KR101295001B1 - Apparatus for separating/concentrating seawater electrolyte, hydrogen producing apparatus using seawater electrolyte in photoelectrochemical cell - Google Patents

Abstract

The present invention provides a photoelectrochemical hydrogen production apparatus and a hydrogen production method using seawater concentrated by natural seawater or seawater electrolyte separation / concentration devices having various ionic components as electrolytes. The present invention provides a titania photoanode formed in such a way that the photocatalyst titania (TiO ₂ ) is stacked in a tubular shape by anodization and exposed to light, and an anode electrolyte portion containing a seawater electrolyte and in which a titania photoanode is immersed; A cathode made of platinum material, capable of generating hydrogen, a cathode electrolyte portion accommodating a seawater electrolyte, and having a cathode immersed therebetween, interposed between the anode electrolyte portion and the cathode electrolyte portion and ion exchanged between the anode electrolyte portion and the cathode electrolyte portion Hydrogen is produced by a nanofiltration membrane that enables this to be achieved, and a solar cell that is connected to the titania photoanode and cathode by conducting wires and formed to be exposed to light.

Description

Photoelectrochemical hydrogen production apparatus using seawater electrolyte {Apparatus for separating / concentrating seawater electrolyte, hydrogen producing apparatus using seawater electrolyte in photoelectrochemical cell}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to hydrogen production, and in particular, a device for separating / concentrating seawater electrolyte to produce hydrogen using seawater having various ionic components as an electrolyte, and supplying seawater electrolyte to a photoelectrochemical cell to supply hydrogen through a photochemical reaction. It relates to a photoelectrochemical hydrogen production apparatus and method using a seawater electrolyte to prepare a.

Rapid industrialization after the Industrial Revolution was accomplished by fossil fuels such as coal and petroleum as energy sources, but excessive use of fossil fuels caused global warming due to the generation of carbon dioxide. Due to reserves, the development of new alternative energy sources is urgent.

As an alternative energy source, hydrogen can be easily stored like conventional fossil fuels, can be produced from water or organic materials, and has almost no pollution. Therefore, countries around the world can efficiently produce and easily store hydrogen. It is struggling to develop

In producing hydrogen, the ultimate raw material is expected to be water in the coming years of the hydrogen economy, and electrolysis or photochemical hydrogen production processes will be required. However, the hydrogen production process through water decomposition is expected to cause a global water shortage because a large amount of water must be input.

At present, the global water consumption is estimated at about 272 trillion liters, including drinking water, agricultural water and industrial water, and the water consumption in the 2030s, when the hydrogen economy will come, is expected to be up to twice that. Therefore, if only 2 ~ 3% of the fresh water resources of the earth's total water resources are used as raw materials for hydrogen production, the water shortage phenomenon will become a reality. Therefore, the seawater, which is the most abundant resource in nature, Hydrogen production process is required.

At present, some electrolysis processes are used to produce hydrogen from seawater or to obtain by-products. However, there are disadvantages of low efficiency and requiring electricity as a separate energy source. In addition, there is also a photochemical hydrogen production method using the sunlight as a natural energy source, because the efficiency is reduced by the pure water decomposition is increasing its efficiency through various additives. On the other hand, since there are various ionic components in seawater, it is expected that if used as an electrolyte for photochemical hydrogen production, it will greatly contribute to the effective utilization of water resources required for hydrogen production in the future.

In recent years, seawater desalination technology has attracted much attention in order to secure drinking water and industrial water all over the world along with energy problems. In Korea, seawater desalination technology is under development to overcome this problem. The seawater desalination method uses an evaporation method, an electrodialysis method, a membrane process, etc., and consumes a lot of energy to separate salts in seawater. Therefore, it is a recent trend to adopt a method using a membrane process having a relatively low energy consumption among seawater desalination methods. The seawater desalination process by membrane is performed by desalting ions in seawater by applying high pressure energy, which inevitably produces concentrated water containing high concentrations of salts. Subsequent problems with coastal ecosystem pollution may arise. In order to solve this problem, researches on utilizing concentrated seawater components are underway, and the concentrated effluent generated during seawater desalination is linked with the photoelectrochemical hydrogen production method (ultimately, hydrogen production method using solar light). The ripple effect is great when energy is produced.

The hydrogen production method using the solar light is to use the characteristics of the photocatalyst, the photocatalyst utilization technology has been used a lot in the treatment of environmental pollutants in the past, by reducing the proton (H ⁺ ) and hydrogen by using sunlight It can be used in manufacturing.

The term 'photocatalyst' is used when referring to a 'catalyst for accelerating the photoreaction', and in order to become a 'photocatalyst', the condition as a general 'catalyst' must be satisfied as well as not directly consumed by participating in the reaction. The reaction rate should be accelerated by providing a mechanism path different from the existing photoreaction. In the latter case, this means that the turn-over ratio per active site must exceed 1.0.

