In this study, fundamental investigation of the double perovskite (DP) oxynitrides is targeted at the electronic/atomic/molecular levels. In particular, this study focuses on the development/characterization of iron-based DP oxynitrides for high-temperature electrocatalytic-NH3 production from N2 and H2O at atmospheric pressure in an oxide-ion-conducting solid-oxide-electrochemical-cell (SOEC). The cell functions as an electrolyzer, reducing/dissociating H2O to O2- and H+/H* at the cathode where H+/H* activates lattice nitrogen within the structure of the DP oxynitrides to form NH3. The resulting nitrogen vacancies are replenished by gaseous N2 while O2- ions are conducted to the anode where they form oxygen.
This project targets acquiring a fundamental understanding of the high-temperature electrocatalytic-nitrogen-reduction-reaction (e-NRR) using DP oxynitrides and manipulation of their anionic/cationic ordering through synthesis parameters. It is aiming to gain insight into the relationship between the DP oxynitride structure and their (electro)-chemical and physical properties, as well as their potential in SOEC applications involving nitrogen fixation/activation.
The DP oxynitrides were designed/characterized using the lab-based-techniques including XRD, XPS, Mössbauer, temperature-programmed desorption/reaction, DRIFTS, and Raman spectroscopy and synchrotron-techniques including XANES/EXAFS, NAP-XPS and NEXAFS. The electrocatalytic-activity experiments showed that the presence of mixed anions in the electrode structure significantly enhances the NH3 production rate. It was also confirmed by an electrochemical-activity-control-experiment with 3% H2O/Ar (absence of nitrogen) that the major source of nitrogen was N2 fed to the reactor and the amount of NH3 produced as a result of lattice nitrogen depletion is negligible.