Patent Publication Number: US-2009226776-A1

Title: Hydrogen charging apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2008-0020084, filed on Mar. 4, 2008, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Aspects of the present invention relate to a hydrogen charging apparatus that generates hydrogen for fuel in an electricity generation reaction in a fuel cell and stores the hydrogen in a storage medium. 
     2. Description of the Related Art 
     A fuel cell is an electrochemical conversion device that changes the chemical energy of a fuel into electrical energy through a chemical reaction. When air including oxygen is supplied to a cathode and hydrogen as fuel is supplied to an anode of the fuel cell, electricity is generated by a reverse reaction of water electrolysis through an electrolyte membrane. In order to maintain such an electricity generation reaction, hydrogen as fuel is generally maintained in an appropriate storage medium in the fuel cell. 
     Recently, in line with the developments to use fuel cells in mobile devices, a solid hydrogen storage medium that has a relatively small volume and can be readily operated has drawn attention for use as a storage medium in which hydrogen is charged, instead of using a large storage container, such as a pressure container. The solid hydrogen storage medium is formed of an alloy that can store hydrogen. At an appropriate pressure and temperature condition for charging hydrogen, the solid hydrogen storage medium stores hydrogen by adsorption, for example, and discharges the hydrogen when an appropriate pressure and temperature condition for discharging the hydrogen is achieved. 
     Thus, if the appropriate pressure and temperature conditions are satisfied, the storage and discharge of hydrogen, i.e., charging and discharging hydrogen, can be readily performed. 
     SUMMARY OF THE INVENTION 
     Aspects of the present invention provide a hydrogen charging apparatus having a hydrogen storage medium that can readily store and discharge hydrogen. 
     According to an aspect of the present invention, there is provided a hydrogen charging apparatus comprising a hydrogen generation unit that generates hydrogen, a hydrogen charging unit that charges hydrogen to a hydrogen storage medium, and a cooling unit that cools the hydrogen storage medium. 
     According to an aspect of the present invention, the hydrogen storage medium may be a solid hydrogen storage medium formed of one selected from a metal hydride, a complex metal hydride, a carbon group material, and a non-carbon material. 
     According to an aspect of the present invention, the cooling unit may be installed in the hydrogen charging unit and may perform a cooling function using one selected from a thermo-refrigerator, a thermo-acoustic refrigerator, and a phase change of a coolant. 
     According to an aspect of the present invention, the hydrogen generation un generate hydrogen using one selected from an electrolysis reaction and a catalyst reaction. 
     According to an aspect of the present invention, the hydrogen generation unit that uses an electrolysis reaction may be one selected from an electrolyzing unit that uses an alkali aqueous solution as an electrolyte, an electrolyzing unit that uses an ion conductive membrane as an electrolyte, and an electrolyzing unit that uses an oxidation and reduction reaction of an optical catalyst by radiating light to the optical catalyst. 
     According to an aspect of the present invention, the hydrogen generation unit that uses the oxidation and reduction reaction of an optical catalyst may generate hydrogen by reacting one optical catalyst selected from an alkali metal and a borohydride (M x BH y ) with water. 
     According to an aspect of the present invention, the pressure of hydrogen that is supplied to the hydrogen charging unit from the hydrogen generation unit may be in a range from 0.01 to 10 atm. The cooling unit may have a cooling temperature range of −20 to +30° C. 
     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  illustrates a schematic drawing of a structure of a hydrogen charging apparatus according to an embodiment of the present invention; and 
         FIG. 2  is a graph showing a hydrogen charging and discharging characteristic of a solid hydrogen storage medium according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
       FIG. 1  illustrates a schematic drawing of a structure of a hydrogen charging apparatus according to an exemplary embodiment of the present invention. Referring to  FIG. 1 , the hydrogen charging apparatus includes a hydrogen generation unit  110 , a hydrogen charging unit  120  that charges hydrogen in a solid hydrogen storage medium  210  built in a hydrogen storage cartridge  200 , and a cooling unit  130  that cools the solid hydrogen storage medium  210  during hydrogen charging. 
     The hydrogen generation unit  110  generates hydrogen by electrolyzing water, and includes a water tank  111  in which water is stored, an electrolyzing unit  113  that generates hydrogen by electrolyzing water supplied from the water tank  111  by a pump  118 , a gas-liquid separation tank  114  that separates water from hydrogen using specific gravity, and a dehumidifier  115  that removes moisture mixed with the hydrogen. 
