CN107641817B - A kind of light anode preparation method and gained light anode structure improving photocatalytic water performance - Google Patents

Abstract

The invention discloses a kind of light anode preparation methods and gained light anode structure for improving photocatalytic water performance.Light anode preparation method is the following steps are included: a. uses resistivity for the n-type silicon chip of 0.01~0.05 Ω cm；B. to preparing silicon micron linear array after Wafer Cleaning；C. using silicon micron linear array as substrate, using containing Fe³⁺Solution, and be mixed into doped source solion wherein, as the precursor liquid of growth iron oxide layer, annealing early period carried out to the silicon micro wire array substrate of precursor liquid absorption in air, obtains silicon/iron oxide micron linear array；D. post annealed processing is carried out in nitrogen or argon atmosphere to silicon/iron oxide micro wire array substrate；E. resulting silicon/iron oxide micro wire array substrate backside deposition conductive layer after post annealed, and draw external conducting wire；F. insulating layer of turning one's coat is coated on the electrically conductive.

Description

A kind of photoanode preparation method for improving the performance of photolysis water and the obtained photoanode structure

technical field

The invention relates to a method for preparing a photoanode for improving the performance of photo-splitting water and the obtained photoanode structure, and belongs to the field of photoelectric conversion and energy.

Background technique

In recent years, the research on sunlight-driven water splitting has received more and more attention, and the photo-splitting technology may become an effective way to solve the problems of energy crisis and fuel pollution. At present, photoelectrochemical cells are a main configuration form to realize photo-splitting of water. It absorbs sunlight by semiconductor photoelectrodes to promote water oxidation and reduction reactions, that is, to complete the capture of solar energy and convert it into high-energy green fuels (ie, H _{2 )} . ). However, the application and promotion of solar hydrogen production has encountered many technical difficulties. Among them, the key problem is that the efficiency of solar energy to hydrogen (STH) is too low and the cost is too high. Evaluation from the perspective of technology and economy shows that in order to make it competitive with fossil energy, the technical bottlenecks that need to be solved are: achieving large-scale (non-small area, small-scale) and STH efficiency reaching 10%. STH efficiency is limited by a number of processes, including: light absorption efficiency, carrier separation efficiency, carrier injection efficiency at the solid-liquid interface, carrier conversion efficiency at the electrode surface (efficiency in participating in chemical reactions), and the generated _H2 Desorption efficiency from the electrode surface. Therefore, to obtain a system with high STH efficiency, the following key conditions must be met: 1) broad-spectrum solar energy absorption; 2) efficient carrier extraction from the interior of the photoelectrode to the solid-liquid interface; 3) chemical properties of the photoelectrode surface The reaction can proceed rapidly and the overpotential is small; 4) The photoelectrode has excellent stability in aqueous solution. Furthermore, in order to achieve complete photosplitting of water, the positions of the conduction and valence bands of the semiconductor material need to span both the hydrogen evolution and oxygen evolution potentials. At present, only a few wide bandgap (>3eV) semiconductor materials (such as KTaO ₃ and GaN) have been found to meet the energy level position requirements, but the stability of the photoelectrodes constructed by these materials is generally deviated, and the STH is even more unsatisfactory. The extreme value of efficiency is only 2%. Therefore, a multi-absorption layer photoelectrochemical cell was constructed, so that the oxidation reaction and reduction reaction of water were respectively realized by the light response of different semiconductors, so as to obtain a complete photo-water splitting system with high performance.

Iron oxide (α-Fe ₂ O ₃ ) is characterized by its excellent stability, suitable forbidden band width (1.9–2.3 eV, theoretical STH efficiency of 12.9–16.8%), good environmental compatibility, and abundant mineral deposits in the earth. It is considered to be an ideal anode material for photo-oxidation of water. Because of its conduction band potential higher than water reduction potential, and its good electrical properties and excellent light absorption properties, silicon materials are widely used as light absorption layers in photo-splitting water systems. The superposition of iron oxide and silicon to form a double-absorbing layer photoelectrode has the following advantages: 1) to achieve sub-band absorption of incident light (iron oxide absorbs the shorter wavelength band, while the longer wavelength band is absorbed by silicon); 2) water oxidation reaction The required holes come from iron oxide, and the electrons required for the reduction reaction come from silicon; 3) The heterojunction formed by iron oxide and silicon can generate photovoltage, thereby promoting the separation of carriers inside the electrode and reducing the chemical reaction on the surface of the electrode. electric potential.

