Composite Cathodes with Oxide and Nitride Phases for High-Temperature Electrocatalytic Ammonia Production from Nitrogen and Water

Abstract

The conventional route for ammonia (NH3) production is the Haber-Bosch (HB) process, which converts nitrogen and hydrogen through a thermo-catalytic reaction at high temperatures and pressures. The HB process is not efficient or economical at smaller scales. Recent years have seen significant effort in producing ammonia electrocatalytically. While direct electrochemical synthesis of NH3 has been reported at low temperatures in aqueous media, studies on high-temperature electrocatalysis are much fewer. High-temperature routes have the potential to increase catalytic activity, lower the kinetic overpotential, and improve Faradaic efficiency for NH3 formation. The focus of the present study is high-temperature (600 °C) electrochemical synthesis of ammonia from N2 and H2O at atmospheric pressure in solid oxide electrolysis cell (SOEC)-type reactors. The catalytic material selection for the working electrode is one of the most important challenges in electrochemical processes. In this work, a composite cathode composed of a perovskite oxide and an iron oxynitride phase was investigated. Both phases were characterized thoroughly using XRD, XPS, Mössbauer spectroscopy, TPD/TPRxn, and 4-probe electrical conductivity techniques. The electrocatalytic activity experiments were performed on the perovskite oxide phase and the composite cathode to study the effect of using a composite electrode on the activity of the cell.