CN109888326B - Air Self-Breathing Membraneless Microfluidic Fuel Cell with Integral Cylindrical Anode - Google Patents

Abstract

The invention discloses an air self-breathing membraneless microfluidic fuel cell with an integrated cylindrical anode, comprising a cathode cover plate, a flow channel and a battery bottom plate, and a cathode air breathing hole is arranged on the cathode cover plate, the cathode air breathing hole The air self-breathing cathode is arranged below the battery; it is characterized in that: the flow channel is arranged between the cathode cover plate and the battery bottom plate; a metal circular tube is arranged in the flow channel; the outer surface of the metal circular tube is coated with a catalytic layer; the The metal round tube is arranged in parallel with the air self-breathing cathode; the front part of the metal round tube is a hollow tube, and the rest is a solid tube; a number of overflow ports are arranged along the circumferential direction on the tube wall at the junction of the hollow tube and the solid tube The front end of the metal round tube is provided with a fuel inlet; the battery bottom plate is provided with a waste liquid outlet; the waste liquid outlet is communicated with the flow channel; the invention can strengthen fuel transmission, is conducive to system integration, and improves battery performance ; Can be widely used in energy, chemical industry, environmental protection and other fields.

Description

Air Self-Breathing Membraneless Microfluidic Fuel Cell with Integral Cylindrical Anode

technical field

The invention relates to the field of fuel cells, in particular to an air self-breathing membraneless microfluidic fuel cell with an integrated cylindrical anode.

Background technique

Currently widely used lithium-ion batteries have shortcomings such as low theoretical energy density, long charging time, and narrow normal operating temperature range. Micro fuel cells often use methanol or formic acid with high energy density as fuel, which is significantly higher than the upper limit of theoretical energy density of lithium batteries; the operating environment has strong adaptability and wide operating temperature range; chemical energy is directly converted into electrical energy, and the theoretical energy conversion efficiency is high. ; The product does not pollute the environment. Therefore, miniature fuel cells (such as miniature direct methanol or formic acid fuel cells) have unique advantages and broad application prospects in the new generation of miniature electronic devices and portable point-of-care detection devices. In addition, methanol or formic acid, etc., can be obtained through biomass conversion, _CO2 reduction, etc., and are renewable and environmentally friendly near-zero carbon cycle fuels. However, micro-fuel cells often use ion-exchange membranes to separate liquid fuels and oxidants, which have technical challenges such as high cost, difficult water management, large ohmic losses, severe fuel permeation, and membrane aging and degradation, which severely limit the development and application of micro-fuel cells.

Membraneless microfluidics fuel cells make use of the characteristics that the fluid viscous force is greater than the inertial force and the surface force is greater than the volume force (such as gravity) in the microchannel (feature size is 1-1000 μm), so that two or more fluids The formation of parallel laminar flow in the microchannel enables the natural separation of fuel and oxidant, and can conduct ions through the laminar interface, thereby eliminating the ion exchange membrane, simplifying the structure, reducing costs, and avoiding membrane-related shortcomings. The introduction of the air self-breathing cathode further eliminates the cathode mass transfer limitation caused by the liquid oxidant and improves the battery performance. Membraneless microfluidic fuel cells contain the main components such as flow channels and electrodes in one microchannel, and are compatible with existing microfabrication processes, which are beneficial to system integration and large-scale manufacturing.

In a typical air self-breathing membraneless microfluidic fuel cell, the fuel and catholyte form parallel laminar flows in the microchannels and form a diffusive mixing zone near the laminar interface. In the acidic electrolyte, the fuel undergoes oxidation reaction in the anode catalytic layer to generate electrons, protons and _{CO 2} . The electrons reach the cathode through the external circuit through the load. The formation of coalescence into bubbles will disturb the laminar interface and affect the performance of the battery. In the alkaline electrolyte, the fuel undergoes oxidation reaction in the anode catalytic layer to generate electrons, water and carbonate, the carbonate is discharged with the waste liquid, and the electrons reach the cathode through the external circuit through the load to combine with oxygen and water to generate hydroxide ions .

The main factor currently limiting the further improvement of membraneless microfluidic fuel cell performance is the fuel concentration boundary layer on the anode surface. The fluid in the membraneless microfluidic fuel cell is a laminar flow, and the fuel diffusion and transport direction is perpendicular to the flow direction. In membraneless microfluidic fuel cells, the Peclet number is generally high (>2000), making the convective transport along the flow direction much stronger than the lateral diffusion transport. Affected by this, the decrease in fuel concentration on the anode surface due to the consumption of electrochemical reactions cannot be effectively supplemented, so that a region where the fuel concentration gradually decreases (ie, the fuel concentration boundary layer) appears on the anode surface along the flow direction, which severely limits the fuel transport and limits the battery. Performance is further improved.

