Zhengdao Li

Ultrathin, Single-Crystal WO3 Nanosheets by Two-Dimensional Oriented Attachment toward Enhanced Photocatalystic Reduction of CO2 into Hydrocarbon Fuels under Visible Light

An ultrathin, single-crystal WO3 nanosheet of ∼4-5 nm in thickness, corresponding to six repeating unit cells of monoclinic WO3 along the c axis, was synthesized with laterally oriented attachment of tiny WO3 nanocrystals formed using a solid-liquid phase arc discharge route in an aqueous solution. Size-quantization effects in this ultrathin nanostructure alter the WO3 band gap to enable the nanosheet to exhibit enhanced performance for photocatalytic reduction of CO2 in the presence of water in hydrocarbon fuels that do not exist in its bulk form.

Fabrication of hierarchically assembled microspheres consisting of nanoporous ZnO nanosheets for high-efficiency dye-sensitized solar cells

Porous nanosheet-assembled ZnO microspheres (PNMSs) were synthesized via one-pot hydrothermal treatment followed by calcination and were used as photoanodes for dye-sensitized solar cells (DSSCs). An overall light conversion efficiency of up to 5.16% has been achieved with this unitary material and structure. Superior to the referenced porous nanosheet-assembled ZnO microflowers (PNMFs) and porous dispersed ZnO nanosheets (PDNs), as well as precedent nanostructures, the present PNMS fully accommodates all indispensable characteristics for a high-performance DSSC through: (1) the hierarchical ZnO microsphere generates a prominent aggregation-induced light scattering center, which is in favor of enhancing the light absorption and the light propagation; (2) the single crystal nature of the nanosheet enhances the transport of injected electrons along the nanosheet, providing a direct electron pathway throughout the film and lowering the hole–electron recombination; (3) the thin thickness and porous character of the nanosheets results in a large surface area for dye adsorption; (4) intersectional contact with one another of the nanosheets of neighboring spheres increases the transport channel of the injected electrons through the adjacent spheres, avoiding the high resistance existing in the nanoparticle-based sphere aggregates due to the relatively small contact area among the aggregates; (5) these spherical assemblies form large external pores in the photoelectrode film, thus providing a “main trunk” for the quick electrolyte diffusion throughout the ZnO layer in the film. Simultaneously, the nanopores embedded in the nanosheet act as “branch lines” for more efficient electrolyte diffusion into the interstices of the densely packing nanosheets in the sphere.

Vertically building Zn2SnO4 nanowire arrays on stainless steel mesh toward fabrication of large-area, flexible dye-sensitized solar cells

Zn(2)SnO(4) nanowire arrays were for the first time grown onto a stainless steel mesh (SSM) in a binary ethylenediamine (En)/water solvent system using a solvothermal route. The morphology evolution following this reaction was carefully followed to understand the formation mechanism. The SSM-supported Zn(2)SnO(4) nanowire was utilized as a photoanode for fabrication of large-area (10 cm × 5 cm size as a typical sample), flexible dye-sensitized solar cells (DSSCs). The synthesized Zn(2)SnO(4) nanowires exhibit great bendability and flexibility, proving potential advantage over other metal oxide nanowires such as TiO(2), ZnO, and SnO(2) for application in flexible solar cells. Relative to the analogous Zn(2)SnO(4) nanoparticle-based flexible DSSCs, the nanowire geometry proves to enhance solar energy conversion efficiency through enhancement of electron transport. The bendable nature of the DSSCs without obvious degradation of efficiency and facile scale up gives the as-made flexible solar cell device potential for practical application.

Unique Zn-doped SnO2 nano-echinus with excellent electron transport and light harvesting properties as photoanode materials for high performance dye-sensitized solar cell

A unique Zn-doped SnO2 nano-echinus, characterized by nanowire-covered mesoporous spheres, was successfully synthesized in a binary ethylenediamine (En)/water solvent system using a solvothermal route. Combination of hierarchically assembled and well-defined spheres, high surface area, and doped-Zn makes our new nanostructures an interesting candidate for photoanode application in dye-sensitized solar cells (DSSCs) with excellent transport and light harvesting properties. Zn doping into the SnO2 framework also induces a negative shift in the flat-band potential (VFB) and increases the isoelectric point. Consequently, the dye-sensitized solar cell employing Zn-doped SnO2 nano-echinus photoanodes exhibit higher open-circuit photovoltages, larger short-circuit currents, longer electron lifetimes, and increased dye loading than their undoped SnO2 counterparts. The energy-conversion efficiency (η) 4.15% is achieved with 4.95 at.% Zn-doped SnO2 photoanodes, a nearly three-fold improvement compared to undoped SnO2 photoanode DSSCs (1.13%). The Zn-doped SnO2 nano-echinus is thus believed to be a very promising material, which has good potential for application in DSSCs.

