Analyse des Betriebsverhaltens von Hochtemperatur-Polymerelektrolyt-Brennstoffzellen

A promising application for high temperature polymer electrolyte fuel cells is the efficient electrical onboard power supply of commercial vehicles. By combining the fuel cell with a fuel processing system the same fuel as for the main engine can be used. In this case the fuel cell will be supplied with reformate gas consisting mainly of hydrogen, nitrogen, carbon dioxide, water and carbon monoxide. In such an environment the use of high temperature polymer electrolyte fuel cells is favorable because of their high tolerance to carbon monoxide. Under these conditions it is a challenge to optimize the operation of fuel cell stacks regarding power density, efficiency and longevity. The chosen approach is the combined analysis of the local and global operating characteristics of the fuel cells. By the combined analysis interrelationships are revealed, which would otherwise remain concealed. For local analysis the current density distribution across the active cell area was measured by introducing a tailor made measuring board into the stack assembly. With the developed method the influence of fuel composition, stoichiometry, flow and thermal management on the operating characteristics is evaluated. This covers the direct influence on power and efficiency as well as the influence on the development of power and efficiency over time. The latter is usually addressed as degradation of fuel cells. The improved understanding of reformate supplied high temperature polymer electrolytefuel cell stacks leads to optimized operating strategies. One major conclusion is that the longevity of the fuel cell stacks can be increased by a homogenization of the current density distribution over the active cell area