Enhanced pseudocapacitance rectification by doping metalloid phosphorus in high entropy oxide (CrMnFeCoNi)3O4

Metalloid phosphorus-doped spinel-type high-entropy oxide (CrMnFeCoNi)3O4 is synthesized to solve the challenges of limited pseudocapacitance rectification for supercapacitor diodes. It demonstrates both pseudocapacitive energy storage and ionic rectification in a 1 M KOH electrolyte. This material achieves a high specific capacitance of 394.05 F g−1 at 0.5 A g−1 along with a reverse rectification ratio of 0.85 at 3 mV s−1. These properties are driven by phosphorus electronegativity, which enhances electron transfer, creates oxygen vacancies, and accelerates ion transport. The assembled supercapacitor diodes delivered a high energy density of 241.35 W h kg−1 at a power density of 5250 W kg−1 while maintaining a rectification ratio RRI of 6.95–8.8 at scan rates of 3–30 mV s−1 and a sustained RRII of 0.86. After 1000 cycles, the diode retained 84% rectification efficiency with minimal capacitance decay. This work advances iontronic circuits through dual-functional electrodes.