PEM Electrolyzer Degradation Explained: Top Causes and How to Fix Them

Proton Exchange Membrane (PEM) electrolyzers have emerged as one of the most promising technologies for producing green hydrogen, a fuel that is increasingly seen as essential for decarbonizing heavy industry, long-haul transport, and energy storage. Their appeal lies in their ability to operate at high current densities, their compact design, and their responsiveness to fluctuating renewable energy inputs such as wind and solar. Yet despite these advantages, PEM electrolyzers face a persistent challenge: degradation over time. Unlike laboratory demonstrations that often focus on short-term efficiency, commercial deployment requires systems that can operate reliably for tens of thousands of hours. Understanding the mechanisms of degradation, identifying methods to mitigate them, and developing troubleshooting strategies are therefore critical for advancing PEM electrolyzer technology from pilot projects to widespread industrial adoption.

Membrane degradation in PEM water electrolyzer

Catalyst Degradation

One of the most significant contributors to PEM electrolyzer degradation is the loss of catalyst activity. The oxygen evolution reaction (OER) at the anode is particularly demanding, requiring catalysts that can withstand high potentials and oxidative environments. Iridium oxide (IrO₂) is the most widely used material, but even this noble metal is not immune to dissolution. Under potentials exceeding 1.8 V, iridium ions can leach into the electrolyte, gradually reducing the electrochemically active surface area. Platinum, used at the cathode for the hydrogen evolution reaction (HER), faces its own challenges. Nanoparticles tend to agglomerate over time, forming larger clusters that reduce the available catalytic sites. This process, known as Ostwald ripening, diminishes efficiency and increases overpotential. Real-world data from long-term testing has shown iridium dissolution rates of approximately 0.2–0.5 μg/cm² per 1000 hours, which translates into efficiency losses exceeding 20% after 10,000 hours of operation. Such losses are unacceptable for industrial systems, making catalyst stabilization a priority area of research.

Membrane Degradation

The polymer electrolyte membrane, typically composed of Nafion, is another critical component that suffers from degradation. Chemically, the membrane is vulnerable to attack by hydroxyl radicals generated during the oxygen evolution reaction. These radicals can break down the polymer backbone, leading to thinning and eventual perforation. Mechanically, the membrane undergoes repeated cycles of swelling and shrinkage as hydration levels fluctuate. Over time, these cycles induce cracks and pinholes, which compromise gas separation. The consequence is hydrogen crossover, where hydrogen molecules permeate through the membrane and mix with oxygen, reducing Faradaic efficiency and posing safety risks. Empirical studies have demonstrated that Nafion 115 membranes experience a lifetime reduction of nearly 30% when operated at 80°C compared to 60°C, underscoring the sensitivity of membrane durability to operating temperature. As electrolyzers are often pushed to higher temperatures to improve kinetics, this trade-off between performance and longevity becomes a central engineering dilemma.

Corrosion of Bipolar Plates and Porous Transport Layers

Beyond catalysts and membranes, the supporting components of PEM electrolyzers also degrade. Titanium is commonly used for porous transport layers (PTLs) due to its corrosion resistance, but even titanium is prone to forming passivating oxide layers such as TiO₂. While protective in some contexts, these oxides are electrically insulating, increasing ohmic resistance and reducing overall efficiency. Stainless steel bipolar plates, chosen for their mechanical strength and cost-effectiveness, can corrode under acidic conditions, releasing iron ions that migrate into the catalyst layer and poison active sites. Measurements from durability tests have shown that corrosion can increase ohmic resistance by 15–25 mΩ·cm² after just 5000 hours of operation. Such increases translate directly into higher energy consumption per kilogram of hydrogen produced, eroding the economic case for PEM technology unless mitigated.

Operational Stress and Environmental Factors

The way PEM electrolyzers are operated also plays a decisive role in their degradation. Systems connected to renewable energy sources often experience dynamic load cycling, with frequent start-stop events as wind or solar power fluctuates. These cycles accelerate catalyst dissolution and membrane stress compared to steady-state operation. High current densities, often exceeding 2 A/cm² in commercial stacks, exacerbate local heating and membrane thinning. Impurities in feed water, particularly chloride ions, can cause pitting corrosion in titanium components, while silica or calcium can deposit within flow channels, obstructing water distribution. Even seemingly minor deviations in water purity can have outsized effects, as PEM electrolyzers rely on ultrapure water with conductivity below 0.1 μS/cm. Thus, operational protocols and water treatment systems are as important as material choices in determining system longevity.

