Construction And Optimization Of High Performance Cotton Yarn-based Microfluidic Microbial Fuel Cells

Common wearable energy collection and storage devices have the problem of limited energy storage and frequent charging.As a wearable device,it is difficult to achieve long-term sustainable energy supply.To address this challenge,a reliable method is to extract energy from biological fluids such as sweat.Microfluidic microbial fuel cell（MMFC）is a new type of green energy source that uses electroactive microorganisms as catalysts to convert stored chemical energy in the substrate into electricity,and it has the advantages of high specific surface area,low energy consumption,and fast response time.Additionally,it can be easily scaled or stacked.However,previously reported MMFCs usually require an external pump to maintain the fuel supply to the battery,or the fuel needs to be manually added,which limits its development towards miniaturization and portability.Cotton yarn is a widely used natural fiber fabric with low cost,high flexibility,and easy to weave or sew.Its capillary action allows it to serve as a microchannel for liquid introduction and flow,replacing external pumps to supply fuel to the device.Based on the background mentioned above,this paper takes Shewanella putrefaciens CN32 as the catalyst to carry out research from three aspects:the structural design and optimization of yarn-based MMFC,the effect of yarn-based microfluidics on battery performance,wearable applications,and structural improvement to reduce internal resistance.The specific research contents and conclusions are as follows:（1）The conductive material modified yarn is used as a fluid collection and liquid flow channel,and the electrolyte is transported by the capillary action of the yarn.By using Prussian blue（PB）as a solid cathode,a segmented yarn-based microfluidic microbial fuel cell（S-MMFC）with a membrane-free structure is successfully designed.Select the best conductive materials and yarns by comparing the core absorption rate and device output performance.Finally,the ratio of anode and cathode electrodes,yarn thickness,electrode length and salt bridge length are optimized.The experimental results show that when the diameter of cotton thread is 1.5 mm,the length of anode and cathode electrode is 2 cm（1:1）and the length of salt bridge is 1 cm,The device can obtain the best output performance in anaerobic environment.（2）First,the parafilm^?sealing film for anode encapsulation allows stable and efficient operation in air.Secondly,the influence of yarn-based microfluidic behavior on the electrical performance of S-MMFC was investigated,including different liquid supply modes,different humidity environments and different electrolyte flow directions.It is found that continuous liquid supply by cotton capillary action is conducive to the formation of electroactive biofilm for S-MMFC anode,which has higher output performance and can run stably for a long time.Meanwhile,the flow direction and velocity of the electrolyte were investigated and it was concluded that the anode in this structure needed sufficient and dynamic flowing electrolyte to maintain the stable operation of S-MMFC.The optimized S-MMFC has a maximum power density of 250μW cm^-3and a current density of 786.4μA cm^-3,and can run stably for 100 h under continuous liquid supply,which is superior to the reported yarn-based MFCs.Then,using the advantages of cotton thread,which is easy to weave and modify,multiple batteries are prepared on one cotton thread,and the three batteries are woven in series into a bracelet,which can continue to supply energy for electronic watches for 18 h.Finally,the device is preserved by freeze-drying technology,which can be activated by sweat directly,and the electrode fixed by BSA can be used repeatedly,which further extends the service life of the device.（3）To further reduce the internal resistance of yarn-based MMFC,a coaxial structure MMFC（Coaxial Microfluidic Microbial Fuel Cell,C-MMFC）was constructed.Anode cotton thread is used as the core,and the PB cathode is wrapped in the outermost part as the cortex.By optimizing the membrane material,electrode length,and membrane thickness.The internal resistance of the device is further reduced,and the distance between the anode and cathode is greatly shortened.By comparing the electrochemical impedance spectra of the two structures,it can be seen that the solution resistance and charge transfer resistance of C-MMFC are smaller than S-MMFC,and the power density increases to 296.7μW cm^-3.As a high-power,long-life,simple and low-cost yarn-based MMFC,it promotes the further development of sweat excited battery.