Liquid metal-embraced photoactive films for artificial photosynthesis.

The practical applications of solar-driven water splitting pivot on significant advances that enable scalable production of robust photoactive films. Here, we propose a proof-of-concept for fabricating robust photoactive films by a particle-implanting technique (PiP) which embeds semiconductor photoabsorbers in the liquid metal. The strong semiconductor/metal interaction enables resulting films efficient collection of photogenerated charges and superior photoactivity. A photoanode of liquid-metal embraced BiVO4 can stably operate over 120 h and retain ~ 70% of activity when scaled from 1 to 64 cm2. Furthermore, a Z-scheme photocatalyst film of liquid-metal embraced BiVO4 and Rh-doped SrTiO3 particles can drive overall water splitting under visible light, delivering an activity 2.9 times higher than that of the control film with gold support and a 110 h stability. These results demonstrate the advantages of the PiP technique in constructing robust and efficient photoactive films for artificial photosynthesis.

Exceptional Electrochemical HER Performance with Enhanced Electron Transfer between Ru Nanoparticles and Single Atoms Dispersed on a Carbon Substrate.

Precisely regulating the electronic structures of metal active species is highly desirable for electrocatalysis. However, carbon with inert surface provide weak metal-support interaction, which is insufficient to modulate the electronic structures of metal nanoparticles. Herein, we propose a new method to control the electrocatalytic behavior of supported metal nanoparticles by dispersing single metal atoms on an O-doped graphene. Ideal atomic metal species are firstly computationally screened. We then verify this concept by deposition of Ru nanoparticles onto an O-doped graphene decorated with single metal atoms (e.g., Fe, Co, and Ni) for hydrogen evolution reaction (HER). Consistent with theoretical predictions, such hybrid catalysts show outstanding HER performance, much superior to other reported electrocatalysts such as the state-of-the-art Pt/C. This work offers a new strategy for modulating the activity and stability of metal nanoparticles for electrocatalysis processes.

Modular Construction of Prussian Blue Analog and TiO2 Dual-Compartment Janus Nanoreactor for Efficient Photocatalytic Water Splitting.

Janus structures that include different functional compartments have attracted significant attention due to their specific properties in a diverse range of applications. However, it remains challenge to develop an effective strategy for achieving strong interfacial interaction. Herein, a Janus nanoreactor consisting of TiO2 2D nanocrystals integrated with Prussian blue analog (PBA) single crystals is proposed and synthesized by mimicking the planting process. In situ etching of PBA particles induces nucleation and growth of TiO2 nanoflakes onto the concave surface of PBA particles, and thus enhances the interlayer interaction. The anisotropic PBA-TiO2 Janus nanoreactor demonstrates enhanced photocatalytic activities for both water reduction and oxidation reactions compared with TiO2 and PBA alone. As far as it is known, this is the first PBA-based composite that serves as a bifunctional photocatalyst for solar water splitting. The interfacial structure between two materials is vital for charge separation and transfer based on the spectroscopic studies. These results shed light on the elaborate construction of Janus nanoreactor, highlighting the important role of interfacial design at the microscale level.

Confined Fe-Cu Clusters as Sub-Nanometer Reactors for Efficiently Regulating the Electrochemical Nitrogen Reduction Reaction.

Electrochemical nitrogen reduction reaction (NRR) over nonprecious-metal and single-atom catalysts has received increasing attention as a sustainable strategy to synthesize ammonia. However, the atomic-scale regulation of such active sites for NRR catalysis remains challenging because of the large distance between them, which significantly weakens their cooperation. Herein, the utilization of regular surface cavities with unique microenvironment on graphitic carbon nitride as "subnano reactors" to precisely confine multiple Fe and Cu atoms for NRR electrocatalysis is reported. The synergy of Fe and Cu atoms in such confined subnano space provides significantly enhanced NRR performance, with nearly doubles ammonia yield and 54%-increased Faradic efficiency up to 34%, comparing with the single-metal counterparts. First principle simulation reveals this synergistic effect originates from the unique Fe-Cu coordination, which effectively modifies the N2 absorption, improves electron transfer, and offers extra redox couples for NRR. This work thus provides new strategies of manipulating catalysts active centers at the sub-nanometer scale.

