Modern Electrolytic Procedures for the Production of Hydrogen by Splitting Water

Abstract

Hydrogen has a number of advantages as an energy carrier. Its production by the splitting of water under technically and economically feasible conditions requires either electrolytic procedures or thermochemical hybrid cycles with an electrochemical step. These procedures for hydrogen production should in future be based on an advanced primary energy source such as nuclear or solar energy. After a review of the general principles of the electrolytic approach, the paper considers the essential features of the various types of electrolytic procedure in the low-temperature range (conventional and advanced water electrolysis), in the elevated temperature range (water vapor electrolysis in a salt melt), and at high temperatures (water vapor electrolysis in a solid electrolyte). Technical and economic parameters and requirements are critically evaluated. Advanced types of electrolysis are compared with the advanced version of the sulfuric-acid hybrid cycle. It is concluded that suitable advanced electrolysis procedures have already reached the stage where they can be scaled up to commercial processes. In contrast, the basically very attractive hybrid cycle still needs substantial research and development work on both the electrochemical step and the thermochemical part of the process (particularly the materials problems involved).