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In this paper, three-dimensional (3D) Co₃O₄ flower-like microspheres have been successfully synthesized via a facile ethylene glycol (EG)-mediated solvothermal method followed by calcination. The as-prepared flower-like precursors microspheres are formed from the assembly of 2D nanosheets in the presence of hexadecyltrimethylammonium bromide (CTAB). The flower-like architectures of the prepared precursors could be tailored by changing the amount of CTAB. Furthermore, when evaluated as a gas sensor, the obtained Co₃O₄ flower-like microspheres exhibit a good response and sensitivity toward ethanol gas, suggesting their promising potential for gas sensors application.

As one of the electrode materials for supercapacitor, Co₃O₄/graphene composite was mainly synthesized via two-steps method. Here, a facile one-pot method was used for Co₃O₄/graphene composite, and the performances of one-pot-synthesized Co₃O₄/graphene composite were carefully investigated. Liquid-phase exfoliation was used for graphene and the $D$-band/$G$-band ratio of liquid-phase exfoliated graphene was only 0.094, which indicated that the graphene had low defect density and enhanced electrical conductivity. Morphologies investigation of Co₃O₄/graphene composites indicated that Co₃O₄ nanoparticles with mean diameter of 14nm were uniformly anchored on graphene sheets. The facile one-pot method associated with liquid-phase exfoliated graphene induced Co₃O₄/graphene composite with enhanced specific capacitance of 392 F$\cdot$g${}^{-1}$ at a current density of 1 A$\cdot$g${}^{-1}$. The Co₃O₄/graphene composite also expressed relatively small internal resistance and diffusion resistance (0.36$\mathrm{\Omega }$ and 0.45$\mathrm{\Omega }$, respectively). Moreover, the synthesized Co₃O₄/graphene composite yielded excellent rate performances with only 9.5% capacitance loss when current density was increased by a factor of 10.

Developing a general, green and effective strategy to improve the hydrogen evolution reaction (HER) electrocatalyst is urgently needed but challenging. Herein, we report a novel conducting polymer/metal/metal oxide composite as HER catalyst prepared by a two-step strategy, in which the Au/Co₃O₄ is synthesized by a one-pot hydrothermal method, subsequently, cyclic voltammetry is employed to electropolymerize polythionine on the Au/Co₃O₄. It is demonstrated that the HER electrocatalytic activity of Au/Co₃O₄ is effectively improved by the coating polythionine layer. The optimal polythionine/Au/Co₃O₄ displays an excellent electrocatalytic ability towards HER with an overpotential of 168mV at $10\mathrm{\text{mA}}\cdot {\mathrm{\text{cm}}}^{-2}$ and low Tafel slope of 79mV$\cdot$dec${}^{-1}$ in 0.5M H₂SO₄, which is greatly superior to those of the Au/Co₃O₄ (an overpotential of 300mV at $10\mathrm{\text{mA}}\cdot {\mathrm{\text{cm}}}^{-2}$ and tafel slope of $157\mathrm{\text{mV}}\cdot {\mathrm{\text{dec}}}^{-1})$. Interestingly, the HER performance of N-doped reduced graphene (N-rGO) can also be significantly boosted by the coating polythionine layers, indicating the multifunctionality of polythionine in the enhancement of HER performance of nano electrocatalysts.