JP2008133491A - Electrode for use in electrolysis of sulfurous acid and apparatus for producing hydrogen through electrolysis of sulfurous acid by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for use in an electrolysis of sulfurous acid, which has a high catalytic activity for a reaction of oxidizing sulfurous acid, does not form an oxide film thereon even in such an environment that the sulfurous acid and sulfuric acid coexist, and has such high durability as to continue the electrolysis reaction for a long period of time, and to provide an apparatus for producing hydrogen through the electrolysis of the sulfurous acid by using the catalyst for the electrolysis of the sulfurous acid. <P>SOLUTION: An electrode for use in the electrolysis of electrolyzing sulfurous acid to produce hydrogen and sulfuric acid, is made from gold or an alloy containing gold as a main component and another noble metal. The electrode for use in the electrolysis has an aspect in which fine particles of gold or the alloy containing gold as the main component and another noble metal are carried on the surface of an electrode made from an oxide material or carbon, or an aspect of a membrane electrode assembly in which fine particles of gold or the alloy containing gold as the main component and another noble metal are carried on the surface of a polymer electrolyte membrane. The apparatus for producing hydrogen through the electrolysis of the sulfurous acid has a structure of dividing the inside of an electrolytic tank into a reaction chamber in an anode side and a reaction chamber in a cathode side by a cation-exchange membrane, and arranging an anode and a cathode respectively in the anode side and the cathode side of the cation-exchange membrane. The anode for the electrolysis of the sulfurous acid employs the electrode made from gold or the alloy containing gold as the main component and another noble metal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

   The present invention relates to an electrode for sulfite electrolysis having high catalytic activity and excellent durability, which can be effectively used for the production of hydrogen by electrolysis of sulfurous acid (aqueous solution of sulfur dioxide), and an apparatus for producing sulfite electrolysis hydrogen using this electrode It is about.

A number of methods have been proposed for hybrid thermochemical processes in which hydrogen is produced from water electrochemically and thermochemically by combining the synthesis and decomposition reaction of sulfuric acid.
For example, sulfuric acid (H ₂ SO ₄ ) is thermally decomposed to produce sulfur trioxide (SO ₃ ) and water (H ₂ O), and sulfuric acid trioxide is converted to sulfur dioxide (SO ₂ ). A hybrid thermochemical process that combines a sulfur trioxide electrolysis process that electrolyzes oxygen (O ₂ ) and a sulfurous acid electrolysis process that generates hydrogen (H ₂ ) and sulfuric acid by electrolyzing sulfur dioxide consisting of an aqueous solution of sulfur dioxide. A hydrogen production method is known.

In such a hybrid thermochemical process, in the sulfite electrolysis step that actually generates hydrogen, sulfuric acid supplied to the anode side of the electrolytic cell is electrolyzed to produce sulfuric acid on the anode side and hydrogen on the cathode side. The As an anode side electrode material for the sulfite oxidation reaction, platinum (Pt) and palladium (Pd), which have conventionally been confirmed to have high catalytic performance in a polymer electrolyte fuel cell or the like, have been studied.
However, in the case of platinum and palladium, it has been confirmed that an oxide film is formed on the surface along with the electrolytic reaction, and the electrolysis current gradually decreases, which is long in the anode environment where sulfurous acid and sulfuric acid are mixed. The development of a highly durable electrode material capable of performing an electrolytic reaction stably over a period has been awaited.

On the other hand, a hydrogen production method using a water gas shift reaction in which carbon monoxide (CO) reacts with water is also known, and it is proposed to use a catalyst containing gold (Au) for this reaction ( Patent Document 1).
Also known is a method of producing a reformed gas mainly composed of hydrogen by steam reforming of a hydrocarbon fuel or an alcohol fuel. When this reformed gas is used as fuel for a fuel cell, CO contained in the reformed gas poisons and deteriorates the catalyst of the fuel cell. Therefore, the CO contained in the reformed gas is selectively oxidized and removed. Therefore, it is necessary to reduce the CO concentration, and a proposal has been made to use a gold-containing catalyst as a CO oxidation catalyst for that purpose (Patent Document 2). In this CO oxidation catalyst, high catalytic activity is recognized when gold is made into ultrafine particles having a particle diameter of 10 nm or less.
However, these gold-containing catalysts proposed in the prior art have been considered to have poor catalytic activity as a sulfite oxidation catalyst, and thus have not been attempted to be applied to a sulfite oxidation reaction.

