Combination of Electrochemical Impedance Spectroscopy and Local Current Density Distribution for Fault Monitoring in PEMFC Stacks

Kurzfassung

The PEMFC stack performance is characterized by gradients that may occur in various parameters. These are e.g. reactant related parameters such as concentration, flow, and humidity or local temperatures. Additionally, material inhomogeneity, such as in component thicknesses and in flow-field deepness, can result in uneven flow distribution between the single cells and in local starvation, flooding, or dry-out phenomena. These occurrences may be due to increasing or lowering the parameter gradients within the individual cells. The presented work is aimed to analyse the nature of these phenomena in stacks operating under system relevant conditions. Through parameter studies the impact of the different operating conditions on the performance homogeneity were identified. This was realised for individual single cells within a 10-cell PEMFC stack from ZSW. The homogeneity across the active area at the cell level was determined using the patented printed circuit board technology (PCB) by the DLR enabling the measurement of the local current density distributions. At the stack level three PCBs were used to investigate effects caused by material inhomogeneity or by the cell positioning within the stack, e.g. by end cell effects. As an operando fault monitoring system electrochemical impedance spectroscopy (EIS) was used. Combined studies of local current density measurements and EIS for all single cells in the stack will be presented. Though these studies we will highlight the occurring links between the EIS response and the local effects within the cells. Technical support by O. Garrot, S. Graf, and A. Anderle is gratefully acknowledged. The presented work is realized in the COALA project (control algorithm and controller for increasing the efficiency of hybrid PEMFC systems in different applications) in the framework of the Polish-German Sustainability Research Call (STAIR II). The funding for this research was received from The National Center For Research and Development (NCBR, Poland) and the Federal Ministry of Education and Research (BMBF, Germany) with the Grant No.: STAIR/6/2016 and 01LX1601, respectively.