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.
As a low cost and environment-friendly solar absorber material, Cu2ZnSnS4 (CZTS) has aroused great interest for both photovoltaic and photocatalytic applications. The development of low temperature and green chemical route for the preparation of this quaternary sulfide compound still remains a challenge. In the present study, we present a surfactant-free hydrothermal method for the preparation of CZTS nanocrystals with an average size of 12 nm and photoactivity in hydrogen production. Ammonia was proposed to play a key role in confining the particle sizes. The properties of the CZTS nanoparticles were characterized using XRD, Raman, XPS, TEM, and UV-vis absorption. The photocatalytic properties of the as-synthesized CZTS nanoparticles were tested both in thin films and in slurry systems.
Cu–Ni alloy nanoparticles (12 ± 3 nm) encapsulated in a silica shell have been successfully synthesized through a microemulsion method followed by polymerization of TEOS. The morphologies of the Cu–Ni@SiO2 nanocomposites can be controlled by tuning the metal ion concentrations. The alloy nanostructure shows a superior performance in catalytic methane dry reforming to the pure Ni nanocomposite catalyst.
Heterostructures are often constructed to modulate the electronic states of the two catalysts, achieving high-performance in alkaline hydrogen evolution reaction (HER). Various mechanisms have been proposed for the heterostructural catalysts, which however awaits further approvement. Herein, a heterostructure composed of Co2P and CoP was successfully prepared with significantly enhanced HER catalytic activity relative to the endmembers. The ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) revealed the effective promotion of the self-driven transferring of electrons from CoP to Co2P and the accumulation of electrons on the P sites in Co2P due to the strong electronic coupling of built-in electric field in the Co2P/CoP interface. In situ electrochemical impedance spectroscopy (EIS) and poison experiments confirmed the Heyrovsky step of H* intermediate depleting on electronegative P sites and contributions of both metal and P to the reactivity in the Co2P/CoP. Density functional theory (DFT) calculations clarify that the electronic structure at interface of the heterojunction significantly weakens the hydrogen adsorption free energy (ΔGH* ads) of P site in Co2P/CoP to near zero. We also propose an electronic redistribution strategy for heterostructures that activates the multiple routes mechanism and production of more active sites. The working mechanism is expected to be further extended to other transition metal compounds for efficient HER activity.
Hierarchical Ni/Al2O3 nanocomposite possesses a high surface area, high loading of well dispersed metal nanoparticles, and a hierarchical hollow structure. The strong interaction between metal and support and the large open accessible surface lead to excellent sintering and carbon resistance, and superior catalytic performance in methane dry reforming.
CZTS thin films possessing outstanding photoelectrochemical (PEC) efficiency and chemical stability have been prepared using a facile spin coating method and their properties can be further improved by surface modification of CdS and TiO 2 layers.