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Abstract: The efficient use of primary energy sources, which can be used for hydrogen production, is addressed by a consideration of four key measures, which reflect the ability of different sources and processing routes to meet underlying needs and the practical demands of energy on a large scale. The measures considered are carbon dioxide emission reduction, primary energy availability, land use implications and hydrogen production costs. Fourteen pathways to hydrogen are considered involving fossil fuels and nuclear energy as well as the range of renewable sources, and including additional strategies for carbon sequestration. The overall comparison of routes, based on simple figures-of-merit, shows a clear division between those using renewable energies and those associated with the traditional ‘high energy density’ primary sources. Emerging from the work is a clearer view of the implications of following a particular production path, the limitations of certain technologies and the research challenges which must be met in addressing future fuel options and global warming. [Copyright &y& Elsevier]

Abstract: HycycleS was a cooperation of nine European partners and further non-European partners and aimed at the qualification and enhancement of materials and components for key steps of solar and nuclear powered thermochemical cycles for hydrogen generation from water. The focus of HycycleS was the decomposition of sulphuric acid (H2SO4) which is the central step of the sulphur-based family of those processes. Emphasis was put on materials and components for H2SO4 evaporation, decomposition, and sulphur dioxide separation. The suitability of materials and components was demonstrated by decomposing H2SO4 and separating its decomposition products in scalable prototypes. Silicon Carbide (SiC) turned out as the material of choice for the components facing the most corrosive environment of the process: the sulphuric acid evaporator and decomposer. Candidate catalysts for the high temperature reduction of sulphur trioxide have been screened and analysed. Cr–Fe mixed oxide (Fe0.7Cr1.3O3) was the most promising material among the ones examined. Based on the use of the highlighted construction and catalyst materials prototype decomposers have been developed and tested. The successful fabrication and testing of a large size heat exchanger/reactor prototype composed of SiC plates shows promise with respect to its use for H2SO4 decomposition in the SI and HyS cycle. A solar specific decomposer prototype was developed, realised and successfully tested on sun in a solar furnace. A novel approach of using dense oxygen transport membranes, made from complex ceramics, for oxygen removal from the H2SO4 decomposition product in order to shift the equilibrium in favour of increased decomposition was investigated. The membranes stability and suitability for carrying out this separation was investigated experimentally. Parallel to this, a conventional oxygen separator, a low-temperature wet scrubbing system, was investigated as well. Scale-up scenarios of components and of the process were addressed. [Copyright &y& Elsevier]