Multiphysics Modeling of Electrochemical Conversion of Potassium Bicarbonate in Porous Electrode Flow Cell

Multiphysics Modeling of Electrochemical Conversion of Potassium Bicarbonate in Porous Electrode Flow Cell

Ansarul Huq, Fathaah (TU Delft Mechanical, Maritime and Materials Engineering)

Delft University of Technology

Mechanical Engineering | Energy, Flow and Process Technology

2023-08-31

Climate change is a pressing global crisis with far-reaching consequences, demanding the rapid advancement of clean energy technologies and effective carbon capture methods to mitigate Carbon Dioxide (CO₂) emissions. Carbon capture technologies offer a crucial pathway for capturing, storing, and reusing CO₂, thus contributing to developing a circular carbon economy with net-zero emissions. Integrating carbon capture with electrochemical conversion is a promising and innovative solution for achieving large-scale carbon capture.

Utilizing concentrated Potassium Hydroxide (KOH) solution for carbon capture to produce Potassium Bicarbonate (KHCO₃) represents a favorable approach for integrated capture and conversion. This study focuses on the electrochemical conversion of bicarbonate solution obtained from the capture column to valuable products. The aim is to use a continuum 1-D model to study the influence of flow cell design and operating parameters on bicarbonate electrolysis used for Electrochemical CO₂ Reduction (CO₂R). A Silver (Ag) porous electrode is defined as the catalyst to produce Carbon Monoxide (CO) and Hydrogen (H₂) at the outlet. The outlet gas concentration is critical for chemical downstream processes, such as synthetic fuel production. The thesis begins with a review of the literature in the field of Carbon Capture, Utilization and Storage (CCUS) and CO₂R to understand recent advances in research and the areas of future work. Inlet flow velocity to the catalyst, membrane-catalyst gap, and temperature were among the critical system variables that were varied to observe the response from the model.

The results shed light on the intricate interplay between the operating parameters and the efficiency of CO₂ conversion to CO. Contrary to experimental observations, increasing inlet flow velocity yields a lower CO product output. Possible explanations for this disparity are attributed to the reduction in residence time resulting from higher inlet velocities, the utilization of reaction rates derived from fitting experimental data, and constraints inherent in modeling flow through 1-D configurations. Operating temperature and CO gas concentration show a positive correlation in this work, in agreement with previous experimental studies. The model was modified to capture all temperature-related phenomena, which outlined the importance of model definitions. Finally, the membrane-electrode gap was varied to understand how separating the acidic and basic regions affects the CO product concentrations. The configurations with a gap presented lower overall CO₂ Reduction Reaction (CO₂RR) toward CO. The results are interpreted with likely factors that reduce the performance.

This thesis aims to simplify replicating previous CO₂R continuum models by offering detailed modeling instructions and parameter list. It was discovered that 1-D models pose limitations in defining the boundary conditions for fluid flow and including convective mass transfer in the transport equations. Additionally, the requirement of various constants as input parameters for solving the governing equations creates dependencies on experimental results.
The concluding sections of the thesis provide an overview of the findings in this study and offer a concise examination of the significant research domains in bicarbonate electrolysis. These areas could establish integrated capture and conversion technology as a feasible solution to close the carbon cycle and foster a sustainable future for future generations.

Electrochemical CO2 reduction
Continuum model
Bicarbonate Electrolysis
Porous electrode flow cell
Bipolar membrane/BPM

http://resolver.tudelft.nl/uuid:8c448d21-0f55-4a92-8d9e-36a85f16315f

2025-08-31

Student theses

master thesis

© 2023 Fathaah Ansarul Huq