Abstract:
Disclosed is a triboelectric energy harvester including an electrolyte solution comprising an electrolyte, and a friction material layer configured to contact the electrolyte solution, wherein the friction material layer is configured to be used as an electrode, and wherein frictional electricity is generated in response to the electrolytic solution contacting the friction material layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit under 35 USC 119(a) of Korean Patent Application No. 10-2015-0029584, filed on Mar. 3, 2015 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The following description relates to method and apparatus for a triboelectric energy harvester capable of generating triboelectricity by using an electrolyte. 
         [0004]    2. Description of Related Art 
         [0005]    Generally, a triboelectric energy harvester operating on friction is a new type of eco-friendly energy harvesting device that can infinitely extract electrical energy not by using the other existing eco-friendly energies, such as solar energy, wind power and fuel cells, but by using mechanical energy that is generated but wasted in our daily life, such as micro-vibration or human motion. The energy conversion using the triboelectric effect has a superior conversion efficiency while ensuring a compact and lightweight structure, and is recognized as a new technology capable of leading to a great leap in technology through fusion with nanotechnology. The triboelectric energy harvester for harvesting an energy using a static electricity caused by friction generates energy from a difference in electrostatic charges that is caused by contact and separation of two materials. 
         [0006]    In the recent years, the triboelectric energy harvester has garnered a large amount of attention, but there is a limitation in which the characteristics of the frictional electricity are specified by the friction material selected based on the triboelectric series. That is, unless a selected friction material is changed into another friction material, the quantity of electric charge induced on one friction material is limited, which causes difficulty in increasing the magnitude of triboelectric energy to be generated. 
         [0007]    In order to improve the above constraint, there is provided a development of a triboelectric energy harvester capable of generating a greater triboelectric energy when compared to using the generally known friction material, by using new material other than the materials disclosed in the triboelectric series, and capable of controlling the magnitude of triboelectric energy to be generated. 
       SUMMARY 
       [0008]    This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
         [0009]    The following description is directed to a triboelectric energy harvester using an electrolyte, capable of generating a greater triboelectric energy when compared to using the materials disclosed in the existing triboelectric series, and capable of adjusting the triboelectric energy to be generated, by controlling the type and the concentration of the electrolyte. 
         [0010]    The following description is not limited to the purposes described above, and other purposes not described above can be understood to the skilled in the art through the description in this disclosure. 
         [0011]    According to an aspect of the following description, there is provided a triboelectric energy harvester including an electrolyte solution comprising an electrolyte, and a friction material layer configured to contact the electrolyte solution, wherein the friction material layer is configured to be used as an electrode, and wherein frictional electricity is generated in response to the electrolytic solution contacting the friction material layer. 
         [0012]    The triboelectric energy harvester may further include a drawing part electrically connected to the friction material layer and a ground. 
         [0013]    The electrolyte includes at least one selected from the group consisting of sodium chloride (NaCl), sodium hydroxide (NaOH), sodium hydrogen carbonate (NaHCO 3 ), silver nitrate (AgNO 3 ), potassium chloride (KCl), potassium carbonate (K 2 CO 3 ), sodium carbonate (Na 2 CO 3 ), potassium hydroxide (KOH), calcium chloride (CaCl 2 ), barium chloride (BaCl 2 ), potassium bromide (KBr), calcium hydrogen carbonate (CaHCO 3 ), potassium iodide (KI), phosphoric acid (H 3 PO 4 ), sulfuric acid (H 2 SO 4 ), magnesium hydroxide (Mg(OH) 2 ), and calcium hydroxide (Ca(OH) 2 ). 
         [0014]    The electrolyte solution may further include a polymer material. 
         [0015]    The polymer material may include at least one selected from the group consisting of polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyphenylene oxide (PPO), polyester, a polyamine and a polysulfide. 
         [0016]    The charging characteristics of the friction material layer and the electrolyte solution may be mutually changed according to a concentration of the electrolyte. 
         [0017]    The charging characteristics of the friction material layer and the electrolyte solution may be mutually changed according to the type of the electrolyte. 
         [0018]    The triboelectric energy harvester may further include an energy storage part connected to the drawing part and to the friction material layer. 
