In general, a gas diffusion electrode (GDE) must be conductive, porous, and hydrophobic so that it allows the passage of gas but not liquid. The established methodology for making GDEs involves coating a pre-existing hydrophobic, porous surface with a metal which acts as a catalyst and conductive layer. This standard architecture reduces if not eliminates the GDE’s through-plane conductivity which in turn limits the design space the GDE can be used in for the overall membrane electrode assembly (MEA), the core component of an electrochemical fuel cell. By using standard GDEs made with carbon felts and polytetrafluoroethylene (PTFE), front contact MEA architectures are required, which increase cell voltage thereby decreasing cell lifetime and charge uniformity. There is a need for GDE designed with through plane conductivity that allow the cell to be constructed with a “back contact” to the GDE, which can significantly reduce cell voltage and improve charge uniformity.
LLNL researchers have developed a novel method of making a GDE that starts with a porous, conductive structural framework made from metallic materials which standalone would be too hydrophilic and macroporous. The conductive structural framework is then infilled with a hydrophobic monomeric solution and subsequently photopolymerized to make a porous hydrophobic polymer resin network that surrounds the conductive structural framework. The tunable nature of the porous hydrophobic resin allows for application-specific tailoring of the infill’s properties. Once surrounded with resin, the GDE becomes hydrophobic and microporous and ready to be used in electrochemical fuel cells. The conductive structure provides the much needed mechanical support for the porous resin and prevents the collapse of pores during operation. Since the entire structure is conductive, the final product contains through-plane conductivity and can therefore utilize a "back contact" method of current conduction instead of using a copper front contact method. This significantly reduces the cell voltage and offers higher charge uniformity, thus increasing cell lifespan and easier scale-up ability.
Image Caption: Process Flow for making the gas diffusion electrode
- Tunable porosity of hydrophobic resin allows for application-specific designs.
- Conductive structural framework prevents collapse of the GDE pores in an operating cell.
- Through-plane conductivity allows for "back contact" method of current conduction.
- Increased cell lifespan and scale-up potential of the technology.
- More plug and play ready design compared with current industry standards.
- PEM and AEM electrolyzers
- CO2 reduction electrochemical fuel cells
- Hydrogen fuel cells
Current stage of technology development: TRL 3
LLNL has filed for patent protection on this invention.