Hydrogen-powered fuel cell electric vehicles (FCEVs) could soon follow battery electric vehicles (BEVs) as the next big thing in the global transportation industry’s transition to a “green” future.
But the environmentally friendly technology must overcome several challenges, just like their BEV counterparts are doing. This includes boosting performance, significant cost reductions, and building a supporting infrastructure. There also are safety and quality concerns, both of which can be addressed through advanced leak-testing procedures.
After years of being relegated to a tiny niche of total vehicle sales—albeit with a huge potential—BEVs have finally arrived en masse. Led by China and Europe, combined global sales of BEVs and plug-in hybrid EVs (PHEV) jumped 41 percent in 2020 and continued to expand in 2021.
The trend is expected to accelerate through the end of the decade with BEV/PHEV penetration rates forecasted to surge to more than 30 percent of the worldwide market by 2030 as automakers add more and more electrified models.
Customers, meanwhile, have become more amenable to plugging in, especially as costs come down and driving ranges are extended.
FCEVs utilize many of the same components as other types of EVs and hybrid vehicles, including an electric motor, inverter, wiring and a high-powered lithium-ion battery. Electricity is created via an onboard chemical reaction between hydrogen and oxygen to power the electric motor. The fuel cell stack is made up of a network of anodes and cathodes, separated by membranes that allow electrons to pass through. Hydrogen is stored in a highly pressurized tank that needs to be refilled like gasoline and diesel fuels.
A handful of carmakers have been offering FCEVs for several years. But the overall volume has been extremely limited, and the development pace for FCEVs, still is at least 10 years behind the BEV market.
So why are companies continuing to pursue FCEVs? Proponents point to several advantages they have over BEVs, including a longer driving range and faster refueling times. FCEVs are particularly well suited for commercial trucks and buses, which have relatively short fixed daily routes and return to a common facility, where they can be refueled overnight. This alleviates concerns about the shortage of hydrogen stations until a supporting infrastructure is created.
Whether it’s passenger cars or commercial truck applications, safety concerns must be alleviated for alternative power vehicles to gain widespread use. This can be achieved in part through advanced leak testing systems. Leak tests have long been one of the most critical quality-control checks performed by automakers and their suppliers. BEVs and FCEVs require even more precise testing.
Reliable leak testing of battery cells is crucial because the highly flammable electrolytes they contain can spark fires. Even small amounts of humidity in a battery module can cause the system to short circuit, reduce service life and degrade performance as well.
“It is vital to prevent electrolytes from leaking from battery cells or coming into contact with water under any circumstances throughout the production process and life of a vehicle,” said Marc Blaufuss, an Inficon application engineer for leak testing tools.
There also are special leak-testing considerations for an EV’s high-voltage electric/electronic components (motors, controllers, sensors) and cooling systems. Moisture is the primary enemy, thus water and humidity tightness are critically important to protect against overheating and system failure.
FCEVs have their own unique requirements. This is mainly due to the extreme flammability of hydrogen—volumetric air concentration rates as little as 4 percent can spark ignition. FCEVs must have leak-tight hydrogen tanks, recirculation systems and fuel-cell stacks (bipolar plates, membrane electrode assemblies and cooling circuits).
Fuel-cell stacks can contain as many as 400 bipolar plates, all of which must be leak tested as a part of a finished module. Potential failure modes include crossover leaks between the anode and cathode or overboard leaks at seals, through which hydrogen reacts uncontrollably with oxygen. Hydrogen also should not be allowed to leak into the cooling circuit.
In addition to hydrogen safeguards, manufacturers must test and protect against possible air and coolant leaks within the fuel cell stack and externally. Even microscopic losses could cause major problems down the road, including performance degradation and safety concerns.
Tracer gases, which can detect leaks that are 1,000 times smaller than traditional air tests, provide the necessary sensitivity and reliability to meet demanding safety requirements and consumer expectations. Inficon recommends using the smallest possible reject leak rate of about 10-5 mbar∙ l/s for all hydrogen carrying components, which is the rate used for testing CNG/LNG components.
While some fuel cell components are best tested with short cycle times in a vacuum chamber, Inficon recommends using automated robotic sniffer leak testing for hydrogen tanks and other sub-assembled systems.
If a leak is detected at any stage, the problem needs to be identified and fixed. Components then must be retested to ensure they are leak-free to proceed before assembly is completed.
Advanced leak-testing equipment with such high sensitivity rates will ensure electrical systems and hydrogen-related components operate as intended, which in turn will increase consumer confidence in BEVs and FCEVs to help drive growth in coming years.
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