KR101444802B1 - Microbial fuel cell for generating hydrogen and metal nanoparticle and method for preparing the same - Google Patents

Abstract

The present invention relates to a microbial fuel cell for generating hydrogen and metal nanoparticles, and a method for manufacturing the same. The microbial fuel cell according to the present invention is capable of producing single crystalline metal nanoparticles having various shapes, and, by using the metal nanoparticles as catalysts, hydrogen can be produced without supply of external power source and oxygen.

Description

TECHNICAL FIELD The present invention relates to a microbial fuel cell for generating hydrogen and metal nanoparticles, and a method for preparing the same.

The present invention relates to a microbial fuel cell for producing hydrogen and metal nanoparticles and a method of manufacturing the same.

A microbial fuel cell (MFC) is a device that produces electricity through biooxidation of biomass by an electron-emitting microorganism (exoelectrogen). Generally, through the oxidation of microorganisms, electrons and protons generated in the anode electrode (oxidizing electrode) generate water by bonding with oxygen in the cathode electrode (reducing electrode). However, in the absence of oxygen in the cathode electrode, the MFC can not generate electricity because the electrons and the protons can not combine to produce hydrogen because of the thermodynamic barrier. Therefore, in order to generate hydrogen at the cathode electrode, external power supply is essential, which is called a microbial electrolysis cell (MEC).

MEC is a recent technology for producing hydrogen from biomass. The process at the anode electrode of the MEC is similar to that of MFC, but the process at the cathode electrode is similar to that of the water electrolytic cell. In the case of MEC, since the reaction does not occur spontaneously due to the negative potential at the cathode electrode, in order to generate the reaction spontaneously, an additional voltage of ~ 0.114 V (practical value ~ 0.25 V) do. This additional voltage is well below the theoretical 1.2 V required for water electrolysis. However, lowering the energy input in a MEC system with a high hydrogen production rate and a cost-effective cathode electrode material will be a challenging issue for practical application of this technology.

Bulk gold is an inert material and has long been regarded as the Cinderella of the periodic table. However, gold nanoparticles have been regarded as excellent catalysts. Due to potential applications in catalysis, optics, electronics, and biomedical applications, the production of gold nanoparticles has received great interest. However, the synthesis of gold nanoparticles is not only complicated, but also requires a seed growth process or a morphological change from spherical to triangular. Chemical methods using various reducing agents such as sodium borohydride are common synthetic methods for gold nanoparticles, but this method requires many chemicals and stringent reaction conditions. It has also been found that many microorganisms, including bacteria and fungi, can be nano-factories for synthesizing metal nanoparticles. However, since most of this synthesis takes place in cells, it has difficulties in separating nanoparticles.

Recently, the present inventors have shown that an electrochemically activated biofilm can be used for extracellular synthesis of metal and metal nanocomposite materials. Gold nanoparticles exhibit a variety of unique properties including quantized charging effects, which have been extensively studied since Murray's pioneering work on quantized capacitance charging. The quantized charge is similar to the classic coulomb staircase charging. Most of the studies on this quantized charge phenomenon have been performed in organic media, but rarely in aqueous environments.

The inventors of the present invention have discovered that hydrogen and metal nanoparticles can be produced using a microbial fuel cell while searching for a method for producing hydrogen and metal nanoparticles without supplying external power and oxygen.

Accordingly, the present invention provides a microbial fuel cell for producing hydrogen and metal nanoparticles and a method of manufacturing the same.

The present invention also provides a method for producing hydrogen and metal nanoparticles using the microbial fuel cell.

The present invention provides a microbial fuel cell for producing hydrogen and metal nanoparticles and a method of manufacturing the same.

The present invention also provides a method for producing hydrogen and metal nanoparticles using the microbial fuel cell.

The microbial fuel cell according to the present invention can produce monocrystalline metal nanoparticles having various shapes and can generate hydrogen without supplying external power and oxygen using the metal nanoparticles as a catalyst.

