(60d) Simultaneous Optimization of Electrochemical CO2 Reduction Process and Reaction System

CO₂ reduction reaction (CO₂RR) has attracted attention for its potential to reduce greenhouse gas emissions and produce renewable chemicals and fuels. In recent years, techno-economic analysis (TEA) and life cycle assessment (LCA) for commercial-scale CO₂RR has been required in many ways with the development of the technology. Due to the low technology readiness level (TRL) of CO₂RR, TEA has been carried out through modeling approaches [1]. In previous TEA studies, the consideration of actual behavior of the electrolyzer was insufficient. In experimental research on electrochemical catalysis, it can be confirmed that the current density and Faradaic efficiency are affected by the cell voltage [2, 3]. However, many TEA studies have treated only fragmentary cases without considering the correlation between current density, cell potential, and Faradaic efficiency, despite considering them as important parameters for CO₂ reduction [4-6]. Additionally, physics occurring within the electrolyzer, such as transport phenomena and reaction kinetics, are not considered in many cases.

To properly perform TEA/LCA for CO₂RR, current density, Faradaic efficiency, and single-pass conversion, which vary with cell voltage, should not be arbitrarily changed, but must be calculated according to physical perspective. Only then can we quantitatively analyze how changes in reactor design variables (membrane type, catalyst layer thickness, etc.) or process variables (cell voltage, CO2 flow rate, CO2 humidity, etc.) affect the overall TEA/LCA metrics. In this attempt, Choi et al [7] implemented a voltammetric model at the MATLAB level, but the physics considered by the model did not reach computational fluid dynamics (CFD) [8, 9]. To perform TEA/LCA with the physical behaviors of the electrolyzers, it is necessary to implement a multiscale simulation between continuum-scale multiphysics simulation and process simulation.

In this study, we developed a boundary interconnection methodology between the electrolyzer model and the process model and proposed a multiscale model that can calculate the entire process TEA/LCA within a computationally feasible time. Simultaneous optimization of process and reactor design was performed, and optimal reactor design variables and optimal operation conditions for CO₂-to-chemical (CO, formic acid, ethylene, etc.) for the entire process were proposed. A finite element method (FEM)-based CFD multiphysics model and process simulation through aspen plus were produced, and TEA/LCA was performed to interconnect two different scale models. To optimize them, the derivative-free optimization (DFO) algorithm was used. For electrolyzer design, the electrolyzer was set up as a full membrane electrode assembly (full-MEA) with no catholyte based on an anion exchange membrane (AEM). The reactor design parameters considered the thickness of the catalyst layer (CL) and the type of AEM, and the process parameters considered cell voltage, pressure, temperature, and CO₂ humidity. The TEA indicator is the levelized cost of chemicals that makes net present value (NPV) zero, and the separation process was included in the evaluation to satisfy purity. The system boundary of LCA is the gate-to-gate from CO₂ to chemicals, and the primary LCA indicator is global warming impact (GWI).

[1] Somoza-Tornos A, Guerra OJ, Crow AM, Smith WA, Hodge B-M. Process modeling, techno-economic assessment, and life cycle assessment of the electrochemical reduction of CO2: a review. iScience. 2021;24(7):102813.

[2] Gao D, Zhang Y, Zhou Z, Cai F, Zhao X, Huang W, et al. Enhancing CO2 Electroreduction with the Metal–Oxide Interface. Journal of the American Chemical Society. 2017;139(16):5652-5.

[3] Varela AS, Kroschel M, Reier T, Strasser P. Controlling the selectivity of CO2 electroreduction on copper: The effect of the electrolyte concentration and the importance of the local pH. Catalysis Today. 2016;260:8-13.

[4] Jouny M, Luc W, Jiao F. General Techno-Economic Analysis of CO2 Electrolysis Systems. Industrial & Engineering Chemistry Research. 2018;57(6):2165-77.

[5] Na J, Seo B, Kim J, Lee CW, Lee H, Hwang YJ, et al. General technoeconomic analysis for electrochemical coproduction coupling carbon dioxide reduction with organic oxidation. Nature Communications. 2019;10(1):5193.

[6] Spurgeon JM, Kumar B. A comparative technoeconomic analysis of pathways for commercial electrochemical CO2 reduction to liquid products. Energy & Environmental Science. 2018;11(6):1536-51.

[7] Shin H, Hansen KU, Jiao F. Techno-economic assessment of low-temperature carbon dioxide electrolysis. Nature Sustainability. 2021;4(10):911-9.

[8] Choi W, Choi Y, Choi E, Yun H, Jung W, Lee WH, et al. Microenvironments of Cu catalysts in zero-gap membrane electrode assembly for efficient CO2 electrolysis to C2+ products. Journal of Materials Chemistry A. 2022;10(19):10363-72.

[9] Choi W, Park S, Jung W, Won DH, Na J, Hwang YJ. Origin of Hydrogen Incorporated into Ethylene during Electrochemical CO2 Reduction in Membrane Electrode Assembly. ACS Energy Letters. 2022;7(3):939-45.