Follow the journey through a solid oxide cell

Symbols and cell parts

SOEC

Solid oxide electrolysis cell: a high-temperature cell using a dense ceramic electrolyte.

O²⁻

Oxide ion: an oxygen atom with two negative charges; it moves from cathode to anode.

V inside the ceramic

An oxygen vacancy: a missing oxygen ion at a crystal-lattice site. This schematic V does not mean voltage.

Vacancy transport

Oxide ions move between available lattice sites; vacancy movement is opposite to oxide-ion movement.

Ceramic electrolyte

A dense solid that conducts oxide ions while limiting electron conduction and gas mixing.

Steam/H₂ electrode

The cathode during electrolysis: steam is reduced here to form H₂ and O²⁻.

Oxygen electrode

The anode during electrolysis: oxide ions are oxidised here to form oxygen.

Interconnect

A conductive structure connecting neighbouring cells, collecting current and separating gas environments.

Heat / °C

Thermal energy supplied to support high-temperature operation / degrees Celsius.

Anode (+)

The positive electrode during electrolysis; oxidation releases electrons here.

Cathode (−)

The negative electrode during electrolysis; reduction consumes electrons here.

DC power supply

A direct-current source that supplies electrical energy and maintains the electrode potential difference.

e⁻

An electron. Electronic charge travels through conductive components and external wires.

H₂O

Water; H₂O(g) means water vapour (steam).

H₂ / O₂

Hydrogen gas / oxygen gas. Subscript ₂ means two atoms per molecule.

OER / HER

Oxygen evolution reaction / hydrogen evolution reaction.

Oxidation / reduction

Loss of electrons / gain of electrons.

Reaction notation

→ means “forms”; + joins reactants or products. A coefficient such as 2 or ½ gives the relative number of molecules or moles.