(Ilmenau) – Solar energy can be used to produce hydrogen through two processes: water electrolysis with solar-generated electricity and direct solar water splitting. The first involves using electricity, a very efficient energy source, to produce hydrogen, another energy source, and then converting it back into electricity.
The process for direct solar hydrogen production via photoelectrochemical processes goes one step further. “This refers to the absorption of sunlight in a semiconductor material, which itself generates a sufficiently large photovoltage (> 1.6 volts) to break water directly into hydrogen and oxygen,” say the scientists at the Technical University of Ilmenau. This is part of the research in the “H2-Demo” joint project.
Researchers should produce demonstrators
According to the information, “so-called tandem absorbers, in which two absorbing materials are electrically connected in series,” are particularly suitable for the process, analogous to tandem solar cells used in photovoltaics. This hydrogen production process has already been demonstrated in a small format. The aim of the “H2-Demo” research project is now to produce larger demonstrators for the first time. 
“The work packages in the H2 demo include the optimization of the III-V tandem absorbers, which are deposited on silicon and whose properties must be further improved and optimized for the specific application,” says project coordinator Frank Dimroth, head of the III-V Photovoltaics department and concentrator technology at the Fraunhofer Institute for Solar Energy Systems (ISE). In addition, “processes and systems will be scaled for later industrial use and new processes with high throughput will be developed.” Finally, a demonstrator with an area of 36 by 36 square centimeters will be built and installed on a test field in order to measure solar hydrogen efficiency - H2 production and module efficiency - in detail.
Difficult interfaces
According to its own information, the Ilmenau University of Technology is primarily concerned with “the difficult interfaces that lie between silicon and the III-V semiconductors in the tandem structure as well as between the component and the aqueous electrolyte” as part of the project. The tandem structure used here consists, on the one hand, of the semiconductor silicon and of III-V semiconductor compounds (i.e. a combination of materials from the main chemical group III 'earth metals/boron' and V 'nitrogen-phosphorus'), “which the silicon in practical refinement of its functionality”. Together they result in a tandem structure that is necessary “to provide enough 'free energy', i.e. a sufficiently high photovoltage for water splitting - and to do so with high efficiency,” says Thomas Hannappel, head of the Fundamentals of Energy Materials department and deputy director from the Thuringian Energy Research Institute (TheEFI), who leads the sub-project at the TU Ilmenau. In addition, the project is trying to “achieve stability and prevent corrosion in another, particularly difficult interface, the solid-liquid interface between the semiconductor and the aqueous solution, the electrolyte.”
Funding for five years by BMBF
The H2Demo joint project is being funded by the Federal Ministry of Education and Research (BMBF) with around 14 million euros over a period of five years. Under the leadership of Fraunhofer ISE in Freiburg, eleven partners are working on demonstrators for direct solar water splitting. In addition to the TU Ilmenau, Azur Space, Helmholtz Zentrum Berlin, HQ Dielectrics, LayTec AG, Plasmetrex GmbH, Philipps University of Marburg, SEMPA, Technical University of Munich and the University of Ulm are involved. The projects complement the three industry-led hydrogen lead projects, which are also scheduled to start in the spring.
deep link
https://www.tu-ilmenau.de/journalisten/pressemeldungen/einzelnachricht/newsbeitrag/26218/
Photo above
Are solar cells a way or a detour in hydrogen production? Researchers try / © University of Central Florida / Florida Solar Energy Center (FSEC)
Photo middle
Building a photocathode with a highly efficient tandem cell / © ACS Energy Letters 3 (2018)
