Impedance Measurement of a Fuel Cell on Load El-Hassane AGLZIM and Amar ROUANE Laboratoire d’Instrumentation Electronique de Nancy Vandoeuvre les Nancy - France Email: el-hassane.aglzim@lien.uhp-nancy.fr amar.rouane@lien.uhp-nancy.fr Bernhard KRAEMER Laboratory for Measurement Technology Saarbr¨ ucken - Germany Email: b.kraemer@lmt.uni-saarland.de Reddad EL-MOZNINE Laboratoire Physique de la Mati` ere Condens´ ee El Jadida - Morocco Email: elmoznine@yahoo.fr Abstract— The improvement of the effectiveness and the life time of fuel cells requires the optimization of components such as membranes and electrodes and enhancement the flow of gases. To this end, the impedance measurement is essential. In this paper we present an electronic measurement instrumentation developed in our laboratory, to measure and plot the impedance of the fuel cell on load. Impedance measurements were taken by using the load modulation method. This instrumentation has been developed around a VXI system stand which controls electronic cards. Software under HPVEE R  was developed for automatic measurements and layout. The theoretical result obtained by a simulation under PSPICE R  consolidates us in the possibility of obtaining correct and exploitable results. The experimental re- sults are preliminary results on a 12V vehicle battery (Impedance measurements on a PEMFC are in progress). The similitude in the graph form and in order of magnitude of the values obtained (both theoretical and practical) enables us to validate our instrumentation. One of the future uses for this instrumentation is to integrate it on a vehicle as an embedded system to monitor the degradation of fuel cell membranes. I. I NTRODUCTION The challengers in energy and climatic conditions are now very well established. The use of hydrogen in fuel cell is an essential vector, and has been the focus of intensive study in recent years as promising alternative energy sources. Thus, various studies have been carried out in the electronic-physic domain of these kinds of generator [1] [2]. The improvement of the effectiveness and the life time of fuel cells requires the optimization of components such as membranes and electrodes and enhancement the flow of gases. To this end, the impedance measurement is essential. Impedance measurement is a pow- erful technique, which can provide useful information on the electro-chemical systems in a real and very short time [3]. This technique can be considered as a good tool to determine the state of charge of batteries or fuel cells. Most of impedance measurements on fuel cells are made without load. Impedance measurement on a battery or fuel cell with load is very important in order to examine the influence of this latter, on its performance. For these reasons, we are interested in the development and the realization of a system in order to achieve impedance measurement of a battery or fuel cell on load, in our laboratory. This system is based on the electrochemical impedance spectroscopy (EIS) method for measuring and plotting the diagram Nyquist of battery or fuel cell impedance. The analysis and the shape of the diagram can provide information about the state of charge of the device under test. II. THEORETICAL CONSIDERATION A. Selected Method The Electrochemical Impedance Spectroscopy (EIS) has the advantage, compared to other methods, to have a less influence on battery or fuel cell during the working of these latter. It can provide more information on the state of the load. Measure- ments are generally carried out without load. It is useful to cover a large frequency range in order to obtain more infor- mation from the impedance spectrum generated. For a PEM fuel cell, the impedance spectrum was generated in a frequency ranging from 1Hz to 10kHz [4]. However, Walkiewicz and al [5] did studies between 1mHz and 65KHz. The number of points collected by decade varies between 8 and 10 points. The principle of measurement is to add a signal, at constant frequency, to the output of the voltage of the battery when this latter is delevring the desired current. The superimposed signal can be obtained by three methods: potentiostatic, galvanostatic or load modulation methods. Among of these three latter methods, we have selected the load modulation method. It consists in varying the resistance of the load according to the signal that we would like to superimpose. Thus, the impedance