In order for the photocatalyst to exhibit photochemical activity, light energy of more than the band energy or the band gap energy (E _g ) is required, which is a valence band (VB), which is the band of the highest energy occupied by the electrons, The difference in conduction band (CB), the lowest energy band not occupied by electrons, is a forbidden interval that electrons cannot occupy, and excites the electrons / holes pairs in the Is the minimum energy that can be generated.

Along with the band gap energy, what is important is the relative position of the covalent and conducting bands (Fermi energy (E _f ), which is made in detail by the position of these bands), which is the redox couple in the aqueous solution from the photocatalyst. This is because it plays an important role in determining whether electrons move and transfer electrons.

As photocatalyst materials having the above characteristics, semiconductor metal oxides are mainly used. Examples thereof include tungsten trioxide (WO ₃ ), zinc oxide (ZnO), silicon carbide (SiC), cadmium sulfide (CdS), and gallium arsenide. (GaAs) and the like, but usually, titania (TiO ₂ ) having an anatase structure is used. This is because stability, such as excellent efficiency, relatively low cost, smooth supply, and no corrosiveness has been confirmed.

The present invention was developed to provide a hydrophobic production apparatus that can be more practically used in place of the conventional hydrogen production method for producing hydrogen from water or an aqueous solution using a photocatalyst, and is abundant resources of seawater or seawater existing in nature. It is an object of the present invention to provide a seawater electrolyte separation / concentration apparatus and a photoelectrochemical hydrogen production apparatus using a seawater electrolyte and a hydrogen production method that can produce hydrogen efficiently and economically by utilizing the concentrated ionic component of.

The present invention for achieving the above object is a seawater reservoir for storing seawater after removal of particulate matter in natural seawater, and a membrane cell which is provided with a nanofiltration membrane therein to separate / concentrate the ionic components in seawater, A seawater supply pipe having a seawater supply pipe for supplying seawater from the seawater reservoir to the membrane cell, and a high pressure pump installed at the seawater supply pipe to provide a supply pressure; Separated seawater discharge section for discharging the separated seawater having TDS (Total Dissolved Component) concentration, and concentrated seawater discharged for discharging concentrated seawater having a TDS concentration higher than natural seawater to the seawater storage section due to the concentration of ions by the membrane cell. It provides a seawater electrolyte separation / concentration device comprising a portion.

The seawater reservoir in the seawater electrolyte separator / concentrator includes a seawater storage tank including a filter for removing particulate matter in the natural seawater, and a cooling water circulation coil immersed in the seawater storage tank to circulate the coolant. It may be made of a configuration including a seawater temperature control unit for providing a constant control of the seawater temperature in the seawater storage tank.

In addition, the seawater supply unit, a damper for removing the vibration of the seawater supply pipe due to the supply pressure of the high pressure pump, a seawater supply pressure gauge for measuring the supply pressure of the seawater provided to the membrane cell through the seawater supply pipe, and this seawater When the supply pressure of the seawater measured by the supply pressure gauge is sharply increased, it may further comprise a safety valve and bypass piping for bypassing the seawater supplied to the membrane cell to the seawater reservoir.

The separated seawater discharge unit may further include: a separated seawater pipe through which the separated seawater is discharged to the outside from the membrane cell; and a separated seawater pressure gauge and a separated seawater flow meter installed in the separated seawater pipe to measure discharge pressure and flow rate of the separated seawater, respectively. And a separate seawater recovery pipe branched from the separated seawater pipe to recover the separated seawater to the seawater storage portion, and a separate seawater sampling unit for branching from the separated seawater pipe to sample the separated seawater, and the separated seawater pipe and the separated seawater. It may be configured to include a separation seawater direction switching valve which is installed at the branch point of the recovery pipe and the separation seawater sampling unit to change the flow path of the separation seawater.

The concentrated seawater discharge unit includes a concentrated seawater pipe where the concentrated seawater is recovered from the membrane cell to the seawater storage unit, and a concentrated seawater pressure gauge and a concentrated seawater flow meter installed in the concentrated seawater pipe to measure discharge pressure and flow rate of the concentrated seawater, respectively. And a flow rate control valve installed in the concentrated seawater pipe for varying the flow rate of the concentrated seawater and the separated seawater and the pressure of the membrane cell, and a concentrated seawater sampling unit for sampling the concentrated seawater branched from the concentrated seawater pipe. It may be configured to include a concentrated seawater direction switching valve which is installed at the branch point of the concentrated seawater pipe and the concentrated seawater sampling unit to change the flow path of the concentrated seawater.

In addition, the allowable operating pressure range of the membrane cell is preferably 20 to 40 atmospheres.

On the other hand, in the photoelectrochemical hydrogen production apparatus using natural seawater or seawater concentrated by the seawater electrolyte separation / concentrator as an electrolyte, the photocatalyst titania (TiO ₂ ) is formed on the surface of the metal titanium support by anodization. A titania photoanode stacked in a tubular shape and formed to be exposed to light, an anode electrolyte portion containing a seawater electrolyte and immersed in the titania photoanode, a cathode made of platinum material to generate hydrogen, and a seawater electrolyte A nano-filtration membrane interposed between the cathode electrolyte portion in which the cathode is immersed, the anode electrolyte portion and the cathode electrolyte portion to enable ion exchange between the anode electrolyte portion and the cathode electrolyte portion, and the titania photoanode and the cathode. Brushes connected to the conductors and formed to be exposed to light It provides a photoelectric chemical hydrogen-producing device using the electrolytic water, characterized in that made, including the cells.

