CN114108027B

CN114108027B - Obviously improved RuO 2 Electrochemical lithium intercalation modification method for OER catalytic performance in acidity

Info

Publication number: CN114108027B
Application number: CN202111287401.6A
Authority: CN
Inventors: 李锴锴; 秦茵; 张统一
Original assignee: Shenzhen Graduate School Harbin Institute of Technology
Current assignee: Shenzhen Graduate School Harbin Institute of Technology
Priority date: 2021-11-02
Filing date: 2021-11-02
Publication date: 2023-02-28
Anticipated expiration: 2041-11-02
Also published as: CN114108027A

Abstract

The invention belongs to the technical field of electrocatalysis, and particularly relates to a method for remarkably improving RuO ₂ An electrochemical lithium intercalation modification method for the catalytic performance of OER in acid. The invention successfully embeds into RuO by an electrochemical method ₂ In the crystal lattice and form a solid solution phase (Li) _x RuO ₂ ). OER electrocatalysis test results show that RuO ₂ The OER performance of (A) is significantly improved by lithium intercalation, in particular, li _0.52 RuO ₂ At 0.5M H ₂ SO ₄ The current density in the electrolyte reaches 10mA cm ^‑2 Has an ultra-low overpotential of 156mV and maintains a current density of 10mA cm at a constant potential of 1.27V ^‑2 No significant decay occurred for at least 70 h.

Description

Obviously improved RuO 2 Electrochemical lithium intercalation modification method for OER catalytic performance in acidity

Technical Field

The invention belongs to the technical field of electrocatalysis, and particularly relates to a method for remarkably improving RuO ₂ An electrochemical lithium intercalation modification method for the catalytic performance of OER in acid.

Background

In the past decades, in order to meet the ever-increasing energy demand, researchers have endeavored to adopt various strategies to develop promising renewable energy sources having high calorific values and no pollution. Needless to say, proton Exchange Membrane (PEM) electrolyzed water is of great interest because of its sensitive system response, superior current density, and negligible gas exchange rate. In order to realize sustainable development of energy, hydrogen, high heat value and low pollution, the electrochemical water decomposition process comprising Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER) is realized by the most ideal product through electrochemistry. For PEM electrolyzers, the conversion of chemical energy conversion efficiency into electrical energy is mainly limited by the slow anodic Oxygen Evolution Reaction (OER), which undergoes an energy evolutionThe amount requires a very high four electron transfer process. Even more unfortunately, anode OER electrocatalysts exhibit instability in acidic electrolytes, thereby limiting the commercial application of PEM electrolyzers. In this context, it is a current research issue to focus on the design and synthesis of efficient and stable anode OER electrocatalysts suitable for acidic media. Among the numerous types of OER electrocatalysts, the solid-state special phenomenon in which oxides of 4d and 5d noble metals are associated with very relevant electrons due to spin-orbit coupling compared to the 3d analogue has been the focus of research. Of course, irO of rutile structure _x /RuO _x Base materials have become part of this tropical research. And ruthenium oxide (RuO) _x ) And iridium oxide (IrO) _x ) Have been recognized as lacking highly active OER electrocatalysts in acidic electrolytes. However, irO _x The electrocatalyst has a relatively low intrinsic OER activity in acidic electrolytes and is specific to RuO _x And more expensive. Indeed, it is necessary to intercalate RuO with suitable guest molecules _x To adjust its electronic structure to improve the OER activity. Furthermore, intercalation with cheaper guest molecules is also advantageous in terms of cost. Most of these catalysts are chemically unstable and are easily corroded/decomposed under the highly corrosive and oxidative operating conditions of OER, and thus it is also required to ensure excellent stability.

Hydrogen production provides a means of storing wind energy and solar power in the form of chemical bonds. Hydrogen fuel cells can power vehicles and stationary equipment; hydrogen can replace carbon or carbon dioxide to reduce global carbon dioxide emissions in chemical and manufacturing processes.

