Application of single-chamber membrane-free microbial fuel cells in flexible wearable devices

【introduction】

Fiber-based flexible wearable electronics enable real-time health detection of the human body. This not only requires the high integration of electronic components such as power supplies and sensors in a small space, but also requires high output power of the device under severe mechanical deformation conditions, and always maintains good contact between the device and the skin as well as high Human comfort. Microbial fuel cell (MFC), as a self-assembled, self-repairing, self-sustaining, and environmentally friendly bio-power source, can not only fully utilize the organic matter in body fluids such as human sweat, saliva, and blood, but also convert the rich chemical energy into a source. Constant electrical energy, also has a very high biocompatibility and electrochemical stability. At present, flexible wearable electronic devices using microbial fuel cells as power sources are mainly faced with major challenges such as low output current density and low output power.

[Introduction]

Recently, the assistant professor Seokheun Choi (Corresponding author) of the State University of New York at Binghamton designed and prepared a single-chamber, membrane-free microbial fuel cell integrated on a single fiber fabric. The researchers used commercially available single-layer fiber fabrics (92% polyester fiber: 8% spandex fiber) as the substrate. The process steps of molding, screen printing, and carbon-spraying were respectively applied to the positive and negative sides of the fiber fabric. The processing is performed, and the positive electrode region and the negative electrode region are defined by hydrophilization or hydrophobization treatment on different regions of the fiber fabric surface. The microbial fuel cell is modified with a poly(3,4-ethylenedioxythiophene):polysulfonated styrene (PEDOT:PSS) slurry in which ethylene glycol (EG) is dissolved, and 3-(2,3- Glycidoxypropyl)propyltrimethoxysilane (3G) to enhance its hydrophilicity, and finally inoculated a certain concentration of Pseudomonas aeruginosa (PAO1) as a microbial catalyst; PEDOT:PSS slurry containing Ag2O for the positive electrode Preparation, Ag2O is reduced to obtain Ag2O/Ag composite positive electrode, wherein Ag is oxidized by the introduced air to obtain Ag2O again. The microbial fuel cell has an internal resistance of approximately 10 kΩ. When the external circuit is loaded with a resistance of 10 kΩ, it can achieve a current density of 52 μA/cm2 and a maximum power density of 6.4 μW/cm2. Its electrochemical performance is close to that of current flexible paper. The level of microbial fuel cells is far beyond the microbial fuel cells based on flexible fabrics. Under the dynamic mechanical test conditions of repeated stretching and torsion, although the conductive carbon layer on the surface of the fiber fabric partially breaks and causes the internal resistance of the battery to rise, the electrode active material can firmly adhere to the surface of the fiber fabric, thereby ensuring mechanical deformation. There is still a relatively stable output current and power density. The research results are published in Adv. Energy Mater. under the title "Flexible and Stretchable Biobatteries: Mo nolithic Integration of Membrane-Free Microbial Fuel Cells in a Single Textile Layer".

[Graphic introduction]

Figure 1. Structure of a microbial fuel cell

(a) A schematic structural view of a 5 x 7 microbial fuel cell array was simultaneously fabricated on a 19 x 19 cm2 single layer fiber fabric.

(b) The positive and negative structures of microbial fuel cells and their working principles.

(c) Schematic diagram of the positive and negative electrodes and their assembly on the same fiber fabric.

(d) Microbial fuel cells under tension and torsion conditions.

Figure 2. Batch manufacturing of microbial fuel cell arrays on a single layer of fabric

(1) First, the filter paper is processed by laser to obtain a template with a specific geometry, and then the template is fixed to the surface of the fiber fabric by means of glue.

(2) Applying a slurry having a specific composition to the surface of the fiber fabric by screen printing.

(3) Carbon blasting on the stencil forms a conductive carbon layer connecting the microbial fuel cells and removing the template.

(4) A hydrophobic wax layer was sprayed on the negative electrode to define a negative electrode chamber boundary, and a 3G slurry was added inside the negative electrode chamber to enhance its hydrophilicity.

(5) Finally, an array of a certain number of microbial fuel cells is obtained by laser cutting.

Figure 3. Characterization of positive and negative polarography

(a) SEM image of the negative electrode treated with 3G/EG/PEDOT:PSS slurry.

(b) SEM image of the negative electrode treated with PEDOT:PSS/Ag2O slurry.