This paper presents a review of the research progress in the carbon-metal oxide composites for supercapacitor electrodes. In the past decade, various carbon-metal oxide composite electrodes have been developed by integrating metal oxides into different carbon nanostructures including zero-dimensional carbon nanoparticles, one-dimensional nanostructures (carbon nanotubes and carbon nanofibers), two-dimensional nanosheets (graphene and reduced graphene oxides) as well as three-dimensional porous carbon nano-architectures. This paper has described the constituent, the structure and the properties of the carbon-metal oxide composites. An emphasis is placed on the synergistic effects of the composite on the performance of supercapacitors in terms of specific capacitance, energy density, power density, rate capability and cyclic stability. This paper has also discussed the physico-chemical processes such as charge transport, ion diffusion and redox reactions involved in supercapacitors.

Plasmonic metal nanostructures have been incorporated into semiconductors to enhance the solar-light harvesting and the energy-conversion efficiency. So far the mechanism of energy transfer from the plasmonic metal to semiconductors remains unclear. Herein the underlying plasmonic energy-transfer mechanism is unambiguously determined in Au@SiO(2)@Cu(2)O sandwich nanostructures by transient-absorption and photocatalysis action spectrum measurement. The gold core converts the energy of incident photons into localized surface plasmon resonance oscillations and transfers the plasmonic energy to the Cu(2)O semiconductor shell via resonant energy transfer (RET). RET generates electron-hole pairs in the semiconductor by the dipole-dipole interaction between the plasmonic metal (donor) and semiconductor (acceptor), which greatly enhances the visible-light photocatalytic activity as compared to the semiconductor alone. RET from a plasmonic metal to a semiconductor is a viable and efficient mechanism that can be used to guide the design of photocatalysts, photovoltaics, and other optoelectronic devices.

Experiments combined with the density functional theory (DFT) calculation have been performed to understand the underlying photocatalysis mechanism of the nitrogen-doped titania nanobelts. Nitrogen-doped anatase titania nanobelts are prepared via hydrothermal processing and subsequent heat treatment in NH(3). Both the nitrogen content and the oxygen vacancy concentration increase with increasing the NH(3) treatment temperature. Nitrogen doping leads to an add-on shoulder on the edge of the valence band, the localized N 2p levels above the valence band maximum, and the 3d states of Ti(3+) below the conduction band, which is confirmed by DFT calculation and X-ray photoelectron spectroscopy (XPS) measurement. Extension of the light absorption from the ultraviolet (UV) region to the visible-light region arises from the N 2p levels near the valence band and from the color centers induced by the oxygen vacancies and the Ti(3+) species. Nitrogen doping allows visible-light-responsive photocatalytic activity but lowers UV-light-responsive photocatalytic activity. The visible-light photocatalytic activity originates from the N 2p levels near the valence band. The oxygen vacancies and the associated Ti(3+) species act as the recombination centers for the photoinduced electrons and holes. They reduce the photocatalytic activity although they contribute to the visible light absorbance.

Molybdenum disulfide (MoS2) is a promising candidate for solar hydrogen generation but it alone has negligible photocatalytic activity. In this work, 5-20 nm sized p-type MoS2 nanoplatelets are deposited on the n-type nitrogen-doped reduced graphene oxide (n-rGO) nanosheets to form multiple nanoscale p-n junctions in each rGO nanosheet. The p-MoS2/n-rGO heterostructure shows significant photocatalytic activity toward the hydrogen evolution reaction (HER) in the wavelength range from the ultraviolet light through the near-infrared light. The photoelectrochemical measurement shows that the p-MoS2/n-rGO junction greatly enhances the charge generation and suppresses the charge recombination, which is responsible for enhancement of solar hydrogen generation. The p-MoS2/n-rGO is an earth-abundant and environmentally benign photocatalyst for solar hydrogen generation.

We introduce a hybrid technique that combines the robustness of frequency-resolved coherent anti-Stokes Raman scattering (CARS) with the advantages of time-resolved CARS spectroscopy. Instantaneous coherent broadband excitation of several characteristic molecular vibrations and the subsequent probing of these vibrations by an optimally shaped time-delayed narrowband laser pulse help to suppress the nonresonant background and to retrieve the species-specific signal. We used this technique for coherent Raman spectroscopy of sodium dipicolinate powder, which is similar to calcium dipicolinate (a marker molecule for bacterial endospores, such as Bacillus subtilis and Bacillus anthracis), and we demonstrated a rapid and highly specific detection scheme that works even in the presence of multiple scattering.

20 nm sized Co 3 O 4 nanoparticles are in-situ grown on the chemically reduced graphene oxide (rGO) sheets to form a rGO-Co 3 O 4 composite during hydrothermal processing. The rGO-Co 3 O 4 composite is employed as the pseudocapacitor electrode in the 2 M KOH aqueous electrolyte solution. The rGOCo 3 O 4 composite electrode exhibits a specific capacitance of 472 F/g at a scan rate of 2 mV/s in a twoelectrode cell. 82.6% of capacitance is retained when the scan rate increases to 100 mV/s. The rGOCo 3 O 4 composite electrode shows high rate capability and excellent long-term stability. It also exhibits high energy density at relatively high power density. The energy density reaches 39.0 Wh/kg at a power density of 8.3 kW/kg. The super performance of the composite electrode is attributed to the synergistic effects of small size and good redox activity of the Co 3 O 4 particles combined with high electronic conductivity of the rGO sheets.

The photocatalytic water oxidation activity of hematite (α-Fe2O3) has been greatly enhanced by incorporating hematite nanoparticles on the reduced graphene oxide (rGO) nanosheets. Photoelectrochemical measurement results show that coupling the hematite nanoparticles with the rGO greatly increases the photocurrent and reduces the charge recombination rate. Transient absorption spectroscopy and time-domain terahertz spectroscopy have provided the direct evidence that the photogenerated electrons have transferred as the mobile carriers from α-Fe2O3 to rGO, which enhances the charge separation and suppresses the charge recombination. This work has provided new insight into the mechanism of photocatalysis enhancement by reduced graphene oxide, which has implications in the design of semiconductor/graphene heterojunction photocatalysts.

It is important to address the challenges posed with the ever-increasing demand for energy supply and environmental sustainability. Activated carbon, which is the common material for commercial supercapacitor electrodes, is currently derived from petroleum-based precursors. This paper presents an effective synthetic method that utilizes waste tires as the precursor to prepare the activated carbon electrodes by the pyrolysis and chemical activation processes. Adjusting the activation parameters can tailor multiple physical properties of the resulting activated carbon, which in turns tunes the performance of the activated carbon electrode. Statistical multiple linear regression and stepwise regression methods are employed to investigate the dependence of the specific capacitance and the rate capability upon the physical properties (such as porosity) of the activated carbon electrode. The specific capacitance of activated carbon electrode is controlled by the micropore volume but independent of the mesopores volume. The rate capability is dominated by the mesopore/micropore volume ratio instead of the absolute value of mesopore volume.