CN115537872A

CN115537872A - Double-doped efficient water electrolysis catalyst and preparation method and application thereof

Info

Publication number: CN115537872A
Application number: CN202211241502.4A
Authority: CN
Inventors: 党杰; 马万森; 汪猛; 高飞宇; 李金洲; 邱泽明; 谭钞文; 侯承真; 胡丽文
Original assignee: Chongqing University
Current assignee: Chongqing University
Priority date: 2022-10-11
Filing date: 2022-10-11
Publication date: 2022-12-30
Anticipated expiration: 2042-10-11
Also published as: CN115537872B

Abstract

The invention discloses a double-doped high-efficiency electrolyzed water catalyst and a preparation method and application thereof, wherein the catalyst is prepared by doping two transition metal elements on the surface of a nickel nitride-based material; the nickel nitride-based nano sheet is characterized in that the nickel nitride-based material is of a nano sheet structure, transition metal elements are attached to the surface of the nickel nitride-based nano sheet in a nanoparticle form, co and V exist in a unique single atom and cluster form in an atomic resolution electron microscope, and the transition metal elements comprise any two of V, cr and Co.

Description

Double-doped efficient water electrolysis catalyst and preparation method and application thereof

Technical Field

The invention relates to the technical field of water electrolysis catalysts, in particular to a double-doped efficient water electrolysis catalyst and a preparation method and application thereof.

Background

The hydrogen gas is a clean energy with great potential because only water is discharged during the use process and other harmful gases or solid particles are not discharged. One of the challenges facing hydrogen energy research is the search for abundant, long-term available, corrosion-resistant, efficient electrocatalysts.

Commercial noble metals (such as Pt and Ru) are the most prominent HER electrocatalysts due to their unique electronic properties, low hydrogen desorption and adsorption gibbs free energy and low water molecule splitting energy barrier. However, its high cost, rarity and lack of durability limit its practical application in the electrolytic water industry.

Transition Metal Nitride (TMN) is one of the superior electrocatalysts for the preparation of HER due to its excellent conductivity and corrosion resistance. However, most reported batches of TMN suffer from two disadvantages: slow kinetics, requiring additional energy to promote water dissociation. Transition Metal Doping (TMD) is one of the simplest solutions, as it can adjust the physicochemical properties and lattice structure of each electrocatalyst to improve HER catalytic performance and stability. However, the existing transition metal doping has problems, and the performance of the obtained catalyst is poor by doping a single transition metal element; the double-doped catalyst has the problems of high doping difficulty, low doping amount and the like, and the performance of the obtained catalyst is not ideal; in addition, the transition metal-doped catalyst prepared by the prior art has poor corrosion resistance in the hydrogen production process by electrolysis, and particularly cannot be continuously used for a long time when the hydrogen production is carried out by electrolysis on seawater.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a double-doped high-efficiency water electrolysis catalyst to solve the problems of high difficulty in doping transition metal elements and poor corrosion resistance in the prior art.

In order to solve the technical problems, the invention adopts the following technical scheme:

a double-doped high-efficiency water electrolysis catalyst is characterized in that two transition metal elements are doped on the surface of a nickel nitride-based material; the nickel nitride-based material is of a nano flaky structure, the transition metal elements are attached to the surface of the nickel nitride-based nanosheet in a nanoparticle form, and the transition metal elements comprise any two of V, cr and Co. When two elements of Co and V are doped, the Co and the V exist in a unique form of single atoms and clusters in an atomic-level resolution electron microscope.

The invention also provides a preparation method of the double-doped high-efficiency water electrolysis catalyst, which is used for preparing the catalyst and specifically comprises the following steps:

step 1: cleaning and pretreating the foam nickel-based material to remove a surface oxidation layer and impurities;

step 2: selecting any two transition metal sources of vanadium source, chromium source and cobalt source, and mixing with Ni (NO) ₃ ) ₂ 、NH ₄ F. Dissolving urea in water, and mixing to form a homogeneous solution; transferring the homogeneous solution and the foam nickel-based material treated in the step (1) into an autoclave for hydrothermal reaction to obtain a double-doped nickel hydroxide nanosheet, and drying after cleaning;

and step 3: subjecting the nickel hydroxide nanosheet obtained in the step 2 to high-purity NH ₃ And carrying out nitridation reaction in the atmosphere to obtain the double-doped high-efficiency electrolytic water catalyst.

