Biofuel cell and printed circuit board electronic device

Abstract

The present invention relates to an electronic device comprising a biofuel cell and a printed circuit board (PCB) having an air breathing opening, the biofuel cell having an outer layer air breathing opening (through a GDL), the electronic device being characterized in that an air breathing opening formed in the PCB faces the outer layer air breathing opening, and the biofuel cell is attached to the PCB.

Description

[Technical field]

[0001] The present invention relates to an electronic device comprising a biofuel cell and a printed circuit board (PCB) having an air breathing opening, the biofuel cell having an outer layer air breathing opening (through a GDL), the electronic device being characterized in that an air breathing opening formed in the PCB faces the outer layer air breathing opening, and the biofuel cell is attached to the PCB.

[0002] In the following description, references in square brackets ([]) refer to the list of references at the end of the text. [Background technology]

[0003] Biological fuel cells (or biofuel cells) offer an attractive means to provide environmentally friendly and sustainable power to electronic devices, especially small portable devices for applications such as healthcare, environmental monitoring, and biodefense. Given that enzyme-based fuel cells can operate using substrates (i.e., glucose and oxygen) that are abundant in biological fluids and environmental effluents while often exhibiting superior power densities to microbial fuel cells, enzyme-based fuel cells offer an attractive proposition for augmenting or self-powering miniaturized wearable or implantable devices [1, 2, 3]. Furthermore, paper-based devices, with their low mass, small form factor, and flexibility that allows them to conform to a variety of different surfaces, are gaining popularity as a proposition for these types of applications.

[0004] It is well known that the current density at the cathode is one of the limiting factors in biofuel cell performance, where oxidoreductases are used in one of the two half-cell reactions, mainly due to the lower concentration of dissolved oxygen available at the electrode-solution interface. Therefore, it is often advantageous to increase the amount of oxygen at the cathode surface, for example by optimizing the morphology of the cathode to expose part of it to air [4, 5, 6]. Such devices are commonly referred to as having an "air-breathing" cathode.

[0005] While increasing the availability of oxygen is important for improving the overall performance of oxygen-based fuel cells, it is also important to maintain sufficient liquid, often needed to provide transport of ionic species in the form of an electrolyte. Simply providing an open aperture can lead to the fuel cell drying out, halting the ability for the reaction to continue.

[0006] Therefore, a membrane that supports oxygen flow while limiting liquid loss is typically implemented. Gas diffusion layers (GDLs), often made from carbon, are frequently used because they can double as current collectors. Carbon-based GDLs are porous materials composed of a dense array of carbon fibers, which can also be modified with other carbon micro / nanostructures. This structure provides inherent hydrophobicity, reducing liquid loss, but can also be further treated to increase hydrophobicity (e.g., inclusion of PTFE).

[0007] As mentioned above, one of the main factors that reduces the operational lifetime is the loss of liquid in a fuel cell. It is therefore interesting to increase the available volume of liquid in the device. One option is to increase the available volume of liquid in the device, especially for miniaturized disposable devices, when it is not possible to provide a constant / continuous supply of liquid (e.g., the body can provide a steady supply of biological fluids). The purpose of the appendage is to provide a fluid reservoir to provide a mechanism for maintaining interfacial wettability [7].

[0008] However, this liquid reservoir naturally occupies a volume. In many applications (wearable health / medical patches, packaging) it is interesting to provide a thin, flexible and conformable biofuel cell. In these examples, it is interesting to reduce the overall thickness of the device. Naturally, by reducing the thickness (z-axis) of the device, the volume must be spread over the plane of the device (x, y-axes). By occupying the entire extent of the xy-plane, the overall thickness can be minimized. As a result of this technique, this surface cannot be used to provide an aperture for providing an air-breathing cathode, especially if the optimal location of the aperture is in the center of the active area of ​​the device (center of the electrode).

[0009] Given a thin biofuel cell (so thin that the design, two flat surfaces surrounded by edges that have no functional surfaces, can be considered a 2D structure rather than a 3D structure), if one surface is occupied by the liquid reservoir, the other surface must be used for all other functions. Functionality would typically include providing electrical terminals (anode and cathode), as well as openings for air flow (for oxygen supply) to provide air breathing capability [8].

