In-situ Activation And Properties Research Of 3D Ni-Co Hydroxide Electeode Materials

Three-dimensional(3D)hybrid nanostructured arrays grown on a flexible substrate show great potential as electrodes in portable and wearable electronic devices.In this work,various Ni/Co-based hydroxide nanostructures grown on carbon cloths were fabricated and their capacitive performances were discussed.Meanwhile,due to the good electrocatalytic performance of Ni/Co compounds,the catalytic activity of the obtained Ni/Co-based hydroxide electrode on oxygen evolution reaction(OER)was also explored.Firstly,an in-situ conversion of Ni-Co active electrode materials for the fabrication of high-performance electrodes has been investigated.Ni-Co carbonate hydroxide nanowire arrays grown on a carbon cloth substrate were synthesized through a facile hydrothermal method,and they were gradually converted to Ni-Co(oxy)hydroxide nanowire-supported nanoflake arrays by soaking in an alkaline solution.As a pseudocapacitor electrode,the nanowire-supported nanoflake arrays exhibited abundant channels and large surface areas to allow the rapid diffusion of electrolyte ions,electron transport,and had good structural stability,which led to excellent electrochemical characteristics.With the soaking time,an obvious increase in the areal capacitance from 281 mF·cm-2 to 3900 mF·cm-2 at 1 mA·cm-2 was obtained.The coulombic efficiency over 100%was observed during charge/discharge due to the long-time soaking in KOH solution.In addition,there was an enhancement in the areal capacity of the ASC after assembling and soaking in alkaline solution for 24 h.Secondly,Ni-Co hydroxide nanoarrays electrodes with different Ni/Co molar ratio were prepared via the in-situ conversion,and the effect of Ni/Co molar ratio onto the capacitive performance was discussed.By using Ni1.5Co(OH)x as electrode material,the areal capacitance increased from 1988 mF·cm-2 at 2 mA·cm-2 to 4544 mF·cm-2 after soaking in 6 M KOH for 10 h.The conversion mechanism and the role of Ni and Co elements were also investigated.The formation of Ni-Co carbonate hydroxide nanowire arrays is due to the growth habit of the Co compounds,and the change to nanoflake arrays is induced by the growth trend of Ni hydroxide.The effect of Co element is the main role in capacitance,while Ni element can improve the conductivity of electrode.Finally,the carbon cloth can be used as a flexible substrate to form a highly catalyzed OER electrode.Ni-Co-Fe carbonate hydroxide nanowire arrays grown on a carbon cloth substrate were synthesized through a facile hydrothermal method.Ni-Co-Fe carbonate electrode produced 10 mA·cm-2 at an overpotential of 402 mV with the minimum Tafel slope of 70 mV·dec-1.After soaking in 6 M KOH,the minimum overpotential at 10 mA cm 2 was 340 mV.