Load Regulation Strategies of Solid Oxide Electrolysis System Coupled with External Heat Sources

Abstract

The asymmetric behavior between the fuel-cell mode and the electrolysis mode of solid oxide cells still needs to be investigated in depth. In this paper, an experimental study was carried out on 10 cm × 10 cm fuel electrode-supported cells. The electrochemical impedance spectra under different DC biases in the two modes were tested, and the resistances were obtained using equivalent circuit model fitting, and then the ohmic overpotential, activation overpotential and concentration overpotential were calculated. The results indicated that the overpotential of the fuel-cell mode and electrolysis mode was asymmetric under the same current in the actual operating current range. The ohmic overpotentials were basically the same, but the activation overpotential and concentration overpotential of the electrolysis mode were higher than those of the fuel-cell mode. The asymmetry between the two modes was negatively correlated with temperature, which was since the asymmetry of activation overpotential decreased with increasing temperature. When the fuel electrode flow rate increased, the asymmetry of both the activation overpotential and concentration overpotential reduced. More importantly, the asymmetry between the two modes increased after a period of operation of the cell. The reason was that the activation overpotential of the electrolysis mode increased sharply due to the deterioration of the fuel electrode charge transfer reaction. That is, for the cell used in this study, the same microstructure changes had a greater impact on the stability of the electrolysis mode. Therefore, the microstructure is more demanding for the electrolysis mode, requiring more careful design and selection.