Characterization of Polycrystalline Nickel Cobaltite Nanostructures Prepared by DC Plasma Magnetron Co-Sputtering for Gas Sensing Applications

In this work, a gas sensor is fabricated from polycrystalline nickel cobaltite nano films deposited on transparent substrates by closed-field unbalanced dual-magnetrons （CFUBDM） co-sputtering technique. Two targets of nickel and cobalt are mounted on the cathode of discharge system and co-sputtered by direct current （DC） argon discharge plasma in presence of oxygen as a reactive gas. The total gas pressure is 0.5 mbar and the mixing ratio of Ar：O2 gases is 5：1. The characterization measurements performed on the prepared films show that their transmittance increases with the incident wavelength, the polycrystalline structure includes 5 crystallographic planes, the average particle size is about 35nm, the electrical conductivity is linearly increasing with increasing temperature, and the activation energy is about 0.41 eV. These films show high sensitivity to ethanol vapor.

NiCo2O4 decorated PANI–CNTs composites as supercapacitive electrode materials

Hierarchical Ni CoO/PANI/CNTs hybrid composites were designed and fabricated having a layer of Ni CoOon the surface of PANI encapsulated CNTs with different morphologies. Physicochemical attributes of the synthesized composites were examined by FTIR, UV–visible and X-ray diffraction（XRD）techniques. Morphological aspects were evaluated by field-emission scanning microscopy（FESEM）,electron diffraction spectroscopy（EDS）, high resolution transmission electron microscopy（HRTEM） and selected area electron diffraction（SAED） studies. Electrochemical measurements revealed an improved specific capacitance of 2250 F/g at a scan rate of 5 m V/s and 2000 F/g at a current density of 1 A/g with good rate capability using a three-electrode system. These enhanced features are achieved from the well designed nanostructure and the synergistic contributions of individual components in the electrode material.

Nickel foam supported Cr-doped NiCo2O4/FeOOH nanoneedle arrays as a high-performance bifunctional electrocatalyst for overall water splitting

Efficient and robust noble-metal-free bifunctional electrocatalysts for overall water splitting(OWS)is of great importance to realize the large-scale hydrogen production.Herein,we report the growth of undoped and Cr-doped NiCo2O4(Cr-NiCo2O4)nanoneedles(NNs)on nickel foam(NF)as bifunctional electrocatalysts for both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).We demonstrate that Cr-doping significantly improves activity for HER and OER by increasing the conductivity of NNs and allowing more active sites on NNs electrochemically accessible.When amorphous FeOOH is electrodeposited on the surface of Cr-NiCo2O4 NNs,the resulting FeOOH/Cr-NiCo2O4/NF exhibits itself as an excellent bifunctional catalyst for OWS.In the two-electrode cell where FeOOH/Cr-NiCo2O4/NF is used both as cathode and anode for OWS,a cell voltage of only 1.65 V is required to achieve an electrolysis current density of 100 mA·cm^−2.In addition,the catalyst shows a very high stability for OWS,the two-electrode cell can operate at a consist current density of 20 mA·cm^−2 for 10 h OWS with the cell voltage being stable at ca.1.60 V.These results demonstrate that FeOOH/Cr-NiCo2O4/NF possesses an OWS performance superior to most of transition-metal based bifunctional electrocatalysts working in alkaline medium.The excellent bifunctional activity and stability of FeOOH/Cr-NiCo2O4/NF are attributed to the following reasons:(i)The NN structure provides a large specific surface area;(ii)the high conductivity of Cr-NiCo2O4 enables more active centers on the far-end part of NNs to be electrochemically reached;(iii)the deposition of FeOOH supplies additional active sites for OWS.