Development of Bilayer Ionomer Coatings for Enhanced Carbon Dioxide Electrolysis Towards Multi-carbon Products
Date
2024-03-26
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Abstract
In the realm of carbon neutrality, electrochemical CO2 reduction (eCO2R) stands as a pivotal technology for converting carbon dioxide into valuable multi-carbon (C2+) products, such as ethylene (C2H4) and ethanol (C2H5OH). Despite significant strides in achieving high Faradaic efficiency (FE) at industrial-scale current densities, persistent challenges like cathode flooding and (bi)carbonate salt accumulation in alkaline electrolytes continue to pose fundamental concerns. This study addresses these challenges by leveraging ion-conducting polymers (ionomers) to tailor the micro-environment mitigating cathode flooding and (bi)carbonate crossover and thus, enhance the local CO2 availability in eCO2R. Exploring the impact of cation and anion exchange ionomer layers, specifically Nafion and Sustainion XA-9, reveals that a cation infused ultra-thin bilayer configuration significantly reduces cathode flooding and salt accumulation by approximately 58%, outperforming commercial anion exchange membranes (AEM). Initially, a Single Layer Ionomer (SLI) using Sustainion XA-9 proves effective in mitigating cathode flooding due to the back convection of the thin hydrophobic cathode. Despite an impressive initial partial current density towards C2+ products (jC2+) of ~280 mA/cm2, challenges arise concerning (bi)carbonate formation and CO2 loss. Introducing an additional Nafion layer mitigates (bi)carbonate crossover, attributed to controlled OH- and K+ ion transport facilitated by the Nafion layer. However, the introduction of a Bilayer Ionomer (BLI) configuration results in lower C2+ selectivity due to insufficient OH- diffusion to establish the alkaline micro-environment essential for C2+ reaction pathways. Subsequently, incorporating cation infusion in this bilayer ionomer system (Cation Infused Bilayer Ionomer or CIBLI) proves beneficial, promoting C-C bond formation and creating a favorable micro-environment for selective C2+ product generation. The CIBLI system achieves a substantial high partial current density of approximately ~284 mA/cm2 towards C2+ products, maintaining stable eCO2R performance over 24 hours. The scalability of the directly deposited ultrathin CIBLI configuration offers a minimal conversion energy of 117 GJ/ton for C2+ products with an electrolyzer energy efficiency (EE) of 29% at 350 mA/cm2 current density. This one-step CO2 conversion process represents a promising advancement, emphasizing both efficiency and sustainability in carbon recycling technologies.
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Keywords
CO2 Electrolysis, Ionomers, Bilayer Ionomer Coating, Multi carbon products, Partial current density, Directly deposited membrane, Cathode Flooding, Nafion, Sustainion XA-9
Citation
Rashid, M. (2024). Development of bilayer ionomer coatings for enhanced carbon dioxide electrolysis towards multi-carbon products (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.