Si Yin Tee

Recent Progress in Energy-Driven Water Splitting

Hydrogen is readily obtained from renewable and non‐renewable resources via water splitting by using thermal, electrical, photonic and biochemical energy. The major hydrogen production is generated from thermal energy through steam reforming/gasification of fossil fuel. As the commonly used non‐renewable resources will be depleted in the long run, there is great demand to utilize renewable energy resources for hydrogen production. Most of the renewable resources may be used to produce electricity for driving water splitting while challenges remain to improve cost‐effectiveness. As the most abundant energy resource, the direct conversion of solar energy to hydrogen is considered the most sustainable energy production method without causing pollutions to the environment. In overall, this review briefly summarizes thermolytic, electrolytic, photolytic and biolytic water splitting. It highlights photonic and electrical driven water splitting together with photovoltaic‐integrated solar‐driven water electrolysis.

Metal nanostructures for non-enzymatic glucose sensing.

This review covers the recent development of metal nanostructures in electrochemical non-enzymatic glucose sensing. It highlights a variety of nanostructured materials including noble metals, other transition metals, bimetallic systems, and their hybrid with carbon-based nanomaterials. Particularly, attention is devoted to numerous approaches that have been implemented for improving the sensors performance by tailoring size, shape, composition, effective surface area, adsorption capability and electron-transfer properties. The correlation of the metal nanostructures to the glucose sensing performance is addressed with respect to the linear concentration range, sensitivity and detection limit. In overall, this review provides important clues from the recent scientific achievements of glucose sensor nanomaterials which will be essentially useful in designing better and more effective electrocatalysts for future electrochemical sensing industry.

Temperature and chemical bonding-directed self-assembly of cobalt phosphide nanowires in reaction solutions into vertical and horizontal alignments.

The preparation of vertically or horizontally aligned self-assemblies of CoP nanowires is demonstrated for the first time by aging them in the reaction solution for a sufficient time at 20 or 0 °C. This strategy opens up a way for exploring the controlled self-assembly of various highly anisotropic nanostructures into long-range ordered structures with collective properties.

Cobalt sulfide nanoparticles decorated on TiO2 nanotubes via thermal vapor sulfurization of conformal TiO2-coated Co(CO3)0.5(OH)·0.11H2O core–shell nanowires for energy storage applications

Core–shell nanowires, consisting of Co(CO3)0.5(OH)·0.11H2O cores (∼80 nm in diameter and ∼2 μm in length) and TiO2 shells (∼20 nm in thickness), have been fabricated on various substrates via hydrothermal synthesis of the crystalline nanowire cores at 90 °C followed by atomic layer deposition (ALD) of the conformal amorphous shells at 25 °C. Post-growth thermal vapor sulfurization of such Co(CO3)0.5(OH)·0.11H2O–TiO2 core–shell nanowires results in hybrid nanostructures of nanotubes decorated by nanoparticles. A combination of X-ray diffraction, transmission electron microscopy, and energy-dispersive X-ray spectroscopy revealed that the nanotubes are anatase crystalline TiO2 while the nanoparticles decorated on the walls of the nanotubes are dominated by Co3S4 crystallites. The hybrid nanostructures have been electrochemically characterized in a 2 M KOH electrolyte, they exhibit a specific capacitance of 650 F g−1 at a scan rate of 10 mV s−1. However, the sulfurized TiO2 nanotubes, from which the nanowire cores were etched away in a dilute HCl (0.2 M) solution before the sulfurization, do not exhibit any apparent pseudocapacitance behaviors. They are more likely supporting templates in the hybrid nanostructures. These properties of the obtained hybrid nanostructures indicate that the cobalt sulfide nanoparticles decorated on TiO2 nanotubes fabricated by thermal vapor sulfurization can be promising electrodes for energy storage applications.

Amorphous ruthenium nanoparticles for enhanced electrochemical water splitting

This paper demonstrates an optimized fabrication of amorphous Ru nanoparticles through annealing at various temperatures ranging from 150 to 700 °C, which are used as water oxidation catalyst for effective electrochemical water splitting under a low overpotential of less than 300 mV. The amorphous Ru nanoparticles with short-range ordered structure exhibit an optimal and stable electrocatalytic activity after annealing at 250 °C. Interestingly, a small quantity of such Ru nanoparticles in a thin film on fluorine-doped tin oxide glass is also effectively driven by a conventional crystalline silicon solar cell that has excellent capability for harvesting visible light. Remarkably, it achieves an overall solar-to-hydrogen efficiency of 11.3% in acidic electrolyte.