         [0019]    The triboelectric energy harvester may include that in response to the electrolyte having weight percents of phosphoric acid H 3 PO 4 , 0 wt % and 5 wt %, the initial voltage and the initial current, at an initial state of about −2 seconds, have negative values, and in response to the electrolyte weight percents of H 3 PO 4 , 10 wt % and 20 wt %, the initial voltage and the initial current have positive values. 
         [0020]    The triboelectric energy harvester may include that in response to each of the electrolyte and the polymer material having a weight percent of 10 wt % and the electrolyte is sulfuric acid H 2 SO 4 , a positive voltage of about 1.4V and a positive current of about 0.15 μA are measured. 
         [0021]    The triboelectric energy harvester may include that in response to the electrolyte being phosphoric acid H 3 PO 4 , a positive voltage of about 1.7V and a positive current of about 0.23 μA are measured. 
         [0022]    According to another aspect of the following description, there is provided a triboelectric energy including an electrolyte solution comprising an electrolyte, an electrode, and a friction material layer disposed on the electrode and configured to contact the electrolyte solution, wherein frictional electricity is generated in response to the electrolytic solution contacting the friction material layer. 
         [0023]    The triboelectric energy harvester may further include a drawing part electrically connected to the electrode and a ground. 
         [0024]    The triboelectric energy harvester may further include an energy storage part connected to the drawing part and to the electrode. 
         [0025]    According to another aspect of the following description, there is provided a triboelectric energy including an electrolyte layer comprising a polymer material and an electrolyte, and a friction material layer configured to contact the electrolyte solution, wherein each of the frictional material and the electrolyte layer is configured to be used as an electrode, and wherein frictional electricity is generated in response to contact and separation between the frictional material layer and the electrolytic layer being repeated. 
         [0026]    The triboelectric energy harvester may further include a drawing part electrically connected to the friction material layer, the electrolyte layer and to ground. 
         [0027]    The triboelectric energy harvester may further include an energy storage part connected to the friction material layer and the electrolyte layer. 
         [0028]    According to another aspect of the following description, there is provided a triboelectric energy including an electrolyte layer comprising a polymer material and an electrolyte, a first electrode, a friction material layer disposed on the first electrode and configured to contact the electrolyte, and a second electrode formed on the electrolyte layer, wherein frictional electricity is generated in response to contact and separation between the frictional material layer and the electrolytic layer being repeated. 
         [0029]    The triboelectric energy harvester may further include a drawing part electrically connected to the first electrode, the second electrode, and to ground. 
         [0030]    The triboelectric energy harvester may further include an energy storage part connected to the drawing part. 
         [0031]    Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    The above and other objects, features and advantages of the following description will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, in which: 
           [0033]      FIG. 1  is a concept diagram illustrating a triboelectric energy harvester using an electrolyte in accordance with an example embodiment; 
           [0034]      FIG. 2  is a concept diagram illustrating a triboelectric energy harvester using an electrolyte in accordance with an example embodiment; 
           [0035]      FIG. 3  is a concept diagram illustrating a principle of how an electrical energy is generated in a triboelectric energy harvester using an electrolyte in accordance with an example embodiment; 
           [0036]      FIG. 4  is a concept diagram illustrating a triboelectric energy harvester using an electrolyte in accordance with an example embodiment; 
           [0037]      FIG. 5  is a concept diagram illustrating a triboelectric energy harvester using an electrolyte in accordance with an example embodiment; 
           [0038]      FIG. 6  is a graph showing that charging characteristics of a friction material layer and an electrolyte layer are changed according to the concentration of an electrolyte in a triboelectric energy harvester using an electrolyte in accordance with an example embodiment; 
           [0039]      FIG. 7  is a graph showing that the magnitude of frictional electricity to be generated is changed according to the type of an electrolyte in a triboelectric energy harvester using an electrolyte in accordance with an example embodiment; 
           [0040]      FIG. 8  is a drawing illustrating a triboelectric energy harvester using an electrolyte in accordance with an example embodiment and a triboelectric energy harvester using a material disclosed in the existing triboelectric series; 
           [0041]      FIG. 9  is graphs obtained by measuring voltages generated from a triboelectric energy harvester using an electrolyte in accordance with an example embodiment and a triboelectric energy harvester using a material disclosed in the existing triboelectric series; and 
           [0042]      FIG. 10  is a graph obtained by measuring voltages and currents generated from a triboelectric energy harvester using an electrolyte in accordance with an example embodiment and a triboelectric energy harvester using a material disclosed in the existing triboelectric series. 
