KR20190071222A - Cathode containing copper oxide and transition metal sulfide, Preparation Method thereof, Microbial electrolysis cell containing the same, Wasted water treatment using the same - Google Patents

Abstract

The present invention relates to a reducing electrode comprising copper oxide and transition metal sulfide, a method for manufacturing the same, a microbial electrolysis cell containing the reducing electrode, and a method for treating wastewater. The reducing electrode has transition metal sulfide formed on one side or both sides of a copper oxide layer. When the electrode is applied to a microbial electrolysis cell, the electrode can produce hydrogen with high purity without deteriorating the performance since methane and carbon dioxide gas are generated in a small amount even when operated for a long time.

Description

TECHNICAL FIELD The present invention relates to a reduction electrode comprising copper oxide and transition metal sulfide, a method for producing the same, a microbial electrolysis cell containing the same, and a method for treating wastewater treatment using the same}

The present invention relates to a reducing electrode comprising copper oxide and a transition metal sulfide, a method for producing the same, a microbial electrolysis cell containing the same, and a method for treating wastewater.

Due to the recent lack of renewable fossil fuel reserves, the reuse of renewable resources has attracted much attention. In particular, clean and highly efficient energy sources are being developed around the world to solve environmental pollution problems. Among them, hydrogen energy is considered a clean green energy source to replace fossil fuels. Hydrogen has great potential as a future energy source because it can reduce greenhouse gas emissions that affect climate change as an environmentally clean energy fuel.

In order to increase the energy efficiency of hydrogen production, microbial electrolysis cell (MEC) technology has been attracting attention. Microbial electrolysis cell technology is a technology for converting biodegradable organic materials into hydrogen gas using electrochemically active microorganisms. The mechanism of action of the microbial electrolytic cell is that the organic matter is anaerobically oxidized and the electrons move to the anode and then the electric potential is applied to the circuit so that the electrons move to the cathode, To generate hydrogen gas.

However, currently developed microbial electrolytic cells have a disadvantage in that methane and carbon dioxide gas are generated during operation for a long time and the performance of the electrolytic cell remarkably drops.

Nano Lett. 2010, 10, 4686-4691

An object of the present invention is to provide a reducing electrode in which a transition metal sulfide is formed on one side or both sides of a copper oxide layer to suppress methane and carbon dioxide generation of the electrolysis cell, a method for producing the same, a microbial electrolytic cell containing the same, .

The present invention provides a semiconductor device comprising: a copper oxide layer; And

A transition metal sulfide layer is formed on one or both surfaces of the copper oxide layer,

The copper oxide layer comprises copper oxide in the form of a nanorod,

And the copper oxide has a structure in which an incident angle is dispersed from 0 DEG to 85 DEG with respect to the copper oxide layer.

The present invention also provides a method of manufacturing a copper-clad laminate, comprising: forming a copper oxide layer on a copper substrate by a heat treatment at 400 ° C to 500 ° C; And

And applying a transition metal sulfide aqueous solution to one or both sides of the copper oxide layer to form a transition metal sulfide layer.

In addition, the present invention relates to a reduction electrode according to the present invention; An oxidation electrode on which a biofilm is formed; And a substrate comprising acetate.

The present invention also provides a method for treating wastewater using the microbial electrolytic cell.

The reduction electrode according to the present invention is capable of producing high purity hydrogen without degrading the performance because the transition metal sulfide is formed on one side or both sides of the copper oxide layer to generate methane and carbon dioxide gas even when operated as a microbial electrolysis cell for a long time. .

FIG. 1 is an SEM image of a reduction electrode according to the present invention, wherein (a) is a scanning electron micrograph of a reducing electrode (substrate) on which copper oxide is grown, (b) 3 is a scanning electron micrograph of the dispersed electrode.
2 is a graph of X-ray photoelectron spectroscopic spectroscopy of a reducing electrode according to the present invention.
FIG. 3 (a) is a tau graph of a reducing electrode according to the present invention, and FIG. 3 (b) is a graph of a Mott-Schottky analysis result of a reducing electrode according to the present invention.
FIG. 4 is a graph showing a performance test result of the microbial electrolytic cell according to the present invention. FIG. 4 (a) is a graph showing the amount of generated hydrogen according to an applied voltage, FIG. 5 is a graph showing the hydrogen production rate (H ₂ production rate). FIG.
5 is a schematic view showing a mechanism occurring in the microbial electrolytic cell according to the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail.

