Wenyao Li

Hierarchical mesoporous NiCo2O4@MnO2 core–shell nanowire arrays on nickel foam for aqueous asymmetric supercapacitors

We demonstrate the design and fabrication of hierarchical mesoporous NiCo2O4@MnO2 core–shell nanowire arrays on nickel foam via a facile hydrothermal and electrodeposition process for supercapacitor applications. In order to increase the energy density and voltage window, a high-voltage asymmetric supercapacitor based on hierarchical mesoporous NiCo2O4@MnO2 core–shell nanowire arrays on nickel foam as the positive electrode and activated carbon (AC) as the negative electrode was successfully fabricated. The as-fabricated asymmetric supercapacitor device achieved a specific capacitance of 112 F g−1 at a current density of 1 mA cm−2 with a stable operational voltage of 1.5 V and a maximum energy density of 35 W h kg−1. The present NiCo2O4@MnO2 core–shell nanowire arrays with remarkable electrochemical properties could be considered as potential electrode materials for next generation supercapacitors in high energy density storage systems.

MnO2 ultralong nanowires with better electrical conductivity and enhanced supercapacitor performances

Single-crystal α-MnO2 ultralong nanowires (∼40 μm in length, ∼15 nm in diameter), which were synthesized by a simple polyvinylpyrrolidone (PVP) assisted hydrothermal route, exhibited a better electrical conductivity, a highest specific capacitance of 345 F g−1 at a current density of 1 A g−1 with high rate capability (54.7% at 10 A g−1) and good cycling stability.

Facile synthesis of porous MnCo2O4.5 hierarchical architectures for high- rate supercapacitors

Porous urchin-like MnCo2O4.5 hierarchical architectures (~4–6 μm in diameter) synthesized by a facile hydrothermal route followed by a calcination process exhibited a specific capacitance of 151.2 F g−1 at 5 mV s−1, outstanding rate capability with 83.6% specific capacitance retention even when the current density is increased 50 times and excellent long-term cycle stability at progressively varied current densities and could be considered as a potential mixed transition metal oxide material for high-rate supercapacitors in some special applications that do not require a high capacitance.

Self-assembling hybrid NiO/Co3O4 ultrathin and mesoporous nanosheets into flower-like architectures for pseudocapacitance

The rational design and synthesis of mesoporous hybrid architecture electrode materials for high-performance pseudocapacitor applications still remains a challenge. Herein, we demonstrate the design and fabrication of hybrid NiO/Co3O4 flower-like mesoporous architectures on a large-scale for high-performance supercapacitors by a facile, environmentally friendly, and low-cost synthetic method. The as-synthesized hybrid NiO/Co3O4 flower-like architectures show a high specific capacitance of 1068 F g−1 at a scan rate of 5 mV s−1 and 1190 F g−1 at a current density of 4 A g−1, a good rate capability even at high current densities and an excellent long-term cycling stability (less than 1% loss of the maximum specific capacitance after 5000 cycles), which can be mainly attributed to their morphological characteristics of mesoporous and ultrathin nanosheets self-assembling into flower-like architectures, as well as a rational composition of the two constituents. The remarkable electrochemical properties, as well as many advantages associated with the synthetic method, should make the present architectures competitive electrode materials for next generation supercapacitors.

Hydrophilic molybdenum oxide nanomaterials with controlled morphology and strong plasmonic absorption for photothermal ablation of cancer cells.

The molybdenum oxide nanosheets have shown strong localized surface plasmon resonance (LSPR) absorption in the near-infrared (NIR) region. However, the long alky chains of ligands made them hydrophobic and less biocompatible. To meet the requirements of molybdenum based nanomaterials for use as a future photothermal therapy, a simple hydrothermal route has been developed for hydrophilic molybdenum oxide nanospheres and nanoribbons using a molybdenum precursor and poly(ethylene glycol) (PEG). First, molybdenum oxide nanomaterials prepared in the presence of PEG exhibit strong localized surface plasmon resonance (LSPR) absorption in near-infrared (NIR) region, compared with that of no PEG. Second, elevation of synthetic temperature leads to a gradual transformation of molybdenum oxide nanospheres into nanoribbons, entailing the evolution of an intense LSPR absorption in the NIR region. Third, as-prepared molybdenum oxide nanomaterials coated with PEG possess a hydrophilic property and thus can be directly used for biological applications without additional post treatments. Moreover, molybdenum oxide nanoribbons as a model of photothermal materials can efficiently convert the 980 nm wavelength laser energy into heat energy, and this localized hyperthermia produces the effective thermal ablation of cancer cells, meaning a potential photothermal material.