In order to strengthen the fuel transfer, domestic and foreign researchers have proposed several schemes. 1) Ortiz-Orteg et al. (E.Ortiz-Ortega et.al., Lab on a Chip, 2014) increased fuel concentration and enhanced fuel mass transfer. However, increasing the fuel concentration will enhance the diffusion/convective transport of the fuel to the cathode, and when the fuel contacts the cathode catalytic layer, mixed potential and parasitic currents will be generated, which will seriously degrade the cell performance. In addition, due to the existence of the fuel concentration boundary layer, a large amount of fuel in the main flow region cannot participate in the reaction and be directly discharged from the cell, resulting in extremely low fuel utilization. 2) Bazylak et al. (A.Bazylak et.al., Journal of Power Sources, 2005) increase the anode fuel flow rate, thereby thinning the fuel concentration boundary layer, increasing the concentration gradient, and enhancing fuel mass transfer. Excessive flow velocity, however, can cause flow instability, disturb the laminar interface, enhance mixing and cause fuel permeation. 3) Ahme et al. (D.H.Ahme et.al., International Journal of Energy Research, 2010) arranged micro-convex structures on the anode surface to generate micro-convection for the fuel fluid near the anode surface, thereby enhancing fuel mass transfer. This solution, however, enhances convective mixing at the laminar interface, causing fuel permeation. 4) Lim et al. (K.G.Lim et.al., Biosensors and Bioelectronics, 2007) employ a discontinuous anode electrode, thereby disrupting the continuous generation of the fuel concentration boundary layer. However, this solution will reduce the effective electrode area and reduce the output power of the battery. 5) Kjeang et al. (E.kjeang et.al., Electrochimica Acta, 2008) used a permeable porous anode to enhance fuel mass transfer in a convection manner. Limited; on the other hand, an additional anode flow channel is required, which reduces the volumetric energy or power density and is not conducive to system integration. 6) Wang et al. (Y. Wang et. al., Applied Energy, 2015) used gaseous methanol vapor as the fuel, but this scheme requires a larger fuel evaporation chamber, which reduces the volumetric energy or power density and is not conducive to system integration. In addition, some studies (W.R.Merida et.al., Journal of Power Sources, 2001) have proved that the use of curved electrolyte-electrode interface can effectively improve the volume power density of membraneless fuel cells, and the curved electrode is beneficial to realize the integrated amplification of the cell change.

SUMMARY OF THE INVENTION

Aiming at the shortcomings of the prior art, the present invention proposes an air self-breathing membraneless microfluidic fuel cell with an integrated cylindrical anode.

The technical scheme of the present invention is: an air self-breathing membraneless microfluidic fuel cell with an integrated cylindrical anode, comprising a membraneless microfluidic fuel cell main body, the membraneless microfluidic fuel cell main body comprising a cathode cover plate, an air self A breathing cathode, a flow channel, a cylindrical anode and a battery bottom plate, a cathode air breathing hole is arranged on the cathode cover plate, and the cathode air breathing hole is arranged above the air self-breathing cathode; it is characterized in that: the flow channel is arranged on the cathode cover plate The front end of the flow channel is provided with an electrolyte inlet; the flow channel is provided with a metal circular tube; the outer surface of the metal circular tube is coated with a catalyst layer; the cylindrical anode consists of a metal circular tube and a catalyst layer. The metal circular tube, the flow channel and the air self-breathing cathode are arranged in parallel; the front part of the metal circular tube is a hollow tube, and the rest is a solid tube; along the circumference of the tube wall at the junction of the hollow tube and the solid tube A number of annular through grooves are arranged in the direction as overflow ports; the front end of the metal circular tube is provided with a fuel inlet; the liquid fuel overflows from the overflow opening and forms a wall-adhering flow on the surface of the metal circular tube; Waste liquid outlet; the waste liquid outlet communicates with the flow channel.

The cathode of the invention directly reduces oxygen in the air and combines electrons and hydrogen ions to generate water under acidic conditions, and reduces oxygen to combine electrons and water to generate hydroxide ions under alkaline conditions; the metal round tube serves as an anode substrate and also As a fuel transport channel; it can directly catalyze and oxidize the fuel and generate electrons and hydrogen ions or carbonates; the fuel overflows into the flow channel at a low speed from the overflow port, and is affected by the flow of the electrolyte, and the fuel is close to the surface of the metal tube flow; and oxidation reaction occurs on the surface of the anode catalytic layer.

