Comparison of the Measured Hydrogen Crossover of Single Cell PEMFC by Cyclic voltammetry, linear sweep voltammetry and chronoamperometry

Quantifying of hydrogen crossover through fuel cell's membrane gives a useful parameter for monitoringof performance, degradation, and state of health of polymer electrolyte membrane fuel cells (PEMFCs). Inthis article three in situ electrochemical techniques including cyclic voltammetry, linear sweepvoltammetry, and chronoamperometry are used to evaluate the hydrogen crossover of single cell PEMFC.A fuel cell with a commercial MEA is used for analysis. The single cell temperature was maintained at ۷۰°C. Under fully humidified hydrogen (۱.۵ slpm, anode) and nitrogen (۱.۵ slpm, cathode), CV and LSVwere performed at scan rates of ۱۰۰ and ۱۰ mV/s, respectively. The results of all three methods are thesame.In voltammetry measurement, the electrode potential is swept at a constant scan rate and the currentresponse is recorded. There are three regions in Voltammogram: Hydrogen region, double layer region,and Oxygen region. The current in the double layer zone is due to both H۲ crossover and double layercharge/discharge. In this zone, the current is given by Eq. (۱) [۱]:(....)In equation ۱ ICrossover, Idl, Cdl, and V are the crossover current, the double layer current, the double layercapacitor and the cell voltage, respectively.For linear sweep voltammetry, a small scan rate (dV/dt) is selected. So the last term in equation ۱ isnegligible and the current in double layer zone is approximately equal to the hydrogen crossover current.The current in double layer zone in our LSV diagram is ۱.۷۶ mA/cm۲.For cyclic voltammetry, the sign of dV/dt for an increasing and a decreasing voltage sweep are positiveand negative, respectively. So, during the anoodic voltage sweep the current in double layer zone is thesum of the crossover current and a positive double layer current and during the cathodic sweep the currentis the sum of the crossover current and a negative double layer current. Thus, the average value betweenthe maximum and minimum current in the double layer region is used as criteria for the hydrogencrossover current. In our CV diagram, the upper and lower plateau currents in double layer zone are ۲.۱۲and ۱.۱۸ mA/cm۲ respectively. The average between upper and lower plateau currents which correspondsto hydrogen crossover current is ۱.۶۵ mA/cm۲.For the chronoamperometry, a few different constant potentials are applied to the cell, and the currentresponse at each potential are recorded (see Figure ۲). The potential is retained constant until adsorption,desorption, and capacitive loading processes are completed. Thereby the current at the end ofmeasurement is related to hydrogen crossover current [۲]. Our results reveal that the current at the end ofmeasurement at ۰.۳۵, ۰.۵۰ and ۰.۶۵ V are ۱.۷۵۳, ۱.۷۵۹ and ۱.۷۵۱ mA/cm۲ respectively (see Figure ۳). Weplotted these current vs applied potentials and linear fitting was done for data. The y-intercept of the fittedline which is corresponding to hydrogen crossover current is ۱.۷۶ mA/cm۲.In this study, we measure the hydrogen crossover current of single cell PEMFC by LSV, CV, andpotentiometry. The determined hydrogen crossover current by LSV, CV, and potentiometry are ۱.۷۶, ۱.۶۵and, ۱.۷۶ mA/cm۲ respectively. Based on our result, there is a good agreement between the predictedhydrogen crossover current by the three methods

کلیدواژه ها:

Fuel cells ، Hydrogen crossover ، CV ، LSV ، chronoamperometry