Research On Cotton Thread-based Microfluidic Microbial Fuel Cell For Wearable Applications

The emergence of wearable portable electronic devices has provided convenience to human life,at the same time,the wearable flexible battery that powers it has gradually become a research hotspot.Microfluidic Microbial Fuel Cell(MMFC)is a micro-battery device that combines microfluidic technology with a scaled down Microbial Fuel Cell(MFC).Its principle is to use microorganisms as a A catalyst that degrades organic matter and generates electricity at the same time.Compared with conventional MFC,MMFC has unique advantages such as small size,fast response speed,and less sample consumption.The good flexibility and wicking ability of cotton thread make it an excellent liquid flow channel for MMFC.In the previous study of wire-based MMFC,it was found that the effective fusion of wire-based materials and traditional fuel cell structure is the key to constructing microfluidic MFC.Based on the above background,this paper prepared a wearable flexible cotton thread-based Microfluidic Microbial fuel cell(C-MMFC).The fusion of wire-based materials and electrodes,the structural design of the ion exchange zone and the structural design of the battery stack and the feasibility of wearable applications are explored in three aspects.The specific research results are as follows:(1)In order to solve the problem of the small effective contact area between the wire-based MMFC electrode and the wire-based material,this paper proposes a C-MMFC structure that combines cotton thread and carbon cloth electrode by sewing.The microstructure and related properties of the four thread-based materials were further compared.The rough surface and disordered microstructure of the cotton thread can be more conducive to the adhesion of bacteria.Therefore,it is determined that the cotton thread is the final liquid flow channel.Finally,the cotton thread was optimized in terms of the diameter of the cotton thread channel,the flow rate and the Plasma treatment time.It was determined that a cotton thread with a diameter of 1 mm can obtain the best and most stable battery performance when the Plasma treatment time is 80 seconds for the anode cotton thread and 60 seconds for the cathode cotton thread.(2)In order to solve the problem of liquid mixing when two cotton threads are in contact due to the wicking ability of cotton fibers.In this paper,combining the method of fiber winding of the cotton thread,the two cotton threads are spirally wound to form the exchange zone.Following the traditional MFC ion exchange membrane design,the Parafilm^?membrane is wrapped around the catholyte flowing cotton thread in the exchange zone as the ion exchange membrane.Compared with the membrane-free structure and the device containing the paper-based membrane and Nafion membrane,the battery constructed with the fully stretched Parafilm^?membrane has the highest and most stable output performance,and the maximum current density that can be achieved is 435m A/m².Through the analysis of the morphology of Parafilm^?membranes with different stretching degrees,it is found that the fully stretched Parafilm^?membranes have pores,which can promote the ion balance between the anode and the cathode.After further discussing the influence of the length and thickness of the Parafilm^?membrane on the battery performance,a Parafilm^?membrane with a length of 2 cm was finally selected as the ion exchange membrane to be wrapped outside the cathode cotton thread,and then spirally wound with the anode cotton thread to form a 1 cm ion exchange zone,forming the final structure of C-MMFC.(3)On the basis of determining the final structure,the output performance of the battery was evaluated.The maximum power density of C-MMFC can reach 92.4 m W/m²under the drive of bacterial liquid,and it can maintain high battery performance and stable battery life for a long time.The device can also operate stably when sweat is used as fuel.The open circuit voltage of a single battery can reach 0.64 V,and the battery has strong mechanical stability and can maintain good output performance under any folding conditions.Utilizing the flexibility of cotton thread and its ability to be combined with fabrics,six batteries are connected in series to form a stack and integrated into the fabric to construct a wearable flexible C-MMFC,which can use human sweat to light up the LED display,which proves the device proposed in this article can be used in real life as a wearable flexible battery.