Carbon nanotube bridge enables record energy storage in new supercapattery electrode

Researchers from Gachon University in South Korea and Najran University in Saudi Arabia have developed a new electrode material featuring oxygenated carbon nanotubes (OCNTs) that enhances the performance of hybrid energy storage devices known as supercapatteries. The study, published in the journal Ionics, details the creation of a Cr₂O₃/MgCo₂O₄@OCNT heterostructure, which combines chromium oxide and magnesium cobaltate with OCNTs to achieve high charge capacity, rapid electrochemical kinetics, and durability over extensive charging cycles.

Supercapatteries aim to merge the rapid charging and long cycle life of supercapacitors with the high energy storage capacity of batteries. The Cr₂O₃/MgCo₂O₄@OCNT material leverages chromium(III) oxide for structural stability, magnesium cobalt oxide for high faradaic activity, and OCNTs for enhanced conductivity and wettability. This combination allows the material to store and release charge efficiently, with a specific surface area of 87.69 m²/g and a low charge-transfer resistance of 31 ohms, facilitating faster charging and improved power delivery.

In testing, the electrode demonstrated specific capacities of 1963 C/g at a scan rate of 10 mV/s and 2214 C/g at a current density of 2 A/g. These results highlight the material's ability to combine battery-like capacity with the rapid charge-discharge capabilities of capacitors. When integrated into a full device with activated carbon as the negative electrode, the supercapattery achieved a maximum energy density of 96.2 Wh/kg and a power density of 2494 W/kg, significantly outperforming conventional supercapacitors.

The device maintained 90.31% of its initial capacity after 10,000 cycles, with a Coulombic efficiency of 94.58%. This durability suggests that the structural integrity provided by the Cr₂O₃ scaffold and the conductive network of OCNTs effectively manage mechanical stress during cycling. The study's kinetic analysis confirmed the hybrid charge storage mechanism, with surface-controlled capacitive processes dominating at higher scan rates and faradaic processes at lower rates.

Funded by Najran University's Deanship of Graduate Studies and Scientific Research, this research contributes to the understanding of spinel cobaltates and chromium oxide composites for energy storage. While practical applications are still in development, the Cr₂O₃/MgCo₂O₄@OCNT heterostructure shows promise for use in systems requiring both fast energy delivery and substantial storage, such as regenerative braking and grid buffering of renewable power.