Solid-oxide electrolyser cell
A solid oxide electrolyzer cell (SOEC) is a solid oxide fuel cell that runs in regenerative mode to achieve the electrolysis of water and which uses a solid oxide, or ceramic, electrolyte to produce oxygen and hydrogen gas. The production of pure hydrogen is compelling because it is a clean fuel that can be stored easily, thus making it a potential alternative to batteries, which have a low storage capacity and create high amounts of waste materials. Electrolysis is currently the most promising method of hydrogen production from water due to high efficiency of conversion and relatively low required energy input when compared to thermochemical and photocatalytic methods.
Solid oxide electrolyzer cells operate at temperatures which allow high-temperature electrolysis to occur, typically between 500 and 850 °C. These operating temperatures are similar to those conditions for an SOFC. The net cell reaction yields hydrogen and oxygen gases. The reactions for one mole of water are shown below, with oxidation of water occurring at the anode and reduction of water occurring at the cathode.
Anode: O2− ---> 1/2O2 + 2e−
Cathode: H2O + 2e− ---> H2 + O2−
Net Reaction: H2O ---> H2 + 1/2O2
Electrolysis of water at 298 K (25 °C) requires 285.83 kJ of energy in order to occur, and the reaction is increasingly endothermic with increasing temperature. However, the energy demand may be reduced due to the Joule heating of an electrolysis cell, which may be utilized in the water splitting process at high temperatures. Research is ongoing to add heat from external heat sources such as concentrating solar thermal collectors and geothermal sources.
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