Browsing by Author "Haufe, Stefan"

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Open Access
Evaluation of absorbent solutions for the integrated CO2 desorption and electrolysis
(2025) Hauf, Fabian; Kollmuß, Ricarda; Haufe, Stefan; Klemm, Elias
CO2 electrolysis is an approach that contributes to mitigating global warming. Integrated CO2 electrolysis is a possibility to reduce operating costs by combining desorption and electrolysis. In this approach, it is important to provide sufficient CO2 directly from the absorbent solution to the catalyst, whereby the physically absorbed CO2 appears to play a central role. Therefore, the absorbent solution used for integrated electrolysis must meet a wide range of requirements, as it needs to supply sufficient CO2 while being compatible with the process conditions in the cell. In this study, it is demonstrated that KOH and piperazine (PZ) are suitable absorbent solutions for integrated CO2 electrolysis among the three tested groups of absorbents - namely, inorganic, amines, and physical absorbents. The results reveal that physical absorbents provide the highest amount of accessible CO2 for electrolysis, whereas inorganic absorbents exhibit the highest compatibility with the membranes. KOH and PZ demonstrate the ability to withstand the electrochemical conditions during CO2 electrolysis and the capability to produce C2+ products during integrated CO2 electrolysis. These results highlight the critical importance of absorbent selection and demonstrate the feasibility of using KOH as well as amine‐based solutions, such as PZ, for integrated CO2 electrolysis.
Open Access
Evaluation of process parameters for integrated CO2 electrolysis to produce ethylene
(2026) Hauf, Fabian; Kollmuß, Ricarda; Haufe, Stefan; Klemm, Elias
Electrochemical CO2 reduction provides a promising strategy for reducing greenhouse gas emissions by converting CO2 into chemicals such as ethylene. Integrated CO2 electrolysis, using CO2‐enriched absorbent solutions, is a cost‐effective alternative to gas‐fed systems due to reduced process complexity. However, for industrial applications, the process parameters need to be optimized to enhance selectivity and efficiency. Despite advances in catalyst and cell design, the impact of operational factors like catholyte flow rate, pressure, and temperature on C2+ product selectivity remains largely unexplored. This study systematically investigates the effects of catholyte flow rate, overpressure, and temperature on ethylene selectivity in integrated CO2 electrolysis with a potassium carbonate absorbent. Our results show that increasing the catholyte flow rate enhances the Faraday efficiency for ethylene by mitigating mass transport limitations between the flow field and the catalyst layer, whereas increasing pressure or temperature does not yield similar improvements. This insight shifts the focus from stoichiometric availability of physically dissolved CO2 to mass transport limitations, suggesting that further advances in cell design could unlock higher conversion efficiencies. Our study provides a foundation for scaling up integrated CO2 electrolysis by highlighting the importance of improving mass transport, a key step toward industrial implementation of sustainable CO2 conversion technologies.
Open Access
Investigation of cell components for increasing ethylene production in integrated CO2 electrolysis
(2026) Hauf, Fabian; Kollmuß, Ricarda; Haufe, Stefan; Klemm, Elias
Sustainable chemical manufacturing relies on closing the carbon cycle by transforming CO2 into useful products such as ethylene. Integrated CO2 electrolysis enables direct use of CO2‐rich absorbents, whereby efficient operation requires optimization of process conditions and cell design. This publication investigates the influence of flow field design, gas diffusion layer properties, catalyst loading, gas diffusion electrode compression, and membrane thickness on ethylene formation in a zero‐gap membrane electrode assembly electrolyzer using CO2‐saturated potassium bicarbonate which is the CO2‐loaded absorbent in the commercial potassium carbonate CO2 scrubbing process. The results show that a flat, uniformly thin copper layer about 2 µm‐thick, placed next to a thin 20 µm anion exchange membrane, creates an enhancing microenvironment for C2+ product formation with a maximum FE of 31% to ethylene at a current density of 50 mA cm-2 and a cell voltage of 5.2 V. These findings highlight the critical role of catalyst layer architecture and membrane selection in the effective conversion of CO2 to C2+ products. By focusing on the interplay between cell components and local reaction environments, this work advances the design of integrated CO2 electrolyzers for efficient ethylene production, supporting the development of scalable, and sustainable carbon utilization.