KR101263177B1 - electrolytic cell for a monolithic photovoltaic-electrolytic hydrogen generation system - Google Patents

Abstract

The present invention is an electrolytic cell for a photovoltaic-integrated hydrogen production system including a PV photoelectrode / anode / separator / cathode, characterized in that a channel is formed on at least one of the anode and the cathode, and the photo-electrolyte integrated hydrogen production By improving the structure of the electrode used in the system, it is possible to reduce the overvoltage during the electrolysis process to improve the hydrogen production efficiency.

Description

Electrolytic cell for a monolithic photovoltaic-electrolytic hydrogen generation system

The present invention relates to an electrolytic cell for a monolithic photovoltaic-electrolytic hydrogen production system. More particularly, the present invention relates to an electrolytic cell for a photovoltaic integrated hydrogen production system having an improved electrode structure and a very high hydrogen production efficiency. .

Photoelectrochemical (PEC) hydrolysis is a promising renewable energy technology for hydrogen production. PEC systems can be defined as devices that use solar energy to produce enough energy to break down water into hydrogen and oxygen. In other words, the PEC may be a device that simultaneously performs the roles of the photovoltaic device (PV) and the electrolytic device. However, PEC is different from simply combining PV and electrolytic devices, because it is unnecessary in terms of collecting current and thus is advantageous in terms of efficiency and cost since there is no transmission loss.

In terms of efficiency and cost, it is ideal to apply a single bandgap material to a PEC where hydrolysis can proceed directly at the semiconductor / liquid interface, using minimal energy to cross the activation barrier for water decomposition. This is because the reaction can proceed advantageously thermodynamically, and a relatively inexpensive oxide can be used. However, such a water decomposition system has a problem in that the photoelectrode semiconductor is unstable under an aqueous electrolyte solution and in some cases an additional externally applied voltage is required. Therefore, with current technology, it is more effective to use PV / electrolyte technology than to immerse semiconductor photoelectrodes in an electrolyte during hydrolysis hydrogen production.

On the other hand, a photovoltaic hydrogen production system has been proposed that combines PV and electrolytic systems into one system, that is, an integrated PV-electrolyte cell. This integrated PV-electrolysis system is designed such that the PV and hydrolysis catalyst membranes are located on both sides of the conductive substrate. Therefore, the stability problem of the photoelectrode can be solved by separating the photoelectrode material, which is generally vulnerable to an acidic or basic aqueous solution, from the aqueous electrolyte solution.

Since the magnitude of the overvoltage during water decomposition greatly depends on the electrode catalyst material, the function of the water decomposition catalyst of the electrode is very important to increase the efficiency of the integrated PV-electrolysis system. In general, an elemental material such as Pt or Ir is used in a PEM electrolytic cell. Some metal oxides also exhibit high activity due to their large surface area and high stability to oxygen-producing electrodes. The present inventors have completed the present invention by conducting a study for improving the material characteristics of the electrode, as well as the structure of the electrode is also important in reducing the overvoltage (eg, bubble overvoltage) in the electrolysis process.

The problem to be solved by the present invention is to provide an electrolytic cell for a photo-electrolytic integrated hydrogen production system that can improve the hydrogen production efficiency by reducing the overvoltage in the electrolytic process by improving the structure of the electrode.

In order to solve the above technical problem,

The present invention is an electrolytic cell for a monolithic photovoltaic-electrolytic hydrogen production system including a PV photoelectrode / anode / separator / cathode, wherein a channel is formed on at least one of the anode and the cathode. Provides an electrolytic cell for an electrolytic integrated hydrogen production system.

According to one embodiment of the invention, it is preferable to use an anode composed of a conductive substrate coated with a metal oxide catalyst layer.

According to one embodiment of the invention, the conductive substrate may be selected from the group consisting of stainless steel, titanium, nickel, molybdenum, glass.

In addition, according to an embodiment of the present invention, the metal oxide catalyst layer coated on the conductive substrate is Co ₃ O ₄ , TiO ₂ , RuO ₂ , IrO ₂ , MnO ₂ or It is preferably selected from the group consisting of mixtures thereof. The metal oxide catalyst layer may be formed by dispersing oxide nanoparticles and then preparing a paste or ink to coat one surface of the conductive substrate. The metal oxide catalyst layer may be coated using a doctor blading method, a screen printing method, or a spin coating method. Can be.

In addition, according to an embodiment of the present invention, the anode is preferably selected from stainless steel foil (SUS foil), stainless steel plate (SUS plate), platinum foil (Pt foil), or conductive glass substrate, the cathode is stainless steel It is preferable to select from a metal substrate or conductive glass substrate on which a foil (SUS foil), platinum foil (Pt foil) or carbon particles such as platinum particles or carbon nanotubes are supported.