It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The present invention relates to a copper oxide layer; And

A transition metal sulfide layer is formed on one or both surfaces of the copper oxide layer,

The copper oxide layer comprises copper oxide in the form of a nanorod,

And the copper oxide has a structure in which an incident angle is dispersed from 0 DEG to 85 DEG with respect to the copper oxide layer.

For example, the reducing electrode according to the present invention comprises a copper oxide layer; And a transition metal sulfide layer in which a transition metal sulfide is dispersed on one surface of the copper oxide layer.

In one example, the copper oxide layer may be in the form of a nano-rod of copper oxide formed, the copper oxide may comprise monovalent copper (Cu ₂ O) and divalent copper (CuO) Specifically, monovalent copper oxide (Cu ₂ O) may be used.

In addition, the copper oxide may have a structure in which the incident angle is dispersed from 0 to 85 degrees with respect to the copper oxide layer in the form of a nano-rod. Specifically, the copper oxide may have a structure in which the angle of incidence is 10 to 70 degrees or 45 to 85 degrees. Copper oxide in the form of nano-rods is dispersed in the above-described manner, and the surface area of the reduction electrode is wide, which is advantageous for generating hydrogen.

In one example, the transition metal sulfide may be molybdenum sulfide or tungsten sulphide. Specifically, the transition metal sulfide may be molybdenum sulfide. When such a transition metal sulfide is included, a hydrogen reduction reaction may actively occur at the reduction electrode. Particularly, when molybdenum sulfide is contained, it can exhibit better physical properties.

The content of the transition metal sulfide may be 0.5 to 5 mg / cm < ² >. Specifically, the content of the transition metal sulfide is 1 to 3 mg / cm ² , 2 to 4 mg / cm ² Or 0.5 to 3 mg / cm < ² >.

In one example, the surface area of the reducing electrode according to the present invention may be between 8 and 15 cm ² / g. Specifically, the surface area of the reducing electrode may be 9 to 12 cm ² / g or 10 to 15 cm ² / g. By having the surface area as described above, hydrogen generation can be advantageous in the reduction electrode.

The present invention also provides a method for manufacturing a copper-clad laminate, comprising: forming a copper oxide layer on a copper substrate by heat treatment at 400 ° C to 500 ° C; And

And applying a transition metal sulfide aqueous solution to one or both sides of the copper oxide layer to form a transition metal sulfide layer.

In one example, the step of forming the copper oxide layer may further include a step of pretreating the copper substrate by carrying it on a mixed solution containing sodium hydroxide and ammonium persulfate before the heat treatment. As described above, the copper substrate may be supported on a mixed solution containing sodium hydroxide and ammonium persulfate to form bivalent copper (Cu (OH) ₂ ] on the copper substrate. After the pre-treatment, the copper substrate on which the copper hydroxide [Cu (OH) ₂ ] is formed may be washed with distilled water at room temperature and dried.

In the step of forming the copper oxide layer, a mixed solution of sodium hydroxide and ammonium persulfate may be prepared by mixing 2 to 3M sodium hydroxide and ammonium persulfate 0.1 to 0.5M.

In one example, the step of forming the copper oxide layer may be a heat treatment at 400 < 0 > C to 500 < 0 > C to form a copper oxide layer on the copper substrate. Specifically, the heat treatment may be performed at a temperature of 400 ° C to 500 ° C or 400 ° C to 500 ° C. When heat treatment is performed as described above, copper oxide (Cu ₂ O) may be formed on the copper substrate, and specifically, monovalent copper oxide (Cu ₂ O) or divalent copper oxide (CuO) may be mixed . More specifically, the monovalent copper oxide may be in a mixed state in an amount of 50% or more or 60 to 80%.

In one example, the transition metal sulfide layer is formed by applying a transition metal sulfide aqueous solution to one or both sides of the copper oxide layer, and the step of forming the transition metal sulfide layer may be performed by a fin coating method, a spray coating method, The transition metal sulfide layer can be formed through any one method selected by vacuum thermal evaporation.

