阅读说明：本技术 一种利用太阳能光电催化合成过氧化氢的方法 (Method for synthesizing hydrogen peroxide by utilizing solar photoelectrocatalysis ) 是由 李�灿 范文俊 施晶莹 张丙青 于 2018-09-11 设计创作，主要内容包括：本发明涉及利用太阳能光电催化合成过氧化氢的方法,具体包括:提供包含光阴极和阳极的光电化学池；光阴极为具有光响应的半导体催化剂电极,与阳极进行耦合,在光照下不需要外加电压或较小电压在光阴极直接将氧气还原成过氧化氢；使光阴极与溶解在连续相内的至少一种含氧介体的反应物接触,所述连续相包含电解质和中性溶剂；本发明有效地利用太阳能实现能量和物质的转化,克服目前工业中蒽醌法制备中高能耗、贵金属催化剂和环境污染等问题,只需要太阳能,氧气和水就能合成过氧化氢,避免了通过电解方式制备过氧化氢过程中需要消耗电能的问题,为过氧化氢清洁、廉价生产提供了一条可行的方法。(The invention relates to a method for synthesizing hydrogen peroxide by utilizing solar photoelectrocatalysis, which comprises the following steps of providing a photoelectrochemical cell comprising a photocathode and an anode; the photocathode is a semiconductor catalyst electrode with photoresponse and is coupled with the anode, and oxygen is directly reduced into hydrogen peroxide at the photocathode without external voltage or lower voltage under illumination; contacting the photocathode with at least one oxygen-containing mediator reactant dissolved in a continuous phase comprising an electrolyte and a neutral solvent; the invention effectively utilizes solar energy to realize the conversion of energy and substances, overcomes the problems of high energy consumption, noble metal catalyst, environmental pollution and the like in the prior anthraquinone method preparation in the industry, can synthesize the hydrogen peroxide by only solar energy, oxygen and water, avoids the problem of electric energy consumption in the process of preparing the hydrogen peroxide by an electrolysis mode, and provides a feasible method for clean and cheap production of the hydrogen peroxide.)

1. A method for green synthesis of hydrogen peroxide by utilizing solar photoelectrocatalysis is characterized in that:

employing a photo-electrochemical cell comprising a photocathode;

the photocathode is an electrode of a semiconductor catalyst with photoresponse, the semiconductor catalyst in the photocathode is not modified by a cocatalyst (or modified by the cocatalyst), and the photocathode and the anode of the photoelectrochemical cell are coupled to form a photocathode-anode photoelectrochemical system, so that oxygen can be directly reduced into hydrogen peroxide at the photocathode without external voltage or only with the voltage below 10V under illumination;

contacting the photocathode with at least one oxygen-containing mediator reactant dissolved in a continuous phase comprising an electrolyte and a neutral solvent comprising water; wherein the reactant of the oxygen-containing mediator is an oxygen-containing gas.

2. The method of claim 1, wherein: the synthesized hydrogen peroxide, which is a general term of academic conception and is commonly called hydrogen peroxide in industry, comprises the specific range of H under acidic and neutral conditions according to the difference of acid and alkali of solution₂O₂In the form of the existing form and in the basic form in the form of the conjugate base thereofPeroxide present (peroxoradical ion HO)₂ ^-Peroxides such as NaHO₂，KHO₂，LiHO₂，CsHO₂One or two or more of the above); the acidic and alkaline hydrogen peroxide have a common property that the hydrogen peroxide contains peroxide HO₂ ^-Is a functional ion thereof.

3. The method of claim 1, wherein: wherein the photocathode semiconductor catalyst with photoresponse comprises one or more than two of the following two materials;

the first type is a bulk heterojunction composite material formed by one or more of organic micromolecules containing 1 thiophene unit or one or more of polymers containing 2-400 thiophene units and containing thiophene units, or one or more of compounds containing thiophene units and one or more of hole transport materials such as PCBM, ICBA and the like. The mass ratio of the thiophene unit-containing compound to the hole transport material in the composite material is 1: 0.1-1: 10, wherein the mass ratio is preferably 1:0.5-1: 2; the basic structure of the thiophene unit is shown on the left, and the polymer of thiophene is shown on the right:

wherein R1 and R2 are H or C1-C10 alkyl, and n is a natural number between 2 and 400;

the second kind of photocathode semiconductor catalyst with photoresponse is one or more than two kinds of active layer materials commonly used in organic solar cells, such as triphenylamine semiconductor catalyst, benzodithiophene semiconductor catalyst and pyrrolopyrrole diketone semiconductor catalyst material, the molecular weight is between 2000 and 60000, and 20000-50000 is preferred; among these materials, one or more of PCDTBT, PCPDTBT, PSBTBT and PBDTTT-C, PTB7 are preferable.

