Mohamed N. Hedhili

Plasmonic gold nanocrystals coupled with photonic crystal seamlessly on TiO2 nanotube photoelectrodes for efficient visible light photoelectrochemical water splitting

A visible light responsive plasmonic photocatalytic composite material is designed by rationally selecting Au nanocrystals and assembling them with the TiO(2)-based photonic crystal substrate. The selection of the Au nanocrystals is so that their surface plasmonic resonance (SPR) wavelength matches the photonic band gap of the photonic crystal and thus that the SPR of the Au receives remarkable assistance from the photonic crystal substrate. The design of the composite material is expected to significantly increase the Au SPR intensity and consequently boost the hot electron injection from the Au nanocrystals into the conduction band of TiO(2), leading to a considerably enhanced water splitting performance of the material under visible light. A proof-of-concept example is provided by assembling 20 nm Au nanocrystals, with a SPR peak at 556 nm, onto the photonic crystal which is seamlessly connected on TiO(2) nanotube array. Under visible light illumination (>420 nm), the designed material produced a photocurrent density of ~150 μA cm(-2), which is the highest value ever reported in any plasmonic Au/TiO(2) system under visible light irradiation due to the photonic crystal-assisted SPR. This work contributes to the rational design of the visible light responsive plasmonic photocatalytic composite material based on wide band gap metal oxides for photoelectrochemical applications.

Selenide‐Based Electrocatalysts and Scaffolds for Water Oxidation Applications

Selenide-based electrocatalysts and scaffolds on carbon cloth are successfully fabricated and demonstrated for enhanced water oxidation applications. A max-imum current density of 97.5 mA cm(-2) at an overpotential of a mere 300 mV and a small Tafel slope of 77 mV dec(-1) are achieved, suggesting the potential of these materials to serve as advanced oxygen evolution reaction catalysts.

Enhanced Rate Performance of Mesoporous Co3O4 Nanosheet Supercapacitor Electrodes by Hydrous RuO2 Nanoparticle Decoration

Mesoporous cobalt oxide (Co3O4) nanosheet electrode arrays are directly grown over flexible carbon paper substrates using an economical and scalable two-step process for supercapacitor applications. The interconnected nanosheet arrays form a three-dimensional network with exceptional supercapacitor performance in standard two electrode configuration. Dramatic improvement in the rate capacity of the Co3O4 nanosheets is achieved by electrodeposition of nanocrystalline, hydrous RuO2 nanoparticles dispersed on the Co3O4 nanosheets. An optimum RuO2 electrodeposition time is found to result in the best supercapacitor performance, where the controlled morphology of the electrode provides a balance between good conductivity and efficient electrolyte access to the RuO2 nanoparticles. An excellent specific capacitance of 905 F/g at 1 A/g is obtained, and a nearly constant rate performance of 78% is achieved at current density ranging from 1 to 40 A/g. The sample could retain more than 96% of its maximum capacitance even after 5000 continuous charge-discharge cycles at a constant high current density of 10 A/g. Thicker RuO2 coating, while maintaining good conductivity, results in agglomeration, decreasing electrolyte access to active material and hence the capacitive performance.

Highly Efficient Perovskite-Quantum-Dot Light-Emitting Diodes by Surface Engineering

A two-step ligand-exchange strategy is developed, in which the long-carbon- chain ligands on all-inorganic perovskite (CsPbX3 , X = Br, Cl) quantum dots (QDs) are replaced with halide-ion-pair ligands. Green and blue light-emitting diodes made from the halide-ion-pair-capped quantum dots exhibit high external quantum efficiencies compared with the untreated QDs.

High performance In2O3 thin film transistors using chemically derived aluminum oxide dielectric

We report high performance solution-deposited indium oxide thin film transistors with field-effect mobility of 127 cm2/Vs and an Ion/Ioff ratio of 106. This excellent performance is achieved by controlling the hydroxyl group content in chemically derived aluminum oxide (AlOx) thin-film dielectrics. The AlOx films annealed in the temperature range of 250–350 °C showed higher amount of Al-OH groups compared to the films annealed at 500 °C, and correspondingly higher mobility. It is proposed that the presence of Al-OH groups at the AlOx surface facilitates unintentional Al-doping and efficient oxidation of the indium oxide channel layer, leading to improved device performance.