For example, the transition metal sulfide may be a transition metal sulfide such as molybdenum sulfide or tungsten sulfide. Specifically, the transition metal sulfide may be molybdenum sulfide. When such a transition metal sulfide is included, a hydrogen reduction reaction may actively occur at the reduction electrode. Particularly, when molybdenum sulfide is contained, it can exhibit better physical properties.

Further, in the step of forming the transition metal sulfide layer, the transition metal sulfide aqueous solution may include transition metal sulfide, distilled water, isopropanol and Nafion solution, and the concentration of the transition metal sulfide in the transition metal sulfide aqueous solution may be 1.5 to 5 g / L. Specifically, the content of the transition metal sulfide may be 1.8 to 4 g / L or 2 to 3 g / L.

In one example, the method for producing a reducing electrode of the present invention may further include a step of drying at 20 to 25 占 폚 for at least 24 hours after the step of forming the transition metal sulfide layer. Specifically, after forming a transition metal sulfide layer, a reducing electrode can be manufactured by drying at 20 to 25 ° C for 24 hours or more for 24 hours to 48 hours.

In addition, the present invention relates to a reduction electrode according to the present invention;

An oxidized electrode formed with a biofilm; And

The present invention provides a microbial electrolytic cell comprising a substrate containing acetate.

Specifically, the hydrogen generation mechanism of the microbial electrolytic cell of the present invention is illustrated in FIG. Referring to FIG. 5, the oxidation electrode and the reduction electrode are opposed to each other. When a voltage is applied, electrons obtained from the acetate in the oxidation electrode migrate to the reduction electrode, and the hydrogen ions on the substrate are converted into hydrogen gas .

In one example, the microorganism of the present invention, the electrolytic cell, upon application of 0.8 V voltage, the hydrogen generation rate of 2.0 to _{^{3.5 m 3 · H 2 · m}} -3 · d - may be ^one. Specifically, in the microbial electrolytic cell, when a voltage of 0.8 V is applied, the hydrogen generation rate is 2.1 to 3.2 m ³ · H ₂ · m ^-3 · d ^-1 , 2.3 to 3.1 m ³ · H ₂ · m ^-3 · d It may be ^{1 - 1} or from 2.5 to _{^{3.0 m 3 · H 2 · m}} -3 · d.

For example, the microbial electrolytic cell of the present invention can satisfy the following general formula 1:

[Formula 1]

H ₂ / H ₁ > 0.8

In the general formula 1,

H ₁ is the theoretical value of the hydrogen generation volume when a voltage of 0.8 V is applied,

H ₂ is an experimental value of the hydrogen generation volume when a voltage of 0.8 V is applied.

Specifically, in the microbial electrolytic cell of the present invention, the overall hydrogen recovery (γ _{H 2} ) represented by the general formula 1 may be 80% or more, 80% to 95% or 83% to 90%. Specifically, the overall hydrogen recovery (γ _{H 2} ) may be 80 to 88%.

The present invention also provides a method for treating wastewater comprising the steps of charging wastewater into a microbial electrolytic cell according to the present invention and applying a voltage while irradiating light.

In one example, the wastewater treatment method according to the present invention can be performed by applying a voltage of 0.5 to 1.0 V while irradiating light. Specifically, it can be performed by applying a voltage of 0.5 V to 0.9 V or 0.6 to 0.85 V. When wastewater treatment is performed under the above conditions, hydrogen gas may be generated.

For example, the light irradiation can irradiate light having a wavelength of 350 to 850 nm.

Best Mode for Carrying Out the Invention Hereinafter, the present invention will be described in more detail with reference to examples and drawings based on the above description. The following examples are intended to illustrate the invention and are not intended to limit the scope of the invention.

Example  One

The copper substrate (or foil) was carried in an aqueous solution containing 2.5 M sodium hydroxide and 0.125 M ammonium persulfate. At this time, Cu (OH) ₂ was formed on the surface of the copper substrate. The copper substrate supported on the aqueous solution was washed with distilled water, dried at room temperature, and then heated at 450 ° C. for 1 hour to form copper oxide.

A mixed solution of 19.2 mg of molybdenum sulfide, 1.59 ml of distilled water, 6.4 ml of isopropanol and 0.13 ml of a 5% Nafion solution was spray-coated on one side of the substrate with copper oxide to form a molybdenum sulfide layer, cm < ^{2 &} gt ;.

