Nanoporous Anion Exchange Membranes for Water Electrolyzers

Renewable energy has the potential to supply energy worldwide, but its variable power output requires it to be coupled with energy storage. Electrochemical electrolysis can split water into hydrogen and oxygen, which can be stored and re-converted into electricity later. However, this hydrogen production process is currently more expensive than the traditional method of making hydrogen from fossil fuel. Alkaline exchange membrane (AEM) water electrolyzers use nonprecious metal catalysts and less expensive metal interconnects than proton exchange membranes (PEMs). As a result, a high performing AEM electrolyzer could potentially reduce the cost of hydrogen generation to meet the DOE 2026 cost target of $2/kg H2. However, the biggest limitation of an AEM electrolyzer is its durability. Under high pH conditions, the membrane quickly falls apart, which reduces or even stops the electrolyzer performance. General statement of how this problem is being addressed. This project will develop an anion exchange membrane made from an ionically conductive, nanoporous, and crosslinked polymer that can be supported on a microporous expanded polytetrafluoroethylene (ePTFE) support membrane. The nanoporous polymer will consist of both chemically stable and ionically conductive domains that contain nanostructures with interconnected ionic channels, allowing hydroxide ions to travel across the membrane. The polymer material will be highly crosslinked to prevent membrane swelling and to resist hydrogen and oxygen crossover. The ion-conducting region will contain stabilized functional groups which can resist hydroxide attack and, thus, can operate at high pH (~14) for extended periods. In Phase I, TDA prepared, characterized, and tested these nanoporous AEMs in electrolyzers. We modified the structure and chemistry of the starting materials, measured the conductivity, physical and chemical properties of the membranes. We measured the mechanical properties, ion exchange capacity, hydroxide conductivity, and stability, and correlate them to the resulting nanoporous structure. Process-structure-property relationships were then used to help select the formulations of these new membrane materials for highly selective anion-exchange membranes. What will be done in Phase II? In Phase II, TDA will optimize the new membranes for use in AEM electrolyzers, scale up the production of all the needed precursors and scale up the membrane production to 1 square foot sheets. These scaled up membranes will be fully tested in an electrolyzer, optimized for operating conditions (temperature) and demonstrated in multi-month tests in a benchtop hydrogen production unit. Commercial applications include electrolysis for long-duration hydrogen generation (to manufacture hydrogen for use in fuel cells, synthesis gas-to-transportation fuels, and back-up electrical power systems).