The influence of a microporous layer (MPL) on polarization and electrochemical impedance behavior of proton exchange membrane fuel cells (PEMFCs) was investigated. Commercial carbon backing electrode with MPL applied on one of its sides were employed for both the anode and cathode. The ohmic, charge-transfer, and mass-transport resistances at various current densities were obtained by deconvolution of electrochemical impedance spectroscopy data. PEMFCs with an MPL showed higher performance and lower variability in the charge-transfer and mass-transport regions of the polarization curve (current density above 300mAcm−2 ) within a batch of identically built cells. For cells with and without MPL, the charge-transfer resistance decreased while mass-transport resistance increased with an increase in current density. The difference in charge-transfer resistance for cells with and without MPLs was found to be statistically insignificant due to the large variability in data for cells without MPLs. Cells with MPLs demonstrated lower mass-transport resistance compared to cells without MPL. The time constant for the mass-transport process probed at a low-frequency regime of the impedance was obtained from the Warburg impedance. Among the various possible oxygen-transport processes, the estimated time constant for oxygen transport in the porous transport layer (PTL) was found to be within an order of magnitude of the Warburg-impedance-derived value. Accordingly, it was assessed that the presence of an MPL helped reduce the water saturation in the PTL, thereby improving the oxygen transport to the cathode catalyst layer.

Infrared Reflection Absorption Spectroscopy (IRRAS) has been applied to study the nature of the co-ordination of Nafion® to a Pt electrode surface. The experiments have been carried out using a Pt electrode coated with a thin film of Nafion® assembled into a thin layer spectroelectrochemical cell. The potential modulation or the subtractively normalized interfacial Fourier transform infrared reflection spectroscopy (SNIFTIRS) experiments have been performed, in order to distinguish between the bulk properties of the Nafion® membrane and the properties of the membrane at the interace with the Pt electrode. The results showed that the interaction between the membrane and a Pt electrode resembles the interaction between a Pt electrode and a sulfuric acid solution.

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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 (1À5 lm) and ultra-low Pt loadings (0.02À0.12 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 ).

The commonly employed the H 2 /N 2 cell impedance method for the determination of PEMFC catalyst layer ionic resistance often results in significant deviations from the predicted idealized homogeneous catalyst layer properties. In this study, the effect of the distribution of resistance and capacitance within the thickness of the CL is modeled to examine whether it explains the observed deviations. It is found that uniformly and non-uniformly distributed CLs show limiting real impedance (vertical line on Nyquist plot) at low frequency, as long as the impedance has no faradaic contribution. However, using this value of real impedance for obtaining the ionic resistance of the catalyst layer leads to significant errors if the system is non-uniformly distributed. It is shown that Nyquist plots with non-vertical mid-frequency regions, resembling experimentally measured H 2 /N 2 cell response, can be generated with a "nested" transmission line circuit (agglomerate model) if there is a significant difference in resistance in different agglomerates.