Electrochemical Impedance Spectroscopy Investigation of the Anodic Functionalities and Processes in LSCM-CGO-Ni Systems
This type of anode composition with split functionalities (ionic conduction, electronic conduction, and catalytic activity) gives a unique opportunity to investigate the specific influence of each of the above functions on the anodic mechanisms and performance. In this work, electrochemical impedance spectroscopy was used to characterize anode compositions containing LSCM and different levels (15, 40, and 60 wt%) of gadolinia doped ceria (CGO), with and without additional submicron Ni, as well as Ni nanoparticles exsoluted from pre-coated larger LSCM particles. Impedance measurements were performed in a three electrode – half cell configuration from 700 to 900°C under two flow rates of 3% wet H2(50 and 150 ml/min).
At 900°C and under 150 mL/min of 3% wet H2, lower values of the polarization resistance (Rp) were measured for the samples containing CGO compared to pure LSCM ones. The Rp showed a slight decrease when the content of CGO was increased (15 to 40 and 60 wt%). This was characterized by a decrease of the high frequency part of the impedance diagrams, likely due to the higher ionic conductivity brought by the addition of CGO. The addition of 5 wt% of submicron Ni to LSCM-CGO led to a remarkable decrease in Rp. This effect was even more spectacular for the samples containing 5 wt% of exsoluted Ni nanoparticles, characterized by a decrease of the whole impedance diagram, and especially the high and the middle frequency parts, which suggests an enhancement of the electrochemical processes related to anode charge transfer. Further analysis of the impedance diagrams, measured for the above anodes at different temperatures and gas flow rates, is in progress in order to define the effect of different anode functionalities on the anodic processes involved, and thus its overall performance.