van de Krol and Liang used spray pyrolysis to grow undoped iron oxide films on n-type planar silicon (10–20 Ω cm), demonstrating that a silicon/iron oxide heterojunction can generate a photovoltage of 0.3 V, and This configuration is thermodynamically feasible for unbiased photo-water splitting (R. van de Krol, and Y. Liang, An n-Si/n-Fe ₂ O ₃ Heterojunction Tandem Photoanode for Solar Water Splitting, Chimia, 2013 , 67:168–171). Wang et al. used atomic layer deposition technology to grow iron oxide thin films on n-type silicon nanowire arrays (5–15 Ω cm) to prepare a core-shell structure double-absorbing photoanode, and observed that the photocurrent turn-on potential was only 0.6 V vs. RHE, at 1.23V vs. RHE, the current density is 0.85 mA/cm ² under a standard sunlight illumination, while the corresponding current density of iron oxide films grown directly on transparent conductive substrates is only ~0.3 mA/cm ² ( MT Mayer, C. Du, and D. Wang, Hematite/Si Nanowire Dual-Absorber System for Photoelectrochemical Water Splitting at Low Applied Potentials, J. Am. Chem. Soc., 2012, 134: 12406–12409). These studies demonstrate that the silicon/iron oxide double-absorber layer structure can realize unbias-assisted water splitting, and the heterostructure has better performance than the single-absorber layer system. However, this double absorption layer system still has many problems or can be improved: 1) the interface of silicon/iron oxide is seriously compounded; 2) the surface compounding of iron oxide is serious; 3) the internal resistance of the double absorption layer of silicon/iron oxide is too large; 4) The preparation cost of the silicon/iron oxide double absorber electrode is high.

In order to realize the industrial application of the photo-splitting water-hydrogen production technology, we have developed the STH efficiency and key performance parameters [such as: turn-on voltage, photocurrent density (@1.23V vs. RHE)], and cost-reducing devices that can effectively improve the STH efficiency of photo-water splitting devices. The solution or implementation technology is the key and difficult point.

SUMMARY OF THE INVENTION

The purpose of the present invention is to propose a method for preparing a photoanode for improving the performance of photo-splitting water and the resulting photoanode structure.

In order to achieve the above purpose, the present invention provides a technical solution: a method for preparing a photoanode for improving the performance of photolysis water, which comprises the following steps:

a. Use n-type silicon wafers with resistivity of 0.01-0.05Ω·cm;

b. After the silicon wafer is cleaned, metal-assisted chemical etching of silicon is performed, and a silicon micro-wire array is prepared. For the specific preparation process of the silicon micro-wire array, please refer to the invention patent with the application number of 201610183558.7;

c1. Taking the silicon micron wire array as the base, using a solution containing Fe ³⁺ , and mixing the doping source ion solution into it, as the precursor liquid for the growth of iron oxide layer, the precursor liquid is adsorbed on the silicon micron by dipping method or spraying method On the wire array substrate, the silicon micron wire array substrate adsorbed by the precursor is obtained;

c2. Perform pre-annealing treatment on the silicon microwire array substrate adsorbed by the precursor solution;

d. Perform post-annealing treatment on the silicon/iron oxide micro-wire array substrate after pre-annealing;

e. A conductive layer is deposited on the backside of the silicon/iron oxide microwire array substrate obtained after post-annealing, and external wires are drawn out;

f. Apply a waterproof insulating layer on the conductive layer.

Further, in step b, the silicon micro-wire spacing is 1-10 μm, the diameter is 1-10 μm, and the length is 5-100 μm.

Further, in step c1, the doping source ion solution is one or a combination of SnCl ₄ , TiCl ₄ , MnCl ₄ , SiCl ₄ , GeCl ₄ , ZrCl ₄ , and NbCl ₄ solutions.

Further, in step d, the conditions of the post-annealing treatment are: using a rapid annealing furnace, treating at 300-600° C. for 3-10 minutes, and the gas atmosphere is nitrogen or argon.

