Hierarchical 3D Mesoporous Conch-like Co3O4 Nanostructure Arrays for High-Performance Supercapacitors

Bi(nanoparticles)/CNx(nanosheets) nanocomposites as high capacity and stable electrode materials for supercapacitors: the role of urea

The evolution of high-performance and stable electrode materials for supercapacitors plays a vital role in the next generation of energy storage devices. In this work we present a simple method for preparing Bi(nanoparticles)/CNx(nanosheets) nanocomposites as electrode materials for supercapacitors, which were synthesized by thermally treating bismuth citrate and urea at 550-700 °C under an Ar atmosphere. According to physicochemical studies (XRD, SEM, TG-DTA, XPS, FTIR, and BET), a "smeared" bismuth formation or the formation of nanoparticles on the CNx surface of interwoven 2D-nanosheets at different calcination temperatures was observed. Electrochemical measurements show that the specific capacity of the composites can reach 1251 F g-1 (more than 90% of the theoretical value) at a current density of 500 mA g-1 in a 6 M KOH electrolyte, and most two-dimensional CNx-based nanostructures remain intact after multiple galvanostatic charge-discharge processes, which is promising for the development of highly efficient supercapacitors. A supercapacitor composed of Bi/CNx nanocomposites for the negative electrode and Ni-layered hydroxide for the positive electrode demonstrates a high energy density of 58 W h kg-1 with a power density of 800 W kg-1 accompanied by a good cycle life (the parameters decreased down to only 78% after 1000 charge-discharge cycles). Our current results indicate that the addition of urea not only determines the morphology of the composites, but also lays the foundation for the development of new types of nanocomposites for the power industry.

Electrochemical oxidation and advanced oxidation processes using a 3D hexagonal Co3O4 array anode for 4-nitrophenol decomposition coupled with simultaneous CO2 conversion to liquid fuels via a flower-like CuO cathode

A novel electrocatalytic system was developed to realize one-pot conversion of organic pollutants into liquid fuels such as methanol (CH₃OH) and ethanol (C₂H₅OH). The process combines the catalytic oxidation of organic pollutants with electrocatalytic reduction of CO₂. We first coupled the electrocatalytic process with SO₄^•--based advanced oxidation processes (AOPs) for the degradation of 4-nitrophenol (4-NP) using a 3D-hexagonal Co₃O₄ anode. In this step, 4-NP was mineralized to CO₂, and then the CO₂ was converted to CH₃OH and C₂H₅OH by electrocatalytic reduction using a flower-like CuO cathode. The experimental results show the destruction of 4-NP (60 mL, 10 mg/L) can be as high as 99%. In addition, the yields of CH₃OH and C₂H₅OH were 98.29 μmol/L and 40.95 μmol/L, respectively, which represents a conversion of 41.8% of 4-NP into liquid fuels; the electron efficiency was 73.1%. In addition, we found that 3D-hexagonal arrays of Co₃O₄ with different morphologies can be obtained by adding different amounts of urea. We also investigated the formation mechanism of novel 3D-hexagonal Co₃O₄ arrays for the first time. A mechanism was proposed to explain the electrocatalytic steps involved in the conversion of 4-NP to CH₃OH and C₂H₅OH and the synergetic effects between AOPs and electrocatalysis.

Facile Self-Cross-Linking Synthesis of 3D Nanoporous Co3O4/Carbon Hybrid Electrode Materials for Supercapacitors

A hybrid electrode material with ultrafine Co3O4 nanoparticles embedded throughout a hierarchically nanoporous graphitic carbon matrix has been obtained via a facile self-cross-linking route. Sodium alginate, a biopolymer with an ability of cross-linking with multivalent cobalt cations to form ordered microcrystalline zones, is used as a carbon source to produce nanoporous carbon frameworks of the hybrids. Ultrafine Co3O4 nanoparticles with tunable particle size (3-30 nm) are in situ grown within the nanoporous graphitic carbon frameworks by a simple carbonization of Co-cross-linked alginate. The obtained hybrid electrodes exhibit high specific capacitance of 645, 548, 486, and 347 F/g at scan rates of 5, 10, 20, and 50 mV/s, respectively, and excellent cycle performance with only 1% fading in capacitance after 10 000 cycles at a high current density of 20 A/g. Such excellent capacitive performance is ascribed to the collaborative contributions of well-dispersed ultrafine Co3O4 nanoparticles and conductive nanoporous carbon frameworks.

Hierarchical structures composed of MnCo2O4@MnO2 core–shell nanowire arrays with enhanced supercapacitor properties

In this paper, hierarchical MnCo₂O₄@MnO₂ core–shell nanowire arrays (MnCo₂O₄@MnO₂ NWAs) with mesoporous and large surface area are synthesized on 3D nickel foam via a facile, two-step hydrothermal approach without any adscititious surfactant and binder.

Application of novel multiple-dimensional cobalt oxides as the electroactive material on supercapacitors

A two-step hydrothermal reaction is used to synthesize the cobalt oxide nanomaterial composed of the one, two, and three dimensional nanostructures on the nickel foam.

Facile construction of graphene-like Ni3S2 nanosheets through the hydrothermally assisted sulfurization of nickel foam and their application as self-supported electrodes for supercapacitors

A facile and low-cost approach has been developed for the fabrication of large-area nickel sulfide nanosheets via the hydrothermally assisted sulfurization of Ni foam.