[0010] When considering attachment of such embodiments to electronic devices, conductive films (such as anisotropic conductive film (ACF) or isotropic conductive film (ICF)) are favored due to their low cost and thin thickness (typically less than 100 microns) and ability to be used in high volume manufacturing (such as roll-to-roll processing); or, alternatively, surface mount technology (SMT) ribbon cable connectors may be used for reusable applications.

[0011] Therefore, biofuel cells are usually fabricated as standalone devices or they are fabricated as part of a PCB. In fact, the combination of a standalone biofuel cell with a functional PCB presents several challenges, such as the supply of oxygen to the cathode of the fuel cell through the PCB. Furthermore, the combination of a biofuel cell with a functional PCB requires spatial constraints and specific arrangements, such as the location of contact pads, the location of inlets, the location of electronic components, sensors, etc.

[0012] For wearable applications or medical patches, the biofuel cell and the PCB are usually connected via electrical wires [9]. Nevertheless, the use of electrical wires is a real weakness for wearable biosensors, as they are easily damaged and not suitable for practical use or mass production. In either case, the biofuel cell can be brought into close proximity (less than 200 μm) with the electronic device. Advantageously, the electronic device can be directly connected to the two electrodes by attaching the PCB to one side of the biofuel cell (for example, using conductive tape). However, this technique results in a high probability of blocking the air-breathing cathode due to the size of the electronic device (usually larger than the contact pads used to connect the biofuel cell's electrochemicals and the electronic device), thus reducing the capacity of the biofuel cell.

[0013] Therefore, there remains a need to provide a new electronic device that combines a biofuel cell with a functional PCB that does not have the drawbacks of the prior art devices, i.e., allows sufficient air flow to reach the biocathode to obtain full performance of the biofuel cell. Summary of the Invention

[0014] The inventors have therefore solved the following technical problem by providing an electronic "sandwich" device comprising a biofuel cell (WO 2019 / 234573) [7] and a printed circuit board (PCB) having an air breathing opening formed opposite an outer layer air breathing opening of the biofuel cell attached to the PCB, with the aim of solving the following problems: - providing clear airflow to the air-breathing area of ​​the biofuel cell (when one surface is occupied by a liquid collection surface (a liquid reservoir or a wet surface such as human skin) and the other is blocked by the PCB on which the fuel cell is mounted) by using an air-breathing design that includes air-breathing openings on one (or more) sides that are covered by a gas diffusion layer (GDL); - Reducing the loss of liquid from the biofuel cell by using GDLs for hydrophobicity and liquid reservoirs to ensure there is enough liquid to maintain operation and may also limit evaporation; - reducing the thickness of the biofuel cell since the liquid collection surface involved occupies the greatest extent of one of the surfaces; Thus, the cathode current density is enhanced and hence the complete biofuel cell performance is improved by about 2.5 times.

[0015] In other words, the claimed electronic device maximizes the airflow available for the oxygen reduction reaction while providing the maximum volume of liquid to improve lifetime, and the minimum overall thickness of the solution. The glucose-oxygen biofuel cell consists of two carbon electrodes functionalized with different enzymes for the oxidation of glucose (e.g., glucose oxidase or glucose dehydrogenase) and the reduction of oxygen (e.g., laccase or bilirubin oxidase), encapsulated by a robust cellulose paper (water-, oil-, and heat-resistant) that contains different types of openings for electrical contacts, oxygen / air flow, and liquid inlets, and bonded to a liquid reservoir to provide increased lifetime by reducing the time it takes for liquid to be lost through the gas diffusion layer. Thus, the current technology of such biofuel cells is based on seven layers: outer layer, current collector (carbon felt, e.g. from Panasonic EYGS, sgl carbon, ProGraphiteShop), anode (nanotube felt with mediator and enzymes, e.g. from DSM, SHIN NIHON CHEMICAL, Sigma Aldrich), microfluidic layer (cellulose paper, e.g. from VWR European, Ahlstrom Munksjo), cathode (nanotube felt with promoter and enzymes, e.g. from Creative enzymes, Sigma Aldrich), current collector and gas diffusion layer (GDL, ideally with a microporous layer, MPL) (hydrophobic carbon felt, e.g. from sgl carbon, FuelCellStore) then the outer layer. A paper biofuel cell with a liquid reservoir is then attached to a PCB that contains an air breathing opening aligned with the (outer layer) air breathing opening to the biofuel cell, which then provides oxygen / air flow to the biocathode.

