Yoshiro Ohgi

Zirconium Oxide-Based Compound as New Cathode Without Platinum Group Metals for PEFC

Partially oxidized zirconium carbonitride (Zr-CNO) powders were evaluated as a nonprecious metal cathode for polymer electrolyte fuel cells (PEFCs). Zr-CNO powders were prepared from zirconium carbonitrides (ZrC 0.5 N 0.5 ) with heat-treatment under N 2 containing 2% H 2 and 0.25% O 2 gas at 1000-1400°C. Voltammetry was performed to evaluate the catalytic activity for oxygen reduction reaction (ORR) under nitrogen and oxygen in 0.1 mol dm ―3 H 2 SO 4 at 30°C. Although the onset potential of the ORR for untreated ZrC 0.5 N 0.5 was 0.55 V vs a reversible hydrogen electrode (RHE), the onset potential of the appropriate oxidized Zr-CNO reached 0.97 V vs RHE. X-ray diffraction and X-ray photoelectron spectroscopy data suggested that the surface of Zr-CNO was oxidized to ZrO 2 , and ZrC 0.5 N 0.5 remained in the inner part of the Zr-CNO particles.

Zirconium Oxynitride-Catalyzed Oxygen Reduction Reaction at Polymer Electrolyte Fuel Cell Cathodes

Most nonplatinum group metal (non-PGM) catalysts for polymer electrolyte fuel cell cathodes have so far been limited to iron(cobalt)/nitrogen/carbon [Fe(Co)/N/C] composites owing to their high activity in both half-cell and single-cell cathode processes. Group IV and V metal oxides, another class of non-PGM catalysts, are stable in acidic media; however, their activities have been mostly evaluated for half-cells, with no single-cell performances comparable to those of Fe/N/C composites reported to date. Herein, we report successful syntheses of zirconium oxynitride catalysts on multiwalled carbon nanotubes, which show the highest oxygen reduction reaction activity among oxide-based catalysts. The single-cell performance of these catalysts reached 10 mA cm–2 at 0.9 V, being comparable to that of state-of-the-art Fe/N/C catalysts. This new record opens up a new pathway for reaching the year 2020 target set by the U.S. Department of Energy, that is, 44 mA cm–2 at 0.9 V.

Group 4 and 5 Oxide-Based Compounds as New Cathodes Without Platinum Group Metals for PEFC

Introduction Polymer electrolyte fuel cells (PEFCs) are expected for the residential and transportable applications, especially for the automobile use, due to their high power density and low operating temperature. However, the estimated amount of Pt reserve is too small to supply for the huge number of fuel cell systems, especially fuel cell vehicles. Thus, in order to commercialize the fuel cell systems, the development of a non-Pt catalyst is strongly required. We have reported that group 4 and 5 transition metal oxidebased compounds were stable in an acid solution and had a definite catalytic activity for the ORR [1-3]. However, their activities were insufficient, and the factor which affected the catalytic activity has not yet been clarified. In this study, the factor which affected the catalytic activity of the partially oxidized tantalum carbonitride (TaC0.58N0.42) was investigated.

Transition Metal Oxide Based Materials for Cathode of Polymer Electrolyte Fuel Cells

Group 4 and 5 metal oxide-based compounds might be candidates for new cathode materials of polymer electrolyte fuel cells, if they have high catalytic activity for oxygen reduction. These materials are stable in acidic and oxidative atmosphere. Among these materials, partially oxidized Ta carbonitride (Ta-CNO) and Zr carbonitride (Zr-CNO) had high catalytic activity for the ORR. Their onset potentials were almost catching Pt/C. The cost of raw material for Ta oxide or Zr oxide is far below the present Pt/C cathode. A significant cost reduction of PEFCs might be possible using these materials.

Catalytic activity of zirconium based cathode without platinum for oxygen reduction reaction

Partially oxidized zirconium carbonitrides (Zr-CNO) powders were evaluated as a non-precious cathode for polymer electrolyte fuel cells. Zr-CNO powders were prepared from zirconium carbonitrides (ZrC0.5N0.5) with heat-treatment under controlled oxygen partial pressure from 10-3 to 10-22 atm at 1000oC. The voltammetry was performed to evaluate the catalytic activity for the oxygen reduction reaction (ORR) under nitrogen and oxygen in 0.1 mol dm-3 H2SO4 at 30oC. The catalytic activity for the ORR significantly improved with partial oxidation. In particular, the onset potential increased drastically with slight increase of ratio of cubic ZrO2 phase, and became constant over 0.90 V vs. RHE. XRD spectrum and the color of specimen indicated that the growing oxide phase had oxygen vacancies by substituting some of the oxygen atoms with nitrogen and carbon atoms. It is predicted that carbon and nitrogen atoms in starting material, ZrC0.5N0.5, may affect the production of oxygen vacancies according to TOF-SIMS measurements. Therefore, the defects such as oxygen vacancies in the Zr-CNO might affect the catalytic activity for the ORR.