JP 2005-521548 A JP 7-48101 A

  Therefore, the present invention has a high catalytic activity for the sulfite oxidation reaction, and has a high durability capable of performing an electrolytic reaction stably for a long time without forming an oxide film even in an environment where sulfurous acid and sulfuric acid are mixed. An object of the present invention is to provide a sulfite electrolysis catalyst provided, and to provide a sulfite electrolysis hydrogen production apparatus using the sulfite electrolysis catalyst.

That is, the electrode for sulfite electrolysis according to the present invention is an electrode for sulfite electrolysis that generates hydrogen and sulfuric acid by electrolyzing sulfite, and is composed of gold or an alloy with other noble metals mainly composed of gold. It is what.
As an embodiment of the above-described electrode for sulfite electrolysis, gold or an alloy with other noble metal mainly composed of gold is supported on the surface of an oxide material or a carbon electrode, and further, gold or Examples thereof include those composed of a membrane electrode assembly in which fine particles of an alloy with other noble metal mainly containing gold are supported on the surface of a polymer electrolyte membrane.

  The apparatus for producing hydrogen sulfite electrolysis according to the present invention divides the inside of an electrolytic cell into an anode side reaction chamber and a cathode side reaction chamber by a cation exchange membrane, and an anode and a cathode on the anode side and cathode side of the cation exchange membrane, respectively. An apparatus for producing sulfite electrolysis hydrogen, in which sulfuric acid is generated in the anode reaction chamber and hydrogen is generated in the cathode reaction chamber by electrolyzing the sulfurous acid supplied to the anode reaction chamber The electrode for sulfite electrolysis made of gold or an alloy with other noble metal containing gold as a main component is used as the anode.

  According to the present invention, in a hybrid thermochemical process of electrochemically and thermochemically producing hydrogen from water by combining sulfuric acid synthesis and decomposition reaction, sulfurous acid electrooxidation in which sulfurous acid is electrolyzed to produce hydrogen and sulfuric acid. An anode electrode material that can be effectively used for the reaction can be provided. By using this electrode material, no oxide film is formed on the electrode surface in the assumed operating voltage range of 0 to about 1.0 V (vs. reference hydrogen electrode), resulting in high electrolysis performance and high durability. It is possible to construct a sulfite electrolysis hydrogen production apparatus.

In addition, since a higher current density can be obtained at the same voltage than in the case of conventional platinum or palladium electrodes, it is possible to reduce the electrical energy consumed by the sulfite electrolysis hydrogen production apparatus, and to improve the electrolysis efficiency of the apparatus. it can.
Furthermore, as a result of the reduction of the electric energy consumed in the sulfite electrolysis hydrogen production apparatus, the electric energy consumed in the entire hybrid thermochemical process can be reduced, and the hydrogen production efficiency of the whole process can be improved.

FIG. 4 shows reactions and reaction formulas constituting a hybrid thermochemical process employed as a hydrogen production method, and the sulfite electrolysis electrode of the present invention can be used in the sulfite electrolysis reaction.
Sulfuric acid heating process:
H ₂ SO ₄ thermal decomposition reaction H ₂ SO ₄ → SO ₃ + H ₂ O [1] (400 ° C.)
Sulfur trioxide electrolysis process:
SO ₃ electrolytic reaction SO ₃ → SO ₂ + 1 / 2O ₂ ... [2] (> 500 ° C.)
Sulfurous acid electrolysis process:
Sulfurous acid electrolysis SO ₂ + 2H ₂ O → H ₂ SO ₄ + H ₂ ... [3] (<100 ° C.)

FIG. 1 shows an example of an apparatus configuration of a hybrid thermochemical process. In the sulfuric acid heating device, the mixed gas of SO ₃ and H ₂ O is obtained according to the sulfuric acid pyrolysis reaction [1] by heating H ₂ SO ₄ supplied from the sulfurous acid electrolysis hydrogen production device to about 400 ° C. .
In the sulfur trioxide electrolysis apparatus, SO ₃ is SO _{2 in} accordance with the SO ₃ electrolysis reaction [2] by electrolyzing the mixed gas of SO ₃ and H ₂ O supplied from the sulfuric acid heating apparatus at about 500 ° C. or higher. And O ₂ , and O ₂ is discharged from the electrolyzer.
In the sulfurous acid electrolysis hydrogen production apparatus, a mixed gas of SO ₂ and H ₂ O supplied from the sulfur trioxide electrolysis apparatus and liquid H ₂ O as a separately supplied raw material are mixed to form sulfurous acid, and the sulfurous acid electrolysis reaction H ₂ SO ₄ and H ₂ are produced by decomposing sulfurous acid according to [3].

