Stainless steel: a solid future for hydrogen fuel cells

Andy Backhouse, Technical Manager at Outokumpu, discusses the evolution of SOFC technology and the leading role that ferritic stainless steel grades can play in the new hydrogen economy.

As the energy transition accelerates, industry is becoming increasingly aware of which technologies hold up to scrutiny. Efficiency, versatility, and long-term stability are key indicators of performance.

For hydrogen in particular, solid oxide fuel cells (SOFCs) stand out in all three categories. This makes them ideal for stationary power generation, which ranges from residential-scale applications to multi-megawatt industrial systems.

Yet, despite their advantages, traditional SOFCs have faced a persistent challenge: intense operating temperatures, up to 1000°C.

This has precipitated the use of costly, specialised materials — but a new generation of SOFCs, designed to function at a much more moderate 650–750°C, is shifting perspectives.

This evolution is an opportunity to use readily available and cost-effective stainless steel grades, without compromising on durability or performance.

Cell stacking, and why materials matter

At their core, SOFCs turn hydrogen into electricity via a highly efficient electrochemical reaction.

Each cell comprises a porous anode, a solid electrolyte, and a porous cathode, forming a structure that facilitates ion transfer.

Hydrogen fuel is introduced at the anode, while atmospheric oxygen enters via the cathode. As oxygen ions pass through the electrolyte, they react with hydrogen, generating electricity with only water as a byproduct.

But a single fuel cell generates a relatively low voltage. To achieve the power output required for commercial applications, cells must be stacked in series. The component holding these stacks together, while also conducting electricity and preventing gas mixing, is the interconnector plate.

Diagram breaking down the fuel cell.

The material chosen for these plates is critical — it needs to withstand extreme conditions for many years.

To be functionally and economically viable, interconnector plates must exhibit:

• A thermal expansion coefficient compatible with other stack materials to prevent undue stress during heating and cooling cycles.
• Robust corrosion resistance in dual atmospheres — withstanding oxidation while resisting hydrogen permeation.
• Stable electrical conductivity over prolonged operational lifespans.
• Minimal chromium volatility, which would otherwise degrade the electrolyte layer and cell efficiency.
• High creep resistance, ensuring physical integrity during stack manufacture and under sustained thermal loads.
• Exceptional formability, allowing the creation of thin, precision-engineered gas flow channels.

For decades these stringent demands led developers toward highly specialist and costly materials.

However, changing operating parameters in next-generation SOFCs now allow advanced ferritic stainless steels, usually in combination with specialist surface coatings, to take centre stage for the interconnects.

The right grade for the job

Coated high-chromium stabilised ferritic stainless steels are an ideal material for SOFC interconnector plates.

These grades offer good creep strength through precipitation of niobium and titanium carbides, good oxidation resistance due to high chromium content, and a low thermal expansion coefficient that aligns with the fuel cell’s ceramic components. Their affordability makes them a practical proposition.

Stainless steel grades like Therma 22FC were developed with the precise requirements of SOFC systems in mind.

This nickel-free, high-chromium stainless steel features a 21% chromium content, which significantly reduces chromium evaporation — an issue that can poison the fuel cell’s reaction over time.

By minimising chromium evaporation, it maintains long-term conductivity and integrity, even under cyclic thermal conditions.

Another advantage is its formability. Interconnector plates must be thin yet structurally sound, precisely crafted to facilitate optimal gas flow while ensuring electrical connectivity. Therma 22FC enables manufacturers to fabricate these components more consistently.

A closeup of the inside of a Therma 22FC steel coil.

Beyond the stack

While interconnector plates serve as the backbone of SOFC stacks, stainless steel plays a far broader role in the overall system architecture. Most of the cells’ other materials must endure prolonged exposure to heat while resisting creep-induced deformation:

• Housing structures, which encase and shield the fuel cell stack.
• Tubing, responsible for fuel and exhaust gas transport.
• Support frameworks, which ensure mechanical stability.

For these surrounding components, heat resistant austenitic stainless steels such as Therma 253 MA® provide excellent creep strength, structural stability and cyclic oxidation resistance, making them suitable for components exposed to sustained high heat.

SOFCs are also part of a broader hydrogen ecosystem, where materials must meet the demands of storage, transportation, and gas conditioning infrastructure.

Here, considerations such as hydrogen embrittlement resistance, superior corrosion toughness, and formability for piping and containment vessels come into play. Austenitic stainless steels, including 1.4420 (Supra 316plus), 1.4435 (Supra 316L/4435) and 1.4404 (Supra 316L/4404) offer robust solutions for these applications.

It’s industry’s turn

While next-generation SOFCs already demonstrate significant efficiency gains, further improvements, ranging from enhanced electrical conductivity to lower-cost fabrication techniques, are key to boosting commercial adoption.

These challenges will require metals specialists, research institutions, and fuel cell manufacturers to work together to refine material properties and optimise system performance.

Outokumpu’s decades of metallurgical expertise enable us to create tailored stainless steel solutions for a wide array of industries. The transition to lower-temperature SOFCs has opened the door for hydrogen applications, with high performance stainless steels set to play a crucial role.

SOFCs, electrolysers, storage and transport networks all demand materials that retain their properties as long as possible, in the most demanding of conditions.

As applications scale from small residential units to megawatt-scale power stations, intelligent material selection will be a deciding factor in the hydrogen economy’s continued progress.