Further, in step c1, the solution of Fe ³⁺ is an ethanol or aqueous solution of Fe(NO ₃ ) ₃ or FeCl ₃ .

Further, in step c1, the specific method of adsorbing the precursor liquid on the silicon microwire array by spraying method is as follows: ultrasonically atomizing the precursor liquid, and pyrolyzing the precursor liquid on the silicon microwire array substrate heated to 100-200°C.

Further, in step c1, the specific method for adsorbing the precursor liquid on the silicon microwire array by the dipping method is as follows: immersing the silicon microwire array substrate in the precursor liquid for 10-60 minutes.

Further, step c1 and step c2 are repeated cyclically, and the cycle repetition times are 1 to 20 times. The greater the Fe ³⁺ concentration in the current flooding solution, the smaller the cycle repetition times.

Further, in step c2, the conditions of the early annealing treatment are: in a tubular annealing furnace, the treatment is performed at 400-600° C. for 2-5 hours, and the gas atmosphere is air.

Further, in step f, the waterproof insulating layer is epoxy resin or 704 silica gel.

Further, in step e, the conductive layer is an In-Ga or Al layer.

Further, in step b, standard RCA cleaning process is used for cleaning.

The present invention also provides another technical solution: a photoanode structure obtained by utilizing the above-mentioned photoanode preparation method for improving the performance of photolysis of water.

By adopting the above technical solutions, the present invention provides a method for preparing a photoanode for improving the performance of photolysis of water and the structure of the photoanode obtained, which has the following advantages compared to the prior art:

(1) In the prior art, silicon nanowires or planar silicon with a resistivity (moderately doped) of 1-20 Ω·cm are used as the substrate, while the resistivity (heavy doping) used in the present invention is 0.01-0.05Ω cm silicon microwire array, the corresponding electrode internal resistance (device series resistance) is small, which is more conducive to the transmission of carriers and the output of photovoltage; compared with silicon nanowire array, silicon microwire array has smaller specific surface area and surface area. The defect state density is much smaller, which greatly improves the serious problem of interface recombination at the silicon/iron oxide interface. Compared with planar silicon, although the interface defect density of silicon microwire array is slightly larger, it has the effect of light antireflection. Iron oxide is no longer a planar structure and has electromagnetic wave coupling effects.

(2) Introducing doping elements in the growth process of iron oxide makes the electrical properties of the grown iron oxide better (multiple carriers are easier to transport, and minority carriers have longer lifetimes, increase the conductivity of silicon and iron oxide, reduce The internal resistance of the silicon/iron oxide double-absorbing layer photoelectrode improves the collection efficiency of carriers).

(3) After the iron oxide growth process is completed, a later heat treatment process is performed in a nitrogen or argon atmosphere, so that the oxygen vacancy density of the grown iron oxide is increased, which is more conducive to the collection and implantation of minority carriers.

(4) Compared with the atomic layer deposition technology, the equipment involved in the present invention has low cost, and the iron oxide growth rate is fast; and for the iron oxide growth process adopted in the present invention, the silicon microwire/iron oxide heterostructure proposed by the present invention is Compared with silicon nanowire/iron oxide (or planar silicon/iron oxide) heterostructures, it has more perfect interfacial properties. On the premise of ensuring low cost, the invention realizes the uniform, shape-preserving, rapid and high-quality growth of iron oxide on the silicon micro-wire substrate.

The above description is only an overview of the technical solutions of the present invention. In order to understand the technical means of the present invention more clearly and implement them according to the contents of the description, the preferred embodiments of the present invention and accompanying drawings are described in detail below.

