18 - Development of high-performance electrochemical reactors

Abstract

This chapter focuses on the development of electrochemical reactors for NOx decomposition and presents a novel reactor that combines the electrochemical and thermoelectric devices. To ensure the effective NOx decomposition in the presence of excess oxygen, a new type of electrochemical cell with a functional multilayer electrode is developed, which can be represented by the asymmetric arrangement of the general symmetric type SOFC cells that consist of an electrolyte sandwiched by the electrodes. Applying nanoscale control at the reaction sites helps in enhancing the selective absorption and decomposition of NOx molecules over the predominant oxygen molecules. The accessibility of gas molecules to restricted spaces and electrochemically active surfaces of ceramics also helps in improving the reduction and oxidation reactions. By combining the NOx reduction accelerator with the oxygen acceptor, the nanoscale reaction spaces can promote very efficient NOx decomposition even under high Po2 conditions, and this method is expected to be applied to treat the exhaust gas from diesel engines. Precise nanostructural control on the electrocatalytic layer also helps in improving the cell properties and reduces its energy consumption to half of those using presently employed catalysts. There are still many problems that have to be solved before commercializing these electrochemical reactors. Some of them include the stacking up of cells to obtain sufficient reaction area, improving the cell properties with the actual gas compositions and flow rates, issues related to the cell durability when operating with actual exhaust gases containing H2O, CO, CH, SOx, and lifetime and overall cell fabrication costs. The electrochemical cells for de–NOx reaction have various properties that are well suited for the de–NOx/PM purification and their electrical power consumption is also very low for the application.