CN109852992B

CN109852992B - Efficient electrocatalytic full-decomposition water nanosheet array electrode and preparation method and application thereof

Info

Publication number: CN109852992B
Application number: CN201910075847.9A
Authority: CN
Inventors: 张兴旺; 郝少云; 陈鲁川; 雷乐成
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2019-01-25
Filing date: 2019-01-25
Publication date: 2020-04-28
Anticipated expiration: 2039-01-25
Also published as: CN109852992A

Abstract

The invention discloses a high-efficiency electrocatalytic catalystWater decomposition nanosheet array electrode and preparation method and application thereof. The method takes foam nickel as a substrate and utilizes a chloride ion corrosion method to prepare the electrode material with the appearance of an ultrathin nanosheet array. By controlling the concentration of the chloride ions and adding the types of the metal ions, the components of different metals in the multi-hydroxide can be effectively regulated and controlled. The Ni with the shape of the ultrathin nanosheet array₅Co₃The Mo-OH electrode shows excellent performance of electrochemically catalyzing and decomposing water to produce hydrogen (η)₁₀52mV) and oxygen generating properties (η)₁₀₀304 mV). Meanwhile, the material is at 100mA cm^‑2Can stably run for 100h under the condition and has excellent electrochemical stability. In addition Ni₅Co₃Mo-OH can be simultaneously used as a cathode and an anode to carry out the full water decomposition reaction at 10 mA-cm^‑2The voltage under current density conditions was 1.43V. We believe that the patent provides a new idea for preparing the multi-metal hydroxide nanosheet array, and promotes the development of the application of the multi-metal hydroxide in the aspects of catalysis and energy.

Description

Efficient electrocatalytic full-decomposition water nanosheet array electrode and preparation method and application thereof

Technical Field

The invention relates to the technical field of electrochemical full-decomposed water, in particular to a preparation method of a multi-metal hydroxide nanosheet array and an application of the multi-metal hydroxide nanosheet array in efficient electrochemical full-decomposed water.

Background

The electrochemical full decomposition of water to produce hydrogen and oxygen is considered to be an environmentally friendly technology for energy storage and utilization. The material with best electrochemical water splitting performance is Pt/C and IrO₂And RuO₂And the like. However, the expensive price and poor stability of noble metals make these electrodes expensive in industrial application, thereby limiting their practical large-scale application. Non-noble metal materials, such as transition metal nitrides, transition metal oxides, transition metal hydroxides and perovskite oxides, can effectively catalyze water to generate hydrogen and oxygen, and are expected to replace noble metal materials in the field of electrochemical water decomposition. However, the application as a two-electrode to total water splitting is challenging, as the activity and stability of these materials is limited to a certain working pH range. In addition, adoptThe use of a single-function catalyst as the anode and the cathode, respectively, requires a correspondingly different production process and equipment, resulting in an increase in production cost. Therefore, the development of the bifunctional catalytic electrode which has excellent hydrogen production and oxygen production performance under alkaline conditions has important application value.

Among many transition metal electrodes, the hydroxide nanosheet array based on the foamed nickel electrode is considered to be an excellent fully-decomposed water material due to the advantages of more active sites, larger active area, higher electron transfer rate, no use of a viscose agent and the like. For example, the electrocatalytic properties of a ternary Ni-Co-M or Ni-Fe-M catalyst can be improved by introducing a third metal into a bimetallic Ni-Co or Ni-Mo double hydroxide. Although much research on multi-metal hydroxides has been carried out in the literature, the research on the array of the bi-functional hydroxide nanosheets with excellent water decomposing performance and electrochemical stability is still insufficient.

In addition, most of the existing methods for preparing the multi-metal hydroxide nanosheets are codeposition method, hydrothermal synthesis method, ion exchange method and Fe⁺³Corrosion engineering, and the like. However, since most synthetic methods are affected by the synthesis temperature, anion type and synthesis pH. Therefore, it can be used only for the synthesis of double or triple metal hydroxides. For example, currently emerging Layered Double Hydroxides (LDHs) must contain trivalent metal ions and divalent metal ions and be synthesized in strict metal ratios, thus limiting the diversity and hence the development of multimetal hydroxides. In summary, a mild and simple method for preparing a multi-component and adjustable multi-metal hydroxide nanosheet array is lacking at present.