In the photoelectrochemical hydrogen production apparatus, the titania photoanode includes 1 to 3 parts by weight of ammonium fluoride (NH ₄ F), 2 to 4 parts by weight of water (H ₂ O), and 93 to 97 based on 100 parts by weight of the total electrolyte. In the mixed component electrolyte solution composed of parts by weight of ethylene glycol (C ₂ H ₆ O ₂ ), anodized at an applied voltage of 40 to 60 V and an applied current of 0.05 to 0.15 A may be used.

In addition, the titania photoanode may be one heat-treated at 450 to 650 ° C after the anodization.

In addition, the nanofiltration membrane may be made of a polyamide having a molecular weight of 200 fraction.

The present invention also provides a photoelectrochemical hydrogen production method, wherein the hydrogen production apparatus generates hydrogen at a minimum applied voltage of 1.0 to 3.0V.

The present invention configured as described above has the effect of overcoming the problem of low efficiency of the conventional photocatalyst hydrolysis hydrogen production apparatus, and the problem of low efficiency of the slurry-type photocatalyst as the photoanode.

In addition, the present invention utilizes the charge-producing ability of the photocatalyst of the photocatalyst and the excellent proton reduction ability of the cathode, and uses an immobilized tubular titania prepared by anodization as an optical anode, and applies zero energy consumption. By applying nanofiltration membranes that act as voltage devices, such as solar cells and ion bridges, and utilizing the most abundant seawater resources on the planet, it is possible to maximize hydrogen production efficiency and economically produce hydrogen.

In addition, the present invention is expected to receive the spotlight desalination process in order to diversify the water resources in order to overcome this situation in the situation that water shortages are being realized at home and abroad in the future, the concentrated seawater generated in the seawater desalination process directly Or after the post-treatment can be used as an electrolyte for producing hydrogen, there is an effect that enables the environment-friendly hydrogen production.

1 is a block diagram showing an embodiment of a seawater electrolyte separation / concentration apparatus according to the present invention.
2 is a view showing an embodiment of a photoelectrochemical hydrogen production apparatus according to the present invention.
3 is a graph showing the results of measuring the photocurrent for each of the titania photoanode and Comparative Examples 1, 2, 3 of the present invention.
Figure 4 is an electron micrograph of the surface of each of the titania photoanode and the photoanode Comparative Examples 1, 2, 3 of the present invention.
5 is a graph showing the hydrogen generation rate according to the voltage applied to the solar cell in the photoelectrochemical hydrogen production apparatus of the present invention.
Figure 6a is a change in flux and TDS by the operation of the 'A membrane' in the seawater electrolyte separation / concentration apparatus of the present invention.
Figure 6b is a change in flux and TDS by the operation of the 'B membrane' in the seawater electrolyte separation / concentration apparatus of the present invention.
Figure 7a is a hydrogen production trend generated by the supply of seawater electrolyte prepared by the 'A membrane' in the present invention.
Figure 7b is a hydrogen production trend generated by the supply of the seawater electrolyte prepared by the 'B membrane' in the present invention.
8 is a correlation chart between the TDS and the hydrogen production rate of the seawater electrolyte in the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, it should be understood that the following embodiments are provided so that those skilled in the art can understand the present invention without departing from the scope and spirit of the present invention. It is not.

First, an embodiment of a seawater electrolyte separation / concentration device according to the present invention will be described.

1 is a configuration diagram showing an embodiment of a seawater electrolyte separation / concentration device according to the present invention, which includes a seawater reservoir 10 for storing seawater, a membrane cell 20 for separating / concentrating ionic components in seawater, and seawater. Seawater supply unit for supplying seawater from the reservoir to the membrane cell 30, seawater having a TDS (total dissolved component) concentration lower than natural seawater by separating the ionic components by the membrane cell 20 (this is referred to as 'separated seawater') Ions are concentrated by the membrane cell 20 and the seawater having a TDS concentration higher than natural seawater (called 'concentrated seawater') is discharged from the seawater reservoir ( The concentrated seawater discharge part 50 discharged | emitted by 10) is made into the main component. Looking at each component in detail as follows.

The seawater storage unit 10 stores the seawater in which the particulate matter is removed from the natural seawater. That is, natural seawater is a general seawater taken from the east coast of Korea, for example, and stores seawater from which particulate matter exceeding 0.45 μm is removed through a filter 11a of 0.45 μm or less. When particulate matter exceeding 0.45 μm is present in seawater, hydrogen is produced for a long time through a photoelectrochemical hydrogen production apparatus described below, and the photosensitive electrode (ie, a titania photoanode) in the form of a tube is subjected to a photochemical reaction. Particulate matter may be deposited to inhibit photochemical reactions or cause problems such as clogging of analytical equipment when analyzing the composition of seawater. Therefore, as a pretreatment process for the separation / concentration of sea water is to filter particulate matter from natural sea water.

