Enhancement Of Wood Fiber Triboelectric Positive Performance For Preparing Paper-based Triboelectric Nanogenerators

At present,the global carbon emissions still result from the utilization of fossil fuel and petroleum,which is harmful for achieving the goal of“carbon neutrality and carbon emissions peak”.Developing the novel technologies and environmentally friendly materials for conversing efficiently clean energy has become an important strategy to reduce the carbon emissions.Triboelectric nanogenerators（TENGs）are a highly efficient and environmentally friendly energy conversion technology based on triboelectric and electrostatic induction effects;they can harvest mechanical energy and convert it into electricity.Cellulose paper is composed of cellulose fibers with disordered or ordered arrangement by hydrogen bonding force.Meanwhile,cellulose paper is also an excellent electron donating material,making it widely apply on the triboelectric positive material of TENGs.Unfortunately,most cellulose paper based TENGs（CPTENGs）has exhibited low output performance in low working frequency.The output performance of CPTENGs would be reduced in high ambient humidity;and CPTENGs have also weak acid and alkaline resistance,leading to a limitation for their application and development.Therefore,in this study,the dielectric property and surface potential of cellulose paper were enhanced through the modification of cellulose fibers,thereby improving the triboelectric positive performance of cellulose paper,developing CPTENGs with outstanding output performance.The impact factors and mechanisms of the output performance of CPTENGs were explored,and the applications of CPTENGs in pressure sensing,human physiological signal detection and self-charging power system were also studied,which promoting the development of sustainable and green energy.The main research contents are as follows:（1）The triboelectric output performance of CPTENGs was improved by high-speed shearing treatment and silver nanoparticles modification in situ synthesis.The effect and mechanisms of high-speed shear treatment and silver nanoparticles（Ag NPs）on the triboelectric output performance of CPTENGs were investigated.After Ag NPs modification,the dielectric constant of Ag NPs modified cellulose paper（Ag@CP）increased from 3.95to 4.63 at frequency of 10,000 Hz;and high-speed shearing treatment made it further increase to 4.81,increased the effective friction area,and reduced the thickness of cellulose paper,thus improving the triboelectric output performance of CPTENGs.Additionally,the Ag NPs content of Ag@CP and the open-circuit voltage(V_OC)and short-circuit current(I_SC)of CPTENGs could be increase with the dosage of Ag NO₃ in situ synthesis process and the degree of high-speed shearing treatment.When the external forces and operating frequency were 40 N and 3.5 Hz,respectively,the proposed modification has given a V_OC of 141.3 V,an I_SC of 5.8μA,a Q_SCof 30.1μC·m^-2and a power density of 192.4 m W·m^-2for CPTENGs;and the CPTENGs also exhibited outstanding duration and stability because the output voltage does not show obvious decline within 20,000 contact separation cycles.The developed CPTENGs could also apply on the field of pressure sensor,which not only detected the changes of external pressure,but also reflected the human motion information.（2）The amino groups were introduced into cellulose fibers,and then combined with PEO to prepare the PEO/cellulose composite paper（PEO/CCP）with different amino groups content.The mechanism of amino group and PEO modification for enhancing triboelectric output performance of CPTENGs was studied.The influence of the amino groups content on the triboelectric output performance of PEO/CCP based TENGs was also researched.Furthermore,the application of the PEO/CCP based TENGs on detecting human physiological signals was also explored.The results suggested that the amino groups improved remarkably the surface potential of cellulose paper from-0.66 V to 1.05 V,thus increasing its triboelectric positive performance;and the introduction of PEO could further enhance triboelectric positive performance of cellulose paper.The voltage,current and power density values of PEO/CCP based TENGs exhibited positive linear relationship with amino groups content of PEO/CCP.The V_OC,I_SC,Q_SC and power density of PEO/CCP based TENGs could reach up to 222.1 V,4.3μA,39.7μC·m^-2,and 217.3 m W·m^-2,respectively.Furthermore,the human-health detection device based on this TENGs could monitor the physiological signals such as eye muscles,respiration,heart beat and wrist pulse.