According to one embodiment of the present invention, an anode is coated with a Co ₃ O ₄ membrane catalyst layer, and the cathode is preferably an electrode which is a stainless steel foil (Pt / SUS foil) in which platinum particles are supported and channel is formed.

According to one embodiment of the present invention, an anion exchange membrane or a cation exchange membrane may be used as the separator depending on the electrolyte.

The electrolytic cell manufactured according to the present invention can be applied to a photovoltaic (PV) -electrolyte integrated hydrogen production system by optimizing anode and cathode electrodes. In order to maximize hydrogen generation rate, a channel was introduced to the electrode substrate, a metal oxide catalyst layer was formed on the anode, and platinum (Pt) particles were supported on the cathode. This optimized electrode configuration is more than twice as active as the case of simply using a metal electrode such as stainless steel or platinum foil as the anode and cathode, so that the hydrogen production efficiency can be significantly improved.

Figure 1 is a schematic diagram of a photovoltaic (PV) -integrated hydrogen production system according to an embodiment of the present invention, a is a conductive substrate, b is a PV photoelectrode, c is a catalyst layer, d is a separator.
Figure 2 is a part of the electrolytic cell used in one embodiment of the present invention, (a) is an acrylic frame, (b) is a SUS electrode substrate (top) and the film (bottom), (c) shows the appearance of the assembled device Indicates.
3 is a graph comparing hydrogen and oxygen production rates when (a) SUS foil-SUS foil, (b) SUS plate-SUS foil, and (c) Pt foil-SUS foil are used as an electrode (anode-cathode). The decomposition was carried out at a voltage of 2 V in aqueous NaOH (1 M) solution.
4 is a graph comparing hydrogen and oxygen production rates when (a) a SUS plate with a channel is formed, (b) a SUS plate without a channel and a SUS plate with a channel are used as an anode, and electrolysis is NaOH (1 M). It was carried out at a voltage of 2 V in aqueous solution.
5 is a SEM image of a Co ₃ O ₄ film formed on an SUS foil, and (b) is a graph comparing hydrogen and oxygen production rates when only a SUS foil or a Co ₃ O ₄ film is formed on an SUS foil and used as an anode. , Electrolysis was performed at a voltage of 2 V in aqueous NaOH (1 M) solution.
6 is a SEM image of (a) SEM images of Pt particles supported on SUS foils, and (b) a graph of comparing hydrogen and oxygen production rates when SUS foils, Pt foils, or SUS foils containing Pt particles were used as cathodes. The decomposition was carried out at a voltage of 2 V in aqueous NaOH (1 M) solution.
7 is a graph comparing hydrogen and oxygen production rates when a SUS plate without a channel and a SUS plate with a channel are used as a cathode.
8 is a graph comparing hydrogen and oxygen production rates when various electrodes (anode-cathodes) are used.

Hereinafter, the present invention will be described in more detail with reference to examples.

The inventor has produced an electrolytic cell for an integrated PV-electrolysis system. In particular, the focus was on anodes and cathodes, which function as catalysts during oxidation and reduction, respectively. By collecting the hydrogen (and oxygen) generated from the electrolytic cell, it was possible to directly measure the production rate of each gas and, as a result, optimize each electrode.

The electrolytic cell for a photovoltaic integrated hydrogen production system including a PV photoelectrode / anode / separator / cathode according to the present invention is characterized in that a channel is formed on at least one of the anode and the cathode.

According to one embodiment of the invention, the conductive substrate may be selected from the group consisting of stainless steel, titanium, nickel, molybdenum, glass.

In addition, according to an embodiment of the present invention, the metal oxide catalyst layer coated on the conductive substrate is Co ₃ O ₄ , TiO ₂ , RuO ₂ , IrO ₂ , MnO ₂ or It is preferably selected from the group consisting of mixtures thereof. The metal oxide catalyst layer may be formed by dispersing oxide nanoparticles, and then forming a paste or ink to coat one surface of the conductive substrate. The metal oxide catalyst layer may be coated using a doctor blading method, a screen printing method, or a spin coating method. Can be.

In addition, the ink or paste is preferably prepared by mixing oxide nanoparticles with a binder and a dispersant in an appropriate ratio to produce a solution having a high dispersibility. The binder and dispersant are 1: 0.8 to 3.0: 0.2 to 1.0 weight ratio based on the oxide nanoparticles. It is more preferable to prepare by mixing. Nafion, polyvinylidene fluoride, and the like may be used as the binder, and alcohol, amine, thiol, or the like may be used as the dispersant. If the binder is added in an amount of less than 0.8 wt.% With respect to the nanoparticles, the nanoparticles and the binder may not be sufficiently mixed to cause the nanoparticles to agglomerate. If the binder is more than 3, the viscosity of the paste may increase. In addition, when the dispersing agent is added in less than 0.2 weight ratio with respect to the nanoparticles, there is a problem that the binder is hardened due to insufficient dispersing of the paysheet, and when the content exceeds 1.0, the viscosity of the paysheet is low.