1 schematically shows the structure of a microbial fuel cell (MFC).
2 is a graph showing the power density of MFC-2.
FIG. 3 is a diagram showing the UV-Vis spectrum of the gold nanoparticles generated in the MFC-2 cathode electrode part.
4 is a TEM image showing the gold nanoparticles generated in the MFC-2 cathode electrode portion.
FIG. 5 is a view showing a SAED pattern of gold nanoparticles generated in the MFC-2 cathode electrode portion. FIG.
6 is a graph showing the amount of hydrogen generated in the MFC-2 cathode electrode portion.
FIG. 7 is a graph showing the results of measurement of the gold nanoparticle DPV produced in the MFC-2 cathode electrode portion.

The present invention

1) a chamber; An anode electrode and a cathode electrode disposed inside the chamber in opposition to each other; An external lead connecting the anode electrode and the cathode electrode; An anode electrode portion including an active microbe and an organic substance; A cathode electrode portion including a buffer solution and supplied with air from the outside; And a cation exchange membrane for separating the chamber into an anode electrode portion and a cathode electrode portion; Preparing a microbial fuel cell comprising the microbial fuel cell; And

2) replacing the buffer solution of the cathode electrode part with a solution containing a metal precursor after the microbial fuel cell of step 1) has a power density of 30 to 50 mW / m ² ; The present invention provides a method for producing a microorganism fuel cell for producing hydrogen and metal nanoparticles.

Hereinafter, a method of manufacturing a microorganism fuel cell for producing hydrogen and metal nanoparticles according to the present invention will be described in detail.

The microbial fuel cell (MFC) according to the present invention is fabricated as an anode electrode unit and a cathode electrode unit in a two-chamber type. 1 schematically shows the structure of a two-chamber type microbial fuel cell. 1, the microbial fuel cell 100 according to the present invention includes an anode 110, a cathode 120, an external lead 165 including an external resistor, an anode electrode 160, A cation exchange membrane 140, and an active microorganism 150, as shown in FIG.

The microbial fuel cell (MFC) produced in the step 1) is referred to as a microbial fuel cell-1 (MFC-1).

The microbial fuel cell (MFC) produced in the step 2) is referred to as a microbial fuel cell-2 (MFC-2).

In step 1), the anode 110 and the cathode 120 may be formed of a conductive material. Examples of the conductive material include carbon paper, carbon cloth, carbon felt, or metal Cloth can be used, but is not limited thereto. In the present invention, it is preferable that the anode electrode 110 includes carbon paper, and the cathode electrode 120 includes carbon paper coated with a platinum (Pt) catalyst.

The external wire 165 may be a copper wire having an external resistance of 500 to 1500 OMEGA, but is not limited thereto.

In the step 1), the anode electrode unit 160 includes the active microbe 150 and organic matter. The active microorganism 150 can be any microorganism capable of generating an electric current by using an organic substance as a fuel and using oxidative power according to fuel consumption for cathode electrode reaction. For example, the active microorganism 150 may be selected from the group consisting of Rhodoferax ferrireducens, Shewanella putrefaciens, Geobacteraceae sulfurreducens, But is not limited to, one or more microorganisms or mixed strains selected from the group consisting of Geobacter metallireducens. That is, all the microorganisms used in conventional fuel cells can be used.

In the step 1), the buffer solution of the cathode electrode part 130 is filled with the phosphate buffer solution, and it is preferable that the air is continuously aerated to 80 to 130 mL by using the tank membrane pump.

In step 1), the pH of the anode electrode unit 160 is adjusted to 6 to 8, and nitrogen is preferably aerated to remove the oxygen present. Since the electrons (e ^- ) and protons (H ⁺ ) are supplied through the decomposition of organic matter in the anode electrode unit 160, the concentration of oxygen is maintained in the same manner as nitrogen aeration to maintain anaerobic conditions. It is important to lower it to the maximum possible.

In the step 1), the cation exchange membrane 140 is disposed between the anode electrode unit 160 and the cathode electrode unit 130 and a Nafion membrane is used. However, the present invention is not limited thereto.