（3）Octadecylamine（ODA）was introduced onto cellulose fibers to prepare hydrophobic cellulose paper（HCP）with abundant hydroxyl groups by means of Schiff base reaction between polydopamine（PDA）and ODA.The mechanism of PDA and ODA improving the triboelectric output performance of CPTENGs was explored;and the effects of ambient humidity and acid and alkali treatment on the triboelectric output performance of CPTENGs were also studied.Additionally,the application prospect of CPTENGs in harvesting energy and detecting the information from human movement was also explored.After the modification of PDA and ODA,the surface potential of cellulose paper was increased from-0.47V to 0.04 V,promoting the electron donating capacity of cellulose paper,therefore enhancing the triboelectric output performance of CPTENGs.In addition,the HCP based TENGs（HCPTENG）could yield a V_OC of 237.8V,an I_SC of 4.2μA,a Q_SC of 42.7μC·m^-2;and the power density of HCPTENG could reach up to 208.1 m W·m^-2.Furthermore,the V_OC and I_SCvalues of HCPTENG could reach up to 181.8 V and 3.0μA,respectively.More importantly,the HCPTENG showed a great output performance stability in a wide range of the p H environment（p H=1～13）.The HCPTENG could also harvest energy from human movement and detect the foot motion like walking and running and hand flapping.（4）The cellulose paper（ODCP）with hydrophobicity and acid-and alkali-resistance was prepared via the Schiff base reaction between dialdehyde cellulose fibers（DCF）and ODA;and the double-layer papers（ODCP/PCP）composed of ODCP and polypyrrole conductive composite paper（PCP）was fabricated by multi-layer forming for papermaking,thus obtaining an all CPTENGs.The influences and mechanisms of the amount of ODA on the triboelectric output performance of ODCP based TENGs were explored.The effects of ambient humidity,acid and alkali on the triboelectric output performance of CPTENGs were also studied.The results indicated that cellulose paper could be introduced into C=N,making its surface potential increase from-0.47 V to 0.15 V,therefore improving the triboelectric output performance of CPTENGs.The results also showed that the V_OC,I_SC and Q_SC of the ODCP based TENGs increased first and then remained unchanged with the increase of the dosage of ODA.In this instance,the ODCP based TENGs could yield an V_OC of 227.1 V,a I_SC of6.9μA,a Q_SC of 41.9μC·m^-2,and a power density of 520 m W·m^-2 at a load resistance of 30 MΩwhen the weight ratio of ODA to DCF was 1:1.In addition,the ODCP based TENGs still exhibited the outstanding triboelectric output performance at a high relative humidity of 90%,whose V_OC and I_SCvalues could attain to 174.2 V and 5.0μA,respectively;and the electricity output maintained unchanged in a wide range of the p H environment even if the conductivity of PCP was reduce after immersing in Na OH solution.It was also demonstrated that the power supplied by the ODCP based TENGs was capable to light up 100 green LEDs connected in series and the patterned“FAFU”letter-shaped LEDs.（5）An all paper-based self-charging power system（PSCPS）with portability and environmental friendliness was constructed by using the ODCP based TENGs as the energy harvester and paper-based zinc supercapacitor（P-ZISC）with a great areal capacitance as the energy storage device.The P-ZISC with sandwich structure was prepared by multi-layer forming for papermaking.It was reported that the areal specific capacitance of the P-ZISC was163.0 m F·cm^-2,and its energy density and power density could be up to 32.6 m Wh·cm^-2and 600 m W·cm^-2 under a current density of 1 m A·cm^-2.It also indicated that this PSCPS could charge the P-ZISC to 2 V within 3.3 h.The results also indicated that this PSCPS was able to drive the electronic watch,temperature/humidity indicator and red LED,and could sustainably drive an electronic watch for long-term working.