The Fraunhofer Institute for Solar Energy Systems ISE creates the technological foundations for supplying energy efficiently and on an environmentally sound basis in industrialized, threshold and developing countries. With our activities in this area, we offer R&D services addressing the generation, conversion and further thermo-chemical processing of hydrogen. Within electrochemical generation of hydrogen, we are concentrating on electrolysis of water in polymer-electrolyte membrane electrolyzers (PEM). We also apply PEM technology to develop fuel cell systems, particularly for the mobility sector. For both water electrolysis and fuel cells, we carry out multi-scale physical simulation and fundamental electrochemical characterization of cells and stacks. Our research encompasses the development, simulation and testing of single cells, cell stacks and complete systems as well as the testing of peripheral and cell components under all climatic conditions that can apply. Furthermore, we synthesize liquid fuels and chemicals from hydrogen and carbon dioxide (power-to-liquids), applying catalysts that we have developed ourselves. These processes create the link from sustainable electricity generation via water electrolysis to other sectors, such as mobility and chemistry.