Example  2

A reducing electrode having a molybdenum sulfide content of 3 mg / cm ² was prepared in the same manner as in Example 1 except that a mixed solution of 28.8 mg of molybdenum sulfide, 2.39 ml of distilled water, 9.6 ml of isopropanol and 0.19 ml of a 5% Nafion solution was used.

Example  3

A reducing electrode having a molybdenum sulfide content of 1 mg / cm ² was prepared in the same manner as in Example 1 except that a mixed solution of 9.6 mg of molybdenum sulfide, 0.8 ml of distilled water, 3.2 ml of isopropanol and 0.06 ml of a 5% Nafion solution was used.

Comparative Example  One

Commercial platinum was obtained and used.

Comparative Example  2

Reductive electrodes containing polyaniline nanofibers were fabricated by oxidative polymerization synthesis of aniline at the interface of perchloric acid and methylene chloride.

Comparative Example  3

A reducing electrode containing only copper oxide was prepared in the same manner except that molybdenum sulfide was not formed.

Comparative Example  4

A reducing electrode having a molybdenum sulfide content of 0.5 mg / cm ² was prepared in the same manner as in Example ¹ except that a mixed solution of 4.8 mg of molybdenum sulfide, 0.4 ml of distilled water, 1.6 ml of isopropanol and 0.03 ml of a 5% Nafion solution was used.

Experimental Example  One

The following experiment was conducted to confirm the composition and structure of the reducing electrode according to the present invention.

First, a scanning electron microscope (SEM) analysis and an X-ray photoelectron spectroscopy (XPS) measurement were performed on the reducing electrode prepared in Example 1, and the results are shown in FIG. 1 and FIG.

1 (a) is a scanning electron microscope (SEM) image of a reducing electrode (substrate) on which copper oxide is grown, in which copper oxide in nanofiber form is dispersed and has a large surface roughness and specific surface area have. Also, FIG. 1 (b) shows that the surface roughness of the reducing electrode formed by dispersing molybdenum sulfide dispersed on the copper oxide layer is smaller than that of the reducing electrode formed only of copper oxide.

FIG. 2 is a graph showing the X-ray photoelectron spectroscopy spectrum measurement result of the reducing electrode. As a result, the copper oxide component of the reducing electrode of Example 1 can be identified. FIG Referring to Figure 2, copper oxide substrate prior to the heat treatment is _{Cu 2p 3/2 (Shake-} up satellite) over an area of 940 to 946 eV peak is, and determine a divalent copper ion, specifically, at 933.7 eV and 934.7 eV CuO and Cu (OH) ₂ were found to be 49.0% and 51.0%, respectively. Copper oxide substrate after the heat treatment are respectively Cu ₂ O and CuO at 932.7 eV and 933.7 eV was confirmed at a rate of 78.4% and 21.6%.

Experimental Example 2

In order to evaluate the optical properties and the photoelectrochemical properties of the reduction electrode according to the present invention, a band gap and a Mott-schottky analysis were measured on the reducing electrode of Example 1. The measurement method is as follows, and the results are shown in Fig.

The bandgap measurement method is a method of measuring a band gap of a tau (tau) expressed by a Y-axis expressed by a square root of a value obtained by multiplying an energy value (E) with respect to a wavelength by an energy value with a value obtained by converting a diffuse reflectance (R) into a Kubelka- In the Tauc plot, the straight line near the absorption edge was extended and measured through the point where it meets the X axis.

The Mott-Schottky analysis can be obtained by using electrochemical impedance analysis. The graph shows the applied voltage as the X-axis and the electric capacity of the interface obtained by the applied voltage as the Y-axis in the graph. We measured through the meeting point.

FIG. 3 (a) is a tau graph of the reducing electrode of Example 1, and FIG. 3 (b) is a graph of Mott-Schottky analysis results of the reducing electrode of Example 1. FIG. Referring to FIG. 3 (a), the band gap energy of the reducing electrode of Example 1 is 1.75 eV, which is larger than 1.24 eV, which is the band gap energy of CuO, and less than 2.04 eV, which is the band gap energy of Cu ₂ O. As a result, it can be seen that the proportion of CuO in the copper oxide contained in the reduction electrode is smaller than Cu ₂ O.