Diagnostic Methods

To address degradation, it is essential to diagnose problems accurately. Electrochemical techniques provide powerful tools for this purpose. Electrochemical impedance spectroscopy (EIS) can reveal increases in charge transfer resistance, indicating catalyst loss or PTL corrosion. Cyclic voltammetry (CV) is used to measure the electrochemically active surface area, allowing operators to track catalyst agglomeration. Linear sweep voltammetry (LSV) provides insights into oxygen evolution kinetics, highlighting changes in overpotential. Physical characterization techniques complement these electrochemical methods. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) can visualize catalyst particle growth and membrane cracks. X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometry (ICP-MS) quantify dissolved catalyst ions in effluent water, while gas chromatography detects hydrogen crossover rates. Together, these diagnostic tools form a comprehensive toolkit for monitoring electrolyzer health and guiding maintenance decisions.

Mitigation Strategies

Mitigation of degradation requires a multifaceted approach. Catalyst stabilization can be achieved by alloying iridium with other metals such as ruthenium or tantalum, which improve stability and reduce dissolution rates. Protective coatings, such as titanium nitride (TiN), can shield catalysts from harsh environments. Studies have shown that IrRuOx catalysts exhibit dissolution rates 50% lower than pure IrO₂, extending operational lifetimes significantly. Membrane reinforcement is another avenue. Composite membranes incorporating polytetrafluoroethylene (PTFE) or inorganic fillers resist radical attack more effectively. The addition of radical scavengers, such as cerium oxide nanoparticles, has been shown to extend membrane lifetimes beyond 20,000 hours under accelerated stress tests. Component protection strategies include coating titanium PTLs with conductive oxides like niobium-doped TiO₂ to prevent passivation, and applying gold or carbon coatings to stainless steel bipolar plates to reduce corrosion. Operational optimization is equally important. Maintaining temperatures below 70°C reduces membrane thinning, while ensuring ultrapure water prevents contamination. Avoiding frequent start-stop cycles through intelligent load management can also slow degradation. These strategies, when combined, offer a pathway to significantly longer lifetimes.

Troubleshooting Approaches

When degradation does occur, troubleshooting is essential to restore performance. A drop in efficiency often points to catalyst dissolution, which can be confirmed through cyclic voltammetry or ICP-MS analysis. Solutions include replacing the catalyst layer or switching to more stable alloy catalysts. Gas crossover, indicated by reduced Faradaic efficiency and detected through gas chromatography, suggests membrane thinning or cracking. In such cases, replacing the membrane with a reinforced composite is necessary. Increased resistance, revealed by EIS measurements, often indicates PTL corrosion, which can be addressed by applying protective coatings or replacing the PTL. Uneven cell performance across a stack may be traced to water impurities, which can be diagnosed through conductivity tests and resolved by upgrading purification systems. Troubleshooting thus requires a systematic approach, combining diagnostics with targeted interventions.

Case Studies and Real-World Data

Several case studies illustrate the effectiveness of these strategies. Research at Fraunhofer IMWS demonstrated that optimized IrRu catalysts extended stack lifetimes by 30% under dynamic load cycling, a significant improvement for systems connected to renewable energy. ITM Power reported that titanium PTL coatings reduced ohmic losses by 20% over 10,000 hours of operation, highlighting the value of component protection. Durability tests conducted by the U.S. Department of Energy showed that reinforced membranes achieved lifetimes exceeding 60,000 hours, compared to 40,000 hours for standard Nafion membranes. These examples underscore the importance of integrating advanced materials with intelligent system management to achieve commercially viable lifetimes.

Conclusion

PEM electrolyzer degradation is a complex phenomenon involving catalyst dissolution, membrane thinning, component corrosion, and operational stress. Each mechanism contributes to reduced efficiency, increased costs, and shortened lifetimes. Yet through a combination of advanced materials, protective coatings, radical scavengers, and optimized operating strategies, these challenges can be mitigated. Diagnostics and troubleshooting provide the tools to identify problems early and implement targeted solutions. The future of PEM electrolyzers depends on the successful integration of these approaches, enabling systems that can operate reliably for decades and support the global transition to a hydrogen economy.