A highly stable Pr2NiO4+δ oxygen electrode in electrolyte supported protonic ceramic electrolysis cells (PCECs) for hydrogen production with high faradaic efficiency

Abstract

Protonic ceramic electrolysis cells are a promising technology for hydrogen production. However, parasitic electronic leakage in the ceramic electrolyte materials has detrimental effects on the faradaic efficiency and hence lowers overall efficiencies. Furthermore, the sluggish kinetics of the oxygen evolution reaction requires the development of efficient oxygen electrodes with high activity and durability at high steam contents. In this study, BaCe_0.7Zr_0.1Y_0.1Yb_0.1O_3−δ (BCZYYb7111) electrolyte supported single cells were fabricated and the electronic and ionic transport numbers in the electrolyte support were determined in dependence on the operating conditions. It was shown that the electronic leakage and thus the faradaic efficiency strongly depends on the operating temperature, steam partial pressure, oxygen partial pressure and current density. Optimal operating conditions were derived and faradaic efficiencies of ∼95% were achieved at 600 °C and 20% H₂O. Furthermore, the comparison of Pr₂NiO_4+δ (PNO) and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) as oxygen electrodes, showed higher current densities in electrolysis and fuel cell mode and lower polarization resistances (R_p) for PNO at intermediate temperatures between 600 to 700 °C. In the end, long-term measurements of the PNO/BCZYYb/Ni-BZY single cells in electrolysis mode showed stable behavior over 590 h.