Beginning and ending with water, the electrolysis cell uses electricity to split water molecules (H2O) into hydrogen (H2) and oxygen (O2). In this way, electrical energy is transformed into chemically bound energy in the hydrogen molecules. This is the reverse of the process that occurs in a fuel cell.
A Solid Oxide Electrolysis Cell (SOEC ) is basically the corresponding fuel cell (Solid Oxide Fuel Cell – SOFC) run in ‘reverse’. Such a cell operates at relatively high temperatures (700-1000 °C), which makes the efficiency very high. The two electrolysis products, hydrogen and oxygen, are formed on each side of the cell. The hydrogen can be stored and – using a fuel cell – reconverted into electricity again when the demand arises. This allows the storage of electricity when production exceeds demand.
An SOEC can also electrolyze carbon dioxide (CO2) to carbon monoxide (CO). If water is electrolyzed at the same time (co-electrolysis), a mixture of hydrogen and CO is produced. This mixture, called syngas, is the starting point of a large number of syntheses of hydrocarbons in the chemical industry. In this way, liquid transport fuels can be produced synthetically. If the electricity is generated by wind turbines or solar cells, the use of the fuel is CO2 neutral.
The Department of Energy Conversion and Storage has been one of the originators of the field of solid oxide electrolysis. Recent notable achievements include a much improved understanding of the degradation mechanisms of the fuel electrode and means of counteracting it, demonstration of high-pressure operation at the stack level, and the commercial availability using licensed technology from the department.
NASA Glenn has been investigating three types of fuel cells: proton exchange membrane fuel cells (PEMFCs), regenerative fuel cell (RFC) systems, and solid-oxide fuel cells (SOFCs). NASA first developed PEMFCs for the Gemini mission, but because PEMFCs had water-management problems, alkaline fuel cells were used through the 1990s.
Throughout the years the materials and internal flow processes have since improved the SOFC to become more powerful, lighter, safer, simpler to operate, and more reliable. In Solid Oxide systems, fuel cells use hydrogen and oxygen to produce electricity, water, and heat. Then a solar-powered electrolyzer breaks the water into hydrogen and oxygen so that the fuel cell can use it again. SOFC systems provide efficient, environmentally friendly, highly reliable, renewable energy conversion.
NASA Glenn researchers have developed SOFC concepts for storing energy on the International Space Station, high-altitude balloons, and high-altitude aircraft. They are now investigating SOFCs for storing energy on the Moon or Mars.
NASA has committed to Solid Oxide Fuel Cells (SOFC) for power generation and for use in space because of their high efficiency, high power density, and extremely low pollution. They have an all-solid construction and can operate at high temperatures producing clean, efficient power from easy-to-transport fuels instead of just pure hydrogen.
Because the SOEC electrolysers operates at high temperatures, light hydrocarbon fuels, such as methane, kerosene, propane, and butane can be internally reformed within the anode. SOFCs can also be fueled by externally reforming heavier hydrocarbons, such as gasoline, diesel, jet fuel (JP-8) or biofuels. Such reformates are mixtures of hydrogen, carbon monoxide, carbon dioxide, steam and methane, formed by reacting the hydrocarbon fuels with oxygen or steam in a device upstream of the SOFC anode. SOFC power systems can increase efficiency by using the heat given off by the exothermic electrochemical oxidation within the fuel cell for endothermic steam reforming process.
Because NASA SOFCs must operate at high temperatures (600 to 1000 °C) for thousands of hours in corrosive environments, Glenn researchers developed special sealing materials as well as a design that combines the separator and sealant. They also developed a novel process to make SOFC parts (anodes, cathodes, and cermets) that weigh less but provide support while correcting fuel-flow problems.
Finally, they developed thinner, lighter, high-temperature interconnects that reduce the weight of the entire SOFC system. The system improvements NASA Glenn has made, will ensure the longevity and reliability operating in space. Our system will run in continuous operation on Earth to identify issues, risks, and mitigate solutions prior to launching into Space.