Ghim Wei Ho

Mesophase Ordering of TiO2 Film with High Surface Area and Strong Light Harvesting for Dye-Sensitized Solar Cell

Mesophase ordering and structuring are carried out to attain optimized pore morphology, high crystallinity, stable porous framework, and crack-free mesoporous titanium dioxide (TiO(2)) films. The pore structure (quasi-hexagonal and lamellar) can be controlled via the concentration of copolymer, resulting in two different types of micellar packing. The calcination temperature is also controlled to ensure a well-crystalline and stable porous framework. Finally, the synthesized mesoporous TiO(2) film is modified by adding P25 nanoparticles, which act as scattering centers and function as active binders to prevent formation of microcracks. Adding P25 nanoparticles into mesoporous structure helps to provide strong light-harvesting capability and large surface area for high -efficiency dye-sensitized solar cells (DSSC). The short-circuit photocurrent density (J(sc)) of the cell made from mixture of mesoporous TiO(2) and P25 nanoparticles displays a higher efficiency of approximately 6.5% compared to the other homogeneous films. A combination of factors such as increased surface area, introduction of light-scattering particles, and high crystallinity of the mesoporous films leads to enhanced cell performance.

Controlled synthesis and application of ZnO nanoparticles, nanorods and nanospheres in dye-sensitized solar cells

Several important synthetic parameters such as precursor concentration, rate of evaporation and reaction time are found to determine the growth of ZnO nanostructures. These reaction parameters can be tailored and tuned to produce a variety of nanostructures ranging from nanoparticles, nanorods and nanospheres. The nanorods are structurally uniform made up of crystallographically oriented attached nanoparticles while the nanospheres are made up of several closely packed and randomly aligned nanocrystallites. XRD spectra of both the nanoparticles and nanorods exhibit typical diffraction peaks of a well-crystalline wurtzite ZnO structure. Finally, solar cells made up of ZnO nanoparticles and nanorods electrodes with absorbed ruthenium dye (N3) were measured to have a power conversion efficiency of 0.87% and 1.32%, respectively.

Structural design of TiO2-based photocatalyst for H2 production and degradation applications

TiO2-based photocatalysts, being inexpensive and abundant, in conjunction with having high photostability and environmentally friendly characteristics, are the most extensively studied photocatalytic material for hydrogen production and pollutant degradation. However, its existing issues, such as wide bandgap, high overpotential and rapid recombination of photogenerated carriers limit its photocatalytic properties. The opportunities for structural development of a TiO2 nanomaterial towards highly efficient and pragmatic photocatalysis applications are evidently plentiful. Hence, in this review, we will look into critical structural engineering strategies that give favorable physicochemical properties such as improved light absorption, photostability, charge-carrier dynamics, increase surface area etc. that benefit photocatalysis functionalities. Amongst the various structural engineering options, we will be covering the most prevalent and elegant core–shell and hierarchical structural designs, which rationally combine the advantages of structural manipulation and multi-material composition engineering. This review aims to provide a comprehensive and contemporary overview, as well as a guide of the development of new generation TiO2 based photocatalysts via structural design for improved solar energy conversion technologies.

Influence of a novel fluorosurfactant modified PEDOT:PSS hole transport layer on the performance of inverted organic solar cells

Under ambient conditions the long term stability of non-encapsulated organic solar cells with conventional device architecture is lower than the technical lifetime of devices with an inverted configuration. The removal of the interface between the ITO (indium tin oxide) layer and the acidic PEDOT:PSS layer along with the substitution of a low work function metal electrode with a high work function metal electrode in the inverted device configuration renders relatively higher stability in these devices. However, one of the main inherent difficulties involving the fabrication of devices with such inverted architecture is the wettability of the hydrophilic PEDOT:PSS onto the photoactive layer such as the P3HT:PCBM blend which is hydrophobic in nature. To overcome this, we have used a novel fluorosurfactant, Capstone® Dupont™ FS-31 (CFS-31), as a substitute to the conventional Zonyl FS-300 as an additive to PEDOT:PSS. A smooth and uniform PEDOT:PSS layer was coated onto the P3HT:PCBM blend layer by addition of CFS-31 alone without any further treatments. Using this surfactant, an efficiency of 3.1% and a stable device performance (up to 400 hours) under ambient conditions without encapsulation have been achieved.

Bidentate-complex-derived TiO2/carbon dot photocatalysts: in situ synthesis, versatile heterostructures, and enhanced H2 evolution

In this paper, we demonstrate a series of metal-free and inexpensive TiO2/carbon dot (CD) nanocomposites via facile hydrothermal synthesis from bidentate complexes of a green carbon source, vitamin C (VC). Other than the importance of deriving CDs from alternate carbon materials instead of graphitic precursors, the in situ transformed CDs from VC ensure the formation of chemically coupled heterostructures, TiO2/CDs, which serve as efficient photocatalysts exhibiting a higher H2 evolution rate from photocatalytic reactions up to 9.7 times than that of bare TiO2. Interestingly, the H2 evolution rate can effectively be tuned by VC amounts, hydrothermal temperatures and reaction durations. The mechanism of the enhanced H2 evolution rate was also discussed, in which the synergetic effects of the hydrothermal treatment along with the favourable electron transfer ability and upconverted photoluminescence of CDs contribute to the improved photocatalytic behaviour.