[0016] In either case (use as a liquid reservoir or as a medical patch) the orientation effect of this "sandwich" device is a key factor for its application and mass production success. For example, for wearable applications / medical patches: - the biofuel cell is brought into contact with the user's skin (or liquid reservoir) through its bioanode-side outer layer; - The bioanode (consisting of a current collector and a bioactive layer) is a current collector that absorbs current from the skin (e.g. It is fed by a liquid reservoir filled with biological fluids (from sweat containing glucose or lactate) or an activation solution (i.e. fuel, e.g. glucose). The outer layer on the bioanode side has one or more openings that allow the biological fluids to enter the interior of the biofuel cell (constant supply of liquid through the microfluidic layer); - on the other side of the biofuel cell, air (containing oxygen) is supplied to the biocathode (consisting of the GDL and the bioactive cathode layer), the outer layer of the biocathode side having one or more air breathing openings that allow air to enter the interior of the biofuel cell (through the GDL) and two openings for electrical contact with the PCB; - On the same side, a PCB with one or more air breathing openings facing one or more air breathing openings on the outer layer on the biocathode side, allowing sufficient airflow to reach the biocathode, is affixed to the biofuel cell and connected (e.g., using conductive tape) to the electrode connectors.

[0017] With regard to the association / combination of a biofuel cell powering an (ultra) low power functional portable electronic platform comprised of electronic components including, but not limited to, sensors, microprocessors, and / or communication modules, the use of at least one aperture through a PCB has not been used to improve energy production from a biofuel cell associated with a functional PCB.

[0018] Therefore, an object of the present invention is an electronic device comprising a biofuel cell and a printed circuit board (PCB) having an air breathing opening (or hole), wherein the biofuel cell has an outer layer air breathing opening, the electronic device is characterized in that an air breathing opening formed in the PCB faces the outer layer air breathing opening, and the biofuel cell is attached to the PCB.

[0019] According to one particular embodiment of the invention, the electronic device is a portable electronic device comprising: - the biofuel cell is composed of (i) a bioanode with an outer layer having one or more openings in contact with the user's skin or a liquid reservoir, and above that (ii) a biocathode with an outer layer having an outer air breathing opening, both electrodes separated by a microfluidic layer (which can be connected together via an external circuit); The PCB has an air breathing opening on the same side as the outer layer of the biocathode to which it is attached, facing the outer layer air breathing opening of the biocathode, and is connected to the bioelectrode.

[0020] According to one particular embodiment of the invention, the electronic device is in the form of a wearable medical patch comprising: - the biofuel cell is composed of (i) a bioanode having an outer layer with one or more openings in contact with the skin, and above that (ii) a biocathode with an outer layer having an outer air breathing opening, both electrodes separated by a microfluidic layer (which can be connected together via an external circuit); The PCB has an air breathing opening on the same side as the outer layer of the biocathode to which it is attached, facing the outer layer air breathing opening of the biocathode, and is connected to the bioelectrode.

[0021] According to one particular embodiment of the invention, the air breathing opening to the PCB is at least one hole.

[0022] According to one particular embodiment of the invention, the air breathing opening to the PCB has an area 1 / 10 to 2 times that of the outer layer air breathing opening of the biofuel cell.

[0023] According to one particular embodiment of the invention, the air breathing opening to the PCB comprises a material that is permeable to oxygen, for example in the form of a material selected from the group consisting of a grid and a membrane.

[0024] According to one particular embodiment of the invention, the air breathing openings to the PCB are in the form of a number of continuous holes fabricated within the PCB itself, which collectively form a grid that faces the GDL air breathing openings of the biofuel cell.

[0025] According to one particular embodiment of the invention, the biofuel cell is attached to the PCB by ACF (Anisotropic Conductive Film) tape, by Teflon tape (e.g., from Techniflon), or by any biodegradable or least environmentally impact means (e.g., biodegradable adhesives such as paper tape or water-soluble tape, e.g., from Adhesives Research), or by snap-fit ​​means.

