PEMION+™ - PP1-HNN8-00

Additional Information

Role of Ion Exchange Polymers in Membrane Electrode Assemblies of Water Electrolyzer and Fuel Cells

Membrane electrode assembly (MEA) is considered the heart of water electrolyzers and fuel cells. It is composed of the gas diffusion layers (or porous transport layers), catalyst layers (CLs), and ion exchange membranes. MEA contains the sites where the significant electrochemical reactions occur. They are also responsible for the mass transport processes that involve transfer of reactants into and products out of the device, as well as electron conduction from the electrodes to the external circuitry of the water electrolyzers and fuel cells. Water electrolyzer and fuel cell performance is considerably affected by the properties of GDLs, CLs, and membranes comprising the MEA. The electrodes should have high electrical conductivity and porosity, whereas the CL should exhibit high catalytic activity. Ideally, MEAs have all of these properties while being inexpensive. For polymer electrolyte membrane water electrolyzers and fuel cells specifically, cost has been an issue since the highly acidic operating conditions necessitates the usage of expensive platinum group metal catalysts, commonly Pt/C.

Balancing out cost effectiveness and device performance requires optimization of the MEA fabrication. MEAs are typically produced through two major techniques. First, the gas diffusion electrode (GDE) method involves depositing the catalyst layer on the GDL. Second, in the catalyst-coated membrane (CCM) technique, the catalyst is directly coated onto the ion exchange membranes through electrostatic spray coating, ultrasonic coating, decal transfer, and screen printing. The CCM method yields MEAs with lower interfacial resistance owing to reduced reactant diffusion path and enlarged contact area. The caveat is that the direct deposition of the catalyst on the membranes may form cracks in the CL owing to the high tendency of the catalyst particles to agglomerate and the evaporation of the solvent used in the ink formulation. 

To improve catalyst utilization, ion exchange polymers or ionomers are added into catalyst ink formulations. Catalyst ink formulations are typically composed of the catalyst, a solvent, and the ion exchange polymer or ionomer. The electrochemical properties, coating characteristics, and coating stability of the CL is highly dependent on the interactions of these three primary components. Ion exchange polymers are adsorbed on the catalyst particles in the CL. This adsorption increases the surface charge of the catalyst particle agglomerates. As the electrostatic repulsion between the catalyst particles dominates over the van der Waals forces, the tendency of forming agglomerates is reduced. On top of that, the ion exchange polymer particles increase the steric hindrance, which keeps CL particles away from each other. Aside from improving catalyst utilization, the ion exchange polymer also improves charge (anion or proton) conduction as it acts as an extended charge conductor from the bulk of the ion exchange membrane. The ionomer also serves as a binder for the catalyst particles, ensuring that there are available reactant transfer and electrical conduction pathways. Lastly, the ion exchange polymers act as an hydrophilic agent, retaining the optimum moisture level to ensure that the membrane is well-hydrated. 

Solvent compatibility with Ion exchange polymers

The way the ionomer interacts with the solvent and the catalyst is a key factor that determines the stability of dispersion and the rheological properties of the ink. Dissolution of Pemion® ionomer is typically achieved following stirring and gentle heating (e.g., 300–600 rpm at 60 °C) in a chosen solvent for 24–72 h, depending on vessel size, concentration, and amount of ionomer being dissolved. Filtration of the polymer solution following dissolution is recommended.

We sell our ionomers in pure polymer powder form and provide comprehensive handling and dissolution instructions for customers to create their own solutions from. This saves both us and you the headache in terms of shipping flammable liquids, and the associated safety and cost considerations.

Both the PEM and AEM are readily soluble in low boiling point, common laboratory solvents.

These are prototype materials only intended to be used for early development activities and not intended for production items. Product information is to be used as a guide only, subject to change at any time.