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Vasileiou E.,Aristotle University of Thessaloniki | Kyriakou V.,Aristotle University of Thessaloniki | Kyriakou V.,Chemical Processes and Energy Resources Institute | Garagounis I.,Aristotle University of Thessaloniki | And 7 more authors.
Solid State Ionics | Year: 2015

The electrochemical synthesis of ammonia from N2 and H+ ions was studied over a Ni-BZCY72 cermet, with and without H2 in the gas phase. The effect of temperature, cathode chamber feed composition and applied voltage was explored in detail. Without H2 in the cathode chamber, the highest rate was 1.7×10-9 mol/s·cm2 at 620°C. When H2 was present in the gas phase, ammonia was synthesized electrochemically at much higher rates and Faradaic efficiencies. The maximum net electrochemical synthesis rate of 4.1×10-9 mol/s·cm2 was obtained with ΡΗ2/ΡΝ2 =1 at 620°C, corresponding to a 140% enhancement of the open circuit rate at the cost of electrical energy. In both cases these high rates were accompanied by a low Faradaic efficiency, pointing to the need for catalyst improvement. © 2016 Elsevier B.V. Source


Kyriakou V.,Aristotle University of Thessaloniki | Kyriakou V.,Chemical Processes and Energy Resources Institute | Garagounis I.,Aristotle University of Thessaloniki | Garagounis I.,Chemical Processes and Energy Resources Institute | And 8 more authors.
Applied Catalysis B: Environmental | Year: 2016

The feasibility of Methane steam reforming (MSR) at low temperatures (450-650 °C) was studied in a Ni-BZCY72/BZCY72/Cu proton conducting membrane reactor, which allowed for the simultaneous separation of hydrogen. The cell reactor was first tested under open-circuit conditions, i.e., with the reactor operating as a catalytic reformer. The impact of several parameters, such as steam to carbon feed ratio, the operating temperature and the total flow rate was evaluated. The Ni-BZCY72 electrode exhibited high catalytic activity with methane conversion close to thermodynamic equilibrium, which was attributed to the high nickel content (45 wt.% after full reduction), as well as to the presence of ceria and zirconia in the support. Carbon dioxide was the main carbonaceous product with a molar ratio to carbon monoxide higher than 9, indicating that the Water Gas Shift reaction was predominant in the process. When hydrogen was electrochemically transported from the Ni-BZCY72 anode to the Cu cathode, a significant increase in methane conversion and hydrogen yield was observed. The methane conversion and hydrogen yield were improved by up to 50% in the temperature range of 550-650 °C over their corresponding open-circuit values. The BZCY72 perovskite exhibited satisfying proton fluxes and transference numbers at all temperatures and applied cell voltages examined. Finally, the Ni-BZCY72 reactor cell showed excellent chemical stability and durability, as well as coke tolerance for 24 h on stream. © 2015 Elsevier B.V. Source

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