Preparation And Electrochemical Properties Of Supercapacitor Electrode Materials From Electroplating Sludge Containing Nickel

Nickel is a very important element in modern industry,which is widely used in supercapacitors,lithium-ion batteries,electroplating,catalysis and other industries.As a result,global demand for nickel is growing at an alarming rate and,at the current rate of consumption,nickel reserves will be exhausted within 30 years.However,due to the rapid development of electroplating industry,a large number of electroplating sludges containing heavy metals are produced every year,and the phase of heavy metals in these sludges is much higher than that of related minerals.The conventional disposal of these sludge is landfill after solidification,which not only causes waste of metal resources,but also causes serious environmental pollution,which seriously violates the concept of sustainable development of the current era.Therefore,the recovery of heavy metals in electroplating sludge is considered to be an economical and effective method,and a large number of studies have been put into it.The technologies of recovering valuable metals from electroplating sludge include acid leaching,ammonia leaching,biological leaching,smelting calcination and so on.However,these methods not only consume a large amount of acid or alkali,but also involve a series of complex extraction and separation processes,which seriously restrict the recycling process of electroplating sludge.Therefore,there is an urgent need to develop a simple recovery process,low cost,pollution-free,high resource recovery technology.In this paper,according to the characteristics of nickel resources in supercapacitor applications,a series of nickel-based electrode materials were prepared by a simple hydrothermal synthesis method.The electrochemical performance of the electrode material can be improved by adjusting the composite morphology between the two compounds with different morphologies,adjusting the crystal morphology of the electrode material,optimizing the structure of the electrode materials and other methods.The metal in the electroplating sludge is directly and directionally converted into the electrode material of the super capacitor,is green,simple,convenient,environment-friendly and economical,realizes the high-value utilization of the metal,and overcomes the problems in the traditional process of separating and recovering metal resources.The main contents are as follows:1.Ni S₂ nanoflowers were synthesized by a simple hydrothermal method using nickel-containing electroplating sludge as raw material,sodium thiosulfate as sulfur source and urea as precipitant.The size of the Ni S₂ nanosheets is 1.5μm,and the porous structure can not only fully cope with the rapid migration and exchange of ions,but also obtain better electrochemical performance(562.3 C g^-1 at 1 A g^-1)and rate capability(73.27%at 10 A g^-1).These results indicate that Ni S₂ flower-like structure has great potential for application in supercapacitors and solid waste recycling.2.The first part is that the electrode material with good electrochemical performance can be obtained by adding sodium thiosulfate,but the addition of sodium thiosulfate may produce harmful intermediate products.In this part,α-Ni（OH）₂/Ni（HCO₃）₂ composite electrode material with high recovery rate and high performance was prepared by using electroplating sludge as raw material and urea as precipitant.The recoveries of Ni,Fe and Al are 92.58%,81.52%and 61.19%,respectively.The specific capacitance of NN-4 is495.6 C g^-1 at 1 A g^-1,the capacity retention rate is 55.58%after 3500 cycles,and the rate performance is 78.77%in the range of 1～10 A g^-1.This excellent performance is mainly based on two unique features.（1）The Fe and Al ions carried by the sludge increased the interlayer spacing ofα-Ni（OH）₂,promoted the diffusion of OH^-into the active material,and improved the electrode reaction activity.（2）The ultrathinα-Ni（OH）₂ nanosheets were embedded in self-assembled Ni（HCO₃）₂ nanowire spheres with a hierarchical structure to obtain large surface area and pore volume.This structure provides a large number of active sites,which makes the OH^-in the electrolyte fully contacts with the active substances and improves the utilization of the active sites.This study provides a simple,convenient,and effective method for the recycling of environmentally hazardous waste,and provides a new way for the resource utilization of industrial waste.3.In order to improve the active sites of the electrode materials,this study continued to use nickel-containing electroplating sludge as raw material,added ascorbic acid as complexing agent,further controlled the hydrothermal temperature,synthesized amorphous nickel bicarbonate electrode materials with hollow structure,improved the active sites of the materials,and then improved the electrochemical performance of the samples.The synthesized AA-120 is a hollow microsphere with a diameter of about 1.5μm,which is self-assembled by numerous small spheres,and a large number of nanowires grow on the surface of the small spheres,this unique structure can produce more electrochemical reaction active sites,promote the permeation of electrolyte and ion transmission.A good specific capacitance(599.8 C g^-1)is displayed under the current density of 1 A g^-1,and the specific capacitance of 366.0 C g^-1 is displayed under the current density of 10 A g^-1,and the excellent rate performance（61.02%）is displayed.In addition,the recoveries of Ni,Fe and Al were 95.57%,99.92%and 92.30%,respectively.