RuO of rutile structure with moderate binding capacity ₂ Is a reference catalytic material of various acidic OERs, and nevertheless, the RuO is still promoted ₂ Acid OER catalytic activity and acid-based catalyst space. In this situation, efforts have been made to design new ruthenium-based OER catalysts, such as promising OER active and bimetallic oxides, including Pb ₂ Ru ₂ O _6.5 、[Ru _2-x Pb _x ]O _6.5 、 Sm ₂ Ru ₂ O ₇ 、Bi _2.4 Ru _1.6 O ₇ 、Y ₂ [Y _x Ru _2-x ]O _7-y 、Y ₂ Ru ₂ O _7-δ 、Ir _0.7 Ru _0.3 O _2.9 Most had a low overpotential of less than 270mV and a Tafel slope approaching 50mV dec ^-1 . However, currently RuO ₂ The catalytic activity of the base electrocatalyst is difficult to meet the requirement of large-scale practical application in an acidic medium. To improve RuO-based ₂ The performance of the electrocatalysts of (a), it is necessary to increase the intrinsic performance of each active site and to increase their density. It is reported that guest incorporation can increase intrinsic RuO by modulating the active surface/coordination environment ₂ Electrochemical performance, it is generally believed that OH and OOH intermediates generally tend towards adsorption sites in the same type of OER process. By using Δ G _O* -ΔG _OH* Evaluation of optimum Activity OER occurs at Δ G _O* -ΔG _OH* = about 1.6 eV. The greater the difference in chemisorption energies between O and OH intermediates, the higher the overpotential of the adsorbed O intermediates. In contrast, the overpotential of desorbed OH intermediates would be high.

Introduction of foreign elements into RuO ₂ After the electrocatalyst is based, the oxidation state of ruthenium is always far away from valence (IV), so that the number of d-orbital electrons is changed, electrons and magnetism are changed, formation of high-activity surface species is promoted, the coordination environment of the electrons is reconstructed, and good OER electrocatalytic performance is caused. Furthermore, the rutile structure RuO is due to various functional properties ₂ Extensive research has been conducted not only to include electrocatalysis and magnetism, but also to act as a host for lithium insertion. And some reports have built electrochemical lithium intercalation as a synthesis strategy for adjusting the structural composition of the layered structure host catalyst, which can significantly improve the catalytic activity and stabilize the crystal structure. Cui et al show that electrochemical lithium intercalation can modulate MoS ₂ Oxidation state and interlayer spacing of, and from 2H-MoS ₂ To 1T-MoS ₂ To continuously increase the catalytic activity towards HER. In addition, lattice strain also has a significant effect on catalytic activity. Cui et al innovatively reported that LiCoO is a rare earth metal oxide ₂ The lattice compression and tension of the induced platinum (Pt) catalyst can regulate the oxygen reduction thereofReaction (ORR) catalytic activity. Therefore, we hope to adjust the degree of coordination of unsaturation on ruthenium sites and RuO by in situ electrochemical lithium intercalation ₂ Oxidation state and formation of lattice strain to improve RuO ₂ Catalytic performance of the base electrocatalyst.

The existing prior art mainly comprises the following steps:

(1) The OER reaction is a four-electron process, and compared to HER, the mechanism of electrocatalytic OER is more complex, the reaction thermodynamics and kinetics are in relatively less favorable positions, and thus typically have higher overpotentials.

(2) Over-oxidation of Ru to soluble RuO in acidic oxidizing environment ₄ In part, many Ru-based electrocatalysts have low stability under acidic conditions, resulting in the current development bottleneck of electrolyzed water in acidic environments and RuO due to the influence of intrinsic structure ₂ The catalytic activity of (2) cannot meet the requirements of practical application.

Disclosure of Invention

In view of the problems of the prior art, the present invention provides a method for significantly improving RuO ₂ An electrochemical lithium intercalation modification method for the catalytic performance of OER in acid.

