Electrochemical membrane cell for NH synthesis from N and H O by electrolysis at 200 to 250 °c using a Ru catalyst, hydrogen-permeable Pd membrane and phosphate-based electrolyte

Ammonia (NH ) is an energy carrier that can be synthesized from nitrogen and water using electricity generated from renewable sources. The present work investigated NH synthesis using an electrochemical system with the structure of Ru/Cs /MgOPd-AgCsH PO /SiP O Pt and operating at 200 to 250 °C. In this system, the NH being generated is isolated from the CsH PO /SiP O electrolyte by the hydrogen-permeable Pd-Ag membrane, resulting in the production of dry NH . A maximum NH synthesis rate of 0.90 nmol s cm was obtained from the cathode at the Ru/Cs /MgOPd-Ag side at a current density of 10 mA cm , temperature of 250 °C and N flow rate of 3 cm min as converted to standard temperature and pressure. Deviations in the NH production rate from the theoretical amounts predicted by Arrhenius plots were observed at temperatures approaching 250 °C, possibly because the reaction approached equilibrium. A current efficiency for NH production of 2.6% was obtained, with the remainder of the current consumed during H generation. The apparent activation energies for the NH synthesis were 69 and 93 kJ mol at 3.2 and 10 mA cm , respectively. These values are significantly lower than that reported for conventional NH synthesis from nitrogen and hydrogen (139 kJ mol ) over the same catalyst in this cell. The optimum N flow rates were approximately 0.5 and 5 cm min at 3.2 and 10 mA cm , respectively, representing nitrogen amounts approximately 42 times the stoichiometric quantities. The provision of an excess of N is believed to reduce the suppression of N activation by so-called hydrogen poisoning of the catalyst.