Redox-reversible perovskite ferrite cathode for high temperature solid oxide steam electrolyser

In this work, perovskite Sr_1−xPr_xFeO_3-δ (SPF) (x = 0.02, 0.04, 0.06, 0.08 and 0.10) are investigated and employed as solid oxide steam electrolyser cathode at 800 °C. X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscopy (TEM) analysis together indicate that the Sr_1−xPr_xFeO_3-δ is redox reversible with a phase transition from cubic to orthorhombic structure in redox cycles. The doping of Pr in A site has remarkably enhanced the electronic conduction to 1.0–1.2 S cm⁻¹ at intermediate temperatures in reducing atmosphere. Electrochemical measurements demonstrate that the polarization resistance with Sr_0.96Pr_0.04FeO_3-δ electrode shows the lowest values of 0.25 Ω cm² in symmetric cells in reducing atmosphere at 800 °C. Direct steam electrolysis with Sr_0.96Pr_0.04FeO_3-δ cathode shows a current density of 1.64 A cm⁻² at 2.0 V when fed with 5%H₂O/Ar. The hydrogen production rate reaches 4.73, 6.68, 8.35 and 10.23 mL min⁻¹ cm⁻² at 1.4, 1.6, 1.8, 2.0 V, respectively, while the highest Faraday efficiency is as high as 97.16% at 1.8 V.