Hollow Au@Pd and Au@Pt core–shell nanoparticles as electrocatalysts for ethanol oxidation reactions

Hybrid alloys among gold, palladium and platinum become a new category of catalysts primarily due to their enhanced catalytic effects. Enhancement means not only their effectiveness, but also their uniqueness as catalysts for the reactions that individual metals may not catalyze. Here, preparation of hollow Au@Pd and Au@Pt core–shell nanoparticles (NPs) and their use as electrocatalysts are reported. Galvanic displacement with Ag NPs is used to obtain hollow NPs, and higher reduction potential of Au compared to Ag, Pd, and Pt helps to produce hollow Au cores first, followed by Pd or Pt shell growth. Continuous and highly crystalline shell growth was observed in Au@Pd core–shell NPs, but the sporadic and porous-like structure was observed in Au@Pt core–shell NPs. Along with hollow core–shell NPs, hollow porous Pt and hollow Au NPs are also prepared from Ag seed NPs. Twin boundaries which are typically observed in large size (>20 nm) Au NPs were not observed in hollow Au NPs. This absence is believed to be due to the role of the hollows, which significantly reduce the strain energy of edges where the two lattice planes meet. In ethanol oxidation reactions in alkaline medium, hollow Au@Pd core–shell NPs show highest current density in forward scan. Hollow Au@Pt core–shell NPs maintain better catalytic activities than metallic Pt, which is thought to be due to the better crystallinity of Pt shells as well as the alloy effect of Au cores.

Inkjet printing for direct micropatterning of a superhydrophobic surface: toward biomimetic fog harvesting surfaces

The preparation of biomimetic superhydrophobic surfaces with hydrophilic micro-sized patterns is highly desirable, but a one-step, mask-free method to produce such surfaces has not previously been reported. We have developed a direct method to produce superhydrophilic micropatterns on superhydrophobic surfaces based on inkjet printing technology. This work was inspired by the efficient fog-harvesting behavior of Stenocara beetles in the Namib Desert. A mussel-inspired ink consisting of an optimized solution of dopamine was applied directly by inkjet printing to superhydrophobic surfaces. Stable Wenzels microdroplets of the dopamine solution with well-defined micropatterns were obtained on these surfaces. Superhydrophilic micropatterns with well-controlled dimensions were then readily achieved on the superhydrophobic surfaces by the formation of polydopamine via in situ polymerization. The micropatterned superhydrophobic surfaces prepared by this inkjet printing method showed enhanced water collection efficiency compared with uniform superhydrophilic and superhydrophobic surfaces. This method can be used for the facile large-scale patterning of superhydrophobic surfaces with high precision and superior pattern stability and is therefore a key step toward patterning superhydrophobic surfaces for practical applications.

Highly Selective and Complete Conversion of Cellobiose to Gluconic Acid over Au/Cs2HPW12O40 Nanocomposite Catalyst

