Ammonia synthesis at intermediate temperatures in solid-state electrochemical cells using cesium hydrogen phosphate based electrolytes and noble metal catalysts

This work reports the electrochemical synthesis of ammonia in solid-state cells at 220 °C and atmospheric pressure. Composites of CsH2PO4 and SiP2O7 were used as the electrolyte, and Pt/C-loaded carbon paper was employed as the anode. Five kinds of electrode materials, including Pt/C-, Pt-Ru/C-, Ru/C-, Ru- and Ag-Pd-loaded carbon paper, were examined as the cathode. Electrochemical activities of the cathode materials were evaluated by cyclic voltammetry. Both H2 and steam were used as the hydrogen source. The successful synthesis of ammonia was confirmed using Nessler's solution. When H2 was used as the hydrogen source, ammonia formation rates higher than 10−10 mol cm−2 s−1 were obtained using Pt/C- or Ru-loaded carbon paper as the cathode. When steam was used as the hydrogen source, ammonia formation rates higher than 10−11 mol cm−2 s−1 were obtained using Pt-Ru/C- or Ru/C- or Ru-loaded carbon paper as the cathode. Ru and Ag-Pd were the most promising noble metal catalysts for electrochemical synthesis of ammonia from N2 and steam.