     When water is supplied to the electrolyzing unit  113  from the water tank  111  and power is supplied to the electrolyzing unit  113  from a power supply unit  117  under the control of a controller  116 , hydrogen is generated in the electrolyzing unit  113  through water electrolysis. The water tank  111  includes a purifying unit  112  that removes impurities prior to supplying the water stored in the water tank  111  to the electrolyzing unit  113 . However, aspects of the present invention are not limited thereto such that the purifying unit  112  need not be disposed in the water tank  111  and may be disposed in the hydrogen generation unit  110  to purify the water before the water reaches the electrolyzing unit  113 . The generated hydrogen is separated from the water in the gas-liquid separation tank  114  and supplied to the dehumidifier  115  via the supply line  140 . A valve  119   c  is disposed in the supply line  140  to control the flow between the gas-liquid separation tank  114  and the dehumidifier  115 . The generated hydrogen is then supplied to the hydrogen charging unit  120  via a supply line  145  in which a valve  119   d  is disposed to control the flow of the generated hydrogen. The remaining water in the electrolyzing unit  113  is returned to the water tank  111  through the water return line  118   a.  Also, the oxygen generated in the electrolyzing unit  113  is returned to the water tank  111  like the remaining water, and then exhausted to the outside through the water tank  111 . Further, pressure sensors  119   a  and  119   b  measure the pressures in the gas-liquid separation tank  114  and the supply line  119   b.  However, aspects of the present invention are not limited thereto such that pressure sensors may be disposed in other places within the hydrogen generation unit  110  and the hydrogen charging unit  120 . 
     The electrolyzing unit  113  may be an alkali aqueous solution electrolyzing unit that uses an alkali aqueous solution having a concentration of 25 to 30 wt % as an electrolyte, a proton exchange membrane (PEM) electrolyzing unit that electrolyzes water using an ion-conducting membrane instead of a liquid electrolyte, or an optical catalyst electrolyzing unit that electrolyzes water through a strong oxidation and reduction reaction generated by radiating light to an optical catalyst. Although the electrolyzing unit  113  is described in the present exemplary embodiment, aspects of the present invention are not limited thereto such that a method of producing hydrogen from water using a catalyst reaction may be employed. That is, an apparatus that directly generates hydrogen by reacting a catalyst, for example, an alkali metal such as Al, Mg, or Na or a borohydride (M x BH y ; M=Na, Li, K), with water may be employed instead of the electrolyzing unit  113 . Although the electrolyzing unit  113  is illustrated as being disposed in or as part of the gas-liquid separation tank  114 , aspects of the present invention are not limited thereto such that the electrolyzing unit  113  may be disposed independent of the gas-liquid separation tank  114 . Also, the power supply  117  is not needed in all aspects. Further, aspects allow for any method of providing hydrogen to the hydrogen charging unit  120  to be charged in the solid hydrogen storage medium  210 . 
     The hydrogen charging unit  120  stores hydrogen generated from the hydrogen generation unit  110 , and more specifically, hydrogen is charged in the solid hydrogen storage medium  210  which is built in the hydrogen storage cartridge  200 . Although described herein as built in, the solid hydrogen storage medium  210  may be attachable to and/or detachable from the hydrogen storage cartridge  200  and the solid hydrogen storage medium  210  need not be constructed together or simultaneously with the hydrogen storage cartridge  200 . The hydrogen storage cartridge  200  is mountable in a charging cradle  121 . If the hydrogen storage cartridge  200  is mounted on the charging cradle  121 , the hydrogen generation unit  110  and the hydrogen storage cartridge  200  are connected to each other through the charging cradle  121  so that hydrogen generated in the hydrogen generation unit  110  can be injected into the solid hydrogen storage medium  210 . The connection structure between the hydrogen generation unit  110  and the hydrogen storage cartridge  200  through an intermediate adaptor such as the charging cradle  121  is well known in the art, and thus, the detailed description thereof will be omitted. 
     The cooling unit  130  is built in the charging cradle  121  of the hydrogen charging unit  120  to cool the charging cradle  121  during hydrogen charging, and thus, cools the solid hydrogen storage medium  210  of the hydrogen storage cartridge  200  mounted to the charging cradle  121 . Although described as built in, the cooling unit  130  may be attachable to or detachable from the charging cradle  121  and need not be constructed together or simultaneously with the charging cradle  121 . The cooling unit  130  may be a thermoelectric refrigerator, a thermo-acoustic refrigerator, or a cooler that uses a phase change of a coolant, and may be configured to cool the charging cradle  121  to a temperature of about −20° C. to +30° C. since the hydrogen storage characteristic varies according to temperature and type of the solid hydrogen storage medium  210 . 
     The temperature of the solid hydrogen storage medium  210  is decreased during hydrogen charging using the cooling unit  130  due to at least reasons described below.  FIG. 2  is a graph showing hydrogen charging and discharging characteristics of the solid hydrogen storage medium  210  according to an exemplary embodiment of the present invention. The graph in  FIG. 2  shows the hydrogen charging and discharging characteristics when the solid hydrogen storage medium  210  is formed of a hydrogen charging alloy of an AB 5  type, such as MmNi 5  [Mm (a mischmetal) is an alloy of La and Ce]. Referring to  FIG. 2 , hydrogen is stored in the solid hydrogen storage medium  210  at the same temperature as when hydrogen is discharged from the solid hydrogen storage medium  210 , i.e., the graph of  FIG. 2  illustrates the hydrogen charging and discharging characteristics at a high temperature and a low temperature. At this point, the hydrogen is stored in the solid hydrogen storage medium  210  (i.e., charged) at a relatively high pressure and is discharged at a relatively low pressure compared to the pressure when hydrogen is stored. 