Also, referring to FIG. 3 (b), when the region shown by a straight line has a negative slope, it means that the monovalent copper oxide has a p-type semiconductor characteristic with a bend bending phenomenon at the interface. The X-intercept value of 1.16 V represents the energy position of the conduction band and the energy band of -0.59 V (= 1.16 - 1.75 V) can be obtained using the band gap energy of 1.75 V.

Experimental Example  3

In order to evaluate the efficiency of the microbial electrolytic cell including the reducing electrode according to the present invention, a microbial electrolytic cell was prepared for the reducing electrode of Example 1, and the performance test of the microbial electrolytic cell was performed. The measurement method is as follows, and the results are shown in FIG. 4, Table 1 and Table 2.

In the microbial electrolytic cell performance test, the oxidation electrode including the reducing electrode of Example 1 and the biofilm was placed facing the opposite side of the chamber in a 15 ml cube chamber, and a spacer (5 ml ) Were installed. Then, various gases (0.4 to 0.8 V) were applied under the dark condition and the light irradiation condition with the acetate solution (1 g / L) as the substrate. Collected gas was collected and analyzed. When 0.8 V voltage was applied, (Molybdenum sulfide) in the microbial electrolytic cell was also analyzed.

FIG. 4A is a graph showing the amount of generated hydrogen according to the applied voltage, FIG. 4B is a graph showing the total hydrogen recovery (γ _H2 ) and the hydrogen generation rate (H ₂ production rate, Q _H2 ).

Referring to FIG. 4 (a), when the voltage was applied to the microbial electrolytic cell fabricated in Example 1 while light irradiation, the hydrogen ratio was more than 85%. Specifically, when a voltage of 0.4 V was applied, only methane and carbon dioxide gas were generated. When a voltage of 0.6 V was applied, the hydrogen ratio (ratio of the amount of generated hydrogen to the total amount of gas generated) was about 87% The hydrogen ratio was 100% and the hydrogen ratio was remarkably increased. Particularly, when a voltage of 0.8 V was applied, methane and carbon dioxide were not generated even when a long time voltage was applied. Although not shown in the graph, 69% of hydrogen was generated even under the dark condition without light irradiation when a voltage of 0.8 V was applied.

4 (b) and Table 1, the overall hydrogen recovery (γ _H2 ) of the microbial electrolytic cell (light irradiation condition) produced by the reducing electrode of Example 1 was 55.4 %, And was 84.9% when a voltage of 0.8 V was applied. In this case, the overall hydrogen recovery (γ _H2 ) is the ratio of the experimental hydrogen production to the theoretical hydrogen production. On the other hand, the microbial decomposition cell made of the reducing electrode of Comparative Example 2 showed a relatively low hydrogen recovery rate of 79.2% when a voltage of 0.8 V was applied.

The H ₂ production rate (Q _H2 ) of the microbial electrolytic cell fabricated from the reducing electrode of Example 1 was 1.09 m ³ · H ₂ / m ³ · day when a voltage of 0.6 V was applied, and 0.8 V 2.72m at the time of voltage application of ³ · H ₂ / m ³ · day was. In addition, the hydrogen yield (hydrogen yield, Y _H2) in Table 1, to mean the number of moles of hydrogen gas to that produced from one mole of acetate, the number of moles of hydrogen gas that can be produced in the usual one mole of acetate is at most 4 mol . The hydrogen yield of the microbial electrolytic cell fabricated from the reducing electrode of Example 1 was 2.2 when a voltage of 0.6 V was applied and close to 4 moles of hydrogen gas when a voltage of 0.8 V was applied at a voltage of 3.4 at a voltage of 0.8 V .

Further, we can know about the energy efficiency through? _W and? _{W + s} , where? _W is the input power and? _{W + s} is about the input power and the substrate. The eta _w value of the microbial electrolytic cell fabricated from the reducing electrode of Example 1 was 231% at the time of applying a voltage of 0.6 V and increased to 100% at 225% when a voltage of 0.8 V was applied, . In addition, the value of? _{W + s} of the microbial electrolytic cell fabricated from the reducing electrode of Example 1 was 80.7% when a voltage of 0.6 V was applied, and 83.0% when a voltage of 0.8 V was applied, .