It is preferable to produce a stable power density of 30 to 50 mW / m ² from the microbial fuel cell produced in the step 1). Specifically, the active microorganism 150 present in the wastewater containing the sludge in the anode electrode unit 160 generates electrons e ^- and protons H ⁺ by decomposing the organic matter, e ^-) and protons (H ⁺⁾ may continue to produce power by reacts with oxygen (O ₂₎ supplied to the cathode electrode 130 to produce water (H ₂ O).

The solution containing the metal precursor in the step 2) may include HAuCl ₄ , but is not limited thereto. The metal may include Au, Ag, Cu, Ni, Pd, Pt, Zn, Cd, Co, But it is not limited thereto.

In the step 2), it is preferable that the cathode electrode unit 130 is maintained in an anoxic state. Specifically, electrons (e ^- ) and protons (H ⁺ ) generated in the anode electrode unit 160 move to the cathode electrode unit 130 through the external conductor 165 and the cation exchange membrane 140, respectively, This is because hydrogen (H ₂ ) can be generated without supplying oxygen by reacting with the metal nanomaterials generated in the cathode electrode unit 130.

In the step 2), the cathode electrode 120 may include stainless steel, but is not limited thereto.

In addition, the present invention provides a microbial fuel cell produced by the above production method.

The present invention also provides a method for producing hydrogen and metal nanoparticles using the microbial fuel cell.

The gold nanoparticles produced using the microbial fuel cell according to the present invention can be formed into a variety of shapes such as spherical, hexagonal, convex, triangular, cut triangular, pyramid, boat, pentagonal rod, sandwich, And the like. It is also confirmed that the generated gold nanoparticles act as a catalyst to generate hydrogen and electricity.

The microbial fuel cell according to the present invention can produce monocrystalline metal nanoparticles having various shapes and can generate hydrogen without supplying external power and oxygen using the metal nanoparticles as a catalyst.

Hereinafter, preferred embodiments of the present invention will be described in order to facilitate understanding of the present invention. However, the following examples are provided only for the purpose of easier understanding of the present invention, and the present invention is not limited by the examples.

Example 1. Method for producing microbial fuel cell (MFC)

The microbial fuel cell (MFC) was fabricated as a two chamber type. MFC-1 consisted of two glass bottles (anode electrode and cathode electrode, 200 mL each) with carbon paper electrodes (2 cm x 4 cm). The cathode electrode was coated with a Pt catalyst (0.5 mg Pt / cm ² ). The bottles were connected by two clamps between the flat ends of two glass tubes (inner diameter = 1.3 cm) with rubber gaskets. A cation exchange membrane was positioned between the flat ends of the glass tube to separate the anode and cathode electrodes. The electrodes were connected to a copper wire with ~ 1000 Ω external resistance wrapped in carbon paste. The anode electrode portion of the MFC was filled with artificial wastewater using sodium acetate as the electron donor (1 g / L). In addition, inorganic salt medium (MSM) was added to the anode medium, and 10 mL of anaerobic sludge containing active microorganisms was treated with Rhodoferax ferrireducens, Shewanella putrefaciens, (Including exoelectrogens such as Geobacteraceae sulfurreducens and Geobacter metallireducens) have been added. Nitrogen was aerated for 10 minutes to remove all existing oxygen in the anode electrode portion (anode pH ~ 7.4). The cathode portion was filled with phosphate buffer (50 mL), and air (110 mL / min) was continuously aerated using a tank membrane pump. And the cathode electrode portion was maintained in the magnet stirrer. After obtaining a stable voltage of 30 to 50 mW / m ² from MFC-1, the cathode electrode portion was replaced with a 1 mM HAuCl ₄ .6H ₂ O (gold precursor) solution (volume = 200 mL, pH ~ 3) The coated carbon paper was replaced with a stainless steel wire mesh (2 cm x 4 cm) (MFC-2). Also, in MFC-2, the supply of oxygen to the cathode electrode portion was stopped, and the cathode electrode portion was maintained in an oxygen-free state to generate hydrogen. All experiments were repeated three times.

