Highly porous CNTs knotted cerium oxide hollow tubes with exalted energy storage performance for hybrid supercapacitors

Abstract Development of porous transition metal oxide nanostructures and their conductive compounds has attracted widespread attention in hybrid supercapacitors (SCs) because of their large surface area, mesoporosity and good electrochemical activity which significantly enhance the energy storage performance. Herein, we reported highly porous cerium oxide hollow tubes (CeO2 HTs) by a facile biomorphic process with waste cotton fibers as a template. The waste cotton fibers were initially infiltrated with aqueous cerium nitrate solution, followed by solution evaporation and thermal treatment, leading to the formation of highly porous CeO2 HTs. To enhance the electrochemical kinetics, the carbon nanotubes (CNTs) were subsequently decorated on CeO2 HTs via ultrasonication and they were used as a cathode material (CNTs@CeO2 HTs) for hybrid SCs. Owing to large surface area, high porosity, and electrochemical conductivity, the prepared CNTs@CeO2 HTs composite showed a higher capacity of 70.7 μAh cm−2 at 1 mA cm−2 than the bare CeO2 HTs (41.9 μAh cm−2) in alkaline electrolyte. A hybrid SC assembled with the CNTs@CeO2 HTs and activated carbon materials as positive and negative electrodes, respectively exhibited an enlarged voltage window of 1.55 V. The device demonstrated a maximum energy density of 0.041 mWh cm−2 at 1 mA cm−2 with superior cycling stability (86.4%). Utilizing the high energy storage properties, two hybrid SCs connected in series could light up commercial light-emitting diodes for several minutes, indicating their potency for portable electronic applications. This facile convincing method may offer a cost-effective approach for the development of high capacity cathode materials for promising hybrid SCs on a large scale.