As shown in FIG. 1, the sulfite electrolysis hydrogen production apparatus has an inside of an electrolytic cell 1 formed into an anode side reaction chamber and a cathode side reaction chamber by a cation exchange membrane 2 such as “Nafion” (trade name of DuPont). The anode 3 and the cathode 4 are disposed on the anode side and the cathode side of the cation exchange membrane 2, respectively, and a voltage is applied between the electrodes from a power supply device (not shown). In the anode side reaction chamber, H ₂ SO ₄ is generated by the electrolytic oxidation reaction of the following reaction [4]. Hydrogen ions (H ⁺ ) generated by this reaction move to the cathode side through the cation exchange membrane 2, and become H ₂ gas by the following reaction [5] on the cathode surface. H ₂ SO ₄ is circulated and supplied to the sulfuric acid heating device, and H ₂ is discharged as a product from the cathode side reaction chamber.
To discharge H _{2 from} the cathode side reaction chamber, purge gas such as N ₂ or liquid sulfuric acid having the same concentration as H ₂ SO ₄ produced in the cathode side reaction chamber is allowed to flow as a purge fluid into the cathode side reaction chamber. Can be performed.
H ₂ SO ₃ + H ₂ O → H ₂ SO ₄ + 2H ⁺ + 2e ⁻ [4]
2H ⁺ + 2e ⁻ → H ₂ [5]

In the anode-side reaction chamber of the sulfurous acid electrolysis hydrogen production apparatus, since sulfurous acid to be supplied and sulfuric acid to be generated exist, an environment in which sulfurous acid and sulfuric acid are mixed is provided. In the hybrid thermochemical process, undecomposed SO ₃ that has not been electrolyzed by the sulfur trioxide electrolyzer in the previous stage is also supplied to the anode side reaction chamber of the sulfite electrolysis hydrogen production apparatus, and this SO ₃ is dissolved in water. Since it becomes H ₂ SO _4, it becomes a mixed environment of sulfurous acid and sulfuric acid. The SO ₂ gas contained in the blast furnace exhaust gas or volcanic gas of the ironworks can be directly supplied to the anode side reaction chamber of the sulfite electrolysis hydrogen production apparatus. In this case, too, part of the SO ₂ gas is H _2. It dissolves in O to become sulfurous acid, and sulfuric acid is generated by electrolytic oxidation reaction at the anode.

In the present invention, an anode-side environment in which sulfurous acid and sulfuric acid are mixed by using an electrode material made of gold (Au) or an alloy with another noble metal containing gold as a main component as an anode in the sulfite electrolysis hydrogen production apparatus. In this case, it is possible to provide high durability capable of performing the electrolytic reaction stably for a long period of time without forming an oxide film on the anode surface with the electrolytic reaction.
In the present invention, gold or an alloy with other noble metal containing gold as a main component is not necessarily formed into fine particles, and can be used in a general electrode shape such as a plate shape or a mesh shape. However, it is preferably used as fine particles having a particle size of several μm or less from the viewpoint that the surface area can be increased. In this case, in order to prevent coarsening due to coalescence of fine particles, alloying with other noble metals (Pt, Pd, Ru, Rh, Ir, etc.), oxide materials (WO ₃ , Ti ₂ , Co ₃ O) ₄ , Al ₂ O ₃ , ZrO _2, etc.) or a method such as loading on the surface of a gas diffusion electrode made of carbon. Moreover, it can also be set as the membrane electrode assembly which carry | supported the microparticles | fine-particles on the surface of a polymer electrolyte membrane. When gold is alloyed with other noble metals, gold is the main component in the alloy, but the content of gold is an effective content to effectively suppress the formation of an oxide film on the anode surface. do it.

The operating temperature of the sulfite electrolysis hydrogen production apparatus can be performed in a range from room temperature to about 100 ° C., and an electrode made of gold or an alloy with other noble metal containing gold as a main component is approximately the reversible hydrogen electrode potential. Used in the range of 0 to 1.0V.
As the cathode material, noble metal materials such as platinum, palladium, ruthenium, rhodium, iridium and carbon-based materials can be used as in the conventional case.

