Enhanced N<sub>2</sub> Activation on a Composite Co<sub>3</sub>Mo<sub>3</sub>N Nitride and La<sub>0.6</sub>Sr<sub>0.4</sub>Co<sub>0.2</sub>Fe<sub>0.8</sub>O<sub>3</sub> Perovskite Cathode for High-Temperature Electrochemical Ammonia Synthesis
Matthew Ferree, Seval Gündüz, Jae-Sung Kim, Raymond LaRosa, Yehia Khalifa, Anne C. Co, Umit S. Ozkan
Abstract
Electrochemical routes for ammonia synthesis could offer improved conversion efficiency, compatible integration with renewable energy sources, and a solution to distributed chemical production. In a conventional Haber–Bosch process, ammonia, NH 3, is produced by reacting N 2 and H 2 at high temperatures and pressures. In an electrochemical pathway, the H 2 production and pressurization steps can be bypassed by using N 2 and H 2 O in an ambient-pressure solid-oxide electrolysis cell (SOEC). In this study, a SOEC with a composite cathode of A-site deficient lanthanum ferrite perovskite oxide and transition metal nitride Co 3 Mo 3 N was fabricated, and its activity for the nitrogen reduction reaction (NRR) was studied. The composite cathode produced ammonia at a rate of 4.0 × 10 –11 mol s –1 cm –2 at 550 °C and 0.65 mA/cm 2, which was an 8-fold enhancement compared to either of the pure phase electrodes. Relevant properties of Co 3 Mo 3 N, such as thermochemical stability, adsorption behavior, and mobility of nitrogen ions, were characterized by various techniques including in situ XRD, XAFS/XANES, NAP-XPS, temperature-programmed experiments, and in situ DRIFTS.