CN110368992A - A kind of preparation method of metal-organic framework elctro-catalyst - Google Patents

Abstract

The invention discloses a kind of preparation methods of metal-organic framework elctro-catalyst, it is characterized by: first on conductive substrates using one layer of metal nanoparticle layer of flexible conductive substrates that obtain that treated, metal-organic framework material layer is directly grown in conductive substrates by Anodic dissolution method again, obtain the elctro-catalyst, wherein, the metal nanoparticle layer with a thickness of the nm of 100 nm~500.The present invention is grown directly upon MOFs material in any conductive substrates as elctro-catalyst, avoids the use of binder and conductive agent, can improve its catalytic performance to a certain extent by using two-step electrochemical sedimentation.

Description

A kind of preparation method of metal-organic framework structure electrocatalyst

technical field

The invention relates to a preparation method of a thin film material, in particular to a preparation method of a metal organic framework thin film material.

Background technique

Hydrogen energy, as one of the most promising alternative energy sources for fossil fuels, has attracted more and more attention due to its cleanness, lightweight and renewable energy. The hydrogen evolution reaction (HER) is an inexpensive and environmentally friendly method for producing high-purity hydrogen by water splitting, and is currently a research hotspot. How to reduce the overpotential of the reaction and continuously produce a large amount of hydrogen are two key issues facing human beings, and this requires efficient electrocatalysts. Pt-based catalysts are recognized as the most efficient HER electrocatalysts in the prior art, but currently available platinum-based catalysts in the market are not only expensive but also prone to deactivation. Therefore, it is urgent to develop non-precious metal-based catalysts with high catalytic activity and low cost for mass production of hydrogen.

Metal-organic frameworks (MOFs)-based materials have been widely used in gas storage and separation, energy storage and conversion systems, and electrocatalysts due to their high porosity, high surface area, and monodisperse metal units. Chinese invention patent CN105289733A discloses a method for preparing a hydrogen evolution electrocatalyst based on a metal organic framework compound. After mixing a copper acetate solution and a trimesic acid solution, ultrasonication is performed, and the product is mixed with an organic solvent in proportion to obtain a Cu-MOF@Nafion hydrogen evolution catalyst. . However, the catalyst obtained by this scheme is a liquid containing an organic solvent, which can only be added to the electrolyte, but cannot be used to prepare cathode catalytic materials.

MOFs are crystalline porous materials formed by the coordination of organic ligands and metal ions or clusters. Organic ligands make MOFs easy to modify, but also make most MOF materials inherently poor in conductivity, which seriously hinders the direct use of MOF materials as hydrogen evolution catalysts. The electrochemical properties of materials can be effectively improved by converting MOF materials into transition metal oxides, phosphides, sulfides, and selenides. However, the high specific surface area and highly dispersed active sites of the material may be lost during the calcination process. Another effective strategy to overcome the poor conductivity of MOFs without calcination is to incorporate conductive materials such as acetylene black, carbon nanotubes, graphene/graphene oxide, or metal nanoparticles. However, the local charge transfer in MOFs is still limited due to the size repulsion effect and the addition of binders or conductive agents.

In order to solve the above problems, one consideration is to prepare metal-organic framework material films directly on the surface of conductive materials. However, for different conductive materials, different interface resistances will be formed between MOFs and conductive substrates. In the prior art, a large number of In the experiment, a specific conductive material was selected as the conductive substrate in order to obtain a material with lower interface resistance for the cathode electrode.

Contents of the invention

The purpose of the present invention is to provide a method for preparing an electrocatalyst with a metal organic framework structure, so as to realize the preparation of an electrocatalyst material with a metal organic framework structure on any conductive substrate.

In order to achieve the above-mentioned purpose of the invention, the technical solution adopted in the present invention is: a preparation method of a metal-organic framework structure electrocatalyst, first adopting an electrodeposition method to deposit a metal nanoparticle layer on a conductive substrate to obtain a treated conductive substrate, Then, a metal-organic framework material layer is directly grown on the conductive substrate by an electrochemical anodic dissolution method to obtain the electrocatalyst, wherein the metal nanoparticle layer has a thickness of 100 nm to 500 nm.

