Electrochemical Energy Conversion

Vanadium Redox Flow Batteries

Vanadium Redox Flow Batteries (VRFBs) provide an attractive solution for large-scale (Megawatt and higher) energy storage. It is desirable to further improve the energy cycle efficiency by reducing energy losses during charging and discharging. Porous carbon materials are commonly used as electrodes in this type of battery. These materials need to have continuous pathways to allow for reactant movement. We monitor this movement by visualizing the electrolyte flow through the porous carbon electrodes using synchrotron X-ray tomography. This technique reveals the flow within the porous materials, helps us understand the impact of saturation on the electrolyte’s mass transport, and quantifies the loss of active reaction sites due to low electrolyte penetration.

We are also investigating changes in these materials‘ carbon fiber structures at different life cycle stages, starting from as received to activation and then aging. The changes in the morphology of the carbon material and its functional groups show the impact of activation and aging on the surface properties and, consequently, the cell’s performance. Differential Electrochemical Mass Spectrometry (DEMS) helps us track typical side reactions in VRFBs that hamper these batteries‘ performance.

High-Temperature PEM fuel cells

The group focuses on developing high-temperature PEM fuel cells based on membranes doped with phosphoric acid. The advantage of this type of membrane is that phosphoric acid acts as a proton conductor instead of water. Therefore, the high-temperature PEM fuel cell can operate at temperatures between 150 °C. and 180 °C and has, due to this fact, a higher tolerance towards carbon monoxide and other fuel gas impurities. Besides, the system technology requirements are significantly lower since the water and heat management is simpler to regulate due to the elevated operating temperatures.

One of the group’s core competencies is developing membrane electrode assemblies (MEAs). By optimizing its key components, the membrane and the electrode, we could fabricate high-performing and durable single cells. For this type of fuel cell, it is essential to optimize the acid household of the MEA. Therefore, we specifically investigate the membranes‘ doping process, the acid distribution within the gas diffusion electrode, and acid loss of the full cell.