Table 2 shows the results of the performance test of the microbial electrolytic cell according to the content of molybdenum sulfide in the reducing electrode by applying a voltage of 0.8 V. As shown in Table 2, the microbial electrolytic cell of Examples 1 to 3 exhibited a hydrogen recovery rate of 48% to 90%, and the hydrogen generation rate H of the microbial electrolytic cell produced by the reduction electrodes of Example 1 and Example 2 ₂ production rate, Q _H2 ) was 2 to ³ m ³ · H ₂ / m ³ · day at a voltage of 0.8 V and Examples 1 to 3 showed a hydrogen yield of 1.9 to 3.4 _H2 ). In particular, the microbial electrolytic cell of Example 1 exhibited a hydrogen recovery rate of 84.9 ± 5.2%, a hydrogen generation rate of 2.72 ± 0.31 m ³ · H ₂ / m ³ · day, and a hydrogen yield of 3.4, Excellent. On the contrary, Comparative Example 2 and Comparative Example 3 showed a hydrogen recovery rate of less than 45%, a hydrogen generation rate of less than 2.1, and a hydrogen yield of less than 1.6, and the microbial electrolysis The efficiency of hydrogen generation was lower than that of batteries. Therefore, it was confirmed that the microbial electrolytic cell including the reducing electrode according to the present invention had excellent hydrogen generation efficiency by controlling the content of molybdenum sulfide.

In addition, the microbial electrolytic cell made of the reducing electrode of Example 1 and Example 2 had an eta _w value of 110 to 240% and a eta _{w + s} value of 60 to 85% when a voltage of 0.8 V was applied, In the microbial electrolytic cell made of the reduction electrodes of Comparative Examples 3 and 4, when the voltage of 0.8 V was applied, the value of eta _w was less than 110% and the value of eta _{w + s} was less than 60% Showed that the microbial electrolytic cell had energy higher than the hydrogen input power and excellent energy efficiency by controlling the content of molybdenum sulfide.

Claims (14)

A copper oxide layer; And
A transition metal sulfide layer is formed on one or both surfaces of the copper oxide layer,
The copper oxide layer comprises copper oxide in the form of a nanorod,
Wherein the copper oxide has a structure in which the angle of incidence is dispersed from 0 DEG to 85 DEG with respect to the copper oxide layer. The method according to claim 1,
Wherein the transition metal sulfide is molybdenum sulfide or tungsten sulfide. The method according to claim 1,
Wherein the content of the transition metal sulfide is 0.5 to 5 mg / cm < ² >. The method according to claim 1,
And the surface area of the reducing electrode is 8 to 15 cm < ² > / g. Subjecting the copper substrate to a heat treatment at a temperature of 400 ° C to 500 ° C to form a copper oxide layer; And
Applying a transition metal sulfide aqueous solution to one side or both sides of the copper oxide layer to form a transition metal sulfide layer. 6. The method of claim 5,
Wherein the step of forming the copper oxide layer comprises, before the heat treatment, carrying the copper substrate in a mixed solution containing sodium hydroxide and ammonium persulfate. 6. The method of claim 5,
Wherein the step of forming the transition metal sulfide layer comprises forming a transition metal sulfide layer by any one method selected from a fin coating method, a spray coating method and a vacuum thermal evaporation method. 6. The method of claim 5,
Wherein the concentration of the transition metal sulfide in the transition metal sulfide aqueous solution in the step of forming the transition metal sulfide layer is 1.5 to 5 g / L. 6. The method of claim 5,
Further comprising, after the step of forming the transition metal sulfide layer, drying at 20 to 25 DEG C for at least 24 hours. A reducing electrode according to claim 1;
An oxidized electrode formed with a biofilm; And
A microbial electrolytic cell comprising a substrate containing acetate. 11. The method of claim 10,
Wherein the electrolysis cell has a hydrogen generation rate of 2.3 to 3.5 m ³ · H ₂ · m ^-3 · d ^-1 when a voltage of 0.8 V is applied. 11. The method of claim 10,
The electrolytic cell satisfies the following general formula (1).
[Formula 1]
H ₂ / H ₁ > 0.8
In the general formula 1,
H _{- 1} is the theoretical value of the hydrogen generation volume when a voltage of 0.8 V is applied,
H ₂ is an experimental value of the hydrogen generation volume when a voltage of 0.8 V is applied. A method for treating wastewater comprising the steps of: injecting wastewater into a microbial electrolytic cell according to claim 10 and applying a voltage while irradiating light. 14. The method of claim 13,
And the applied voltage is 0.5 to 1.0 V.

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