Electrochemical NOxreduction on an LSM/CGO symmetric cell modified by NOx adsorbents

Abstract

This study investigated the effect of modifying a (La_0.85Sr_0.15)_0.99MnO₃ (LSM)/Ce_0.9Gd_0.1O_1.95 (CGO) symmetric cell by NO_x adsorbents on the electrochemical reduction of NO_x under O₂-rich conditions. The modification was based on a full ceramic cell structure without any noble metals. Three cells were prepared and tested: a blank cell, a cell impregnated with BaO, and a cell coated with a BaO/Pt/Al₂O₃ layer. The electrochemical reduction of NO_x on the three cells was studied by conversion measurement, degradation testing, and microstructure characterization. The modification, either by impregnating the BaO into the electrode or by coating the Ba/Pt/Al₂O₃ layer on the surface of the electrode, significantly increased the activity and selectivity of the NO_x reduction on the LSM/CGO symmetric cell by enhancing the adsorption and storage of the NO_x species or providing reaction sites for direct nitrate reduction. The cell with the BaO/Pt/Al₂O₃ layer exhibited a preferable performance at low temperatures (350 and 400 °C) and low voltages (1.5 to 2 V) due to the NO oxidation ability of the Pt catalyst, although its performance was relatively poor at elevated temperatures and voltages due to the impedance of the diffusion of NO_x to the reaction sites by the adsorption layer. For lowering the operation temperature and minimizing the power consumption, adding an adsorption layer was shown to be the optimum approach for modifying the electrochemical cell by NO_x adsorbents. The square wave (SV) polarization can balance the trapping and reduction rates of NO_x species on the electrochemical cells to further improve the NO_x reduction relative to the direct current (DC) polarization.