The AMRI-AIST has been engaged in R&D of technology of electrochemical purging for NOx by using electrochemical reactor based on oxygen ion-conductive ceramics, and succeeded in decomposing NOx in oxygen-rich (3 % or more) gas mixture into N₂ and O₂ with an electrochemical reactor selectively and continuously, using very little electric power. The technology is attracting worldwide attention as zero emission purging, characterized by directly decomposing NOx by electrical means, in comparison to the conventional catalytic method with combined reductive agents. On the other hand, the electrochemical reactor system requires electric power to drive the reactor, in contrast to the catalyst method. As one of means to solve this problem, it has been attempted to provide electric power for driving the electrochemical reactor through power generation based on temperature difference between exhaust heat in waste gas and atmosphere by using thermoelectric conversion ceramics (Fig1).

It has been demonstrated that the thermoelectric conversion as high as 40 mW/cm² is obtained for a temperature difference of 500 °C with a pair of thermoelectric ceramic devices. Moreover, the characterization of a compound module prepared by combining in series 37 pairs of 2x 2 x 20 mm rectangular solid modules has proved to generate 300 mW power (at 3.5 V) for around 650 °C temperature difference (with one end of junction heated to 800 °C while air-cooling the other, verifying the availability of the module as power supply for NOx purging electrochemical reactor.