Effect of temperature on the performance of ultrafine MnO2 nanobelt supercapacitors

We have reported a facile, template-free and effective electrochemical method to grow MnO2 ultrafine nanobelts on Ni foam. Electrochemical measurements showed that the MnO2 nanobelt electrode exhibited an enhanced specific capacitance of 509 F g−1 at 200 mA g−1 at 50 °C. More importantly, the specific capacitance of the MnO2 nanobelt electrode nearly has 91.3% retention after 5000 cycles with repeated heating and cooling in the temperature range of 0 to 50 °C, showing good high temperature-resistive long-term cycle stability.

One pot synthesis of nickel foam supported self-assembly of NiWO4 and CoWO4 nanostructures that act as high performance electrochemical capacitor electrodes

In this work, we report a facile one-step hydrothermal approach to synthesize NiWO4 and CoWO4 nanostructures on nickel foam as binder-free electrodes for use as supercapacitors. The as-synthesized materials showed excellent electrochemical performance, with a high specific capacitance of 797.8 F g−1 and 764.4 F g−1 at a current density of 1 A g−1 after 3000 cycles. On increasing the current density by 20 times, the rate capabilities still maintained 55.6% and 50.6% of the original value for NiWO4/Ni foam and CoWO4/Ni foam, respectively. Moreover, both of these materials exhibited outstanding cycling stability, the 6000th cycle at 50 mV s−1 demonstrated 2.06 and 2.81 times better capacitance than the initial cycles for NiWO4/Ni foam and CoWO4/Ni foam, respectively. To our knowledge, this capacitance performance is better than any previously reported value for these materials and is a consequence of the highly evolved surface area/microstructure of the materials formed by this technique.

S, N‐Co‐Doped Graphene‐Nickel Cobalt Sulfide Aerogel: Improved Energy Storage and Electrocatalytic Performance

Metal sulfides are commonly used in energy storage and electrocatalysts due to their redox centers and active sites. Most literature reports show that their performance decreases significantly caused by oxidation in alkaline electrolyte during electrochemical testing. Herein, S and N co‐doped graphene‐based nickel cobalt sulfide aerogels are synthesized for use as rechargeable alkaline battery electrodes and oxygen reduction reaction (ORR) catalysts. Notably, this system shows improved cyclability due to the stabilization effect of the S and N co‐doped graphene aerogel (SNGA). This reduces the rate of oxidation and the decay of electronic conductivity of the metal sulfides materials in alkaline electrolyte, i.e., the capacity decrease of CoNi2S4/SNGA is 4.2% for 10 000 cycles in a three‐electrode test; the current retention of 88.6% for Co—S/SNGA after 12 000 s current–time chronoamperometric response in the ORR test is higher than corresponding Co—S nanoparticles and Co—S/non‐doped graphene aerogels. Importantly, the results here confirm that the Ni—Co—S ternary materials behave as an electrode for rechargeable alkaline batteries rather than supercapacitors electrodes in three‐electrode test as commonly described and accepted in the literature. Furthermore, formulas to evaluate the performance of hybrid battery devices are specified.

Phase-controlled synthesis and gas-sensing properties of zinc stannate (ZnSnO3 and Zn2SnO4) faceted solid and hollow microcrystals

Well-defined faceted zinc stannate, including cubic ZnSnO3 and octahedral Zn2SnO4, microcrystals were synthesized in a large scale by a one-step chemical solution route, in which the phase control was simply accomplished by only changing stannic precursors. These faceted cubic ZnSnO3 and octahedral Zn2SnO4 microcrystals are easily converted to faceted hollow structures with a shape preserved through an acid etching process. Possible growth and etching mechanisms of these faceted microcrystals have been proposed. The hollow structures of zinc stannate were exploited as gas sensors and exhibit improved sensing performances to a series of gases (especially with regard to H2S and C2H5OH); moreover, the sensitivity and recovery time of Zn2SnO4 hollow octahedral structures to H2S and C2H5OH are both higher than those of the cubic structures, which may find potential industrial applications in detecting gases.

Ni(OH)2/CoO/reduced graphene oxide composites with excellent electrochemical properties

Ni(OH)2/CoO/rGO composites, which were synthesized via a one-step solvothermal route, exhibit excellent electrochemical properties, e.g., a specific capacitance up to 1317 F g−1 at a current density of 2 A g−1 and 1056 F g−1 at 5 mV s−1 with good cyclability.