Efficient Production of Green Hydrogen using Tandem Cells
Green hydrogen can be produced off-grid by splitting water using sunlight in a photoelectrochemical (PEC) cell. The functional components of the PEC cell essentially consist of the photoabsorbers and electrocatalysts. Tandem cells absorb different wavelengths of the visible light to different degrees. This effect is to be used to increase the light-to-hydrogen conversion efficiency. The project “TWOB – Tandem cell-based photoelectrochemical hydrogen production with novel high-entropy electrocatalysts and oxynitride photoabsorbers” aims to use novel synthesis concepts to produce nanostructured catalysts and absorbers based on resource-efficient materials. The research focus is particularly on improving light absorption and charge separation, as well as coupling with the catalysts. The synthetic optimization of the materials is intended to meet the requirements for increased efficiency and longevity and to advance the degree of technologization of tandem cells.
Direct Conversion of Sunlight to Hydrogen without External Electricity
The main advantage of PEC tandem cells over electrolysers or photovoltaic-based hydrogen production technologies is the direct conversion of solar energy into H2, which means that no additional external electricity is required and there are cost savings due to the lower complexity in the combination of components. In the first work package, nanoporous electrocatalysts are produced using the cost-effective process of dip coating and special polymers. The thermodynamic stability of complex materials will then be predicted on the basis of density functional calculations and previously unknown multimetallic oxides will be synthesized in the laboratory. In a further work package, a multi-conceptual approach will be used to create short charge transfer paths through nanostructuring, improve electrical conductivity through doping, enable efficient spatial separation of charge carriers through the formation of heterocontacts and create protection against direct contact with water with the aid of atomic layer deposition. The photovoltages of the photoelectrodes are to be determined in collaboration with the University of California, Davis (USA) using photovoltage spectroscopy. The goal is to determine the optimal material properties and to test the components in the laboratory as a tandem cell device.
Increasing Efficiency by Optimizing the Components’ Properties
During the six-year funding period, a total of three doctoral students, one postdoc and one technician will work in the research field of artificial photosynthesis. One doctoral student will work on the production and characterization of electrocatalysts, photocathodes and photoanodes. The PostDoc will carry out the theoretical calculations on the stability of the compounds to be synthesized and work closely with the doctoral students. One focus of the project is the creation of structural property relationships that lay the foundation for property optimizations. The aim is to produce highly efficient electrocatalysts with record overvoltages of less than 200 mV (at 10 mA/cm2). Several working groups from TU Darmstadt (Prof. Weidenkaff), Justus Liebig University Giessen and TU Berlin (Prof. Hess) as well as international US cooperation partners (Prof. Osterloh) will be involved in the envisaged experiments. The results obtained in the project will be published as open access in specialist journals and at conferences and will therefore also be of use to other working groups worldwide.
