25 Polish Hydrogen Bus Princesses Likely Need New Fuel Cells – CleanTechnica

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Last Updated on: 4th March 2025, 02:55 pm

​On March 3, 2025, all 25 hydrogen-powered Solaris Urbino 12 Hydrogen buses operated by MPK Poznań were abruptly withdrawn from service. This decision followed onboard diagnostic systems detecting unexpected malfunctions across the entire fleet. ​

The affected buses had been refueled at a public hydrogen station in Poznań, supplied by Orlen. Preliminary investigations suggest that the malfunctions may be linked to the quality of the hydrogen fuel. Samples have been collected for analysis, and results are pending. In response to the issue, MPK Poznań collaborated with Solaris and Orlen to identify and address the root cause. During this period, diesel and electric buses were deployed to maintain uninterrupted public transport services. ​

I’m unsurprised by this. Fuel cells are basically batteries that aren’t hermetically sealed, but require ultra-pure hydrogen and air to enter into the electrochemical cell. How pure? A lot purer than for industrial use cases for hydrogen as a feedstock, orders of magnitude purer.

As I’ve noted before, fuel cells require pure hydrogen and pure air at specific pressures, temperatures and humidities in order to operate. A great deal of the challenges with hydrogen vehicles is providing this degree of purity with onboard sensors and kit that manages filtering, thermal control, humidity control, and pressure control. Maintaining vehicles to ensure this quality requires a lot of care, and clean conditions as well.

The air entering a fuel cell has to be at the same level as air entering the best operating theatres or chip fab clean rooms globally, and far better than the filtration and climate control passengers get. By contrast, batteries are sealed and quality checked in factories and are closed boxes with no inputs or outputs except electrons. They require a lot less care in handling, assembly, and operation to achieve reliability.

Proton exchange membrane fuel cells rely on platinum catalysts, which are particularly vulnerable to poisoning. Carbon monoxide (CO), even at concentrations as low as 0.2 parts per million (ppm), can bind to the platinum surface, blocking hydrogen oxidation and reducing efficiency. Hydrogen sulfide (H₂S) is even more damaging—exposure beyond 50 parts per billion (ppb) can permanently deactivate the catalyst. By contrast, industrial processes use bulk catalysts that can handle ppm levels of CO, CO₂, and even H₂S.

The reliability of hydrogen fuel cells depends on the integrity of their proton exchange membrane, but exposure to ammonia (NH₃) and moisture (H₂O) can degrade this crucial component. Ammonia, often present as an impurity in hydrogen fuel, interferes with the membrane’s proton conductivity, reducing efficiency and, in severe cases, causing irreversible damage. Moisture contamination can further weaken the membrane’s chemical stability, accelerating wear and shortening its lifespan. While such impurities pose a serious threat to fuel cells in transportation and energy applications, they are far less problematic in industrial hydrogen uses like ammonia synthesis, where PEMs are not required and hydrogen purity standards are less stringent.

Hydrogen fuel cell performance can be severely impacted by particulate contamination and hydrocarbon exposure, both of which can clog critical components and reduce efficiency. Unlike industrial hydrogen applications, such as oil refining, where hydrocarbons and particulates are already present in feedstocks and can be managed by existing filtration systems, fuel cells require ultra-pure hydrogen to maintain functionality. Even microscopic particles can block gas diffusion layers and degrade the membrane, leading to voltage losses and long-term damage. In contrast, refining processes are designed to tolerate a broader range of impurities.

That’s a big reason why fuel cell vehicles have always had reliability issues when used as intended.

The EU’s IMMORTAL program was intended to significantly improve longevity of fuel cells. It failed miserably, with 28% of the target kilometers run in heavy trucks before 10% degradation, and no vehicles on roads seeing membrane durability that is experienced in labs. Fuel cell cars don’t see significant reliability issues mostly because they are barely used compared to internal combustion or battery electric cars by their owners. California’s fuel cell cars were driven only 15 miles a day in 2021, a long way under the 37 miles per day average for the USA. Quebec’s governmental fleet was driven 13.5% of the North American fleet vehicle average over four years, less if you take out the first year when usage was highest.

Back to Poznań, what are the implications of impure hydrogen? Well, it depends on the impurity and the percentage. 

