Electrolysis Technologies

Advanced electrochemical technologies for hydrogen and sustainable fuel production

Electrolyzers, which use electricity to split water into hydrogen and oxygen, are critical to building a low‑carbon hydrogen economy as nations seek to decarbonize hard-to-abate sectors.

What Is Electrolysis?

Electrolysis is the electrochemical process that converts electrical energy into chemical energy by splitting water into hydrogen and oxygen. When an external voltage is applied, water molecules at the cathode are reduced to form hydrogen gas, while water oxidation at the anode releases oxygen. The efficiency of this process depends on the ionic conductivity of the electrolyte, the catalytic activity of the electrodes, and the ability of the system to manage heat and mass transport.

In the context of a transition to sustainable energy systems, electrolysis enables the direct storage of renewable electricity in the form of hydrogen — a versatile energy carrier that can be stored, transported, and later reconverted into electricity or used as a feedstock for chemical synthesis. Hydrogen produced through electrolysis can decarbonize sectors such as steel manufacturing, refining, and chemical synthesis, and can serve as a building block for power-to-X pathways (e.g., synthetic fuels, ammonia).

Electrochemical impedance spectroscopy (EIS) plays a critical role in understanding electrolysis performance and degradation mechanisms. By probing the frequency-dependent response of an electrochemical cell, EIS separates resistive and capacitive contributions arising from bulk ionic transport, interfacial charge transfer, and electrode processes — making it indispensable for optimizing materials and cell designs.

Electrolysis Technology Platforms

Electrolyzers vary in component materials and operating conditions, each optimized for specific conditions of temperature, reactants, and targeted application options.

Solid Oxide Electrolyzer (SOEC)

Advantages	Disadvantages
High electrical-to-hydrogen efficiency at high temperature Can utilize waste heat or renewable heat sources High current density operation possible	High operating temperatures (700–850 °C) lead to material degradation Complex sealing and thermal management required High initial capital cost

Alkaline Electrolyzer (AEL)

Advantages	Disadvantages
Proven and mature technology Low-cost materials (Ni-based electrodes, KOH/NaOH electrolyte) High durability and long lifetime	Lower current density compared to PEM and SOEC Large footprint due to electrolyte tank and circulation system Hydrogen purity slightly lower due to gas crossover

Proton Exchange Membrane Electrolyzer (PEM)

Advantages	Disadvantages
High hydrogen purity (>99.99%) Compact design, high current density operation Fast dynamic response to variable power input	High cost due to platinum-group metal catalysts Membrane degradation over time in acidic conditions Requires high-purity water

Anion Exchange Membrane Electrolyzers (AEM)

Advantages	Disadvantages
Uses non-precious metal catalysts High hydrogen purity and moderate current densities Lower cost potential compared to PEM	Membrane durability still under research Limited commercial maturity Performance sensitive to water management

Proton-Conducting Ceramic Electrolyzer (PCC)

Advantages	Disadvantages
Intermediate temperatures (400–600 °C) Produces dry hydrogen at the cathode Employs non-precious metals	Relatively new technology with limited commercialization Ceramic membranes are brittle and sensitive to thermal/mechanical stress Material and stack development still under research

Materials & Components — Cell Level

The performance and durability of electrolysis technologies are governed not only by operating conditions but fundamentally by the materials and components used within the cell and stack. Transport properties, interfacial stability, and mechanical compatibility between components strongly influence efficiency and degradation behavior. While these fundamental components are common to all electrolysis technologies, their material requirements and operating challenges vary significantly with temperature. In high-temperature electrolysis systems, component design must additionally account for enhanced transport rates, thermochemical effects, and long-term stability under extreme operating conditions.

Electrolytes

For high-temperature electrolysis, ceramic electrolytes like yttria-stabilized zirconia (YSZ) or gadolinium-doped ceria (GDC) are widely used. These materials exhibit high oxide-ion conductivity at elevated temperatures and enable efficient ion transport between electrodes. Current research focuses on improving ionic conductivity while minimizing degradation mechanisms such as grain growth and chemical instability at interfaces.

Fuel Electrodes (Cathodes)

Nickel-based cermet electrodes such as Ni-YSZ and Ni-GDC are state-of-the-art for hydrogen electrodes. However, under SOEC conditions, nickel agglomeration and migration can alter microstructure and reduce active surface area over time. Alternative mixed ionic–electronic conducting materials are under investigation to enhance chemical stability and durability while maintaining adequate catalytic activity.

Oxygen Electrode (Anode)

The oxygen electrode must catalyze the oxygen evolution reaction (OER) while maintaining structural integrity under oxidizing conditions at high temperatures. Conventional perovskite materials such as LSC(F) show good performance but suffer from strontium segregation and secondary phase formation at interfaces, which degrade long-term performance. Emerging electrode materials, including layered Ruddlesden–Popper nickelates and double perovskites, exhibit enhanced oxide ion diffusion and surface exchange activity, resulting in improved performance and potentially lower degradation rates.

Electrolytes

In alkaline electrolyzers, aqueous solutions of potassium hydroxide (KOH) or sodium hydroxide (NaOH) are commonly used as electrolytes. These alkaline solutions offer high ionic conductivity at moderate temperatures and enable efficient hydroxide-ion transport between electrodes. Current research focuses on improving conductivity, minimizing electrode corrosion, and enhancing long-term chemical stability.

