Electrochemical and degradation behaviour of single cells comprising Ni-GDC fuel electrode under high temperature steam- and co-electrolysis conditions

Abstract

The present study investigates the electrochemical performance and degradation behaviour of a Nickel - Gd2O3 doped CeO2 (Ni-GDC) electrode containing single cell under steam electrolysis and co-electrolysis modes. The cell consists of the Ni-GDC fuel electrode, an 8 mol% Y2O3 stabilized ZrO2 (8YSZ) electrolyte layer, a GDC barrier layer and a (La,Sr)(Co,Fe)O3 (LSCF) oxygen electrode. Firstly, the electrolyte-supported single cells were fabricated and characterized using DC- and AC-techniques in the 750–900 °C temperature range. Distribution of relaxation times (DRT) analysis was employed to resolve frequency-dependent electrode processes. The observed processes were further modelled using an equivalent circuit model (ECM) with 3 R//CPE (resistor//constant phase element) in series with a finite length diffusion element (Warburg short - Ws). Long-term stability tests of the single cells were carried out under steam electrolysis (H2O:H2, 50:50) and co-electrolysis (H2O:CO2:CO, 40:40:20) conditions at 900 °C with −0.5 A‧cm−2 current density for 500 h. Steam electrolysis conditions exhibit the highest degradation rate of 499 mV‧kh−1, while a lower degradation rate of 308 mV‧kh−1 is observed under co-electrolysis conditions. The post-test analysis of the operated cell shows increased Ni particles size, suggesting Ni agglomeration in both electrolysis modes.