       
    
    
     DETAILED DESCRIPTION 
       [0043]    The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. However, after an understanding of the disclosure, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein will be apparent to one of ordinary skill in the art. The sequences of operations described herein are merely examples, and are not limited to those set forth herein, but may be changed as will be apparent to one of ordinary skill in the art, with the exception of operations necessarily occurring in a certain order. Also, descriptions of functions and constructions that may be well known to one of ordinary skill in the art may be omitted for increased clarity and conciseness. 
         [0044]    Hereinafter, example embodiments of the following description will be described in detail with reference to the accompanying drawings. The same reference numerals are used to designate the same elements throughout the drawings. 
         [0045]      FIG. 1  is a concept diagram illustrating a triboelectric energy harvester using an electrolyte in accordance with an example embodiment. 
         [0046]    Referring to  FIG. 1 , a triboelectric energy harvester  1000  using an electrolyte in accordance with an example embodiment includes a friction material layer  110 , an electrolyte solution  120 , a drawing part  130  and an energy storage part  140 . 
         [0047]    The friction material layer  110  is a layer composed of friction material, for example, Teflon. The friction material may be selected from the generally known triboelectric series. The selected friction material is a material that may be charged with a polarity opposite to that of an electrolyte solution  120  when the friction material layer  110  is in contact with the electrolyte solution  120 . The friction material may be varied according to the charging characteristics of the electrolyte solution  120 . In addition, when the friction material layer  110  has electrical conductivity, the friction material layer  110  may be used as an electrode. 
         [0048]    The electrolyte solution  120  may include an electrolyte, and may be manufactured by dissolving an electrolyte into a solvent, such as water. For example, the electrolyte may include at least one selected from the group consisting of sodium chloride (NaCl), sodium hydroxide (NaOH), sodium hydrogen carbonate (NaHCO 3 ), silver nitrate (AgNO 3 ), potassium chloride (KCl), potassium carbonate (K 2 CO 3 ), sodium carbonate (Na 2 CO 3 ), potassium hydroxide (KOH), calcium chloride (CaCl 2 ), barium chloride (BaCl 2 ), potassium bromide (KBr), calcium hydrogen carbonate (CaHCO 3 ), potassium iodide (KI), phosphoric acid (H 3 PO 4 ), sulfuric acid (H 2 SO 4 ), magnesium hydroxide (Mg(OH) 2 ), and calcium hydroxide (Ca(OH) 2 ). 
         [0049]    The electrolyte solution  120  may be dropped onto the friction material layer  110 . For example, the electrolyte solution  120  may be dropped onto the friction material layer  110  by using a dropper (Spoid), such that the electrolyte solution  120  in the form of droplets contacts the friction material layer  110 . At the moment that the electrolyte solution  120  comes into contact with the friction material layer  110 , the electrolyte solution  120  and the friction material layer  110  may be charged with opposite polarities to each other. It should be noted that in order to resolve the imbalance in charges, a transfer of charges occurs between the electrolyte solution  120  and the friction material layer  110 . By repeatedly dropping the electrolyte solution  120  onto the friction material layer  11 , generation of electrical energy can be continuous. 
         [0050]    In addition, the charging characteristics of the friction material layer  110  and the electrolyte solution  120  may be changed according to the concentration of the electrolyte in the electrolyte solution  120 . In addition, the charging characteristics of the friction material layer  110  and the electrolyte solution  120  may be changed according to the type of the electrolyte in the electrolyte solution  120 . The concentration of and type of the electrolyte in the electrolyte solution  120  may be varied in consideration of the type of material constituting the friction material layer  110 . 
         [0051]    In addition, the electrolyte solution  120  may further include a polymer material, and in this case, the electrolyte solution  120  shown in  FIG. 1  may be cured to form a single layer. The polymer material comprises at least one selected from the group consisting of polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyphenylene oxide (PPO), polyester, a polyamine and a polysulfide. Description thereof will be made below with reference to  FIG. 3 . 
         [0052]    The method of curing the electrolyte solution  120  may be achieved by maintaining the electrolyte solution  120  at the room temperature so as to gradually evaporate the solvent, or in the alternative, by heating the electrolyte solution  120  to evaporate the solvent. 