4. A method according to claim 1, characterized in that: the material modified by the cocatalyst is selected from one or more than two of metals such as gold, palladium, silver and the like or non-metals such as graphene, carbon nano tubes, carbon powder and the like, the cocatalyst can be used for modifying the photocathode, and the photocathode can also be free of the cocatalyst; the cocatalyst modifies the photocathode semiconductor catalyst by one or more of methods of electrodeposition, light deposition, spin coating, drop coating, dipping, solution mixing and evaporation and the like, and the supporting amount of the cocatalyst on the semiconductor catalyst is 0-5 wt% of the semiconductor catalyst, wherein the preferable weight percentage is 0.5-2 wt%.

5. The method of claim 1, wherein: wherein the reactant of the oxygen-containing mediator is one or more than two of oxygen-containing gases such as pure oxygen, air, compressed air, oxygen-nitrogen mixed gas and the like; wherein the oxygen-containing mediator in the continuous phase has an oxygen content in the continuous phase of at least 2ppm, preferably from 20ppm to 30 ppm.

6. The method of claim 1, wherein: the electrolyte is selected according to the pH value of the reaction solution, one or more than two of sulfuric acid, hydrochloric acid and phosphoric acid are selected as the electrolyte in the acidic reaction solution, one or more than two of sodium chloride, potassium chloride, ammonium chloride and sodium bicarbonate are selected as the electrolyte in the neutral reaction solution, and one or more than two of potassium hydroxide, sodium hydroxide or ammonia water are selected as the electrolyte in the alkaline reaction solution; one or more than two of the electrolytic salts can be added into the acid reaction solution or the alkaline reaction solution as supplementary electrolyte; the content of electrolyte in the continuous phase is 0.1 to 30% by weight, preferably 5 to 10% by weight;

wherein the aqueous neutral solvent is water or a mixed solvent of water and one or more organic solvents selected from acetonitrile, dichloromethane and dimethyl sulfoxide, and the content of water in the aqueous neutral solution is 10-100 vol%, preferably 80-99 vol%. The neutral solvent is mixed with the electrolyte to form a continuous phase.

7. The method of claim 1, wherein: the photoelectrochemical cell comprises a photocathode chamber and an anode chamber device which are separated from each other by a diaphragm, wherein a photocathode electrode is arranged in the photocathode chamber, an anode electrode is arranged in the anode chamber, and the photocathode and the anode are connected and coupled by an external circuit (such as a lead) to form a photocathode-anode photoelectrochemical system.

8. The method of claim 1, wherein: the photocathode in the photoelectrochemistry system is formed by depositing a semiconductor catalyst on a conductive substrate, the deposition method comprises one or more than two of electropolymerization, spin coating, drop coating, light deposition, spray coating and screen printing, and the deposited electrode is washed and dried to obtain an electrode; the photocathode modified by the cocatalyst modifies the surface or bulk phase of the semiconductor catalyst by one or more of methods such as spin coating, drop coating, photo-deposition, electro-deposition and the like on the semiconductor electrode; the conductive substrate is made of electrochemical inert materials, has good conductivity and mainly comprises one or more than two of metal and nonmetal electrodes such as FTO, carbon paper, carbon cloth, carbon sheets, titanium sheets and the like.

9. The method of claim 1, wherein: the light source of the illumination adopted by the photoelectrochemical system is one or more than two of sunlight, xenon lamp, mercury lamp, laser, LED and the like, and preferably the sunlight or the condensation thereof is mainly used in the industrialization; the light intensity can be adjusted in a wide range according to actual requirements, and the illumination intensity is 0.05-1W/cm²Among them, 0.7 to 1W/cm is preferable²。

10. The method of claim 1, wherein: the photoelectrochemical system is formed by connecting a photocathode and an anode through an external circuit, and the voltage of the reaction (namely the voltage between the photocathode and the anode) is regulated through a voltage-adjustable circuit, wherein the selected applied voltage is 0-10V, and the preferred voltage is 0-5V; when the applied voltage is 0V, no voltage is applied to the external circuit, namely, the external circuit can drive the reaction to generate hydrogen peroxide only by light.

Technical Field

The invention belongs to the fields of photoelectrocatalysis, solar energy utilization and correlation, and particularly relates to a method for producing hydrogen peroxide by absorbing solar energy at a photocathode to generate photo-generated electrons to reduce oxygen.

