High-temperature electrolysis of water vapor—status of development and perspectives for application

Abstract

Electrolysis of water vapor using solid-oxide electrolyte cells has been demonstrated to be a very efficient method of hydrogen production from water. As a result of an eight-year development program in Germany, the technology of vapor electrolysis cells and their integration into larger molecules has reached an advanced status: Single cells have been operated during long-term tests with current densities of 0.3 A cm −2 and 100% Faraday efficiency at a voltage of only 1.07 V [corresponding to a specific electrical energy consumption of 2.57 kWh Nm −3 (H 2)]. With electrolysis tubes of series-connected cells an enrichment of hydrogen in the vapor stream of up to 85% could be demonstrated without major concentration polarization losses. Concepts for integrated modular electrolysis units made up of serial- and parallel-connected tubular cells have been developed and successfully tested. A pre-prototype unit of 3.5 kW hydrogen output power is under development. The high efficiency of this hydrogen production process will allow an extension of the use of electrolytic hydrogen in the near future. The reasons for such a development will be explained and an example for a modified synfuel process will be given.