Using XRF for quality control of hydrogen fuel cells

In the race to reduce carbon emissions, fuel cell technology is developing rapidly. Both lithium-ion battery technology and hydrogen fuel cell systems are part of the solution in reducing the world’s carbon dioxide emissions.

All types of fuel cells include three basic components: two electrodes (anode and cathode), and an electrolyte sandwiched between them. Hydrogen fuel cells used for powering electric vehicles are called Polymer Electrolyte Membrane (PEM) fuel cells as they use a proton-conducting polymer membrane as the electrolyte. They are also known as proton exchange membrane fuel cells with the electrodes typically coated with conductive carbon mixed with platinum (Pt) particles. Pt acts as a catalyst for the continuous conversion of fuel (hydrogen) and oxidant (oxygen) into electricity.

In the fabrication process, it’s critical to control the Pt coating uniformity, and amount or weight on the electrode’s surface to ensure efficient chemical reactions in the cell, while minimizing raw material costs and finished product waste.

This is where energy-dispersive X-ray fluorescence (EDXRF) spectrometry, one of the simplest elemental analytical techniques, can be used for rapid quality control to assure performance, improve production yield and support sustainability through waste reduction.

Using XRF for quality control of hydrogen fuel cells

 

Hydrogen fuel cells for a cleaner mobility

On paper, hydrogen fuel cells are the perfect zero-emission energy source. You simply feed the fuel - hydrogen (which is classed as a renewable energy source because it’s so abundant) and air to the electrodes of the cell and the cell produces electricity, heat and water. There are no greenhouse gases emitted by the cells and the only by-products are water and heat, and you can use the heat in some systems, making them even more efficient than electricity-producing systems alone.

However, like the lithium-ion battery where fossil fuels are still required to provide the electricity for charging, large amounts of energy from fossil-fuels are also often used to produce hydrogen, making their overall green credentials less positive. Fortunately, other hydrogen production processes are being developed, increasing hydrogen fuel cells’ environmental credentials even further.

And, with developments on renewable energy, such as wind, and biomass used for generating electricity, the situation is improving.

Polymer electrolyte membrane fuel cells (PEMs)

The main advantage of hydrogen fuel cell technology is that it can be used at relatively low temperatures and their output can be easily varied – both necessary conditions for personal vehicle use.

PEMs use platinum as a catalyst to convert the hydrogen into H+ plus an electron (hydrogen oxidation reaction) at the anode, and as the catalyst for the oxidation reduction reaction at the cathode that generates the oxygen ready for combination with the hydrogen ions to produce water.

In Pt coating quality, both in terms of weight on film and the presence of iron (Fe) particle contaminants has a major impact on fuel cell operation. In the case of iron, particles can enter the production process through raw materials and wear and tear of process equipment. When present in the fuel cell, iron can react with hydrogen peroxide (H2O2) and form free radicals (Fenton reaction). This reaction can lead to the damage of the cell’s ion-exchange membrane and the deterioration of the fuel cell.

Fenton reaction:   Fe2+ + H2O2 → Fe3+ + HO. + OH-

  H2O2 + HO. → HO2. + H2O

Conventional X-ray computerized tomography systems require several hours to detect small metal particles in membrane electrode assemblies, and while scanning electron microscopy can detect particles smaller than 10 µm in size, it doesn’t “see” particles within the sample.

We’ve developed a new particle inspection technology that detects and analyzes metal contaminants down to 30 µm in as little as 15 minutes, greatly increasing testing throughput. The same technology can also determine the Pt distribution on the membrane.

EA8000A for the detection of metal contaminants

Our EA8000A combines X-ray transmission technology, optical microscopy and EDXRF spectrometry to locate and characterize metal contaminants within membrane electrode assemblies (MEAs). EDXRF is also used to map the Pt distribution on the membrane.

While other techniques often only identify small particles when they’re on the surface of the sample, the EA8000A uses unique, focused X-ray optics to locate and identify the elements in metal particles deeper within the sample.

Sample preparation is fast and easy: simply place the MEA (250 mm x 200 mm maximum size) in the sample jig and sit the jig on the analysis stage to carry out the measurement.

For a comprehensive analysis, the EA8000A measurement stages are:

  1. Obtain an optical image of the sample using transmitted X-rays
  2. Auto-detect the position of any contaminants using image processing
  3. Observe morphology and automatically capture image of contaminated areas
  4. Carry out elemental mapping of the contaminated areas and/or the whole membrane by EDXRF
  5. Generate report

These steps can be fully automated, freeing the operator to perform other tasks and increasing productivity.

To see how the EA8000A detects contaminants and studies Pt coating uniformity, we’ve created an application note that shows the performance of this analyzer.

But that’s not all the XRF instrumentation we offer to help you increase yield and reduce waste:

LAB-X5000 for platinum coating weight measurements

Our LAB-X5000 benchtop EDXRF analyzer makes platinum coating weight on film analysis easy. Once the LAB-X is calibrated, routine analysis is simple. Simply place the coated sample in the LAB-X’s analysis port, press the start button and the instrument takes care of the rest.

Preliminary results are available within seconds, showing the Pt coating weight with full results in minutes. Pass/Fail messages can also be setup for fast decision making and process adjustments if needed to ensure consistent product quality. The LAB-X5000 is compact and durable enough to slot alongside any production.

To see how the LAB-X5000 performs when analyzing Pt-coated films for PEM use, we’ve created an application note that shows calibration performance of this analyzer and how samples need to be prepared.

X-Strata920 for pinpoint coating weight measurements for components and films

The X-Strata920 XRF coatings analyzer uses a small analysis spot size to measure platinum coating weight on specific features or areas of a coated part or film.  The motorized XY stage can be programmed to measure multiple membranes automatically or perform a multi-point (e.g. grid-type) analysis routine to show platinum distribution across the membrane so you can monitor and adjust the coating process. 

X-MET8000 when portable XRF analysis is needed

The X-MET8000 handheld X-ray fluorescence (XRF) analyzer, with no requirement for a power source or bench space is ideal for spot analysis of coatings. Its robustness (IP54 rated) and long battery life (up to 10-12 hours use on a single battery charge) make it the tool of choice when true portability is needed, for example incoming materials inspection.




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Date: 11 August 2022

Author: Christelle Petiot, Senior Product Manager - Benchtop XRF

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