Background

Hydrogen peroxide (H)₂O₂) The product is a high-efficiency and green oxidant, and the reaction product only contains water and oxygen, and is one of the most important chemicals in the world. With the rapid development of global economy, the application field of hydrogen peroxide is gradually expanded from the fields of environmental protection, pulp bleaching and the like to the fields of propylene epoxidation and organic synthesis (Mario Pagliaro, et al. ChemSusChem,2016,9(24): 3374-3381.). The global market for hydrogen peroxide has increased to 550 million tons (2015) and has grown at a rate of 8% -11% per year. At present, hydrogen peroxide is mainly produced industrially through a multi-step hydrogenation and oxidation process of anthraquinone, and a palladium-based catalyst and a quinone organic solvent used in the reaction greatly increase the production cost and cause serious environmental pollution. Therefore, researchers at home and abroad develop brand new production approaches on the basis of the method, and the production approaches mainly comprise an isopropanol oxidation method, a hydrogen-oxygen direct-combination method, an electrochemical method, a plasma method and the like. These methods have advantages and disadvantages, respectively, and need to be perfected. The hydrogen-oxygen direct synthesis method is characterized in that hydrogen and oxygen are introduced into a reactor according to a certain proportion to obtain hydrogen peroxide under the action of a palladium catalyst, and the process is simple and environment-friendly (Jennifer K.Edwards, et al. science,2009,323(5917):1037-₂And O₂The mixing is explosive and side reaction is easy to occur in the reaction, so that the selectivity is reduced, which is a main factor for limiting the method, and the reaction has strict requirements on production process and equipment and is difficult to realize industrialization.

In addition, electrochemical methods can also be used for the production of hydrogen peroxide, and there are two main methods among conventional electrochemical methods: (i) electrolyzer type process (Follerand boron, J.appl.electrochem.1995, 25, 613-. Unfortunately, both types of processes require a large energy input and also require a large hydrogen consumption for fuel cell type processes, which makes these processes expensive and unsuitable for industrial deployment.

Solar energy is inexhaustible clean energy, and the total amount of solar radiation received by land areas in China every year is 3.3 multiplied by 10³kJ/(m²Year) -8.4×10³kJ/(m²Year) corresponding to 24 hundred million tons of standard coal. The method has important significance for energy structure and environmental protection based on fossil fuel, and has wide application in the fields of photovoltaic cells and photocatalysis at present. Such as silicon solar cells (patent WO _8505119_ a), organic solar cells (patent US _20090029053), and organic pollutant degradation, etc. In addition, the solar energy can be used for photochemical conversion under the action of the catalyst to realize the synthesis of chemicals and the storage of energy, thereby providing a green and environment-friendly mode for industrial production. CN 103086866B reports selective aldehyde oxidation under light induction to synthesize acid, and CN 103130755B reports one-step conversion of xylose by an acidic photocatalyst to prepare furfural.

So far, no patent report is found for preparing hydrogen peroxide by utilizing a semiconductor material as a photocathode to absorb solar energy and carrying out photoelectrocatalysis oxygen reduction, so that catalysts which can absorb solar energy, reduce oxygen with high selectivity to obtain hydrogen peroxide, avoid environmental pollution, high catalyst price and the like in the production process of an anthraquinone method are developed, and the method has important significance for environmental protection and cost reduction.

Disclosure of Invention

The object of the present invention is to provide a method for producing hydrogen peroxide by means of photoelectrocatalysis in a simple apparatus using photocathode to absorb solar energy.

It is another object of the present invention to provide a method for producing hydrogen peroxide by directly reducing oxygen at a photocathode by coupling with an anode under illumination without requiring an external voltage or requiring a small voltage (voltage can be adjusted according to illumination intensity or actual production requirements). Wherein the two-electron process is generated by directly reducing oxygen into hydrogen peroxide by the photocathode, and an intermediate species O generated by the photocathode in the reaction process₂ ^-、HOO^-Hydrogen peroxide is also obtained by continued reduction.

According to the present invention, it has been found that these objects can be achieved in a process for producing hydrogen peroxide comprising the steps of:

providing a photo-electrochemical cell comprising a photocathode and an anode;

contacting the photocathode with at least one oxygen-containing mediator reactant in a continuous phase comprising an electrolyte and a neutral solvent;

the semiconductor photocathode catalyst with photoresponse is provided, is modified by a cocatalyst and is coupled with an anode to form a photocathode-anode photoelectrochemical system, and oxygen can be directly reduced into hydrogen peroxide at the photocathode without external voltage or with smaller external voltage under illumination.

