ChE MS Thesis Defense: Daniel Sekyere

Name: Daniel Sekyere

Title: Integrating Direct Air Capture with Bicarbonate Electrolysis

Date: 04/01/2026

Time: 10:00:00 AM

Committee Members:
Prof. Magda Barecka (Advisor)
Prof. Richard West
Prof. Damilola Daramola
Prof. Aaron Stubbins

Location: Snell Library 013

Abstract:
Bicarbonate electrolysis offers a compelling pathway to integrate direct air capture (DAC) with electrochemical CO₂ reduction, bypassing the energy-intensive thermal regeneration that is a bottleneck in alkaline solvent-based DAC. Yet a critical flaw undermines most laboratory studies: the electrolytes used do not accurately reflect solvents produced from real atmospheric CO₂ capture. This thesis investigates quantification of carbon speciation during CO₂ absorption in 0.1 M potassium hydroxide (KOH), potassium bicarbonate (KHCO₃), and potassium carbonate (K₂CO₃) under pure CO₂, 1000 ppm CO₂ in N₂, and ambient air (~430 ppm), using a non-destructive real-time DIC quantification method based on inline pH and conductivity measurements.

The central finding is that fresh KHCO₃, typically used for bicarbonate electrolysis, off-gases a substantial amount of CO₂ and therefore should not be used in bicarbonate
electrolysis studies. Using Henderson-Hasselbalch equation, it is demonstrated that 0.1 M KHCO₃ equilibrates with ~14,700 ppm dissolved CO₂, 34 times above ambient air, driving desorption by Le Chatelier’s principle. Measured DIC losses of 1,400 mg/L (air) and 1,046 mg/L (CO₂+N₂), alongside pH increases from 8.65 to ~10.12, confirm this mechanism. By contrast, KOH retains 87–91% of its pure CO₂ absorption capacity under dilute conditions and produces authentic DAC effluent of bicarbonate-carbonate mixtures (54-65% HCO₃⁻, 35-46% CO₃²⁻) with negligible dissolved CO₂, unlike the CO₂-saturated solvent. Equilibration times extended 35-161-fold under dilute CO₂, marking a transition from kinetic to mass-transfer control with direct implications for contactor design.

These findings challenge the validity of performance metrics reported across a substantial body of bicarbonate electrolysis research and provide a rigorous experimental framework for electrolyte preparation that accurately reflects integrated DAC-electrolysis systems.

Daniel is a Chemical Engineering graduate student at Northeastern University, where he is completing his Master of Science thesis titled Integrating Direct Air Capture with Bicarbonate Electrolysis. His research examines whether common laboratory electrolytes used in bicarbonate electrolysis studies accurately represent real direct air capture (DAC) solvents – a question with significant implications for how the field designs and interprets experiments. In doing so, his work challenges a foundational assumption in the bicarbonate electrolysis literature and offers a methodological corrective with broad relevance to carbon capture research. His findings are being prepared for journal submission alongside his thesis, expected April 2026. Beyond the laboratory, Daniel is an active member of the African Graduate Student Association at Northeastern, where he contributes to a community that supports and uplifts African scholars in graduate education. He has also presented his research at the American Institute of Chemical Engineers (AIChE), engaging a broader professional audience with his work on DAC-electrolysis integration. With strong competencies in carbonate equilibrium chemistry, electrochemical systems, and system modeling, Daniel is driven by the goal of developing rigorous, scalable pathways for carbon dioxide removal.