Xiao Shang

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.

In situ sulfurized CoMoS/CoMoO4 shell–core nanorods supported on N-doped reduced graphene oxide (NRGO) as efficient electrocatalyst for hydrogen evolution reaction

Many strategies, such as doping metal, designing low-dimensional nanostructures, and enhancing the utilization of active sites based on a conductive support, have been intensively pursued to improve the intrinsic activity of transition metal chalcogenides for the hydrogen evolution reaction (HER). However, integrating all the above-mentioned merits into one electrocatalyst is still a significant challenge. Herein, we have successfully prepared uniform CoMoS/CoMoO4 (CMS) shell–core nanorods, with a diameter of 60 nm and a length of 800 nm, supported on N-doped reduced graphene oxide (NRGO). The obtained CMS/NRGO can combine many advantages, including transition metal doping, one-dimensional nanorods, and the superior conductivity of NRGO, resulting in very promising HER properties and excellent stability. The optimum sulfurization temperature for unsupported CMS nanorods has been explored using uniform CoMoO4 nanorods as a precursor. Although CMS-3 prepared with a sulfurization temperature of 300 °C has been found to possess the optimum activity for the HER, when adopting NRGO as a support, CMS-3/NRGO exhibits an impressive enhancement in HER performances with a low overpotential of 80 mV, a small Tafel slope of 58 mV dec−1, and a large exchange current density of 428 μA cm−2. In addition, the electrocatalytic activity of CMS-3/NRGO shows a negligible delay after 1000 cycles, indicating its robust electrochemical stability in acid electrolyte solution. Therefore, adopting low-temperature sulfurization of one-dimensional metal oxide precursors supported on NRGO may be a promising strategy for obtaining excellent electrocatalysts for the HER.

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.

Coupling Ag-doping and rich oxygen vacancies in mesoporous NiCoO nanorods supported on nickel foam for highly efficient oxygen evolution

A crucial challenge still remains in the development of efficient and stable electrocatalysts for oxygen evolution reaction (OER) with desirable conductivity, a high surface area and rich oxygen vacancies. Herein, a type of Ag-doped mesoporous NiCoO nanorod with rich oxygen vacancies (NiCoO@Ag40/NF-Ar) for OER is prepared via an electrodeposition-hydrothermal reaction and the subsequent annealing treatment process under an Ar atmosphere. The electrodeposited Ag film is found to direct the uniform growth of the nanowire arrays of NiCo hydroxide precursors compared to the nanoparticles of NiCo hydroxide in the absence of the Ag film. Interestingly, the addition of C2H8N2 (EN) during the electrodeposition of the Ag film and the subsequent calcination under an Ar atmosphere collectively contribute to the formation of mesoporous nanorod structures and rich oxygen vacancies. The calcined NiCoO in air mainly have the Co3O4 phase, implying that it has fewer oxygen vacancies and weak activity for OER. The high surface area and one-dimensional feature of mesoporous nanorods are responsible for the increased exposure of active sites and fast charge transport behavior. Moreover, Ag doping can also improve the conductivity of NiCoO nanorods. NiCoO@Ag40/NF-Ar exhibits a highly efficient activity for OER with a current density of 140 mA cm−2 at an overpotential of 370 mV and a remarkable stability. The suitable Ar annealing treatment coupling Ag films and oxygen vacancies into transition metal oxide precursors may be a facile and promising method for constructing mesoporous nanostructures with rich oxygen vacancies for efficient water oxidation.

Tuning the morphology and Fe/Ni ratio of a bimetallic Fe-Ni-S film supported on nickel foam for optimized electrolytic water splitting

The surface composite and morphology of binary metal sulfides are the key for efficient overall water splitting. However, tuning the morphology and surface composition of binary metal sulfides in a facile way is still a challenge. Herein, binary Fe-Ni sulfides supported on nickel foam (FeNi-S/NF) with different morphology and composition ratio of Fe/Ni have been synthesized through a facile one-step electrodeposition assisted by liquidcrystaltemplate (LCT). The binary FeNi-S has improved activity and conductivity compared to single metal sulfides. LCT-assisted porous FeNi-S film composed of uniform nanospheres is obviously different from planar film electrodeposited in water solution. LCT-assisted FeNi-S nanospheres are covered by many interwoven nanosheets, implying more exposed active sites for water splitting. Furthermore, the different Fe/Ni ratios of FeNi-S/NF samples have been systematically studied to explore the influence of Fe-incorporation on intrinsic activity of FeNi-S/NF. And the sample with Fe/Ni ratio (3/1) demonstrates the best activity and excellent stability for overall water electrolysis. Therefore, our work provides a facile and controllable access to binary metal sulfides with excellent performances for overall water splitting.

In-situ grown interwoven NiSe on Ni foam as a catalyst for hydrazine oxidation

Abstract NiSe was prepared in-situ on nickel foam (NiSe/NF), using a solvothermal process. The NiSe/NF consisted of interwoven nanorods and nanowires. The interwoven NiSe/NF was of good crystallinity and contained no impurities, and consisted of many nanorods and a few nanowires. The interwoven structure uniformly covered the NF substrate, which can potentially yield a large surface area with abundant active sites, and thus high catalytic activity. The NiSe/NF was used as a working electrode for hydrazine oxidation, in 1.0 mol L−1 KOH containing 20 mmol L−1 N2H4 · H2O. Excellent electrocatalytic activity and stability of NiSe/NF for hydrazine oxidation was observed, with a current density of 22 mA cm−2 at −0.53 V. The interwoven structure and good conductivity of NiSe/NF promoted its electrocatalytic activity.