Jia Hong Pan

CdSe-sensitized mesoscopic TiO2 solar cells exhibiting >5% efficiency: redundancy of CdS buffer layer

Semiconductor-sensitized TiO2 solar cells employing CdSe as a light absorber demonstrate superior photovoltaic performance to the best-performing cascaded CdS/CdSe cells with practically identical optical density in the study. A careful comparison between CdSe and CdS/CdSe sensitized cells reveals that while CdS can greatly promote the subsequent growth of CdSe in the cascade electrodes and hence light harvesting, the presence of a CdS buffer layer impedes the injection of electrons from CdSe to TiO2 and accelerates charge recombination at the TiO2/sensitizer interface. As a result, better performance was achieved with CdSe-sensitized solar cells when light absorption is identical to that of CdS/CdSe cells, making the CdS buffer layer redundant. CdSe-sensitized TiO2 solar cells incorporating light scattering layers and an aqueous polysulfide electrolyte yielded an unprecedented power conversion efficiency of up to 5.21% under simulated AM 1.5, 100 mW cm−2 illumination.

Hierarchical N-doped TiO2 hollow microspheres consisting of nanothorns with exposed anatase {101} facets

A green solvothermal synthesis approach employing water as a hollowing controller and diethylenetriamine as both crystal growth stabilizer and N dopant source to the preparation of hierarchical N-doped TiO(2) hollow microspheres comprised of nanothorns with exposed anatase {101} facets is established. The superstructured TiO(2) shows excellent photocatalytic activities in degrading dyes under visible light irradiation.

Scalable synthesis of urchin- and flowerlike hierarchical NiO microspheres and their electrochemical property for lithium storage.

A nickel salt-urea-H2O ternary system has been developed for the large-scale synthesis of hierarchical α-Ni(OH)2 microspheres, the solid precursor for the subsequent topotactic transition to NiO upon calcination. In this facile synthetic system, hierarchical structure is self-assembled under the cooperative direction of urea and anions in nickel salts. Thus, simply tuning the Ni salts leads to the selective construction of urchin and flowerlike hierarchical α-Ni(OH)2 and NiO microspheres consisting of radial 1D nanowires and 2D nanoplates, respectively. The obtained NiO microspheres possessing accessible nanopores, excellent structural stability and large surface area up to 130 m(2)/g show promising electrochemical performance in anodic lithium storage for lithium-ion battery.

Mesoporous TiO2 photocatalytic films on stainless steel for water decontamination

Coating of mesoporous TiO2 nanocrystalline films on stainless steel (Grade 304) was conducted using an evaporation-induced self-assembly (EISA) process in the presence of a PluronicF127 triblock copolymer. The photocatalytic properties of mesoporous TiO2 films were evaluated using orange II in aqueous solution under ultraviolet irradiation. Surface analysis shows that leaching of metals (e.g., Fe, Cr) from the stainless steel occurred during the EISA process. The leached metal species came to the interface between the titanium species and the copolymer, adversely influencing the self-assembly of the mesophase, leading to a poor mesoporous structure and a low photocatalytic activity in the resultant TiO2 films. Pre-treatment of stainless steel by acid washing followed by coating a SiO2–SnO2 interlayer has been demonstrated to effectively avoid the acid leaching and thermal diffusion of metal species from stainless steel. The photocatalytic activities of the subsequently deposited mesoporous TiO2 films were significantly improved, which can be attributed to the enhanced charge carrier separation and excellent optical reflection properties of the interlayer.

Self-Template Synthesis of Porous Perovskite Titanate Solid and Hollow Submicrospheres for Photocatalytic Oxygen Evolution and Mesoscopic Solar Cells

We describe a general synthesis strategy, which combines sol-gel and hydrothermal processes, for the large-scale synthesis of porous perovskite titanates spheres with tunable particle size and inner structures. Amorphous hydrous TiO2 solid spheres (AHTSS) are first synthesized by a sol-gel method and are then used as precursor and template for the subsequent hydrothermal reaction with alkaline earth metal ions in an alkaline medium. This strategy can be generalized to synthesize porous spheres of various perovskite titanates (i.e., SrTiO3, BaTiO3, and CaTiO3) consisting of single-crystalline nanocubes. By controlling the textural properties (i.e., size, porosity, and structure) of AHTSS, perovskite titanates with tunable size and inner structures are selectively synthesized. The underlying formation mechanism is manifested by XRD and TEM to involve in situ crystallization or Ostwald ripening during the hydrothermal process. The obtained porous SrTiO3 spheres present superior performance in photocatalytic oxygen evolution and CdSe-sensitized mesoscopic solar cells.

Reconstruction of Colloidal Spheres by Targeted Etching: A Generalized Self-Template Route to Porous Amphoteric Metal Oxide Hollow Spheres

Despite the significant progress in developing various synthetic strategies for metal oxide hollow spheres (h-MO), the so-far explored materials are mostly chemically inert metal oxides. Very few attempts have been made for amphoteric metal oxides such as Al2O3 and ZnO due to the difficulties in the control of the dissolution and recrystallization process. Herein, a facile self-template route to the synthesis of amphoteric h-MO with tunable size and shell thickness is developed by targeted etching via an acid-base reaction. With the protection of polyvinylpyrrolidone (PVP) on the surface, the interior of metal oxide solid colloidal spheres (c-MOs) that possess radially divergent structures could be selectively etched with acid/alkali as an etchant, forming h-MO of Al2O3 and ZnO. Our results also show that a wide variety of metal oxide colloidal spheres can be potential self-templates for targeted etching, which paves the way for developing a generalized strategy for the synthesis of various metal oxide hollow spheres.