The NO_x (mainly NO and NO₂) pollutions that come from the exhaust of the thermal engines can give rise to a serious threat to the environment and human health. The design of more efficient and stable catalysts to reduce NO_x to nitrogen in atmospheres containing excess oxygen (typically, from exhaust gas emitted by diesel and lean-burn gasoline engines) has attracted so much attention in the last years. The two actual technologies are using an additional reducing agent to remove NOx, i.e. Diesel fuel post-injection for the NOx storage reduction process and urea for the selective catalytic reduction. An alternative solution could be the electrochemical reduction of NOx in solid oxide electrolysis cell (SOEC)^[1,2]that can save the huge reducing agents storage system.

This study reports the electrochemical properties for NO_x reduction of a Mixed Ionic Electronic Conducting (MIEC) porous electrode promoted by Pt nanoparticles, as efficient catalyst for oxidation reactions, and BaO, as sorbents to store NO_x. Pt and BaO nanoparticles were finely dispersed in the porosity of a MIEC film, based on a composite between LSCF (La_0.6Sr_0.4Co_0.8Fe_0.2O_3-δ) and GDC (Gd_0.2Ce_0.8O_1.9), which was deposited using screen-printing. This catalytic layer was interfaced on a dense pellet of gadolinium doped ceria (GDC), an O^2- ionic conductor. The Ba and Pt loadings were around and 150 and 5 µg/cm², respectively. The catalytic performances, upon positive and negative polarizations, have been measured as a function of temperature in the range 200°C-500°C, partial pressure of oxygen and in the presence of propene in the feed. The NO_x electrochemical conversion into N₂ was found to be driven by the current (Figure 1) and the catalytic activity of the electrode for NO oxidation. In parallel, electrochemical properties have been carried out by using cyclic voltammetry and electrochemical impedance spectroscopy to investigate the electrocatalytic mechanism. Finally, the Pt and BaO nanoparticles in the LSCF/GDC film were characterized by transmission electronic microscopy.

References

1. T.J. Huang, C.Y. Wu, S.H. Hsu, C.C. Wu, Energy Environ. Sci., 4, 4061 (2011).
2. R. M. L. Werchmeister, J. J. Bentzen, K. B. Andersen, and K. Kammer Hansen, J. Electrochem. Soc., 161(10) H663-H669 (2014)