Enhancement of the intrinsic Ni/GDC activity under rSOC operation by means of Fe–Au doping: An electro-kinetic study

Abstract

The investigation dealt with the effect of Fe and Au wt.% concentrations on the enhanced performance and stability of Ni/GDC under rSOC operation. Moreover, it focused on the comparison of the intrinsic electro-kinetics between the best performing Fe–Au-modified cell and Ni/GDC under SOE operation. The rSOC performance and stability of all cells was examined in the temperature range of 900–800 °C. The electro-kinetic measurements took place at 900 °C by varying the pH2O. All Fe–Au–Ni/GDC electrodes exhibited enhanced activity, compared to the SoA Ni/GDC, with variations in their stability after three rSOC cycles. Specifically, the fuel electrode with the lowest wt.% concentration in Fe and Au (0.5Fe–1Au–Ni/GDC) exhibited the highest activity and stability under rSOC operation. By increasing the wt.% loadings to 2 wt% Fe and 3 wt% Au, there was rapid degradation of the initially high performance, mainly due to increase of the ohmic resistance. SEM analysis showed higher macro-porosity on the reduced state of the modified electrodes, which in the case of the best performing 0.5Fe–1Au–Ni/GDC was the least affected after rSOC operation. Interestingly, the SOE performance of the examined Fe–Au-modified electrodes was not similarly inhibited by the decrease of temperature, compared to Ni/GDC. This was further clarified through electro-kinetic measurements, aiming to verify the effect from the Fe–Au doping on the intrinsic electrochemical activity of Ni/GDC for the H2O electrolysis reaction. Comparison between the SoA and the best performing 0.5Fe–1Au–Ni/GDC showed an enhancing effect on the intrinsic electro-kinetics of the modified electrode. Specifically, the dependence of the polarization resistance on the pH2O was found to be strongly positive, resulting in a higher apparent reaction order, compared to Ni/GDC.