The invention also provides application of the double-doped high-efficiency water electrolysis catalyst, and the catalyst prepared by the preparation method is used for producing hydrogen by electrolyzing water or seawater.

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

1. the catalyst is a diatomic doped catalyst, the electronic structure of the catalyst can be further adjusted, more catalytic sites and high electron transfer rate are provided, the electron transfer rate of the catalyst interface and the number of active sites are increased, and the mass transfer dynamics is improved.

2. In the catalyst, the doped transition metal element greatly contributes to alkaline HER activity, wherein V can improve water molecule adsorption so as to enhance the surface hydrophilicity of the electrode, co increases the surface active sites of the catalyst, and Cr promotes the catalysisAdsorption of the agent to oxygen atoms; co, V-Ni near the Fermi level ₃ N shows the maximum density of states, indicating Co, V-Ni ₃ The N surface has good conductivity and interface electron transfer kinetics.

3. The double-doped efficient water electrolysis catalyst disclosed by the invention has excellent catalytic performance, extremely low charge transfer resistance and abundant electrochemical active sites; co, V-Ni ₃ The N nanosheet exhibits excellent electrocatalytic properties and durability. At 10mA cm ^-2 At a current density of (2), co, V-Ni ₃ The overpotential for the N electrode is only 10mV (over commercial Pt), the Tafel slope is only 43mV dec ^-1 The catalyst is the lowest value of HER overpotential in the precious metal and non-precious metal catalysts which are disclosed at present, so the actual voltage required by the catalyst to reach relative current density is lower, the energy consumption is relatively lower, and the catalytic activity is higher; under the same conditions, co, cr-Ni ₃ N and Cr, V-Ni ₃ The overpotential of N is 70mV and 80mV, the Tafel slope is 75mV and 94mV dec ^-1 Therefore, the catalyst has good catalytic activity in seawater electrolysis, and particularly, the Co, V-Ni3N electrode has more excellent performance at 10mA cm ^-2 The overpotential at the current density of (a) is only 41mV.

Drawings

FIG. 1 is a photographic image of the morphology of example 1 of the present invention; wherein: FIGS. 1a to 1c show examples 1 (Co, V-Ni) ₃ N) scanning electron microscope images; FIGS. 1d to 1e are transmission electron micrographs of example 1; FIG. 1f is a high resolution transmission electron microscope image of nanoplatelets of example 1; FIG. 1g is the electron diffraction pattern of example 1; FIGS. 1h to 1l are HAADF-STEM images and element mapping images of Ni, co, V and N of example 1.

FIG. 2 is a photographic image of the topography of examples 2 and 3 of the present invention: wherein FIGS. 2a to 2b show examples 2 (Co, cr-Ni) ₃ N) SEM pictures; FIGS. 2c to 2d show examples 3 (Cr, V-Ni) ₃ N) SEM pictures.

FIG. 3 is a graph of fresh water hydrogen evolution performance of examples of the present invention, comparative examples and commercial catalysts Pt/C; FIG. 3a is the LSV curve of Pt/C in 1mol KOH for the examples, comparative examples and commercial catalysts;FIG. 3b is a Tafel plot of Pt/C polarization curves for the examples, controls and commercial catalysts; FIG. 3C is a Nyquist plot of the example, control and commercial catalyst Pt/C, with the inset being an enlarged image; FIG. 3d is the Cdl values of the Pt/C catalysts of the examples, controls and commercial catalysts; FIG. 3e shows Pt/C at 10mA cm for examples, controls and commercial catalysts ^-2 And 100mA cm ^-2 Comparing the lower overpotential; FIG. 3f is a volcano plot of example, control and commercial catalysts Pt/C; FIG. 3g is a graph of I-t for 100 hours at different current densities for example 1; fig. 3h is a durability test of example 1 before and after 3000CV cycles, with the inset being an SEM image of example 1 after the durability test.

