The Evaluation of Ionomers in Alkaline Membrane Electrode Assemblies for Water Electrolysis

The cost of water electrolysis can be reduced by transitioning from an acid to an alkaline environment. The chemistry and electrochemistry of alkaline electrolyte-based electrolyzers allows for less expensive materials-of-construction and catalysts.

The ionomers used to construct the three-dimensional electrodes on the anion conducting membrane (collectively called the membrane electrode assembly (MEA)) contribute to the overall performance of the electrolyzer. First, the ionomer provides the ion pathway between the anion conducting membrane and catalyst particle. Second, the ionomer must solubilize and transport the chemical reactants to the catalyst surface and facilitate the removal of the reaction products. Third, an electrochemical double layer is formed within the ionomer at the catalyst surface. The nature of the double layer affects the overvoltage at the electrode which contributes to the overall cell potential. Fourth, the ionomer provides mechanical stability and adhesion of the particles in the three-dimensional electrode. Thus, the ionomer should have high chemical and mechanical stability so that it does not degrade by the electrochemical or have excess swelling and adversely affect the mass and ion transport to the catalyst.

In this project, a number of ionomers were studied in an alkaline electrolysis cell. The overvoltage and chemical stability of the ionomers was compared. The ionomers tested in this project include those with an all-hydrocarbon backbone, ionomers with partial fluorination in the backbone and ionomers with a block copolymer backbone.