Description of drawings

1 is a schematic diagram of a silicon wafer in step a of a method for preparing a photoanode for improving photo-water splitting performance according to the present invention;

Accompanying drawing 2 is a schematic diagram of the product obtained in step b of a photoanode preparation method for improving photo-water splitting performance of the present invention;

Accompanying drawing 3 is a schematic diagram of the product obtained in step c1 of a photoanode preparation method for improving photo-water splitting performance of the present invention;

Accompanying drawing 4 is a schematic diagram of the product obtained in step d of a photoanode preparation method for improving photo-water splitting performance of the present invention;

Accompanying drawing 5 is a schematic diagram of the product obtained in step e of a photoanode preparation method for improving photo-water splitting performance of the present invention;

6 is a schematic diagram of the product obtained in step f of a photoanode preparation method for improving the performance of photolysis of water according to the present invention;

FIG. 7 is a schematic diagram of the structure of the photoanode obtained by the preparation method of the photoanode for improving the performance of photolysis of water according to the present invention and its photohydrolysis.

FIG. 8 is a current-potential diagram of the silicon/iron oxide heterojunction photoanode obtained by several different treatment processes in the performance test experiment.

Detailed ways

The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and embodiments. The following examples are intended to illustrate the present invention, but not to limit the scope of the present invention.

Example 1

In the present embodiment, a method for preparing a photoanode for improving the performance of photo-splitting water comprises the following steps:

a. An n-type silicon wafer with a resistivity of 0.01 to 0.05 Ω·cm is used, referring to FIG. 1 .

b1. Perform a standard RCA cleaning process on the silicon wafer, spin-coat photoresist, perform UV exposure, and then develop to obtain a pattern of photoresist micro-column array (square arrangement with a diameter of 4 μm and a period of 8 μm);

b2. Titanium and gold films were evaporated by electron beam evaporation, respectively, with thicknesses of 3nm and 40nm;

b3. Corrosion in a mixed aqueous solution of hydrofluoric acid and hydrogen peroxide (concentrations of 8 mol/L and 0.4 mol/L, respectively) for 20 hours, and the etching temperature is 5°C to obtain a silicon micro-wire array (length of 30 μm, diameter of 4 μm) , a square arrangement with a period of 8 μm), refer to Figure 2.

c1. Prepare an ethanol solution of FeCl ₃ with a concentration of 0.05mol/L, and mix the doping source ion solution into it, as the precursor solution for growing the iron oxide layer, and immerse the silicon microwire array substrate in the precursor solution for 10 to 60 minutes Then, the substrate is taken out to obtain a silicon micro-wire array substrate adsorbed by the precursor solution, referring to FIG. 3 . The above-mentioned immersion time is preferably 30 minutes; the above-mentioned doping source ion solution is preferably one or a combination of SnCl ₄ , TiCl ₄ , MnCl ₄ , SiCl ₄ , GeCl ₄ , ZrCl ₄ , and NbCl ₄ . In the example, adopt the _SnCl solution of 0.005mol/L;

c2. Perform pre-annealing treatment on the silicon/micron wire array substrate adsorbed by the precursor liquid in a tubular annealing furnace: the time is 2-5 hours, preferably 3 hours, the temperature is 400-600°C, preferably 500°C, and the gas atmosphere for air.

d. Repeat step c1 and step c2 in a cycle, which can be cycled 1 to 20 times, and the number of times is related to the concentration of Fe ³⁺ in the precursor solution. d. Perform post-annealing treatment in a rapid annealing furnace: the time is 3-10 minutes, preferably 5 minutes, the temperature is 300-600°C, preferably 400°C, and the gas atmosphere is N ₂ ; refer to Figure 4 .

e. Coating a conductive layer on the back of the silicon/iron oxide microwire array substrate obtained after post-annealing, and drawing out external wires, refer to FIG. 5 . In this embodiment, the conductive layer is an In-Ga or Al conductive layer.

f. Coating a waterproof insulating layer on the conductive layer to completely cover the back conductive layer to obtain a photoanode, refer to FIG. 6 . The waterproof insulating layer is preferably epoxy resin or 704 silica gel.

g. Immerse the prepared photoanode in a 1 mol/L NaOH aqueous solution, use the platinum mesh electrode as the counter electrode and the Ag/AgCl electrode as the counter electrode, use an electrochemical workstation to connect the three electrodes to construct a three-electrode test system .

This embodiment also provides another technical solution: a photoanode structure obtained by using the above-mentioned method for preparing a photoanode for improving the performance of photolysis of water.