Vacancy Engineering of Iron-Doped W18 O49 Nanoreactors for Low-Barrier Electrochemical Nitrogen Reduction.

The electrochemical nitrogen reduction reaction (NRR) is a promising energy-efficient and low-emission alternative to the traditional Haber-Bosch process. Usually, the competing hydrogen evolution reaction (HER) and the reaction barrier of ambient electrochemical NRR are significant challenges, making a simultaneous high NH3 formation rate and high Faradic efficiency (FE) difficult. To give effective NRR electrocatalysis and suppressed HER, the surface atomic structure of W18 O49 , which has exposed active W sites and weak binding for H2 , is doped with Fe. A high NH3 formation rate of 24.7 µg h-1 mgcat -1 and a high FE of 20.0 % are achieved at an overpotential of only -0.15 V versus the reversible hydrogen electrode. Ab initio calculations reveal an intercalation-type doping of Fe atoms in the tunnels of the W18 O49 crystal structure, which increases the oxygen vacancies and exposes more W active sites, optimizes the nitrogen adsorption energy, and facilitates the electrocatalytic NRR.

2D Porous TiO2 Single-Crystalline Nanostructure Demonstrating High Photo-Electrochemical Water Splitting Performance.

Porous single crystals are promising candidates for solar fuel production owing to their long range charge diffusion length, structural coherence, and sufficient reactive sites. Here, a simple template-free method of growing a selectively branched, 2D anatase TiO2 porous single crystalline nanostructure (PSN) on fluorine-doped tin oxide substrate is demonstrated. An innovative ion exchange-induced pore-forming process is designed to successfully create high porosity in the single-crystalline nanostructure with retention of excellent charge mobility and no detriment to crystal structure. PSN TiO2 film delivers a photocurrent of 1.02 mA cm-2 at a very low potential of 0.4 V versus reversible hydrogen electrode (RHE) for photo-electrochemical water splitting, closing to the theoretical value of TiO2 (1.12 mA cm-2 ). Moreover, the current-potential curve featuring a small potential window from 0.1 to 0.4 V versus RHE under one-sun illumination has a near-ideal shape predicted by the Gartner Model, revealing that the charge separation and surface reaction on the PSN TiO2 photoanode are very efficient. The photo-electrochemical water splitting performance of the films indicates that the ion exchange-assisted synthesis strategy is effective in creating large surface area and single-crystalline porous photoelectrodes for efficient solar energy conversion.

Ambient scalable synthesis of surfactant-free thermoelectric CuAgSe nanoparticles with reversible metallic-n-p conductivity transition.

Surfactant-free CuAgSe nanoparticles were successfully synthesized on a large scale within a short reaction time via a simple environmentally friendly aqueous approach under room temperature. The nanopowders obtained were consolidated into pellets for investigation of their thermoelectric properties between 3 and 623 K. The pellets show strong metallic characteristics below 60 K and turn into an n-type semiconductor with increasing temperature, accompanied by changes in the crystal structure (i.e., from the pure tetragonal phase into a mixture of tetragonal and orthorhombic phases), the electrical conductivity, the Seebeck coefficient, and the thermal conductivity, which leads to a figure of merit (ZT) of 0.42 at 323 K. The pellets show further interesting temperature-dependent transition from n-type into p-type in electrical conductivity arising from phase transition (i.e., from the mixture phases into cubic phase), evidenced by the change of the Seebeck coefficient from -28 µV/K into 226 µV/K at 467 K. The ZT value increased with increasing temperature after the phase transition and reached 0.9 at 623 K. The sintered CuAgSe pellets also display excellent stability, and there is no obvious change observed after 5 cycles of consecutive measurements. Our results demonstrate the potential of CuAgSe to simultaneously serve (at different temperatures) as both an n-type and a p-type thermoelectric material.

Nonstoichiometric rutile TiO2 photoelectrodes for improved photoelectrochemical water splitting.

A new type of nonstoichiometric rutile titanium dioxide (TiO2) film with around 15 at% oxygen vacancies homogeneously distributed throughout the bulk was prepared. The resultant films, when used as a photoelectrode, showed a photoelectrochemical water splitting activity 1.7 times that of stoichiometric TiO2 at a bias of 0.9 V vs. Ag/AgCl. This is believed to result from the synergistic effect of the improved bulk transport and surface transfer of charge carriers compared to the stoichiometric rutile TiO2.

