Electrochemical reduction of NO_x pollutant based on solid oxide electrolysis cells (SOEC) is one of the promising technologies for post-combustion NO_x emission control. NO_x can be splitted with electric current instead of reductants in SOEC. This technology can avoid the risk of secondary pollution due to the leakage of reductants and can effectively reduce the sub-system for reductant storage and conversion which is usually complicated and space consuming. The working principles of SOECs for NO_x reduction, the NO_x conversion electrode materials, the SOEC structure features and the construction of SOEC stacks are summarized in details. The state of art, the key issues and the forefront of research are reviewed. Considering the characteristics of the NO_x decomposition reaction, the performance evaluation indexes of NO_x electrochemical reduction cell are proposed. Several novel concepts for practical cell designing such as additional electro-catalyst layer, porous electrolyte, symmetrical electrodes and the NO_x storage agent are illustrated. The potential developing direction for NO_x electrochemical reduction in SOEC is discussed.

Contents
1 Introduction
2 NO_x reduction on SOECs
2.1 Basic theory
2.2 Judgments of cell performance
3 NO_x reduction electrode materials
3.1 Noble metal electrodes
3.2 Mixed oxide electrodes
3.3 Perovskite electrodes
4 Art of NO_x electrolyzer designing
4.1 Different types of NO_x electrolyzers
4.2 Electrochemical NO_x reduction stacks
5 Prospect of NO_x electrolyzer researching
5.1 Mechanism of NO_x electrochemical reduction
5.2 Material research
5.3 Principles of NO_x electrolyzer designing