In the above technical solution, the interfacial resistance between MOFs and the conductive substrate is reduced through the arrangement of the metal nanoparticle layer, and its conductivity is directly improved, so that the material of the present invention can be directly used as a cathode electrode.

In a preferred technical solution, the metal nanoparticle layer is composed of copper nanoparticles, and the particle size of the copper nanoparticles is 100nm-500nm.

In the above-mentioned technical scheme, the preparation method of the metal nanoparticle layer is to adopt a three-electrode system to deposit copper nanoparticles, with Ag/AgCl as a reference electrode, a Pt sheet as a counter electrode, a working electrode as a conductive substrate, and an electrolyte solution of Mixed aqueous solution of CuCl2 and _KCl .

In the above technical solution, the deposition time is 300 s to 800 s at a voltage of -0.2 V to -0.5 V. Preferably, deposit at a voltage of -0.4V for 500 s.

In the above-mentioned technical scheme, the method for growing the metal-organic framework structure material layer is to use Ag/AgCl as the reference electrode, the Pt sheet as the counter electrode, the working electrode as the conductive substrate, and the electrolyte solution as 20-40 mM trimesic acid, 20 ～40 mM tetrabutylammonium perchlorate, the volume ratio of ethanol and water in the solution is 3:1; deposit at a voltage of 0V～1 V for 100 s～300 s to obtain HKUST-1, which is a metal organic framework structure Material layer; then put it in a vacuum oven at 60°C-120°C for 6 h-12h.

The preferred technical scheme, the electrolyte solution is 25 mM trimesic acid, 25 mM tetrabutylammonium perchlorate, and the volume ratio of ethanol and water in the solution is 3:1; deposit 100 s at a voltage of 1 V to obtain HKUST -1, is the metal organic framework material layer; then placed in a vacuum oven at 120 °C for 12 h.

In the above technical solution, the thickness of the metal organic framework material layer is 500nm-800nm.

Due to the use of the above-mentioned technical solutions, the present invention has the following advantages compared with the prior art:

1. The present invention adopts a two-step electrochemical deposition method, so that the MOFs material can be directly grown on any conductive substrate, as an electrocatalyst, avoiding the use of binders and conductive agents, and can improve its catalytic performance to a certain extent.

2. The product of the present invention can effectively prevent the stripping of active materials under the conditions of high current density and severe gas evolution, and provides a simple and feasible method for preparing high-efficiency and low-cost MOFs-based electrocatalyst materials.

3. The electrocatalyst material obtained in the present invention can be directly used as a cathode electrode for hydrogen evolution reaction.

4. The thickness of the metal nanoparticles in the present invention is only a few hundred nanometers, and a relatively thin layer covers the surface of the carbon paper, so that the metal particles are directly converted into MOF materials in the follow-up, directly grown on the carbon paper, and the carbon paper directly plays a role Conductivity; Compared with the scheme of directly converting metal substrates into MOF materials in the prior art, the substrates in the present invention can be any kind of conductive materials, such as carbon paper, nickel mesh and other current collectors, and the synthesized MOF materials are Nano-scale, more conducive to electrocatalytic reactions.

Description of drawings

Figure 1 is the SEM image of copper nanoparticles and HKUST-1 particles deposited on carbon paper in Example 1; among them, (a-c) electroplated copper nanoparticles; (d) electrodeposited HKUST-1; (e-f) single enlarged HKUST - 1 pellet;

Figure 2 is the SEM image of Comparative Example 1; (a) HKUST-1 prepared by hydrothermal method; (b) single enlarged HKUST-1 particle;

Fig. 3 SEM images of copper nanoparticles and HKUST-1 particles deposited on nickel mesh; among them, (a-c) electroplated copper nanoparticles; (d-e) electrodeposited HKUST-1; (f) single enlarged HKUST-1 particles;

