Diesel engines are widely used in automobiles for their high fuel efficiency, low carbon monoxide emissions, and low hydrocarbon emissions [1]. Unfortunately, due to their lean-burn operating environment, diesel engines emit higher amounts of NOx than gasoline engines. Although NOx Storage and Reduction (NSR) and Selective Catalytic Reduction (SCR) technologies have been commercialized and offer high deNOx (i.e. NOx decomposition) efficiency, they suffer from a loss of fuel efficiency during catalyst regeneration and a need for large-volume, on-board ammonia storage and replenishment, respectively [2]. Further, expensive precious metal catalysts are needed to enable deNOx chemical reactions in these conventional technologies. In contrast, Solid Oxide Electrochemical Reduction Cells (SOERCs) utilizing an external bias to electrochemically drive NOx decomposition promise precious-metal-free operation without the need for catalyst regeneration or large-volume, on-board storage.

Here, the deNOx performance of barium oxide (BaO) infiltrated lanthanum strontium manganese oxide (LSM)-gadolinium doped ceria (GDC) SOERCs were measured as a function of operating temperature, AC amplitude, and AC frequency. Under all test conditions, SOERC performance was reproducible across different samples with the application, removal, and subsequent reapplication of electrical bias. The BaO-LSM-GDC SOERCs tested here displayed better low-temperature NO_x conversion efficiencies than those previously reported in the literature; achieving 22% at 350^oC compared to the 3% reported in the literature [3, 4]. In agreement with this literature 1) the application of an AC electric bias was found to produce higher BaO-LSM-GDC NO_x conversion efficiencies than a DC bias of the same magnitude, and 2) BaO-LSM-GDC SOERCs exhibited current and thermodynamic efficiencies of a few percent, and a few tenths of a percent, respectively. Unfortunately, as shown previously [3, 4], these conversion efficiencies decreased by several percent after only a few hours of operation at 450^oC due to microstructural coarsening of the BaO infiltrate.

References

[1] D.B. Kittelson, Journal of Aerosol Science, 29 (1998) 575-588.

[2] W.S. Epling, L.E. Campbell, A. Yezerets, N.W. Currier, J.E. Parks, Catalysis Reviews, 46 (2004) 163-245.

[3] J. Shao, K.K. Hansen, Journal of Materials Chemistry A, 1 (2013) 7137-7146.

[4] J. Shao, K.K. Hansen, Journal of the Electrochemical Society, 160 (2013) H494-H501.