Fuel cells are a further option to convert hydrogen into electricity and heat, producing only water and no direct emissions. Fuel cells can achieve high electric efficiencies of over 60% (above 80% overall efficiency when also including the heat output) and reveal a higher efficiency in part load than full load, which makes them particularly attractive for systems that run for extended periods of time without frequent start and stop cycles and flexible operations such as load balancing. Molten carbonate fuel cells (MCFCs) and solid oxide fuel cells (SOFCs) operate with 600°C and 800 - 1 000°C, respectively, at higher temperatures, which allows them to run on different hydrocarbon fuels, without the need for an external reformer to produce hydrogen first. MCFCs are used in the MW scale for power generation (due their low power density, resulting in a relatively large size). The produced heat can be used for heating or cooling purposes in buildings and industrial applications. SOFCs have similar application areas but are used at smaller scale in the kW range, such as micro-CHP units or for off-grid power supply. The high-temperature systems can also be utilized in tri-generation mode to produce electrical power, heat, and hydrogen. For MCFCs, R&D would further limit electrolyte loss and prevent microstructural changes in the electrolyte support that lead to early stack failure. R&D would also benefit the development of more robust cathode materials.