In addition, according to an embodiment of the present invention, the anode is preferably selected from stainless steel foil (SUS foil), stainless steel plate (SUS plate) or platinum foil (Pt foil), the cathode is a stainless steel foil (SUS foil) It is preferable to select from platinum foil (Pt foil) or stainless steel foil (Pt / SUS foil) on which platinum particles or carbon particles are supported.

According to one embodiment of the present invention, an anode is coated with a Co ₃ O ₄ membrane catalyst layer, and the cathode is preferably an electrode which is a stainless steel foil (Pt / SUS foil) in which platinum particles are supported and channel is formed.

According to one embodiment of the present invention, an anion exchange membrane or a cation exchange membrane may be used as the separator depending on the electrolyte.

Hereinafter, the present invention will be described in more detail with reference to examples, which are only illustrative for the purpose of understanding the present invention, and the scope of the present invention should not be construed as being limited to these examples.

Example : Manufacture of Electrolytic Cell

In the photo-electrolyte integrated hydrogen decomposition system according to the present invention, an electrolytic cell (10 × 10 cm ² ) having an activation area of 36 cm ² was used (FIG. 2). The frame of the battery was made of acrylic, and anion exchange membranes (Aha, Neosepta) were used as membranes for oxygen and hydrogen. Inlets and outlets were formed on the side of the acrylic frame to allow the electrolyte to pass through the cell. The anode, membrane and cathode substrates were placed between the acrylic frames and bolted to complete the unitary device.

Stainless steel (SUS 316) foils or plates were used as substrates for the anode and cathode. Pt foils were also tested as electrodes. An electrocatalyst film was introduced to the anode using a paste coating method. Specifically, a paste was prepared by dispersing Co ₃ O ₄ powder (˜50 nm, Aldrich) in isopropanol and then adding Nafion solution (20 wt%, DuPont). The resulting solution was mixed at 1500 RPM using a paste mixer (Deawha Tech, PDM-300) and then doctorblade coated on stainless steel (SUS 316) foil. The obtained sample was placed in a cast oven.

For cathode fabrication, Pt particles were prepared by dropwise addition of Pt precursor solution on a SUS substrate. The Pt precursor solution was prepared by dissolving hydrogen hexchloroplatinate hydrate (H ₂ PtCl ₆ xH ₂ O x = 5.8, Kojima) in isopropanol (5 mM). Structural characteristics of the electrodes were investigated by scanning electron microscopy (SEM, Hitachi, S-4200) and X-ray diffraction (XRD, Shimadzu, XRD-6000).

All electrolysis was performed at 2 V using a DC power source (Itech). NaOH (1 M) solution was used as electrolyte. The production rate of hydrogen and oxygen was measured by measuring the change of gas collection volume with reaction time using a self-made apparatus.

Experimental Example : Hydrogen Production Efficiency Measurement

Since most of the overvoltages in the water decomposition process are caused by the oxidation of water at the anode, the anode is very important in the electrolytic cell. As mentioned above, SUS foil or plate was used as the substrate of the catalyst film. SUS itself is known to have excellent catalytic properties upon water decomposition. First, the hydrogen production capacity of foils and plates made of the same SUS material (SUS 316) was compared. In addition, Pt foils, which are well known as electrocatalyst materials for water electrolysis, were tested for comparison. As expected, SUS foils and plates showed no significant difference in hydrogen production rate. However, SUS material showed a significantly higher hydrogen production rate compared to the case of using Pt foil (FIG. 3).

Since the gas (bubble) generated on the electrode surface is not easily removed to reduce the effective area of the current, the bubble overvoltage is not small among various factors of overvoltage generated during the electrolysis process. In order to reduce the bubble overvoltage, a channel was formed in the SUS plate as shown in FIG. 4A. The distance and depth of the grooves formed were 1.0 mm and 0.25 mm, respectively. The channeled SUS plate was used as an anode to compare activity with the same SUS plate without the channel. As shown in Figure 4b, the channel-formed SUS plate showed about 19% higher activity than the plate without the channel.

