Solid oxide electrolysis cells

Solid Oxide Electrolysis Cells

An electrolysis cell uses electricity to split, e.g., 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. SOECs may be used for the production of hydrogen from surplus electricity generated by, e.g., wind turbines. 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 of a CO-producing unit from the Danish company Haldor Topsøe, using licensed technology from the department.

The main research topics within high temperature electrolysis are:

  • Density-functional based modelling in combination with model electrodes and in situ studies to clarify how the interplay of materials properties and geometry impacts electrode performance
  • Novel processing routes such as net shaping to achieve stronger cells with a large footprint
  • Sealants, interconnects, protective coatings for and design of SOEC stacks
  • High pressure co-electrolysis for production of synthetic fuels.


Henrik Lund Frandsen
Senior Researcher
DTU Energy
+45 46 77 56 68