Synthesis of NiS thin films on Ti foil by CBD process.

A simple, rapid, and inexpensive solution-processed synthesis strategy for mass production of cobalt oxide (Co 3 O 4 ) micro-dandelions has been applied and reported. As-synthesized Co 3 O 4 micro-dandelions are initially characterized for their structure and morphology confirmations and subsequently utilized for the fabrication of low-cost high-performance hydrogen sulfide (H 2 S) gas sensor. Structural analysis is in accordance with the formation of polycrystalline facecentered cubic Co 3 O 4 . Several aggregated Co 3 O 4 micro-dandelions, composed of number of individual nano-needles, with substantial porosity are evidenced from the surface morphological analysis. Gas sensing results demonstrate that the Co 3 O 4 micro-dandelions reveal higher selectivity to H 2 S gas at the operating temperature of 200 °C. Maximum response of 481% is corroborated to 200 ppm of H 2 S at 200 °C. In addition, Co 3 O 4 micro-dandelions detect H 2 S at levels as low as 5 ppm with enhanced response of 68%, rapid response time of 5 s and recovery time of 30 s, demonstrating its potential as a sensing material in the development of H 2 S related sensors.

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In the present study, beta-cobalt hydroxide (β-Co(OH)) electrodes of various nanostructures and surface areas, viz. nano-rhombuses (NRs), nano-plates (NPs), and nano-grass (NGs), have been synthesized directly onto a stainless-steel (SS) substrate using a simple, economical and binder-free chemical solution-process, utilizing three cobalt precursor salts, i.e. cobalt acetate, cobalt chloride, and cobalt nitrate, respectively. Structural elucidation proves the crystallite size, type and phase-purity of β-Co(OH), whereas the surface morphology analysis supports the evolution of the above mentioned nanostructures of various surface areas. The electrochemical pseudocapacitor performance investigation demonstrates a specific capacitance (S) of 367 F g at 1 mA cm for the NP-type morphology, which is higher than that that displayed by the other morphologies. This change in S value is attributed to different charge transfer resistance values, which have been obtained from electrochemical impedance spectroscopy spectra. Finally, we attempt to correlate the relationship between the surface morphology, i.e. surface area, and the charge transfer resistance with the obtained specific capacitance value of the respective electrode.