No abstract

In this study, effects of operating conditions on the electrochemical reduction of CO 2 on solid oxide electrolysis cell (SOEC) were systematically investigated. Experimental results revealed that the reducing gas can influence the behavior of Ni-YSZ cermet cathode. Supply of hydrogen as a reducing gas was found to be the most promising approach to obtain better cell performance for CO 2 reduction. Even a small amount of H 2 can facilitate the CO 2 reduction due to the kinetically fast reverse water gas shift reaction. High temperature operation is favorable from thermodynamic viewpoint because the Gibbs free energy significantly decreases at elevated temperature. The partial pressure of oxygen at the cathode side is another critical factor that found to be beneficial. A considerable increase in cell voltage was observed when Ni-YSZ | YSZ | LSM-YSZ cell operated under constant current densities of −0.75 and −0.90 A cm −2 at 900°C, whereas the stable cell performance could be possible at −0.15 A cm −2 for 7 h. The increase in cell voltage was attributed to the degradation of anode.

In this study, the performance of anode-supported and electrolyte-supported cells was compared under similar operating conditions for direct ammonia-fueled solid oxide fuel cells (SOFCs); the cell configuration of both types of cells was as follows, Ni-YSZ|YSZ|GDC|LSCF. The anode-supported cell (ASC) showed better performance as compared with that of the electrolyte-supported cell (ESC). The influence of the humidity of inlet gas on the performance of ASC was investigated at 700 o C. The cell performance did not change substantially under different humidified conditions. In addition, the long-term discharge operation of direct ammonia-fueled ASC was conducted at 600 o C for ca. 235 h. The durability of ASC under polarization was evaluated on the basis of the measured current-voltage and power density curves. The cell showed slight degradation in current density and power density after discharge operation. Furthermore, the formation temperature of Ni 3 N under ammonia-fueled SOFC conditions was investigated in detail.

In this article, two Ni-based cermet electrodes have been fabricated and their electrochemical performances have been evaluated for CO2 electrolysis on solid oxide electrolysis cell (SOEC). It was found that Ni–SDC cermet electrode showed lower cathodic overpotential than Ni–YSZ electrode. The improved cell performance indicated that Ni–SDC cermet was a better and more effective electrode material for CO2 reduction. The results revealed that the conductivity of Ni–SDC cermet cathode for CO2 reduction strongly depended on the operating parameters, and the effect of these operating parameters on the electrochemical activity of Ni–SDC cermet cathode was closely interlinked. The most critical operating parameter for CO2 reduction was appeared to be the gaseous atmosphere, which can be controlled by changing the oxygen partial pressure at Ni–SDC electrode.

The present study focuses on the comparison of Ni–GDC cathodes fabricated by the mechanical mixing (MM) and the spray pyrolysis (SP) methods toward the reduction of CO2 on solid oxide electrolysis cells (SOECs). The synthesized powders are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The short-term performance and stability of each cathode are measured during the galvanostatic experiment at −1.20 A cm−2 and 1000°C. A relatively better performance and improved stability have been achieved for the cathode fabricated by SP method, which was supported by the pre- and post-test microstructural analyses. At the same time, effects of preparation methods on the triple phase boundary (TPB) length, two-phase boundary (contact area fraction of active GDC/pore), and isolated phase ratio are also evaluated from the focused ion beam-scanning electron microscope (FIB-SEM) tomography. The computed tomography results reveal that the cathode prepared by SP has larger TPB length and two-phase-boundary as compared with the one prepared by MM, which will be the one of the reasons for the better performance of the cell with Ni–GDC cathode prepared by SP.