In this project, microorganisms were used to convert carbon dioxide (greenhouse gas) to volatile fatty acids. These fatty acids can be used in the food, pharmaceutical or chemical industry as building blocks for e.g. food supplements or fuel. To convert the carbon dioxide to fatty acids, microorganisms need energy. The energy is provided to the microorganisms as electricity to graphite felt, a conductive carbon material on which the microorganisms can grow. The microorganisms can use the electricity directly as electrons or indirectly via a mediator compound such as hydrogen. In this project, the hydrogen availability for microorganisms was stimulated by incorporating a hydrogen formation catalyst in the graphite felt. The hydrogen formation catalyst is made of trace nutrients from the microorganisms. Besides the catalyst, we also measured where in the reactor the hydrogen is most available and we developed strategies to better divide the hydrogen.