Coordinator: Juan Morante, IREC (ES)& Deputy: Roel van de Krol, HZB (DE)
The generation of fuels from sunlight and water is considered as a task of paramount importance for a sustainable energy supply in the future. Decomposition of water by a photoelectrochemical process is a possibility to store solar energy in form of hydrogen on a large scale. Alternatively, the electrons and protons recovered from water can be used for CO2 reduction and hydrocarbon production. In both cases the catalysts for the oxidation and reduction half-reactions have to be developed and the two processes combined in a suitable device.
For a direct photochemical energy conversion, two main approaches can be distinguished:
Molecular approaches using a plethora of catalysts for oxidation and reduction interfaced with different chromophores for their activation by visible light.Similarly a broad range of materials have been developed based on low-bandgap semiconductors and co-catalysts. For a practical use, these photocatalytic systems can be incorporated in a photoelectrochemical cell (PEC) device rather than be used in homogeneous phase.
A third approach is based on an indirect conversion process by combining solar cells with electrolysis systems. For these systems, different degrees of integration can be envisioned and their advantages and disadvantages discussed. Examples for a highly integrated system are multi-junction photovoltaic devices with catalyst layers for oxidation and reduction on both surfaces, frequently addressed as an artificial leaf. Independent of the chosen approach it became clear that any economically viable solution for solar fuel production has to meet three essential criteria: high efficiency, high robustness and low cost. The latter criterion is sometimes replaced by “scalability” to take into account elemental abundance, raw material cost, and capital costs. To establish research activities on an European level from basic aspects to working devices, a Description of Work and Roadmap on this topic within the AMPEA EERA Joint Programme addressing molecular, inorganic and hybrid approaches is formulated.