The schematic structure of a microbial fuel cell (MFC) according to the present invention is shown in Fig.

Experimental Example 1. Measurement of power density of MFC-2 produced by using the produced gold nanoparticles as a catalyst without external power and oxygen supply

The voltage across the external resistors was measured at 10 minute intervals via a digital multimeter (Agilent 3445A, USA). The power density was calculated by varying the external resistance using a variable resistance box and the power P was calculated by P = IV (I = current, V = voltage) and then by the surface area of the anode electrode Standardized.

Stable power of 30-50 mW / m ² was produced by the oxidation of active microorganisms in MFC-1. Thereafter, the power generated in the MFC-2 was measured while the supply of oxygen was stopped. The power density of MFC-2 produced by oxidation-reduction reaction using gold nanoparticles generated from MFC-2 as a catalyst is shown in FIG.

As shown in Figure 2, MFC-2 produced a stable power density of ~ 42 mW / m < ² > after 10 hours of operation. Initially, MFC-2 showed a voltage of 0.45 V, with an open circuit voltage (OCV) of 1.4 V. When MFC-2 was operated, a large amount of gold trivalent ions (Au ³⁺ ) were present in the cathode electrode portion in the initial stage. The standard reduction potential of Au ³⁺ / Au ⁰ is +1.5 V. The high reduction potential causes high OCV in the early stages of MFC-2 operation. As the gold reduction reaction proceeds, the OCV and the voltage gradually start to decrease, and gold nanoparticles are generated at the cathode electrode portion. After 10 hours of operation of MFC-2, the open-circuit potential (OCP) of each electrode decreases from 0.94 V to 0.26 V, while the anode potential remains almost unchanged. Thus, reduction at the cathode potential could be seen as a major cause of OCV reduction. The MFC-2 produced a stable power density of ~ 42 mW / m ² after 10 hours of operation, indicating that gold reduction is over. It remained stable over a month. Coulomb efficiency for electricity production was measured as 62.4%.

Experimental Example 2: UV-Vis spectra of gold nanoparticles produced in the MFC-2 cathode electrode portion

UV-Vis spectra were measured using a UV-Vis spectrometer (UV-1800, Shimadzu, Japan) to confirm the formation of gold nanoparticles at the MFC-2 cathode electrode. The absorbance of the generated gold nanoparticles with increasing time was measured. The UV-Vis spectra of the gold nanoparticles produced at the MFC-2 cathode electrode portion are shown in FIG.

As shown in Fig. 3, the generation of gold nanoparticles was observed by the appearance of ruby color in the MFC-2 cathode solution. Figure 3 shows one peak near about 550 nm, which is proportional to gold nanoparticles. The peak increased with time, but no further increase after 10 hours of operation of the MFC-2. It showed that the Au ³⁺ ions were completely reduced. Also, the absorbance at higher wavelengths increases with time, indicating that the gold nanoparticles are anisotropic.

Experimental Example 3 TEM image of gold nanoparticles generated at the MFC-2 cathode electrode portion

The morphology of the gold nanoparticles was measured by a high resolution transmission electron microscope (HRTEM; Tecnai G2F20, USA) with energy dispersive X-ray (EDX). The crystallinity of the generated gold nanoparticles was also analyzed by selected area electron diffraction (SAED) pattern.

The TEM measurement results of the gold nanoparticles generated at the MFC-2 cathode electrode portion are shown in FIG. 4, and the SAED measurement results are shown in FIG.

As shown in FIG. 4, the TEM images of the gold nanoparticles generated in the MFC-2 cathode electrode portion can be formed into a rectangular shape, a hexagonal shape, a hollow shape, a triangular shape, a cut triangle, a pyramid shape, a boat shape, a pentagonal bar shape, Structure and so on.

Also, as shown in FIG. 5, SAED measurement results showed that the gold nanoparticles produced were composed of monocrystals in a natural state.

