Cobalt manganese oxide flexible electrode and preparation and application thereofTechnical Field
The invention belongs to the field of zinc-air battery air electrode materials, and particularly relates to a cobalt manganese oxide flexible electrode, and preparation and application thereof.
Background
The zinc-air battery has the advantages of high energy density, safety, reliability, environmental friendliness, low cost and the like, and the flexible rechargeable zinc-air battery is hopeful to be used as a new generation matching power supply of wearable equipment, and research and development of the zinc-air battery are widely focused in recent years. The cathode metal zinc of the zinc-air battery is cheap and easy to obtain, the discharge product zinc oxide can be completely recovered, and the cathode air of the zinc-air battery has no cost and can be infinitely supplied, which is far lower than that of a lithium ion battery product. The zinc-air battery has lower current density, and is more suitable for application scenes with high energy density requirement and low power requirement, such as a hearing aid power supply, an emergency lighting device and the like.
While significant development has been achieved with flexible zinc-air batteries, a number of bottleneck problems have been encountered. First is a further increase in electrochemical performance (capacity, rate, cycle life and efficiency of the cell, etc.). And secondly, the actual energy density of the zinc-air battery is improved. Zinc-air cells, while having a relatively high theoretical energy density, have greatly reduced cell performance (far below the theoretical energy density) due to the slow redox reactions in zinc-air cells. Therefore, the oxygen catalyst in the air electrode plays a critical role in improving the oxidation-reduction reaction rate and the energy conversion rate. The oxygen catalyst catalyzes mainly the oxygen reduction (ORR) and Oxygen Evolution Reaction (OER) in the air electrode. The ORR catalyst meets oxygen in the air, promotes the reduction of oxygen to hydroxyl, and achieves catalysis by accelerating electron transfer between the electrode and oxygen. Whereas the catalytic mechanism of OER is diametrically opposed to ORR, it is difficult to obtain a catalyst that is sufficiently active for both OER and ORR. The current commercial noble metal oxygen catalysts only catalyze OER/ORR one reaction, e.g., pt-based oxidants catalyze predominantly ORR reactions, ru and its oxides are used to catalyze OER reactions. However, the conventional noble metal oxygen catalyst has problems of high cost, limited reserve resources, etc., and thus, it is necessary to develop a novel OER/ORR bifunctional oxygen catalyst to improve the catalytic activity of the electrode.
Compared with noble metals, the transition metals have the advantages of low cost, high reserves, environmental protection and the like. The transition metal has various valence states, can form various oxides with different crystal structures, and can improve the electrocatalytic activity by adjusting the morphological structure, chemical composition and the like. By utilizing strategies such as doping hetero atoms by transition metal or compounding carbon materials, the catalytic active sites of the materials are increased, and further the bifunctional catalytic activity of the catalyst is improved. And further, the charge-discharge reaction rate and the cycle stability in the flexible zinc-air battery are effectively improved, and the over-potential of the battery is reduced, so that the flexible zinc-air battery with high specific energy density and excellent cycle performance is obtained.
Disclosure of Invention
In order to overcome the defects and shortcomings of the prior art, the primary purpose of the invention is to provide a preparation method of a cobalt manganese oxide flexible electrode material.
Another object of the present invention is to provide the cobalt manganese oxide flexible electrode material prepared by the above method.
It is still another object of the present invention to provide the use of the above cobalt manganese oxide flexible electrode material in zinc-air batteries.
The aim of the invention is achieved by the following scheme:
the preparation method of the cobalt manganese oxide flexible electrode material comprises the following steps:
(1) Dissolving urea, ammonium fluoride, soluble cobalt salt and soluble manganese salt in water, uniformly stirring to form a mixed solution, adding the mixed solution into a reaction kettle, suspending a conductive substrate in the mixed solution, performing a hydrothermal reaction, taking out the conductive substrate after the reaction is finished, washing and drying the conductive substrate with water and absolute ethyl alcohol, and placing the conductive substrate into a muffle furnace for calcining under air to obtain a product MnCo2O4/conductive substrate;
(2) And (3) placing the MnCo2O4/conductive substrate in a tube furnace, and calcining in Ar/H2 atmosphere to obtain the Co/MnOx electrode, namely the cobalt manganese oxide flexible electrode material.
