CN108193227A - Oxygen electrode and its preparation and application are analysed in the electro-catalysis of nickel-ferric spinel base - Google Patents

Abstract

The invention belongs to materials science field and electro-catalysis hydrogen producing technology fields, and in particular to a kind of nickel-ferric spinel base electro catalytic electrode and its preparation available for electrolysis water oxygen evolution reaction in alkaline medium.For the electrode system using nickel-ferric spinel structure as catalytic active center, nickel foam is electrode material.It efficiently electrolysis water can prepare oxygen in alkaline medium, and the entirety electricity excessively for greatly reducing electrolysis water is thrown, and show good stability.Its preparation process grows nickel-ferric spinel composite construction by electrodeposition process in situ in foam nickel base, required raw material sources are extensive, cheap, technical maturity is stable, simple and efficient to handle, controllability is strong, process is nontoxic, is reacted suitable for large-scale production and industrial electrolysis water.

Description

Nickel-iron hydrotalcite-based electrocatalytic oxygen evolution electrode and its preparation and application

technical field

The invention belongs to the technical field of material science and the technical field of electrocatalytic hydrogen production, and specifically relates to a nickel-iron hydrotalcite-based electrocatalytic oxygen evolution electrode capable of efficiently electrolyzing water to produce hydrogen in an alkaline medium and its preparation.

Background technique

Hydrogen is an important clean energy, and it is considered as a promising new energy to replace fossil energy, and has been widely concerned all over the world. In recent years, with the continuous development of new power generation technologies and the continuous optimization and upgrading of power grid systems, the advantages of electrolytic water hydrogen production technology have been further amplified, and it has even been widely praised as "the most ideal industrial hydrogen production method". However, in the process of electrocatalytic water splitting, the kinetic hindrance of oxygen evolution reaction seriously restricts the improvement of water splitting efficiency. At present, noble metal oxides such as iridium, ruthenium, and platinum are recognized as the most efficient and oxygen-evolving electrocatalysts, but the high price and low storage capacity of noble metals limit the wide application of such catalysts in electrolysis of water for oxygen production and electrolysis of water. The considerable development of the hydrogen production process. Therefore, finding efficient, stable, environmentally friendly and inexpensive electrocatalysts to replace noble metals is the key to the development of electrolyzed water.

The latest research shows that layered transition metal oxides or hydroxides exhibit high activity and stability in the electrocatalytic oxygen production reaction. Hydrotalcite is a layered compound formed by the orderly assembly of interlayer anions and positively charged lamina, in which the main lamina is composed of divalent transition metal oxide octahedral shared edges. The divalent metal cations located in the laminates can be replaced by trivalent metal cations with similar ionic radius within a certain proportion, so that the main layer is partially positively charged; the guest anions that can be exchanged between the layers and the interlayers The positive charges are balanced so that the overall structure of the hydrotalcite is electrically neutral. Among the many hydrotalcite structures, nickel-iron hydrotalcite formed by divalent nickel and ferric iron and its derivatives have extremely high electrolytic water oxygen evolution activity, and are considered to be the most likely electrocatalysts to replace noble metals. However, the synthesis methods of such materials reported at this stage and the methods of electrode preparation have limitations, such as the use of solvothermal method, high temperature tempering method and other synthesis methods, complex process, high energy consumption, and unfriendly environment; in addition, usually Loading the prepared electrocatalyst on the two-dimensional substrate by spin coating, spray coating, drop coating, etc. requires additional binders, and the catalyst is not firmly bonded, poorly contacted, and unevenly dispersed on the electrode surface, resulting in hindered charge transport and easy Problems such as falling off seriously affect the final catalytic activity and life of the electrode.

Contents of the invention

One of the objectives of the present invention is to provide an electrocatalytic oxygen evolution electrode with three-dimensional nickel foam as the electrode substrate and nickel-iron hydrotalcite layered structure as the active center. The electrocatalytic electrode has a wide range of raw materials and low cost, and exhibits high catalytic activity and long-term structural and chemical stability in alkaline media, and is suitable for industrial electrolysis of water to produce oxygen.

