Performance and Stability of Solid Oxide Electrolysis Cell for CO2 Reduction under Various Operating Conditions

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.

Feasibility of alternative electrode materials for high temperature CO2 reduction on solid oxide electrolysis cell

“…The effect of reducing gases, H 2 and CO, on the electrochemical performance of NieYSZ cathode for CO 2 reduction was reported in the preceding article [6]. The experimental results clearly demonstrated the effectiveness of H 2 usage as a reducing gas.…”

“…For comparison, the time course of terminal voltage for NieYSZjYSZjLSMeYSZ cell (abbreviated as cell B) is depicted in Fig. 5 (b) [6]. The spikes in figures correspond to the measurement points of impedance spectra under the open circuit condition.…”

“…As reported in the prior study, the delamination of LSMeYSZ anode occurred after galvanostatic operation at À0.90 A cm À2 for 9 h at 900 C, resulting in an increment in area specific resistance (ASR) [13]. Several mechanisms have been proposed for the delamination of LSM or LSMeYSZ composite anodes; the delamination was caused by the high oxygen partial pressure near the anode/electrolyte interface [6,12,14].…”

“…The delamination of LSMeYSZ electrode occurred when the cell was operated under severe conditions, such as at high temperature and high current density [6]. This issue can be resolved by employing more efficient and active alternative electrode materials, e.g.…”

“…Some studies have reported the degradation of NieYSZ cathode during steam electrolysis including the segregation of impurities near grain boundary and nickel evaporation [4,5]. Another possible degradation factor is the agglomeration and coarsening of nickel particles [6,7].…”