Figure 4 SEM images of copper nanoparticles and HKUST-1 particles deposited on stainless steel mesh; among them, (a-c) electroplated copper nanoparticles; (d-e) electrodeposited HKUST-1; (f) single enlarged HKUST-1 particles;

Figure 5 is the HER polarization curve;

Figure 6 is the corresponding Tafel diagram;

Figure 7 and Figure 8 are the cyclic voltammograms of hydrothermal HKUST-1 and electrodeposited HKUST-1 at different scan rates when the potential is 0.425V-0.625V;

Figure 9 is the electric double layer capacitance of hydrothermal HKUST-1 and electrodeposited HKUST-1;

Figure ₁₀ is the durability measurement of electrodeposited HKUST-1 and hydrothermal HKUST- ₁ in 0.5MH2SO4;

Fig. 11 is the electrochemical impedance spectrum of electrodeposited HKUST-1 and hydrothermal HKUST-1 in embodiment one;

Figure 12 is an equivalent circuit corresponding to electrodeposition.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing and embodiment:

Example 1: Preparation of HKUST-1 metal-organic framework electrocatalyst on carbon paper.

(1) Deposit copper nanoparticles with Autolab electrochemical workstation:

A three-electrode system was adopted, with Ag/AgCl as the reference electrode, a Pt sheet as the counter electrode, and a 1×2 cm ² carbon paper as the working electrode. The electrolyte solution was 5 mM CuCl ₂ , 0.1 M KCl and 100 mL of deionized water, deposited at -0.4 V for 500 s.

Referring to Figure 1, it can be seen from (a, b, c) in Figure 1 that copper nanoparticles have been evenly plated on the carbon paper.

(2) Under the same electrode, replace the electrolyte solution with 25 mM H ₃ BTC (trimesic acid), 25 mMBTAP (tetrabutylammonium perchlorate), and the volume ratio of ethanol and water in the solution is 3:1 . Deposited at a voltage of 1 V for 100 s, HKUST-1 was obtained.

Then placed in a vacuum oven at 120 °C for 12 h.

Referring to accompanying drawing 1, it can be seen from d) in Fig. 1 that HKUST-1 is deposited on the carbon paper, and e, f) are single HKUST-1 particles, and it can be seen that the size is only about 500 nm.

Comparative example 1: The traditional hydrothermal method was used to prepare HKUST-1, the specific process is as follows:

5 mM CuCl ₂ and 25 mM H ₃ BTC were dissolved in ethanol and water (ratio 3:1), heated in water at 180 °C for 24 h, and then placed in a vacuum oven at 120 °C for 12 h.

In Figure 2, a) and b) are enlarged views of hydrothermal HKUST-1 and a single HKUST-1 particle. Comparing e) and f) in Figure 1, it can be found that the size of hydrothermally synthesized HKUST-1 is microns level, while the size of HKUST-1 synthesized by electrodeposition is only a few hundred nanometers.

Fig.3 SEM images of copper nanoparticles and HKUST-1 particles deposited on nickel mesh

(a–c) Electroplated Cu nanoparticles; (d–e) Electrodeposited HKUST-1; (f) Individual enlarged HKUST-1 particles.

Fig.4 SEM images of copper nanoparticles and HKUST-1 particles deposited on stainless steel mesh

(a–c) Electroplated Cu nanoparticles; (d–e) Electrodeposited HKUST-1; (f) Individual enlarged HKUST-1 particles.

It can be seen from Figure 3 and Figure 4 that HKUST-1 can still be synthesized by replacing the substrate with nickel mesh and stainless steel mesh, and the single particle size is nanometer level.

