Ela Halliop

An Experimental Investigation of Water Transport in PEMFCs The Role of Microporous Layers

This experimental study was undertaken to resolve the contrasting viewpoints on the role of a microporous layer (MPL), attached to carbon paper porous transport layer (PTL), on the net water transport in a polymer electrolyte membrane fuel cell (PEMFC). Experimental results on single cells with and without cathode MPL show no statistically significant change in the net drag coefficient that could be attributed to the presence of the MPL. In contrast to the two prevailing but contrasting viewpoints, our results indicate that the MPL on the cathode neither enhances back-diffusion nor increases water removal from the cathode catalyst layer to the PTL.

Electrochemical Activity and Catalyst Utilization of Low Pt and Thickness Controlled Membrane Electrode Assemblies

An improved catalyst deposition methodology based on a piezo-electric printing technique has been developed and used to fabricate catalyst coated membranes (CCM) with thin catalyst layers (1-5 μm) and ultra-low Pt loadings (0.02-0.12 mg Pt /cm 2 ). The performance of these CCMs was examined in proton exchange membrane fuel cells (PEMFCs). The catalyst utilization was observed to increase with decreasing catalyst layer thickness (decreasing Pt loading). The printed CCM with two layers containing an ultra-low Pt loading (0.02 mg Pt /cm 2 ) exhibited Pt utilizations of 100%. Neglecting the anode contributions, the mass activity at 850 mV for the printed CCM is nearly 76.5 mA/mg Pt which is 3.5 times higher than that for the CCM fabricated by conventional spraying method (22.5 mA/mg Pt ).

Effect of Relative Humidity on Electrochemical Active Area and Impedance Response of PEM Fuel Cell

The influence of humidity of supplied gases on on electrochemically active surface area and charge transfer resistance in cathode process of PEM fuel cell was studied. Impedance spectra for cells operated with various gas stream combinations - H2/Air, H2/O2, H2/H2 and H2/N2 - was analyzed to determine the physical/chemical origin of the spectra features. Cathode charge transfer resistance increased with a decrease in the humidity of supplied gases. As well, a reduction in the electrochemically active surface area with a decrease in relative humidity was observed.

Non-destructive characterization of sealed lead/acid battery cells with electrochemical impedance spectroscopy

Abstract The potential of using electrochemical impedance spectroscopy (EIS) as a routine testing technique for the characterization of sealed lead/acid batteries was investigated with several generations of Gates ‘J’ type cells sampled from batteries with known histories. It was found that EIS measurements are sensitive to many fundamental cell characteristics such as cell design and standing time or shelf period but more importantly they were also very sensitive to temperature variations. For this reason and for the considerable effort required to standardize such a technique it is believed that EIS measurements are not a practical technique for a battery shop environment. In a controlled laboratory environment the same sensitivity to a multitude of parameters becomes very valuable for studying the internal mechanisms of these sealed systems.

Monitoring voltage fluctuations for the characterization of lithium cells

Abstract A technique based on monitoring small voltage fluctuations was applied to the study of Li/SO 2 and Li/SOCl 2 cells during their normal resistive discharge. In a purely resistive circuit the cell internal resistance is a key variable which can fluctuate with internal modifications occurring during the cell discharge. By filtering and properly recording the spontaneous electrochemical transients it was possible to reveal some interesting differences between the Li/SO 2 and Li/SOCl 2 systems. The electrochemical noise patterns can thus be seen as a characteristic signature that is sensitive to the cells operation which, in the case of Li cells, is a compromise between a passivated metal with an extra long shelf life and an active state triggered by the galvanic coupling to an ever-ready cathode.