Shigeyuki Kawatsu

Advanced PEFC development for fuel cell powered vehicles

Abstract Vehicles equipped with fuel cells have been developed with much progress. Outcomes of such development efforts include a Toyota fuel cell electric vehicle (FCEV) using hydrogen as the fuel which was developed and introduced in 1996, followed by another Toyota FCEV using methanol as the fuel, developed and introduced in 1997. In those Toyota FCEVs, a fuel cell system is installed under the floor of each RAV4L, to sports utility vehicle. It has been found that the CO concentration in the reformed gas of methanol reformer can be reduced to 100 ppm in wide ranges of catalyst temperature and gas flow rate, by using the ruthenium (Ru) catalyst as the CO selective oxidizer, instead of the platinum (Pt) catalyst known from some time ago. It has been also found that a fuel cell performance equivalent to that with pure hydrogen can be ensured even in the reformed gas with the carbon monoxide (CO) concentration of 100 ppm, by using the Pt–Ru (platinum ruthenium alloy) electrocatalyst as the anode electrocatalyst of a polymer electrolyte fuel cell (PEFC), instead of the Pt electrocatalyst known from some time ago.

Ionic conductivity of gadolinium-doped barium praseodymium oxide

Abstract To clarify the ionic conduction of Ba(Pr 0.6 Gd 0.4 )O 3−α , the electrical conductivity was measured in moist air and hydrogen atmospheres. The ionic transport number was estimated by a steam concentration cell, a hydrogen permeation cell, and a fuel cell. Temperature dependence of the conductivity in a moist air atmosphere differed from that in a moist H 2 atmosphere. The conductivity under reducing conditions increases with time according to the crystal structure change of Ba(Pr 0.6 Gd 0.4 )O 3−α due to oxygen loss in the lattice site. Under moist air conditions, the dominant conduction species in the Ba(Pr 0.6 Gd 0.4 )O 3−α electrolyte were mainly holes. However, the species changed into proton, oxide ion and hole by means of structure change in a reducing atmosphere. It was considered that the ionic conduction occurred due to the crystal structure change. It was predicted that this peculiarity of the conductivity of barium praseodymium oxide influenced the nonstoichiometric behaviour of Pr in the crystal structure.

Conductivity of BaPrO3 based perovskite oxides

Abstract To develop higher protonic conductivity, we have been studying a new perovskite-type oxide and found that BaPrO 3 based perovskite oxides showed high conductivity in a moist H 2 atmosphere. Their conductivity was about 0.1 S/cm at a temperature of 500°C and remained almost constant up to 700°C, which is much higher than that of Ba(Ce 0.8 Gd 0.2 )O 3− α . Ba(Pr 1− x Gd x )O 3− α prepared by solid state reaction exhibited an orthorhombic and/or cubic perovskite structure and with a high Gd content was stable in a reducing atmosphere. When Ba(Pr 0.7 Gd 0.3 )O 3− α was used as an electrolyte, the open circuit voltage of the cell was about 1 V and this cell was able to operate at 500°C. During the testing of the cell, the formation of water on an air electrode led us to conclude that mobility of protons in the electrolyte occurred. The dominant conduction species in Ba(Pr 1− x Gd x )O 3− α electrolyte were considered as oxygen ions and/or protons.