Preparation Of Carbon-based Composite Materials And Their Energy Storage And Photo-thermal Conversion Properties

Developing efficient clean energy storage and conversion technology has become one of the hot research topics around the world.The exploitation of various advanced functional composite materials is the key to realize the technology.The micro-and nano-carbon-based composites with unique physical and chemical properties have become the focus in the field of functional composites.In this thesis,a variety of micro-and nano-carbon-based composites have been constructed and functionalized using the three-dimensional(3D)printing and electrospinning methods.In addition,their electrochemical energy storage and solar steam generation properties have been tested.The main content can be divided into the following four parts:Developing advanced supercapacitors with both high areal and volumetric energy densities is significant for the compact electrochemical energy storage.In this chapter,we design self-supported,compact carbon composite electrodes with tunable thickness and graphene oxide(GO)separator using the 3D printing technology for high-energy-density supercapacitors.The 3D carbon composite electrodes are composed of the closely stacked and aligned active carbon/carbon nanotube/reduced graphene oxide(AC/CNT/r GO)composite filaments.The AC microparticles are uniformly embedded in the wrinkled CNT/r GO conductive networks without using polymer binders,which contributes to the formation of abundant open and hierarchical pores,leading to electrolyte permeation and transport.The 3D-printed ultrathick AC/CNT/r GO composite electrode(10 layers)features high areal and volumetric capacitance of 9.16 F cm-2 and 32.8 F cm-3 at 10 m V s-1,respectively.The symmetric cell assembled with the 3D-printed thin GO separator and ultrathick AC/CNT/r GO electrodes can possess both high areal and volumetric capacitances of 4.56 F cm-2 and 10.28 F cm-3,respectively.Correspondingly,the assembled ultrathick and compact symmetric cell achieves high areal and volumetric energy densities of 0.63 m Wh cm-2 and 1.43 m Wh cm-3,respectively.The all-component extrusion-based 3D printing offers a promising strategy for the fabrication of multiscale and multidimensional structures of various high-energy-density electrochemical energy storage devices.High-performance flexible energy storage devices are an important prerequisite to the utilization of various advanced wearable electronics,such as healthcare sensors and smart textiles.In this study,we design a wearable,all-solid-state,all-in-one asymmetric supercapacitor by integrating current collectors,separator,negative and positive electrodes into a thin,flexible and porous polyamide nanofiber film using the electrospinning,vacuum filtration and galvanostatic electrodeposition.The positive(MnO2 NWs)and negative(Fe OOH NSs)electrodes are respectively electrodeposited into each side of the carbon nanotubes(CNT)modified porous polyamide nanofiber film to form the integrated and compact asymmetric cell.The all-in-one,thin-film asymmetric supercapacitor is binder-,conductive additives-and metal current collector-free,which can effectively decrease the cost,simplify the assembly procedures and increase the energy density.The assembled flexible all-in-one asymmetric supercapacitor with a compact structure shows high gravimetric and volumetric specific capacitance of 70 F g-1 and 3.1 F cm-3 under a current density of 0.5 A g-1 in a neutral PVA/Li Cl gel electrolyte,respectively.Additionally,the all-in-one asymmetric cell displays a favorable volumetric energy density of 1.1 Wh L-3,which is among the highest compared with other reported flexible solid-state supercapacitors.Notably,multiple cell units can be integrated in one piece of polyamide nanofiber film and connected in series to satisfy the need of high output voltage.Using solar energy to generate steam is a clean and sustainable approach to address the issue of water shortage.The current challenge for solar steam generation is to develop easy-tomanufacture and scalable preparation and assembly methods which can convert solar irradiation into exploitable thermal energy with high efficiency.In this chapter,for the first time,3D printing is used to construct a carbon-based all-in-one evaporator for high-efficiency solar steam generation under 1 sun illumination.The solar steam generator has a concave structure and is composed of the CNT/GO absorption layer,NFC/GO support and NFC/GO water intake layer.The solar-steamgeneration device has a high porosity(97.3%)and efficient broadband solar absorption(>97%).The 3D-printed porous evaporator with intrinsic low thermal conductivity enables heat localization and effectively alleviates thermal dissipation to the bulk water.As a result,the 3D-printed evaporator has a high solar steam efficiency of 85.6% under 1 sun illumination(1 k W m-2),which is among the best compared with other reported evaporators.The all-in-one structure design using the advanced 3D printing fabrication technique offers a new approach to solar energy harvesting for high-efficiency steam generation.Solar steam generation has been extensively investigated recently as a sustainable and environmentally friendly technology for water purification.Although various materials such as graphene and cellulose have been utilized for the construction of solar steam generators,high cost and inferior durability greatly hinder their practical application.In this chapter,we design a lowcost,floatable,durable and scalable evaporator with an open nanofiber-based bifunctional structure for high-efficiency solar steam generation using the electrospinning method.The integrated bilayer evaporator is successively composed of electrospun hydrophobic polyvinylidene fluoride(PVDF)nanofibers and hydrophilic carbon black/polyacrylonitrile(CB/PAN)composite nanofiber layers from the bottom up.The porous hydrophobic PVDF nanofiber layer,due to their intrinsic low thermal conductivity,serves as the floating support and thermal barrier to suppress the irreversible heat dissipation.The hydrophilic CB/PAN composite nanofiber layer on the top has a high broadband solar adsorption of 98.6% from the wavelength of 250 to 2500 nm,which can effectively convert solar irradiation into available heat energy.The assembled CB/PAN//PVDF(CP/P) evaporator possesses an impressive solar energy conversion efficiency of 82.0% under one-sun illumination and superior long-term stability.The electrospun cost-efficient polymer-nanofiberbased evaporator with excellent flexibility,durability and scalability holds great promise in the practical application of water desalination and sterilization.