| Recently,researches have been paying more attention to wood because of its many useful properties,such as its hierarchical porous structure,durable mechanical profile,eco-friendliness,renewability,and biodegradability.The hierarchical porosity and chemical composition of wood allow modifications to tune its ionic,optical,thermal,conductance,and mechanical properties through physicochemical treatments.Among these,the delignification,densification,and functionalization of bulk wood are the most fascinating to provide a scaffold for cutting-edge applications.The delignification removes lignin and hemicellulose from wood by leaving the cellulose in place,maintaining the wood’s hierarchical structure and physical integrity.At the same time,densification allows for tuning wood’s density,and functionalization offers opportunities to design versatile,functional 3D materials offering applications in smart devices,portable electronics,and grid-scale devices.The delignification,densification,and functionalization are focal points of this thesis,comprising（I）design of porous flexible scaffolds from wood,（II）functionalized porous scaffolds for energy storage,（III）designing thick electrodes from porous wood scaffolds,and（IV）exploitation of novel redox capacitance from the wood surface.（I）The natural wood（NW）has been meticulously modified via physicochemical approaches,making it ideal for next-generation structural and functional applications.We herein have developed flexible wood（FW）scaffolds from radial-cut（RC）and longitudinal-cut（LC）NW through delignification and alkaline crystallization-assisted vacuum densification.This method is based on the swelling of wood cell walls by chemical treatment followed by alkaline crystallization-assisted vacuum densification.The as-prepared FW membranes are so flexible that they can be rolled into different shapes in any direction and easily knotted/unknotted—readily tailored for sewable devices,flexible electronics,biomedical,sensors,and structural applications.The delignification was aimed at improving the scaffold’s porosity,functionality,and densification.The modification increased micro-mesopores for higher surface area and decreased macropores to improve scaffold density.The scaffolds exhibit ultra-high flexibility along with excellent mechanical strength.The chemical treatment was also beneficial in enriching the scaffold’s hydroxyl functionality.Furthermore,the characterization was done by performing scanning electron microscopy（SEM）,Fourier transform infrared spectroscopy（FTIR）,X-ray diffraction（XRD）analysis,Brunner-Emmitt-Teller（BET）,and density functional theory（DFT）for surface area and pore size analysis,and mechanical testing.Our findings reveal that the combination of Na OH/Na2SO3 is better than Na OH for the delignification of wood as it gives delignified wood（DW）two times higher OH functionalities.A high number of pores were generated during delignification and were preserved during densification,which played an essential role in the flexibility of wood.The pores expand and shrink to accommodate any external stress making wood flexible.The crystalline-assisted vacuum densification helps to prepare porous and flexible wood from both samples,i.e.,NW-RC and NW-LC.（II）The natural wood has been meticulously modified via physical/chemical approaches,making it ideal for next-generation structural and functional applications.We have developed flexible wood scaffolds from radial-cut through delignification and alkaline crystallization-assisted vacuum densification.The modification increased micro-mesopores for higher surface area and decreased macropores to improve scaffold density.The scaffolds exhibit ultra-high flexibility along with excellent mechanical strength.The chemical treatment was also beneficial in enriching the scaffold’s hydroxyl functionality.Furthermore,the functionalization of wood samples was done by chemically cross-linking carbon nanotubes（CNTs）.The as-prepared,highly conductive electrodes were characterized through SEM,FTIR,XRD analysis,and electrochemical analysis of as-prepared electrodes.Our findings reveal that the as-designed CNT@FW electrode exhibited excellent electrochemical energy storage in terms of high energy/power densities and rate performance and low electrode and electrolyte resistances,outperforming representative carbonized wood electrodes in the literature.A maximum energy density of 390 m Wh cm-3 was achieved for CNT@FW based on all-solid-state asymmetric supercapacitors.New hierarchical electrode composites via in-situ deposition of conductive polymers have successfully demonstrated with electropolymerization of 3,4-ethylene dioxythiophene,where surprisingly specific capacitance～320 m F cm-2has been obtained at 1m A cm-2 current density.Here,it is believed the as-developed porous and conductive FW scaffolds have opened a new venue for researchers to explore their applications for biomedical,energy storage,sensors,smart textile,filtration,and related devices.（III）The exploration of thick wood electrodes toward high-performance grid-scale,portable electronics,artificial intelligence,and electric vehicles is advancing due to its low tortuosity,ease of functionalizability,and mechanical robustness accompanied by its abundance,low cost,and renewability.Thick electrode designs require a highly conductive layer for fast electron transport,a special distribution of electrode material for high specific capacitance,and low tortuous pores for fast ion transport.We present a surprisingly low electrochemical impedance for an ultrathick electrode with a thickness of 2 mm and a mass loading of 20 mg cm-2.In order to prepare the electrode,first a conductive network of CNTs was generated on the internal and exterior surface of the DW cell walls,and then polypyrrole（PPy）structures were grown in the lumen of the DW cells.The electrode in its unmodified state presented a high areal capacitance of 1.45 F cm-2(16 F cm-3),in addition to an exceptionally high energy density of 4.4 KWh L-1(30.5 Wh kg-1),and a remarkable high power density of605 W L-1(4.188 W kg-1).Additionally,the electrode provided an exceptionally low electrochemical impedance,with a resistance of 0.61?for the electrode and 1.57?for the electrolyte.The electrodes have a low resistance and a high energy and power density,both of which are even higher than those of thin carbonized wood electrodes and other electrodes composed of high energy and power density materials that are considered to be state-of-the-art.This work provides handy design strategies for 3D thick electrode preparation from eco-friendly and porous natural wood.（IV）Bio-organic molecules with quinone activity are intriguing alternatives for reusable energy storage devices due to their diverse availability and chemical variability.The energy storage and long-term stability of redox-active materials may be greatly enhanced by using hybridized bio-materials with conducting polymers and carbon-based active materials,which promote the interaction between these substances.Lignocellulose is the most abundant bio-material on earth,and interestingly it has got the redox capability（quinone/hydroquinone）.However,it is used either in the form of lignosulfonate or kraft lignin which causes several battery chemistries issues like material dissolutions in electrolytes resulting in short battery life.Here,the raw wood was used as the source of redox capacitance resulting from oxygen-containing surface functional groups of wood.The electrodes were prepared by conjugating CNTs on raw wood named CNTs@NW and CNTs@Tr W.Cyclic voltammetry curves for both electrodes showed that both faradaic and non-faradaic interactions were taking place on the wood and CNTs interfaces,respectively.Amazingly,at a scan rate of 10 m V s-1,the CNTs@Tr W electrode showed an extremely high areal capacitance of 165 m F cm-2.The CNTs@Tr W electrode performed admirably in cycling tests,as predicted.In particular,after5,000 charging-discharging cycles,with 100%Coulombic efficiency,there was still over 96%capacitive retention.This cyclic stability is contrary to the very unstable cyclic performance of lignosulfonate composites,where the lignin material dissolves into the electrolyte and results in poor cyclic performance. |
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