Mcfc

Kazumi TANIMOTO, Masahiro YANAGIDA, Toshikatsu KOJIMA Yukiko TAMIYA and Yoshinori MIYAZAKI

Osaka National Research Institute Midorigaoka 1-8-31, Ikeda, Osaka 563, Japan

Abstract

The R&D on Molten Carbonate Fuel Cell (MCFC) is proceeding as one of the New Sun Shine Project sponsored by Japanese government. In ONRI (Osaka National Research Institute), the tested MCFCs were assembled with the state-of-the-art components and operated under the load condition for 40000 hours and 34000 hours. We analyzed the performance reduction.

1. Introduction

The R&D on MCFC in Japan is proceeding as one of the New SunShine Project sponsored by Japanese government. The main target of the second stage started in 1987 is the demonstration of the lOOOkW class MCFC power generating system in 1999. ONRI has participated in the research of the alternative materials and the evaluation of material for MCFC. We evaluated the conventional material from the viewpoint of stability by the operation of 100-cm2 class single cell for up to 40000 hours.

2. Experimental 2-1. Operation

The tested single 100-cm2 class cell were assembled with the state-of-the-art components, which are shown in Table 1. The normal operation condition is shown in Table 2. We started to operate the two MCFCs in 1991. The cell performances were measured once a day. The cell resistance was measured by using the milliohm meter, 1kHz AC. The carbonates as electrolyte were added at the appropriated time.

In this test the C02 supply was accidentally interrupted due to the equipment failure. There was no heat-cycle for both cells. Two cells were kept at the operating temperature, 650 °C. The single cells were operated for 34000 hours and 40000 hours.

2-2. Analysis of degradation of cell performance

The reduction of cell voltage at 150 mA/cm2 was analyzed to clearify a contribution of life-limting-factor.

Table 1. Materials for tested MCFC

Component

Material

Anode

Ni-Al base alloy

Cathode

NiO

Matrix/

LiA102/

Carbonate

Li2C03:K2C03=62:38mol%

Housing

Stainless Steel

Table 2. Normal operation condition

Pressure

Atmospheric

Temperature

650 °C

Anode gas

H2/C02:80/20 (50 °C Humidify)

Cathode gas

Air/C02:70/30

Gas Utilization

40%@150mA/cm2 (both side)

Normal load

150mA/cm2

3. Results and discussions 3-1. The long term operation (a). 400p0-hour-operation MCFC

The performance with time was shown in Figure 1. This cell experienced the interruption of C02 three times for 40000-hour-operation. Though the first interruption did not influence the cell performance, the second and the third interruption influenced the cell performance positively. It has not been recognized that the C02 interruption brought this effect. The anode outlet pipe was closed at 26000 hours due to something entering it. The close of outlet pipe for two days may make the break of gas seal at the part of wet seal..

The reduction of OCV began at 12000 hours. It was due to the short circuit induced by the deposited nickel in matrix. This phenomenon was initiated by the dissolution of NiO cathode. Ota et al. reported that solubility of NiO in carbonate was proportional to the pressure of C02!). The cathode gas was diluted by the addition of nitrogen after 16000 hours to reduce the dissolution of NiO cathode. After then cathode gas composition was C02/02/N2:22/l 1/67. However, OCV gradually reduced during the operation.

The carbonates were added seventeen times during operation. * The addition of carbonate reduced the cell resistance and improved the cell performance until 20000 hours. After that, the addition of carbonate do not maintain the cell resistance The matrix cannot hold the carbonate electrolyte due to the degradation of LiAlO,.

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