Challenges and Expected Improvements for PEM Electrolysis
Presentation of Stacks Technology
Stacks Technology was created in May 2021, following a preparatory phase in 2020. The company received its first investment support in August 2022 and began initial production in 2023.
The team comprises around fifteen people, primarily in technical roles. The combined experience of its collaborators enables Stacks Technology to offer deep technical expertise in PEM electrolysis — at the stack, test bench and electrolyzer levels.
Stacks Technology is positioned in the large-scale PEM electrolysis market, targeting refinery, ammonia, e-fuel (methanol) and power-to-gas applications via grid injection.
The flagship product is the Megascale project: a stack designed for high-power industrial production, with high availability, low downtime and controlled capex. Its design integrates industrial constraints with a manufacturing process enabling automation and optimized assembly operations.
Principles of PEM Electrolysis
PEM electrolysis is a hydrogen production method that passes an electric current through demineralized water in an electrolytic cell.
At the anode, released electrons react with water to form oxygen ions and hydroxyl ions. At the cathode, protons react with electrons to form gaseous hydrogen molecules. The proton exchange membrane (MEA) separates the two electrodes: it allows only protons (H⁺ ions) to pass through while blocking electrons and keeping the produced gases separate. The hydrogen produced is then purified and collected.
The key advantage of PEM electrolysis lies in its rapid response and efficiency at low temperatures.
The Proton Exchange Membrane
The PEM membrane is typically made from proton-conducting polymers — derivatives of polyfluorocarbon sulfonates. Sulfonic acid groups facilitate H⁺ ion conduction through the membrane. It is thin to maximize ionic conductivity, durable to withstand operating conditions (pure water, prolonged electrochemical reactions), and effective at relatively low temperatures — a significant advantage over other electrolysis technologies.
Composition of an Electrolysis Cell
A cell comprises five main elements:
— Bipolar plate: provides electrical conduction throughout the cell
— Spacer: transmits current and evenly distributes compression pressure during stack assembly
— PTL (porous transport layer): porous element facilitating the reaction between water and electricity
— MEA: acts as a selective barrier, allowing only H⁺ ions to pass through
— Gasket: ensures sealing of all compartments
Assembly and Precision
Assembly precision is a determining factor in achieving good performance. Optimal alignment of each element improves chemical reactions. Uniformity of clamping and compression forces improves electrical conductivity. Managing evolution over time is essential to maintain optimal efficiency throughout the stack's operational lifetime.
Electrolyzer System Overview
The stack sits at the center of the system. The electrical supply passes through a rectifier that delivers current at the correct intensity and signal. Pure water is fed into an O₂ separator tank, then temperature-conditioned via a heat exchanger before being injected into the stack by two pumps.
At the outlet, two separators recover water and oxygen on one side, and water and hydrogen on the other. By immiscibility, the gas headspace of each separator fills with the corresponding gas. Oxygen passes through a plate condenser to extract and retain the water before being vented. Hydrogen follows the same process, then passes through a purification unit and an analyzer to verify conformity with client specifications.
Challenges and Expected Improvements
1. Pressure Increase
Increasing pressure in PEM stacks presents both advantages and drawbacks.
Advantages: improved power density and overall efficiency, acceleration of electrochemical reactions, better gas separation reducing the risk of H₂/O₂ mixing.
Drawbacks: more demanding and costly design to withstand higher pressures, increased leakage risk requiring adapted materials and designs, energy cost of compression potentially offsetting gains if the energy source is not renewable, and heightened safety requirements.
2. Increasing Active Cell Area
Increasing the active surface area of the PEM membrane offers several advantages: improved overall electrochemical efficiency, increased hydrogen production capacity for high-volume industrial applications, and reduced ohmic losses by lowering the electrical resistance of components. Increasing the active area also enables greater automation and reliability in cell production and stack assembly.
3. Other Performance Improvement Pathways
— Optimization of operational parameters: voltage, current, temperature, within safety and durability limits
— Improved catalysts: advances in catalyst research represent a major efficiency lever
— Cell design optimization: electrode geometry, cell arrangement
— Ohmic loss reduction: high-quality conductive materials, minimizing electrical resistance
— Gas recirculation: improved gas transport through the membrane, reduced losses
— Water quality control: monitoring and treating feed water to prevent contamination
— Optimized membranes: high ionic conductivity and efficient gas separation
— High-pressure electrolysis: increased volumetric hydrogen production density
— Heat recovery: valorizing thermal energy generated during electrolysis
4. Environmental Challenges
Improving Membrane Tolerance to Impurities
Several approaches are being explored: hydrophobic membranes repelling aqueous impurities, anti-fouling coatings facilitating surface cleaning, chemically degradation-resistant polymers extending membrane lifespan, reinforcement materials (nanomaterials, fibers) reducing sensitivity to damage, composite membranes combining the advantages of multiple materials, and contamination-resistant ionomers maintaining ionic conductivity.
Water Management in the Balance-of-Plant
Water management is a critical challenge: deionization treatment represents 22% of the total BOP cost of a 1 MW electrolyzer.
Key optimization levers include: condensate collection systems (condensers, efficient drainage), recovered water purification systems, water recycling to reduce dependence on external sources, real-time water quality monitoring, optimized drainage systems to minimize losses, effluent treatment where necessary, and an overall sustainable approach to water resource management.
Hydrogen Purification
Several methods are used depending on the required purity level: physical absorption (activated carbon, molecular sieves) for gaseous impurities, absorption-based dehydration (hygroscopic agents) for water removal, filtration for liquid and solid impurities, and compression-cooling to promote condensation of residual impurities.
5. Critical Metals: Platinum and Iridium
In 2022, global platinum production was approximately 200 tonnes per year, while iridium production amounted to only a few tens of tonnes — quantities that are limited relative to the potential needs of large-scale PEM electrolysis deployment.
Demand for these metals could increase considerably as the sector develops. Significant research efforts are underway to develop catalysts based on non-noble metals and less scarce materials, aiming to reduce or replace platinum and iridium. These advances are essential to ensure the long-term sustainability and economic viability of large-scale PEM electrolysis.
