Enhancing the catalytic activity and stability of the Pr₂NiO_4+δ Ruddlesden−Popper perovskite air electrode for high-temperature steam electrolysis with barium doping

Ruddlesden−Popper oxides Pr₂NiO_4+δ (PNO) as air electrode of solid oxide electrolysis cells (SOECs) have attracted considerable attention due to their excellent electrochemical performance. However, the thermal stability of PNO is poor at high temperatures (600–800 ℃). Thus, the long-term stability of SOECs with PNO air electrode may be affected. In this work, the structural stability, electrochemical performance, and durability of PNO are modified by substituting praseodymium with barium. Pr_2−xBa_xNiO_4+δ (PBNO-x, x = 0, 0.1, 0.2, 0.3, and 0.4) samples are prepared using the solid-state method and evaluated for high-temperature steam electrolysis in SOECs. X-ray diffraction and thermal expansion coefficient results show that Ba-doped sample PBNO-0.2 has good chemical and thermal compatibility with GDC electrolyte. Electrochemical impedance measurement indicates that Ba doping can decrease the polarization resistance (R_p) of the samples. PBNO-0.2 electrode exhibits an R_p value of 0.06 Ω cm² at 800 ℃, which is 66% lower than that of the sample without Ba-doped PNO. The PBNO-0.2 half-cell is extremely stable under a high current density of 1 A cm⁻² for 126 h at 800 ℃. Furthermore, an electrolysis current density as high as − 723 mA cm⁻² at 1.3 V is obtained for the full cell with PBNO-0.2 air electrode when the temperature and feed gas are 800 ℃ and 70% H₂O− 30% H₂, respectively. It indicates an increase of about 27% than that of the PNO electrode, which suggests that Ba doping can effectively enhance the electrochemical performance of the PNO air electrode. The high catalytic performance of the PBNO-0.2 air electrode can be attributed to its high oxygen vacancy concentration by X-ray photoelectron spectroscopy analysis. The results prove that PBNO-0.2 is an air electrode with high catalytic activity and stability for high-temperature steam electrolysis in SOECs.