This patent proposes an air self-breathing membraneless microfluidic fuel cell with an integrated cylindrical anode. The air self-breathing cathode is used to eliminate the mass transfer limitation of the cathode oxidant (oxygen); the integrated cylindrical anode is used as a fuel flow channel and an anode electrode at the same time. , which further improves the integration; the cylindrical anode is used to increase the effective anode reaction area; the fuel is input from the metal circular tube, first flows in the tube, and then flows into the flow channel at a low speed by overflowing through the annular channel on the surface of the cylindrical anode. Due to the hydraulic aggregation effect of the electrolyte fluid, the fuel forms a thin layer that flows close to the surface of the metal tube, enhancing the fuel mass transfer and reducing the fuel penetration to the cathode; in addition, the fuel thin layer directly covers the anode catalytic active site, which has Conducive to improving fuel efficiency.

According to the preferred solution of the air self-breathing membraneless microfluidic fuel cell with an integrated cylindrical anode according to the present invention, the metal circular tubes are arranged in a single or parallel arrangement in the flow channel.

According to the preferred solution of the air self-breathing membraneless microfluidic fuel cell with an integrated cylindrical anode of the present invention, several layers of liquid flow ports are layered on the tube wall of the hollow tube part of the metal circular tube; The orifice is composed of several annular through grooves arranged on the same circumferential wall surface.

According to the preferred solution of the air self-breathing membraneless microfluidic fuel cell with an integrated cylindrical anode of the present invention, the air self-breathing cathode is composed of a hydrophobic carbon paper, a leveling layer and a Pt/C catalyst layer.

The beneficial effects of the air self-breathing membraneless microfluidic fuel cell with an integrated cylindrical anode according to the present invention are:

1) In the present invention, the anode cylindrical electrode serves as a fuel channel at the same time, which improves the integration degree and further improves the energy density of the system. The anode electrode, anode fuel flow channel, main flow channel, and cathode electrode are all contained in a tiny channel, which is beneficial to system integration.

2) The use of an integrated cylindrical anode increases the effective reaction area, and the hydraulic aggregation effect is used to enhance fuel transmission and reduce fuel penetration, which is beneficial to improve cell performance.

3) The effective volume of the battery is reduced, the hydrogen ion transmission distance is shortened, the hydrogen ion transmission resistance is reduced, the volume power density of the battery is improved, and the miniaturization and system integration are facilitated.

4) Good performance in acid/alkali electrolyte, good adaptability and flexibility.

5) The cheap and readily available oxygen in the air is directly used as the oxidant, which effectively reduces the operating cost of the battery.

6) The present invention has a simple structure, does not need complex microchannels and fuel membranes, can realize fuel operation, and avoid fuel permeation.

The invention can be widely used in the fields of energy, chemical industry, environmental protection and the like.

Description of drawings

Figure 1 is a front view of an air self-breathing membraneless microfluidic fuel cell with an integral cylindrical anode.

FIG. 2 is a plan view of FIG. 1 .

FIG. 3 is a left side view of FIG. 1 .

FIG. 4 is a schematic diagram of the arrangement of the overflow port 7 .

Detailed ways

Referring to FIGS. 1 to 4, an air self-breathing membraneless microfluidic fuel cell with an integrated cylindrical anode includes a membraneless microfluidic fuel cell body, and the membraneless microfluidic fuel cell body includes a cathode cover plate 2, an air Self-breathing cathode 4, flow channel 5, cylindrical anode 8 and battery bottom plate 9, the cathode cover plate, flow channel and battery bottom plate 9 are all made of plastic; The air breathing hole 3 is arranged above the air self-breathing cathode 4; the flow channel 5 is arranged between the cathode cover plate 2 and the battery bottom plate 9; the front end of the flow channel 5 is provided with an electrolyte inlet 6, and the flow channel 5 is provided with There is a metal round tube 1; the outer surface of the metal round tube 1 is coated with a Pd/Nafion catalytic layer by repeated electrochemical deposition; the metal round tube 1 and the Pd/Nafion catalytic layer constitute the cylindrical anode 8; The circular tube 1 and the flow channel 5 are arranged in parallel with the air self-breathing cathode 4; the front part of the metal circular tube 1 is a hollow tube, and the rest is a solid tube; along the circumferential direction on the tube wall at the junction of the hollow tube and the solid tube A plurality of annular through grooves are provided as the overflow port 7; the annular through groove is a rectangular annular hole with a width of 10-1000 microns; the front end of the metal circular tube 1 is provided with a fuel inlet 11; the liquid fuel overflows from the overflow port , and form a wall-to-wall flow on the surface of the metal round tube 1 ; the battery bottom plate 9 is provided with a waste liquid outlet 10 ; the waste liquid outlet 10 is communicated with the flow channel 5 .

In a specific embodiment, the metal circular tubes 1 are arranged in a single or multiple parallel arrangement in the flow channel.

Referring to FIG. 4 , several layers of liquid flow ports are arranged in layers on the tube wall of the hollow tube portion of the metal circular tube 1;

The air self-breathing cathode 4 is composed of a hydrophobic carbon paper, a leveling layer and a Pt/C catalytic layer.

