Concepts and challenges in the production of structured Electrodes

Regarding the conversion of electrical energy into chemical energy carrier and vice versa, electrodes with a high efficiency are required. During the different production steps the electrode structure is formed and influenced by changing process parameters.

The chemical processes inside an MEA of a PEM-water electrolysis cell are shown below.

The crucial physical and chemical processes are:

• Diffusion of water to the catalyst layer (wetting, diffusion)
• Electrochemical reaction at the catalyst
• Transport of oxygen from the electrode to the flow field
• Transport of protons through the catalyst layer and membrane to the cathode
• Transport of electrons through the diffusion layer and catalyst
• The amount of unconnected catalyst and electrolyte phases should be small

One way to influence the electrode structure is to use the intermolecular forces between catalyst, catalyst support, and polymer particles by using different process parameters and additives during dispersion production. Following investigations are necessary:

• Correlation between production parameters, additives and the dispersion structure
• Understanding of the structure-forming processes during dispersing, coating and drying
• Relationship between electrode structure and the electrode efficiency
• Rules for scale-up of laboratory processes into pilot plant scale

Challenges and targets for the safe operation of PEM water electrolysis stacks

For a large scale manufacturing of PEM stacks, the production methods for the components need to be scalable and inexpensive.

To achieve high stack efficiencies of 70% or more at low voltages and high current densities, a decrease in membrane thickness is required to reduce membrane resistances. However, with decreasing membrane thickness gas crossover is increasing. Hydrogen, produced on the cathode permeates across the membrane to the anode, forming explosive hydrogen in oxygen gas mixtures.

One requirement here is to find ways to develop the MEAs using manufacturing methods that are scalable and can therefore be manufactured using processes that are as close to industry as possible.