In-situ Diagnostics for Cell Performance and Degradation

INTRODUCTION Advanced diagnostic methods that provide deeper insights into the relationship between cell design, operating conditions and cell performance and degradation are essential in oder to meet the cost, durability, power density and freeze-startup targets necessary for commercialization. Consequently, AFCC and Ballard have been developing diagnostic test methods related to localized performance measurement as well as the breakdown of cell voltage into kinetic, ohmic and mass transport related components [1-3]. One of the challenges in stack design is the achievement of uniform operating conditions for all cells, such as for example uniform reactant flow distribution over all cells and/or uniform temperature distribution within each cell while taking into account the unavoidable manufacturing tolerances for stack components. Additional complications arise from a number of coupling phenomena between i) current flow and reactant gas flow and ii) reactant gas flow and liquid water presence within each cell as well as couplings between neighbour cells [4-5]. This paper illustrates how current mapping in combination with other in-situ techniques used on a 10cell Mk 9 stack can be used to gain deeper insights into performance and degradation phenomena.