Preparation Of Nanofiber-based Flexible Enzymatic Electrode And Its Performance In Enzymatic Biofuel Cells

With the development of the artificial intelligence and Internet of things era,flexible electronics have attracted widespread attention and gradually become new demand of various information receiving,processing,transmission and display devices due to its softness and comfort.In order to provide a matching energy supply for these flexible electronics,the energy conversion and storage devices with high performance,flexible and scalable need to be developed.Enzymatic biofuel cell（EBFC）with high biofuel conversion efficiency,biocompatibility and miniaturization has been regarded as a reliable flexible wearable energy system.However,the current EBFC generally has the problems of poor stretchability,low output performance and instability.Therefore,the construction of flexible stretchable EBFC with high output and excellent stability is key to promote the further development of flexible electronics.The novel electron transfer strategy based on nanomaterials could effectively shorten the electron transfer path and realize the high-speed electron transfer between enzyme and electrode.Metal-organic framework（MOF）could act as a novel platform for biomacromolecule immobilization to achieve long-term protection of enzyme effectively,and improve the stability of immobilized enzyme.Therefore,bacterial cellulose（BC）and electrospun nanofibers with mechanical flexibility were selected as flexible substrates to constructing EBFC system in this thesis,and the application of EBFC-based self-powered biosensors were further explored.Mainly carried out the following aspects of work:（1）A flexible Amidoxime-modified BC（AOBC）-laccase（LAC）/carboxylated multi-walled carbon nanotubes（c-MWCNTs）electrode was prepared by by vacuum filtration technique using AOBC nanofibers as substrate.An EBFC based on intramolecular electron transfer was constructed by using BPA as fuel.The results showed that the maximum working voltage and maximum power density(P_max)of EBFC were 0.143 V and 1896.8 m W·m^-3,respectively,and the BPA degradation efficiency of EBFC was 88.17%.Furthermore,the output voltage of EBFC system could also reached 0.111 V and 0.098 V while choosing hydroquinone and catechol as fuels,respectively.（2）In order to improve the stability of EBFC system,MOF was used as the platform for enzyme immobilization to endow the excellent stability for immobilized enzyme.A highly flexible BC/c-MWCNTs/zeolitic imidazolate framework-8（ZIF-8）/LAC enzymatic electrode was obtained by vacuum extraction the mixture of ZIF-8/LAC,BC nanofibers and c-MWCNTs,then the self-powered BPA biosensor was established based on intramolecular electron transfer.The working voltage of the biosensor was 0.197 V,and the degradation efficiency of BPA reached 98%.Moreover,the output voltage and power density of the biosensor showed excellent stability after repeated operation for 5 times.In addition,the maximum power density(P_max)of the biosensor exhibited an excellent linear relationship with BPA in the concentration range from 0.01-0.4 m M,and the detection limit was 1.95×10^-3m M.（3）In order to improve the structure stability of enzymatic electrode,a strategy of simultaneous in situ growth of MOF and enzyme encapsulation was proposed.The electrospun cellulose acetate（CA）nanofibers were selected as the skeleton material,and the CA/ZIF-8@glucose oxidase（GOx）/MWCNTs/Au and the CA/ZIF-8@LAC/MWCNTs/Au bioelectrode were obtained by introducing gold nanoparticles（Au NPs）.The flexible enzymatic electrodes were used to establish glucose/O₂self-powered biosensor,and the biosensor showed excellent detection performance in the range of glucose concentration from1 m M to 10 m M with the detection limit of 5.347μM.In addition,the designed self-powered glucose biosensor maintained good stability during the continuous work of up to 15 h,which proposed a meaningful strategy for the future population research on the correlation between glucose concentration in human sweat and physiological state.（4）In order to improve the stretchability of the enzymatic electrode,the electrospun polyurethane（PU）nanofibers were selected as the skeleton material and the stretchable PU/ZIF-8@LAC/CNTs flexible enzymatic electrode was prepared by using in-situ growth and enzyme encapsulation strategies.The good elasticity and electrochemical stability of the stretchable enzymatic electrodes were confirmed after repeated stretching cycles.The established EBFC based on intramolecular electron transfer showed an open circuit voltage of87.33 m V and maximum power density of 1.33 W·m^-3.In addition,the EBFC showed stable output performance while the PU/ZIF-8@LAC/CNTs stretchable enzymatic electrode after repeated stretching and relaxing,stretching and holding,twisting and relaxing cycles.（5）In order to achieve the stretchable EBFC system,hydrogel electrolyte was introduced to replace the liquid electrolytic cell.The PU/regenerated cellulose（RC）/ZIF-8@GOx/CNTs bioanode and PU/RC/ZIF-8@LAC/CNTs biocathode were attached to both sides of glucose-polyacrylamide（G-PAM）hydrogel.The results showed that a piece of EBFC（5×1 cm）could generated an open circuit voltage of 0.35 V and reached a maximum power density of 1.09 W·m^-3at 0.25 V.The voltage could still remained above 0.325 V after 7h of continuous work.Moreover,the EBFC maintained relatively stable output performance after repeated stretching,bending and twisting cycles.