Experimental characterization of anodic degradation in direct methanol fuel cell

Fuel Cell is a very promising technology as energy source for several applications because of high efficiency, low pollutant emissions and modularity. However, because the transition to a hydrogen economy seems to be distant and uncertain, interest in using methanol as fuel for fuel cells is growing. Direct Methanol fuel cells are promising power sources for portable devices, back-up power systems, and low-power vehicles, e.g., forklifts. Degradation is one of the most critical issues that hinder the commercialization of Direct Methanol Fuel Cells (DMFC). There are several interconnected and complex phenomenon that contribute to the degradation such as catalyst dissolution and agglomeration, membrane delamination and changing of hydrophobic properties of the gas diffusion layer. It is believed that that the components responsible for the great part of performance loss are the electrodes. The great part of experimental works on DMFC degradation follows the same approach: electrochemical characterization of fresh cell, degradation test and characterization of faded cell. Among the diagnostic tools, polarization curves are the primary in-situ method characterisation techniques of performance and degradation. Unfortunately the overall polarization curves of fuel cell do not permit to differentiate the cathode and anodic loss. Another diagnostic tool is the Electrochemical Impedance Spectroscopy (EIS) that is a characterization technique which allows to evaluate single phenomena contributions to overall fuel cell impedance. The aim of this work is to study the degradation that occurs at the anode of the fuel cell when the cathode is set as a reference electrode by measuring continuously the anodic overpotential. Polarization curves and EIS were performed in order to evaluate the influence of operating conditions on the anodic degradation test. Experimental tests show the presence of two different degradation contributions: a temporary degradation that can be recovered by switching off and restarting the cell and a permanent degradation that cannot be recovered. Linear regression analyses were performed in order to quantify both the contributions. Parametric analyses on anode degradation were performed by changing current density, anodic stoiochiometry and operation strategy.