Micromodel of a Gas Diffusion Electrode Tracks In‐Operando Pore‐Scale Wetting Phenomena

Abstract

Utilizing carbon dioxide (CO2) as a resource for carbon monoxide (CO) production using renewable energy requires electrochemical reactors with gas diffusion electrodes that maintain a stable and highly reactive gas/liquid/solid interface. Very little is known about the reasons why gas diffusion electrodes suffer from unstable long‐term operation. Often, this is associated with flooding of the gas diffusion electrode (GDE) within a few hours of operation. A better understanding of parameters influencing the phase behavior at the electrolyte/electrode/gas interface is necessary to increase the durability of GDEs. In this work, a microfluidic structure with multi‐scale porosity featuring heterogeneous surface wettability to realistically represent the behavior of conventional GDEs is presented. A gas/liquid/solid phase boundary was established within a conductive, highly porous structure comprising a silver catalyst and Nafion binder. Inoperando visualization of wetting phenomena was performed using confocal laser scanning microscopy (CLSM). Non‐reversible wetting, wetting of hierarchically porous structures and electrowetting were observed and analyzed. Fluorescence lifetime imaging microscopy (FLIM) enabled the observation of reactions on the model electrode surface. The presented methodology enables the systematic evaluation of spatio‐temporally evolving wetting phenomena as well as species characterization for novel catalyst materials under realistic GDE configurations and process parameters.

Advances and challenges in membrane electrode assembly electrolyzers for CO2 reduction

“…The electrowetting phenomenon including (b) the electrowetting pore filling rate of GDE over time, (c) the corresponding confocal laser scanning microscopy (CLSM) images, and (d) the contact angle of electrolyte in the presence of potential or not. 67 Copyright © 2023, the author(s). (e) The observation of electrolyte penetrating and salt precipitation in a GDE over electrolysis at 100 mA cm −2 .…”

Direct Imaging of Local pH Reveals Bubble-Induced Mixing in a CO2 Electrolyzer

“…For example, Kalde et al used FLIM to qualitatively determine electrochemically active areas in a microfluidic model of a GDE. 50 In this work, we study the electrochemical performance and the local pH profile of a CO 2 electrolyzer with a flowing K 2 SO 4 catholyte and a bipolar membrane. The effects of process parameters, i.e., current density, CO 2 saturation, and catholyte flow rate, on the Faradaic efficiency for CO are investigated.…”

“…In another example, de Valença et al investigated the mass transfer of Cu 2+ ions in an electrochemical cell. , So far, only a limited number of studies have applied FLIM to CO 2 electrolysis. For example, Kalde et al used FLIM to qualitatively determine electrochemically active areas in a microfluidic model of a GDE …”

Quinolinium-Based Fluorescent Probes for Dynamic pH Monitoring in Aqueous Media at High pH Using Fluorescence Lifetime Imaging

“…Recently, real-time monitoring of complex systems in three dimensions using FLIM has also been employed for abiotic processes. Using conventional probes, pH gradients in electrochemical processes and flow-through porous catalysts have been monitored . In our current research, we are investigating electrochemical processes that are relevant for the coming energy transition, such as electrochemical water splitting and CO 2 reduction.…”

“…The 1-methyl-7-amino-quinolinium fluorophore has (photo)­physical properties that are highly suitable for developing lifetime probes for FLIM applications. The fluorophore has a high fluorescence quantum yield in the 0.7–0.8 range and fluorescence lifetimes in the 12–13 ns range, which is well above the 4 ns lifetime of common fluorophores that may pollute a sample . On top of that, this fluorophore is inherently water-soluble and highly photostable.…”