Qi Xun Xia

Facile synthesis of manganese carbonate quantum dots/Ni(HCO3)2–MnCO3 composites as advanced cathode materials for high energy density asymmetric supercapacitors

We have developed a high performance supercapacitor cathode electrode composed of well dispersed MnCO3 quantum dots (QDs, ∼1.2 nm) decorated on nickel hydrogen carbonate–manganese carbonate (Ni(HCO3)2–MnCO3) hedgehog-like shell@needle (MnCO3 QDs/NiH–Mn–CO3) composites directly grown onto a 3D macro-porous nickel foam as a binder-free supercapacitor electrode by a facile and scalable hydrothermal method. The MnCO3 QDs/NiH–Mn–CO3 composite electrode exhibited a remarkable maximum specific capacitance of 2641.3 F g−1 at 3 A g−1 and 1493.3 F g−1 at 15 A g−1. Moreover, the asymmetric supercapacitor with MnCO3 QDs/NiH–Mn–CO3 composites as the positive electrode and graphene as the negative electrode showed an energy density of 58.1 W h kg−1 at a power density of 900 W kg−1 as well as excellent cycling stability with 91.3% retention after 10 000 cycles, which exceeded the energy densities of most previously reported nickel or manganese oxide/hydroxide-based asymmetric supercapacitors. The ultrahigh capacitive performance is attributed to the presence of the high surface area core–shell nanostructure, the well dispersed MnCO3 quantum dots, and the high conductivity of MnCO3 quantum dots as well as the synergetic effect between multiple transition metal ions. The superior supercapacitive performance of the MnCO3 QDs/NiH–Mn–CO3 composites makes them promising cathode materials for high energy density asymmetric supercapacitors.

High volumetric energy density annealed-MXene-nickel oxide/MXene asymmetric supercapacitor

A Ti3C2Tx MXene electrode decorated with NiO nanosheets was synthesized by a facile and cost-effective hydrothermal method. The NiO nanosheets were grown and immobilized on the carbon-supported TiO2 layer which was derived from Ti3C2Tx-MXene during a thermal annealing process. An electrode based on the NiO-grown derived-TiO2/C-Ti3C2Tx-MXene nanocomposite (Ni-dMXNC) exhibited a remarkable maximum specific capacity of 92.0 mA h cm−3 at 1 A g−1 and 53.9 mA h cm−3 at 10 A g−1. Furthermore, an asymmetric supercapacitor (ASC) device composed of Ni-dMXNC as the positive electrode and Ti3C2Tx MXene as the negative electrode was demonstrated to be better with a high energy density of 1.04 × 10−2 W h cm−3 at a power density of 0.22 W cm−3, and cycling stability with 72.1% retention after 5000 cycles, compared to ASCs using previously reported Ti3C2Tx MXene materials. The enhanced capacitive performance is attributed to the newly formed high-surface-area multilayers of the Ni-dMXNC architecture, the active surface of NiO layer, and a favourable synergetic behaviour of the Ti3C2Tx MXene negative electrode.

Enhanced electrochemical activity of perforated graphene in nickel-oxide-based supercapacitors and fabrication of potential asymmetric supercapacitors

We synthesize a hierarchically porous electrode material with a high specific capacity composed of nickel oxide (NiO) nanosheets and perforated graphene (PG) sheets grown on a three-dimensional (3D) macroporous nickel foam via a facile hydrothermal method. Employing perforated graphene instead of non-perforated graphene greatly improves the electrochemical performance of the composite by increasing the specific surface area of the NiO/PG composite owing to the small perforations in the graphene and by improving the mechanical strength and electrical conductivity of NiO due to the graphene covering layer. The PG also provides (a) the accessibility and diffusion of ions onto NiO and PG surfaces through the perforations; (b) the electrolyte cages in the spaces below the perforations to allow ion-reversible adsorption to the inner surface of the graphene; (c) the inevitable edge defects around the holes causing reactivity with ions. After assembling an asymmetric supercapacitor coin cell composed of NiO/PG as the positive electrode, a separator, PG as the negative electrode, and a 1 M KOH electrolyte, the coin cell exhibits a high energy density of 57.8 W h kg−1 at a power density of 1030.9 W kg−1 and excellent cycling stability (82.1%) after 10 000 cycles.

Polycrystalline and Mesoporous 3-D Bi2O3 Nanostructured Negatrodes for High-Energy and Power-Asymmetric Supercapacitors: Superfast Room-Temperature Direct Wet Chemical Growth

Superfast (≤10 min) room-temperature (300 K) chemical synthesis of three-dimensional (3-D) polycrystalline and mesoporous bismuth(III) oxide (Bi2O3) nanostructured negatrode (as an abbreviation of negative electrode) materials, viz., coconut shell, marigold, honey nest cross section and rose with different surface areas, charge transfer resistances, and electrochemical performances essential for energy storage, harvesting, and even catalysis devices, are directly grown onto Ni foam without and with poly(ethylene glycol), ethylene glycol, and ammonium fluoride surfactants, respectively. Smaller diffusion lengths, caused by the involvement of irregular crevices, allow electrolyte ions to infiltrate deeply, increasing the utility of inner active sites for the following electrochemical performance. A marigold 3-D Bi2O3 electrode of 58 m2·g-1 surface area has demonstrated a specific capacitance of 447 F·g-1 at 2 A·g-1 and chemical stability of 85% even after 5000 redox cycles at 10 A·g-1 in a 6 M KOH electrolyte solution, which were higher than those of other morphology negatrode materials. An asymmetric supercapacitor (AS) device assembled with marigold Bi2O3 negatrode and manganese(II) carbonate quantum dots/nickel hydrogen-manganese(II)-carbonate (MnCO3QDs/NiH-Mn-CO3) positrode corroborates as high as 51 Wh·kg-1 energy at 1500 W·kg-1 power and nearly 81% cycling stability even after 5000 cycles. The obtained results were comparable or superior to the values reported previously for other Bi2O3 morphologies. This AS assembly glowed a red-light-emitting diode for 20 min, demonstrating the scientific and industrial credentials of the developed superfast Bi2O3 nanostructured negatrodes in assembling various energy storage devices.

Room-temperature successive ion transfer chemical synthesis and the efficient acetone gas sensor and electrochemical energy storage applications of Bi2O3 nanostructures

The acetone gas sensor and electrochemical supercapacitor applications of bismuth oxide (Bi2O3) nanostructures, synthesised using a facile and cost-effective quaternary-beaker mediated successive ion transfer wet chemical method and deposited onto soda-lime-glass (SLG) and Ni-foam substrates, respectively, are explored. The as-deposited Bi2O3 nanostructures on these substrates exhibit polycrystalline nature and a slight change in their surface appearance (i.e. upright-standing nanoplates on SLG and a curvy nanosheet structure on Ni-foam), suggesting the importance of the deposition substrate in developing Bi2O3 morphologies. The Bi2O3 nanoplate gas sensor on the SGL demonstrated a room temperature sensitivity of 41%@100 ppm for acetone gas, whereas the nanosheet structure of Bi2O3 on the Ni-foam elucidated a specific capacitance of 402 F g−1 at 2 mA cm−2, long-term cyclability, and rate capability with moderate chemical and environmental stability in a 6 M KOH electrolyte solution. The Bi2O3//graphite pencil-type asymmetric supercapacitor device revealed a specific capacitance as high as 43 F g−1, and an energy density of 13 W h kg−1 at 793 W kg−1 power density, turning a light emitting diode ON, with considerable full-brightness light intensity, during the process of discharging.