When an electrolyte layer is formed on the metal surface, galvanic reactions, i.e. corrosion, occur. During the corrosion process, chloride ions play an important role. This is because chloride ions can be easily adsorbed on the metal surface to destroy the inert protective layer, thereby promoting the formation of the electrolyte layer and accelerating the corrosion reaction. Under humid conditions, oxygen and water in the air are reduced at the cathode to form hydroxide, which subsequently combines with metal ions at the anode to form metal hydroxide. At present, many researches are devoted to preventing metals from being damaged by corrosion reaction, and the researches convert the metals into a method for preparing the multi-metal hydroxide nanosheet array electrode in a mild way by utilizing the corrosion reaction.

Disclosure of Invention

The invention aims to solve the problem of providing a method for preparing an efficient fully-decomposed water nanosheet array electrode by mildly etching metal by chloride ions, realizing the adjustability of multi-metal hydroxide components and synthesizing ternary Ni₅Co₃The Mo-OH nanosheet array bifunctional electrode material improves the electrocatalytic hydrogen production and oxygen production performance, and realizes the application of full water decomposition. And provides a good idea and method for preparing other multi-metal hydroxide nanosheet array electrodes.

In order to achieve the purpose, the invention mainly adopts the following technical scheme,

a preparation method of an efficient electrocatalytic full-decomposition water nanosheet array electrode comprises the following steps: adding at least one metal salt and nickel foam into the high-concentration chloride ion solution; controlling the pH value of the initial reaction liquid to be less than or equal to 6; and (3) carrying out reaction under an aerobic condition to obtain the high-efficiency electro-catalytic total-water splitting electrode, wherein the concentration of the halogen ions in the high-concentration halogen ion solution is more than 50 millimoles per liter.

Preferably, the nickel foam further comprises a pretreatment step before the reaction, wherein the pretreatment step comprises: and (3) pretreating the foamed nickel substrate by acid and solvent to remove an oxide layer on the surface, and drying the treated foamed nickel for later use.

Preferably, the metal salts added to the chloride ion solution are preferably two or more.

Preferably, the metal salt is metal halide salt, metal nitrate, metal sulfate, metal acetate; the redox potential of the metal cation of the metal salt is less than that of the nickel ion.

Preferably, the concentration of metal ions is in the range of greater than 0.5 millimoles per liter.

The invention also discloses application of the high-efficiency electrocatalytic full decomposition water electrode in high-efficiency electrocatalytic hydrogen production, oxygen production or full decomposition water. The electrode is used as a cathode of a three-electrode system to produce hydrogen and an anode to produce oxygen, or used as a working electrode of a two-electrode system to be applied to fully decompose water.

Preferably, the foamed nickel substrate of the step 1) has the size of 2 x 2cm²。

Preferably, the concentration of the hydrochloric acid in the step 1) is 1M; ultrasonic treating with hydrochloric acid, acetone and ethanol for 15 min.

Preferably, the reaction conditions are: the temperature of the constant-temperature water bath shaking table is 30 ℃, the rotating speed is 150rpm, and the reaction time is 12 h.

The invention prepares Ni by the method₅Co₃Mo-OH/foamed nickel electrode materials.

Electrochemical workstation using a three-electrode system, Ni₅Co₃Mo-OH/foamed nickel is used as a working electrode, a graphite rod is used as a counter electrode, saturated Ag/AgCl is used as a reference electrode, an electrolyte is 1M KOH solution, 50ml of 1M KOH solution is added into an electrolytic cell, and the constant potential is +10 mA-cm^-2Collecting oxygen under current density; -10mA cm^-2Hydrogen was collected at current density.

