Self-supporting high-entropy-oxide@layered-Ni electrode for high-performance supercapacitors

High-entropy oxides (HEOs) have recently garnered attention for use in supercapacitors owing to their tailoring metal cations and entropy stabilizing effect. Current HEOs require insulative polymer binders to immobilize them on a disorder conductive substrate, which leads to high interfacial resistance and limits electron transfer. Here, three-dimensional high-performance self-supporting HEO@Ni electrodes for supercapacitors are developed through a combination of directional freeze casting (at -20 to -40 degrees C) and solution combustion synthesis. The 3D layered HEO@-40Ni electrode demonstrated an impressive specific capacitance of 942 F g- 1 at 1 A g- 1, maintaining 90.2 % of its capacitance after 10,000 cycles. An asymmetric HEO@-40Ni//activated carbon supercapacitor achieved an energy density of 37.12 Wh kg- 1 at a power density of 825 W kg- 1, retaining 81 % of its capacitance after 10,000 cycles at 10 A g- 1. The remarkable electrochemical performance of the supercapacitor can be attributed to the increased specific surface area and effective electron transport caused by the highly oriented straight-through structure of the Ni current collector. Furthermore, electrolytes penetrated the hierarchical porous active material of the HEO@Ni electrode, enhancing the activation rate. This research introduces a straightforward and scalable technique for producing high-performance self-supporting electrodes for supercapacitors.