The major component analysis results of the natural seawater used in the present invention are summarized in Table 1.

Analysis of main components of natural seawater Hydrogen ion concentration (pH) 7.98 Total dissolved ingredient concentration (TDS, mg / l) 33,500 Sodium (mg / l) 9,521 Potassium (mg / l) 518 Calcium (mg / l) 460 Magnesium (mg / l) 1,465 Silica (mg / l) 1.1 Chloride (mg / l) 21,705 Sulfate (mg / l) 2,556 Boron (mg / l) 4.27

In general, Total Dissolved Solids (TDS), which is an indicator of salt concentration in seawater, was 33,500 mg / l, and the hydrogen ion concentration (pH) was 7.98. The salinity of seawater distributed on the earth varies according to region and season, but in Korea, TDS is between 31,500 ~ 34,600mg / l depending on the region and water temperature distribution. Based on these data, it can be seen that the seawater used in the present invention is also within the range.

The seawater storage unit 10 of the present embodiment has a seawater storage tank 11 containing seawater, and a seawater temperature control unit 12 having a coolant circulation coil 12a immersed in the seawater storage tank 11 to circulate the cooling water. Consists of The filter 11a is provided in the seawater storage tank 11. In addition, the seawater temperature controller 12 increases the temperature of the seawater due to an increase in the temperature of the high pressure pump 32 when the membrane cell 20 is operated in the seawater recirculation filtration mode as described below. It is provided to prevent or to maintain a constant temperature of the supply sea water, to allow the coolant to circulate through the coolant circulation coil 12a to increase the heat exchange efficiency.

The membrane cell 20 is made of stainless steel, and can apply pressure up to 100 atm, which is preferably operated at 20 to 40 atm considering the recovery rate of seawater electrolyte and the appropriate level of operation time. The detailed description will be described later. The membrane cell 20 is provided with a nanofiltration membrane (not shown), and is operated in a cross-flow filtration mode to separate / concentrate ions in seawater. Then, the separated seawater having a lower ion concentration than the seawater supplied from the seawater supply unit 30 (that is, 'supply seawater') is sent to the separated seawater discharge unit 40, and the concentrated seawater having a higher ion concentration than the supplied seawater discharges the concentrated seawater. Send to section 50.

The seawater supply unit 30 is installed in the seawater supply pipe 31 for supplying seawater from the seawater storage unit 10 to the membrane cell 20, and in the conduit of the seawater supply pipe 31 to be installed in the membrane cell 20. It is provided with the high pressure pump 32 which provides the pressure required, ie, supply pressure. In addition, the seawater supply pipe 31 is provided with a damper 33 for removing or minimizing vibrations that may occur in the seawater supply pipe 31 due to the supply pressure during the high pressure operation of the high pressure pump 32. In addition, the seawater supply pipe 31 is provided with a seawater supply pressure gauge 34 at the inlet side of the membrane cell 20, in particular, to measure the supply pressure of seawater provided to the membrane cell 20 through the seawater supply pipe 31. do. In the pipeline of the seawater supply pipe 31, a safety valve 35 and a bypass pipe 36 are installed. When the seawater supply pressure of the seawater measured by the seawater supply pressure gauge 34 rises rapidly, The safety valve 35 is opened and the seawater supplied to the membrane cell 20 is diverted to the seawater reservoir 10 through the bypass pipe 36, so that safe operation is achieved.

The separated seawater discharge part 40 of the present embodiment is provided with a separated seawater pipe 41 through which the ions are separated by the membrane cell 20 and the seawater having a lower TDS concentration than the natural seawater is discharged to the outside. The separated seawater pipe 41 is provided with a separated seawater pressure gauge 42 for measuring the discharge pressure of the separated seawater, and a separated seawater flowmeter 43 for measuring the flow rate of the separated seawater. In addition, a separate seawater recovery pipe 44 branched from the separate seawater pipe 41 is provided, which separates the seawater when the membrane cell 20 is operated by the supplied seawater recycle filtration method. It is to be recovered to the sea water storage (10). In addition, the separated seawater sampling section 45 branches from the separated seawater pipe 41 as a pipe for collecting and analyzing a sample of the separated seawater, if necessary. At the branch points of the separated seawater pipe 41, the separated seawater recovery pipe 44, and the separated seawater sampling section 45, a separate seawater direction switching valve 46 for changing the flow path of the seawater is provided.