The soluble manganese salt and the soluble cobalt salt in the step (1) are at least one of nitrate, sulfate and acetate relatively independently;
The mass ratio of the soluble manganese salt to the soluble cobalt salt in the step (1) is 1:3-3.5, the mass ratio of the total mass of the soluble manganese salt to the soluble cobalt salt to the urea is 2-2.5:1, and the mass ratio of the total mass of the soluble manganese salt to the soluble cobalt salt to the ammonium fluoride is 4-4.5:1.
The water consumption in the step (1) is satisfied that the mass concentration of the soluble manganese salt in the mixed solution is 0.5-1g/L, and the area of the conductive substrate in the step (1) is satisfied that 1 conductive substrate with the mass concentration of 2 x 2.5cm is correspondingly added into each 30-40 mL of the mixed solution.
The stirring time in the step (1) for uniformly stirring to form the mixed solution is preferably 0.5-1 hour.
The hydrothermal reaction in the step (1) is carried out at 90-110 ℃ for 6-10 hours.
The cleaning in the step (1) is to repeatedly clean the sample surface by water and absolute ethyl alcohol in sequence until free sediment does not exist on the sample surface, and the drying in the step (1) is to dry for 2-6 hours at 40-80 ℃.
The calcination in step (1) means calcination at 400 ℃ for 1 hour.
The volume percentage of H2 in the Ar/H2 atmosphere in the step (2) is 8%.
The calcination in the step (2) is calcination at 300-450 ℃ for 1-3 hours.
The cobalt manganese oxide flexible electrode material prepared by the method is provided.
The cobalt manganese oxide flexible electrode material is applied to zinc-air batteries. The cobalt manganese oxide flexible electrode material has mechanical flexibility and electrocatalytic activity. The cathode is used as an air cathode of liquid and all-solid zinc-air batteries and has high cycle stability. After circulation, the electrolyte shows good circulation stability, can provide open-circuit voltage of up to 1.524V in a liquid zinc-air battery, and can stabilize circulation for a plurality of hours.
The preparation method comprises the steps of carrying out hydrothermal reaction and then calcining in a muffle furnace to obtain the MnCo2O4 electrode with the nano-array structure, and then calcining at high temperature in Ar/H2 atmosphere to finally obtain the Co/MnOx electrode. The Co/MnOx electrode is obtained through one simple hydrothermal reaction, one air calcination and one Ar/H2 calcination, the operation is simple and efficient, and a large amount of time and raw material resources are saved.
The cobalt-manganese nano array structure grown on the conductive substrate by utilizing the hydrothermal reaction has the overall appearance of wool fiber needle shape, grows along the horizontal direction of the foam nickel and is closely arranged. The nanometer structures are mutually staggered to form a porous structure, the specific surface area of Co/MnOx is increased, and meanwhile, the holes are beneficial to the permeation of electrolyte and the diffusion of oxygen, so that the dynamic process of oxygen catalytic reaction is improved, the surface active sites are increased, the electrochemical catalytic effect of the electrode is increased, and the bifunctional oxygen catalytic activity of the electrode is improved.
The cobalt manganese oxide flexible electrode forms a porous net shape by utilizing the three-dimensional self-supporting structure, thereby promoting the permeation of electrolyte and the diffusion of oxygen. Through transition metal diatomic recombination, catalyst active sites are increased, and linear nano arrays are combined to be staggered, so that the active surface area of the electrode is further increased, and the flexible electrode with high-efficiency OER/ORR bifunctional catalytic activity is obtained.
Compared with the prior art, the invention has the following advantages:
(1) The cobalt manganese oxide flexible electrode material prepared by the invention has high electrochemical activity, good cycle performance and good application and development prospects.
(2) The cobalt manganese oxide flexible electrode material prepared by the method has stable oxygen catalysis and oxygen reduction catalysis performances.
(3) The invention adopts the hydrothermal reaction synthesis technology, has simple operation, easily controllable reaction conditions, strong operability and high repeatability, and can be widely applied to industrialization.
Drawings
FIG. 1 is a Scanning Electron Microscope (SEM) image of the Co/MnOx electrode obtained in example 1.
Fig. 2 is an OER performance graph and ORR performance graph for Co/MnOx electrodes prepared in example 1 and example 2 under a three electrode system at different reduction reaction temperatures.