         [0053]    The drawing part  130  has one end electrically connected to the friction material layer  110  for transfer of the charges, and the other end grounded. For example, the drawing part  130  may be provided using a wire. One end of the wire is electrically connected to the friction material layer  110  and the other end is grounded. The drawing part  130  may be provided using various materials as long as it allows the transfer of charges. 
         [0054]    In addition, the energy storage part  140  may be connected to the drawing part  130  and configured to store the electrical energy generated by the transfer of charges. The energy storage part  140  may be provided using a general storage battery. In addition, a load connected to the drawing part  130  may be provided with an electrical energy from the general storage battery for operating the load. 
         [0055]      FIG. 2  is a concept diagram illustrating a triboelectric energy harvester using an electrolyte in accordance with an example embodiment. 
         [0056]    Referring to  FIG. 2 , a triboelectric energy harvester  2000  using an electrolyte in accordance with an example embodiment includes an electrode  150 , a friction material layer  110 , an electrolyte solution  120 , a drawing part  130  and an energy storage part  140 . The triboelectric energy harvester  2000  is provided by adding the electrode  150  to the triboelectric energy harvester  1000  described with reference to  FIG. 1 , and has the same components as those of the triboelectric energy harvester  1000 . However, the electrode  150  is disposed below the friction material layer  110  and the drawing part  210  is electrically connected to the electrode  150 . 
         [0057]    The details of the drawing part  210  is similar to the drawing part  130  of the triboelectric energy harvester  1000  except the drawing part  210  has one end electrically connected to the electrode  150  for transfer of the charges, and the other end grounded. The other details of the friction material layer  110 , the electrolyte solution  120 , and the energy storage part  140  are described with reference to  FIG. 1 . 
         [0058]      FIG. 3  is a concept diagram illustrating a principle of how an electrical energy is generated in a triboelectric energy harvester using an electrolyte in accordance with an example embodiment. 
         [0059]    Referring to  FIG. 3 , when the electrolyte solution  120  is dropped on the triboelectric energy harvester  2000 , the electrolyte solution  120 , for example, raindrops, may be charged positively (+). When the electrolyte solution  120  contacts the friction material layer  110  which is electrically neutral, an interface at a region at which the electrolyte solution  120  contacts the friction material layer  110  is negatively charged (−) to offset the positive charges (+) of the electrolyte solution  120 . Accordingly, the electrode  150  is positively charged (+). In order to overcome the charge imbalance of the electrode  150  charged positively (+), negative charges (−) are transferred to the electrode  150 , thereby generating an electrical energy. 
         [0060]      FIG. 4  is a concept diagram illustrating a triboelectric energy harvester using an electrolyte in accordance with an example embodiment. 
         [0061]    Referring to  FIG. 4 , a triboelectric energy harvester  3000  using an electrolyte in accordance with an example embodiment includes a friction material layer  110 , an electrolyte layer  122 , a drawing part  220 , and an energy storage part  140 . 
         [0062]    The electrolyte layer  122  may include a polymer material and an electrolyte, and the electrolyte layer  122  may be formed by evaporating a solvent in the electrolyte solution  120  including the polymer material described with reference to  FIG. 1 . In order to generate electrical energy using the electrolyte solution  120 , there is need to continuously drop the electrolyte solution  120 , whereas as for the electrolyte layer  122 , there is a need to repeat contact and separation of the electrolyte layer  122  and the friction material layer  110  to generate electrical energy. 
         [0063]    When each of the electrolyte layer  122  and the friction material layer  110  has electrical conductivity, each of the electrolyte layer  122  and the friction material layer  110  may be used as an electrode. 
         [0064]    When the electrolyte layer  122  and the friction material layer  110  contact each other, the electrolyte layer  122  and the friction material layer  110  may be charged with opposite polarities to each other, and a friction material constituting the friction material layer  110  may be selected from the generally known triboelectric series. The friction material may be selected as a material that is charged with a polarity opposite to that of the electrolyte layer  122  upon contact with the electrolyte layer  122 , and the friction material may be varied according to a charging characteristic of the electrolyte solution  120 . The triboelectric energy harvester  3000  according to the an example embodiment has the same construction as that described above except for using the electrolyte layer  122  that is provided in the form of a solid changed from the electrolyte solution  120  in the form of a liquid. 