Embodiment 2

In the present embodiment, a method for preparing a photoanode for improving the performance of photo-splitting water comprises the following steps:

a. An n-type silicon wafer with a resistivity of 0.01 to 0.05 Ω·cm is used, referring to FIG. 1 .

b1. Perform a standard RCA cleaning process on the silicon wafer, spin-coat photoresist, perform UV exposure, and then develop to obtain a photoresist micro-column array (square arrangement with a diameter of 3 μm and a period of 6 μm) pattern;

b2. Titanium and gold films were evaporated by electron beam evaporation, respectively, with thicknesses of 3nm and 40nm;

b3. Corrosion in a mixed aqueous solution of hydrofluoric acid and hydrogen peroxide (concentrations of 8 mol/L and 0.4 mol/L, respectively) for 20 hours, and the etching temperature is 5°C to obtain a silicon micro-wire array (30 μm in length and 3 μm in diameter) , the period is the square arrangement of 6μm), refer to Figure 2;

b4. Treat the silicon microwire array with oxygen plasma at a power of 400W for 20 minutes.

c1. Prepare 0.05mol/L Fe(NO ₃ ) ₃ ethanol solution and mix it with doping source ion solution as the precursor solution for growing iron oxide layer, store the precursor solution in a syringe pump, and use ultrasonic spray to pyrolyze The equipment sprays the precursor liquid on the silicon micron wire array substrate to obtain the silicon micron wire array substrate adsorbed by the precursor liquid, referring to FIG. 3 . The injection rate of the precursor solution is 0.1 mL/min, and the substrate temperature is 200° C. The above-mentioned doping source ion solution is preferably one of SnCl ₄ , TiCl ₄ , MnCl ₄ , SiCl ₄ , GeCl ₄ , ZrCl ₄ , and NbCl ₄ . Or several combinations, adopt the _SnCl solution of 0.005mol/L in the present embodiment;

c2. Perform pre-annealing treatment on the silicon microwire array substrate adsorbed by the precursor in a tubular annealing furnace: the time is 2-5 hours, preferably 3 hours, the temperature is 400-600°C, preferably 500°C, and the gas atmosphere is Air.

d. Perform post-annealing treatment in a rapid annealing furnace: the time is 3-10 minutes, preferably 5 minutes, the temperature is 300-600°C, preferably 400°C, and the gas atmosphere is N ₂ ; refer to Figure 4 .

e. Coating a conductive layer on the back of the silicon/iron oxide microwire array substrate obtained after post-annealing, and drawing out external wires, refer to FIG. 5 . In this embodiment, the conductive layer is an In-Ga conductive layer.

f. Coating a waterproof insulating layer on the conductive layer to completely cover the back conductive layer to obtain a photoanode, refer to FIG. 6 . The waterproof insulating layer is preferably epoxy resin or 704 silica gel.

g. Immerse the prepared photoanode in a 1 mol/L NaOH aqueous solution, use the platinum mesh electrode as the counter electrode and the Ag/AgCl electrode as the counter electrode, use an electrochemical workstation to connect the three electrodes to construct a three-electrode test system .

This embodiment also provides another technical solution: a photoanode structure obtained by using the above-mentioned method for preparing a photoanode for improving the performance of photolysis of water.

working principle:

Referring to accompanying drawing 7, under sunlight, photoanode 1 and cathode 2 are both in electrolyte, silicon/iron oxide photoanode 1 absorbs incident light, generates electron-hole pairs, and holes migrate to photoanode/electrolyte interface , and participate in the oxidation reaction of water to generate oxygen; electrons are transported to the back of the photoanode 1 to reach the counter electrode (ie, the cathode 2), and participate in the reduction reaction of water on the surface of the counter electrode to generate hydrogen.

Performance Testing:

Linear voltage sweep tests were performed under no illumination and a standard sunlight intensity. The test results are shown in Figure 8, in which: 31 is the introduction of Sn doping and rapid annealing in N ₂ atmosphere, and a standard sunlight irradiation is given at the same time; 32 is the introduction of Sn doping and rapid annealing in N ₂ atmosphere is carried out, No illumination; 33 was subjected to N ₂ atmosphere rapid annealing treatment without introducing doping, and a standard sunlight irradiation was given at the same time; 34 was introduced Sn doping without N ₂ atmosphere rapid annealing treatment, and a standard sunlight treatment was given at the same time. Light irradiation; 35 is no doping introduced and no N ₂ atmosphere rapid annealing treatment, while giving a standard sunlight irradiation.

