Stable High-Entropy Double Perovskite Cathode SmBa(Mn_0.2Fe_0.2Co_0.2Ni_0.2Cu_0.2)₂O_5+δ for Intermediate-Temperature Solid Oxide Fuel Cells

High-entropy double perovskite SmBa(Mn_0.2Fe_0.2Co_0.2Ni_0.2Cu_0.2)₂O_5+δ(HE-SBC) as a cathode material was prepared by a modified Pechini method, and the performance of HE-SBC with 10% (in mole fraction) Gd₂O₃-doped CeO₂ (GDC) (HE-SBC-GDC) was optimized. The results show that the thermal expansion of Co ions caused by the change of valence state can be reduced due to the formation of high-entropy at B-site, thereby reducing the thermal expansion coefficient of SBC. The polarization impedance (R_p) of the HE-SBC symmetrical cell with yttria-stabilized zirconia (YSZ) as an electrolyte is 1.04 Ω·cm² at 800 ℃ and the maximum power density and R_p of the anode-supported single cell are 683.53 m W/cm² and 0.46 Ω·cm², respectively. Furthermore, the catalytic activity of HE-SBC is improved by the addition of GDC[m(HE-SBC):m(GDC)=7:3] due to the enlarged three-phase interface. The polarization resistance of HE-SBC-GDC composite cathode symmetric cell is only 0.09 Ω·cm² at 800 ℃ and the maximum power density and R_p of the anode-supported single cell are 838.66 m W/cm² and 0.12 Ω·cm², respectively.