Ammonia synthesis from nitrogen and steam using electrochemical cells with a hydrogen-permeable membrane and Ru/Cs+/C catalysts

The ammonia (NH3) synthesis from nitrogen (N-2) and steam (H2O) using electrochemical cells with a hydrogen-permeable membrane, Ru/Cs+/C catalysts, and CsH2PO4/SiP2O7 electrolytes at 250 C-degrees was investigated. The highest formation rate was achieved in the hydrogen-permeable membrane cell with 30 wt%-Ru/Cs+/VXC72R catalysts, where VXC72R represents a carbon black powder of Cabot Vulcan XC-72R, reaching 32 nmol s(-1 )cm(-2) at 60 mA cm(-2), 1.0 MPa, and 250 C-degrees, corresponding to 15% current efficiency for NH3 formation. This rate can be converted to 1.8 mmol h(-1) gcat(-1) as a catalyst-based unit. At 10 mA cm(-2), 1.0 MPa, and 250 C-degrees, a rate of NH3 formation of 9.8 nmol s-1 cm-2 was obtained with a corresponding current efficiency of 28%. The rate of NH3 formation under this condition was close to the maximum current efficiency of 36% determined by the theoretical chemical equilibrium on thermodynamics. Three-electrode measurements with a reference electrode were conducted on the present cell. It was observed that the anode exhibited significant overpotential, especially at higher current density.