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Despite its large band gap, ZnO has wide applicability in many fields ranging from gas sensors to solar cells. ZnO was chosen over other materials because of its large exciton binding energy (60 meV) and its stability to high-energy radiation. In this study, ZnO nanorods were deposited on ITO glass via a simple dip coating followed by a hydrothermal growth. The morphological, structural and compositional characteristics of the prepared films were analyzed using X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), and ultraviolet-visible spectroscopy (UV-Vis). Photoelectrochemical conversion efficiencies were evaluated via photocurrent measurements under calibrated halogen lamp illumination. Thin film prepared at 120 °C for 4 h of hydrothermal treatment possessed a hexagonal wurtzite structure with the crystallite size of 19.2 nm. The average diameter of the ZnO nanorods was 37.7 nm and the thickness was found to be 2680.2 nm. According to FESEM images, as the hydrothermal growth temperature increases, the nanorod diameter become smaller. Moreover, the thickness of the nanorods increase with the growth time. Therefore, the sample prepared at 120 °C for 4 h displayed an impressive photoresponse by achieving high current density of 0.1944 mA/cm2.

One of the major challenges in the fields of heterogeneous catalysis and carbon nanotubes (CNTs) synthesis via chemical vapour decomposition (CVD) method is lack of established theoretical model for direct selection of carbon precursor/metal catalyst matrix, which constitutes the most important material parameters of the whole process. In the present report, a theoretical model is proposed via kinetic theory and applied in correlating gas stoichiometry equations and the decomposition of carbon precursors with electrons of metal atoms. Theoretical predictions of this model were found to be in conformity with recent advances in the fields of heterogeneous catalysis in general and CVD synthesis of CNTs in particular. The proposed theory may compliment the current selection of carbon precursor/catalyst matrix through experimental trial and error.

Many attempts have been done to improve the capacitive performance of reduced titania nanotubes (R-TNTs) by incorporation of metal oxides via electrodeposition method. In this study, pulse reverse electrodeposition technique has been applied to deposit Mn2O3 and Co3O4 onto the R-TNTs as this technique has the ability to control the composition of targeted materials while at the same time helps in facilitating the uniformity of deposition and the size of the metal oxides onto the reduced nanotubes. Based on FESEM and TEM analyses, it is proven that both metal oxides were uniformly deposited without covering the nanotubes opening. Besides, Mn2O3 and Co3O4 with crystallite size of 13.6 nm and 12.4 nm were recorded in XRD analysis. Electrochemical analyses were performed to evaluate the capacitive performance of both deposited metal oxides. The CV profiles of both metal oxides showed similar patterns attributed to simultaneous charge-storage mechanisms of electric double-layer in R-TNTs and pseudocapacitance in the metal oxides. Galvanostatic charge-discharge showed Mn2O3/R-TNTs exhibits higher specific capacitance of 37.0 mF cm-2 compared to Co3O4/R-TNTs of 16.9 mF cm-2 at 0.1 mA cm-2. Moreover, these deposited samples also exhibit good electrochemical stability by retaining 87% of the initial capacity over 1000 cycles.

Particular interest has been given to the self-organized titania nanotube TiO2 thin films prepared by using anodisation method followed by annealing in the air, while the CdSe layer was potentiostatically electrodeposited onto the TiO2 nanotube films at various pH. The resulting films were studied by using energy dispersive X-ray spectroscopy, X-ray diffraction, field emission scanning electron microscopy, UV–Vis spectroscopy and photoelectrochemical analysis to characterize their compositional, crystalline structure, surface morphological, optical, and photoconversion efficiency characteristics. The resulting CdSe/TiO2 nanotube exhibits significant enhancement in optical absorption, photocurrent density and photoconversion efficiency. CdSe/TiO2 nanotube prepared at pH 3 exhibited the highest photocurrent density of 2.13 mA cm−2 and photoconversion efficiency of 1.02 % which is 51 times higher than TiO2 nanotube array. This may due to the formation of CdSe nanocrystals which were well crystallized and bonded with TiO2 NTAs contributing to the enhanced photoresponse and photostability of the overall performance of CdSe/TiO2 NTAs heterostructures.

Titania nanotube is gaining tremendous interest for its unique features including high surface area, ion-exchange ability, photocatalytic potential and prominent electrical properties. Many attempts were made to manipulate the unique properties of titania nanotubes for supercapacitor application. In this review a comprehensive list of literatures on fabrication of titania nanotubes via anodisation method in fluoride-based electrolytes and its application as supercapacitor are discussed. This review shows that the nanotube morphology can be optimized by varying the anodisation parameter such as electrolyte concentration, pH, voltage, and bath temperature. The review also includes studies on the application of titania nanotubes as supercapacitor on improving the specific capacitance value by doping with metal oxides and conducting polymers.

