Lin Yu,Jingyuan Liu,Wenyan Yin,Jing Yu,Rongrong Chen,Dalei Song,Qi Liu,Rumin Li,Jun Wang
Ionic liquids are promising electrolytes for electrochemical gas sensors that have unique physicochemical properties such as negligible vapor pressure and high thermal stability. The modification of ionic liquid (IL) by combining metal oxide with reduced graphene oxide (rGO) is an effective method to improve its gas-sensing properties. In this study, the mesoporous structure of NiCo 2 O 4 /rGO is synthesized by simple one-step method, and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF 6 ]) is mixed with it to form the composite material NiCo 2 O 4 /rGO/[BMIM][PF 6 ]. Electrochemical test results indicate that the three electrolytes exhibit response current and long-term stability in the oxygen environment. The oxygen sensor based on NiCo 2 O 4 /rGO/[BMIM][PF 6 ] significantly improves the response current and working stability of pure ionic liquid. The sensitivity of the sensor is 0.1087 μA/[%O 2 ], and the linear regression coefficient of the reduction peak current calibration curve is 0.9995. After continuous cyclic voltammetry , the reduction peak current remains at 90% of the initial current value. The interaction of IL and NiCo 2 O 4 /rGO significantly enhances electrochemical oxygen sensing performance.
We developed a hydrothermal synthesis and high temperature calcination method to synthesize the metal–organic framework (MOF)-derived NiCo2O4/NiO and NiCo2O4/NiO-rGO. These composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Brunner–Emmet–Teller measurements. This work combines excellent catalytic efficiency of the transition metal with large specific surface area and large number of pores of the MOF. Consequently, catalysts for oxygen evolution with high efficiency and low cost were obtained. Both materials show lower overpotential at 430 and 350 mV, respectively, under 10 mA·cm–2. The Tafel slopes are 49 and 66 mV·dec–1, respectively, with very small performance attenuation for long-term catalytic reaction. Therefore, the catalysts reported herein possess great potential for application in oxygen evolution reaction.
Electrochemical performance of electrode in structural supercapacitor is much lower than that in common supercapacitor owing to solidification confinement of ions movement. Herein, NiCo2O4/reduced graphene oxide (rGO) nanosheets are firstly assembled with KOH/polyacrylic acid (PAA)/cement, LiOTf/PAA cement, KOH/polyethylene oxide (PEO) cement and LiOTf/PEO cement into four structural supercapacitors through hydration process. As the NiCo2O4 content in NiCo2O4/rGO composite exceeds 13 wt%, the areal capacitance of NiCo2O4/rGO electrode at high current densities decreases. The (13%) NiCo2O4/rGO electrode presents the best electrochemical performances with initial areal capacitance of 3.16 F cm−2 at 0.5 mA cm−2, capacitance retention rate of 61% after current density increasing by 80-fold and retention of 86.1% after 10000 cycles at 10 mA cm−2. The corresponding four structural supercapacitors show superior electrochemical performances with areal capacitances of ∼ 330.4 mF cm−2, coulombic efficiencies of ∼ 100%, power densities of ∼ 2.7 mW cm−2 and energy densities of ∼ 0.64 mWh cm−2. The electrochemical efficiencies of (13%) NiCo2O4/rGO electrodes in four structural supercapacitor devices are in the range of 0.16 ∼ 0.12, which are prominent in high-end structural supercapacitors. Thus NiCo2O4/rGO electrode is demonstrated to enhance the electrochemical matching with polymer cement electrolyte for structural supercapacitor.
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