Investigating viability of low temperature co-sintering to produce Ni-YSZ supported solid oxide electrolysis cells with a Ni-GDC active layer

Abstract

Solid oxide cells (SOC) are attractive for large scale electrolysis because of their unmatched efficiency. The current performance limitation for fuel electrode supported cells, is the Ni-YSZ fuel electrode, which suffers critical degradation at high current density. This limits their hydrogen production capacity. Aiming to overcome said limitation, this work demonstrates the integration of Ni-GDC (Ce_0.9Gd_0.1O_1.95) fuel electrodes into co-sintered thin electrolyte cells. Ni-GDC is widely used in electrolyte supported cells without signs of similar degradation. The novelty of the manufacturing approach adopted was to reduce the co-sintering temperature to 1250 ${}^{\circ }$C to limit detrimental interdiffusion between GDC and the zirconia-based electrolyte. It was possible to make testable and gas-tight cells at 1250 ${}^{\circ }$C, and the temperature reduction was effective at reducing interdiffusion. However, microstructural characterization of the realized cells documented poor contact between GDC in the fuel electrode and the ScYSZ electrolyte (Sc₂O₃-Y₂O₃ stabilized ZrO₂). This was the main cause for an approximate 50 pct drop in electrochemical performance compared to cells with Ni-YSZ electrodes. Despite the poor performance, the long-term stability was found to be improved relative to Ni-YSZ fuel electrode cells. One test operating between −1 and −1.75 A/cm² for more than 500 h showed no Ni migration. Moreover, it was found that this cell layout did not suffer mechanical failure despite large chemical expansions of GDC. If future work can solve the electrode-electrolyte contact issue, the reported cell concept has the potential to enable a significant increase in the area specific hydrogen production capacity of SOCs.