate-based CO₂ capture and conversion to CO. The authors demonstrate CO₂ desorption from bicarbonate absorbents at 3.90 kWh/kg-CO₂, and report that the integrated system achieves 98% CO₂-to-CO selectivity at 34.00 kWh/kg-CO, a 17% energy reduction compared to two decoupled subsystems operating at the same selectivity (39.22 kWh/kg-CO). A techno-economic analysis further indicates a 42% reduction in the levelized cost of CO production and a shift from an unprofitable baseline to a profitable scenario at 193/ton−CO.</p><p><b>Strengths</b></p><p>Thedirect,matched−selectivitycomparisonbetweentheintegratedandstandaloneconfigurationsisaclearstrength:isolatingenergyconsumptionatafixed98<p><b>Questionsandconcerns</b></p><ol><li><p>Bothconfigurationsarereportedat98193/ton-CO.</p> <p><b>Strengths</b></p> <p>The direct, matched-selectivity comparison between the integrated and standalone configurations is a clear strength: isolating energy consumption at a fixed 98% selectivity makes the reported 17% improvement a specific, testable claim rather than a qualitative one. The work also builds naturally on the authors' prior demonstration of bicarbonate electrolysis via bipolar membranes, addressing the stability and selectivity limitations noted there by moving toward system-level integration. Coupling bench-scale energetics with a techno-economic analysis is valuable in this field, where many bipolar-membrane CO₂ capture-and-conversion studies report Faradaic efficiency without translating results into cost terms.</p> <p><b>Questions and concerns</b></p> <ol><li><p>Both configurations are reported at 98% selectivity. It would help to clarify whether this is the natural operating optimum for both systems or a condition selected to enable a fair comparison, since selectivity and energy consumption typically trade off against one another.</p></li><li><p>Are the 34.00 and 39.22 kWh/kg-CO figures obtained under directly comparable current densities, stack designs, and balance-of-plant assumptions, or does the standalone-subsystems case rely partly on modeled rather than measured performance? This affects how much of the reported gain reflects genuine integration synergy versus differing boundary conditions between the two cases.</p></li><li><p>The techno-economic conclusions (193/ton-CO profitability, 42% LCOP reduction) depend strongly on assumed electricity price, capital cost, stack lifetime, and CO market price. A sensitivity analysis across these parameters would strengthen confidence in the profitability claim beyond a single point estimate.

  • The abstract does not specify current density, active cell area, or operating duration. Bipolar-membrane systems commonly show a gap between short bench demonstrations and performance at industrially relevant current densities and durations; clarifying stability over extended operation would help readers assess scale-up readiness.

  • The introduction frames the work around seawater decarbonization and direct ocean capture, while the demonstrated system uses bicarbonate-based absorbents. It would be helpful to confirm whether real seawater (with its associated Mg²⁺, Ca²⁺, and SO₄²⁻ content, which can affect membrane performance) or a synthetic bicarbonate solution was used in the reported experiments.

    • Minor comment

    It would be useful to clarify whether the 39.22 kWh/kg-CO figure for the decoupled case includes the combined energy input of both BMED and CO2E, or CO2E alone with capture accounted separately, as this affects comparison with conventional capture-and-conversion benchmarks.

    Overall assessment

    This is a well-scoped and clearly presented extension of the authors' prior bicarbonate-electrolysis work, with a genuinely useful comparison between integrated and standalone configurations. The main open question is the extent to which the reported energy and cost improvements reflect true integration synergy versus differences in operating conditions or techno-economic assumptions between the two cases. Addressing the points above, particularly around comparability of the two configurations and sensitivity of the TEA, would strengthen the manuscript.

    Competing interests

    The author declares that they have no competing interests.

    Use of Artificial Intelligence (AI)

    The author declares that they did not use generative AI to come up with new ideas for their review.