| Supercapacitor is an important energy storage device with high power density,long cycle life and rapid charge/discharge.However,traditional carbon materials such as graphene and carbon nanotubes used as electrodes for supercapacitors have problems such as complex preparation process,relatively high cost and low energy density,which limit the further commercial application of carbon-based electrode.To overcome these challenges,the development of low-cost carbon source to prepare high energy density carbon electrode for supercapacitor has become an important topic in this field.As a renewable biomass material with hierarchical porous structure,basswood（Tilia americana）is a typical broad-leaved wood with straight texture,uniform pore structure,good mechanical strength and easy processing.It is an excellent carbon source precursor for the preparation of low-cost electrode for supercapacitor.The transport kinetics of the electrolyte with wood-derived carbon electrode has an important effect on its capacitance performance.However,the relationship between the pore structure,mass transfer kinetics and electrochemical performance is still unclear,which seriously hinders the research and development of wood-derived carbon electrode energy storage devices.Hence,the basswood as the raw material,through exploring the relationship between the pore structure of wood-derived carbon electrode ion transport kinetics of electrolyte and capacitance performance,reveals the influence mechanism of the pore structure wood-derived carbon electrode on the performance of supercapacitor.（1）The wood cross and radical sections were selected to investigate the influence of pore structure on electrochemical performance.Compared with the radical section,the cross section of wood-derived carbon electrode showed large specific surface area of 542 m2 g-1 and pore volume of 0.389 cm3 g-1.It is due to the natural vertical open pore and hierarchical porous structure in the cross section,which provides more electrochemically active sites.Furthermore,the cross-sectional wood-derived carbon electrode with low tortuosity provides an accelerated channel for electrolyte transport,which is crucial to electrochemical rate performance.In addition,the influence of different scanning rates on the capacitance contribution was investigated.The cross-section wood-derived carbon electrode exhibit high capacitance contribution at high scanning rate with the capacitive behavior contribution of 92.18%.It was related to the unique hierarchical porous structure of cross-section wood-derived carbon electrode.（2）The effect of cellulase dosage and treatment time on the pore structure of wood-derived carbon electrodes were studied.The results showed that the amount of cellulase～100 mg and treatment time～48 h,the wood-derived carbon electrode（WC-E-100-48）exhibited the highest specific surface area of 1412 m2 g-1 and pore volume of 0.689 cm3 g-1,which can accommodate large amount of charge storage space.The pore size mainly concentrates between 10-20 nm,which is attributed to a large number of cellulase quickly hydrolyze the cellulose on the wood surface.It was led to much cellulose hydrolysis,leaving different degrees of shallow pores and thus forming rich pore structure.In addition,after enzymatic hydrolysis of wood-derived carbon electrode showed obviously improvement for the electrochemical performance.Furthermore,the assembled symmetrical supercapacitor（WC-E-100-48//WC-E-100-48,SSC）could maintain the capacitance retention of 86.58%at high current density of 20 m A cm-2for 15000 cycles with the high areal/volumetric energy density of 0.21 m Wh cm-2/0.99 m Wh cm-3.（3）The effects of different content of silver nanoparticles on the electrochemical performance of wood-derived carbon electrodes were investigated by in-situ impregnation.The results showed that the excellent electrical conductivity of WC@Ag-20 was 12.6 S cm-1,which was 9.6 times higher than the WC of 1.3 S cm-1.In addition,after loading silver nanoparticles,the electrical and electrochemical performance have been significantly improved.The WC@Ag-20 shows more excellent rate performance and cycling performance,which is related to the well electrical conductivity and abundant defect structure.A symmetrical supercapacitor（WC@Ag-20//WC@Ag-20,SSC）can provide specific energy density of 13.54 Wh kg-1 and area energy density of 0.345 m Wh cm-2,corresponding power density of 19.59 W kg-1 and 500 m W cm-2 at the current density of 1.0 m A cm-2.At the same time,the SSC device can still maintain the capacity retention rate of 80.75%at the current density of 20 m A cm-2 for 10000 cycles,indicating that it has excellent cycle stability.In addition,the density functional theory calculation also show that the electron distribution of Ag atom is affected by the substrate of wood-derived carbon electrode.There is a trend of D-band transfer to lower energy,which makes WC@Ag as a whole wood-derived carbon electrode have better charge storage performance and superior electron conductivity.（4）A highly doped phosphorus P（9.24 at%）hierarchically porous wood-derived carbon electrode was first realized by treating wood with phytic acid as a carbon source.Six negatively charged phosphate groups of phytic acid provide rich cross-linking sites to allow high level doping of P on carbon,enabling substantially superior capacitance.A assemble symmetric supercapacitor（WC-P-9.24//WC-P-9.24,SSC）showed an area capacitance of 4.7 F cm-2 and specific capacitance of 206.5 F g-1 at the current density of 1.0 m A cm-2,respectively.Meanwhile,the cycle performance of SSC device can reach 104%after 12000 long-term cycles at the current density of 20 m A cm-2.This long-term stability is not only related to the wetting ability of electrolyte and surface reaction,but also math up with the slow wetting time caused by the electrode thickness.Moreover,the LEDs（1.8V,1.0W）can be illuminated by two SSCs in series for 20 minutes,demonstrating the potential for practical applications.The SSC device exhibit high energy density of 0.94 m Wh cm-2(41.2Wh kg-1)at power density of 14400 m W cm-2(437.4 W kg-1).In addition,according to the theoretical calculation,the electron distribution of Ag atom is affected by the substrate of wood-derived carbon electrode.There is a trend of D-band transfer to lower energy,which makes WC@Ag as a whole electrode has better charge storage performance and superior electron conductivity.（5）The assembled asymmetric supercapacitor（WC@Ag-20//WC-P-9.24,ASC）has an area capacitance of 1.86 F cm-2 and specific capacitance of 265.3 F g-1 at the current density of 1.0 m A cm-2,respectively.The ASC can achieve high energy density of 0.582 m Wh cm-2(82.9 Wh kg-1)at the power density of 37419 m W cm-2(5310 W kg-1).It was also indicated that the construction of asymmetric supercapacitors significantly improves the energy density of wood-derived carbon electrode supercapacitors.In addition,the multi-angle comparison with the reported carbon-based supercapacitors has obvious advantages,which were expected to be extended to other related application fields.In summary,different modifiers such as cellulase,silver acetate and phytic acid were selected to regulate the pore structure of wood-derived hierarchical porous carbon electrode.From the perspective of regulating the specific surface area,pore size distribution,electrical conductivity and pseudo capacitance of carbon electrode,the rapid transport of electrolyte ions through wood-derived carbon electrode was promoted to achieve the regulation of the electrochemical performance.The results show that the excellent pore structure of wood-derived carbon electrode can promote rapid electrolyte transport,and the abundant defect structure can accommodate a large number electrolyte ions,which can guarantee the outstanding electrochemical performance.In addition,maintaining high electrical conductivity of wood-derived carbon electrode is an important means to solve high interface impedance of wood-derived carbon thick electrode.Furthermore,keeping the well wettability of the electrode and electrolyte is also an effective strategy to achieve attractive electrochemical performance.Therefore,the application range of the wood-derived carbon electrode energy storage device is also expanded by realizing high energy density.This method can provide reference and analysis for the development of wood-derived carbon electrode energy storage device and functional applications... |
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