Figure 5 and Figure 6 are the hydrogen evolution performance curves and corresponding Tafel curves of three samples of electrodeposited HKUST-1, hydrothermal HKUST-1 and pure carbon paper. It can be seen from the figure that the electrodeposited HKUST- 1 The performance of hydrogen evolution is better than that of HKUST-1 prepared by hydrothermal treatment, the Tafel slope is lower, and the hydrogen evolution overpotential is reduced by about 100 mV. Figure 7 is a diagram of the electrochemical active area of hydrothermal HKUST-1, and Figure 8 is the electrochemical active area of electrodeposited HKUST-1. It can be seen that the electrochemical active area of electrodeposited HKUST-1 is larger than the electrochemical activity of hydrothermal HKUST-1 The area is large, and the electric double layer capacitance of electrodeposited HKUST-1 in Figure 9 is also larger than that of hydrothermal HKUST-1. Figure 10 is the stability test, and it is found that the stability of electrochemical deposition is significantly better than that of hydrothermal materials.

Figure 11 is the electrochemical impedance spectrum of electrodeposited HKUST-1 and hydrothermal HKUST-1, and Figure 12 is the corresponding equivalent circuit.

The resistance values of the corresponding components of the EIS spectrum fitting equivalent circuit are shown in Table 1.

HKUST-1 electrodeposition HKUST-1 HT water heating R_s (Ω) 1.65 1.80 R_f (Ω) 30.90 66.20 R_ct (Ω) 98.35 126.30

It can be seen from Table 1 that the R _f and R _ct of electrodeposited HKUST-1 _{are smaller than those of hydrothermal HKUST-1 (R f is the catalyst resistance, and R ct is the charge} transfer resistance).

Claims (8)

1. a kind of preparation method of metal-organic framework elctro-catalyst, it is characterised in that: first on conductive substrates using electricity Conductive substrates that one layer of metal nanoparticle layer of deposition method obtains that treated, then by Anodic dissolution method in conduction Metal-organic framework material layer is directly grown in substrate, obtains the elctro-catalyst, wherein the metal nanoparticle layer With a thickness of 100nm~500nm.

2. the preparation method of metal-organic framework elctro-catalyst according to claim 1, it is characterised in that: the metal Nanoparticle layers are made of copper nano particles, and the partial size of copper nano particles is the nm of 100 nm~500.

3. the preparation method of metal-organic framework elctro-catalyst according to claim 2, it is characterised in that: metal nano The preparation method of particle layer is that the deposition of copper nano particles, using Ag/AgCl as reference electrode, Pt are carried out using three-electrode system Piece is to electrode, and working electrode is conductive substrates, and electrolyte solution is CuCl₂With the mixed aqueous solution of KCl.

4. the preparation method of metal-organic framework elctro-catalyst according to claim 3, it is characterised in that: -0.2 The s of 300 s~800 is deposited under the voltage of the V of V~-0.5.

5. the preparation method of metal-organic framework elctro-catalyst according to claim 4, it is characterised in that: -0.4 500 s are deposited under the voltage of V.

6. the preparation method of metal-organic framework elctro-catalyst according to claim 1, it is characterised in that: growth metal The method of organic framework material layer is, using Ag/AgCl as reference electrode, Pt piece is to electrode, and working electrode is conductive base Bottom, electrolyte solution are 20~40 mM trimesic acids, 20~40 mM tetrabutylammonium perchlorates, second alcohol and water in solution Volume ratio is 3:1；The s of 100s~300 is deposited under the voltage of the V of 0 V~1, obtains HKUST-1, as metal organic frame knot Structure material layer；The dry h of 6 h~12 is subsequently placed into 60 DEG C~120 DEG C of vacuum drying oven.

7. the preparation method of metal-organic framework elctro-catalyst according to claim 6, it is characterised in that: electrolyte is molten Liquid is 25 mM trimesic acids, and 25 mM tetrabutylammonium perchlorates, the volume ratio of second alcohol and water is 3:1 in solution；In the electricity of 1 V Pressure 100 s of deposition, obtain HKUST-1, as metal-organic framework material layer；It is subsequently placed into 120 DEG C of vacuum drying oven In 12 h.

8. the preparation method of metal-organic framework elctro-catalyst according to claim 1, it is characterised in that: metal is organic Frame structure material layer with a thickness of 500nm~800nm.