particular, monitoring of the exhaust duct, especially the
Introduction
Different sensing technologies are employed to detect hydrogen. Classification of hydrogen sensors based on a range of technologies including catalytic combustion, thermal conductivity, work-function based, mechanical effects and optical effects has been established and reviewed by Hu¨bert [1]. A market analysis shows a wide selection of highly qualified commercially available hydrogen sensors [2]. However, it has been shownthat not all sensorperformance requirements can be fulfilled for specific applications by any individual product. There is for example a strong need to monitor and check the environment of the fuel cells for traces of leaked hydrogen. In waste air duct is necessary. Membrane leakages as well as potentially explosive H2eO2 gas mixtures can be detected by the measurement of hydrogen in the waste air duct. In most existing applications monitoring of the single cell voltage is used to indicate possible membrane leakages. Sensors for temperature, pressure, flow and humidity are used for control functions. In addition to system design measures e.g. redundant provision of shutoff and safety valves, hydrogen sensors can also contribute to the safety of the system. Therefore, a lot of research is on-going to develop new sensing materials and to improve and optimise various elements of established hydrogen sensor types. We give an overview on new commercially available sensors and upcoming sensors under development using new materials or novel technologies. The presented results on scientific activities are based on different literature reviews. For the time range from 2010 to 2013, for