CN1308489C

CN1308489C - Apparatus for preparing boron hydride by electrolysis

Info

Publication number: CN1308489C
Application number: CNB2004100132952A
Authority: CN
Inventors: 曹余良; 杨汉西; 光先勇; 艾新平; 喻敬贤
Original assignee: Wuhan University WHU
Current assignee: Wuhan University WHU
Priority date: 2004-06-15
Filing date: 2004-06-15
Publication date: 2007-04-04
Anticipated expiration: 2024-06-15
Also published as: CN1584122A

Abstract

The present invention discloses a device for preparing borohydride by electrolysis-a three electrolytic tank system. Each electrolytic tank for preparing the borohydride by the electrolysis can be divided into three chambers mutually separated, namely an anode chamber, a cathode chamber A and a cathode chamber B, wherein the anode chamber and the cathode chamber A are separated by a cation exchange membrane, and the cathode chamber A and the cathode chamber B are separated by a porous cathode. The device is favorable for increasing the contact area of reactants and the inner parts of electrodes and dredging a diffusion channel of products, and simultaneously, necessary conditions needed by reduction reactions are provided by different electric field environments in the porous cathode; therefore, compared with the structure of the traditional electrolytic tanks, the present invention has higher current efficiency. The device of the present invention provides a more economical and feasible way for the preparation of the borohydride, simultaneously provides a cheaper hydrogen source material for the development of fuel batteries, and therefore, has important application prospects.

Description

Device for preparing borohydride by electrolysis

Technical Field

The invention relates to an electrolysis device, in particular to a device for preparing borohydride by electrolysis, namely a three-electrolytic-cell system, belonging to the field of energy materials and fuel cell hydrogen sources.

Background

The hydrogen energy economy is an energy development direction proposed by the human society for relieving resource and environmental problems, and the core content of the development is to replace the existing fossil fuel (coal and petroleum) with hydrogen as a clean, green and portable fuel. The fuel cell using hydrogen as fuel is an efficient and clean power generation device, and is gradually becoming an ideal matching power source for portable electronic products and electric vehicles. At present, the main problem limiting the development and application of fuel cells is hydrogen storage, and the existing hydrogen storage mode is low in hydrogen storage amount, such as a high-pressure hydrogen bottle (1%), a hydrogen storage alloy (1.5-3%) and the like. Borohydride is a material with a high hydrogen storage content, such as LiBH₄(36.8％)、NaBH₄(21.2％)、KBH₄(14.8%), not only can the compounds catalyze hydrolysis to release hydrogen as a high-capacity and high-purity hydrogen source material, but also can be directly used as a high-capacity cathode material in an electrochemical mode.

Borohydride catalytic hydrolysis reaction:

borohydride direct electrochemical oxidation reaction:

because of this, recently, Millennium Cell corporation, usaNew fuel cells are being developed that use alkali metal borohydrides as direct fuels. They indicate that higher energy densities can be provided by direct electrochemical reaction of borohydrides (e.g., NaBH)₄A theoretical capacity of 5673mAh/g) and a simple battery device.

At present, the conventional Schlesinger method and Bayer method are mainly used for preparing borohydride industrially. These two synthetic routes prepare 1mol of NaBH₄All consume 4mol of metallic sodium, and are produced by high-temperature electrolysis, thus preparing NaBH₄The cost is high and the yield is small. Considering that hydrolysis and discharge products of borohydride are both BO₂ ^-If BO can be achieved electrochemically₂ ^-Recovery and recycle of BH₄ ^-The method is an attractive way for greatly reducing the cost of the borohydride, and develops the application of the borohydride into a wide market.

Electrolytic production of borohydrides has been reported in Cooper (US3437842), Hale (US4931154), but the current efficiency is low (<20%) due to the use of noble metal catalysts. Meanwhile, the traditional electrolysis device for preparing borohydride by electrolysis adopts a two-tank structure, namely a basic cathode chamber and an anode chamber, and the single cathode chamber is not beneficial to the contact of reactants and the inside of the electrode and the formation of an electric field environment suitable for reaction for preparing borohydride by electrolysis, so the current efficiency is low. The core technology of preparing borohydride by adopting an electrolytic method is to provide a catalyst with low price, low hydrogen release and high catalytic activity, and more importantly, to establish an electrolytic device with a reasonable structure.

Disclosure of Invention

In order to overcome the defect of low current efficiency of the conventional electrolytic device, the invention provides a novel device for preparing borohydride by electrolysis, namely a three-electrolytic-tank system, so that metaborate is efficiently electrochemically reduced into borohydride.

