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Redox stabilities of the hydrogen electrode with in situ exsolved Fe–Ni nanoparticles from Sr 2 Fe 1.4 Ni 0.1 Mo 0.5 O 6−δ (SFMNi) perovskite are studied by analyzing the evolution of the phase composition and morphology during the redox cycles. It is found that certain amount of the exsolved nanoparticles have been oxidized to the transition metal oxide (Ni,Fe)O instead of reincorporating into the parent perovskite lattice upon re-oxidizing at 800 °C in air. However, the (Ni,Fe)O secondary phases show no adverse effect on the subsequent reduction treatment. The redox reversibility mechanism is explained by the regular-solution model. The electrodes are almost fully recovered in the reducing atmosphere, and the symmetrical cells measured under 9.7% H 2 –3% H 2 O–87.3% N 2 conditions show a stable specific area polarization resistance of around 1.93 Ω cm 2 at 800 °C during 13 redox cycles. Single cells using the Ni–Fe nanoparticles structured electrode exhibit a stable electrode polarization resistance of about 0.598 Ω cm 2 at 800 °C under open circuit voltage conditions and a steady electrolysis current density of about −653 mA cm −2 at 1.5 V during the steam electrolysis process over 5 redox cycles. These results indicate that the SFMNi material is a very promising electrode candidate for steam electrolysis application with robust redox reversibility. 

In this work, a robust solid oxide electrolysis cell with Sr 2 Fe 1.5 Mo 0.5 O 6−δ –Ce 0.8 Sm 0.2 O 1.9 (SFM–SDC) based electrodes has been utilized to verify the conceptual process of partial oxidation of methane (POM) assisted steam electrolysis, which can produce syngas and hydrogen simultaneously. When the cathode is fed with 74%H 2 –26%H 2 O and operated at 850 °C, the open circuit voltage (OCV), the minimum energy barrier required to overcome the oxygen partial gradient, is remarkably reduced from 0.940 to −0.012 V after changing the feed gas in the anode chamber from air to methane, indicating that the electricity consumption of the steam electrolysis process could be significantly reduced and compensated by the use of low grade thermal energy from external heat sources. It is found that after ruthenium (Ru) impregnation, the electrolysis current density of the electrolyzer is effectively enhanced from −0.54 to −1.06 A cm −2 at 0.6 V and 850 °C, while the electrode polarization resistance under OCV conditions and 850 °C is significantly decreased from 0.516 to 0.367 Ω cm 2 . Long-term durability testing demonstrates that no obvious degradation but a slight improvement is observed for the electrolyzer, which is possibly due to the activation of the SFM–SDC electrode during operation. These results indicate that the robust Ru infiltrated solid oxide electrolyzer is a very promising candidate for POM assisted steam electrolysis applications. Our result will provide insight to improve the electrode catalysts used in POM assisted steam electrolysis.