Solar heat integrated solid oxide steam electrolysis for highly efficient hydrogen production

Abstract

Water electrolysis is considered as a suitable pathway for the production of large amounts of hydrogen to be used as energy carrier for electricity storage. Among the existing water electrolysis technologies solid oxide steam electrolysis exhibits the highest electrical efficiency. Moreover, from thermodynamic considerations the efficiency can be further increased when part of the energy demand is provided by the integration of external high temperature heat to reduce the electrical energy for the water splitting reaction. This paper reports on the successful integration of solar heat into a solid oxide electrolyzer. The experimental setup of the prototype system consisting of a solar simulator, a solar steam generator, a steam accumulator and a solid oxide electrolyzer as well as first results with regard to solar steam generation and electrochemical performance of the electrolyzer are presented. Hot steam with a maximum flow rate of 5.0 kgh−1 was produced with the solar steam generator. A small fraction (0.58 kgh−1) mixed with 10% of H2 was supplied to a 12-cell solid oxide electrolyzer stack with approx. 2 kW electrical power. At 770 °C and a current density of −1.25 Acm−2 a steam conversion rate of 70% at 93% electrical electrolyzer efficiency was achieved.