Hajime Murata

Measurement of Flooding in Gas Diffusion Layers of Polymer Electrolyte Fuel Cells with Conventional Flow Field

The objective of this work is to clarify the location and magnitude of flooding in polymer electrolyte fuel cells with a conventional flow field experimentally and by a numerical calculation. In the experiment, a newly developed cell with a conventional, interdigitated-switchable gas-flow field was used and the pressure drop between the inlet and outlet of the cathode was measured with the interdigitated flow field after the cell was operated with the conventional flow field. Significant pressure drop was observed after high current densities were flown; the pressure drop indicates the flooding level in a gas diffusion layer (GDL) during the conventional flow field operation. The cell performance and the flooding behavior depended significantly on wetting properties of catalyst layers and GDLs. In the simulation, liquid water distribution in the cathode GDL was predicted using a two-phase model, and validated by comparing the pressure drop measured and calculated using a gas-flow model. The simulation results agreed well with experimental data at high humidity condition and showed that a large amount of liquid water exists in the cathode GDL at high current densities.

Activities and Stabilities of Au-Modified Stepped-Pt Single-Crystal Electrodes as Model Cathode Catalysts in Polymer Electrolyte Fuel Cells

The purpose of this study is to test the concept of protecting vulnerable sites on cathode catalysts in polymer electrolyte fuel cells. Pt single-crystal surfaces were modified by depositing Au atoms selectively on (100) step sites and their electrocatalytic activities for oxygen reduction reaction (ORR) and stabilities against potential cycles were examined. The ORR activities were raised by 70% by the Au modifications, and this rise in the activity was ascribed to enhanced local ORR activities on Pt(111) terraces by the surface Au atoms. The Au modifications also stabilized the Pt surfaces against potential cycles by protecting the low-coordinated (100) step sites from surface reorganizations. Thus, the surface modification by selective Au depositions on vulnerable sites is a promising method to enhance both the ORR activity and durability of the catalysts.

Analysis of the Relation between Oxidation State and ORR Activity of Pt by Linear Sweep Voltammetry

Platinum oxide grown by potential cycles or hold was analyzed using linear sweep voltammetry, and its influence on the oxygen reduction reaction (ORR) was investigated using a carbon-supported Pt nano-particle catalyst. Two types of platinum oxides having different reduction potentials were identified and their amounts and ratio were found to depend on the applied potential history. The ORR current decreased linearly with increase in the total amount of the platinum oxides, regardless of the types of the platinum oxides.