[0026] According to one particular embodiment of the invention, the snap-fitting means comprises at least one spur formed either on a surface of the biofuel cell in contact with a surface of the PCB or on a surface of the PCB in contact with a surface of the biofuel cell, and at least one slot complementary to said at least one spur formed either on a surface of the PCB in contact with a surface of the biofuel cell or on a surface of the PCB in contact with a surface of the biofuel cell, respectively, such that said at least one spur fits into said at least one slot, thereby attaching the biofuel cell to the PCB. Preferably, said at least one spur and said at least one slot surround the (outer layer) air-breathing opening of the biofuel cell and the air-breathing opening formed in the PCB, while the air-breathing opening formed in the PCB faces the outer layer air-breathing opening of the biofuel cell.

[0027] According to one particular embodiment of the invention, the snap-fitting means comprises a number of spurs formed either on the surface of the biofuel cell in contact with a surface of the PCB or on the surface of the PCB in contact with a surface of the biofuel cell, and a number of slots complementary to the number of spurs formed either on the surface of the PCB in contact with a surface of the biofuel cell or on the surface of the biofuel cell in contact with a surface of the PCB, respectively, such that the number of spurs fit into the number of complementary slots, thereby attaching the biofuel cell to the PCB. Preferably, the number of spurs and the number of slots surround the (outer layer) air-breathing opening of the biofuel cell and the air-breathing opening formed in the PCB, while the air-breathing opening formed in the PCB faces the GDL air-breathing opening of the biofuel cell.

[0028] According to one particular embodiment of the invention, the biofuel cell is an enzymatic fuel cell.

[0029] According to a particular embodiment of the invention, the PCB is composed of different electronic components, for example the PCB comprises sensors, microprocessors, user interaction and communication modules, etc. or a combination thereof. [Brief description of the drawings]

[0030] [Figure 1] 1 depicts an electronic device of the present invention resulting from the installation of an enzymatic fuel cell having a liquid reservoir mounted on a functional printed circuit board (PCB) having an air breathing opening facing the outer layer air breathing opening of the enzymatic fuel cell. [Diagram 2] 1 depicts the sandwich structure of a medical patch comprised of a PCB and an enzymatic fuel cell, showing the alignment of the air breathing openings in the PCB with the air breathing openings in the enzymatic fuel cell. [Diagram 3] 1 depicts a sandwich structure of a portable electronic device consisting of a PCB, an enzymatic fuel cell, and a liquid reservoir, showing the alignment of the air breathing openings of the PCB with the air breathing openings of the enzymatic fuel cell. EXAMPLES

[0031] Example 1: PCB Fabrication Film substrate materials: Polyimide (PI) or similar polymers, Polyester (PET), Polyethylene Naphthalate (PEN), PTFE, Aramid. There are approximately 2000 additional plastic film categories that could potentially be suitable for flexible PCB manufacturing.

[0032] FPCBs (Flexible Printed Circuit Boards) are usually composed of three layers: substrate, adhesive, and copper foil. Adhesive reduces both the electrical and mechanical performance of the FPCB, hence there are two-layer FPCBs that do not have adhesive. Methods for manufacturing two-layer FPCBs include electroplating, film coating, and lamination. Electroplating is usually used for smaller and cheaper substrates, film coating is more suitable for low-cost mass production, and lamination is usually used for double-sided FPCB manufacturing. Since all of our substrates are double-sided, they will most likely be manufactured using a lamination process.