When the microfluidic fuel cell is running, a certain flow rate, such as 50 μl min ^-1 of deoxygenated liquid fuel, is introduced into the metal circular tube 1 , and the liquid fuel can be a mixed solution of 5M formic acid and 1M dilute sulfuric acid; and the electrolyte inlet 6 A certain flow of electrolyte such as 1M dilute sulfuric acid solution is passed into the flow channel 5, and the liquid fuel flows into the flow channel 5 at a low speed from the overflow port 7, and flows close to the surface of the metal circular tube 1, and flows toward the surface of the metal circular tube 1. The catalytic layer Convective/diffusion transport. In the acidic electrolyte, the anode catalytic layer catalyzes the electrochemical oxidation of formic acid molecules to generate hydrogen ions, electrons and carbon dioxide. The hydrogen ions reach the cathode through electromigration, the electrons reach the cathode from the external circuit through the load, and the carbon dioxide bubbles flow from the downstream waste liquid of the flow channel. Outlet discharge. The oxygen in the air is transported to the Pt/C catalytic layer through the hydrophobic carbon paper with porous structure, and electrochemical reduction takes place in the cathode Pt/C catalytic layer to combine hydrogen ions and electrons to generate water. In the alkaline electrolyte, the anode Pt/C catalytic layer catalyzes the electrochemical oxidation of formate ions to generate water, electrons and carbonates. The electrons reach the cathode from the external circuit through the load, and the carbonate dissolves in the water from the waste liquid outlet. discharge.

Taking the air self-breathing direct formic acid microfluidic fuel cell as an example, the reactions that take place in the acidic electrolyte are as follows:

Anodic formic acid oxidation

HCOOH→CO ₂ ↑+2H ⁺ +2e ^- , E ⁰ =－0.198V vs. SHE (standard hydrogen electrode)

Cathode Oxygen Reduction Reaction

O ₂ +4H ⁺ +4e ^- →2H ₂ O, E ⁰ =1.229V vs. SHE

overall response

2HCOOH+O ₂ →2CO ₂ ↑+2H ₂ O, ΔE=1.427V

The reactions that take place in an alkaline electrolyte are as follows:

Anodic formate oxidation

Cathode Oxygen Reduction Reaction

O ₂ +2H ₂ O+4e ^- →4OH ^- , E ⁰ =0.4V vs. SHE

overall response

Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, The scope of the invention is defined by the claims and their equivalents.

Claims (4)

1. An air self-breathing membraneless microfluidic fuel cell with an integral cylindrical anode, comprising a membraneless microfluidic fuel cell main body, the membraneless microfluidic fuel cell main body comprising a cathode cover plate (2), an air self-breathing cathode (4), the flow channel (5), the cylindrical anode (8) and the battery bottom plate (9), the cathode cover plate (2) is provided with a cathode air breathing hole (3), and the cathode air breathing hole (3) is provided with Above the air self-breathing cathode (4); it is characterized in that: the flow channel (5) is arranged between the cathode cover plate (2) and the battery bottom plate (9); the front end of the flow channel (5) is provided with an electrolyte inlet ( 6); a metal round tube (1) is arranged in the flow channel (5); the outer surface of the metal round tube (1) is coated with a catalyst layer; the cylindrical anode (8) is formed by the metal round tube (1) and a catalyst layer; the metal circular tube serves as both an anode substrate and a fuel transport channel; the metal circular tube (1), the flow channel (5) and the air self-breathing cathode (4) are arranged in parallel; The front part of the pipe (1) is a hollow pipe, and the rest is a solid pipe; a number of annular through grooves are arranged along the circumferential direction on the pipe wall at the junction of the hollow pipe and the solid pipe as overflow ports; the metal round pipe ( The front end of 1) is provided with a fuel inlet (11); the liquid fuel overflows from the overflow port and forms a wall-to-wall flow on the surface of the metal circular tube (1); the battery bottom plate (9) is provided with a waste liquid outlet (10) ; The waste liquid outlet (10) is communicated with the flow channel (5). 2 . The air self-breathing membraneless microfluidic fuel cell with an integrated cylindrical anode according to claim 1 , wherein the metal circular tubes ( 1 ) are arranged singly or in parallel in the flow channel. 3 . 3. The air self-breathing membraneless microfluidic fuel cell with an integrated cylindrical anode according to claim 1 or 2, characterized in that: on the tube wall of the hollow tube part of the metal circular tube (1), layered is provided with Several layers of liquid flow openings; each layer of liquid flow openings is composed of several annular through grooves set on the same circumferential wall surface. 4. The air self-breathing membraneless microfluidic fuel cell with an integrated cylindrical anode according to claim 3, wherein the air self-breathing cathode (4) is composed of hydrophobic carbon paper, leveling layer and Pt/ C catalytic layer composition.

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