The full water decomposition reaction adopts a double-electrode system, Ni₅Co₃Mo-OH/foamed nickel is used as the positive pole and the negative pole respectively to carry out electrocatalytic full-water decomposition. The electrolyte is 50ml of 1M KOH solution, Ni₅Co₃The working areas of Mo-OH/foamed nickel are respectively 1cm²At constant potential +10mA · cm^-2Collecting oxygen under current density; -10mA cm^-2Hydrogen was collected at current density.

The invention uses chloride ion to corrode foam nickel, and uses electrochemical corrosion reaction in metal corrosion process, metal cation Ni generated on cathode, Co and Mo ion Co-transferred to anode and generated OH^-The reaction is carried out to generate the NiCoMo-OH nano-sheet array. Electrochemical tests show that in 1M KOH solution, amorphous trimetallic catalyst Ni₅Co₃Mo-OH shows excellent hydrogen evolution performance (at-10 mA cm)^-2The overpotential under the current density is 52mV), and meanwhile, the oxygen evolution performance is very good (at +10mA cm)^-2The overpotential at current density was 304 mV). And, Ni₅Co₃Mo-OH in +100 and-100 mA cm^-2Can be stabilized for 100 hours under the current density respectively. Based on Ni₅Co₃Good hydrogen and oxygen evolution properties of Mo-OH, we convert Ni₅Co₃Application of Mo-OH to two-electrode system, Ni₅Co₃Mo-OH is in the range of +10mA cm^-2The voltage at current density is only 1.43V. At 100mA cm^-2Good stability at current density can be maintained for 100 hours. This property is the best electrocatalytic effect among the hydroxides reported so far.

Compared with the prior art, the invention has the following advantages:

1. the synthesis process is simple, the reaction conditions are mild, and the catalytic electrode is synthesized in one step by means of a chloride ion corrosion method, so that the process flow is simplified.

2. The synthesis method can regulate and control the nano sheet component. By controlling the types and the concentrations of metal ions in the reaction solution, the multi-metal hydroxide nanosheets with different components can be generated, and the types of the multi-metal hydroxide nanosheets are expanded.

3. The prepared electrode has excellent hydrogen production performance ((η)₁₀52mV) and oxygen generating properties (η)₁₀₀304 mV). Meanwhile, the material is at 100mA cm^-2Can stably run for 100 hours under the condition.

4. The prepared electrode has bifunctional electrocatalytic activity. Simultaneously used as a cathode and an anode to carry out the full water decomposition reaction at 10mA cm^-2The voltage under the density condition is only 1.43V.

Drawings

Fig. 1 is a mechanism diagram of the formation of the nanosheet array electrode material of example 1.

FIG. 2-1 is a photograph of the blank nickel foam morphology obtained by scanning electron microscopy according to example 1;

FIG. 2-2 is a picture of the morphology of the nanosheet array electrode prepared in example 1 under different chloride ion concentrations via a scanning electron microscope;

FIG. 3 is a picture of the morphology of the nanosheet array electrode prepared in example 2 under different pH conditions, as obtained by scanning electron microscopy;

FIG. 4 is an analysis of Ni by X-ray photoelectron spectroscopy in example 2₅Co₃The valence state of the elements of the Mo-OH nanosheet array and the interaction of the elements;

FIG. 5-1 is a transmission electron microscope image of Ni obtained in example 3₅Co₃The Mo-OH nanosheet array morphology and element distribution diagram;

FIG. 5-2 shows Ni in example 3₅Co₃The Mo-OH nanosheet array electrode is applied to a polarization curve of anode oxygen production;

FIGS. 5 to 3 show Ni in example 3₅Co₃The Mo-OH nanosheet array electrode is applied to a polarization curve of cathode hydrogen production;

FIGS. 5 to 4 show Ni in example 3₅Co₃A current-time curve of Mo-OH nanosheet array electrode stability test;

FIG. 6-1 shows Ni in example 4₅Co₃The Mo-OH nanosheet array electrode is applied to a performance test chart of fully decomposed water;

FIG. 6-2 shows Ni in example 4₅Co₃The Mo-OH nanosheet array electrode is applied to a stability test chart of the fully decomposed water;

fig. 7 is a picture of the morphology of the nanosheet array electrode prepared by controlling the composition and type of the metal ions obtained by a scanning electron microscope in example 5.