The concentrated seawater discharge section 50 of the present embodiment is provided with a concentrated seawater pipe 51 in which the concentrated seawater is recovered from the membrane cell 20 to the seawater storage section, and the discharge pressure of the concentrated seawater pipe 51 is provided. The concentrated seawater pressure gauge 52 and the concentrated seawater flowmeter 53 which measure a flow volume, respectively are provided. In addition, the concentrated seawater pipe 51 is provided with a flow rate control valve 54 for controlling the flow rate of the concentrated seawater. The flow rate of the concentrated seawater and the separated seawater and the membrane cell by fine adjustment of the flow rate control valve 54 are provided. It is possible to fluctuate the pressure. In addition, a concentrated seawater sampling section 55 branched from the concentrated seawater piping 51 is provided to collect samples of the concentrated seawater, and the branch of these concentrated seawater piping 51 and the concentrated seawater sampling section 55 is provided. The branch is provided with a concentrated seawater diverting valve 56 for changing the flow path of the concentrated seawater.

On the other hand, the nanofiltration membrane for preparing a seawater electrolyte has a molecular weight cutoff (MWCO) of the intermediate characteristics of reverse osmosis membrane and ultrafiltration (Ultrafiltration).

The membrane used in the present invention is a polyamide material, which has a relatively low fractional molecular weight in the nanofiltration membrane (called 'A membrane'), and a relatively high fractional molecular weight in the nanofiltration membrane. (This is called 'B membrane') can be applied.

In the case of 'A membrane', it has a low flux instead of having a relatively low fractional molecular weight, and the ion removal rate in seawater is high, so that the TDS increases in the concentrated seawater discharge section 50 than the general seawater. On the other hand, the 'B membrane' has a relatively high fractional molecular weight, low ion removal rate in seawater, but high flux, and has a feature of low concentration of TDS in the concentrated seawater discharge unit 50.

The operation for producing the seawater electrolyte in the seawater electrolyte separator / concentrator of the present invention is pressurized to obtain an electrolyte recovery rate of 25% in the supplied seawater recycle filtration method. When the area of the membrane is small, it is preferable to operate by supply seawater recycle filtration to accumulate ion concentration, and the calculation of electrolyte recovery in the supply seawater recycle filtration can be calculated by Equation 1.

In Equation 1, 'R' is an electrolyte recovery rate, and means a percentage of the amount of seawater (V _P ) separated from the membrane relative to the amount of seawater (V _F ) supplied. Based on the recovery rate of 25%, the recovery time of the seawater electrolyte has a short advantage in the recovery rate of less than that, but the concentration efficiency is low, the concentration efficiency can be increased to obtain more recovery rate, but the production time is longer or the inorganic scale on the membrane surface It is more likely to form.

In the present invention, the allowable operating pressure range of the membrane cell 20 for producing the seawater electrolyte is 20 to 40 atm, and more preferably at 20 to 30 atm. When operating at a pressure lower than 20 atm, the operating time for obtaining 25% of seawater electrolyte recovery becomes longer, and when exceeding 40 atm, the operating time for obtaining 25% of seawater electrolyte recovery is shortened, but separation / concentration Efficiency decreases and the likelihood of forming inorganic scale on the membrane surface increases.

Next, the photoelectrochemical hydrogen production apparatus of the present invention using seawater concentrated as natural electrolyte or seawater electrolyte separation / concentration device configured as described above as an electrolyte will be described.

2 is a view showing an embodiment of the photoelectrochemical hydrogen production apparatus according to the present invention, the titania photoanode 110, the anode electrolyte portion 120 in which the titania photoanode 110 is immersed while receiving the seawater electrolyte, A cathode 130 which is made of platinum material to generate hydrogen, and is interposed between the cathode electrolyte part 140, the anode electrolyte part 120, and the cathode electrolyte part 140 in which the cathode 130 is immersed while receiving the seawater electrolyte. The nanofiltration membrane 150 allows ion exchange between the anode electrolyte portion 120 and the cathode electrolyte portion 140, and is connected to the titania photoanode 110 and the cathode 130 by a wire to be exposed to light. The solar cell 160 is configured.

The titania photoanode 110 is formed by stacking a photocatalyst titania (TiO ₂ ) in a tubular shape by anodization on a surface of a metal titanium support, and is exposed to light such as sunlight. That is, the titania photoanode 110 has a structure in which the tubular titania, which is a photocatalytic material, is integrally formed and bonded to the surface of the metallic titanium, which is a support, through an anodization reaction. At this time, the hollow side of each titania tube is facing outward while making a right angle with the surface of the metal titanium support. In other words, Titania tubes, which are transition metal oxide layers, are stacked and arranged on the surface of the metal titanium support, and a voltage is applied to the solar cell 160 between the titania photoanode 110 and the cathode 130. As the electrons move in one direction, the redox reaction can be separated and caused.

Anodization of the titania photoanode 110 is performed by washing the metal titanium support, followed by 1 to 3 parts by weight of ammonium fluoride (NH ₄ F) and 2 to 4 parts by weight of water (H ₂ O) based on 100 parts by weight of the total electrolyte. And 93 to 97 parts by weight of a mixed component electrolyte consisting of ethylene glycol (C ₂ H ₆ O ₂ ) using a copper or platinum coil as a negative electrode as a counter electrode to oxidize a metal titanium support as a positive electrode. If the content of ammonium fluoride is less than 1 part by weight, it is difficult to form a tubular oxide film, and if it exceeds 3 parts by weight, the tubular oxide film is deformed into a nonuniform form. In addition, when the water content is less than 2 parts by weight, it is difficult to dissolve the ammonium fluoride. When it exceeds 4 parts by weight, the viscosity of the electrolyte is lowered, and thus, the rate of anodization may be changed. And, in the case of ethylene glycol is less than 93 parts by weight, the etching rate of the oxide is faster, if it exceeds 97 parts by weight it is difficult to form a long oxide tube.

