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Material solutions to increase tank-to-wheel efficiency & reliability of fuel cells

17 April 2020
  • Yu Bin Global Advanced Engineering Manager for E-Mobility

  • Dr Tamim Peter SidikiGlobal Marketing Director Electronics at DSM Engineering Materials

Advanced technologies are transforming how people commute—the automotive industry is undergoing a radical change in connectivity and electrification. Analysts predict that electric vehicles will represent a total share of 35% of new vehicles sold in 2025. Most often when we think of electric vehicles, we think of them being powered by lithium ion batteries, but if it’s the most environmental friendly solution? Maybe not. As an alternative, automobiles can be powered by fuel cell technology.

Compared to battery electric vehicles the technical benefits of fuel cell vehicles include:

  • Much shorter refueling/charging time (comparable to gasoline refueling)
  • Longer drive distance without the extra loading of heavy weight batteries
  • Zero emission and less environmental impact, based on green hydrogen source, and lower weight especially in combination with long driving range

As a result, almost all major OEMs are already investing or planning to invest in commercialization of fuel cell vehicles, first targeting buses and vans due to the higher relevance of weight and range gains. Of the various fuel cells technologies, in particular the proton exchange membrane fuel cell (PEMFC) is preferred due to its sufficiently low working temperature (80 to 100°C ), a short start up time of around one second and ability to run on pure hydrogen and ambient air as the oxidant. Such vehicles are equipped with a fuel cell stack as the electrochemical device to covert hydrogen and oxygen into water, heat and electricity.

The heart of the vehicle

A fuel stack as the heart of the vehicle consists of hundreds of individual cells and various components manufactured from plastic or metal; each individual cell consists of a sandwich structure of bipolar plates, gas dissipation layer, and most importantly, the proton exchange membrane with a Platinum catalyst layer (see Fig.1 below).

The catalyst oxidizes the hydrogen molecules, lets it selectively pass the hydrogen ions from the anode to the cathode and forces the electrons to travel as current through an external device to the cathode. Given the nature of chemical reaction in the cell, ions that leached out from the material utilized to make the necessary components for the fuel cell stack has to be minimized and ideally prevented.

Impurities and ions leaching out of the components used in the fuel cell stack are poisoning to the catalyst and clog up the membrane, which will significantly decrease the efficiency of the fuel cell stack and affect its lifetime. Most critical for Pt in PEMFC applications are sulfur species and carbon monoxide.

Meanwhile, PEMFC is working at a harsh condition, which has the temperature range of 80 to 120°C with almost 100% humidity and PH value ranging from three to five. To ensure the efficiency and reliable lifetime performance of fuel cell systems, a material solution with minimum ion leaching performance and highest hydrolytic resistance and highest chemical resistance is absolutely needed.

DSM’s fuel cell experts and scientist have taken the effort to carefully study all those elements, which can affect the fuel cell system performance. Among various material solutions, PPS has been found to be the most suitable candidate, which combines the advantage of excellent chemical/hydrolytic resistance together with low ionic leaching and excellent mechanical performance.

Based on a deep analysis of fuel cell poisoning mechanisms, specifically for optimum performance in fuel cells, DSM has developed a tailor-made PPS compound with industries lowest ionic leaching levels. The patented PPS Xytron 4080HR is capable to deliver:

  • Lowest ion leaching of its kind even up to 120°C to ensure highest fuel cell efficiency
  • Best strength and toughness retention in hydrolytic environment amongst all engineering plastics, outperforming every other PPS and PPAs enabling maximum design flexibility for engineers
  • Best dimensional stability, fatigue and creep resistance of its kind, even after aging ensuring high system integrity also after longer operation times
  • Best welding line strength before and after hydrolytic and heat aging to ensure highest mechanical reliability

Moreover, DSM proactively works with industrial leaders to increase the power density of the fuel cell vehicles. As an example, DSM brings new materials solutions for the Type IV Hydrogen storage tank, which can be made from polyamide 6 blow molding inner tank, surrounded with carbon fiber reinforce UD tape, to achieve a low weight and a low hydrogen penetration rate without scarifying the strength required to ensure safety under high pressure (70Mpa).

Since DSM’s Xytron PPS 4080HR shows the lowest leaching and has the best long-term hydrolytic performance, challenges of designing components in the fuel cell system, such as media distribution plates/manifold, insulation plates, hydrogen recirculation components, hydrogen pressure regulation valves, etc., can be overcome and consumers and the environment can benefit.

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To learn more about DSM PPS Xytron grades you can reach out to the authors of this blog, contact us or visit plasticsfinder.com for additional information.

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