The invention is realized by the following technical scheme:

obviously improve RuO ₂ The electrochemical lithium intercalation modification method for the catalytic performance of OER in acid comprises the following steps: mixing RuO ₂ Uniformly mixing carbon nano tube CNT and polyvinylidene fluoride PVDF in a certain amount of N-methyl pyrrolidone to obtain uniform slurry, then coating the uniform slurry on a Cu foil, and drying the Cu foil to obtain a positive electrode material of the battery; taking lithium material as the cathode material of the battery, forming the battery with the cathode material, discharging the battery to ensure RuO ₂ Different degrees of lithium were inserted.

As a preferred technical scheme of the invention, the RuO ₂ The material composition of the carbon nano tube CNT and the polyvinylidene fluoride PVDF is as follows: ruO ₂ (80 wt%), carbon nanotube CNT (10 wt%) and polyvinylidene fluoride PVDF (10 wt%). The N-methyl pyrrolidone is used in such an amount that the corresponding substances are uniformly mixed to form a flowable slurry.

Through the selection of the materials and the proportion, the catalytic activity and the stability of the materials can be greatly improved, the synthesis process is simple, the doped lithium amount can be regulated, and the consumption of noble metals is saved.

As a preferred technical scheme of the invention, the drying method comprises the following steps: dried in an oven at 110 ℃ for at least 12 hours and further punched into small disks with a diameter of 12 mm.

As a preferred embodiment of the present invention, ruO is introduced into an argon filled glove box ₂ The electrodes were assembled into a 2032 coin cell for electrochemical lithium intercalation, using RuO separately ₂ Electrodes and a piece of lithium with a diameter of 15.6mm were used as positive and negative electrodes.

As a preferred technical scheme of the invention, the RuO with rutile structure is adopted at room temperature ₂ As a positive electrode material of a lithium ion button battery, the lithium ion button battery is tested by a blue battery test system at 0.05C (1C =201.03mA g) in a certain time range ^-1 ) Discharging for 0-16h to make RuO ₂ Different degrees of lithium were inserted.

RuO, a preferred embodiment of the present invention ₂ + Li-xh, x =0, 2, 9, 12 and 16, corresponding to Li, respectively _x RuO ₂ The lithium concentration x in (a) was estimated to be 0.07, 0.29, 0.39 and 0.52.

As a preferred technical scheme of the invention, after the discharging process is finished, all electrodes are washed by NMP solvent to remove PVDF and electrolyte, and are dried at 60 ℃ to obtain Li _x RuO ₂ Powder samples (CNT content: 11.11-10 wt%).

The invention further provides Li _x RuO ₂ Prepared by the method.

Wherein x =0.07-0.52.

In a preferred embodiment of the present invention, x is 0.07, 0.29, 0.39, or 0.52.

In a preferred embodiment of the present invention, x is 0.52 _0.52 RuO ₂ 。

The excellent effects of the present invention over the prior art include:

(1) Successful intercalation of lithium ions into RuO by electrochemical methods ₂ In the crystal lattice and form a solid solution phase (Li) _x RuO ₂ ). OER electrocatalysis test results show that RuO ₂ The OER performance of (A) is significantly improved by lithium intercalation, and is best achieved when x is 0.52. In particular, li _0.52 RuO ₂ At 0.5M H ₂ SO ₄ The current density in the electrolyte reaches 10mA cm ^-2 Has an ultra-low overpotential of 156mV and maintains a current density of 10mA cm at a constant potential of 1.27V ^-2 No significant decay occurred for at least 70 h.

(2)Li _x RuO ₂ Due to the dual role of lithium intercalation, namely, the adjustment of the electron structure and the catalytic RuO ₂ The creation of lattice strain. I.e., the lithium ions donate electrons and the valence state of Ru is reduced. Meanwhile, the d band center of Ru is far away from the Fermi level, but the p band center of O is close to the Fermi level, so that Ru-O4 d-2p hybridization is weakened, and Ru-O covalent property is reduced. Therefore, the activity of Ru sites is improved, and the participation of lattice oxygen is suppressed. Meanwhile, the inherent lattice strain causes the distortion of the surface atomic structure, and shortens the distance between the surface O near the Ru active site and the H atom in OOH. Therefore, the binding energy of O to OOH is reduced, and RuO is significantly increased ₂ OER performance of (2).

