Power generating film and power generation method

Abstract

To provide a power generation film using graphene that is capable of generating a high power generation voltage.SOLUTION: The power generation film comprises graphene oxide flakes having an oxygen content of 50 wt.% or more, and is configured to generate electric power when a power-generating liquid flows over the surface thereof.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a power generation film and a power generation method.

Background Art

[0002] Techniques for using graphene in power generation are known. When a specific liquid flows on the surface of a graphene film, a potential difference is generated in the graphene film. Utilizing this phenomenon, it is expected to use the graphene film as a power generation film.

[0003] As a related art described above, Patent Document 1 (CN105305884A) describes a method for manufacturing an electrical device based on the sliding of a reduced graphene oxide film, including a specific process.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When using graphene as a power generation film, it is desirable to obtain a large power generation voltage. Therefore, an object of the present invention is to provide a power generation film using graphene that can obtain a large power generation voltage.

Means for Solving the Problems

[0006] In one aspect, the present invention relates to a power generation film. This power generation film includes graphene oxide flakes having an oxygen content of 50 wt% or more, and is configured to generate electricity when a power generation liquid flows on its surface.

[0007] In one aspect, the present invention relates to a power generation method. This power generation method includes a step of preparing the above-described power generation film and a step of flowing a power generation liquid on the surface of the power generation film.

Advantages of the Invention

[0008] According to the present invention, there is provided a power generation film using graphene, which can obtain a large power generation voltage.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described.

[0011] FIG. 1 is a diagram schematically showing a power generation device 1 using the power generation film 2 according to the present embodiment. FIG. 1(a) shows the overall configuration of the power generation device 1, and FIG. 1(b) shows the main part of the power generation device 1.

[0012] As shown in FIG. 1, the power generation device 1 has a power generation film 2. The power generation film 2 is disposed, for example, on a substrate. The power generation film 2 contains graphene oxide flakes 4. During power generation, a power generation liquid 3 is supplied onto the surface of the power generation film 2. The power generation liquid 3 is supplied so as to flow on the surface of the power generation film 2. When the power generation liquid flows on the surface of the power generation film 2, an electrical interaction between the power generation liquid 3 and the power generation film 2 causes a charge bias in the power generation film 2. That is, a voltage is generated in the power generation film 2. By utilizing this, the power generation device 1 can be made to function.

[0013] Here, the graphene oxide flakes 4 have an oxygen content of 50 wt% or more. According to the findings of the present inventors, the power generation voltage of the power generation film is related to the oxygen content of the graphene oxide flakes. When graphene oxide flakes having an oxygen content of 50 wt% or more are used, a high power generation voltage can be obtained. The oxygen content of the graphene oxide flakes is more preferably 55 wt% or more. The upper limit of the oxygen content is not particularly limited, but is, for example, 70 wt% or less, or 60 wt% or less.

[0014] (Graphene oxide flakes) The graphene oxide flakes are flaky graphene oxide. Graphene oxide means a substance in which graphene is modified with oxygen-containing functional groups.

[0015] The "oxygen content of the graphene oxide flakes" means the content of oxygen chemically bonded to graphene. The oxygen content of the graphene oxide flakes can be measured by CHNS analysis and XRD analysis using an elemental analyzer. That is, the total amount of oxygen content in the power generation film can be determined by CHNS analysis. In addition, by performing XRD analysis, the amount of oxygen bonded to carbon, that is, the amount of oxygen chemically bonded to graphene, can be determined. Therefore, by combining these, the "oxygen content of the graphene oxide flakes" can be determined.

[0016] The oxygen-containing functional groups contained in the graphene oxide flakes are not particularly limited, and examples thereof include -COH, -OH, -CO, and -COOH. The oxygen-containing functional groups preferably include hydrophilic functional groups. If hydrophilic functional groups are included, when an aqueous liquid is used as the liquid for power generation, the affinity between the power generation membrane and the liquid for power generation increases. Therefore, a high power generation voltage can be easily obtained. As the hydrophilic functional group, a carboxyl group (-COOH) is preferably mentioned. According to the simulation by the present inventor, when graphene is modified with a carboxyl group, the output (power generation voltage) is improved compared to the case where it is modified with other oxygen-containing functional groups.

[0017] The method for preparing graphene oxide flakes having an oxygen content of 50 wt% or more is not particularly limited. Graphene oxide flakes having an oxygen content of 50 wt% or more are known, and for example, commercially available ones can be used.

[0018] The graphene oxide flakes may be single-layer graphene oxide, multi-layer graphene oxide, or a mixture thereof. Preferably, the graphene oxide flakes contain single-layer graphene oxide. Single-layer graphene oxide often has a large oxygen content. Whether it is single-layer graphene oxide or multi-layer graphene oxide can be confirmed by XRD analysis.