Fuel cell contamination from carbon monoxide (CO) can sometimes be reversed through targeted remediation techniques. One method, known as air bleeding or oxygen purging, involves introducing a small amount—typically around 2%—of oxygen to the fuel cell’s anode. This process helps oxidize and remove CO from the platinum catalyst, potentially restoring performance if the poisoning is not severe. Another approach is increasing the cell temperature beyond 100°C, which accelerates CO desorption and can clear the contamination. However, this method is only viable if the system is designed to withstand thermal cycling.

Fuel cell contamination from hydrogen sulfide (H₂S) and ammonia (NH₃) poses a significant challenge, with potential long-term damage to critical components. In cases of ammonia exposure, some recovery may be possible by flushing the fuel cell with high-purity hydrogen at elevated temperatures to clear residual contaminants. However, if NH₃ has degraded the proton-conducting membrane, a full replacement may be required. Hydrogen sulfide contamination is even more problematic—while minor exposure might be mitigated through careful purging, concentrations above 50 parts per billion (ppb) can permanently poison the platinum catalyst, rendering it ineffective.

Hydrogen fuel cell contamination from hydrocarbons or particulates can lead to serious operational failures, requiring extensive remediation. In cases where impurities have entered the system, flushing the hydrogen lines with high-purity hydrogen or nitrogen purge cycles may help clear minor contamination. However, if hydrocarbons have caused carbon buildup on the catalyst—a process known as coking—the only solution may be replacing the affected electrode or, in severe cases, the entire membrane electrode assembly (MEA). Additionally, if particulate matter such as dust or oil has infiltrated the fuel system, swapping out clogged hydrogen filters can prevent further damage.

Severe contamination from hydrogen sulfide (H₂S), ammonia (NH₃), carbon monoxide (CO), or hydrocarbon buildup can require factory-level disassembly and repair of a fuel cell. If poisoning is irreversible, the platinum catalyst or the entire membrane electrode assembly (MEA) may need replacement, a process that cannot be done in the field. In extreme cases, a full fuel cell stack replacement may be necessary. This process can take weeks to months, depending on manufacturer capacity and supply chain constraints, with costs potentially reaching hundreds of thousands of dollars per unit, significantly impacting fleet operations.

The Poznań incident isn’t the first and won’t be the last. In Mallorca, Spain, the deployment of hydrogen fuel-cell buses encountered significant setbacks due to refrigerant leaks infiltrating the fuel cells, rendering all five buses inoperative. Many refrigerants contain fluorinated and chlorinated compounds, which can degrade the proton exchange membrane, reducing its conductivity and accelerating wear. If chlorine is present, it can form hydrochloric acid, corroding key fuel cell components. Additionally, refrigerant breakdown products can poison the platinum catalyst, much like carbon monoxide or sulfur contaminants, leading to voltage losses and reduced efficiency. The chemicals can also degrade seals and gaskets within the system, increasing the risk of further leaks. In some cases, refrigerants may absorb moisture from the membrane, disrupting its humidity balance and causing cracks over time.

As of August 2023, Palma de Mallorca’s five hydrogen-powered buses remained out of service due to a malfunction at the Lloseta hydrogen production plant, which had been inactive since shortly after its inauguration in March 2022. The plant’s electrolyser, responsible for producing green hydrogen, experienced technical issues, halting local hydrogen production. While there were attempts to import hydrogen from the mainland, these efforts have not been sufficient to resume bus operations. Consequently, the buses were sidelined, awaiting a reliable hydrogen supply to return to service, something I have no data indicating has occurred. The lack of hydrogen, pure or impure, remains a constant inhibitor, along with the deep unreliability of hydrogen refueling stations.

From the same end-of-2023 status report from the EU on its hydrogen funding initiatives, only a subset of hydrogen buses were being offered with even 20-month warranties, never mind the five- to eight-year full parts, labor, and replacement warranties being offered on battery electric buses. The manufacturers know very well how delicate their kit is, so refuse to back it.

My recommendation to all transit agencies is to demand diesel and battery electric equivalent warranty and maintenance clauses in contracts, and when vendors refuse to provide them, use that as a very good reason to not adopt hydrogen buses.