Carrying out two-electron reduction reaction on an oxygen-containing mediator at a photocathode, wherein the oxygen-containing mediator comprises pure oxygen, air, compressed air and oxygen-nitrogen mixed gas, and preferably the compressed air; preferably, the two-electron reduction product of the oxygen-containing mediator is hydrogen peroxide, which is present as a peroxide, such as sodium peroxide NaHO, when the reaction is under alkaline conditions₂KHO, potassium peroxide₂. Without wishing to be bound by theory, it is believed that the reaction scheme to obtain hydrogen peroxide involves the transfer of two electrons in a simultaneous reaction, either alone or in combination, and that the intermediate species O is involved₂ ^-、HOO^-。

A continuous phase comprising an electrolyte comprising at least one cation or anion, preferably in an amount of about 0.1 wt% to 30 wt% within the continuous liquid phase; the electrolyte includes an acidic electrolyte, a neutral electrolyte and an alkaline electrolyte, preferably an alkaline inorganic electrolyte.

The alkaline inorganic electrolyte includes sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, disodium hydrogen phosphate, among which potassium hydroxide is preferred. The photocathode incorporates an alkaline inorganic electrolyte to adjust the pH of the catholyte, with a preferred pH of about 14.

The continuous liquid phase comprises a neutral solvent, for example water or small molecule alcohols, such as methanol, ethanol, propanol or mixtures thereof, of which water is preferred. The amount thereof is preferably at most about 99 wt%, most preferably about 90 wt%.

The photocathode semiconductor catalyst with photoresponse is a bulk heterojunction composite material formed by organic micromolecules containing 1 thiophene unit and polymers containing 2-400 thiophene units or hole transport materials such as PCBM, ICBA and the like. The photocathode can be composed of one thiophene and more than two thiophene components or a compound of thiophene and one or more than two of PCBM and ICBA. The ratio of the thiophene to the composite material composed of hole transport materials such as PCBM or ICBA is 1:0.1 to 1:10, wherein the ratio is preferably 1:0.5-1: 2. The basic unit of thiophene is as follows (left), and the polymer of thiophene is as follows:

wherein R1 and R2 are H or C1-C10 alkyl, and n is a natural number between 2 and 400.

Other photocathode semiconductor catalysts with photoresponse include active layer materials commonly used in organic solar cells, such as triphenylamines, benzodithiophenes, pyrrolopyrrolediones, having molecular weights between 2000 and 60000, preferably 20000-50000. Preferred among these materials are PCDTBT, PCPDTBT, PSBTBT, PBDTTT-C, PTB 7.

The photocathode catalyst promoter is modified by adopting metals such as gold, palladium and silver or non-metals such as graphene, carbon nano tubes and carbon powder, wherein the graphene is preferred, the photocathode semiconductor catalyst is modified by methods such as electrodeposition, light deposition, spin coating, drop coating, dipping, solution mixing and evaporation, and the like, and the loading capacity of the photocathode semiconductor catalyst is 0-5 wt%, and the preferred loading capacity is 0.5 wt%.

The photoelectrochemical system comprises a photocathode, an anode and a diaphragm, wherein the diaphragm is positioned between the photocathode and the anode and used for the material exchange and barrier effects of the photocathode and the anode. The separator may be a non-selective physical barrier, such as a porous membrane; the membrane may also be a permselective membrane, such as a cation or anion permselective membrane. In addition, composite membranes, such as bipolar membranes that can be broken down into protons and hydroxide ions, can be used. The non-selective barrier layer may be made of asbestos, ceramic, glass, polypropylene, etc., and the cation selective membrane may be PTFE, polystyrene, styrene/distyrylbenzene modified with acidic groups such as sulfonate, carboxylate or phosphonate, etc., organic polymers. The anion selective membrane may be made of polystyrene, organic polymers such as styrene/divinylbenzene modified with basic groups such as quaternary ammonium. Bipolar membranes include anion permeable membranes and cation permeable membranes laminated together with a catalytic layer in between. Ion selective and bipolar membranes are commercially available under the trade names Nafion, Flemium, Neoseptabipolar.

The electrolyte may contain 1 or more liquid phases within the photocathode compartment. In a single liquid phase system, the majority is the inorganic liquid electrolyte phase, and the solvent is primarily water.