The second object of the present invention is to provide a method for preparing a nickel-iron hydrotalcite-based electrocatalytic oxygen evolution electrode for efficient electrolysis of water to produce oxygen. The method has clear and novel design ideas, mature and stable process, simple and fast operation, strong controllability, and is suitable for large-scale production.

The preparation method of the nickel-iron hydrotalcite-based electrocatalytic hydrogen evolution electrode provided by the invention, the specific operations are as follows:

1. Pretreatment of nickel foam: Ultrasonic in acetone or ethanol to degrease and remove oil, ultrasonic in ultrapure water and repeat at least twice for cleaning, ultrasonic acidification and activation in 1-2mol/L hydrochloric acid for 1-20 minutes, and finally Sonicate again in ultrapure water for 1-20 minutes and repeat at least twice.

2. Electrolyte preparation: Dissolve nickel-based soluble salt and iron-based soluble salt directly in ultrapure water. The sum of the molar concentrations of the nickel and iron elements is 0.1mmol/L-1mol/L, and the molar content of the iron element is 10%-80%.

3. The assembly of the standard three-electrode system: the nickel foam electrode processed in the step (1) is used as the working electrode and the counter electrode, the saturated calomel electrode is used as the reference electrode, and the solution prepared in the step (2) is used as the electrolyte. Assemble into a standard three-electrode system.

4. Electrodeposition: Connect the three-electrode system assembled in step (3) to the electrochemical workstation, pass inert gas into the electrolyte, keep the flow rate at 5-100mL/min, and conduct constant-potential or constant-current electrodeposition for 10-600s Finally, the working electrode was taken out, the excess electrolyte was cleaned with ultrapure water, and dried at room temperature to obtain the electrocatalytic moisture-analysis oxygen electrode.

Preferably, in step (2), the nickel-based soluble salt is one or more of nickel chloride, nickel nitrate, nickel sulfate, and the iron-based soluble salt is one or more of ferrous chloride and ferrous sulfate .

Preferably, the constant potential electrodeposition potential in step (4) is -1~-2V relative to the saturated calomel electrode, and the constant current electrodeposition current is -0.01~-0.1A/cm ² .

The technical principle of the present invention is: use divalent nickel ions and ferrous ions close to the ion radius and electrodeposition potential as the electrodeposition precursors, and can grow uniformly on the foamed nickel substrate under the condition of constant potential or constant current A layered nickel-iron hydroxide thin film with uniform element distribution. With the drying process in the air, the divalent iron ions on the film are gradually oxidized into ferric ions by the air, so that the original main layer is partially positively charged. At this time, in order to balance the excess positive charges, carbon dioxide in the air enters the interlayer and reacts with hydroxyl groups to form carbonyl groups, and stretches the local laminates, so that many stray layers grow in situ on the originally flat two-dimensional layered structure. Tiny laminates form a three-dimensional structure. This hydrotalcite structure formed in situ due to the in situ oxidation of divalent metals has a special three-dimensional layered structure, which greatly increases the effective active surface area of the catalyst; at the same time, the in situ oxidation process is only carried out on the laminate of the catalytic material , the good contact and close combination between the pre-oxidation catalyst film and the substrate are retained, so that the catalytic electrode has excellent electrochemical stability and reaction life.

Compared with the prior art, the present invention has the following beneficial effects:

1. The present invention utilizes an in-situ electrodeposition method to directly grow nickel-iron hydrotalcite layered structure electrocatalysts on a foamed nickel substrate. The method has wide source of raw materials, low price, mature process, simple and fast operation, only needs ten seconds to ten minutes of preparation time, process is controllable, and is suitable for large-scale industrial production.

2. The present invention utilizes in-situ oxidation of divalent metals to form a three-dimensional layered structure of nickel-iron hydrotalcite, which has a large electrochemically active surface area, greatly increases the oxygen evolution activity of the electrocatalyst, and can replace precious metals to promote alkalinity Development of water electrolysis systems in media.