Effect of La-Doping on optical bandgap and photoelectrochemical performance of hematite nanostructures

La-doped hematite nanotubes are fabricated by electrospinning of a sol–gel solution consisting of La(III) acetylacetonate hydrate/polyvinylpyrrolidone(PVP)/ferric acetylacetonate, and subsequent sintering at 500 °C for 5 h in air. Further grinding of these nanotubes affords La-doped hematite nanoparticles. FESEM EDX indicates that the La content is 3.66 mol% in La-doped hematite. HRTEM and XRD reveal that La3+ cations are doped into the hematite crystal lattice. UV-Vis diffuse reflectance shows increased light absorption for La-doped hematite, with the bandgap reduced from 2.58 eV to 2.46 eV. EIS and four-probe characterization demonstrate that La-doping reduces charge transfer resistance and increases the electrical conductivity, thus leading to improved charge transportation. Photoelectrochemical (PEC) water splitting studies show that under 100 mW cm−2 simulated solar irradiation, La-doped hematite nanoparticles demonstrate a net photocurrent density up to 0.112 and 0.270 mA cm−2 at 1.23 and 1.60 V vs. RHE, which are 187% and 63% higher than pristine hematite nanoparticles, respectively. The effect of La-doping on improving electrical conductivity, light absorption, and PEC performance is mainly attributed to the intensification of crystal orientation along the (110) plane and the lattice expansion caused by the La3+ cations, which have much larger radii and are more electron-rich than Fe3+.

Preparation, Functionality, and Application of Metal Oxide-coated Noble Metal Nanoparticles.

With their remarkable properties and wide-ranging applications, nanostructures of noble metals and metal oxides have been receiving significantly increased attention in recent years. The desire to combine the properties of these two functional materials for specific applications has naturally prompted research in the design and synthesis of novel nanocomposites, consisting of both noble metal and metal-oxide components. In this review, particular attention is given to core-shell type metal oxide-coated noble metal nanostructures (i.e., metal@oxide), which display potential utility in applications, including photothermal therapy, catalytic conversions, photocatalysis, molecular sensing, and photovoltaics. Emerging research directions and areas are envisioned at the end to solicit more attention and work in this regard.

Electrostatic-Driven Exfoliation and Hybridization of 2D Nanomaterials

Here, direct and effective electrostatic-driven exfoliation of tungsten trioxide (WO3 ) powder into atomically thin WO3 nanosheets is demonstrated for the first time. Experimental evidence together with theoretical simulations clearly reveal that the strong binding of bovine serum albumin (BSA) on the surface of WO3 via the protonation of NH2 groups in acidic conditions leads to the effective exfoliation of WO3 nanosheets under sonication. The exfoliated WO3 nanosheets have a greatly improved dispersity and stability due to surface-protective function of BSA, and exhibit a better performance and unique advantages in applications such as visible-light-driven photocatalysis, high-capacity adsorption, and fast electrochromics. Further, simultaneous exfoliation and hybridization of WO3 and MoS2 nanosheets are demonstrated to form hybrid WO3 /MoS2 nanosheets through respective electrostatic and hydrophobic interaction processes. In addition, this electrostatic-driven exfoliation strategy is applied to exfoliate ultrathin black-phosphorus nanosheets from its bulk to exhibit a greatly improved stability due to the surface protection by BSA. Overall, the work presented not only presents a facile and effective route to fabricate 2D materials but also brings more opportunities to exploit unusual exotic and synergistic properties in resulting hybrid 2D materials for novel applications.

Selective Formation of Ternary Cu-Ge-S Nanostructures in Solution

In this paper, special attention is given to ternary copper germanium sulfides (Cu–Ge–S), which belong to an important class of mixed-metal chalcogenide materials called the copper-based multinary sulfides (CMSs). Like most members of the CMS family, the Cu–Ge–S compounds display enormous potential in energy-related applications especially in their nanostructured forms, but there exists very little research on the preparation of Cu–Ge–S materials in the nanometer size range. Herein, we report a simple noninjection protocol for the selective synthesis of Cu–Ge–S nanomaterials. We show that variations in the solvent environment can lead to different types of Cu–Ge–S nanostructures (i.e., from large, faceted Cu8GeS6 to smaller, irregularly-shaped Cu2GeS3). Our investigation of the growth process revealed interesting formation pathways, which could help advance our understanding of the selective formation of compositionally and structurally diverse multinary materials in solution.