Preparation Of Nickel-based Supercapacitor Electrode Material And Its Electrochemical Performance

Nowadays,energy storage and environmental problems are becoming more and more serious due to the increasing problems such as the consumption of fossil fuels,rapid population growth and global warming.Therefore,in order to seek sustainable use of energy to reduce dependence on traditional non-renewable energy sources,developing new energy sources and new energy storage devices has become a hot spot in the 21st century.Due to its high power density,good rate performance,long cycle life,high safety factor,and good performance at low temperature,supercapacitors are considered to be the most popular candidates from various energy storage devices.The energy storage of supercapacitors is through the interaction between the electrode and the electrolyte,and its charge storage capacity is closely related to the electrode material.Therefore,the electrode material plays a vital role in the performance of the supercapacitors.At present,research hotspots on supercapacitors mainly focus on how to optimize the structure of electrode materials and improve their electrochemical performance.In this paper,foam nickel was used as the substrate.Firstly,the effects of different acid activation processes on the structure and properties of the substrate were studied.Then,nickel hydroxide,nickel sulfide and its nano-electrode materials compositing with carbon nanotubes on the surface of the optimal acid-activated nickel foam substrate were fabricated by hydrothermal and electrochemical deposition techniques.From the perspective of widening the application of electrode materials,we prepared electrode materials with superhydrophobic properties providing enlightenment for the preparation and research of superhydrophobic electrode materials.Various methods and tests are used to characterize and analyze the morphology,chemical composition,electrochemical properties and wettability of the prepared electrode materials.The main results are as follows:?1?By researching the effects of different acid activation processes on the structure and properties of nickel foam substrate,it was determined that the optimum activation process is the acid activation temperature of 90°C and the activation time of 20 min.Ni₃S₂ electrodes with the ultra-high specific surface area were prepared on the optimal acid-activated nickel foam substrate by two-step hydrothermal reaction using two different sulfur sources.The electrochemical performance test results showed that the two Ni3S2 electrodes exhibited Faraday pseudo-capacitor characteristics in alkaline electrolyte.At the same current density(2A·g^-1),the specific capacitance of Ni₃S₂//Na₂S electrode was 1276.5 F·g^-1,while the specific capacitance of the Ni₃S₂//TAA electrode was 1005.5 F·g^-1;the capacitance retention of the Ni₃S₂//Na₂S electrode was still 87.5%after 1000 cycles at a current density of 5 A·g^-1,while the Ni₃S₂//TAA electrode was 79.3%,indicating that the Ni₃S₂//Na₂S electrode has superior specific capacitance and stability.It was mainly attributed to the uniform honeycomb petal-like morphology of Ni₃S₂//Na₂S electrodes,showing a unique porous nanosheet structure,which provides a richer electrochemical active site and ion diffusion channels.?2?In order to obtain an electrode with better electrochemical performance,it was considered to combine a metal sulfide with a carbon material to prepare a composite electrode.Firstly,Ni?OH?₂/CNTs composite electrodes were prepared by one-step electrodeposition on the optimal acid-activated nickel foam substrate.The microstructure and electrochemical properties of Ni?OH?2/CNTs composite electrodes were studied by changing the deposition voltage.Therefore,it was determined that 100 V was the optimum deposition voltage,and then the Ni?OH?₂/CNTs electrodes under the optimal deposition conditions were treated by hydrothermal vulcanization process to prepare Ni₃S₂/CNTs self-supporting nanocomposite electrodes.Electrochemical performance tests showed that the specific capacitance of Ni₃S₂/CNTs composite electrodes(1380.0 F·g^-1)was much higher than Ni?OH?₂/CNTs composite electrode(634.5 F·g^-1)at the same current density(2 A·g^-1).This was mainly due to the synergistic complementation between Ni₃S₂ active materials and CNTs,and its good open 3D network-like nanolayer structure also facilitates the transfer of electrolytes in the electrode material,providing more channels for electron transport.As a result,the electrochemical performance of Ni3S2/CNTs was excellent,and the capacitance retention rate was 91.5%after circulating 2000 times at a current density of 5 A·g^-1,which showed a good cycle life.?3?Based on the research above,nickel-based superhydrophobic electrodes were prepared on the optimal acid-activated nickel foam substrate by one-step electrodeposition.The parameters such as deposition time and deposition current were analyzed and discussed.Determining the deposition at 0.1 A for 7 min was the best electrodeposition process.The contact angle of the electrode material was raised to 154.3°and the rolling angle was as low as 2°.It was found that the surface of the electrode consists of a uniform micro-nano coarse sphere structure,and the chemical composition were mainly Ni?OH?2 and Ni[CH₃?CH₂?₁₆COO]₂,and the reaction mechanism was proposed.The results of the electrochemical performance test showed that the specific capacitance of the superhydrophobic Ni?OH?₂ electrode was lower than that of the common Ni?OH?₂ electrode.Due to the hydrophobic film layer on the surface of the Ni?OH?₂ superhydrophobic electrode principally,it was inferred that the conductivity of the electrodes was lowered,and the ion exchange between the active material and the electrolyte was hindered.However,the capacitance retention rate was still 80.4%after 1000 cycles at a current density of 1 A·g^-1,which showed relatively stable electrochemical performance.