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Applied potential-dependent performance of the nickel cobalt oxysulfide nanotube/nickel molybdenum oxide nanosheet core–shell structure in energy storage and oxygen evolution
- Chiu, Kuan-Lin, Lin, Lu-Yin
- Journal of materials chemistry A 2019 v.7 no.9 pp. 4626-4639
- batteries, cobalt, cobalt sulfide, electrical conductivity, electrochemistry, electrodes, energy, molybdenum, nanosheets, nanotubes, nickel, oxidation, oxygen production, surface area
- Nickel cobalt sulfide is widely applied to energy storage and electrocatalysis owing to its high electrical conductivity and multiple oxidation states. This study proposes NiCo₂S₄ and NiCo₂OₓSy@NiMoO₄ core–shell structures as energy storage materials and electrocatalysts for the oxygen evolution reaction. A higher specific capacity of 2.22 mA h cm⁻² (168.18 mA h g⁻¹) at 10 mA cm⁻² is obtained for the NiCo₂OₓSy@NiMoO₄ electrode which is applied as the battery-type electrode in the battery supercapacitor hybrid, but a better electrocatalytic activity is achieved for the NiCo₂S₄ electrode with a smaller overpotential of 1.567 VRHE at 0.12 A cm⁻² and a smaller Tafel slope of 86.1 mV dec⁻¹. The electrochemically active surface area (ECSA) is larger for NiCo₂S₄ due to the nanoparticle-assembled nanotube wall, whereas NiCo₂OₓSy@NiMoO₄ shows higher electrical conductivity owing to the presence of molybdenum. Different performances in energy storage and electrocatalysis for NiCo₂S₄ and NiCo₂OₓSy@NiMoO₄ nanomaterials are caused by different potentials applied for driving the electrochemical reactions. This study for the first time proves that the trade-off between ECSA and electrical conductivity is important for designing nanomaterials applied in different electrochemical fields.