It can be seen that the reason that the gold nanoparticles generated in the MFC-2 cathode electrode part have various shapes and grows anisotropically is due to the difference in the partial pressure of hydrogen near the gold nucleus. In other words, the generated gold nanoparticles have unstable surface energy. In order to reduce the surface energy, hydrogen is adsorbed on the surface of the generated gold nanoparticles, thereby achieving surface stabilization through surface passivation. Density Functional Theory (DFT) calculations have shown that the interaction between gold nanoparticles and hydrogen can make a dramatic change in the structure of gold nanoparticles. In the DFT calculations, it was shown that when hydrogen molecules pass through a gold nanoparticle solution, hydrogen molecules are preferentially adsorbed on the [111] surface of gold nanoparticles. Therefore, the reason that various types of gold nanoparticles are produced is that the surface of gold nanoparticles is selectively stabilized due to the interaction between gold nanoparticles and hydrogen. The resulting gold nanoparticles having various non-spherical shapes are believed to play an important role in cancer diagnosis and treatment methods due to their unique optical properties, catalysts, or electrical properties.

Experimental Example 4: Electrical Properties of Gold Nanoparticles Generated in MFC-2 Cathode Electrode

The electrical properties of the gold nanoparticles generated at the MFC-2 cathode electrode portion were measured by zeta potential analysis. The zeta potential was calculated by determining the electrophoretic mobility using a Delta ^TM Nano zeta potential (Beckman Coulter, USA).

The zeta potential analysis shows that the generated gold nanoparticles are fully charged (+ 33 ± 2 mV), and their charge is that the protons are adsorbed on the surface of the gold nanoparticles.

Experimental Example 5. Measurement of the amount of hydrogen produced in the MFC-2 cathode electrode portion

The amount of hydrogen produced in MFC-2 was measured by inhalation of gas pressure into a glass syringe (20 mL capacity) until the pressure in the syringe equilibrated with atmospheric pressure. The volumetric fraction of hydrogen in the gas was measured by gas chromatography (GC5890, USA).

The results of measurement of the amount of hydrogen produced in the MFC-2 cathode electrode portion are shown in FIG.

As shown in FIG. 6, the gas chromatography analysis showed that significant hydrogen was generated at the MFC-2 cathode electrode portion. The hydrogen production rate was measured at 1.5 mL / h, and the hydrogen yield was 0.69 mL H ₂ / mg chemical oxygen demand (COD).

Generally, MFC can not make hydrogen spontaneously at the cathode electrode because the total potential is negative without the presence of oxygen. To overcome this thermodynamic failure, the external power supply must be applied to the MFC (MEC mode). However, MFC-2 produced hydrogen at the cathode electrode portion without external power and oxygen supply. Without external power and oxygen supply, how hydrogen gas is generated is a problem. This is because the gold nanoparticles generated at the MFC-2 cathode electrode portion show "quantized capacitor charge" phenomenon by accepting electrons and protons. In detail, at pH = 7 (298K), the biological standard potential of CO ₂ / acetate is -0.29 V and H ⁺ / H ² is known to be -0.414 V. As a result, since the cell voltage is -0.124 V, the reaction does not occur spontaneously. However, in the present invention, since the pH of the 1 mM gold precursor is ~ 3, the pH at the cathode electrode is ~ 3. Therefore, if the cathode electrode portion pH is taken as ~ 3, the cathode potential for hydrogen production becomes -0.177 V (Nernst equation E = -0.059 X pH). Therefore, the resulting voltage is +0.113 V, and the MFC can operate spontaneously without external power supply. In the present invention, the pH of the cathode electrode portion was regularly monitored, and as a result, the pH of the cathode portion was hardly changed even after one month of operation of the MFC, because the pH of the cathode electrode portion changed in a normal MFC. The adsorption of the protons on the surface of the generated gold nanoparticles acts as a proton buffer to prevent the pH from changing in the cathode electrode. It is known that the electron transfer rate is greatly improved in the MFC cathode part having a pH of 3 and it is known that when the gold nanoparticles have many edges or edges, the catalyst activity is greatly improved due to the increase of the surface area. The edges or edges of the nanoparticles can act as active sites for catalytic activity. Thus, the catalyst activity in the cathode electrode area will be further improved since the cathode solution contains various gold nanoparticles with many edges or edges rather than spherical nanoparticles. The gold nanoparticles charged at the cathode electrode portion are charged as electrons by the electrons passing through the external circuit. This catalytic activity increases significantly with increasing electron density in the gold core.