In the anodization, the applied voltage is 40 to 60 V and the applied current is 0.05 to 0.15 A. If the applied voltage is less than 40V, the formation of oxide becomes irregular, and if it exceeds 60V, the oxide is released. If the applied current is less than 0.05A, anodization may not be performed or may proceed very slowly. If the current exceeds 0.15A, the anode may burn. The time required for anodizing is about 2 to 4 hours.

After such anodization, the titania photoanode 110 is heat-treated at 450 to 650 ° C. while supplying 400 to 600 ml per minute of oxygen per unit surface area of the metal titanium support to be oxidized in a furnace capable of controlling the atmospheric gas and the processing temperature. do. This heat treatment is a process for crystallizing the amorphous oxide layer produced by anodization into a uniform structure. If the oxygen supply amount does not reach 400ml / min during the heat treatment process, the time for forming the oxide layer may become long, and the oxide layer may be unstable. If the amount exceeds 600ml / min, no more effect is obtained. The heat treatment time for the titania photoanode 110 changes depending on the oxygen supply amount, the heat treatment temperature, the surface area of the titanium support, and the like, and generally takes about 2 to 5 hours. If the heat treatment temperature is less than 450 ° C, crystallization to an anatase structure becomes difficult, and if it exceeds 650 ° C, rutile structure may be generated. Therefore, heat treatment is preferably performed in a temperature range of 450 to 650 ° C.

Through the above process, the titania photoanode 110 formed on the surface of the metal titanium support is formed on the surface of the metal titanium support having a tubular oxide layer having a photosensitive ability, and irradiated with ultraviolet rays or sunlight causes photoelectrochemical reaction from seawater. It can be used as an electrode.

That is, when the titania photoanode 110 is irradiated with light equal to or greater than the bandgap energy of the photocatalytic material titania, electrons / holes are generated, and electrons / holes are separated by the potential difference applied by the solar cell 160. . The remaining holes oxidize seawater to generate oxygen and chlorine gas and protons, and the electrons moved to the cathode 130 through the conductive wires are transferred from the anode electrolyte portion 120 to the cathode electrolyte portion 140 through the nanofiltration membrane 150. Hydrogen is generated by reducing protons moved to.

The nanofiltration membrane 150 is preferably used having a fraction molecular weight of 200 made of polyamide having a relatively high chemical resistance to seawater. If the fractional molecular weight is less than 200, ion exchange may not be easy, and thus the circuit configuration may not be smoothly generated, and thus the amount of hydrogen generated may be low. In addition, when the fractional molecular weight is greater than 200, the seawater electrolyte of the anode electrolyte portion 120 and the cathode electrolyte portion 140 is easily moved, which is not suitable.

On the other hand, the solar cell 160 may use a single crystal or polycrystalline silicon solar cell, the minimum applied voltage is preferably in the range of 1.0 to 3.0V.

In the following, test examples for the photoelectrochemical hydrogen production apparatus using the seawater electrolyte of the present invention configured as described above will be described.

≪ Test Example 1 >

After anodizing the mixed component electrolyte solution (ammonium fluoride (NH ₄ F) + water (H ₂ O) + ethylene glycol (C ₂ H ₆ O ₂ )) for 3 hours under a constant voltage of 0.1 A, an oxygen atmosphere 400 ml / min Titania photoanode 110 of the present invention obtained by heat treatment at 450 ° C. for 2 hours, other anodized electrolyte 1 (fluoric acid (HF), other anodized electrolyte 2 (potassium fluoride + sodium nitrate + phosphoric acid) and other anodized electrolyte The properties of the photoanode Comparative Examples 1, 2, and 3 respectively prepared from 3 (ammonium fluoride + water + glycerol) were tested.

Figure 3 shows the results of measuring the photocurrent (photocurrent) for each of the titania photoanode 110 and the photoanode Comparative Examples 1, 2, 3 of the present invention. Referring to the graph of FIG. 3, it can be seen that the titania photoanode 110 manufactured through the mixed component electrolyte solution of the present invention has the highest current value compared with the photoanode comparative examples 1, 2, and 3 prepared through other electrolyte solutions. have.

FIG. 4 is an electron micrograph of the surface of each of the titania photoanode 110 and the photoanode comparative examples 1, 2, and 3 of the present invention. The surface currents of the photocurrent value graph of FIG. have. That is, the titania photoanode 110 manufactured through the mixed component electrolyte of the present invention has a very regular and relatively long tube-like titania, whereas in the case of the photoanode comparative example 1, the tube wall has a tube shape but This is a relatively thick result. In addition, in the case of the photoanode Comparative Examples 2 and 3, the unstable tube shape or particulate (spherical) titania is shown to be stacked in a cone shape.