Detailed Description

Example 1

The mechanism of nanosheet array formation is as follows: in the anode region of the galvanic cell, high concentrations of Cl^-The solution can intensify corrosion and oxidize foam nickel into Ni²⁺Followed by Cl^-Will continuously migrate to the anode region and continuously enrich, as shown in formula 1; at the same time, the water reacts with oxygen in the air and is reduced to hydroxyl (OH) in the cathode region^-) As shown in equation 2; final metal ion M^x+And Ni²⁺Bonding with OH on the surface of the foamed nickel^-And reacting to generate the multi-metal hydroxide nanosheet array as shown in formula 3. The mechanism diagram is as followsAs shown in fig. 1. According to this mechanism, the following experiment was carried out.

Cathode:O₂+2H₂O+4e^-→4OH^-(2)

Ni²⁺+M^x++(2+x)OH^-→Ni-M-OH_2+x(3)

The size of the sample is 2 x 2cm²The foamed nickel substrate (thickness 1mm) of (2) was subjected to ultrasonic cleaning with 1M hydrochloric acid, acetone and absolute ethanol in this order for 15 minutes to remove surface oxides. And blowing the liquid on the surface of the electrode by using argon, and putting the electrode into a sealing bag for later use. The figure of the blank foam nickel obtained by scanning electron microscopy is shown in figure 2-1. The blank foamed nickel has a three-dimensional pore structure and a smooth and flat surface.

A reaction solution was prepared, and the volume of the solution was 50 mL. Reaction solution NaCl, CoCl₂·6H₂O and MoCl₅Composition in which the NaCl concentrations are 5mM,50mM,500mM and 1000mM, respectively, CoCl₂·6H₂O concentration 0.5mM, MoCl₅The concentration was 0.5 mM. The initial pH of the solution was adjusted to 3.5 by 1M hydrochloric acid. The treated nickel foam is put into a conical flask with the volume of 100mL, the reaction solution is added, and the conical flask is sealed by a preservative film. And putting the reactor into a constant-temperature water bath shaking table for reaction. The temperature of the constant-temperature water bath shaking table is 30 ℃, the rotating speed is 150rpm, and the reaction time is 12 h. And after the prepared nanosheet array electrode is taken out of the reactor, the nanosheet array electrode is respectively cleaned with deionized water and ethanol for three times, and then is dried and stored by argon. The topography of the electrode prepared under the conditions of different concentrations of chloride ions can be obtained as shown in FIG. 2-2. As can be seen, no nanosheet structure is observed under low chloride ion concentration conditions; with the increasing concentration of chloride ions, the nano-sheet structure gradually grows.

Example 2

Referring to the electrode preparation method of example 1, multi-metal hydroxide nanosheet electrodes were prepared under different initial pH conditions. The initial pH of the reaction solution was adjusted to 2, 3.5 and 5.5 with 1M hydrochloric acid, respectively. The NaCl concentration in the reaction solution was 0.5M, and the remaining reaction conditions were the same as in example 1. After the prepared electrode is taken out of the reactor, the electrode is respectively cleaned with deionized water and ethanol for three times, and then is dried and stored by argon. The morphology of the prepared polymetallic hydroxides under different initial pH conditions can be seen in FIG. 3. As can be seen from fig. 3, the nanosheet structure occurs under acidic conditions, and the lower the pH, the larger the nanosheet size and the greater the number.

Example 3

Ni was prepared according to the method described in example 1 under the conditions of NaCl concentration in the reaction solution of 0.5M and initial pH of 3.5₅Co₃Mo-OH nanosheet array electrode. FIG. 4 is an analysis of Ni by X-ray photoelectron spectroscopy₅Co₃The valence state of each element of the Mo-OH nanosheet array electrode. FIG. 5-1 shows Ni obtained by scanning electron microscopy and transmission electron microscopy₅Co₃The morphology and the element distribution map of the Mo-OH electrode. From the figure, the obtained material has a nanosheet array structure, and each element is uniformly distributed in the nanosheet structure. FIG. 5-2 shows that the material is at 10mA cm^-2Under the condition of density, the overpotential of hydrogen production is 52mV respectively. FIGS. 5-3 show that the material was at 100mA cm^-2The overpotential for oxygen generation under the density condition is 304mV respectively. FIGS. 5-4 show that the material was at 100mA cm^-2Under the condition of density, the electrochemical stability is higher.