In the anode compartment an oxidation reaction takes place, comprising oxidation of formic acid, acetic acid, methanol, ethanol, sodium sulphite and water, wherein water oxidation is preferred, and the oxygen and protons formed may be used as reaction raw materials at the photocathode to form hydrogen peroxide. Furthermore, it is also possible to take place in the anode compartment within the scope of the invention, for example to oxidize various organic wastes, to oxidize white liquor, for example to indirectly oxidize anthracene to anthraquinone or to indirectly oxidize naphthalene, or to use the redox couple Cr (III)/Cr (IV).

The material of the anode compartment comprises BiVO₄，WO₃，TiO₂，Ta₃N₅N-type semiconductor such as ZnGaON and electrocatalytic material, and BiVO is preferable among them₄(ii) a The anode is modified by metals such as gold, palladium and silver or non-metals such as graphene, carbon nano tubes and carbon powder to improve the photoelectric catalytic performance of the anode, wherein the graphene is preferred; the anode catalyst is deposited on the substrate such as FTO, carbon paper, carbon sheet, stainless steel sheet and foamed nickel by methods such as electrodeposition, light deposition, spin coating, drop coating, dipping, solution mixing and evaporation to dryness, and the like, wherein the carbon paper is preferred.

After the photocathode and the anode are assembled into a photoelectrochemical system, the photocathode and the photoanode are connected through an external circuit, the external circuit provides a certain voltage of 0-10V for controlling the generation rate of the hydrogen peroxide, and the provided voltage is adjustable in a certain range, wherein the voltage is preferably 0V, namely the preparation of the hydrogen peroxide is realized without external bias. Other cases may also prefer 5V as the bias provided to increase the rate of hydrogen peroxide generation; the supplied electric energy is from a mobile power supply, industrial power, solar cell power generation, wind power generation, and preferably solar cell power generation.

The light source provided by the illumination of the invention is sunlight, a xenon lamp, a mercury lamp, laser, an LED and the like, wherein the sunlight and the condensation thereof are preferably selected, the light intensity is adjusted in a certain range according to the actual production requirement, and the adjustment range is 10-1000 mW/cm². The illumination is directed to the photocathode and the photoanode from the horizontal, the vertical or a certain angle, wherein the illumination from the vertical direction is preferred.

Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages:

1. the photocathode has the property of absorbing light, generates photoproduction electrons under the excitation of light and is directly used for reducing oxygen

2. The photoelectric system is constructed by coupling the photocathode and the anode, only oxygen and water are needed under illumination, the oxygen can be directly reduced at the photocathode to generate hydrogen peroxide under the condition of no external bias, and the energy consumption problem in the industrial production process is greatly reduced

3. The catalyst and the device adopted by the invention have simple structure, simple process and flexible production form, can be adjusted according to actual production without local limitation, can greatly reduce the production cost and meet different requirements.

Drawings

Fig. 1 is a scanning electron micrograph of a PTTh photocathode prepared on carbon paper obtained by means of electrochemical polymerization.

FIG. 2 is a graph representing the number of transferred electrons for photocatalytic cathodic oxygen reduction using a Rotating Disk Electrode (RDE) and a rotating disk ring electrode (RRDE).

FIG. 3 is a schematic representation of a device utilizing a photoelectrochemical system and a PTTh photocathode and BiVO₄The photo-anode is at 200mW/cm²Concentration variation of unbiased production of hydrogen peroxide under illumination of light and faraday efficiency plot.

Detailed Description

To further illustrate the present invention, the following examples are given in conjunction with the accompanying drawings, which are not intended to limit the scope of the invention as defined by the appended claims.

The invention provides a catalyst with photoresponse, which can reduce oxygen to generate hydrogen peroxide with high selectivity, wherein the whole reaction is completed in a photoelectrochemical system, the oxygen reduction is positioned at a photocathode of the system, the photocathode consists of a photocathode chamber and is separated from an anode through a membrane, the anode consists of an anode chamber, the photocathode is connected with the anode through an external circuit, light irradiates on a catalyst electrode from the horizontal direction or the vertical direction, oxidation reaction is carried out on the anode, generated electrons reach the photocathode through the external circuit, meanwhile, continuous oxygen is introduced into the photocathode to saturate the solution, the electrons from the anode participate in the oxygen reduction reaction to generate hydrogen peroxide on the surface of the electrode, and hydrogen peroxide molecules can be quickly dissolved in the solution, thereby obtaining hydrogen peroxide solution. The photoelectrochemical system used includes not only a photocathode chamber including a photocathode, an anode chamber including an anode, but also a photocathode gas inlet for supplying an oxygen-containing gas to the photocathode, and a photocathode gas outlet for removing an excess gas from the photocathode chamber. The photocathode chamber and the anode chamber are respectively provided with a feeding hole.