Sunlight-powered photoelectrochemical and thermochemical water splitting using concentrated natural sunlight
Martin Roeb, Dorottya Kriechbaumer, Michael Wullenkord, Gerd Dibowski, Stefan Brendelberger
German Aerospace Center (DLR), Institute of Future Fuels, Linder Höhe, 51147 Köln, Germany
Corresponding author, e-mail: firstname.lastname@example.org
Thermochemical and photo-electrochemical multistep processes can be used to enhance the availability of solar energy in terms of energy transport, of energy demand/supply management and of potential energy carrier related applications. Coupling concentrated sunlight to suitable steps of thermochemical reaction or to a suitable spot of a photoelectrochemical (PEC) cell enables the production of fuels like hydrogen or syngas and other fuels by water- and/or CO2-splitting as well as the storage of solar energy by breaking and forming chemical bonds in suitable reversible reactions. These processes are sustainable and environmentally attractive since water and CO2 are used as the only raw materials and solar power and heat as the only energy source. All other materials involved are recycled within the process. The concentrated solar energy is converted into storable and transportable chemicals and fuels. One of the major barriers to technological success of many of those processes is the identification of suitable active materials like catalysts and redox materials exhibiting satisfactory durability, reactivity and efficiencies.
Beyond material screening, identification and qualification aspects the present contribution investigates how concentrating solar systems can be applied to integrate solar radiation into processes forming the basis for production of such kind of products – let it be through moderate concentration of sunlight to run PEC processes at room temperature or slightly above, let it be through concentration factor in the range of 1000 suns or more to run high temperature processes. It will be shown how key components like optics, solar cells, receivers, reactors, and heat exchangers are developed and tested for such applications. In some cases, the full production chain from the raw material to the product is demonstrated using a solar facility like a solar tower. Besides materials aspects also process engineering issues needs to be overcome to develop such processes. Challenges are to couple an intermittent energy source to a chemical process and to efficiently recover high temperature heat. The most promising integration schemes and processes are being described and discussed with respect to further development and future potential.