Designing high-entropy oxide cathodes for improved oxygen reduction reaction in ceramic fuel cells

Ceramic fuel cells (CFCs) are promising electrochemical energy conversion devices due to their high efficiency, fuel flexibility, and low emissions. However, their widespread adoption is hindered by high operating temperature, sluggish oxygen reduction reaction (ORR) kinetics, and electrode degradation, which limit performance and durability. To overcome these limitations, we designed a high–entropy oxide (HEO) cathode with five elements in equimolar shares (Co_0.2Cu_0.2Ni_0.2Mg_0.2Zn_0.2)O (5E–HEO), using multi-cation coordination engineering to facilitate efficient oxygen reduction at lower temperatures (550–450 °C). The 5E–HEO cathode exhibits enhanced catalytic activity, improved ORR kinetics, and optimizes conductivity through a synergistic multi-cation mechanism. The 5E–HEO demonstrated exceptional performance, achieving a peak power density of 752 mW/cm² at 550 °C, along with reasonable stability over a 28-h operation. The cathode also exhibited a reduced polarization resistance (0.57 Ω cm²) and area specific resistance (0.285 Ω cm²). The ORR mechanism was elucidated through in situ advanced microscopy, spectroscopy, thermal analysis, and Density Functional Theory (DFT) calculations. Electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) analyses confirmed lower electrolyte–electrode resistance, highlighting the cathode's superior catalytic activity. This study demonstrates the potential of 5E–HEO–based cathodes to enhance CFC performance by leveraging high configurational entropy for improved material properties. This finding paves the way for more efficient and durable low-temperature CFCs.