[0033] Manufacturing process steps: Material Selection. This step may not be part of every manufacturer's process. Some boards require a thicker copper layer. Materials with different copper layer thicknesses can be selected at this stage, or the sheet with the thinnest copper layer can be used and the additional copper can be added in a later step. Chemical pre-cleaning of the material. This step ensures that the copper clad substrate sheet is free of oxide films and other potential contaminants. Photoresist layer application. Application of a thin layer of photoresist material that is selectively removed in the next step. Exposure of the material to UV light to transfer the layout onto the material. For double-sided boards, both sides of the material can be exposed to UV simultaneously or each side can be exposed in turn. Chemical etching, which removes copper based on the layout transferred onto the material in the previous step. Drilling (for boards with more than two layers). Holes (vias) are used to connect contact points between the individual layers. These need to be drilled based on the supplied design file. · Copper plating. Since the copper layers are separated by an insulating substrate, it is necessary to add conductive material to the vias so that they can make electrical contact between the different layers. This is done through electrolytic copper plating. Another goal achieved by this step is to increase the thickness of the copper layer, if necessary. · Applying a surface finish. The surface finish protects the exposed copper from oxidation and corrosion. There are various surface finishes such as HASL (hot air solder levelling), tin, silver, gold or so-called organic coatings. · Coverlay application and lamination. This material is applied both to protect the copper from oxidation and to provide a physical barrier between the exposed copper portions (pads). This barrier prevents the molten solder from crossing between the pads and forming an undesired electrical connection (during reflow soldering in the final stages of final product assembly). The coverlay can be almost any color, in our design we use a black coverlay. After application, heat, pressure, and vacuum are used to bond the coverlay material to the substrate. · Application of stiffening material (if applicable). Some FPCBs require certain areas to be rigid while the rest of the board remains flexible. This is done by reinforcing these areas with a stiffening material (usually FR4) that is added to one (or both) of the faces of the FPCB (according to the design file). The thickness of this material is also determined at the design stage. It is selectable. Silkscreen printing (if applicable). Silkscreen is a graphical layer that can be printed on the outer layer of the FPCB. The purpose of this layer is to provide visual information such as board name, version, component names and locations, show logos, serial numbers, display CE or RoHS compliant markings, or even provide instructions to the end user on how to use the product. This layer can have both graphics and text, none of which can overlap exposed portions (pads) of the board. Electrical testing: At this stage, the connectivity between different points on the PCB is tested to ensure that there were no issues during the manufacturing process. · Cutting. In this step, the PCBs are cut from their panels (if requested by the customer) or cut in such a way that they are held to the panel only by small tabs, facilitating their removal from the panel later. This is the step where any additional holes (such as air breathing and inlet holes in our case) can be drilled. Cutting is done via any applicable method such as laser cutting, mechanical routing, or die cutting in case of large scale production.

[0034] All of the above steps are applicable to standard PCBs as well as Flex PCBs with some adjustments to some of the steps. In our case, whether we use a standard rigid PCB or a Flex PCB, holes for air, blisters, and injection ports may need to be drilled anyway. The biggest difference is during the cutting step, where it is more difficult to die cut a rigid PCB due to its thickness, so laser or more practical mechanical routing techniques may be used.

[0035] The same applies to PCBs with more than two layers. In this case, they are fabricated as separate PCBs, but before the copper plating step, they are joined together to constitute a single board with the inner layers. For example, for a four-layer board, two two-layer boards can be made, then an insulator can be applied to one side of one of the boards and the other glued on top of it. The result is a board with two outer layers and two inner layers, and the connections between the layers can be made with the help of vias (the vias need to be plated, so this is done before the plating step).

[0036] For our purposes, the shape and dimensions of the substrate are arbitrary as we adjust their shape and size based on the application. Furthermore, we may also place components on both sides of the substrate for some use cases.

[0037] Example 2: Biofuel Cell Fabrication Anode / Cathode The device for generating electrical energy comprises an anode and a cathode. To ensure the redox reactions that allow the generation of electrical energy, the anode and the cathode are made of materials that allow ion exchange. The anode and the cathode must have specific properties (thickness, electrical conductivity, surface resistance) that are selected depending on the application. These elements can be impregnated with enzymes and mediators.

[0038] For example, the anode and cathode comprise nanotube sheets, in particular sheets composed of multi-walled carbon nanotubes (MWNTs) as described above. In the case of a glucose battery, the nanotube sheets are impregnated with mediators and enzymes that allow for the oxidation of glucose at the anode and the reduction of oxygen from air to water at the anode. For example, the anode may comprise the enzymes glucose oxidase and / or FAD dehydrogenase for the oxidation of glucose, and naphthoquinone and / or phenanthroline quinone as redox mediators that transfer electrons to the electrode.

[0039] The cathode may contain the enzymes laccase, bilirubin oxidase, and ABTS as mediators.

[0040] Microfluidic Layer (Separator) The microfluidic diffusion layer is placed between the anode and the cathode. The latter allows the diffusion of the solution causing the generation of electrical energy by redox between the anode and the cathode. The microfluidic layer can for example be a simple gap or, more advantageously, it can comprise or consist of a paper-like material through which the solution causing the redox can diffuse by capillary action. A compromise must be made between its thickness and its cellular capacity (volume of voids).

