Electrochemical Ammonia Synthesis in a Proton-Conducting Ceramic Cell: A Parameter Study of an Iron-Based Electrode

Proton-conducting ceramic cells with a Ni-BaCe 0.8 Zr 0.1 Y 0.1 O 3− δ || BaCe 0.7 Zr 0.2 Y 0.1 O 3− δ || Fe/BaCe 0.7 Zr 0.2 Y 0.1 O 3− δ -backbone structure were studied in a dual-chamber setup to evaluate the effects of temperature, gas flow, voltage, and electrolyte thickness on electrochemical ammonia synthesis. Three gas feed configurations were tested to differentiate surface reaction mechanisms. Thermodynamic calculations were conducted to evaluate the experimental results in the context of equilibrium limitations. The results showed that proton transport through the electrolyte plays a minor role in the formation of ammonia, while production rates correlated more strongly with applied voltage than with current density. Ammonia synthesis appeared significantly limited by thermodynamics, making an increased hydrogen partial pressure at the cathode essential. A feed configuration supplying only nitrogen to the cathode was ineffective, whereas introducing hydrogen increased the ammonia formation rate from 1.42 × 10 −10 mol cm −2 s −1 to 3.23 × 10 −9 mol cm −2 s −1 at −1.4 V and 500 °C. When proton conduction was suppressed under the same conditions, the rate further increased to 4.32 × 10 −9 mol cm −2 s −1 . Varying the cathodic gas flow rate across the 12.57 cm 2 active area from 8 NL h −1 to 20 NL h −1 , the ammonia formation rate improved by a factor of 3.1 at −1 V, at both 500 °C and 600 °C.