     However, ideally, a reverse trend of the above case is preferable. That is, hydrogen must be readily charged in the solid hydrogen storage medium  210  even though the hydrogen pressure is low during charging, and the hydrogen pressure must be high during discharging hydrogen so that hydrogen is smoothly supplied to an anode of a fuel cell. If the charging is not satisfactory due to the low pressure of hydrogen supplied from the hydrogen generation unit  110 , a booster, such as a compressor for increasing pressure, may be installed in the hydrogen generation unit  110 , and if the pressure of hydrogen is low during discharging, an additional heating apparatus may be installed around the solid hydrogen storage medium  210  in order to induce a smooth discharge of hydrogen. 
     As depicted in  FIG. 2 , since the practical situation shows trends in which charging pressure is high and discharging pressure is low, a proper operation can hardly be expected. However, although in the case of the same solid hydrogen storage medium  210 , if the temperature is reduced, as shown in  FIG. 2 , both the charging pressure and the discharging pressure of hydrogen are reduced. That is, the hydrogen pressure for charging is reduced using the above characteristics. In other words, if the temperature for hydrogen charging is reduced when hydrogen is charged in the solid hydrogen storage medium  210 , as shown in the graph, the pressure of the hydrogen charging characteristics is reduced. This denotes that the hydrogen charging is achieved satisfactorily in the solid hydrogen storage medium  210  compared to a case when a temperature is high although the pressure of hydrogen supplied from the hydrogen generation unit  110  is low. Accordingly, the hydrogen charging may be satisfactorily achieved without the need for an installation of an additional booster. Also, when the solid hydrogen storage medium  210 , in which hydrogen is charged, is used for an operation of an electronic apparatus, since the temperature is raised to room temperature, the characteristics of the solid hydrogen storage medium  210  return to the original characteristic. Accordingly, the pressure of hydrogen when hydrogen is discharged is raised higher than a cooled state, and thus, hydrogen supply to the anode is achieved smoothly. That is, the ideal hydrogen charging and discharging characteristic (corresponding to solid lines in  FIG. 2 ), are achieved such that the characteristics that hydrogen is charged at a low pressure and is discharged at a high pressure is realized through a cooling process. 
     Also, in order to rapidly charge hydrogen within  10  minutes, the charging pressure of hydrogen may be increased twice or more than a normal charging pressure. In this way, hydrogen is rapidly cooled, the charging pressure of hydrogen is reduced to half of the normal charging pressure or less, and thus, the hydrogen charging and discharging characteristic according to aspects of the present invention is advantageous for realizing a rapid charging function. 
     Further, a reaction in which hydrogen reacts with the solid hydrogen storage medium  210  during charging is an exothermic reaction. Thus, if the solid hydrogen storage medium  210  is cooled, charging efficiency is also increased. 
     The hydrogen charging apparatus may be used in the following manner. The hydrogen storage cartridge  200  to be charged, including the solid hydrogen storage medium, is mounted in the charging cradle  121  of the hydrogen charging unit  120 . Thus, the solid hydrogen storage medium  210  built in the hydrogen storage cartridge  200  and the hydrogen supply line  145  are connected through the charging cradle  121 . 
     When hydrogen charging starts in this state, the cooling unit  130  is operated to cool the solid hydrogen storage medium  210 , and thus, a hydrogen charging pressure is reduced. Hydrogen is produced from the electrolyzing unit  113  when the hydrogen generation unit  110  is operated, and the hydrogen is charged in the solid hydrogen storage medium  210  of the hydrogen storage cartridge  200  mounted in the charging cradle  121  after the hydrogen passes through the dehumidifier  115 . At this point, the pressure sensor  119   b  installed on an outlet of the dehumidifier  115  detects the pressure of the hydrogen and sends the result to the controller  116  to determine whether the pressure of hydrogen is suitable for charging. When the pressure of hydrogen reaches a suitable level, i.e., above a predetermined pressure, the controller  116  opens the valve  119   d  to charge hydrogen in the solid hydrogen storage medium  210 . Although a suitable pressure for charging hydrogen varies according to the type of the solid hydrogen storage medium  210 , a conventional pressure range is 0.01 to 10 atm, and thus, the pressure sensor  119   d  may have a measuring range of 0.01 to 10 atm. Pressure values suitable for charging hydrogen according to the type of the solid hydrogen storage medium  210  may be set in the controller  116  in advance. 
     Afterwards, when the hydrogen storage cartridge  200  in which the charging of the hydrogen is completed is removed from the charging cradle  121 , the hydrogen storage cartridge  200  exhibits hydrogen charging and discharging characteristics at room temperature as the temperature increases. When the hydrogen storage cartridge  200  is used at room temperature, hydrogen is discharged at a relatively high pressure, and thus, hydrogen is smoothly supplied to an anode. Thus, both charging and discharging hydrogen are easily and smoothly performed. 
     The solid hydrogen storage medium  210  may be formed of a metal hydride; a complex metal hydride, such as MmNi 5  described above, a carbon group material, such as porous carbon, carbon nanotube, or carbon nanofiber; or a non-carbon material, such as zeolite metal organic framework, mesoporous organosilica, or metal nanotube. 
     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these exemplary embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.