Preparation And Electrochemical Performance Of Several Carbon/Nickel-Based Composites

Owing to the excellent properties,supercapacitors have been regarded as one of the most promising electrochemical energy devices.Among all the components of capacitor,electrode material plays a decisive role in the electrochemical performance of supercapacitors.In view of their practical application,electrode materials should possess the properties of low-cost,abundant reserves,ease of synthesis and environmental friendly character.The electrode materials usually contain carbon materials,metal oxides and conducting polymers.However,each kind of electrode material owns its intrinsic shortcomings,which can hinder its electrochemical performance.The composites containing carbon materials and metal-based materials could combine the advantages and mitigate the shortcoming of both components,which would own superior electrochemical stability and specific capacitance.Herein,we have designed and prepared carbon/nickel-based composites and analyzed their electrochemical properties.The main contents are summrized as follows:Using the AlOOH sol as aluminium resource,we have developed a facile hydrothermal process to prepare a sandwich-type rGO/NiAl-LDH composite.NiAl-LDH nanosheet arrays have grown on both sides of graphene nanosheets in formation of a unique sandwich structure,which has a large specific surface area（184.7 m²/g）and typical mesoporous characteristic.Based on the electrochemical study,it reveals that the sandwich-type rGO/NiAl-LDH composite has a specific capacitance of 1325 F/g at the current density of 3.57 A/g.When the current density is increased to 17.56 A/g,the specific capacitance of rGO/LDH composite still exhibits as high as 851 F/g.After 500 cycles at the current density of 15.30 A/g,the high specific capacitance only decrease by 9%,indicating the excellent electrochemical stability.The reason for this superior performance may be that the rGO/NiAl-LDH composite with intersting sandwich-structure is beneficial to the mass transfer during the electrochemical process.This in situ growth route may pave an important way to design and fabricate diverse LDH/graphene composites with unique structure for promising application in capacitors and other fields.By doping the Co²⁺ions,a series of rGO/Ni_1-xCo_xAl-LDH composites have been fabricated through an in situ growth route.As-doped Co²⁺ions can increase the active sites in the electrode materials,influence the morphology and electrochemical properties of the composites.When the Co content is 0.17,0.33,and 0.55,as-obtained ternary–component LDH/graphene composites still own the sandwich structures.As the Co content further increases,the unique architecture has been changed and turned irregularly.Based on the systematical electrochemical analyses,it is revealed that Co content and morphology of composites play important roles in their electrochemical properties.The results show that when the Co content is 17%,Ni_0.83Co_0.17Al-LDH nanosheets self-assemble on the graphene nanosheets,constructing an interesting rGO/Ni_0.83Co_0.17Al-LDH composite with a high specific surface area（171.5 m²/g）.And rGO/Ni_0.83Co_0.17Al-LDH composite shows the best electrochemical performance with a highest specific capacitance of 1902 F/g at the current density of 1 A/g,and excellent cycling stability.Through a simple and versatile synthetic strategy,we have prepared a unique double-shelled N-C@NiAl-LDH composite employing nitrogen-doped carbon hollow microsphere（HMS）as substrate.Therein,N-C HMS is obtained by an in situ polymerized and post-treatment process taking SiO₂ as template,using RF as precursor and employing melamine as nitrogen source.The as-designed N-C@NiAl-LDH composite adopts nitrogen-enriched carbon hollow sphere as interior shell and intercrossed LDH nanosheets as exterior shell.This composite owns high nitrogen content,large specific surface（337 m²/g）and open mesoporous structure.The electrochemical performances of N-C@LDH HMS,C@LDH HMS and LDH HMS are studied to analysis the influences of carbon shell and nitrogen-doped.It is found that double-shelled N-C@LDH HMS displays a high specific capacitance of 1711.5 F/g at the current density of 1 A/g.More importantly,this high specific capacitance still can be kept to 997.3 at the current density of 10 A/g with an excellent electrochemical cycling stability.Taking SiO₂@RF core-shell spheres as template,double-shelled C@NiO hollow spheres have been prepared through a facile hydrothermal process,followed by a heat treatment.SiO₂spheres have been employed as template to construct hollow architecture and used as source to form NiSilicate precursor.The calcination process in the Ar atmosphere can simultaneously give rise to the carbonization of RF and decomposition of NiSilicate.The C@NiO composite maintains the morphology of parent precursor,displaying the porous carbon inner shell and flower-like NiO exterior shell.The carbon shell and NiO nanosheet contact with each other closely,in formation of the composite with a large specific surface area（217 m²/g）and favorable pore structure.As expected,double-shelled C@NiO composite has superior electrochemical properties to that of NiO hollow sphere with similar morphology.When the current density is increased from 1 A/g to 10 A/g,the specific capacitance of C@NiO composite can still be kept to 84.54%.After 1000 cycles at the current density of 5 A/g,as-prepred C@NiO hollow spheres exhibit good stability.This synthetic strategy can be expanded to fabricate other carbon-based functional composites,which should be highly potential in deverse fields.A hybrid composite has been prepared through a simple and scalable hydrothermal method combined with suitable heat treatment.The composite composed of ultrathin NiCo₂O₄nanobelts and graphene nanosheets has large specific surface area（222 m²/g）and mesoporous structure.The calcination temperature has been optimized by investigating the pseudocapacitive behaviour of bare spinel NiCo₂O₄ prepared at different calcination temperatures.The rGO/NiCo₂O₄ composite yields a high specific capacitance of 1072.91 F/g at the current density of 1 A/g with desirable rate performance and cycling stability.As the current density is increased to 10 A/g,the specific capacitance still retains 69.2%,and after3000 cycles,the value can be kept to 98.55%.In view of simple,high-yield synthetic route and remarkable electrochemical properties,this NiCo₂O₄ nanobelt/graphene hybrid composite should be a promising electrode material for supercapacitors.