The specific technical scheme is as follows: a device for preparing borohydride by electrolysis, namely a three-electrolytic cell system, is shown in a schematic structural diagram in figure 1. The electrolytic cell for preparing borohydride by electrolysis is divided into three chambers which are isolated from each other: namely an anode chamber, a cathode chamber a and a cathode chamber B. The anode compartment is separated from the cathode compartment a by a cation exchange membrane, and the cathode compartment a is separated from the cathode compartment B by a porous cathode. The bottom of the anode chamber is provided with an anode liquid inlet pipe, the upper part of the anode chamber is provided with an anode liquid outlet pipe and an air outlet pipe, the cathode chamber A and the cathode chamber B are respectively provided with a cathode liquid inlet pipe, the upper parts of the cathode chamber A and the cathode chamber B are respectively provided with a cathode liquid outlet pipe, and the anode is arranged on the inner wall of the electrolytic bath of the anode chamber and is opposite to the cation exchange membrane.

The anode of the electrolytic cell system adopts ruthenium titanium oxide, lead oxide, nickel, platinum or graphite, or a mixture of any two of the ruthenium titanium oxide, the lead oxide, the nickel, the platinum or the graphite; the porous cathode adopts hydrogen storage alloy, carbon material, metal boride, nickel or iron, or the mixture of any two of the hydrogen storage alloy, the carbon material, the metal boride, the nickel or the iron; the cation exchange membrane is a perfluorosulfonic acid membrane, a sulfonated phenylimidazole membrane or cation exchange resin.

1-8 mol/L alkali liquor (KOH, NaOH, LiOH) or acid liquor (HCl, H) is contained in the anode chamber₂SO₄、HNO₃、H₃PO₄) The cathode A chamber contains 0.1-6 mol/L alkali solution (KOH, NaOH, LiOH), and the cathode B chamber contains 0.1-4 mol/L metaborate or a mixture of 0.1-6 mol/L alkali solution (KOH, NaOH, LiOH).

The working principle of the electrolysis for preparing the borohydride is as follows: external current passes through the anode to generate anodic polarization and oxygen, while the external current passes through the cathode to generate cathodic polarization, and the metaborate in the cathode chamber B generates reduction reaction in the process of transferring to the cathode chamber A through the cathode to generate the borohydride radical.

Because the solution in the cathode A chamber and the solution in the cathode B chamber are separated by the cathode, the solutions in the two chambers do not communicate with each other, but can exchange substances through the porous cathode.

Whenthe device works, the alkali liquor or the acid liquor flows into the anode chamber from the anode liquor inlet pipe, oxidation reaction is carried out on the surface of the anode to generate oxygen, and the oxygen is discharged from the upper part of the anode chamber. The solution containing metaborate or the mixture of the metaborate solution and the alkali liquor flows in through a liquid inlet pipe of the cathode chamber B, the metaborate passes through the cathode and simultaneously carries out electrochemical reduction reaction to generate corresponding borohydride which is diffused to the cathode chamber A and the cathode chamber B, and the solution containing the borohydride flows out through a liquid outlet pipe of the cathode chamber A and a liquid outlet pipe of the cathode chamber B.

The metaborate suitable for the device comprises potassium salt, sodium salt or lithium salt of metaborate, and the concentration of the metaborate is 0.1-4 mol/L.

The electrolysis temperature range of the invention is 10-80 ℃, and the current density is 10-500 mA/cm²The current efficiency is greater than 50%.

The invention has the advantages that the electrolysis device adopts a three-electrolytic-tank system different from the traditional two electrolytic tanks, the structure is more favorable for increasing the contact area between reactants and the inside of the electrode and smoothening the diffusion channel of products, and meanwhile, different electric field environments in the porous cathode provide necessary conditions required by reduction reaction, so compared with the traditional electrolytic tank structure, the current efficiency is higher.

The device of the invention provides a more economical and feasible way for preparing borohydride, and provides a cheaper hydrogen source material for the development of fuel cells, thereby having important application prospect.

Drawings

FIG. 1 is a schematic diagram of the structure of the apparatus for the electrolytic production of borohydride in accordance with the invention.

In the figure: 1-electrolytic cell, 2-anode chamber, 3-cathode chamber A, 4-cathode chamber B, 5-anode, 6-cation exchange membrane, 7-porous cathode, 8-anode liquid inlet pipe, 9-cathode chamber A liquid inlet pipe, 10-cathode chamber A liquid outlet pipe, 11-cathode chamber B liquid inlet pipe 11, 12-cathode chamber B liquid outlet pipe 13-anode liquid outlet pipe, 14-anode gas outlet pipe.