Fuel Electrodes (Cathodes)

Nickel-based materials, often in the form of porous nickel foam or nickel-coated substrates, are state-of-the-art cathodes for hydrogen evolution. These electrodes provide high catalytic activity for the hydrogen evolution reaction (HER). Research efforts aim to reduce nickel degradation, prevent surface passivation, and improve durability while maintaining high reaction rates.

Oxygen Electrode (Anode)

The anode in alkaline electrolyzers catalyzes the oxygen evolution reaction (OER) and must maintain structural integrity under strongly oxidizing conditions. Nickel-iron oxides and layered double hydroxides (LDHs) are widely used and show good performance. Emerging materials focus on enhancing catalytic activity, improving stability, and reducing overpotentials for long-term operation.

Electrolytes

PEM electrolyzers use a solid polymer electrolyte, typically a proton-conducting membrane such as Nafion®. This membrane conducts protons from the anode to the cathode while acting as a separator for gases, enabling high-purity hydrogen production. Research focuses on improving proton conductivity, chemical stability, and durability under high current densities and variable operating conditions.

Fuel Electrodes (Cathodes)

Cathodes in PEM electrolyzers are typically made of platinum or platinum-based catalysts supported on carbon. These materials provide high activity for the hydrogen evolution reaction (HER). Ongoing research aims to reduce the amount of precious metals, improve catalyst stability, and maintain high catalytic efficiency over long-term operation.

Oxygen Electrodes (Anodes)

The anode catalyzes the oxygen evolution reaction (OER) and is usually composed of iridium or iridium oxide-based catalysts. These materials must withstand highly oxidizing conditions and acidic environments within the membrane. Current research focuses on enhancing activity, reducing catalyst loadings, and improving long-term durability while minimizing degradation mechanisms.

Electrolytes

AEM electrolyzers use a solid anion-conducting membrane, typically based on quaternary ammonium-functionalized polymers. This membrane conducts hydroxide ions from the cathode to the anode while separating the gases. Research focuses on improving ionic conductivity, chemical stability under alkaline conditions, and mechanical durability at moderate temperatures.

Fuel Electrodes (Cathodes)

Cathodes in AEM electrolyzers are typically made of non-precious metal catalysts such as nickel or cobalt-based materials on conductive supports. These materials catalyze the hydrogen evolution reaction (HER) efficiently in alkaline environments. Research is focused on improving catalytic activity, durability, and long-term performance while minimizing cost.

Oxygen Electrodes (Anodes)

The anode catalyzes the oxygen evolution reaction (OER) and is usually composed of nickel, cobalt, or mixed metal oxides compatible with alkaline conditions. Research aims to enhance activity, chemical stability, and durability while reducing overpotential and material degradation over time.

Electrolyte

Proton-conducting ceramic membranes such as barium zirconate-based perovskites (BaZrO₃ doped with Y, Sc, or Ce) are used. These materials provide high proton conductivity at intermediate temperatures (400–600 °C) while maintaining chemical stability under humidified hydrogen and oxygen atmospheres.

Fuel Electrode (Cathode)

Nickel-based cermets combined with protonic ceramics are employed as hydrogen evolution electrodes. These electrodes ensure efficient proton reduction and high catalytic activity while maintaining mechanical compatibility with the ceramic electrolyte.

Oxygen Electrode (Anode)

Perovskite-based mixed ionic-electronic conducting materials, such as layered Ba₃Ca₁.₁Nb₁.₉O₉ or related double perovskites, catalyze oxygen evolution. These materials provide high chemical stability under oxidizing conditions and enable rapid proton and oxide ion transport at intermediate temperatures.

Materials & Components — Stack & System Level

Beyond individual cells, the full electrolyzer stack incorporates additional engineering components that govern scale-up, thermal management, and system integration.

Interconnects & Bipolar Plate:
These components provide electrical pathways between cells and separate gas streams. Material choices must balance electrical conductivity, oxidation resistance at high temperature, and coefficient of thermal expansion compatibility with adjacent cell materials.

Seals & Coatings:
Gas-tight seals prevent cross-contamination of reactants in the stack and must endure long-term thermal cycling without cracking or creeping. Protective coatings on metallic interconnects and cell surfaces can mitigate corrosion and extend service life.

Thermal & Flow Management Systems:
Efficient heat distribution and reactant supply are vital for uniform cell operation. For SOEC systems, thermal integration with external heat sources and waste heat recovery are major design considerations that can significantly influence overall system efficiency.

Interconnects & Bipolar Plate

Ferritic stainless steels (e.g., Crofer 22 APU) or nickel-based alloys are used for interconnects and bipolar plates. Protective coatings such as spinel (Mn, Co, Fe oxides) or ceramic layers improve oxidation resistance at operating temperatures of 700–850 °C while maintaining electrical conductivity and thermal expansion compatibility with adjacent cell components.

Seals & Coatings

Glass-ceramic or high-temperature gasket materials are applied for gas-tight sealing between cells. Metallic interconnects and exposed components are often coated with conductive ceramic layers or spinel coatings to mitigate high-temperature oxidation and corrosion under steam and oxygen-rich conditions.