[0019] Note that, even if there are small amounts of substances other than graphene oxide flakes in the power generation film 2, it may be acceptable. For example, graphene oxide flakes are usually produced from graphite. Therefore, residual graphite, which is the raw material, may be present in the power generation film 2. However, it is preferable that the main component (50 wt% or more) of the power generation film 2 is "graphene oxide flakes having an oxygen content of 50 wt% or more". More preferably, 90 wt% or more of the components of the power generation film 2 are "graphene oxide flakes having an oxygen content of 50 wt% or more". Even more preferably, 95 wt% or more of the components of the power generation film 2 are "graphene oxide flakes having an oxygen content of 50 wt% or more". Most preferably, 99 wt% or more of the components of the power generation film 2 are "graphene oxide flakes having an oxygen content of 50 wt% or more".

[0020] (Power generation film) As shown in Fig. 1(b), in the power generation film, it is preferable that a plurality of graphene oxide flakes 4 are oriented in the same direction. That is, it is preferable that a plurality of graphene oxide flakes 4 are arranged in parallel. According to the findings of the present inventor, if a plurality of graphene oxide flakes 4 are oriented in the same direction, a high power generation voltage can be obtained. The reason for this will be described with reference to a reference example. Fig. 2 is a schematic diagram showing a power generation film according to the reference example. In the reference example, some graphene oxide flakes 4 are arranged so as to be non-parallel to other graphene oxide flakes. As a result, irregularities are formed on the surface of the power generation film 2. In such a configuration, it becomes difficult for the power generation liquid 3 to flow on the surface of the power generation film 2. Also, in the power generation film 2, the path through which separated charges (ionized electrons and ions) pass is easily blocked. Therefore, the function as a power generation film is easily hindered. On the other hand, as shown in Fig. 1(b), if a plurality of graphene oxide flakes 4 are oriented in the same direction, the power generation liquid 3 can flow smoothly on the surface of the power generation film 2. Also, a path through which ionized electrons and ions pass is easily formed. Therefore, it is considered that high power generation power can be obtained.

[0021] (Void aspect ratio) The orientation of the graphene oxide flakes 4 can be evaluated by the aspect ratio of the voids in the power generation film (hereinafter sometimes simply referred to as the void aspect ratio). That is, if a plurality of graphene oxide flakes are arranged in the same direction, the aspect ratio of the voids formed between adjacent graphene oxide flakes increases. Therefore, it can be said that the higher the void aspect ratio, the higher the orientation, and a higher power generation voltage can be obtained.

[0022] In a preferred embodiment, the median of the void aspect ratio is 1.5 or more. More preferably, the median of the void aspect ratio is 1.8 or more. Even more preferably, the median of the void aspect ratio is 2.0 or more.

[0023] The "median of the void aspect ratio" can be obtained by image analysis of the SEM image. Specifically, a cross-sectional image of the power generation film is acquired by SEM. Then, an area in the range of 60 μm × 40 μm in the acquired image is binarized using software. At this time, the intermediate value between the brightness of the void part and the brightness of the graphene oxide is adopted as the threshold value. Next, from the binarized image, voids of 0.04 μm 2 or more and 80 μm 2 or less are identified. And for each identified void, the aspect ratio is determined. The aspect ratio of each void can be determined by ellipse approximation using commercially available software (Image J, without using a special analysis mode). Specifically, after approximating each void to an ellipse, "length of the major axis / length of the minor axis" can be determined as the aspect ratio. Then, the median of the aspect ratios of all the voids in the area is calculated as the "median of the void aspect ratio".

[0024] (Void fraction) It is preferable that the void fraction of the power generation film is small. The void fraction of the power generation film is, for example, 40% or less, preferably 35% or less, more preferably 30% or less, and most preferably 27% or less. The smaller the void fraction, the higher the power generation voltage that can be obtained.

[0025] The porosity of the power generation film can be determined in the same manner as the method for measuring the median value of the above-described void aspect ratio. That is, the SEM cross-sectional image (60 μm × 40 μm region) of the power generation film is binarized to identify the void portions. Then, the ratio of the area of the void portions to the total area can be determined as the porosity.

[0026] Note that the film thickness of the power generation film is not particularly limited.

[0027] (Method for preparing power generation film) A power generation film having the above-described orientation and porosity can be obtained, for example, by adopting a specific method as described below.

[0028] First, graphene oxide flakes with an oxygen content of 50 wt% or more are prepared. Subsequently, the prepared graphene oxide flakes are put into pure water to obtain a dispersion of the graphene oxide flakes. The content of the graphene oxide flakes in the dispersion is, for example, 3 to 30 wt%, preferably 5 to 15 wt%.

