Wen-i Hu

Two-step synthesis of binary Ni–Fe sulfides supported on nickel foam as highly efficient electrocatalysts for the oxygen evolution reaction

A facile two-step method has been used to synthesize binary Ni–Fe sulfides supported on nickel foam (NF) as electrocatalysts for the oxygen evolution reaction (OER). Firstly, NiFe hydroxide nanosheets have been electrodeposited on NF (NiFe/NF) as a precursor with a large surface area. Secondly, the as-prepared NiFe/NF has been subjected to a hydrothermal sulfuration process in order to prepare NiFeS/NF as an efficient electrocatalyst for the OER. The as-prepared samples have been characterized by XRD, XPS and SEM. The SEM images show that the NiFeS film was composed of needle-like nanostructures covering the surface of the NF. The corresponding OER performances in alkaline media have been systematically investigated. NiFeS/NF shows a superior overpotential of 65 mV at 10 mA cm−2, which is much lower than most Ni-based electrocatalysts. The overpotential of 189 mV at 100 mA cm−2 of NiFeS/NF suggests very promising OER activity for industrial applications. The electrochemically active surface area (251.25 cm2) of NiFeS/NF is obviously larger than that of NiFeS/NF (173.75 cm2) and NiFeS/NF (205.00 cm2). However, the stability of NiFeS/NF is not very good due to the intrinsic nature of metal sulfides in alkaline solution. An approach of electrodeposition of Fe hydroxide film on NiFeS/NF (NiFeS–Fe/NF) has been used to protect NiFeS/NF for better stability for the OER. The OER performances of NiFeS–Fe/NF demonstrate enhanced stability but lower activity with 101.6 mV at 10 mA cm−2. Therefore, there may be an optimal balance between activity and stability of transition metal sulfides for the OER.

NiSe@NiOOH Core-Shell Hyacinth-like Nanostructures on Nickel Foam Synthesized by in Situ Electrochemical Oxidation as an Efficient Electrocatalyst for the Oxygen Evolution Reaction.

NiSe@NiOOH core-shell hyacinth-like nanostructures supported on nickel foam (NF) have been successfully synthesized by a facile solvothermal selenization and subsequent in situ electrochemical oxidation (ISEO). First, the unique NiSe/NF nanopillar arrays were prepared in N,N-dimethylformamide (DMF) as a precursor template that can provide a large surface area, excellent conductivity, and robust support. Next, amorphous NiOOH covering the surface of NiSe nanopillars was fabricated by ISEO, as confirmed by XPS andEDX spectroscopy. SEM images revealed the hyacinth-like morphology of NiSe@NiOOH/NF with NiOOH as the shell and NiSe as the core. The electrochemical performance of NiSe@NiOOH/NF for the oxygen evolution reaction (OER) was investigated. NiSe@NiOOH/NF demonstrates an obviously enhanced OER activity with much lower overpotential of 332 mV at 50 mA cm(-2) compared to other Ni-based electrocatalysts. The low charge-transfer resistance (Rct), large electrochemical double-layer capacitance (Cdl) of electrochemically active surface areas (ECSAs), and excellent long-term stability of NiSe@NiOOH/NF confirm the enhancement of its electrochemical performance for the OER, which can be ascribed to the large amount of active sites derived from the amorphous NiOOH shell and the good conductivity and stability derived from the NiSe core. In addition, the synergistic effect between the NiSe core and NiOOH shell could serve for a highly efficient OER electrocatalyst.

Controllable synthesis of three dimensional electrodeposited Co–P nanosphere arrays as efficient electrocatalysts for overall water splitting

Novel three dimensional (3D) electrodeposited Co–P nanosphere arrays on FTO (Co–P/FTO) have been successfully prepared as efficient bifunctional electrocatalysts for overall water splitting in alkaline media. The morphologies and properties of the 3D Co–P nanosphere arrays can be controlled by the electrolyte concentration. At the middle concentration, Co–P nanospheres have a more homogeneous size and array distribution and a rough surface, implying a larger surface area and an increased number of active sites for water splitting. The electrochemical measurements confirm the best electrocatalytic performances of Co–P/FTO at the middle concentration. They show excellent activity, with an overpotential of 125 mV for HER, 420 mV for OER and Tafel slopes of 54 mV dec−1 and 83 mV dec−1, respectively. The fabricated bifunctional systems of Co–P/Co–P can efficiently catalyse HER and OER at the same time, solving the incompatible problem of different media between HER and OER. Therefore, controlling the synthesis of 3D Co–P/FTO nanosphere arrays through electrodeposition can provide a facile way for the bifunctional electrocatalysis of both HER and OER.

Facile synthesis of highly dispersed WO 3 ·H 2 O and WO 3 nanoplates for electrocatalytic hydrogen evolution

The highly dispersed WO3ċH2O nanoplates have been synthesized by a facile hydrothermal reaction assisted by citrate acid. WO3 nanoplates have been prepared by the calcination of as-prepared WO3ċH2O at 450°C. XRD data show thatWO3ċH2O and WO3 have good crystal structure and high purity. SEMimages show that WO3ċH2O and WO3 have the uniform nanoplates morphology with the edge length of about 100-150 nm. The selective absorbance of citrate acid with many OH groups onto [010] facet of tungsten oxide precursors can result in the controlled growth of WO3ċH2O, thus leading to the good dispersion and small size of WO3ċH2O nanoplates. The electrocatalytic activity of WO3ċH2O and WO3 for hydrogen evolution reaction (HER) has been investigated in detail.The good electrocatalytic activity for HER has been obtained, which may be attributed to the good dispersion and small size of nanoplates. And the growth mechanisms of WO3ċH2O and WO3 nanoplates have been discussed.

Facile hydrothermal synthesis of monodispersed MoS 2 ultrathin nanosheets assisted by ionic liquid Brij56

Monodispersed MoS2 ultrathin nanosheets have been successfully fabricated by a facile hydrothermal process assisted by ionic liquid Brij56. The effect of Brij56 on the morphology and structure of MoS2 has been obviously observed. XRD shows that the as-prepared MoS2 assisted by Brij56 has the weak and broad peak of (002) planes, which implies the small size and well dispersed structure of MoS2 nanosheets. TEM and SEM images reveal that MoS2 ultrathin nanosheets have small size and few stacking layers with the adding of Brij56. HRTEM images prove that MoS2 appears to have a highly monodispersed morphology and to be monolayer ultrathin nanosheets with the length about 5-8 nm, which can provide more exposed rims and edges as active sites for hydrogen evolution reaction. Brij56 has played a crucial role in preparing monodispersed MoS2 ultrathin nanosheets as excellent electrocatalysts. The growth mechanism of monodispersed MoS2 has been discussed in detail.

Facile synthesis of TiO2 nanoplates decorated with Ag nanoparticles for electro-oxidation of hydrazine

Abstract TiO2 nanoplates decorated with Ag nanoparticles have been synthesized by a facile method. The as-prepared Ag/TiO2 nanoplates have been characterized using transmission electron microscopy and X-ray diffraction. Transmission electron microscopy results show that TiO2 nanoplates have a uniform side length of about 40 nm and mono-dispersed morphology, which implies that TiO2 nanoplates may be pomising supports. Ag nanoparticles with diameter ranging from 10 to 20 nm can be observed to disperse homogeneously on the surface of TiO2 nanoplates. The electro-oxidation of Ag/TiO2 nanoplates for hydrazine oxidation has been investigated in detail. The results show that Ag/TiO2 nanoplates have excellent electrocatalytic activity. The electro-oxidation of hydrazine may be an irreversible process being controlled by diffusion of hydrazine.