Michio Hori

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.

Renewing Accelerated Stress Tests Correlated to Actual Deterioration in Proton Exchange Membrane Fuel Cells to Evaluate the Durability of Perfluorinated and Hydrocarbon Proton Exchange Membranes

Perfluorinated and hydrocarbon proton exchange membranes (PFSA and HC-PEM) have been developed for proton exchange membrane fuel cells (PEMFCs). Especially, an aromatic HC-PEM has high strength though inferior flexibility because of a hard molecular frame and high gas barrier of O2 and H2 compared with PFSA-PEM. Based on such characteristics of HC-PEM, thin types of HC-PEMs have been developed for practical use. As generally known, in case of increasing the ionexchange capacity aiming at obtaining the enough proton conductivity, the other characteristics such as membrane formability, mechanical strength, the dimensional stability, the resistance to water and the oxidation resistivity become insufficient. Nowadays, many HC-PEM developers have been challenging to overcome such problems, which leaded to the development of the HCPEM exceeding PFSA-PEM in the durability at the open circuit voltage (OCV) and for the relative humidity (RH) cycles introduced as the accelerated stress tests (ASTs) [1]. However, it is too early to conclude that HC-PEM is superior to PFSA-PEM for automobile use. Regarding ASTs of PEM for automobile use, a lot of data should be accumulated in order to decide the common protocols for both the PFSA-PEM and HC-PEM or the original protocols for the HC-PEM, alternating the present AST protocols which were developed based on the deterioration mechanism of a PFSA-PEM in PEMFC. In order to obtain the conditions of ASTs and the deterioration indexes from fuel cell that suit a chemical and mechanical deterioration of both the PEMs especially occurred in the PEMFC system for automobile use, the authors are examining the deterioration behavior of PEMs from the single cell test and the element test under the Cell Evaluation Project supported by New Energy and Industrial Technology Development Organization (NEDO) while obtaining the advice from Toyota Motor Corp., Nissan Motor Co., Ltd, Honda R&D Co., Ltd. and Fuel Cell Commercialization Conference of Japan (FCCJ). The chemical AST protocol for the single cell test proposed from FCCJ and DOE is OCV test at 90 °c of cell temperature (Tc) with 61 °c of anode and cathode humidifier temperature (Tha, Thc), presently. The mechanical AST protocol is RH cyclic test at 80 °c of Tc, 90 °c of Tha and Thc for 2 min. and dry for 2 min with air or N2 in anode and cathode [2, 3]. In this study, the following deterioration behaviors are hypothecated for HC-PEM in the single cell. Firstly, an oxidative decomposition with hydrogen peroxide by-product at the cathode and/or the hydrolysis with water of a main chain progress. Secondarily, the mechanical property of the HCPEM decreases with main chain decomposition. Finally, the HC-PEM is mechanically failed.

溶融炭酸塩型燃料電池用ガスシール構造に関する研究 : 第2報,ガスシール構造の実験的検討(熱工学,内燃機関,動力など)

A reactant gas seal is one of critical issues to achieve the reliability of the MCFC stack which is a key equipment in MCFC power plant. The wet-gas seal with carbonate melted at operating temperature (650°C) is generally expected to be suitable for such a seal. We develop the wet seal configuration composed of thin sheet metal parts to be cost-competitive with other power plants. In this report, the proposed configuration of wet-gas seal using thin sheet metal parts is produced for trial, which is assembled in single cells. The leak rates from wet seals were examined under the condition of MCFC operating temperature. Then, the superior seal performance was found and it is confirmed that the wet seal configuration composed of thin sheet is reliable.

溶融炭酸塩型燃料電池用ガスシール構造に関する研究〔熱工学, 内燃機関, 動力など〕

Molten carbonate fuel cells (MCFCs) are expected to be large-scale, highly efficient energy sources in the future. A reactant gas seal is one of the critical issues in achievement of reliability of the MCFC stack, which is a key piece of equipment in an MCFC power plant. At present, the wet gas seal with carbonate molten at the operating temperature (650°C) is generally considered to be suitable as such a seal. On the other hand, to be cost-competitive with existing power plants, the MCFC stack must consist almost entirely of thin sheet metal parts. In this report, a wet gas seal configuration composed of thin sheet metal parts is proposed. Then, the long-term performance of the wet gas seal in an actual MCFC is evaluated.