They combined a tandem solar cell of III-V semiconductors with a catalyst of rhodium nanoparticles and a crystalline titanium dioxide coating. Teams from the California Institute of Technology, the University of Cambridge, Technische Universität Ilmenau, and the Fraunhofer Institute for Solar Energy Systems ISE participated in the development work. One part of the experiments took place at the Institute for Solar Fuels in the Helmholtz-Zentrum Berlin.