3. The present invention utilizes the in-situ growth of the electrocatalyst on the foamed nickel substrate, without the need for additional binders, and the electrode and the substrate are in good contact and tightly bonded, ensuring the charge transfer efficiency and greatly improving the structural stability of the electrocatalytic electrode .

Description of drawings

Fig. 1 is the X-ray diffraction spectrum (a) and the infrared spectrum (b) of the nickel-iron hydrotalcite prepared by in-situ electrodeposition method;

Transmission electron micrographs (a) and (b) and X-ray photoelectron spectra (c) and (d) of nickel-iron hydrotalcite prepared by in-situ electrodeposition in Fig. 2;

Figure 3 is the optical photo (a) and scanning electron micrograph (b) of the fresh nickel-iron hydrotalcite catalytic electrode prepared by in-situ electrodeposition, and the optical photo (c) and scanning electron micrograph (c) of the electrode after drying and oxidation in air (d);

Fig. 4 is the activity test of nickel-iron hydrotalcite catalytic electrode;

Figure 5 is the stability test of nickel-iron hydrotalcite catalytic electrode.

Detailed ways

The present invention will be described in detail through specific examples below, but these examples do not limit the content of the present invention.

Example 1

A preparation method of a nickel-iron hydrotalcite-based electrocatalytic oxygen evolution electrode is carried out according to the following steps.

(1) Nickel foam was ultrasonically cleaned in acetone for 10 minutes, cleaned in ultrapure water for 10 minutes, and repeated twice, ultrasonically in 1mol/L hydrochloric acid for 10 minutes, and finally cleaned in ultrapure water for 10 minutes, And repeat twice.

(2) Electrolyte preparation: directly dissolve nickel nitrate and ferrous sulfate in ultrapure water. The sum of the molar concentrations of nickel and iron elements is 50mmol/L, and the molar content of iron elements is 25%.

(3) With the nickel foam electrode processed in step (1) as the working electrode and the counter electrode, the saturated calomel electrode as the reference electrode, and the solution prepared in the step (2) as the electrolyte, assembled into a standard three-electrode system.

(4) Connect the three-electrode system assembled in step (3) to the electrochemical workstation, pass nitrogen gas into the electrolyte, keep the flow rate at 20mL/min, and under the electrode potential of -1.241V relative to the saturated calomel electrode After 300 s of constant potential electrodeposition, the working electrode was taken out, the excess electrolyte was cleaned with ultrapure water, and dried at room temperature to obtain the electrocatalytic moisture-analysis oxygen electrode.

Figure 1 (a) is the XRD pattern of the catalyst dried in the air obtained according to the in-situ constant potential electrodeposition method of Example 1. By comparing the standard spectra, it can be concluded that the catalyst is nickel-iron hydrotalcite intercalated with carbonate radicals Layered structure. The infrared spectrum of the catalyst (Fig. 1(b)) also further confirms the layered structure of nickel-iron hydrotalcite intercalated by carbonate radicals. A clear layered structure can be seen in the transmission electron microscope image of Figure 2(a). The X-ray photoelectron spectrum of Figure 2(b) proves that the catalyst is composed of divalent nickel and ferric iron, which can be considered as the divalent iron added in the preparation process is oxidized to trivalent by air during the drying process at room temperature. iron. Fig. 3 (a) is the optical photo of the fresh catalyst electrode just prepared according to the method of Example 1, it can be seen that the catalyst electrode is green, and the corresponding scanning electron micrograph (Fig. 3 (b)) of the electrode shows that the catalyst It is composed of lamellar structure with smooth surface. When the catalyst electrode is dried in the air for a period of time, the optical photo in Figure 3(c) shows that the color of the electrode turns yellow obviously, and the corresponding scanning electron microscope image (Figure 3(d)) shows that the catalyst grows on a smooth sheet surface Many tiny sheets are produced, and the original two-dimensional structure becomes a three-dimensional structure.