Plasmonic photothermic directed broadband sunlight harnessing for seawater catalysis and desalination

Using readily available renewable resources, i.e. solar energy and seawater, to secure sustainable fuel and freshwater for humanity is an impactful quest. Here, we have designed solar thermal collector nanocomposites (SiO2/Ag@TiO2 core–shell) that possess efficient photothermic properties for highly targeted interfacial phase transition reactions that are synergistically favorable for both seawater catalysis and desalination reactions. The photothermic effect arising from plasmonic metal nanoparticles causes localized interfacial heating which directly triggers surface-dominated catalysis and steam generation processes, with minimal heat losses, reduced thermal masses and optics implementation. The solar thermal collector nanocomposites are seawater/photo stable for practical solar conversion of seawater to simultaneously produce clean energy and water. Finally, a proof-of-concept all-in-one compact solar hydrogen and distillate production prototype demonstrates the viability of sustainable photothermic driven catalysis and desalination of seawater under natural sunlight. Importantly, this approach holds great promise for enhancing energy and water productivity without considerable capital, infrastructure and environmental ramifications.

In Situ Transformation of MOFs into Layered Double Hydroxide Embedded Metal Sulfides for Improved Electrocatalytic and Supercapacitive Performance

Direct adoption of metal-organic frameworks (MOFs) as electrode materials shows impoverished electrochemical performance owing to low electrical conductivity and poor chemical stability. In this study, we demonstrate self-templated pseudomorphic transformation of MOF into surface chemistry rich hollow framework that delivers highly reactive, durable, and universal electrochemically active energy conversion and storage functionalities. In situ pseudomorphic transformation of MOF-derived hollow rhombic dodecahedron template and sulfurization of nickel cobalt layered double hydroxides (NiCo-LDHs) lead to the construction of interlayered metal sulfides (NiCo-LDH/Co9 S8 ) system. The embedment of metal sulfide species (Co9 S8 ) at the LDH intergalleries offers optimal interfacing of the hybrid constituent elements and materials stability. The hybrid NiCo-LDH/Co9 S8 system collectively presents an ideal porous structure, rich redox chemistry, and high electrical conductivity matrix. This leads to a significant enhancement in its complementary electrocatalytic hydrogen evolution and supercapacitive energy storage properties. This work establishes the potential of MOF derived scaffold for designing of novel class hybrid inorganic-organic functional materials for electrochemical applications and beyond.

Synthesis of well-aligned multiwalled carbon nanotubes on Ni catalyst using radio frequency plasma-enhanced chemical vapor deposition

Abstract Well-aligned multiwalled nanotubes (MWNTs) have been deposited by plasma-enhanced chemical vapor deposition of acetylene (C2H2) on nickel-coated quartz glass at 650°C. The growth reaction of the carbon nanotubes was found to be dependent on the morphology of the metal catalyst, which was related to the thickness of the Ni catalyst film. The flow rate of the hydrocarbon gases was observed to be crucial for the growth of high density carbon nanotubes. Well-aligned and dense carbon nanotubes were grown uniformly on 15-nm thick Ni film with a flow rate of 15 and 30 sccm for C2H2 and NH3, respectively. Transmission electron microscopy confirmed the structures to be hollow with Ni particles encapsulated by the multi-walls at the tip of the nanotube.

Hierarchical Assembly of SnO2/ZnO Nanostructures for Enhanced Photocatalytic Performance

SnO2/ZnO hierarchical heterostructures have been successfully synthesized by combining electrospinning technique and hydrothermal method. Various morphologies of the secondary ZnO nanostructures including nanorods (NRs) and nanosheets (NSs) can be tailored by adding surfactants. Photocatalytic performance of the heterostructures was investigated and obvious enhancement was demonstrated in degradation of the organic pollutant, compared to the primary SnO2-based nanofibers (NFs) and bare ZnO. Furthermore, it was found that the H2 evolution from water splitting was achieved by photocatalysis of heterostructured nanocomposites after sulfurization treatment. This synthetic methodology described herein promises to be an effective approach for fabricating variety of nanostructures for enhanced catalytic applications. The heterostructured nanomaterials have considerable potential to address the environmental and energy issues via degradation of pollutant and generation of clean H2 fuel.

Green chemistry synthesis of a nanocomposite graphene hydrogel with three-dimensional nano-mesopores for photocatalytic H2 production

In this work, we have developed a nanocomposite graphene hydrogel (NGH) based on green chemistry, employing vitamin C (VC) to attain a supramolecular 3D network of hybrid nanostructured materials. Here, it is shown that the hydrogel is an appropriate and robust host for stable a TiO2 semiconductor catalyst sensitized with visible light responsive nanostructured particles. The NGH is tailored with well-defined nano-mesopores, a large surface area, a highly dispersive nanosheet–nanorods–nanoparticle composite, and enhance visible light absorption. Finally, we demonstrate practical applications of utilizing the NGH with water containing pores for photocatalytic H2 production. An important pragmatic consideration of using a NGH is the ease of separation and recovery of the nanosized catalyst after the photoreaction which would otherwise require extensive and expensive nanofiltration.