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Research Papers

# Partially Oxidized Tantalum Carbonitride as New Cathodes Without Platinum Group Metals for Polymer Electrolyte Fuel Cell

[+] Author and Article Information
Akimitsu Ishihara

Chemical Energy Laboratory, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama-shi, Kanagawa 240-8501, Japana-ishi@ynu.ac.jp

Motoko Tamura, Koichi Matsuzawa, Shigenori Mitsushima, Ken-ichiro Ota

Chemical Energy Laboratory, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama-shi, Kanagawa 240-8501, Japan

J. Fuel Cell Sci. Technol 8(3), 031005 (Feb 18, 2011) (6 pages) doi:10.1115/1.4003161 History: Received March 15, 2010; Revised July 15, 2010; Published February 18, 2011; Online February 18, 2011

## Abstract

A partially oxidized $TaC0.58N0.42$ has been investigated as a new cathode for polymer electrolyte fuel cells. The catalytic activity for oxygen reduction reaction (ORR) significantly depended on an oxidation state of the $TaC0.58N0.42$. $TaC0.58N0.42$ and $Ta2O5$ had a poor catalytic activity for the ORR. The onset potential on the partially oxidized $TaC0.58N0.42$ for the ORR had a maximum value of 0.9 V versus reversible hydrogen electrode in $0.1 mol dm−3$$H2SO4$ at $30°C$, which indicated that the partially oxidized $TaC0.58N0.42$ had definite catalytic activity for the ORR. Hard X-ray photoelectron spectroscopy and X-ray diffraction analyses revealed that the surfaces of the partially oxidized $TaC0.58N0.42$ were oxidized, although the inner parts of the partially oxidized $TaC0.58N0.42$ remained tantalum carbonitride. These results suggested that an appropriate oxidation of the $TaC0.58N0.42$ was essential to enhance the catalytic activity for the ORR.

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## Figures

Figure 1

XRD patterns of the powder specimens with different holding times of heat treatment. The holding time of the upper specimen was longer, and the lowest specimen was the starting material, TaC0.58N0.42.

Figure 2

Effect of the mixture of the partial oxidized TaC0.58N0.42(DOO=0.43) with carbon black on the potential–current curves under N2 and O2 in 0.1 mol dm−3H2SO4 at 30°C with a scan rate of 5 mV s−1. (a) No addition of carbon black and (b) mixture with carbon black (5 wt %).

Figure 3

Dependence of the onset potential EORR on the carbon content in the powder catalyst

Figure 4

Effect of the DOO on the iORR at 0.8 V versus RHE using the mixture of the partially oxidized TaC0.58N0.42 with the carbon black (7 wt %) catalysts

Figure 5

Relationship between the DOO and the EORR

Figure 6

XPS of (a) Ta 4f, (b) O 1s, and (c) N 1s

Figure 7

Relationship between the square root of the photoelectric quantum yield Y1/2 and the photon energy

Figure 8

Relationship between the DOO and the ionization potential

Figure 9

Relationship between the ionization potential and the onset potential of the ORR

Figure 10

Onset potential for oxygen reduction reaction of nonprecious metal oxide-based cathodes developed at Yokohama National University (0.1 mol dm−3H2SO4, 30°C)

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