Experimental example

FIG. 3 shows a current-voltage curve obtained by the cyclic voltammetry method in an aqueous solution containing sulfurous acid and sulfuric acid using the Pt, Pd and Au electrodes by the apparatus shown in FIG. The apparatus shown in FIG. 2 includes a flask having a working electrode, a counter electrode, and a reference electrode, and a power source that applies a voltage between the electrodes. Temperature control can be performed by a thermocouple.
An aqueous solution containing 4.5 mass% sulfurous acid and 0.1 M sulfuric acid is placed in the flask, Pt-black is used as the counter electrode, a reference hydrogen electrode is used as the reference electrode, and Pt, Pd or a surface area of 0.1 cm ² is used as the working electrode. An Au electrode was used. FIG. 3 shows a current-voltage curve when the scanning speed is 100 mV / second, the temperature is 20 ° C., and the voltage is 0.3 to 1.5 V (vs. reference hydrogen electrode).

  As can be seen from FIG. 3, when the Pt and Pd electrodes are scanned to the high voltage side, a decrease in current density, which is considered to be due to surface oxidation, is observed. On the other hand, in the case of the Au electrode, almost no decrease in current density is observed in the voltage range from 0 to about 1.5 V (vs. reference hydrogen electrode). Further, when compared at the same voltage, the current density is highest when the Au electrode is used. From these experimental results, the Au electrode has high durability in a mixed solution of sulfurous acid and sulfuric acid, and at the same time, a high current density (hydrogen generation amount) can be obtained at the same electrolytic voltage. It was confirmed that energy use efficiency was obtained.

When a hybrid thermochemical process is used as the hydrogen production method, electrolysis is performed at two locations, SO ₃ electrolysis [2] and sulfite electrolysis [3], but SO ₃ electrolysis is performed at a high temperature of about 500. Since it is performed at a high temperature of ℃ or higher, the voltage loss can be recovered as heat, but since the electrolysis of sulfurous acid is performed at a low temperature of 100 ℃ or less, the energy of the voltage loss cannot be recovered, and the entire process The impact on the energy use efficiency of For this reason, it becomes possible to aim at the improvement of hydrogen production efficiency by using a low voltage loss electrode material with a sulfurous acid electrolysis hydrogen production device.

It is explanatory drawing which shows an example of the apparatus structure of a hybrid thermochemical method process, and the Example of the sulfurous acid electrolysis hydrogen manufacturing apparatus incorporated in it. It is explanatory drawing which shows the experimental apparatus used for the experiment for calculating | requiring a current-voltage curve by a cyclic voltammetry method using Pt, Pd, and Au electrode. It is a graph which shows the current-voltage curve about Pt, Pd, and Au electrode calculated | required using the experimental apparatus of FIG. It is explanatory drawing of reaction and reaction formula which comprise the sulfurous acid electrolysis hydrogen manufacturing method in a hybrid thermochemical process.

Explanation of symbols

1: Electrolytic cell 2: Cation exchange membrane 3: Anode 4: Cathode

Claims (4)

An electrode for sulfite electrolysis that generates hydrogen and sulfuric acid by electrolyzing sulfite, and is made of gold or an alloy with other noble metals mainly composed of gold. 2. The electrode for sulfite electrolysis according to claim 1, wherein fine particles of gold or an alloy with other noble metal containing gold as a main component are supported on the surface of an oxide material or a carbon electrode. 2. The electrode for sulfite electrolysis according to claim 1, comprising a membrane electrode assembly in which fine particles of gold or an alloy with other noble metal containing gold as a main component are supported on the surface of the polymer electrolyte membrane. The inside of the electrolytic cell is divided into an anode side reaction chamber and a cathode side reaction chamber by a cation exchange membrane, and an anode and a cathode are arranged on the anode side and the cathode side of the cation exchange membrane, respectively. 4. The sulfite electrolysis hydrogen production apparatus in which sulfuric acid supplied to the chamber is electrolyzed to generate sulfuric acid in the anode-side reaction chamber and hydrogen in the cathode-side reaction chamber, respectively. A sulfurous acid electrolysis hydrogen production apparatus characterized by using an electrode for sulfurous acid electrolysis made of gold or an alloy with another noble metal containing gold as a main component.

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