MnO₂-decorated metallic framework supercapacitors fabricated from duplex-phase FeCrCoMnNiAl_0.75 Cantor high entropy alloy precursors through selective phase dissolution

To exploit functional applications of high entropy alloys (HEAs), HEA metallic frameworks (MFs) have been fabricated through selective phase dissolution of fcc and bcc duplex-phase FeCrCoMnNiAl_0.75 HEAs precursors in H₂SO₄. Preferential dissolution of less-noble cubic fcc phases leads to the formation of three dimensional continuously-distributed residual bcc-phase MFs with wall thickness of 31–45 nm and the regular cubic voids with an average size of 121–150 nm similar with cubic fcc phases in size. Microstructural inheritance of Cantor HEAs governs the formation of MFs. MnO₂-decorated HEA metallic framework (MnO₂/MF) have been fabricated by electrodepositing MnO₂ thin layers on MFs with average thickness of about 9 nm. The MnO₂ layers-decorated MnO₂/MF composite electrodes can fulfill the high specific capacitance of 961 F g⁻¹, close to the theoretical value, due to the large specific surface area and superior electronic conductivity. Enhanced capacitive performances may result from the fast ion/electron transports between the active MnO₂ and the electrolytes. The results suggest that the uniform MF composite electrodes are capable for improving capacitance performance of MnO₂ in supercapacitors.