Co-precipitation method was adopted in the preparation of nickel–cobalt oxides for potential application in supercapacitors. The formation of spinel nickel–cobalt oxide, NiCo2O4 started below 400 °C as confirmed by X-ray diffraction analysis. Pure phase nickel cobaltite with cation ratio of 1:2 (Ni:Co) was obtained at calcination temperature of 400 °C. The spinel phase decomposed gradually until 700 °C. The calcination time for the formation of NiCo2O4 was found to be between 2 to 4 h. The particle size of the prepared sample studied by transmission electron microscopy showed a value of 9.47 nm. The electrochemical properties of the metal oxide were measured in various acidic, neutral and alkaline electrolyte systems (1.0 M HCl, 1.0 M KCl and 1.0 M KOH) by employment of cyclic voltammetry, galvanostatic charge–discharge test and electrochemical impedance spectroscopy. Ideal capacitor behaviour with the largest operating voltage of 1.0 V and good electrochemical stability were observed in NiCo2O4 using neutral KCl aqueous electrolyte. Meanwhile, the prepared sample displayed the highest surface redox activity in 1.0 M KOH alkaline electrolyte but showed the lowest electrochemical performance in acidic electrolyte. At the current density of 0.5 A g−1, 1.0 M HCl, 1.0 M KCl and 1.0 M KOH gave specific capacitance values of 3.8, 41.9 and 249.8 F g−1 respectively.

Precious metal oxides exhibit impressive characteristics that caught worldwide attention due to their promising capacitive performance, excellent electrochemical stability and low resistance, and these metal oxides have been extensively employed in supercapacitor application. This type of supercapacitors is known as redox supercapacitors or pseudocapacitors which applied faradaic process in storing energy in their systems. Thus, new materials with impressive electrochemical performance are highly demanded. In this aspect, cobaltite system with spinel structure has been the subject of intense research due to its established applications in electrochemistry. Besides, carbonaceous materials like activated carbons, carbon nanotubes, graphites, graphenes and fullerenes utilize electric double-layer capacitance whereby energy is stored by charge separation at an electrode/electrolyte interface. With greater development conducted on metal oxides and carbonaceous materials for supercapacitor application, introduction of hybrid and composite electrodes comprise of these two types of materials have been well received.

Quantum dots-sensitized solar cell (QDSSC) is one of the third generation solar cell that is the most promising low cost, easy to manufacture and highly efficient solar cell. Compared to Dye-sensitized solar cell (DSSC), quantum dots (QDs) of QDSSC has a narrow bandgap and possess excellent properties such as tunable band gaps, strong light absorption and high multiple electron generation. Titanium dioxide or titania (TiO2) is an oxides semiconductor material that is frequently used as a photoanode in this photovoltaic system due to high stability under visible light illumination. TiO2 is also known as a good photocatalyst and an excellent choice in environmental purification. The efficiencies of electron injection and light harvesting in QDSSC are affected by the nature, size morphology, and quantity of this nanomaterial. In this review, the concept and principles of the QDSSCs are reviewed. The preparation and fabrication method ofTiO2 electrode in QDSSC are also discussed. It is worthwhile to know the architecture of TiO2 in order to enhance the efficiency of QDSSC.

Co-precipitation method was adopted in the preparation of nickel-cobalt oxides for potential application in supercapacitors. The formation of spinel nickel-cobalt oxide, NiCo2O4 prepared by oxalate co-precipitation started below 400 °C as confirmed by Xray diffraction (XRD) analysis. Single phase nickel-cobalt oxide with cation ratio of 1:2 (Ni:Co) was obtained at calcination temperature of 400 °C. The spinel phase decomposed gradually until 700 °C. The calcination time for the formation of NiCo2O4 was found to be between 2 to 4 hours. The particle size of the prepared sample studied by transmission electron microscopy (TEM) showed a value of 9.5 nm. Investigation on the compositional effect of NiCo2O4 revealed that the crystallinity of the synthesized oxides improved with the increment of Ni content. The entire range of Ni:Co compositions at 400 C and 700 C were investigated with respect to the formation of phases, lattice parameter and crystallite size. Nickel-cobalt oxide series was prepared through solid-state route as well. However, NiCo2O4 co-existed with NiO in this method preparation. Moreover, solid-state route produced metal oxides with larger crystallite size than co-precipitation method. Therefore, co-precipitation served as a better method in synthesizing pure phase nanostructured NiCo2O4 compared to solid-state technique. The electrochemical properties of NiCo2O4 were measured in various acidic, neutral and alkaline electrolyte systems (1.0 M HCl, 1.0 M KCl and 1.0 M KOH) by employment of cyclic voltammetry (CV), galvanostatic charge-discharge test and electrochemical impedance spectroscopy (EIS). Ideal capacitor behaviour with the largest operating voltage of 1.0 V and good electrochemical stability were observed in NiCo2O4 using neutral KCl aqueous electrolyte. Meanwhile, the prepared sample displayed the highest surface redox activity in 1.0 M KOH alkaline electrolyte but showed the lowest electrochemical performance in acidic electrolyte. Single