It can be seen that the silicon microwire array/iron oxide thin film photoanode with Sn doping and rapid annealing in N ₂ atmosphere of the present invention is better than the photoanode without doping or rapid annealing or both. For the photoanode, under the same potential, the corresponding photocurrent density is higher than that of other comparative samples.

The photoanode preparation method and the obtained photoanode structure for improving the performance of photo-splitting water, the internal resistance of the silicon/iron oxide double absorption layer photoanode is very small; the iron oxide has good light absorption performance; the silicon/iron oxide interface defect The density of states is small, and the recombination of the carrier interface is small; the iron oxide film has a high oxygen hole density, and the carrier injection and conversion efficiency at the iron oxide/solution interface are high; the photoelectrochemical test results are reflected as: photocurrent turn-on voltage lower, the short-circuit current density relative to the _H2O / _O2 potential is larger.

The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. It should be pointed out that for those skilled in the art, some improvements can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention.

Claims (9)

1. it is a kind of improve photocatalytic water performance light anode preparation method, it the following steps are included:

A. use resistivity for the n-type silicon chip of 0.01~0.05 Ω cm；

B. silicon is corroded to the laggard row metal assistant chemical of Wafer Cleaning, and prepares silicon micron linear array；

C1. using silicon micron linear array as substrate, using containing Fe³⁺Solution, and be mixed into doped source solion wherein, as The precursor liquid for growing iron oxide layer, makes precursor liquid be adsorbed in silicon micro wire array substrate by spray-on process；

C2. annealing early period is carried out to the silicon micro wire array substrate for having precursor liquid to adsorb, obtains silicon/iron oxide micron linear array Column；

D. post annealed processing is carried out under nitrogen or argon atmosphere to the silicon/iron oxide micron linear array；

E. resulting silicon/iron oxide micro wire array substrate backside deposition conductive layer after post annealed, and draw external lead Line；

F. waterproof insulating layer is coated on the conductive layer.

2. a kind of light anode preparation method for improving photocatalytic water performance according to claim 1, it is characterised in that: described In step b, the silicon micro wire spacing is 1~10 μm, diameter is 1~10 μm, length is 5~100 μm.

3. a kind of light anode preparation method for improving photocatalytic water performance according to claim 1, it is characterised in that: described In step c1, the doped source solion is SnCl₄、TiCl₄、MnCl₄、SiCl₄、GeCl₄、ZrCl₄、NbCl₄In solution One or more of combinations.

4. a kind of light anode preparation method for improving photocatalytic water performance according to claim 1, it is characterised in that: described In step d, the condition of post annealed processing are as follows: use quick anneal oven, handled 3~10 minutes at 300~600 DEG C, gas Atmosphere is nitrogen or argon gas.

5. a kind of light anode preparation method for improving photocatalytic water performance according to claim 1, it is characterised in that: described In step c1, Fe³⁺Solution be Fe (NO₃)₃Or FeCl₃Ethyl alcohol or aqueous solution.

6. a kind of light anode preparation method for improving photocatalytic water performance according to claim 1, it is characterised in that: described In step c1, precursor liquid is set to be adsorbed in silicon micro wire array substrate by spray-on process method particularly includes: to surpass the precursor liquid Sound atomization, and the silicon micro wire array substrate that will warm up 100~200 DEG C is placed in below atomizer.

7. a kind of light anode preparation method for improving photocatalytic water performance according to claim 6, it is characterised in that: circulation weight Multiple to carry out the step c1 and step c2, circulating repetition number is 1~20 time, as Fe in precursor liquid³⁺Concentration is bigger, then recycles Number of repetition is smaller.

8. a kind of light anode preparation method for improving photocatalytic water performance according to claim 1, it is characterised in that: described In step c2, early period annealing condition are as follows: in tubular annealing furnace, handled 2~5 hours at 400~600 DEG C, gas Atmosphere is air.

9. a kind of light anode preparation method for improving photocatalytic water performance using one of any one of claim 1-8 is resulting Light anode structure.