Electrolyzer stacks are the core component of electrolysis systems, responsible for the efficient conversion of electrical energy into hydrogen gas through water splitting. The engineering of these stacks involves careful consideration of cell configuration, materials, and sealing techniques to ensure performance, durability, and scalability. Recent advancements in manufacturing, such as automated assembly, are further enhancing the feasibility of large-scale deployment.

Cell configuration is a fundamental aspect of electrolyzer stack design. The two primary arrangements are the zero-gap and the gap configuration. In zero-gap designs, the membrane electrode assembly (MEA) is pressed directly against the bipolar plates, minimizing ionic resistance and improving efficiency. This setup reduces ohmic losses but requires precise mechanical tolerances to avoid uneven compression, which can lead to hotspots or membrane degradation. In contrast, gap configurations incorporate a small space between the electrode and the separator, often filled with a liquid electrolyte. While this design is more tolerant to manufacturing variances, it introduces higher resistive losses due to the increased ionic transport distance.

Bipolar plates serve multiple critical functions within the stack. They distribute reactants evenly across the active area, conduct electrical current between cells, and provide structural support. Materials must exhibit high electrical conductivity, corrosion resistance, and mechanical strength. Stainless steel with protective coatings, such as gold or titanium nitride, is commonly used in proton exchange membrane (PEM) electrolyzers to prevent oxidation under high potentials. For alkaline systems, nickel-coated steel is preferred due to its stability in alkaline environments. Recent developments explore the use of titanium-based composites and graphite-polymer hybrids to reduce weight and cost while maintaining performance.

Sealing techniques are essential to prevent gas crossover and electrolyte leakage, which can compromise efficiency and safety. Elastomeric gaskets, such as ethylene propylene diene monomer (EPDM) or fluorocarbon-based materials, are widely used due to their chemical resistance and compressibility. However, long-term exposure to high temperatures and pressures can degrade these materials, leading to failure. Laser-welded metallic seals offer a more robust alternative for PEM systems, eliminating the risk of organic material degradation but increasing manufacturing complexity. Another approach involves adhesive-bonded frames that integrate sealing and structural functions, simplifying assembly while maintaining reliability.

Scalability presents significant challenges in electrolyzer stack engineering. As stack size increases, maintaining uniform compression across all cells becomes more difficult. Uneven pressure distribution can cause localized stress, leading to membrane thinning or rupture. Advanced compression systems, such as spring-loaded or hydraulic mechanisms, help mitigate this issue by dynamically adjusting force distribution. Thermal management is another critical factor in scaling; larger stacks generate more heat, requiring optimized cooling strategies like integrated coolant channels or phase-change materials to maintain stable operating temperatures.

Manufacturing innovations are accelerating the transition to cost-effective, high-volume production. Automated assembly lines reduce human error and increase throughput, particularly in stacking and sealing processes. Robotic pick-and-place systems precisely position MEAs and gaskets, while vision systems ensure alignment accuracy. Additive manufacturing is also emerging as a viable method for producing complex bipolar plate geometries with embedded cooling channels, reducing part count and assembly time. Roll-to-roll manufacturing techniques, adapted from fuel cell production, enable continuous fabrication of electrode layers, further lowering costs.

Material selection plays a pivotal role in balancing performance and manufacturability. Thin, high-conductivity membranes enhance efficiency but require careful handling during assembly to avoid damage. Sintered porous transport layers (PTLs) in PEM electrolyzers must maintain adequate gas permeability while ensuring low electrical resistance. Advances in laser perforation and electroforming techniques allow for precise control over PTL pore structure, improving mass transport without sacrificing mechanical integrity.

Durability remains a key focus in stack design. Degradation mechanisms, such as catalyst dissolution or membrane chemical attack, can reduce operational lifespan. Accelerated stress testing protocols help identify failure modes and guide material improvements. For instance, iridium oxide catalysts in PEM systems are being optimized to reduce dissolution rates, while alternative catalysts based on non-precious metals are under investigation for alkaline systems.

The transition to gigawatt-scale electrolysis demands stacks that are not only efficient but also compatible with rapid manufacturing and maintenance. Modular designs, where individual stacks can be easily replaced or upgraded, facilitate scalability and reduce downtime. Standardization of components, such as cell dimensions and interface connections, is critical to enabling interoperability across different systems and manufacturers.

In summary, electrolyzer stack engineering is a multidisciplinary challenge that integrates materials science, mechanical design, and advanced manufacturing. Innovations in cell configuration, bipolar plate materials, and sealing techniques are driving improvements in efficiency and durability. Scalability is being addressed through advanced compression systems, thermal management strategies, and automated production methods. As these technologies mature, electrolyzer stacks will play a central role in enabling large-scale hydrogen production for a sustainable energy future.