FIG. 4 is a graph of the hydrogen evolution performance of alkaline seawater of Pt/C catalyst of the comparative example, inventive example and commercial catalyst; wherein FIG. 4a is the LSV curve of Pt/C in alkaline seawater for the examples, comparative examples and commercial catalysts; FIG. 4b is a Tafel plot of example, control and commercial catalysts Pt/C from their polarization curves; FIG. 4C shows Pt/C at 10mA cm for examples, controls and commercial catalysts ^-2 And 100mA cm ^-2 Comparative plot of overpotential below; FIG. 4d is a graph of the results of example 1 and comparative example 1 at 10mA cm ^-2 The I-t curve chart of the next 6 h; FIG. 4e is a durability test of example 1 before and after 3000CV cycles with the inset being an SEM image of example 1 after the durability test; FIG. 4f is an XPS plot of example 1 before and after 3000CV cycles; fig. 4g to 4i are TEM images of example 1 after HER.

Detailed Description

The invention will be further explained with reference to the drawings and examples.

1. Double-doped efficient water electrolysis catalyst

The catalyst is prepared by doping more than two transition metal elements on the surface of a nickel nitride-based material; the nickel nitride-based material is of a nano flaky structure, transition metal elements are attached to the surface of the nickel nitride-based nano sheet in a nanoparticle form, and the transition metal elements comprise any two of V, cr and Co. According to the mass percentage, in the catalyst, the mass percentage of the transition metal element is 5-10%. The thickness of the nickel nitride-based material is 20-30nm, and the average particle size of the transition metal element nano-particles is 100-300 nm.

After the catalyst for producing hydrogen by electrolyzing water is deeply researched, the invention discovers that the seawater is rich in various anions and cations, is a high-quality raw material and can improve the conductivity of the electrolyte. However, unlike fresh water, the composition of seawater is very complex, high-concentration chloride ions not only compete with electrolyzed water in the Oxygen Evolution Reaction (OER) at the anode to release chlorine gas, but also severely corrode most catalysts containing metal elements, and hypochlorite, which is a highly corrosive by-product of the Chlorine Evolution Reaction (CER), blocks active sites of the noble metal catalyst, so if the noble metal catalyst is used, the noble metal catalyst is not only consumed quickly and is high in cost, but also cannot exert the catalytic effect of the noble metal catalyst in the process of electrolyzing seawater to produce hydrogen. Therefore, the invention adopts the introduction of transition metal elements and combines the excellent conductivity and corrosion resistance of Transition Metal Nitride (TMN) to improve the catalyst. After doping a large number of transition metal elements into TMN, it was found that some transition metal elements were difficult to dope into TMN, and some transition metal elements were doped in too small amounts, contributing little to the catalyst performance. In the series of researches, the invention discovers that in an atomic-level resolution electron microscope, when two elements of Co and V are doped simultaneously, co and V exist in a unique monoatomic form and a unique cluster form, part of Co and V exist in a monoatomic form respectively, and part of Co and V are aggregated in a monoatomic form to form a cluster, the synergistic effect of the Co and V brings a favorable influence on the performance of the catalyst.

2. Examples and comparative examples

TABLE 1

The kind and amount of raw materials	Vanadium source	Chromium source	Cobalt source	Molar ratio of metal ions
					Example 1	NH ₄ VO ₃	--	Co(NO ₃ ) ₂ ·6H ₂ O	1:1
Example 2	--	Cr(NO ₃ ) ₂ ·9H ₂ O	Co(NO ₃ ) ₂ ·6H ₂ O	1:1
					Example 3	NH ₄ VO ₃	Cr(NO ₃ ) ₂ ·9H ₂ O	--	1:1
Practice ofExample 4	NH ₄ VO ₃	--	Co(NO ₃ ) ₂ ·6H ₂ O	1:0.5
					Example 5	NH ₄ VO ₃	--	Co(NO ₃ ) ₂ ·6H ₂ O	1:2
Example 6	--	Cr(NO ₃ ) ₂ ·9H ₂ O	Co(NO ₃ ) ₂ ·6H ₂ O	1:0.5
					Example 7	--	Cr(NO ₃ ) ₂ ·9H ₂ O	Co(NO ₃ ) ₂ ·6H ₂ O	1:2
Example 8	NH ₄ VO ₃	Cr(NO ₃ ) ₂ ·9H ₂ O	--	1:0.5
					Example 9	NH ₄ VO ₃	Cr(NO ₃ ) ₂ ·9H ₂ O	--	1:2

Note: - -indicates that no such starting material was added.

