JPS5871380A - Production of hydrogen by electrolysis - Google Patents

Abstract

PURPOSE:To obtain H2 together with I2 or Br2 at a low voltage by carrying out the electrolysis of HI or HBr in a vapor phase using an electrolytic cell contg. a porous holding matrix impregnated with phosphoric acid as an electrolyte between electrodes. CONSTITUTION:Said known electrolytic cell is used as a fuel cell, gaseous HI is introduced into the anode chamber, and vapor phase electrolysis is carried out. I2 produced on the anode is slightly soluble in concd. phosphoric acid. Gaseous H2 is generated from the cathode chamber. When gaseous HI contg. steam is introduced, the steam is dissolved in phosphoric acid on the anode side and shifts to the cathode side in accordance with the difference between the anode and cathode chambers in the partial pressure of steam, and it is evaporated on the cathode side. Accordingly, H2 obtd. from the cathode chamber contains steam, yet the steam can be separated by condensation. Since the transfer of steam in the electrolytic chambers facilitates the transfer of H<+>, the current density can be increased in the presence of steam contained in gaseous HI.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing hydrogen and iodine or bromine by electrolyzing hydrogen iodide or hydrogen bromide, and particularly relates to a method for electrolyzing the halide in a gas phase.

The decomposition of hydrogen halides, especially hydrogen iodide, has been investigated by various methods such as thermal decomposition, electrolysis, and photolysis. Equilibrium decomposition rate 11.3
Numerous studies have been carried out, including the separation of fractions (%). Of these, regarding the electrolytic method, the standard monopolar potential difference (25°C) of solid iodine and liquid bromine is 0.53, respectively.
6 and 1.0.65 V, the theoretical cell voltage for generating hydrogen at 1 atm by electrolyzing an aqueous solution of hydroiodic acid and hydrobromic acid with an activity of 1 (approximately 1 molar concentration) is Requires 0.536 and 1.065V. According to the results of Kanzaki who actually performed electrolysis (Patent No. 178878), for a hydroiodic acid solution with a specific gravity of 1.7, the bath voltage was 1 to obtain a current of 44 mA/cIrL2 at 18°C.
needed v. On the other hand, FeeSs et al.
k, k6sterand Ci, H,5chi
itz, Jnt, J, HydrogenEne
rgy 6 NO-4pp-377-388, 1981
1.) In the electrolysis of an aqueous solution of hydrobromic acid, the bromine produced at the anode is directly dissolved in the aqueous solution. It states that it shows a tendency to move to the cathode through convection, diffusion, etc. and recombine with hydrogen, reducing the current efficiency rate accordingly.

The present invention provides a method for electrolyzing the above-mentioned hydrogen at a low voltage, and is based on gas phase electrolysis. Decomposition reaction of hydrogen iodide gas and hydrogen bromide gas at a temperature of 127"C (4000K), 2Hi(9)-, H2V)+ I
Aya and 21-I B rty>--"t' 2 (q
)” Bra no freedom
/・νItti II 2, the theoretical cell pressure is 0.
067 V and Q, calculated as 58V. That is, the gas phase 11fi of hydrogen iodide gas, solution f, requires a cell voltage of about 1/8 of that of an aqueous solution of hydrogen hydroxide having a concentration of about 1 molar.

Furthermore, we have found that a fuel clarification pond type device using phosphoric acid as an electrolyte can be effectively used as an actual device for carrying out such an advantageous decomposition reaction.

That is, the device used in the present invention is known as a structure of a fuel cell (for example, R. D. Prolt JP-A-52-299
33), in which a porous phosphoric acid retention matrix impregnated with a phosphoric acid electrolyte is placed between a pair of spaced apart gas diffusion electrodes. Here, the gas diffusion electrode may be a highly conductive carbon fiber woven cloth coated with a platinum catalyst, etc., and the matrix for retaining phosphoric acid may be an electrically insulating porous material that is resistant to erosion by concentrated phosphoric acid. Materials such as woven tantalum oxide are useful. Regarding hydrogen iodide gas, the preferred electrolysis temperature is such that the iodine produced is in the form of liquid or gas. Under these temperature conditions, when the gas is introduced into the anode chamber, a cell voltage of approximately 0.085 V is produced. It was approved to start electrolysis. At this time, iodine produced on the anode side is poorly soluble in concentrated phosphoric acid, while hydrogen gas is generated from the cathode chamber. Additionally, when hydrogen iodide gas containing water vapor is introduced, the water vapor is dissolved in phosphoric acid from the anode side, moves to the cathode side, and evaporates there, depending on the difference in water vapor partial pressure between the anode and cathode compartments. . Therefore, the hydrogen obtained from the cathode chamber contains water vapor, which can be condensed by conventional means to purify hydrogen gas. What should be noted here is that this circular movement of water vapor in the electrolyte promotes the movement of hydrogen ions toward the cathode, which increases the current density compared to hydrogen iodide gas electrolysis where no water vapor is present. I can talk with you. The amount of water vapor is
The amount is preferably in the range of 0.01 to 20 mol per mol of hydrogen iodide. Hydrogen bromide can also be used in place of hydrogen iodide in the present invention.

