A heterojunction of VO(OH)2 nanorods onto hemp stem derived carbon for high voltage (1.5 V) symmetric supercapacitors

A stratagem is implemented to widen the potential window in aqueous supercapacitors beyond the 1.23 V restrictions. The widening of the potential window is accomplished by a heterojunction design combining both negative and positive redox potential material. For the positive potential, VO(OH)2 is employed and intentionally synthesized with a nanorod morphology to transform the battery's mechanistic behavior into extrinsic pseudocapacitive behaviour. Then, a VO(OH)2 heterojunction is designed with low-cost activated carbon (HAC) derived from sustainable plant waste (hemp stem), which works in a negative potential window. The designed heterojunction not only harvested a large energy density (149.31 W h kg−1 @ 1468.6 W kg−1) in a symmetric cell, but also achieved a large voltage of 1.5 V. Here HAC, in addition to widening the potential window, also supports the VO(OH)2 nanorods by preventing them from dissolution. The stabilization of the VO(OH)2 phase was displayed in the attainment of a high rate capability (82.6% capacitance retention) upon a 5-fold current density increase. Supplementary to this, a stable cycling performance is also evaluated (96%, 10 000 cycle), which again precludes any doubt about the dissolution of VO(OH)2. This work offers a distinctive approach and can also be applied to other charge storage materials to remove the 1.23 V limitation.