Method for Systematic Validation of a Physically Based PEMFC Model By Spatially Resolved Impedance Measurements

Abstract

Loss mechanisms in PEM Fuel Cells related to charge transfer reactions or diffusive gas transport result in a strongly nonlinear performance, which is furthermore affected by operating conditions as temperature, relative humidity of the gases and stoichiometries. These dependencies have to be considered and validated in fuel cell models to ensure accuracy. Thus, the interpretation of the simulated results becomes more reliable.Direct comparison of simulated and measured current/voltage-relation only allows to evaluate deviations in resulting cell voltages but exclude internal state variables of the model such as overvoltages due to different loss mechanisms. In consequence, simulated and measured values of voltage or current can concur by unnoticed compensation of different errors in magnitude and sign. Additionally, limited numbers of measurements and comparisons increase the probability and impact of this effect.Aggravating, every single process within the cell depends on the comprehensive combination of all operating conditions and runs simultaneously with all other ones. A direct comparison of individual simulated and measured polarization curves therefore is not a suitable and sufficient validation.We address this challenge by applying measurements of electrochemical impedance spectroscopy (EIS) during systematically varied operating conditions spatially resolved along the gas flow direction [1]. The loss processes within the cell can be separated by distribution of relaxation times (DRT) and quantified by a physico-chemical meaningful transmission line model. The resulting amount and distribution of resistances caused by loss processes is compared with the corresponding simulated values of a multiphysical model for observation and monitoring during operation [2]. These insights support the investigation of deviations between simulated and measured polarization curves and therefore the validation the model.In this contribution, the resulting physical interpretation is discussed. Consequences and conclusions for the further development of the cell model are demonstrated.[1]: P. Oppek et al., „ Spatially Resolved Deconvolution of Loss Processes in PEM Fuel Cells”, 241st ECS Meeting, Vancouver[2] T. Goosmann et al. „Impedance-Based, Multi-physical DC-Performance-Model for a PEMFC Stack”, 241st ECS Meeting, Vancouver