Differential pulse voltammetry (DPV) was operated using a potentiostat using a standard three electrode system. Ag / AgCl was used as the standard electrode, Pt foil as the counter electrode and stainless steel wire mesh as the working electrode. The gold nanoparticle solution produced in MFC-2 was used as the electrolyte.

The results of DPV analysis of the gold nanoparticles produced in the MFC-2 cathode electrode portion are shown in FIG.

As shown in Figure 7, the DPV plat showed a pair of distinct quantized charge peaks. The peak current shows a higher value than the results of many earlier documents, indicating that the gold nanoparticles with the various forms produced serve as "quantized capacitors". The surfaces of the charged gold nanoparticles are compared to one electrode. According to the Volmer-Heyrovsky mechanism, protons are adsorbed on the surface of (-) charged gold nanoparticles, and then hydrogen molecules are desorbed when the second protons are reduced at the same location.

 [Formula 1]

Au + H ⁺ + e ^{- - - -} & gt ^; Au-H (1a)

Au - H + H ⁺ + e ^{- - - -} > Au - H ₂ (1b)

It can be seen that each electron trapped by the gold nanoparticles attracts the protons to the surface. These results show the proton reduction due to the electrocatalytic action of gold nanoparticles.

Claims (12)

1) a chamber;
An anode electrode and a cathode electrode disposed inside the chamber in opposition to each other;
An external lead connecting the anode electrode and the cathode electrode;
An anode electrode portion including an active microbe and an organic substance;
A cathode electrode portion including a buffer solution and supplied with air from the outside; And
A cation exchange membrane for separating the chamber into an anode electrode portion and a cathode electrode portion;
Preparing a microbial fuel cell comprising the microbial fuel cell; And
2) replacing the buffer solution of the cathode electrode part with a solution containing a metal precursor after the microbial fuel cell of step 1) has a power density of 30 to 50 mW / m ² ; Wherein the hydrogen and metal nanoparticles are produced by a method comprising the steps of: The method according to claim 1, wherein the anode electrode and the cathode electrode in the step 1) are at least one selected from the group consisting of carbon paper, carbon cloth, carbon felt, The method for producing a microorganism fuel cell for producing hydrogen and metal nanoparticles according to claim 1, The method according to claim 1, wherein in step 1), the anode electrode comprises carbon paper, and the cathode electrode comprises carbon paper coated with a platinum (Pt) catalyst. Gt; The method according to claim 1, wherein the external conductor is a copper wire having an external resistance of 500 to 1500?. The method according to claim 1, wherein the active microorganisms contained in the anode electrode part in step 1) are selected from the group consisting of Rhodoferax ferrireducens, Shewanella putrefaciens, Wherein the microbial fuel cell is at least one microorganism selected from the group consisting of Geobacteraceae sulfurreducens and Geobacter metallireducens. The method according to claim 1, wherein the buffer solution in the cathode electrode part in step 1) is a phosphate buffer solution and air is supplied at 80 to 130 mL / min. The method of claim 1, wherein the solution containing the metal precursor in step 2) comprises HAuCl ₄ . The method according to claim 1, wherein the metal in step 2) is at least one metal selected from the group consisting of Au, Ag, Cu, Ni, Pd, Pt, Zn, Cd, Co, And a method for manufacturing a microbial fuel cell for producing metal nanoparticles. The method of claim 1, wherein the cathode electrode unit is in an anoxic state in step 2). The method according to claim 1, wherein the cathode electrode in step 2) comprises stainless steel. 11. A microbial fuel cell produced by the method of any one of claims 1 to 10. A method for producing hydrogen and metal nanoparticles using the microbial fuel cell according to claim 11.

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