Detailed Description

The structure device of the present invention is further explained with reference to the accompanying drawings.

The schematic diagram of the device for preparing borohydride by electrolysis is shown in figure 1. The electrolytic cell 1 for the electrolytic production of borohydride comprises three chambers isolated from each other: anode chamber 2, cathode a chamber 3, and cathode B chamber 4. The anode compartment 2 is separated from the cathode a compartment 3 by a cation exchange membrane 6, and the cathode a compartment 3 is separated from the cathode B compartment 4 by a porous cathode 7. The alkali liquor or acid liquor flows into the anode chamber 2 from the anode liquor inlet pipe 8, and oxidation reaction is carried out on the surface of the anode 5 to generate oxygen, and the oxygen is discharged from the anode gas outlet pipe 14 at the upper part of the anode chamber. The solution of metaborate or the mixture of metaborate and alkali liquor flows in through a liquid inlet pipe 11 of a cathode B chamber 4, the metaborate passes through a cathode 7, electrochemical reduction reaction is carried out simultaneously, corresponding borohydride is generated and is diffused to a cathode A chamber 3 and the cathode B chamber 4, and the solution containing the borohydride flows out through a liquid outlet pipe 10 of the cathode A chamber and a liquid outlet pipe 12 of the cathode B chamber.

Example 1: selecting a nickel sheet as an anode, a porous hydrogen storage alloy electrode as a cathode, wherein the solution in the anode chamber is 2mol/L NaOH solution, the solution in the cathode chamber A is 0.5mol/L NaOH solution, and the solution in the cathode chamber B is 0.5mol/L NaBO₂The solution has an electrolysis temperature of 25 ℃ and a current density of 25mA/cm²And electrolyzing for 1 hour to reach 50 percent of current efficiency.

Example 2: selecting a nickel sheet as an anode, a porous hydrogen storage alloy electrode as a cathode, wherein the solution in the anode chamber is 2mol/L NaOH solution, the solution in the cathode chamber A is 0.5mol/L NaOH solution, and the solution in the cathode chamber B is 0.5mol/L NaBO₂The mixed solution of the solution and 2mol/L NaOH solution has the electrolysis temperature of 25 ℃ and the current density of 25mA/cm²And electrolyzing for 1 hour to reach 50 percent of current efficiency.

Claims

1. An apparatus for the electrolytic production of borohydride, comprising: electrolytic bath (1) is divided into three anode chambers (2) that are isolated from each other, cathode A chamber (3) and cathode B chamber (4), anode chamber (2) and cathode A chamber (3) adopt cation exchange membrane (6) to separate, and cathode A chamber (3) and cathode B chamber (4) adopt porous cathode (7) to separate, the bottom of anode chamber (2) is equipped with anode feed liquor pipe (8), upper portion is equipped with anode drain pipe (13) and outlet duct (14), cathode A chamber (3) and cathode B chamber (4) bottom are equipped with cathode feed liquor pipe (9) and 11 respectively, upper portion also is equipped with cathode drain pipe (10 and 12) respectively, electrolysis trough (1) inner wall of anode chamber (2) is arranged in anode (5) and is relative with cation exchange membrane (6).

2. The apparatus of claim 1, wherein: the anode (5) is ruthenium titanium oxide, aluminum oxide, nickel, platinum or graphite.

3. The apparatus of claim 1, wherein: the porous cathode (7) is made of hydrogen storage alloy, carbon material, metal boride, nickel and iron.

4. The apparatus of claim 1, wherein: the cation exchange membrane (6) is a perfluorosulfonic acid membrane, a sulfonated phenylimidazole membrane or cation exchange resin.

5. The apparatus of claim 1, wherein: the solution in the anode chamber (2) is an acidic solution or an alkaline solution, and the concentration of the solution is 1-8 mol/L.

6. The apparatus of claim 1, wherein: the solution in the cathode chamber A (3) is alkaline solution, and the concentration of the solution is 0.1-6 mol/L.

7. The apparatus of claim 1, wherein: the solution in the cathode B chamber (4) is metaborate or alkaline solution or the mixture of the metaborate and the alkaline solution.

8. The apparatus of claim 7, wherein: the metaborate is potassium salt, sodium salt or lithium salt of metaborate.