Toyoaki Matsuura

In Situ Analysis of Performance Degradation of a PEMFC under Nonsaturated Humidification

A 2700 h life test of a single proton exchange membrane fuel cell (PEMFC) with Nafion 112 membrane under nonsaturated humidification was conducted. In situ measurements of hydrogen crossover rate through the membrane and electrochemical active surface area (EAS) of Pt catalyst, in combination with cell polarization curves, were applied to investigate the degradation mechanism. A slow decrease of the EAS of Pt catalyst from 400 to 1900 h running was found to cause a slight voltage decay only at high current densities. However, a subsequent dramatic degradation of the membrane results in an accelerated collapse of the fuel cell.

Lifetime behavior of a PEM fuel cell with low humidification of feed stream

A 2520 h lifetime test of a single proton exchange membrane (PEM) fuel cell under low humidification (65.8% relative humidity for both anode and cathode feed stream) at a low current density of 200 or 300 mA cm−2 was conducted. H2 crossover rate through electrolyte membrane and open circuit voltage of the cell with time were measured to understand the membrane degradation in the membrane electrode assembly (MEA) during the life test. The results show that low humidification of feed stream accelerates membrane physical degradation, and results in membrane pin-holes and reactant gas crossover. A novel sub-cell approach coupled with SEM and TEM were employed as post mortem analyses. The performance of the sub-cell at H2 inlet region is unacceptably lower than that at the H2 outlet region. SEM images of the used MEA in cross-section apparently revealed that membrane thinning occurred mainly at the H2 inlet region. TEM analysis of the electrocatalysts in the pre- and post-test cell demonstrated that the agglomeration of the Pt particles took place both at the anode and the cathode. Therefore, the non-uniform degradation of electrolyte membrane and the agglomeration of Pt catalysts are concurrently responsible for the degraded performance of the PEM fuel cell.

Preparing Gas-Diffusion Layers of PEMFCs with a Dry Deposition Technique

To improve the ease of production and reproducibility, a novel approach was developed for preparing gas-diffusion layers (GDL) of proton-exchange membrane fuel cells (PEMFCs). In this approach, the GDL was prepared by drydeposition of a mixture of carbon black and polytetrafluoroethylene powders onto water-proofed carbon paper in combination with a subsequent rolling process. Three kinds of carbon black, including Ketjenblack EC-600JD, Vulcan XC-72, and Denka, were investigated. Furthermore, the reproducibility of the GDL with Vulcan XC-72 was also tested. The results indicate that this dry-deposition technique is feasible for mass production applications with simple operation, solvent-free coating and excellent repeatability.

Experimental Evidence of Stability of Pt Clusters on and in Carbon Particles

The stability of Pt clusters deposited on and embedded in carbon particles has been examined by in situ transmission electron microscopy. Commercial Pt clusters deposited on carbon particles began to move and coalesce upon heating above 150°C by surface melting coalescence, and the alterations were observed predominantly upon heating above 400°C. The embedded Pt clusters with the size of 1–3 nm disappeared by the diffusion of Pt atoms through the covered amorphous carbon layer upon heating above 1200°C. The Pt clusters embedded in carbon particles are more stable at higher temperatures about three times than the commercial Pt clusters deposited on carbon particles.