The Conventional Gas Diffusion Electrode May Not Be Resistant to Flooding during CO₂/CO Reduction

Abstract

Electrochemical CO2 or CO reduction to chemicals and fuels using renewable energy is a promising way to reduce anthropogenic carbon emissions. The gas diffusion electrode (GDE) design enables low-carbon manufacturing of target products at a current density (e.g., 500 mA/cm2) relevant to industrial requirements. However, the long-term stability of the GDE is restricted by poor water management and flooding, resulting in a significant hydrogen evolution reaction (HER) within almost an hour. The optimization of water management in the GDE demands a thorough understanding of the role of the gas diffusion layer (GDL) and the catalyst layer (CL) distinctively. Herein, the hydrophobicity of the GDL and CL is independently adjusted to investigate their influence on gas transport efficiency and water management. The gas transport efficiency is more enhanced with the increase in hydrophobicity of the GDL than the CL. Direct visualization of water distribution by optical microscope and micro-computed tomography demonstrates that the water flow pattern transfers from the stable displacement to capillary fingering as GDL hydrophobicity increases. Unfortunately, only increasing the hydrophobicity is not sufficient to prevent flooding. A revolutionary change in the design of the GDE structure is essential to maintain the long-term stability of CO2/CO reduction.

CO2 flow electrolysis – limiting impact of heat and gas evolution in the electrolyte gap on current density

“…Despite recent advances, flooding and salt formation within the GDE are still commonly reported in the literature. 26,51 We did not observe any salt depositions on the gas-side of the GDEs or notable amounts of permeate. In experiments in which the catholyte was pressurized, small amounts of salt crystals were found in the gas flow channel.…”

Tailoring hydrophilic and hydrophobic microenvironments for gas–liquid–solid triphase electrochemical reactions

“…However, GDEs also suffer from low product selectivity and stability issues due to the competition with HER and ooding (i.e., complete wetting of GDEs) issues. [149][150][151] In particular, the ooding of GDEs occurs when they can no longer uphold their Cassie-Baxter state and shi toward the Wenzel state. Consequently, preventing the CWT directly correlates with prolonging the lifetime of GDEs.…”

Advances and challenges in membrane electrode assembly electrolyzers for CO2 reduction

“…The occurrence of ooding is determined by electrowetting effects, highlighting the need for signicant innovations in GDEs for CO 2 RR to achieve long-term stable electrolysis. 109 In reality, the crossover phenomenon is the reason why AEM or CEM membranes exhibit conductivity in MEA cells. However, in practical CO 2 RR systems, these membranes are rarely solely selective.…”

“…The occurrence of flooding is determined by electrowetting effects, highlighting the need for significant innovations in GDEs for CO 2 RR to achieve long-term stable electrolysis. 109…”