Non-invasive current collectors for improved current-density distribution during CO2 electrolysis on super-hydrophobic electrodes

Abstract

Electrochemical reduction of CO2 presents an attractive way to store renewable energy in chemical bonds in a potentially carbon-neutral way. However, the available electrolyzers suffer from intrinsic problems, like flooding and salt accumulation, that must be overcome to industrialize the technology. To mitigate flooding and salt precipitation issues, researchers have used super-hydrophobic electrodes based on either expanded polytetrafluoroethylene (ePTFE) gas-diffusion layers (GDL’s), or carbon-based GDL’s with added PTFE. While the PTFE backbone is highly resistant to flooding, the non-conductive nature of PTFE means that without additional current collection the catalyst layer itself is responsible for electron-dispersion, which penalizes system efficiency and stability. In this work, we present operando results that illustrate that the current distribution and electrical potential distribution is far from a uniform distribution in thin catalyst layers (~50 nm) deposited onto ePTFE GDL’s. We then compare the effects of thicker catalyst layers (~500 nm) and a newly developed non-invasive current collector (NICC). The NICC can maintain more uniform current distributions with 10-fold thinner catalyst layers while improving stability towards ethylene (≥ 30%) by approximately two-fold.

Nonconductive Metal Oxide Gas Diffusion Layer for Mitigating Electrowetting during CO2 Electrolysis

“…These types have seen cases of durability in the time scale of 100+ h, , whereas in other instances, flooding started to compromise the stability of the product distribution in less than a few hours or only minutes of operation. ,, Carbon paper-based electrodes are porous and conductive but liable to electrowetting, ,,,, which was equally shown to be the case for the Vulcan carbon GDL in this work. The polymeric membrane has a much better hydrophobicity, but it lacks conductivity so that it often requires modification of the catalyst layer or a redesign of the electrolyzer. ,− Our system consisting of metal oxide GDL and Cu mesh has the advantage of mitigating the electrowetting in the GDL layer while at the same time enabling good conductivity through the catalyst layer via the Cu mesh. In addition, through annealing, it creates a firm adherence between the GDL and catalyst layer that prevents delamination throughout use.…”

“…Incorporating dielectric hydrophobic materials such as PTFE can be beneficial to retard the onset of electrowetting to higher voltages. ,− PTFE or polyvinylidene fluoride (PVDF) membranes have been employed as stand-alone GDL substrates, the most common candidate being known as expanded or sintered PTFE. ,− While they hinder the passage of water molecules from high hydrophobicity, however, these materials lack electrical conductivity. This places constraints on the loading of the catalyst and may require the addition of carbon black , or a tailored current collector plate design to ensure uniform current distribution.…”

In situ/Operando Synchrotron Radiation Analytical Techniques for CO2/CO Reduction Reaction: From Atomic Scales to Mesoscales

“…In this regard, a comprehensive understanding of the real active site is particularly important for rational design of materials and thus promoting reactivity. Additionally, the gas diffusion electrode (GDE) also suffers from severe stability challenges related to flooding issues and salt formation [6] . Taking into account that the performance and stability of CO (2) RR electrolysis are highly dependent on the electrocatalysts and electrolysis devices, the oxidation state and local structure of electrocatalysts at the microscale as well as the evolution of electrodes in membrane electrode assembly (MEA) configuration at the mesoscale under operating conditions deserve in‐depth investigations.…”

Scale-Up of PTFE-Based Gas Diffusion Electrodes Using an Electrolyte-Integrated Polymer-Coated Current Collector Approach

“…To date, the low conductivity of PTFE-based GDEs has precluded their scalability: Current must be supplied via edge-contacts relying entirely on the in-plane conductivity of the thin catalyst layer, which is why this type of electrode has so far been limited to 1–5 cm 2 size. Therefore, scale-up of CO 2 RR electrolyzers has only been demonstrated with conductive, e.g., carbon-based, GDEs. − A number of different PTFE GDE scale-up concepts have been recently proposed; ,,, however, these approaches were limited to an electrode area of 5 cm 2 or were plagued by very thick catalyst layers in order to ensure sufficient in-plane conductivity.…”

“…Therefore, scale-up of CO 2 RR electrolyzers has only been demonstrated with conductive, e.g., carbon-based, GDEs. 25 − 29 A number of different PTFE GDE scale-up concepts have been recently proposed; 6 , 7 , 30 , 31 however, these approaches were limited to an electrode area of 5 cm 2 or were plagued by very thick catalyst layers in order to ensure sufficient in-plane conductivity.…”