Example 1 The electrolytic cell used had a structure known as an intoxicating electrolyte battery (Tezawa, Gendai Kagaku, December 1973 issue, p. 18).
It is. That is, a pair of graphite substrates (9.5 cm x 1
t, (1 am, thickness 2 儂) are closely combined to form the outer shell of the cell, and each have two connections "1",
From here, a current collector (5 crrL x 5 (-In
), or the generated gas can be discharged. This current collector contains 0.75% platinum as a catalyst.
m9/cIrL2 coated graphite fiber cloth (thickness 0.5 mm
A gas diffusion electrode made of tantalum oxide woven fabric (thickness Q, 75 mm, fiber thickness 5 μm) was stacked on top of the gas diffusion electrode (fiber thickness 5 μm), and a dense gas diffusion electrode made of tantalum oxide fabric (thickness Q, 75 mm, fiber thickness 5 μm) was placed so as to space this pair of electrodes apart. A matrix impregnated with phosphoric acid (85%) is placed. Therefore, the experimental electrolytic cell consisted of a lower anode chamber and an upper cathode chamber symmetrically centering on this matrix fabric, and the entire cell was placed in an air constant temperature chamber and maintained at a predetermined temperature. The electrical resistance of the electrolytic cell at 150°C is approximately 0.
It is 1 ohm.

Raw material hydrogen iodide gas (mixed molar ratio HI/l-1zO/
N2 = 0.50/0.41/0.09) was supplied to the anode chamber at a rate of 500 ml/min under atmospheric pressure.
When electrolysis was performed at 50°C, the cell voltage was approximately 0.
Starting from 08V, the current density at 0.4V is "Om'
/lx 2. Water vapor and hydrogen were discharged from the cathode chamber, and the hydrogen iodide content was very small (less than 5 molar proportion of hydrogen) and was condensed together with the water vapor in the attached condenser vessel. On the other hand, it was confirmed by the I/it 711 unit after cooling that liquid iodine was produced at the anode.The current efficiency determined from the generated hydrogen tfL was about 95 coefficients.

Example 2 This example shows the effect of coexisting water vapor on the electrolysis of hydrogen iodide gas. As the raw material gas, anhydrous hydrogen iodide gas (mixed molar ratio 1 (I/N2 = 0.510.5) was used,
When the same experiment as in Example 1 was conducted, the cell Ichikawa was 0.4
5 current density below V remained at 30 mA.

Example 3 In this example, electrolysis of hydrogen bromide gas will be described. Raw material hydrogen bromide gas $≦(Mixed molar ratio HB r/Ll 2
0/N2SO,47/ 0.44/0.09
) was supplied to the anode chamber at a rate of 500 me/min at a temperature of 143° C. in the atmosphere using the apparatus of Example 1.

Electrolysis was started with a 0.58V pretrowel, the current density at 084V was 1 o mA, and the current efficiency calculated from the amount of hydrogen generated from the cathode chamber was about 95 yen.

Continuation of page 1 @ Originated by Chisho Kawamura Takatsuki City Area Nishimachi 6-6 Yuasa Battery Inside the corporation (7) Author: Hiroshi Aburofu Takatsuki City Area Nishimachi 6-6 Yuasa Battery Inside the corporation ■Submitted by: Yuasa Battery Co., Ltd. 6-6 Kennishimachi, Takatsuki City Patent attorney Toshiaki Ikeura 45

Claims (1)

[Scope of Claims] (]) a pair of spaced apart gas diffusion electrodes, a porous retention matrix disposed between the electrodes, and a hyperphosphoric acid electrolyte impregnated into the matrix; A method for producing electrolytic hydrogen, which comprises introducing hydrogen iodide or hydrogen bromide gas into the anode chamber of an electrolytic cell containing hydrogen, and removing iodine or bromine from the anode chamber and hydrogen from the cathode chamber by electrolysis. (2) The method according to claim 1, wherein the hydrogen iodide gas or hydrogen bromide gas contains water vapor. (3) The method according to claim 2, wherein the amount of water vapor is 0.01 to 20 moles per mole of hydrogen iodide or hydrogen bromide gas.