Ni-Doped PrBaFe₂O5+δ as Cobalt-Free Cathode for IT–SOFCs: Enhanced Electrochemical Performance via Oxygen Vacancy Engineering

PrBaFe 2 O 5+δ (PBF) is a promising cathode material for intermediate-temperature solid oxide fuel cells (IT–SOFCs). However, its relatively low electrical conductivity at intermediate temperatures limits its practical application. Doping with an appropriate amount of Ni is considered an effective strategy to enhance its electrochemical performance. In this study, cobalt-free perovskite oxides PrBaFe 2– x Ni x O 5+δ (PBFN x, x = 0, 0.1, 0.2, 0.3, 0.4) were synthesized using the sol–gel method. The results showed that Ni doping significantly increased the electrical conductivity of PBF. At 400 °C, PBFN 0.3 exhibited a conductivity of 152.28 S·cm –1, approximately eight times that of undoped PBF (19.31 S·cm –1 ). The incorporation of lower-valence Ni promoted the formation of oxygen vacancies, which enhanced the electrochemical performance of PBF. At 800 °C, the polarization resistance ( R p ) values of PBF and PBFN 0.3 were 0.13 and 0.09 Ω·cm 2, respectively, indicating a 30.77% reduction in R p due to Ni doping. This reduction facilitated more efficient electrochemical reactions at the cathode, thereby improving energy conversion efficiency and reducing energy losses. Furthermore, Ni doping led to a marked increase in the peak power density (PPD) of the fuel cell. Compared to undoped PBF (307 mW·cm –2 ), the PPD of NiO-SDC|SDC|PBFN 0.3 reached 591 mW·cm –2, nearly doubling the power output. These findings suggest that PBFN x exhibits excellent electrochemical properties and is a promising cathode material for IT–SOFCs.