Template-free synthesis of Ta3N5 nanorod arrays for efficient photoelectrochemical water splitting.

We report the template-free synthesis of Ta3N5 nanorod array films grown on Ta foil by a combination of a vapor-phase hydrothermal process and subsequent nitriding. The Ta3N5 nanorod array film modified with Co(OH)x when used as a photoanode in a photoelectrochemical cell for water splitting yields a stable photocurrent density of 2.8 mA cm(-2) at 1.23 VRHE under AM 1.5G simulated sunlight. The incident photon-to-current conversion efficiency at 480 nm is determined to be 37.8%.

One-pot preparation of highly fluorescent cadmium telluride/cadmium sulfide quantum dots under neutral-pH condition for biological applications.

Water-soluble CdTe/CdS quantum dots (QDs) with tuneable emissions were prepared in aqueous solution at pH=6-7 via refluxing and hydrothermal treatment. The resultant CdTe/CdS QDs are stabilized with mercaptosuccinic acid (MSA) and show high fluorescence quantum yields (maximum QY is 84%). Characterization with UV-Vis, PL, XPS, XRD and TEM demonstrates a core (CdTe)-shell (CdS) structure, which leads to high fluorescence quantum yields. The effective protection from CdS shell and MSA enables CdTe QDs to be chemically stable in a pH range of 6-9 and less toxic. These merits make our CdTe/CdS QDs very promising for bio-imaging applications, as exemplified by labelling HEK 293 cells.

Changes in surface chemistry of carbon materials upon electrochemical measurements and their effects on capacitance in acidic and neutral electrolytes.

Four porous carbon samples with very similar porosities but visible differences in their surface chemistry are investigated as supercapacitor electrodes in 1 M H2SO4 and 3 M NaCl. The key objective is to monitor the changes to the oxygen- and nitrogen-containing functionalities in oxygen- and nitrogen+oxygen-rich carbons upon a three-electrode test and the effect of these changes on the energy storage capacity in a real two-electrode supercapacitor setup. The carbon samples are thoroughly characterized by nitrogen sorption measurements, Raman spectroscopy, potentiometric titrations, elemental analysis, and synchrotron XPS. The findings presented in this work imply that the pretreatment of the oxygen- and nitrogen+oxygen-rich carbons under the conditions of the three-electrode test in an acidic electrolyte are beneficial to the overall energy storage capacity as the pores become more accessible to the electrolyte ions and the contribution of pseudocapacitive oxygen-containing groups increases in the oxygen-rich carbons, whereas favorable changes to the electronic structure take place in the nitrogen+oxygen-rich carbons. Thus, the total capacitance increases as a result of the improved double-layer capacitance as well as pseudocapacitance. Greater capacitance after the three-electrode test is also measured in a neutral electrolyte for both sets of samples, which is a result of improved double-layer capacitance upon the removal of some oxygen-containing functional groups that leads to better accessibility of the pores.

In situ growth of a ZnO nanowire network within a TiO(2) nanoparticle film for enhanced dye-sensitized solar cell performance.

ZnO nanowire networks featuring excellent charge transport and light scattering properties are grown in situ within TiO(2) films. The resultant TiO(2) /ZnO composites, used as photoanodes, remarkably enhance the overall conversion efficiency of dye-sensitized solar cells (DSSCs) by 26.9%, compared to that of benchmark TiO(2) films.

A microporous-mesoporous carbon with graphitic structure for a high-rate stable sulfur cathode in carbonate solvent-based Li-S batteries.

A microporous-mesoporous carbon with graphitic structure was developed as a matrix for the sulfur cathode of a Li-S cell using a mixed carbonate electrolyte. Sulfur was selectively introduced into the carbon micropores by a melt adsorption-solvent extraction strategy. The micropores act as solvent-restricted reactors for sulfur lithiation that promise long cycle stability. The mesopores remain unfilled and provide an ion migration pathway, while the graphitic structure contributes significantly to low-resistance electron transfer. The selective distribution of sulfur in micropores was characterized by X-ray photoelectron spectroscopy (XPS), nitrogen cryosorption analysis, transmission electron microscopy (TEM), X-ray powder diffraction and Raman spectroscopy. The high-rate stable lithiation-delithiation of the carbon-sulfur cathode was evaluated using galvanostatic charge-discharge tests, cyclic voltammetry and electrochemical impedance spectroscopy. The cathode is able to operate reversibly over 800 cycles with a 1.8 C discharge-recharge rate. This integration of a micropore reactor, a mesopore ion reservoir, and a graphitic electron conductor represents a generalized strategy to be adopted in research on advanced sulfur cathodes.