The electrochemical performance test of the prepared nickel-iron hydrotalcite-based electrocatalytic oxygen evolution electrode is carried out as follows:

(1) A three-electrode system was adopted, the working electrode was a molybdenum-nickel composite carbonitride foam nickel electrode with a thickness of 1 cm ² , the counter electrode was a platinum sheet electrode, and the reference electrode was a saturated calomel electrode. The electrochemical test is carried out on a solarton electrochemical workstation, the electrolyte is 0.1mol/L or 1mol/L potassium hydroxide solution, high-purity nitrogen gas is injected into the test process for saturation treatment, and the test temperature is controlled at 25°C .

(2) Linear scanning voltammetry curve test: the scanning rate is 1mV/s, and the electrode potential is corrected by iR, and converted into the electrode potential relative to the reversible hydrogen electrode (RHE). The calculation formula is: overpotential = electrode potential + 0.059×pH+0.2415-iR-1.23(V).

(3) The stability test is divided into two procedures: first, the potential-time curve is scanned under the current step procedure, and the current density changes from 50mA/cm ² to 500mA/cm ² , stepping once every 600s, each time 50mA/cm ² ; Secondly, without any treatment, apply a current density of 50mA/cm ² on the same electrode, record the potential-time curve for 5 hours, and then directly adjust the current density to 100mA/cm ² , and then record the potential-time curve for 5 hours, and then adjust the current density to 200mA/cm ² , and record the potential-time curve for 5 hours.

As shown in ^Figure 4, the electrocatalytic electrode exhibits extremely high oxygen evolution activity in alkaline media ^{. 2} , the overpotentials are 280mV, 310mV and 370mV respectively; in 1mol/L electrolyte, the current density is 50mA/cm ² , 100mA/cm ² and 200mA/cm ² , the overpotentials are 250mV, 260mV and 280mV respectively . The oxygen evolution reaction overpotential of the catalyst is far lower than that of other catalysts reported so far, showing extremely high catalytic activity.

As shown in Figure 5(a) and (c), under varying current densities, the electrode exhibits good stability against current fluctuations in electrolytes of different concentrations, at a current density of 500mA/ ^cm2 It still shows good activity and stability. Figure 5(b) and (d) show that the electrode also exhibits excellent resistance to mechanical disturbance and long catalytic lifetime under constant high current and vigorous gas bubbling.

Example 2

A preparation method of a nickel-iron hydrotalcite-based electrocatalytic oxygen evolution electrode is carried out according to the following steps.

(5) Nickel foam was ultrasonically cleaned in acetone for 10 minutes, cleaned in ultrapure water for 10 minutes, and repeated twice, ultrasonically in 1mol/L hydrochloric acid for 10 minutes, and finally cleaned in ultrapure water for 10 minutes, And repeat twice.

(6) Electrolyte preparation: directly dissolve nickel nitrate and ferrous sulfate in ultrapure water. The sum of the molar concentrations of nickel and iron elements is 50mmol/L, and the molar content of iron elements is 25%.

(7) With the nickel foam electrode processed in step (1) as the working electrode and the counter electrode, the saturated calomel electrode as the reference electrode, the solution prepared in the step (2) as the electrolyte, assembled into a standard three-electrode system.

(8) Connect the three-electrode system assembled in step (3) to the electrochemical workstation, pass nitrogen gas into the electrolyte, keep the flow rate at 20mL/min, and conduct constant current electrodeposition at a current density of -0.05A/ ^cm2 After 300 s, the working electrode was taken out, the excess electrolyte was cleaned with ultra-pure water, and dried at room temperature to obtain the electrocatalytic moisture-analysis oxygen electrode.

The electrochemical performance test of the prepared nickel-iron hydrotalcite-based electrocatalytic oxygen evolution electrode was carried out according to the method in Example 1.