Example 4

Preparation of Ni in example 3₅Co₃The Mo-OH nanosheet array is used as an electrode, and a full decomposition water performance test and a stability test are carried out in a 1M KOH solution by adopting a double-electrode system. As shown in FIG. 6-1, the material was measured at 10mA cm^-2The voltage under the density condition is only 1.43V; meanwhile, as shown in FIG. 6-2, the current density was 10mA cm^-2And 100mA · cm^-2The stable operation was continued for 100 hours at the current density.

Example 5

The composition and morphology of the multi-metal hydroxide are regulated by changing the types and concentrations of different metal ions in the reaction solution according to the method described in example 1. For monometallic Ni (OH)₂Preparation of nanosheet by subjecting the reaction solution toThe concentration of NaCl was changed to 0.5M and the concentration of NiCl was changed to 0.5mM₂·6H₂And O. For the preparation of the double hydroxide, the reaction solution was changed to 0.5M NaCl and 0.5mM CoCl₂·6H₂And O. For the preparation of the multimetal hydroxides, the reaction solution for preparing the bimetallic oxides is based on NaCl (0.5M) and CoCl₂·6H₂O (0.5/n mM)), FeCl was added separately₃·6H₂O, CuCl₂·2H₂O,MoCl₅,MnCl₂·4H₂O, and ZnCl₂The concentrations were 0.5/n mM, and n represents the kind of metal. As shown in FIG. 7, the shapes and element distribution maps of different multi-metal hydroxides can be obtained by a scanning electron microscope and a transmission electron microscope. According to the figure, different metal salt solutions can generate the nano-sheet, and elements are uniformly distributed in the nano-sheet structure.

Example 6

The composition and morphology of the multi-metal hydroxide are controlled by changing the anion types of different metal salts in the reaction solution according to the method described in example 1. For the preparation of the double hydroxide, the reaction solution was changed to 0.5M NaCl and 0.5mM Co (NO)₃)·6H₂And O. For the preparation of the multimetal hydroxide nanosheets, the reaction solution for preparing the bimetallic oxide nanosheets was based upon (i.e., NaCl (0.5M) and Co (NO)₃)·6H₂O (0.5/n mM)), Fe (NO) was added thereto, respectively₃)₃·9H₂O,Mn(CH₃COO)₂·4H₂O, and Zn (CH)₃COO)₂·2H₂O concentration is 0.5/n mM, and n represents the metal species.

Claims

1. A preparation method of an efficient electrocatalytic full-decomposition water nanosheet array electrode is characterized by comprising the following steps: adding at least one metal salt and nickel foam into the high-concentration chloride ion solution; controlling the pH value of the initial reaction liquid to be less than or equal to 6; carrying out reaction under an aerobic condition to obtain a high-efficiency electro-catalytic total water decomposition electrode, wherein the concentration of chloride ions in the high-concentration chloride ion solution is more than 50 millimoles per liter; the metal salt is metal halide salt, metal nitrate, metal sulfate and metal acetate; the redox potential of the metal cation of the metal salt is less than that of the nickel ion.

2. The method according to claim 1, wherein the nickel foam further comprises a pretreatment step before the reaction, wherein the pretreatment step comprises: and (3) pretreating the foamed nickel substrate by acid and solvent to remove an oxide layer on the surface, and drying the treated foamed nickel for later use.

3. The method according to claim 1, wherein the metal salt added to the chloride ion solution is preferably two or more.

4. The method of claim 1, wherein the concentration of the metal ion is in a range greater than 0.5 millimoles per liter.