Nitrogen-doped carbon monolith for alkaline supercapacitors and understanding nitrogen-induced redox transitions.

A nitrogen-doped porous carbon monolith was synthesized as a pseudo-capacitive electrode for use in alkaline supercapacitors. Ammonia-assisted carbonization was used to dope the surface with nitrogen heteroatoms in a way that replaced carbon atoms but kept the oxygen content constant. Ammonia treatment expanded the micropore size-distributions and increased the specific surface area from 383 m(2) g(-1) to 679 m(2) g(-1). The nitrogen-containing porous carbon material showed a higher capacitance (246 F g(-1)) in comparison with the nitrogen-free one (186 F g(-1)). Ex situ electrochemical spectroscopy was used to investigate the evolution of the nitrogen-containing functional groups on the surface of the N-doped carbon electrodes in a three-electrode cell. In addition, first-principles calculations were explored regarding the electronic structures of different nitrogen groups to determine their relative redox potentials. We proposed possible redox reaction pathways based on the calculated redox affinity of different groups and surface analysis, which involved the reversible attachment/detachment of hydroxy groups between pyridone and pyridine. The oxidation of nitrogen atoms in pyridine was also suggested as a possible reaction pathway.

Poly-L-lysine functionalized large pore cubic mesostructured silica nanoparticles as biocompatible carriers for gene delivery.

Large pore mesoporous silica nanoparticles (LP-MSNs) functionalized with poly-L-lysine (PLL) were designed as a new carrier material for gene delivery applications. The synthesized LP-MSNs are 100-200 nm in diameter and are composed of cage-like pores organized in a cubic mesostructure. The size of the cavities is about 28 nm with an entrance size of 13.4 nm. Successful grafting of PLL onto the silica surface through covalent immobilization was confirmed by X-ray photoelectron spectroscopy, solid-state (13)C magic-angle spinning nuclear magnetic resonance, Fourier transformed infrared, and thermogravimetric analysis. As a result of the particle modification with PLL, a significant increase of the nanoparticle binding capacity for oligo-DNAs was observed compared to the native unmodified silica particles. Consequently, PLL-functionalized nanoparticles exhibited a strong ability to deliver oligo DNA-Cy3 (a model for siRNA) to Hela cells. Furthermore, PLL-functionalized nanoparticles were proven to be superior as gene carriers compared to amino-functionalized nanoparticles and the native nanoparticles. The system was tested to deliver functional siRNA against minibrain-related kinase and polo-like kinase 1 in osteosarcoma cancer cells. Here, the functionalized particles demonstrated great potential for efficient gene transfer into cancer cells as a decrease of the cellular viability of the osteosarcoma cancer cells was induced. Moreover, the PLL-modified silica nanoparticles also exhibit a high biocompatibility, with low cytotoxicity observed up to 100 µg/mL.

Field-effect transistors fabricated from diluted magnetic semiconductor colloidal nanowires.

Field-effect transistors (FETs) fabricated from undoped and Co(2+)-doped CdSe colloidal nanowires show typical n-channel transistor behaviour with gate effect. Exposed to microscope light, a 10 times current enhancement is observed in the doped nanowire-based devices due to the significant modification of the electronic structure of CdSe nanowires induced by Co(2+)-doping, which is revealed by theoretical calculations from spin-polarized plane-wave density functional theory.

Boron oxynitride nanoclusters on tungsten trioxide as a metal-free cocatalyst for photocatalytic oxygen evolution from water splitting.

Here we show that B(2)O(3-x)N(x) nanoclusters can be formed on the surface of WO(3) particles by a combination of thermal oxidation of tungsten boride (WB) in air and the subsequent nitriding process in gaseous ammonia. The resultant nanoclusters are found to play an apparent role in improving the photocatalytic oxygen evolution of WO(3) by promoting the surface separation of photoexcited charge-carriers.