The electrocatalytic electrode is in 0.1mol/L electrolyte, the current density is 50mA/cm ² , 100mA/cm ² and 200mA/cm ² , and the overpotentials are 250mV, 290mV and 350mV respectively; in 1mol/L electrolyte In , the overpotentials are 230mV, 250mV and 270mV at the current density of 50mA/cm ² , 100mA/cm ² and 200mA/cm ² , respectively.

In summary, the in-situ electrodeposition method can uniformly grow layered nickel-iron hydrotalcite film on the foamed nickel substrate under the condition of constant potential or constant current. Due to the in-situ oxidation of divalent metals, a special three-dimensional layered hydrotalcite structure is formed in situ, which greatly increases the effective active surface area of the catalyst; at the same time, the in-situ oxidation process is only carried out on the layer of the catalytic material, retaining the oxidation The good contact and tight bonding between the procatalyst film and the substrate endow the catalytic electrode with excellent electrochemical stability and reaction life.

The above content is only a basic description of the concept of the present invention, and any equivalent transformation made according to the technical solution of the present invention shall fall within the scope of protection of the present invention.

Claims (7)

1. oxygen electrode is analysed in a kind of nickel-ferric spinel base electro-catalysis, which is characterized in that the catalyst activity component is nickel-ferric spinel, Its electrode basement is nickel foam；Nickel-ferric spinel compound structure film is grown in foam nickel base by electrodeposition process in situ.

A kind of 2. nickel-ferric spinel base electro-catalysis analysis oxygen electrode as described in claim 1, which is characterized in that the electrode basement For the three-dimensional porous foams nickel of purity 99.99%, porosity is 90~98%.

A kind of 3. preparation method of the nickel-ferric spinel base electro-catalysis analysis oxygen electrode described in claims 1 or 2, it is characterised in that system Standby step is as follows：

(1) pretreatment of nickel foam：Ultrasound is repeated twice in ultra-pure water ultrasound and at least with degreasing degreasing in acetone or alcohol With cleaning, ultrasound acidification activation 1~20 minute in the hydrochloric acid of 1~2mol/L is finally 1~20 minute ultrasonic in ultra-pure water again And it is at least repeated twice；

(2) preparation of electrolyte：Ni-based soluble-salt and iron-based soluble-salt are directly dissolved in ultra-pure water；Ferro-nickel element is rubbed The sum of your concentration is 0.1mmol/L~1mol/L, and wherein ferro element molar content is 10%~80%；

(3) assembling of standard three electrode system：Using the foam nickel electrode handled in step (1) as working electrode and to electrode, satisfy It is reference electrode with calomel electrode, using prepared solution in step (2) as electrolyte, is assembled into the three-electrode system of standard；

(4) electro-deposition in situ：The three-electrode system assembled in step (3) is connected to electrochemical workstation, will be led in electrolyte Enter inert gas, keep flow after 5~100mL/min, 10~600s of constant potential or constant current electro-deposition, take out work electricity Excess electrolyte with ultra-pure water is cleaned up, dried at room temperature by pole, obtains the electro-catalysis moisture parsing oxygen electrode.

4. preparation method according to claim 3, it is characterised in that：Ni-based soluble-salt is nickel chloride, nitre in step (2) One or more of sour nickel, nickel sulfate, iron-based soluble-salt is frerrous chloride, ferrous nitrate, ferrous sulfate, iron chloride, nitre One or more of sour iron, ferric sulfate.

5. preparation method according to claim 3, it is characterised in that：The constant potential electro-deposition current potential of step (4) is opposite In saturated calomel electrode -1~-2V, constant current electro-deposition electric current is in -0.01~-0.1A/cm²。

A kind of 6. application of the compound carbonitride electrocatalytic hydrogen evolution electrode of molybdenum nickel described in claim 1, which is characterized in that the electricity Catalytic hydrogen evolution electrode can be used as anode electrolysis water decomposition oxygen in alkaline medium.

7. according to the application described in claim 6, which is characterized in that alkaline medium is in potassium hydroxide or sodium hydroxide solution One or more, a concentration of 0.1~10mol/L.