Electrochemical Acceleration of Ammonia Synthesis on Fe-Based Alkali-Promoted Electrocatalyst with Proton Conducting Solid Electrolyte

Abstract

To accelerate ammonia synthesis, the effect of the electrode potential on the kinetics of ammonia synthesis was investigated with a proton-conducting solid electrolyte, BaCe0.9Y0.1O3 (BCY), at temperatures between 500–650 °C. Ammonia synthesis was conducted using a double chamber electrochemical setup with an electrolyte-supported Pt|BCY|K,Al-modified Fe-BCY cell. Although slow ammonia formation kinetics by cathodic polarization was observed when pure N2 was supplied to the cathode side, obvious acceleration of the ammonia formation rate by cathodic polarization was observed following addition of 15% H2 to the cathode side. The ammonia formation rate increased more than 20 times at −1.5 V relative to that at the open circuit voltage, which was not observed by anodic polarization. Notably, the acceleration at the cathodic potential was observed over 610 °C. These results indicate that the enhancement of ammonia formation occurs because of promotion of nitrogen dissociation by cathodic polarization and a change in the transport properties of the BCY electrolyte. The acceleration mechanism was discussed based on kinetic measurements and the dependence of the reaction kinetics on temperature and partial pressure.