[0041] This layer forms a separating layer between the anode and the cathode and may also constitute, at least in part, a diffusion support for the electrolyte.

[0042] Gaz diffusion layer / current collector The device for generating electrical energy may also include the usual elements of an electrochemical cell, in particular a fuel cell. The device may therefore comprise an electrically conductive element in contact with the electrode (in particular on the side opposite the electrode surface in contact with the microfluidic layer).

[0043] If the device is to be supplied with gas, the gas diffusion means (GDL) is arranged to allow the supply of gas.

[0044] outer layer Finally, the electrical energy generating device may comprise a preferably very rigid support and a covering element (blister, liquid reservoir, protective material), for example a glass fibre, plastic or polystyrene band or preferably a material of biological origin, surrounding all the elements described above, except the reservoir, which is accessible to allow the release of its contents. The purpose of this element is to fix and protect the device.

[0045] Example 3: Fabrication of Electronic Devices The resulting electronic device with a liquid reservoir is shown in FIG.

[0046] FIG. 1 is a schematic (top and bottom views) of an enzymatic fuel cell (B, E) mounted on a functional PCB (C, D) and covered by a blister (or liquid reservoir) mounted on a substrate (A, F). The top view (left column) shows the blister mounted on a substrate (A) which is itself mounted on the back of the enzymatic fuel cell (B). The last layer of the device is a functional PCB populated with electronic components, two contact terminals / pads, and an air-breathing opening that faces the outer layer air-breathing opening of the biofuel cell (C). The inverted view (right column) shows a functional PCB populated with electronic components and with an air-breathing opening that faces the outer layer air-breathing opening of the biofuel cell (E) which is mounted on the back of a blister that is mounted on a substrate (F).

[0047] The resulting electronic device, in the form of a wearable medical patch, is shown in FIG.

[0048] FIG. 2 is an illustration of an electronic device of the present invention in the form of a wearable medical patch that can be in contact with a user's skin on the anodic side, comprising: - an enzymatic fuel cell, (i) in contact with the skin 4, having one or more openings 5 ​​that allow biological fluids from the skin (e.g. from sweat containing glucose or lactate) to enter the inside of the biofuel cell (for a constant supply of fluid through the microfluidic layer 6); above (ii) a bioanode (made of a GDL and a bioactive cathode layer 8) having an outer layer 9 with an air breathing opening 10 allowing air (and therefore oxygen) to enter the interior of the biofuel cell (through the GDL 7), both electrodes being separated by a microfluidic layer 6 (which also acts as a separator) and which can be connected to an electronic device (e.g. via two openings 11) for power supply; - a functional PCB 12, on the same side as the outer layer 9 of the biocathode to which the PCB 12 is attached, having an air-breathing opening 13 facing the air-breathing opening 10 of the biocathode to allow sufficient air flow to reach the biocathode, and connected to the electrode (e.g. using conductive tape).

[0049] Therefore, the openings in the outer layers and the air breathing openings of the bioanode and biocathode, respectively, of the electronic device of the present invention do not exhibit the same functions.

[0050] FIG. 3 is an illustration of a portable electronic device having the same sandwich structure as shown in FIG. 2, where the enzymatic biofuel cell is supplied with activation solution from a liquid reservoir 4′ in contact with the outer layer on the bioanode side.

[0051] List of References [1] P. Atanassov, MYEl-Naggar, S. Cosnier and U. Schroder, ChemElectroChem, 2014, 1, 1702-1704. [2] E. Katz and K. MacVittie, Energy Environ. Sci., 2013, 6, 2791. [3] S. Cosnier, A. J. Gross, A. Le Goff and M. Holzinger, J. Power Sources, 2016, 325, 252-263. [4] P. Manoj Kumar and AKKolar, Int. J. Hydrogen Energy, 2010, 35, 671-681. [5] P. Ferreira-Aparicio and AM Chaparro, Int. J. Hydrogen Energy, 2014, 39, 3997-4004. [6] Z. Xiong, S. Liao, S. Hou, H. Zou, D. Dang, X. Tian, ​​H. Nan, T. Shu and L. Du, Int. J. Hydrogen Energy,2016,41,9191-9196. [7] International Application No. 2019 / 234573 [8] International Application No. 2021 / 170826 [9] Patent application US 2020 / 337,641

Claims

1. 1. An electronic device comprising a biofuel cell and a printed circuit board (PCB) having an opening, the biofuel cell having an outer layer air breathing opening, the electronic device being characterized in that the air breathing opening formed in the PCB faces the outer layer air breathing opening, and the biofuel cell is attached to the PCB.

