•A novel α-Fe2O3 coated p-Si photoelectrode was prepared by an APCVD method.•The PEC performance of planar p-Si was significantly enhanced by α-Fe2O3.•The catalytic effect on PEC hydrogen production of α-Fe2O3 on planar Si is discussed.•The morphology and thickness of the surface oxide layers for their effects on PEC performances are discussed.Pt nanoparticles are the most frequently used catalyst for Si photocathode. Alternative catalyst based on transition metal or metal oxide as cathode catalyst is greatly desired to replace Pt. A mesoporous α-Fe2O3 thin film (80 nm) was deposited on the surface of planar p-Si using a facile atmospheric pressure chemical vapor deposition (APCVD) method through pyrolysis of ferrocene. The planar Si photocathode shows a 400% enhancement in photocurrent at −1.0 VRHE and an anodic onset potential shift of 0.5 V upon deposition of surface mesoporous α-Fe2O3 layer. This composite photoelectrode also shows superior photoelectrochemical performance to the Pt/planar Si photoelectrode.Download high-res image (207KB)Download full-size image

Two-dimensional (2D) materials have attracted wide attention in photonic, electric, catalysis, and energy fields. Compared to the gas phase synthesis, the liquid phase route enables mass production of 2D materials with relatively low costs. However, these free-standing 2D materials obtained via the wet chemical route have a strong tendency to stack on each other; moreover, their 2D structure and the relevant functions degrade over time. Thus, we developed a strategy to achieve the reversibility of assembly/disassembly in Pd nanosheets (NSs) by utilizing anionic/cationic surfactants. Based on this methodology, the 2D structure of free-standing Pd NSs can be preserved with excellent performances for long-term use. Our results showed that free-standing Pd NSs were extremely unstable and decomposed into nanoparticles in 9 days. However, the assembled Pd NSs stacks maintained their 2D structure and preserved the methanol oxidation reaction (MOR) properties after disassembling.

Si nanowire (SiNW) arrays decorated with Pt nanoparticles are passivated with TiO2 surface layer using atomic layer deposition (ALD). The sandwich structure TiO2/Pt/SiNW shows superior photoelectrochemical performance to the control planar silicon electrodes, especially under the concentrated solar radiation. Pt nanoparticles separated from aqueous electrolyte by TiO2 layer of more than 15 nm still well catalyze surface photoelectrochemical hydrogen production without direct contact to the electrolyte. This structural configuration shows remarkable chemical stability and anodically shifted onset potential, suggesting great promise for applications in solar hydrogen production. The maximum photon-to-energy conversion efficiency of the TiO2/Pt/SiNW reaches 15.6%.Keywords: ALD; hydrogen; passivation; photoelectrochemical; Si nanowire arrays; TiO2

Nanocasting synthesis of quaternary chalcogenide Cu2ZnSnS4 (CZTS) nanocrystals remains a big challenge due to the difficulty in the impregnation of the quaternary precursors and the competition of the formation of binary and ternary sulfides. We herein report the first successful nanocasting synthesis of nanorods of the quaternary sulfide compound, CZTS, based on mesoporous SBA-15 template through a sol–gel process. Kesterite CZTS nanorods with a diameter of 6.8 nm and a surface area of 76.19 m2 g−1 are obtained. The compositions and concentrations of the quaternary precursors are investigated for the impregnation and crystallization of CZTS in the silica template.

Hydrogen reduction of hierarchical spinel intermediates that were synthesized by a facile hydrothermal method results in Ni/γ-Al2O3 nanocomposites with Ni nanoparticles (∼5.5 nm) well dispersed and embedded in nanoflakes of the hollow Al2O3 microspheres. The good dispersion of small metal nanoparticles and strong metal–support interactions that resulted from decomposition of spinel intermediates during reduction are essential for the efficient and sustainable high temperature dry reforming of methane (DRM) catalysis. The high surface area (170 m2 g−1) composite catalysts show coke and sintering resistance in long term DRM catalysis at 750 °C, the highest temperature ever tested for hierarchical nanostructures. Ni loadings and the calcination temperatures of the spinel intermediate are investigated for their effect on the morphology and the catalytic performance of the final catalysts. It is interesting that some initially non-active control catalysts can be activated during long term testing.

•Ultrathin (50 nm) Ti-doped α-Fe2O3 photoanode was prepared by an APCVD method.•The ultrathin Ti-doped α-Fe2O3 photoanode shows photocurrent of 0.9 mA/cm2 at 0.6 VSCE under AM 1.5 G.•The ultrathin hematite thin film deposited on Ti foil has superior PEC performance than deposited on TiO2 or FTO substrate.•The doping mechanism and the performance–microstructure relationship of the ultrathin films are discussed.Ultrathin Ti-doped α-Fe2O3 photoanode was prepared by a facile atmospheric pressure chemical vapor deposition method through pyrolysis of ferrocene at 450 °C on Ti foil. The as prepared ultrathin hematite thin film has a surface feature size of 70 × 30 nm and a thickness of 50 nm. The photocurrent of this ultrathin hematite photoanode prepared at 450 °C in 1 M NaOH reaches 900 μA/cm2 at 0.6 VSCE under AM 1.5G illumination. The superior performance to the thin films prepared on FTO glass was ascribed to the diffusion and doping of Ti4+ from the metal substrate during pyrolysis deposition of hematite on Ti substrate.

Cu2ZnSnS4 (CZTS) has attracted great interest in both photovoltaic and photoelectrochemical applications as a low cost and environmentally-friendly solar absorber material. The development of a facile and green chemical route for the preparation of a well crystallized and stable CZTS photoelectrode still remains a challenge. We present here the preparation of well crystallized CZTS thin films using a facile spin-coating method based on methanol solution and their applications as photoelectrocathodes for hydrogen production. The bare CZTS thin films demonstrate outstanding photoelectrochemical (PEC) efficiency and chemical stability, which are further improved by surface modification of CdS and TiO2 layers using chemical bath and atomic layer deposition, respectively. The incident-photon-to-current efficiency (IPCE) and long term photoelectrochemistry of the CZTS thin films are measured. The characterization of XRD, Raman, SEM, and UV-vis absorption is also performed.

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.