Cellulose is the most abundant source of biomass and holds potential as an alternative to the currently dominant, but nonsustainable, fossil feedstocks. Cellulose is a polysaccharide that consists of a linear chain of d-glucose connected by a b1,4-glycosidic linkage, normally in a robust crystalline form. Although some success has been achieved in catalytic conversion of cellulose to alcohols, the effective and environment-friendly utilization of cellulose is still a challenge, mainly because cellulose is highly stable and insoluble in most solvents. Cellobiose is a glucose dimer connected by a b-1,4-glycosidic bond and represents the basic repeating structural unit as well as the major decomposition product of cellulose. Therefore, cellobiose is a good model compound for the studies of cellulose conversion. Gluconic acid is a widely used food additive and also an important intermediate for the synthesis of fine chemicals and pharmaceuticals; it is conventionally produced by the fermentation of glucose. Transitionmetal particles were used to catalyze the oxidation of glucose to gluconic acid, but the direct conversion of cellobiose to gluconic acid has been seldom reported. Hence, the selective oxidation of cellobiose to gluconic acid should attract both scientific and commercial interest, and an insight into the mechanism of this catalytic reaction would be helpful for designing new strategies for the direct conversion of cellulose. The conversion of cellobiose to gluconic acid basically requires two successive steps: the hydrolysis of cellobiose and the oxidation of the produced glucose. The desired catalyst should therefore be an acidic/oxidative bifunctional that can provide both acid sites for hydrolyzing the b-1,4-glycosidic bond and redox sites for activating oxygen to oxidize the aldehyde group to the carboxyl group (see the Supporting Information, Scheme S1). Moreover, eco-benign reactions with heterogeneous catalysts in water media are preferred. To this end, one would consider the use of a solid acid supported transition metal catalyst. Gold nanoparticles (NPs) have been extensively employed as catalysts for various mild aerobic oxidation reactions. Herein we report a novel heterogeneous cesium hydrogen phosphotungstate-supported Au catalyst (Au/ Cs2HPW12O40) for the oxidation of cellobiose to gluconic acid. Cs2HPW12O40 is selected as the catalyst support for its strong acidity and solid form. More important, as discovered in this work, it possesses a special ability to modulate the oxidative activity of Au NPs, which leads to a specifically high selectivity toward gluconic acid. Density functional theory (DFT) calculations indicate that the strong metal–support interfacial interaction accounts for the catalytic activity modulation. A series of Au catalysts were prepared by loading AuCl3 on different support materials, followed by reduction with hydrogen at 300 8C. The Au loading amount was controlled to be 1 wt % for all the catalysts. The transmission electron microscopy (TEM) image shows that the Au/Cs2HPW12O40 catalyst consists of irregular particles with overall sizes ranging from 15 to 40 nm (Figure 1 a). The Au NPs deposited on the support are not clearly discernible in the TEM image because of their ultrasmall sizes, as well as the fact that tungsten and gold have little difference in atomic number, which results in a low-contrast image. Scanning transmission electron microscopy (STEM) was, therefore, employed to identify the Au particles on the support because in STEM the electron beam is focused into a

High performance solution-deposited amorphous indium gallium zinc oxide thin film transistors by oxygen plasma treatment

Solution-deposited amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) with high performance were fabricated using O2-plasma treatment of the films prior to high temperature annealing. The O2-plasma treatment resulted in a decrease in oxygen vacancy and residual hydrocarbon concentration in the a-IGZO films, as well as an improvement in the dielectric/channel interfacial roughness. As a result, the TFTs with O2-plasma treated a-IGZO channel layers showed three times higher linear field-effect mobility compared to the untreated a-IGZO over a range of processing temperatures. The O2-plasma treatment effectively reduces the required processing temperature of solution-deposited a-IGZO films to achieve the required performance.

Microwave-Assisted Self-Doping of TiO2 Photonic Crystals for Efficient Photoelectrochemical Water Splitting

In this article, we report that the combination of microwave heating and ethylene glycol, a mild reducing agent, can induce Ti(3+) self-doping in TiO2. A hierarchical TiO2 nanotube array with the top layer serving as TiO2 photonic crystals (TiO2 NTPCs) was selected as the base photoelectrode. The self-doped TiO2 NTPCs demonstrated a 10-fold increase in visible-light photocurrent density compared to the nondoped one, and the optimized saturation photocurrent density under simulated AM 1.5G illumination was identified to be 2.5 mA cm(-2) at 1.23 V versus reversible hydrogen electrode, which is comparable to the highest values ever reported for TiO2-based photoelectrodes. The significant enhancement of photoelectrochemical performance can be ascribed to the rational coupling of morphological and electronic features of the self-doped TiO2 NTPCs: (1) the periodically morphological structure of the photonic crystal layer traps broadband visible light, (2) the electronic interband state induced from self-doping of Ti(3+) can be excited in the visible-light region, and (3) the captured light by the photonic crystal layer is absorbed by the self-doped interbands.