Taken together, the results show that when the shape of the photoanode has a regular tube shape, the longer the length of the tube increases the amount of titania produced per unit area of titanium, and the photocurrent value increases under these conditions. Indicates that the move can be made easily.

≪ Test Example 2 &

The hydrogen generation rate (μmol / cm 2 -hr) was measured by increasing the applied voltage to the solar cell 160 constituting the photoelectrochemical hydrogen production apparatus using the seawater electrolyte of the present invention by 0.5V by 1.0V to 3.0V. The influence of external bias was identified. The seawater electrolyte used here is natural seawater from which particulate matter is removed by a 0.45 μm filter, and has an electrolyte having main ionic components shown in Table 1.

5 is a graph showing the hydrogen generation rate according to the voltage applied to the solar cell 160, it can be seen that the hydrogen generation rate increases as the applied voltage increases, the applied voltage (3.5V or more based on 3.0V) ) Can be observed that the rate of hydrogen evolution no longer increases.

Through these results, it can be seen that in the photoelectrochemical hydrogen production using seawater as an electrolyte material, the solar cell 160 has an optimum hydrogen generation rate when a voltage of 3.0 V or more is applied.

In addition, when the titania photoanode 110 was irradiated with a light source and confirmed whether or not the rate of electrolysis hydrogen generation by the solar cells (3.0 and 3.5V) with different voltages was obtained, hydrogen was not generated at all. In addition, even when the photochemical reaction is induced without a solar cell, which is an external bias, hydrogen may not be generated.

<Test Example 3>

Natural seawater (Table 1 natural seawater) from which particulate matter was removed through a 0.45 μm filter was used as a seawater, 'A membrane' having a relatively low fractional molecular weight among nanofiltration membranes, and a relatively high fraction of nanofiltration membranes. A pressure of 20 atm and 30 atm was applied using a 'B membrane' having a molecular weight to perform an operation for adjusting the electrolyte recovery rate by 25% by supplying seawater recycle filtration.

Prior to the preparation of the seawater electrolyte, the pure water permeability of the 'A membrane' and the 'B membrane' was measured, and the 'A membrane' was 5.9 L / m 2 -hr-bar, and the 'B membrane' In the case of 10.39L / ㎡-hr-bar, the 'A membrane' is more compact and the ion removal rate (concentration rate) is high, but the flux is expected to be low, and the operation for seawater electrolyte production was performed based on this. .

As shown in FIG. 6A, in order to obtain an electrolyte recovery rate of 25%, an operating time of about 9 hours at 20 atm and 4.5 hours at 30 atm was required. The flux tends to decrease with the time of operation compared to the initial stage because the inorganic ions are deposited on the membrane surface to form fouling. According to the pressure-dependent operation, TDS is gradually increased compared to general seawater 33,500mg / L for concentrated seawater discharge, and shows value of about 40,600mg / L at 20 atmosphere and about 43,400mg / L at 30 atmosphere. It was about 15,600 mg / L at 30 atm and 12,000 mg / L at 30 atm.

In the case of 'B membrane', as shown in FIG. 6B, the operation time for obtaining an electrolyte recovery rate of 25% is shorter than that of 'A membrane', since the flux is high. According to the pressure-dependent operation, TDS is gradually increased compared to general seawater 33,500mg / L in concentrated seawater discharge, showing about 38,800mg / L at 20 atm and about 38,600mg / L at 30at. At about 30,400 mg / L and 30 atm, it was 29,600 mg / L.

Comparing TDS separation and concentration trends for the membranes of FIGS. 6A and 6B, it can be seen that the degree of separation / concentration of 'A membrane' is higher than that of 'B membrane'.

Table 2 shows the results of analyzing the concentrations of the main ionic components of the seawater electrolyte according to the pressure conditions. This analysis also shows the same trend as TDS, which shows that separation / concentration at 'A membrane' is higher than 'B membrane'.

Main Components of Natural Seawater Electrolyte and Seawater Electrolyte Prepared from Separation / Concentration Device of the Present Invention
main ingredient

Natural sea water
'A membrane' 'B membrane' Seawater Concentrated seawater Seawater Concentrated seawater 20 atmospheres 30 atmospheres 20 atmospheres 30 atmospheres 20 atmospheres 30 atmospheres 20 atmospheres 30 atmospheres TDS (mg / L) 33,500 15,635 12,000 40,651 43,388 30,455 29,559 38,833 38,609 Sodium (mg / L) 9,521 3,857 2,605 11,709 11,333 8,251 8,072 9,410 9,422 Potassium (mg / L) 518 227 158 665 625 461 458 538 533 Calcium (mg / L) 460 47 26 643 611 317 302 519 516 Magnesium (mg / L) 1,465 147 86 2,059 1,923 812 762 1,728 1,719 Silica (mg / L) 1.1 0 0 1.4 1.2 0.4 0.5 3.6 1.2 Chloride (mg / L) 21,705 9,402 6,465 28,810 27,735 21,388 21,222 23,861 24,271 Sulfate (mg / L) 2,556 168 97 3,831 3,548 372 339 3,570 3,589 Boron (mg / L) 4.27 4.2 4.1 5.01 4.95 4.4 4.4 4.8 4.8

<Test Example 4>

Hydrogen was prepared by supplying various seawater electrolytes prepared as in Test Example 3 to the photoelectrochemical hydrogen production apparatus of the present invention.