In order to form an electrocatalyst layer on the anode SUS substrate, the metal oxide powder was paste coated. In particular, in the case of integrated PV-electrolyte cells, it is necessary to form the electrocatalyst film at a low temperature in order to prevent deterioration of the PV first formed on the opposite side of the substrate. Co ₃ O ₄ as a metal oxide electrocatalyst The paste was made using the powder. After the paste was coated on the SUS substrate by the doctorblade method, the formed film was dried at 50 ºC. The thickness of the membrane was about 12 μm. As a result of the analysis of the film, Co ₃ O ₄ nanoparticles having an average size of about 50 nm were observed, but the nanoparticles were embedded or enclosed in the amorphous material, suggesting that the organic material is present in the film (FIG. 5A). Co ₃ O ₄ Due to the electrocatalyst properties of the film, the rate of hydrogen evolution was increased by about 10% compared to when only the SUS substrate was used (FIG. 5B).

Unlike the case of the anode, the use of Pt material results in relatively low overvoltage at the cathode. Experimental results show that the Pt foil provides better performance than the SUS foil in water electrolysis. However, since Pt is a very expensive material, it is necessary to replace Pt with a cheaper material or to reduce the amount of Pt used. In the present invention, the Pt precursor was added dropwise to the SUS substrate and then heat-treated at 360 ºC for 10 minutes to deposit Pt particles. As shown in the SEM image of FIG. 6A, randomly dispersed rod-shaped Pt particles having a length of about 100 nm were formed on the SUS substrate. As a result of comparing the hydrogen production rate, the Pt particles loaded on the SUS foil showed better activity than the Pt foil or the SUS foil (FIG. 6B). As with the anode, the effect of the channel on the cathode was tested. The SUS plate on which the channel was formed showed about 21% higher activity than the case without the channel (FIG. 7).

To sum up the above results, it is considered that the optimum electrode combination is a case where a Co ₃ O ₄ catalyst film is formed on the SUS on which the channel is formed and used as an anode, and Pt particles are supported on the SUS on which the channel is formed and used as a cathode.

In the present invention, an electrolysis experiment was performed on a combination of forming a Co ₃ O ₄ film on the SUS foil and supporting Pt particles in the SUS on which the channel was formed. As shown in FIG. 8 comparing the hydrogen generation rates for the various electrodes, when the Co ₃ O ₄ film was formed on the SUS foil as an anode, and the Pt particles were supported on the SUS plate on which the channel was formed, the excellent hydrogen generation rate was obtained. Obtained. Compared to the case of simply using a metal electrode (for example, SUS-SUS or SUS-Pt), hydrogen production rate nearly doubled was obtained. Therefore, it can be seen that the material and structure of the electrode is very important in the water decomposition by the electrolytic cell.

The electrolytic cell manufactured according to the present invention is optimized for the anode and cathode electrodes, and is applicable to a PV-electrolyte integrated hydrogen production system. In order to maximize hydrogen generation rate, a channel was introduced to the electrode substrate, and a Co ₃ O ₄ catalyst layer was formed as an anode and Pt particles were supported as a cathode. This optimized electrode configuration showed two times higher activity than using a metal electrode such as SUS or Pt foil as an anode and a cathode.

Claims (10)

An electrolytic cell for a monolithic photovoltaic-electrolytic hydrogen production system comprising a PV photoelectrode / anode / separator / cathode, wherein Co ₃ O ₄ , TiO ₂ , RuO ₂ , IrO ₂ , MnO ₂ or An anode composed of a conductive substrate coated with a metal oxide catalyst layer selected from the group consisting of mixtures thereof, stainless steel foil (SUS foil), platinum foil (Pt foil) or stainless steel foil (Pt / SUS) carrying platinum or carbon particles Electrolyte cell for photo-electrolytic integrated hydrogen production system, characterized in that the channel is formed on at least one electrode of the cathode selected from the foil. delete The method of claim 1,
The conductive substrate is a stainless steel, titanium, nickel, molybdenum, glass electrolytic cell for an integrated hydrogen production system, characterized in that selected from the group consisting of glass. delete The method of claim 1,
The metal oxide catalyst layer is prepared by dispersing oxide nanoparticles and then forming a paste or ink to coat one surface of a conductive substrate. The method of claim 1,
The coating of the metal oxide catalyst layer is an electrolytic cell for a photo-electrolyte integrated hydrogen production system, characterized in that selected from the doctor blading method, screen printing method or spin coating method. The method of claim 1,
The anode is selected from a stainless steel foil (SUS foil), a stainless steel plate (SUS plate), platinum foil (Pt foil) or a conductive glass substrate, characterized in that the electrolytic cell for a photovoltaic integrated hydrogen production system. delete The method of claim 1,
The anode is coated with a Co ₃ O ₄ membrane catalyst layer, and the cathode is a platinum particle-bearing, channel-formed stainless steel foil (Pt / SUS foil) characterized in that the electrolytic electrolysis integrated hydrogen production system battery. The method of claim 1,
The separator is an anion exchange membrane or a cation exchange membrane electrolytic cell for a photovoltaic integrated hydrogen production system, characterized in that.

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