Yong-Sheng Hu

Improved photoelectrochemical performance of Ti-doped α-Fe2O3 thin films by surface modification with fluoride

CoF(3) aqueous solution was used to modify the surface of Ti-doped iron oxide thin film photoanodes to negatively shift the flat-band potential and allow photogenerated electrons to directly reduce water to hydrogen without an external bias; the zero bias performance was further improved by the use of glucose (a biomass analog) to bypass the relatively slow oxygen evolution reaction to provide a source of electrons to rapidly consume photogenerated holes.

Highly active and sinter-resistant Pd-nanoparticle catalysts encapsulated in silica

) that aresufficiently porous to allow unhindered mass transfer? 2) Howdoes the activity of the encapsulated catalysts compare totraditional supported Pd catalysts for CO oxidation andacetylene hydrogenation? 3) Do the shell structures providestability with respect to sintering at high temperatures?Nanoscale core/shell Pd@SiO

Oriented Ti doped hematite thin film as active photoanodes synthesized by facile APCVD

To improve the optoelectronic properties of iron oxide as a photoelectrode, hematite (α-Fe2O3) thin films were doped with titanium using atmospheric pressure chemical vapor deposition (APCVD) for synthesis. The films were prepared by pyrolysis of Fe(CO)5 and TiCl4 precursors on fluorine-doped tin oxide (FTO) substrates and found to have a polycrystalline morphology with faceted particulates ∼20 to 50 nm in size with a preferred crystallographic growth along the [110] direction. The performance of the photoanodes was measured as a function of titanium concentration. A maximum efficiency was observed at ∼0.8 atom% Ti in hematite. The Incident Photon-to-current Conversion Efficiency (IPCE) to hydrogen was measured in alkaline electrolyte. Under an applied bias of 0.6 V vs.Ag/AgCl at 400 nm the IPCE for water splitting in alkaline solution was found to be 27.2%, the highest efficiency reported for Ti doped hematite photoanodes. The IPCEs of the photoanode thin films at lower applied bias were further increased by calcination at 500 °C and by use of glucose as an anolyte.

Silica‐Encapsulated Pd Nanoparticles as a Regenerable and Sintering‐Resistant Catalyst

Irreversible, thermally induced sintering of heterogeneous catalysts is one of the most deleterious causes of activity loss during catalytic reaction and/or regeneration. Silica‐coated Pd catalysts (Pd@SiO2) were prepared by a simple one‐pot, water‐in‐oil microemulsion method and investigated as models for a general synthesis to encapsulate active nanoparticle catalysts to provide stability during extended periods of cycling and regeneration under harsh experimental conditions. An idealized stability test would involve both a catalyst whose activity changes significantly as particles sinter and test conditions that could readily induce sintering. Acetylene hydrogenation was chosen as the test reaction because its catalytic and regenerative (oxidative coke removal) cycling induce the destructive sintering conditions desired for such a test. When compared with Pd particles deposited on the outside of an identical silica support (Pd/SiO2 catalyst), the silica‐encapsulated catalyst Pd@SiO2 deactivates at a much slower rate and is readily regenerated without sintering over multiple reaction and regeneration cycles. It is also found that silica encapsulation suppresses coking and in situ formation of PdC. TEM, XRD, BET, XPS, and TGA, before and after reaction and regeneration, were used to characterize the encapsulated Pd@SiO2 catalysts and compare them to conventionally supported Pd/SiO2.

Synthesis and characterization of sintering-resistant silica-encapsulated Fe3O4 magnetic nanoparticles active for oxidation and chemical looping combustion

A nanocomposite catalyst composed of ferromagnetic magnetite cores (15.5 +/- 2.0 nm) and silica shells with a thickness of 4.5 +/- 1.0 nm (Fe(3)O(4)@SiO(2)) was prepared by a two-step microemulsion-based synthesis. X-ray photoelectron spectroscopy and Raman spectroscopy after oxidation support the presence of a stable Fe(3)O(4) core and a surface phase of gamma-Fe(2)O(3). The nanocomposite structure exhibited 100% conversion of CO in oxygen at a residence time of 0.1 s at 310 degrees C. When pre-oxidized, the Fe(3)O(4)@SiO(2) catalyst is shown to be a suitable solid oxygen carrier for chemical looping combustion of methane at 700 degrees C. The nanocomposites retain their magnetism following the reaction which provides the potential for use of magnetic separation and capture in moving bed reactor applications. The core magnetite within the silica shell is resistant to sintering and a bulk phase transition to temperatures as high as 700 degrees C. These catalysts can be of use in applications of high temperature applications where catalyst recovery by magnetic separation may be required.

Photoelectrochemical Hydrogen Production on α-Fe2O3 (0001): Insights from Theory and Experiments

The photoelectrochemical (PEC) decomposition of organic compounds in wastewater is investigated by using quantum chemical (DFT) methods to evaluate alternatives to water splitting for the production of renewable and sustainable hydrogen. Methanol is used as a model organic species for the theoretical evaluations of electrolysis on the surface of the widely available semiconductor hematite, α-Fe2 O3 , a widely studied photocatalyst. Three different α-Fe2 O3 surface terminations were investigated, including the predominant surface found in aqueous electrolytes, (OH)3 R. The PEC oxidation of methanol is energetically downhill, producing CO2 and protons. The protons are reduced to hydrogen on the cathode. Experimental PEC measurements were also performed for several polyalcoholic compounds, glycerol, erythritol, and xylitol, on α-Fe2 O3 as the photocatalyst and showed high incident-photon-to-current-efficiencies (IPCE) that were much greater than those of water splitting. Interestingly, high IPCEs were observed for hydrogen production from polyalcohols in the absence of any applied bias, which was not thought to be possible on hematite. These results support the potential application of PEC for hydrogen production by using widely available hematite for the PEC oxidation of selected components of organic wastewater present in large quantities from anthropogenic and industrial sources.