Fuel Cell Diagnostics

Fuel cell characterization by various diagnostic methods and understanding of the function and lifetime behavior of fuel cell components for PEFC and HTPEFC's is the vision and the mission of the fuel cell diagnostic activity. This encloses the ex-situ characterization, the in-situ performance and durability testing, as well as the numerical modeling of the processes. The diagnostic methods comprise impedance spectroscopy, local gas phase analytics, in-situ tomographic characterization, as well as locally resolved electrochemical experiments on various scales. Active area of sub cm² single cells up to several 100 cm² stacks for mobile applications can be tested.

Water management is the major limiting factor in PEFC for further increasing the power density. Fast synchrotron and conventional CT X-ray tomographic microscopy (XTM) enables the investigation of the water management by 3D visualization and quantification of stationary and transient water saturation in the porous materials in model experiments and under real operating conditions. This data is key for future developments with respect to performance, durability and cost.

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Fast start-up, dynamic operation, high differential pressures and production of high purity hydrogen up to high current densities make PEWE an interesting technology for storage of fluctuating (excess) renewable power. The fundamental understanding of kinetic and mass transport process in PEWE is our core interest. Porous materials are characterized using X-ray tomographic imaging and electrochemical methods.

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HIRESTEASER

High resolution in plane imaging of electrochemical systems

In conventional through plane imaging the neutron beam is perpendicular to the membrane. To image the distribution between the different cell layers, high resolution in plane imaging can be used, where the neutron beam is parallel to the membrane. Due to the low thickness of the fuel cell layers (e.g. 200 µm for a GDL), high resolution is required. To optimize the trade-off between spatial and temporal resolution, we developed a set of anisotropic resolution enhancement methods.

PGATEASER

Measurement of mass transport losses breakdown: The Pulsed Gas Analysis (PGA) method

Mass transport losses represent a significant limitation for the maximal reachable power density of polymer electrolyte fuel cells (PEFCs). The ability to measure them, in order to minimize them, is of high interest for the design of the structure of fuel cell components. Helox/oxygen voltage gain measurement is a known method to evaluate these losses.

DFITEASER

Dark field imaging of water in GDLs

Liquid water accumulated in the gas diffusion layers (GDL) can lead to reduced performance due to mass transport losses. Neutron dark-field imaging offers new possibilities to visualize water in the GDL, as this technique is selectively sensitive to microstructures. The dark-field image (DFI) is obtained simultaneously to the conventional transmission image (TI) when a neutron grating interferometer is placed in the beam.

Water/ice distribution measured using time-of-flight neutron imaging

Water/ice distinction using time-of-flight (TOF) neutron imaging

The successful start-up of polymer electrolyte fuel cell stacks (PEFCs) under sub-zero conditions (cold-start) with a minimal input of auxiliary power is an important requirement for the broad market introduction of fuel cell cars. Typically, cold start failures occur when the water produced by the electrochemical reaction freezes and blocks the access of oxygen to the catalyst. However, water produced by the reaction in sub-zero conditions can remain in liquid (super-cooled) state [1]. Methods that allow visualizing the location of freezing events during cold-starts help to understand which parameters influence the phase transitions.