Drawings

FIG. 1. Series of Li of the present invention _x RuO ₂ Schematic synthesis of the catalyst.

FIG. 2. Li according to the invention _x RuO ₂ With respect to structural characterization of the crystal surface 110, ruO ₂ (a),(c)、Li _0.39 RuO ₂ (b) HRTEM image of (d); SEM image (e) Li _0.52 RuO ₂ EDX mapping for Ru (f), O (g), and Li (h).

FIG. 3. Li of the present invention _x RuO ₂ The performance test result of (a), wherein:

(a) Series of Li _x RuO ₂ Catalyst at 0.5M H ₂ SO ₄ OER polarization curve in aqueous solution;

(b) Series of Li _x RuO ₂ Catalyst at 10mA cm ^-2 A lower overpotential;

(c) Series of Li _x RuO ₂ Tafel slope of catalyst;

(d)Li _0.52 RuO ₂ and control samples at 10mA cm ^-2 Testing the stability of the timing voltage method;

(e) From Li after electrocatalysis at different reaction times _0.52 RuO ₂ Percent Ru dissolved in;

(f) Comparison of various RuOs ₂ The base electro-catalyst reaches 10mA cm in an acid medium ^-2 Overpotential and 10mA cm required by cathode current density ^-2 The durability was measured by the chronopotentiometry.

Detailed Description

The invention will be further illustrated, but not limited, by the following examples and the accompanying drawings:

example 1

Referring to FIG. 1: by mixing RuO ₂ (80 wt%), CNT (10 wt%) and PVDF (10 wt%) were mixed homogeneously in a quantity of N-methylpyrrolidone to give a homogeneous slurry, which was then coated on a Cu foil, dried in an oven at 110 ℃ for at least 12 hours and further punched into small disks of 12mm diameter.

RuO in argon filled glove box ₂ The electrodes were assembled into a 2032 coin cell for electrochemical lithium intercalation (RuO was used separately) ₂ Electrodes and a piece of lithium with a diameter of 15.6mm as positive and negative electrodes).

At room temperature, we adopted RuO of rutile structure ₂ As a positive electrode material of a lithium ion button battery, the lithium ion button battery is tested by a blue battery test system at 0.05C (1C =201.03mA g) in a certain time range ^-1 ) So as to make RuO ₂ Insertion of varying degrees of lithium (RuO) ₂ + Li-xh, x =0, 2, 9, 12 and 16), corresponding to Li, respectively _x RuO ₂ The lithium concentration x in (a) was estimated to be 0.07, 0.29, 0.39 and 0.52. After the discharge process was completed, all electrodes were washed with NMP solvent to remove PVDF and electrolyte, and dried at 60 ℃ to obtain Li _x RuO ₂ Powder samples (CNT content: 11.11-10 wt%).

Wherein, the bookInventive Li _x RuO ₂ Structural characterization with respect to the crystal surface 110 is shown in FIG. 2

Example 2

Li of the invention _x RuO ₂ The performance test method and results are shown in fig. 3, in which:

Li _x RuO ₂ at 0.5 MH ₂ SO ₄ On the electrolyte, a standard three-electrode configuration was controlled at room temperature by an electrochemical workstation. Catalyst coated Glassy Carbon (GC) electrodes (diameter: 5 mm), ag/AgCl electrodes and carbon rods were used as working, reference and counter electrodes, respectively. In a typical case, 4mg of powder sample Li _x RuO ₂ Added to a mixed solution containing 200ul of ethanol and 200ul of aqueous Nafion solution (5 vl%, ethanol is a solvent), and ultrasonically dispersed for 15 minutes to form a uniform black ink. Linear Sweep Voltammetry (LSV) curves were performed at a typical voltage range of 0.8-1.6V and a sweep rate of 5 mV/s. The timing potential is measured at 10mA cm ^-2 Is performed for at least 70 hours at a constant current.