Example 1 was prepared using the following method:

1) Pretreatment of foamed nickel substrates

Pretreating the foam nickel substrate by using a dilute hydrochloric acid solution to remove an oxide layer and impurities on the surface, and then washing the foam nickel substrate for multiple times by using deionized water and ethanol;

2) Double-doped nickel hydroxide (Co, V-Ni (OH) ₂ ) Preparation of nanosheet arrays

0.05mmol of NH ₄ VO ₃ 、0.05mmol Co(NO ₃ ) ₂ ·6H ₂ O、0.90mmol Ni(NO ₃ ) ₂ ·6H ₂ O、5mmol Co(NH ₂ ) ₂ And 2mmol NH ₄ F was dissolved in 20mL of deionized water and stirred to form a homogeneous solution. Transferring the solution and a piece of foam nickel (NF, 2cm multiplied by 3 cm) into a 50mL autoclave, sealing, and carrying out hydrothermal treatment at 120 ℃ for 8h to obtain the double-doped nickel hydroxide (Co, V-Ni (OH) ₂ ) And (4) a nanosheet array, and washing the obtained product with water and ethanol respectively. In the absence of addition of Co (NO) ₃ ) ₂ ·6H ₂ In the case of O, V-Ni (OH) was synthesized in a similar manner ₂ ；

3)Co,V-Ni ₃ Preparation of N

Mixing the prepared nickel hydroxide (Co, V-Ni (OH) ₂ ) Placing the nanosheets into a tube furnace in high purity NH ₃ Nitriding the nickel hydroxide nanosheets at the temperature of 450 ℃ for 2h under the atmosphere, and respectively naming the obtained products as Co, V-Ni ₃ N。

The preparation was carried out according to table 1 and table 2, and examples 2 to 9 were prepared using the process conditions of table 2 and the preparation method of example 1. At the same time, undoped transition elements are usedNi of plain ₃ N was defined as comparative example 1.

3. Catalyst morphology and Performance testing

The performances of examples 1 to 3 and comparative example 1 were analyzed and compared. Detection of example 1 (Co, V-Ni) ₃ N) the morphology of the catalyst, and carrying out a hydrogen evolution performance test on the catalyst. FIGS. 1a-1b show example 1 (Co, V-Ni) ₃ N) typical low power Scanning Electron Microscope (SEM) images with thin (typically around 20-30 nm) nanoplate morphologies, thinner nanoplate structures with higher surface areas exposing more active sites. The Transmission Electron Microscopy (TEM) images shown in fig. 1d-1e are sufficient to demonstrate the typical nanoplatelet structure of example 1. The high resolution transmission electron microscopy (HR-TEM) image of example 1 (FIG. 1 f) shows that the 0.18nm lattice fringes correspond to Ni ₃ Surface (201) of N, and XRD card Ni ₃ N (JCPDS No. 89-5144). After detection, it was found that the incorporation of Co and V did not cause lattice distortion, but rather were in the form of unique single atoms and clusters. In addition, it was further confirmed from the Selected Area Electron Diffraction (SAED) and elemental mapping that the Ni, co, V and N elements were uniformly distributed in the area in fig. 1g-1l, providing more definite evidence for the successful preparation of example 1. FIGS. 2a-2b show example 2 (Co, cr-Ni) ₃ N) exhibit typical nanoparticle structure. After annealing, the nanoplatelets of example 2 completely collapsed and were difficult to observe directly in electron microscopy due to Co, cr-Ni (OH) in example 2 ₂ The nanosheet structure is unstable. Meanwhile, example 3 (Cr, V-Ni) ₃ N) and example 1 (Co, V-Ni) ₃ N) electrode surface (fig. 2c-2 d), the surface of example 3 is more sparse and disordered due to the coordination of Cr and V, and the disordered nanosheet structure is not beneficial to the generation of redox active sites and the storage of charges, resulting in the reduction of the electrochemical performance of the material, and these results prove that the micro-morphology of the catalyst has a great relationship with the type of doping element.

