PEG-mediated particle assembly and pore evolution in a Cr–Mn–Fe–Co–Ni spinel high-entropy oxide

High-entropy oxides (HEOs) have attracted considerable attention for energy storage applications because of their multi-principal synergistic effects and excellent structural stability. In this study, polyethylene glycol (PEG) was used as a surfactant to synthesize (CrMnFeCoNi) 3 O 4 HEOs by tuning the molar ratio of PEG to metal cations ( P / M ). The results show that PEG plays three roles during synthesis, serving simultaneously as a coordinating dispersant, a structure-directing agent, and an in situ porogen. The optimized HEO ( P / M = 4/5) exhibits a uniform nanoparticle morphology and a well-developed pore architecture, delivering a specific capacitance of 557.6 F g –1 . Kinetic analysis further indicates that its pseudocapacitive behavior is from a cooperative effect involving both capacitive-controlled and diffusion-dominated mechanisms. The assembled asymmetric supercapacitor device achieves an energy density of 64.2 Wh kg –1 at a power density of 375.3 W kg –1 and retains 81.3% of its capacitance after 10000 charge/discharge cycles. These outstanding electrochemical properties highlight the promise of PEG template (CrMnFeCoNi) 3 O 4 HEOs for advanced energy storage applications. Graphical abstract