All RuO ₂ The + Li-xh catalysts all show excellent OER activity, where RuO ₂ 、Li _0.07 RuO ₂ 、Li _0.29 RuO ₂ 、 Li _0.39 RuO ₂ And Li _0.52 RuO ₂ Has an initial potential of-1.425, -1.400, -1.360, -1.325 and-1.300V vs. RHE, respectively representing 0.5 MH ₂ SO ₄ Overpotentials of-195, -190, -130, -95 and-70 mV in solution. In addition, when the current density reached 10mA cm ^-2 ，RuO ₂ 、Li _0.07 RuO ₂ 、Li _0.29 RuO ₂ 、Li _0.39 RuO ₂ And Li _0.52 RuO ₂ Overpotentials of 320, 266, 196, 180, and 156mV were shown. And Li _0.52 RuO ₂ Only the overpotential of 335mV is needed to reach 200mA cm ^-2 Excellent OER current density. More exciting is that Li _0.52 RuO ₂ The potential of 1.6V and RHE of (2) can generate 233mA cm ^-2 OER current density of (d). To our knowledge, with the previously reported RuO in acidic media ₂ Base catalyst phase ratio，Li _0.52 RuO ₂ The catalyst showed the best OER activity catalysis. In addition, stability is an extremely important indicator of electrocatalyst performance. Thus, li _0.52 RuO ₂ The chronoamperometry is performed at a constant potential, indicating that Li _0.52 RuO ₂ The catalyst remained essentially stable for at least 70 hours, indicating that Li _0.52 RuO ₂ Has great potential in the practical application of the PEMBE.

The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, numerous simple deductions or substitutions may be made without departing from the spirit of the invention, which shall be deemed to belong to the scope of the invention.

Claims

1. Obviously improved RuO ₂ The electrochemical lithium intercalation modification method for the catalytic performance of OER in acid is characterized by comprising the following steps: mixing RuO ₂ Uniformly mixing carbon nano tube CNT and polyvinylidene fluoride PVDF in a certain amount of N-methyl pyrrolidone to obtain uniform slurry, then coating the uniform slurry on a Cu foil, and drying the Cu foil to obtain a positive electrode material of the battery; taking lithium material as the cathode material of the battery, forming the battery with the cathode material, discharging the battery to ensure RuO ₂ Inserting lithium with different degrees, after the discharging process is finished, all electrodes are cleaned by NMP solvent to remove PVDF and electrolyte, and are dried to obtain Li _x RuO ₂ Powder sample, x =0.07-0.52, powder sample Li _x RuO ₂ Adding the mixture solution into a mixed solution containing ethanol and aqueous solution, and coating to prepare the OER catalytic electrode.

2. The method as claimed in claim 1, wherein said RuO ₂ The material composition of the carbon nano tube CNT and the polyvinylidene fluoride PVDF is as follows: ruO ₂ 80wt%, carbon nanotube CNT 10wt% and polyvinylidene fluoride PVDF 10wt%.

3. The method according to claim 1, characterized in that the drying method is: dried in an oven at 110 ℃ for at least 12 hours and further punched into small disks of 12mm diameter.

4. The method of claim 1, wherein the RuO is introduced into an argon filled glove box ₂ The electrodes were assembled into a 2032 coin cell for electrochemical lithium intercalation, using RuO separately ₂ Electrodes and a piece of lithium with a diameter of 15.6mm were used as positive and negative electrodes.

5. The method of claim 1, wherein the blue cell test system discharges at a rate of 0.05C, 1C =201.03mAg, at room temperature over a time range ^-1 To make RuO ₂ Lithium is inserted to varying degrees.

6. A method according to claim 1, characterized in that the discharge time is 0-16h.

7. A method according to claim 1, characterized in that after the end of the discharge process, all electrodes are washed with NMP solvent to remove PVDF and electrolyte and dried at 60 ℃ to obtain Li _x RuO ₂ Powder sample, wherein CNT content: 11.11-10wt%.

8. The method of claim 1, wherein x is 0.07, 0.29, 0.39, and 0.52.

9. A process according to claim 1, characterized in that said x is 0.52 _0.52 RuO ₂ 。