2. 10. An electronic device according to claim 1 in the form of a portable electronic device, comprising: - said biofuel cell is composed of (i) a bioanode with an outer layer having one or more openings in contact with the user's skin or a liquid reservoir, and above that (ii) a biocathode with an outer layer having an outer layer air breathing opening, both electrodes being separated by a microfluidic layer; - the PCB has an air-breathing opening facing the outer layer air-breathing opening of the biocathode on the same side as the outer layer of the biocathode to which it is attached, and is connected to the bioelectrode; Electronic devices.

3. 10. An electronic device according to claim 1 in the form of a wearable electronic device, comprising: - said biofuel cell is composed of (i) a bioanode having an outer layer with one or more openings in contact with the skin of a user, and above that (ii) a biocathode with an outer layer having an outer air breathing opening, both electrodes being separated by a microfluidic layer; - the PCB has an air-breathing opening facing the outer layer air-breathing opening of the biocathode on the same side as the outer layer of the biocathode to which it is attached, and is connected to the bioelectrode; Electronic devices.

4. The electronic device according to any one of claims 1 to 3, wherein the air breathing opening to the PCB and / or the outer layer air breathing opening to the biofuel cell is at least one hole.

5. The electronic device of any one of claims 1 to 4, wherein the air breathing opening to the PCB has an area 1 / 10 to 2 times that of the outer layer air breathing opening of the biofuel cell.

6. The electronic device of any one of claims 1 to 5, wherein the air breathing opening to the PCB comprises a material that is permeable to oxygen.

7. The electronic device of claim 6 , wherein the material is in a form selected from the group consisting of a grid and a film.

8. 8. An electronic device as claimed in any one of claims 1 to 7, wherein the air breathing opening to the PCB is in the form of a plurality of continuous holes formed in the PCB itself, the holes collectively forming a grid facing the GDL air breathing opening of the biofuel cell.

9. The electronic device of any one of claims 1 to 8, wherein the biofuel cell is attached to the PCB by ACF tape or by biodegradable or minimal environmental impact means.

10. 10. The electronic device of claim 9, wherein the biodegradable or least impact means is a biodegradable adhesive and / or a snap-fit ​​means.

11. The electronic device of claim 10, wherein the snap-fitting means comprises at least one spur formed either on a surface of the biofuel cell in contact with a surface of the PCB or on a surface of the PCB in contact with a surface of the biofuel cell, and at least one slot complementary to the at least one spur formed either on the surface of the PCB in contact with the surface of the biofuel cell or on the surface of the PCB in contact with the surface of the biofuel cell, such that the at least one spur fits into the at least one slot, thereby attaching the biofuel cell to the PCB.

12. The electronic device of claim 11, wherein the at least one spar and the at least one slot surround the (outer layer) air breathing opening of the biofuel cell and the air breathing opening formed in the PCB, while the air breathing opening formed in the PCB faces the outer layer air breathing opening of the biofuel cell.

13. The electronic device of claim 10, wherein the snap-fitting means comprises a plurality of spurs formed either on the surface of the biofuel cell in contact with a surface of the PCB or on the surface of the PCB in contact with the surface of the biofuel cell, and a plurality of slots complementary to the plurality of spurs formed either on the surface of the PCB in contact with the surface of the biofuel cell or on the surface of the PCB in contact with the surface of the biofuel cell, such that the plurality of spurs fit into the plurality of complementary slots to attach the biofuel cell to the PCB.

14. 14. The electronic device of claim 13, wherein the plurality of spars and the plurality of slots surround the (outer layer) air breathing opening of the biofuel cell and the air breathing opening formed in the PCB, while the air breathing opening formed in the PCB faces the outer layer air breathing opening of the biofuel cell.

15. The electronic device according to any one of claims 1 to 14, wherein the biofuel cell is an enzymatic fuel cell.

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