         [0065]    The details of the drawing part  220  is similar to the drawing part  130  of the triboelectric energy harvester  1000  except the drawing part  220  is electrically connected to the electrolyte layer  122  and the friction material layer  110  for transfer of the charges at one end, and the other end grounded. The other details of the friction material layer  110 , and the energy storage part  140  are described with reference to  FIG. 4  and  FIG. 1 . 
         [0066]      FIG. 5  is a concept diagram illustrating a triboelectric energy harvester using an electrolyte in accordance with an example embodiment. 
         [0067]    Referring to  FIG. 5 , a triboelectric energy harvester  4000  using an electrolyte in accordance with an example embodiment includes a first electrode  150 , a friction material layer  110 , an electrolyte layer  122  and a second electrode  160 . The triboelectric energy harvester  4000  using an electrolyte in accordance with an example embodiment has the same construction as that described with reference to  FIG. 3  except that the friction material layer  110  is disposed on the first electrode  150 , the second electrode  160  is disposed on the electrolyte layer  122 . Additionally, the first electrode  150  and the second electrode  160  are electrically connected to each other through the drawing part  130 . 
         [0068]    The details of the drawing part  230  is similar to the drawing part  130  of the triboelectric energy harvester  1000  except the drawing part  230  is electrically connected to first electrode  150  and the second electrode  160  for transfer of the charges at one end, and the other end grounded. The other details of the energy storage part  140  are described with reference to  FIG. 1 . 
         [0069]      FIG. 6  is a graph showing that charging characteristics of a friction material layer and an electrolyte layer are changed according to the concentration of an electrolyte in a triboelectric energy harvester using an electrolyte in accordance with the above example embodiments. The electrolyte may be implemented using phosphoric acid H 3 PO 4 . 
         [0070]    Referring to  FIG. 6 , when measurements are performed at respective weight percents of phosphoric acid H 3 PO 4  (0 wt % and 5 wt %), the initial voltage and the initial current (at an initial state of about −2 seconds) have negative values, but at the increased weight percents of H 3 PO 4  (10 wt % and 20 wt %), the initial voltage and the initial current have positive values. Therefore, the charging characteristics of the friction material layer and the electrolyte layer are changed by changing the concentration of the electrolyte. 
         [0071]      FIG. 7  is a graph showing that the magnitude of frictional electricity to be generated is changed according to the type of an electrolyte in a triboelectric energy harvester using an electrolyte in accordance with an example embodiment, an experiment of which is performed by using the triboelectric energy harvester  2000  described with reference to  FIG. 2 . 
         [0072]    Referring to  FIG. 7 , when each of the electrolyte and the polymer material has a weight percent of 10 wt % and the electrolyte is sulfuric acid H 2 SO 4 , a positive voltage of about 1.4V and a positive current of about 0.15 μA are measured. When the electrolyte is phosphoric acid H 3 PO 4 , a positive voltage of about 1.7V and a positive current of about 0.23 μA are measured. Therefore, the magnitude of electrical energy to be generated may be changed by changing the type of an electrolyte. 
         [0073]      FIG. 8  is a drawing illustrating a triboelectric energy harvester using an electrolyte in accordance with an example embodiment and a triboelectric energy harvester using a material disclosed in the existing triboelectric series. The left side of  FIG. 8  shows a triboelectric energy harvester using an electrolyte in accordance with the above example embodiments, and the right side of  FIG. 8  shows a triboelectric energy harvester using a material disclosed in the existing triboelectric series. 
         [0074]    Referring to  FIG. 8 , according to the triboelectric energy harvester using an electrolyte in accordance with the above example embodiments (experimental example), a friction material layer composed of polyamide 6-6 is disposed on an electrode composed of gold (Au). In addition, an electrolyte layer composed of a polymer and an electrolyte (phosphoric acid H 3 PO 4 ) is disposed above the friction material layer, and an electrode composed of aluminum (Al) is disposed on the electrolyte layer. Oscilloscope  800  may be used to measure the positive (+) and negative (−) charge of the triboelectric energy harvester using an electrolyte in accordance with the above example embodiments. 
         [0075]    The triboelectric energy harvester using a material disclosed in the existing triboelectric series (a comparison example) has the same construction as the experimental example except that the electrolyte layer is replaced with a friction material layer composed of Teflon (polytetrafluoroethylene (PTFE)). Teflon (PTFE) is a material having the largest negative polarity in the triboelectric series. Oscilloscope 810 may be used to measure the positive (+) and negative (−) charge of the triboelectric energy harvester using a material disclosed in the existing triboelectric series. 