The performance was compared with the inventive examples using commercial Pt/C as the control. As shown in FIGS. 3a,3e, the Linear Sweep Voltammetry (LSV) curve shows that of example 1 (Co, V-Ni) ₃ N), example 2 (Co, cr-Ni) ₃ N), example 3 (Cr, V-Ni) ₃ N), comparative example 1 (Ni) ₃ N) and commercial Pt/C Current Density of 10mAcm in 1M KOH solution ^-2 The overpotentials of (a) are 10mV,70mV,82mV,141mV and 38mV, respectively. The results show that example 1 (Co, V-Ni) ₃ N) in DTMD Ni ₃ The alkaline electrochemical hydrogen evolution performance in N is the best, and the activity of the hydrogen evolution catalyst even significantly exceeds that of commercial Pt/C. Overpotential of 75mV dec with example 2 (Co, cr-Ni 3N) ^-1 Example 3 (Cr, V-Ni) ₃ N) over-potential of 94mV dec ^-1 And comparative example 1 (Ni) ₃ N) overpotential of 123mV dec ^-1 In contrast, example 1 (Co, V-Ni) ₃ N) Tafel slope (43 mV dec ^-1 ) Smaller, example 1 (Co, V-Ni) is directly indicated ₃ N) more favorable HER kinetics (fig. 3 b). As shown in fig. 3c, the charge transfer resistance (Rct) was studied by Electrochemical Impedance Spectroscopy (EIS). Example 1 (Co, V-Ni) ₃ N) was small, about 0.98. Omega. And was significantly lower than those of the other examples (2.4. Omega. For example 2 and 4.3. Omega. For example 3) and comparative example 1 (Ni) ₃ N7.0. Omega.) and commercial Pt/C (Pt/C1.3. Omega.). This confirms that the type of doping element is critical to the regeneration of a high efficiency electrocatalyst. Example 1 (Co, V-Ni) ₃ N) has high electron transfer speed, good conductivity and better reaction kinetics, and contributes to the enhancement of the catalytic activity of the compounds on HER. Cyclic Voltammograms (CV) of the non-Faraday region were then recorded at different scan rates (10-60 mV s-1) to further study Ni ₃ Intrinsic activity of N. The electrochemical specific surface area (ECSA) was determined from the Cdl curve obtained by CV. Example 1 (Co, V-Ni) as shown in FIG. 3d ₃ N) (11.8 mF cm) ^-2 ) Higher than example 2 (Co, cr-Ni) ₃ Cdl value of N is 10.1mF cm ^-2 ) Example 3 (Cr, V-Ni) ₃ Cdl value of N5.5 mF cm ^-2 ) Comparative example 1 (Ni) ₃ Cdl value of N2.6 mF cm ^-2 ) And commercial Pt/C (Cdl value of Pt/C11.7 mF cm) ^-2 ). Meanwhile, example 1 showed excellent performance at a large current density, and example 1 showed excellent performance at 500mA cm ^-2 The overpotential in this case is only 203mV. The operating durability of the electrocatalysis is another indispensable indicator, the catalyst of example 1 (Co, V-Ni 3N) is at 3000The overpotential after CV cycling was negligibly higher than the overpotential before the test, and the results of chronopotentiometric measurements also demonstrated its excellent stability (fig. 3 h). As shown in fig. 3h, neither the electrocatalytic properties nor the macroscopic morphology changed after long cycling.

For practical application, the invention further researches the catalytic performance of the catalyst in seawater electrolysis. Pure seawater was collected from a certain coast (pH ≈ 8.1). Natural seawater as an electrolyte has the following problems: first, chlorine Evolution Reaction (CER) takes place at the anode of seawater electrolysis, competing with OER; the generated chlorine and hypochlorite dissolved in the electrolyte corrode the cathode material. Secondly, high concentration of toxic cations (Ca) in natural seawater ²⁺ And Mg ²⁺ ) Can be electrodeposited on the cathode surface and obstruct the active sites. Third, CER is more competitive in natural seawater than OER, produces more chlorine and hypochlorite, and corrodes the electrodes. Therefore, the present inventors have further studied Ni ₃ HER performance of N-based catalysts in alkaline seawater (pH = 13.1). Example 1 (Co, V-Ni 3N) at 10mA cm ^-2 The overpotential of time is only 41mV, the Tafel slope is 46mV dec ^-1 (FIGS. 4 a-c), which is superior to the performance of example 2 (88 mV), example 3 (82 mV) and control 1 (197 mV). Meanwhile, the embodiment 1 also has the fastest reaction kinetic speed. In addition to activity, the most critical catalytic performance indicator is stability. Thus, a continuous chronoamperometric test of 6h and 3000CV cycles was performed for example 1 and comparative example 1 (FIGS. 4d,4 e). After a long period of operation, the catalyst of example 1 still had excellent activity, which corresponds to essentially no shift in the Ni peak in fig. 4 f. HR-TEM images (fig. 4g-4 i) show that the nanoplate morphology after HER reaction is very similar to the original morphology. The above tests show that Co and V doping also provides higher corrosion resistance due to the introduction of a greater variety of metal bonds (Co-Co). Therefore, the continuous long-term hypertonic process had little corrosive effect on the surface structure of example 1.

