(653e) Electrocatalytic Synthesis of Ammonia on Composite Bimetallic Nitride-Perovskite Oxide Soec Cathode

In the past century, the human population has become increasingly dependent on commercial NH₃ production to grow food, but the technology has evolved very little to keep up with the accelerating demand. In the conventional Haber-Bosch process, N₂ and H₂ are reacted at high temperatures and pressures, but the H₂ production and pressurization steps can be bypassed by using N₂ and H₂O in a solid-oxide electrolysis cell (SOEC). Perovskite oxides are known to be active cathode materials for high-temperature electrolysis of H₂O, but certain transition metal nitrides may be more capable of activating N₂.

In this study, a composite SOEC cathode of the perovskite (La_0.6Sr_0.4)_0.95Co_0.2Fe_0.8O₃ (LSCF) and the nitride Co₃Mo₃N was fabricated, and its activity for NRR was studied. A layer of LSCF was sintered on both sides of the YSZ electrolyte, and a mixture of Co₃Mo₃N and LSCF was deposited on the cathode side. During NRR, 3% H₂O/N₂ was supplied to the cathode at 500–600°C with applied current densities of 0–2 mA/cm². NRR activity was quantified, and the measured production rates were corrected by Ar and OCV control experiments. The composite cathode performed significantly better than the pure perovskite cathode or pure Co₃Mo₃N cathode, indicating a synergistic relationship between the two materials. These results imply that Co₃Mo₃N increases the rate of nitrogen activation, while the ionic/electronic conduction properties of LSCF improve the overall cell performance. Relevant properties of Co₃Mo₃N were analyzed such as electronic conductivity, stability in the reaction environment, and mobility of nitrogen ions. Co₃Mo₃N was characterized by in­-situ XRD, NAP-XPS, XANES, and temperature-programmed experiments.

Few non-noble metal materials have been identified as effective electrochemical NRR catalysts for the high-temperature range. The activity and stability of Co₃Mo₃N and its compatibility with proven perovskite catalysts allow for this unique composite cathode approach to high temperature NH₃ production.