ＲＩＴＥ−YＡＭＡＴＯＫＯＲＩＹＡＭＡ ＬＡＢＯＲＡＴＯＲＹ
in Matsushita Electric Industrial Co., Ltd. 

Electrochemical NOx decomposition using YSZ solid electrolyte substrate has been studied to remove NOx from combustion exhaust gases.

As a result, there has been developed a device, which can decompose electrochemically a small amount of NOx in the presence of excess O2.

This device comprised a tubular YSZ substrate (I.D. 10mm x 100mm, thickness 0.8mm), an electroless plated Pt electrode (area 31mm2) on an inside surface and a fired Pt/YBCO electrode (area 35mm2) on an outside surface. The Pt/YBCO electrode was prepared as follows. A mixed paste was prepared by adding YBCO powders [YBa2Cu3O7-x powders, diameter (1-3) micron meter] in a conventional Pt paste to make a YBCO weight concentration of 20%. The mixed paste was printed on the outside surface, dried and fired at 820? for 10min in air. This device was placed in a quartz tube (diameter 32mm) and the experiments were carried out at 450℃ by passing a mixture of 380ppm NOx and 10%O2 in helium at a flow rate of 300cc/min. The concentrations of N2 and N2O in the outlet gas were measured with a gas chromatography. Those of NOx and NO were also measured with a chemiluminescent NOx analyzer.

When the Pt/YBCO electrode operated as anode, no change was measured in NOx concentration with no relation to current. On the other hand, when the Pt/YBCO electrode operated as cathode and a DC current of 175mA was applied, there were detected the amount of removed NOx of 200ppm and that of removed NO of 100ppm. At the same time, the amount of increased N2 of 90ppm and that of increased N2O of 10ppm were also detected. These results suggest that NOx was converted to N2 and a small amount of N2O was produced as a by-product. The maximum current efficiency for electrolyzing NOx was estimated to be about 2%. When the device was placed in a mixture of 2%NOx and 10%O2 in helium at 450℃, the XRD pattern of the Pt/YBCO electrode showed the production of Ba(NO3)2, which may be essential in the decomposition.

However, the addition of 5% CO2 to the mixture gas was very harmful to the decomposition. In the mixture, the XRD pattern of the Pt/YBCO electrode showed the production of BaCO3, which may prevent the decomposition from proceeding efficiently.