         [0076]      FIG. 9  is graphs obtained by measuring voltages generated from a triboelectric energy harvester using an electrolyte in accordance with the above example embodiments and a triboelectric energy harvester using a material disclosed in the existing triboelectric series. The graph shown on the left side of  FIG. 9  measures a voltage of the experimental example, and the graph shown on the right side of  FIG. 9  measures a voltage of the comparison example. 
         [0077]    Referring to  FIG. 9 , the magnitude of a voltage of the experimental example is significantly greater than that of a voltage of the comparison example. That is, the electrolyte layer including phosphoric acid H 3 PO 4  has a negative polarity greater than using the Teflon (PTFE), which has the largest negative polarity in the triboelectric series. Accordingly, it is proved that the triboelectric energy harvester using an electrolyte in accordance with example embodiments generate frictional electricity that is significantly greater than that generated using material disclosed in the triboelectric series, by using the electrolyte. 
         [0078]      FIG. 10  is a graph obtained by measuring voltages and currents generated from a triboelectric energy harvester using an electrolyte in accordance with the above example embodiments and a triboelectric energy harvester using a material disclosed in the existing triboelectric series. 
         [0079]    The triboelectric energy harvester using a material disclosed in the existing triboelectric series is manufactured by replacing the PTFE and the polyamide 6-6 of the structure shown in the right side of  FIG. 8  with nylon and PVA, respectively. 
         [0080]    In addition, the triboelectric energy harvester using an electrolyte in accordance with the above example embodiments is manufactured by replacing the PTFE and the polyamide 6-6 of the structure shown in the right side of  FIG. 8  with nylon and an electrolyte layer, including PVA and an electrolyte (sodium chloride NaCl 2 ), respectively, in which the measurements are performed at electrolyte molarities of 0.5 mol and 1 mol. 
         [0081]    Referring to  FIG. 10 , the graph shown on the left side of  FIG. 10  measures a voltage and a current of the triboelectric energy harvester using a material disclosed in the existing triboelectric series, that is, using PVA and nylon. The graphs shown on the middle and right side of  FIG. 10  measure, with the electrolyte molarities at 0.5 mol and 1 mol, respectively, a voltage and a current of the triboelectric energy harvester in accordance with the above example embodiment. 
         [0082]    As for the triboelectric energy harvester using PVA and nylon, the first voltage peak and the first current peak appearing at around −1.7 seconds have negative values. Meanwhile, as for the triboelectric energy harvester using nylon and the electrolyte layer including PVA and an electrolyte (sodium chloride NaCl 2 ), the first voltage peak and the first current peak at around −1.7 seconds have positive values. That is, by including the electrolyte and PVA, the electrolyte layer provides a further positive polarity than using nylon, which has the largest positive polarity on the existing triboelectric series. Accordingly, it is proved that the triboelectric energy harvester using an electrolyte generates a triboelectric energy that is significantly greater than that generated using the material disclosed in the existing triboelectric series, by using the electrolyte. In addition, as the concentration of electrolyte is higher, the voltage and current generated are increased. Accordingly, the magnitude of triboelectric energy being generated is adjusted by adjusting the concentration of electrolyte. 
         [0083]    As is apparent from the above, a greater triboelectric energy can be generated when compared to using the materials disclosed in the existing triboelectric series. 
         [0084]    In addition, charging characteristics of a friction material layer and an electrolyte solution or electrolyte layer including an electrolyte can be changed by controlling the type and the concentration of the electrolyte. 
         [0085]    While this disclosure includes specific examples, it will be apparent to one of ordinary skill in the art that various changes in form and details may be made in these examples without departing from the spirit and scope of the claims and their equivalents. The examples described herein are to be considered in a descriptive sense only, and not for purposes of limitation. Descriptions of features or aspects in each example are to be considered as being applicable to similar features or aspects in other examples. Suitable results may be achieved if the described techniques are performed in a different order, and/or if components in a described system, architecture, device, or circuit are combined in a different manner, and/or replaced or supplemented by other components or their equivalents. Therefore, the scope of the disclosure is defined not by the detailed description, but by the claims and their equivalents, and all variations within the scope of the claims and their equivalents are to be construed as being included in the disclosure.