It should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the technical solutions, and those skilled in the art should understand that the technical solutions of the present invention can be modified or substituted with equivalent solutions without departing from the spirit and scope of the technical solutions, and all should be covered in the claims of the present invention.

Claims

1. The double-doped high-efficiency water electrolysis catalyst is characterized in that the catalyst is formed by doping two transition metal elements on the surface of a nickel nitride-based material; the nickel nitride-based material is of a nano flaky structure, transition metal elements are attached to the surface of the nickel nitride-based nano sheet in a nanoparticle form, and the transition metal elements comprise any two of V, cr and Co.

2. The double-doped efficient water electrolysis catalyst according to claim 1, wherein the mass percent of the transition metal element in the catalyst is 5-10% by mass.

3. The double-doped efficient water electrolysis catalyst as claimed in claim 1, wherein the thickness of the nickel nitride-based material is 20 to 30nm, and the average particle size of the transition metal nanoparticles is 100 to 300nm.

4. A preparation method of a double-doped high-efficiency water electrolysis catalyst is characterized by being used for preparing the catalyst of any one of claims 1 to 3, and specifically comprising the following steps:

step 2: selecting any two transition metal sources of vanadium source, chromium source and cobalt source, and mixing with Ni (NO) ₃ ） ₂ 、NH ₄ F. Dissolving urea in water, and mixing to form a homogeneous solution; transferring the homogeneous solution and the foam nickel-based material treated in the step (1) into an autoclave for hydrothermal reaction to obtain a double-doped nickel hydroxide nanosheet, and drying after cleaning;

5. The method of claim 4, wherein the vanadium source comprises metavanadate; the chromium source comprises one of a nitrate or a chloride salt; the cobalt source comprises one of a nitrate or chloride salt.

6. The preparation method of the double-doped high-efficiency electrolytic water catalyst according to claim 5, wherein in the step 2, when the transition metal source is a vanadium source and a chromium source, the molar ratio of metal ions of V to Cr is 1: (0.5 to 2); when the transition metal source is a vanadium source and a cobalt source, the molar ratio of metal ions of V to Co is 1: (0.5 to 2); when the transition metal source is a chromium source and a cobalt source, the molar ratio of metal ions of Cr and Co is 1: (0.5 to 2).

7. The method for preparing the double-doped high-efficiency water electrolysis catalyst according to claim 6, wherein in the step 2, ni (NO) in the homogeneous solution ₃ ） ₂ The concentration of (b) is 0.04 to 0.05mol/L, NH ₄ The concentration of F is 0.08 to 0.12mol/L, and the concentration of urea is 0.2 to 0.3mol/L.

8. The preparation method of the double-doped efficient water electrolysis catalyst according to claim 4, wherein in the step 2, the hydrothermal reaction is carried out at 100-140 ℃ for 6-10 h.

9. The preparation method of the double-doped high-efficiency water electrolysis catalyst according to claim 4, wherein in step 3, the nitridation reaction is: nitriding for 1h to 3h at the temperature of 400-500 ℃; high purity NH ₃ Is ammonia gas with the mass fraction of at least 99 percent.

10. The application of the double-doped high-efficiency water electrolysis catalyst is characterized in that the catalyst prepared by the preparation method of any one of claims 4 to 9 is used for electrolyzing water or producing hydrogen from seawater.