FIG. 7A is a hydrogen production trend generated by the supply of seawater electrolyte prepared by 'A membrane', and FIG. 7B is a hydrogen production trend generated by the supply of seawater electrolyte manufactured by 'B Membrane'.

As can be seen in Figure 7a, when producing hydrogen using a general natural seawater electrolyte of TDS 33,500mg / L, it was possible to obtain a result of about 200μmol / ㎠-hr, seawater electrolyte separation / In the case of the seawater electrolyte concentrated by the membrane cell of the concentrator, a result higher than that of the hydrogen produced in general seawater was obtained. That is, it can be seen that the hydrogen production rate is high when the seawater electrolyte prepared by 'A membrane' is used. In addition, the seawater electrolyte separated under the same pressure condition shows a significantly lower hydrogen production rate than the general seawater.

As shown in FIG. 7B, when the concentrated or separated seawater electrolyte is used, the hydrogen production rate is almost the same as or lower than that of the general seawater electrolyte. As shown in the results of the main ions and TDS analysis in Table 2, the separation and concentration of the main components of seawater differs significantly in the case of 'A membrane', whereas in the case of 'B membrane', separation / concentration differs. Since the efficiency is low, the concentration of the prepared seawater electrolyte is higher than that of the 'A membrane' in terms of hydrogen production rate.

&Lt; Test Example 5 >

8 is a correlation diagram between the TDS of the seawater electrolyte and the hydrogen production rate in the present invention. This is a result of summarizing the correlation between the hydrogen production rate and the TDS of the seawater electrolyte.

As can be seen in Figure 8, when the general seawater (TDS 33,500mg / L) is fed to the photoelectrochemical hydrogen production apparatus of the present invention to induce a photochemical reaction, the hydrogen production rate is about 200μmol / ㎠-hr (Fig. (Indicated by dashed lines in Fig. 8), but the hydrogen production rate is higher when the TDS is used with concentrated seawater electrolyte than the general seawater, and the separated seawater electrolyte is higher than when the TDS is lower than the general seawater. The results show that the hydrogen production rate is significantly lower.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, This is possible.

10: seawater reservoir 11: seawater reservoir
11a filter 12 seawater temperature control unit
12a: cooling water circulation coil 20: membrane cell
30: seawater supply unit 31: seawater supply piping
32: high pressure pump 33: damper
34: seawater supply pressure gauge 35: safety valve
36: bypass piping 40: separated sea water discharge
41: separate seawater pipe 42: separated seawater pressure gauge
43: separate seawater flow meter 44: separated seawater recovery pipe
45: separated seawater sampling unit 46: separated seawater direction switching valve
50: concentrated seawater discharge part 51: concentrated seawater piping
52: concentrated seawater pressure meter 53: concentrated seawater flow meter
54 flow rate control valve 55 concentrated seawater sampling unit
56: concentrated seawater diverter valve 110: titania photoanode
120: anode electrolyte portion 130: cathode
140: cathode electrolyte 150: nanofiltration membrane
160: solar cell

Claims (11)

delete delete delete delete delete delete In the photoelectrochemical hydrogen production apparatus using the seawater or natural seawater concentrated by the seawater electrolyte separation / concentrator comprising a seawater reservoir, a membrane cell, a seawater supply, a seawater discharge and a concentrated seawater discharge.
On the surface of the metal titanium support, the photocatalyst titania (TiO ₂ ) is formed to be laminated in a tubular shape by anodization and exposed to light, and 1 to 3 parts by weight of ammonium fluoride (NH ₄ F) and 2 to 3 parts by weight of the total electrolyte are used. After being anodized at an applied voltage of 40 to 60 V and an applied current of 0.05 to 0.15 A in a mixed component electrolyte consisting of 4 parts by weight of water (H ₂ O) and 93 to 97 parts by weight of ethylene glycol (C ₂ H ₆ O ₂ ). A titania photoanode which is heat-treated at 450 to 650 캜;
An anode electrolyte portion accommodating a seawater electrolyte and immersing the titania photoanode;
A cathode made of platinum material to generate hydrogen;
A cathode electrolyte portion accommodating seawater electrolyte and having the cathode immersed therein;
A nanofiltration membrane interposed between the anode electrolyte portion and the cathode electrolyte portion to enable ion exchange between the anode electrolyte portion and the cathode electrolyte portion, wherein the nanofiltration membrane is formed of polyamide having a molecular weight of 200;
And a solar cell connected to the titania photoanode and the cathode by conducting wires and configured to be exposed to light. delete delete delete delete

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