[0029] Subsequently, the obtained dispersion is stirred by ultrasonic waves. Next, the dispersion is applied onto a substrate using an applicator. Subsequently, the obtained sample is dried at a high temperature for a long time. The drying temperature is, for example, 100 to 160°C, preferably 120 to 140°C. The drying time is, for example, 300 minutes or more, preferably 350 minutes or more, and for example, 700 minutes or less, preferably 600 minutes or less. By using such a method, a power generation film having the above-described orientation and porosity can be obtained.

[0030] (Power generation voltage) According to the present embodiment, a power generation film having a power generation voltage of, for example, 2.5 mV or more, preferably 2.7 mV or more, more preferably 3.8 mV or more, and still more preferably 5 mV or more can be realized by measuring by the measurement method described in the examples below.

[0031] (Liquid for power generation) The power generation liquid flowing on the surface of the power generation membrane may be any liquid that can generate a voltage in the power generation membrane, and is not particularly limited. For example, a polar liquid can be used as the power generation liquid. When a polar liquid is used, charge bias is likely to occur on the surface of the power generation membrane. Thereby, a high power generation voltage is likely to be obtained. Examples of the polar liquid include aqueous liquids mainly composed of water. Aqueous liquids are generally preferred because they are stable against participation, decomposition, etc. The aqueous liquid may be pure water. On the other hand, the aqueous liquid may be an ionic liquid containing alkali metal ions, alkaline earth metal ions, or the like. Since these ionic liquids have a high ion density in the liquid, high power generation power is likely to be obtained.

[0032] (Example) Hereinafter, in order to explain the present invention in more detail, examples implemented by the inventor will be described. However, the present invention should not be construed as being limited to the following examples.

[0033] (Example 1) Commercially available graphene oxide flakes were prepared. The oxygen content of the prepared graphene oxide flakes was 58.8 wt%. 10 g of the prepared graphene oxide flakes were put into 90 g of pure water to obtain a dispersion. The obtained dispersion was ultrasonically stirred (28 kHz, 110 W, 10 minutes). After ultrasonic stirring, the dispersion was applied onto a Kapton film (thickness 25 μm) using an applicator. Next, the obtained sample was put into an electric furnace at 130 ° C and held for 480 minutes. Thereby, a power generation membrane according to Example 1 was obtained.

[0034] (Example 2) As the graphene oxide flakes, commercially available graphene oxide flakes having an oxygen content of 50.5 wt% were used as raw materials. In other respects, the same method as in Example 1 was used to obtain a power generation membrane according to Example 2.

[0035] (Comparative Example 1) Commercially available reduced graphene oxide flakes (oxygen content 49.3 wt%) were used as raw materials. In other respects, the same method as in Example 1 was used to obtain a power generation membrane according to Comparative Example 1.

[0036] (Comparative Example 2) As a raw material, commercially available reduced graphene oxide flakes (oxygen content: 39.3 wt%) were used. A power generation film according to Comparative Example 2 was obtained in the same manner as in Example 1 except for other points.

[0037] (Example 3) Similar to Example 1, graphene oxide flakes having an oxygen content of 58.8 wt% were used as a raw material to prepare a dispersion, and ultrasonic stirring was performed. However, instead of coating with an applicator, a spray gun was used. That is, the dispersion was applied onto a Kapton film (thickness: 25 μm) heated to 100° C. using a spray gun. Then, the obtained sample was held in an electric furnace at 130° C. for 30 minutes. Thereby, a power generation film according to Example 3 was obtained.

[0038] (Porosity and Void Aspect Ratio) For Example 1 and Example 3, the porosity and the median value of the void aspect ratio were measured. The results are shown in Table 1. In addition, FIG. 3 shows the SEM image obtained for Example 1 and its binarized image. Further, FIG. 4 shows the SEM image obtained for Example 3.

[0039] (Power Generation Voltage Measurement) For each of the obtained samples, the power generation voltage was measured. Figure 5 is a schematic diagram showing the method for measuring the power generation voltage. As shown in Figure 5(a), an acrylic plate was prepared. Also, the shape of the power generation film was adjusted to a rectangle of 20 mm × 70 mm. Current collecting foils (made of copper or aluminum) were connected to both ends of the power generation film and placed on the acrylic plate. Then, as shown in Figure 5(b), the acrylic plate was held at an angle of 45° with respect to the horizontal direction. Specifically, the acrylic plate was tilted so that the longitudinal direction of the power generation film was in the vertical direction. As shown in Figure 5(a), in the acrylic plate, the supply position of the power generation liquid was set at a position 15 mm above the upper end in the longitudinal direction of the power generation film. A 1M-LiCl aqueous solution with a liquid temperature of 25°C was prepared as the power generation liquid. The prepared power generation liquid was supplied to the set supply position, and the power generation liquid was made to flow on the power generation film. The supply liquid volume per time was set to 150 ml. Then, the power generation voltage generated in the power generation film was measured via the current collecting foil. This measurement was performed 5 times, and the average value was taken as the result of the power generation voltage. The measurement results are shown in Table 1.

