Preparation And Capacitance Performance Of Nanostructured Ni(OH)₂ And NiO

Nickel hydroxide and nickel oxide possess excellent electrochemical performance and have a good application prospective in electrode material for ultracapacitors. Nano-sized nickel hydroxide and nickel oxide with different structure and morphology were prepared. Techniques such as XRD, TEM, TG/DTG, FT-IR, cyclic voltammetry, chronopotentiomtry, AC impedance were used to study the physical properties and electrochemical performances of the synthesized materials.β-Ni(OH)2 was synthesized by liquid-phase precipitation and hydrothermal method with Ni₂SO₄ and NaOH as source materials. Hexagonal nanosheet or nanorod NiO was prepared by thermal decomposition ofβ-Ni(OH)2 at 255℃for 3h. When NiSO4 concentration was 0.8mol·L-1, the filling fraction was 90%, pH=12, and treated hydrothermally at 120℃for 24h, the NiO possessed a specific capacitance of 122.9 F·g-1 between -0.1⁰.4V(vs.SCE) in 1mol·L-1 KOH aqueous solution, and had a good cycling performance.β-Ni(OH)2 was synthesized by precipitation transformation and hydrothermal method with NiC2O4 and NaOH as source materials. Hexagonal nanosheet or nanorod NiO was prepared by thermal decomposition ofβ-Ni(OH)2 at 255℃for 3h. When n[NiC2O4]:n[NaOH]=1:3, the filling fraction was 75%, and treated hydrothermally at 180℃for 12h, the NiO possessed a specific capacitance of 72.2F·g-1 between -0.1⁰.4V(vs.SCE) in 1mol·L-1 KOH aqueous solution.NiO nanoparticles were synthesized in W/O microemulsion solution containing aqueous solution, surfactant, cyclohexane and n-pentanol. Several factors such as the type of surfactants, reagent concentration, the ratio of water to surfactant, ageing time were studied for their effects on specific capacitance of samples. With the CTAB as surfactant, the NiO possessed a specific capacitance of 115.6F·g-1 between -0.1⁰.35V(vs.SCE) in 1mol·L-1 KOH aqueous solution.The initial product ofα-Ni(OH)2 was synthesized by homogeneous precipitation method, then it was treated at 255℃for 3h to get theα-Ni(OH)2 with good electrochemical performance and the morphology of curly nanofilm. Several factors such as reagent concentration, molar ratio, reaction temperature and time were studied for their effects on specific capacitance of samples. When NiSO4 concentration was 0.1mol·L-1, n[Ni₂SO₄]:n[CO(NH2)2]=1:7.5, reaction temperature and time was 98℃and 3h, the NiO possessed a specific capacitance of 95.65F·g-1 between -0.1⁰.3V(vs.SCE) in 1mol·L-1 KOH aqueous solution.