Generalized synthesis of a family of multishelled metal oxide hollow microspheres

Varieties of multishelled hollow spheres with a high yield have been successfully prepared via a simple route with gluconate salt as the carbon source. The product yield of the multishelled hollow spheres was determined by the pH value of the solution. Multiple light reflecting and scattering in between the hierarchical spherical shells enhanced the photo-energy conversion efficiency of the ZnO hollow sphere-based DSSC.

Fiber dye-sensitized solar cells consisting of TiO2 nanowires arrays on Ti thread as photoanodes through a low-cost, scalable route

TiO2 nanowire arrays were prepared through the low-cost, scalable alkali hydrothermal treatment of Ti threads (Φ = 250 μm) followed by dehydration sintering. Utilization of the nanowire-covered Ti thread as a photoanode allows for the fabrication of flexible, fiber-type dye sensitized solar cells (FDSSC), configurationally different from their traditional flat counterparts. The conversion efficiency of the FDSSC reaches 5.38% through optimizing the length of the nanowires.

Versatile nanobead-scaffolded N-SnO2 mesoporous microspheres: one-step synthesis and superb performance in dye-sensitized solar cell, gas sensor, and photocatalytic degradation of dye

Nanobead-scaffolded N-containing SnO2 mesoporous microspheres (NSMMs) with a high surface area were synthesized in an ethylenediamine (En) solvent system using a one-pot solvothermal route. These spheres are micrometer-sized and consist of packed nanobeads with diameters of ∼10 nm, and possess a specific surface area of 93.64 m2 g−1 and main pore sizes of ∼3.56 nm. All structural features of the hierarchically assembled and large well-defined spheres, diameter range, mesoporous properties, higher specific surface areas, high-level donor density, and negative shift of the conduction band could have applications in a variety of areas. As an example, dye-sensitized solar cells (DSSCs) employing NSMM photoanodes exhibit a high overall power conversion efficiency (η) of 2.3%, nearly 116% improvement compared to commercial nanoparticle (CNP) photoanode DSSCs. The distinct photovoltaic behavior of the NSMMs is their large short-circuit current (JSC = 10.08 mA cm−2), which, to the best of our knowledge, is the highest recorded so far among pure SnO2 photoanodes other than TiO2 or other modified ones. The NSMMs were also configured as high-performance gas sensors for detecting ethanol gas, exhibiting a remarkable sensitivity and short response/recovery times. Moreover, they were also determined to be high-efficiency photocatalysts for the degradation of rhodamine B solution under simulated sunlight irradiation.

Synthesis of Bi6Mo2O15 sub-microwires via a molten salt method and enhancing the photocatalytic reduction of CO2 into solar fuel through tuning the surface oxide vacancies by simple post-heating treatment

Monoclinic phase Bi6Mo2O15 sub-microwires consisting of MoO4 tetrahedra have been successfully synthesized by a molten salt method. The wide-bandgap sub-microwire exhibits photocatalytic activity toward the photoreduction of CO2 into CH4. The existence of surface oxide vacancies enhanced the photocatalytic activity, which can be easily tuned via different post-heating temperatures, through capturing photo-generated electrons at the surface, thus being beneficial for the separation of electrons and holes and prolonging the lifetime of the electrons.

Controllable electrophoresis deposition of TiO2 mesoporous spheres onto Ti threads as photoanodes for fiber-shaped dye-sensitized solar cells

Complex TiO2 mesoporous spheres (MSs) were deposited on a Ti thread using an electrophoresis deposition (EPD) technique as working electrodes of the fiber-shaped dye-sensitized solar cell (FDSSC). The thickness of the TiO2 MS film can be controlled by altering EPD time in a constant voltage. Electrochemical impedance spectroscopic measurement demonstrates the film thickness-dependent photovoltage performance of the FDSSC. The total conversion efficiency of the FDSSC achieves 3.8% through optimizing the thickness of the film.