[0040] (Results and Discussion) As shown in Table 1, the power generation voltage was higher in the order of Example 1, Example 2, Comparative Example 1, and Comparative Example 2. From this, it can be understood that the higher the oxygen content of the graphene oxide flakes, the higher the power generation power that can be obtained. And it can be seen that when the oxygen content is 50 wt% or more, a particularly high power generation voltage can be realized.

[0041] When comparing Example 1 and Example 3, the power generation voltage of Example 1 was higher. And the median value of the aspect ratio of the voids in Example 1 was higher, and the porosity was smaller. From this, it was found that the larger the median value of the aspect ratio of the voids, the higher the power generation voltage that can be obtained. Also, it was found that the smaller the porosity, the higher the power generation voltage that can be obtained. Furthermore, it was found that the median value of the aspect ratio of the voids, the porosity, etc. change depending on the manufacturing method (coating method) of the power generation film.

[0042] [Table 1]

[0043] The main configurations and effects included in the present invention are summarized below as appendices.

[0044] (Appendix 1) A power generation film containing graphene oxide flakes having an oxygen content of 50 wt% or more, and configured such that the surface generates electricity when a liquid for power generation flows thereon. According to such a configuration, a high power generation voltage can be obtained.

[0045] (Appendix 2) The power generation film according to Appendix 1, wherein the graphene oxide flakes have an oxygen content of 55 wt% or more. According to such a configuration, a higher power generation voltage can be obtained.

[0046] (Appendix 3) The power generation film according to any one of Appendices 1 to 2, wherein the graphene oxide flakes have hydrophilic functional groups. According to such a configuration, a higher power generation voltage can be obtained.

[0047] (Appendix 4) The power generation film according to Appendix 3, wherein the hydrophilic functional groups include carboxyl groups. According to such a configuration, a higher power generation voltage can be obtained.

[0048] (Appendix 5) The power generation film according to any one of Appendices 1 to 4, wherein the median value of the void aspect ratio is 1.3 or more. According to such a configuration, a high power generation voltage can be obtained.

[0049] (Appendix 6) The power generation film according to any one of Appendices 1 to 5, wherein the median value of the void aspect ratio is 1.8 or more. According to such a configuration, a higher power generation voltage can be obtained.

[0050] (Appendix 7) The power generation film according to any one of Supplementary Notes 1 to 6, wherein the graphene oxide flakes include single-layer graphene oxide or multi-layer graphene oxide. According to such a configuration, a higher power generation voltage can be obtained.

[0051] (Supplementary Note 8) A power generation method comprising the steps of preparing a power generation film according to any one of Supplementary Notes 1 to 7, and flowing a power generation liquid on the surface of the power generation film. According to such a method, a high power generation voltage can be obtained.

Explanation of Reference Signs

[0052] 1 ··· Power generation device, 2 ··· Power generation film, 3 ··· Power generation liquid, 4 ··· Graphene oxide flakes

Claims

1. comprising graphene oxide flakes having an oxygen content of 50 wt% or more, configured such that electricity is generated when a liquid for power generation flows over the surface, a power generation membrane.

2. The power generation membrane according to Claim 1, wherein the graphene oxide flakes have an oxygen content of 55 wt% or more, a power generation membrane.

3. The power generation membrane according to Claim 1 or 2, wherein the graphene oxide flakes have hydrophilic functional groups, a power generation membrane.

4. The power generation membrane according to Claim 3, wherein the hydrophilic functional groups include carboxyl groups, a power generation membrane.

5. The power generation membrane according to Claim 1 or 2, having a median void aspect ratio of 1.5 or more, a power generation membrane.

6. The power generation membrane according to Claim 1 or 2, having a median void aspect ratio of 1.8 or more, a power generation membrane.

7. The power generation membrane according to Claim 1 or 2, wherein the graphene oxide flakes include single-layer graphene oxide or multi-layer graphene oxide, a power generation membrane.

8. A power generation method comprising the steps of preparing the power generation membrane according to Claim 1 or 2, and flowing a liquid for power generation over the surface of the power generation membrane. a power generation method.

Images