FIG. 3 is an OER performance graph and an ORR performance graph for the Co/MnOx electrodes prepared in example 1 and example 3 under a three electrode system at different reduction reaction times.
Fig. 4 is an OER performance graph and ORR performance graph for Co/MnOx electrodes prepared in example 1 and example 4 under a three electrode system at different hydrothermal reaction temperatures.
Fig. 5 is an OER performance graph and ORR performance graph for Co/MnOx electrodes prepared in example 1 and example 5 under a three electrode system at different hydrothermal reaction times.
FIG. 6 is an OER performance graph and an ORR performance graph comparing the Co/MnOx electrode obtained in example 1 with the MnCo2O4 electrodes.
FIG. 7 is an XRD pattern for the Co/MnOx electrode prepared in example 1 under a three electrode system.
Fig. 8 is a cycle performance chart of the Co/MnOx electrode obtained in example 1 as an air cathode for a liquid zinc-air cell for constant current charge-discharge test.
Fig. 9 is an open circuit voltage plot of the Co/MnOx electrode obtained in example 1 as an air cathode for a liquid zinc-air cell for constant current charge-discharge testing.
Fig. 10 is a graph of power density for the Co/MnOx electrode obtained in example 1 as an air cathode for a liquid zinc-air cell for constant current charge-discharge testing.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but embodiments of the present invention are not limited thereto. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
The voltage (potential) values described in the examples are all expressed with reference to a Reversible Hydrogen Electrode (RHE).
Example 1
The preparation method of the cobalt manganese oxide flexible electrode material in the embodiment comprises the following specific preparation steps:
(1) The Co/MnOx electrode is prepared by dissolving 0.36g of urea, 0.19g of ammonium fluoride, 0.58g of cobalt nitrate hexahydrate and 0.18g of manganese nitrate in deionized water, and uniformly stirring to form a mixed solution, wherein the concentration of the manganese nitrate in the mixed solution is 0.9g/L. A portion of the mixture was taken in a reaction vessel, and 2 x 2.5cm of the pretreated nickel foam was suspended in 35ml of the mixture and subjected to a hydrothermal reaction at 110 ℃ for 6 hours. And after the reaction is finished, taking out foam nickel, washing and drying the foam nickel by using deionized water and absolute ethyl alcohol, putting the foam nickel into a muffle furnace, heating to 400 ℃ at 5 ℃ per min, and calcining the foam nickel for 1 hour to obtain the product MnCo2O4/NF. Subsequently, mnCo2O4/NF was placed in a tube furnace and calcined at 450℃for 3 hours in an Ar/H2 atmosphere (H2 volume percent: 8%) to obtain a Co/MnOx electrode.
(2) At room temperature, tests were carried out on an electrochemical workstation with a standard three-electrode system, using a synthetic Co/MnOx electrode (1 x 1cm2 active area) as the working electrode, a platinum sheet (2 x 2cm2) as the counter electrode, and an Ag/AgCl electrode as the reference electrode. The OER and ORR properties of the Co/MnOx electrodes were tested in 1M KOH solution and 0.1M KOH solution, respectively, for the electrolytes.
(3) The battery (battery assembly using a conventional die, electrolyte of 6M KOH and 0.2M zinc acetate mixture, co/MnOx electrode and zinc sheet respectively used as cathode and anode of zinc-air battery) was tested for charge-discharge performance (cycle performance, open circuit voltage, power density, etc.) using NEWARE battery test system.
An SEM of the Co/MnOx electrode obtained in example 1 is shown in FIG. 1. The nanostructure of the electrode can be seen in fig. 1, and Co/MnOx grown on the nickel foam is in the form of floss-wool nanowires, and the nanowires are closely arranged to form a porous structure.
FIG. 6 is an OER performance graph (a in FIG. 6) and an ORR performance graph (b in FIG. 6) of the Co/MnOx electrode obtained in example 1 compared to two electrodes of MnCo2O4. As can be seen from fig. 6, the Co/MnOx electrode subjected to the two heat treatments showed excellent OER performance at a current density of 10mA/cm2 with a corresponding potential of only 1.51V compared to the MnCo2O4 electrode subjected to the single heat treatment. Meanwhile, the Co/MnOx electrode exhibits an excellent half-wave potential (about 0.8V) significantly higher than the MnCo2O4 electrode (about 0.61V).
FIG. 7 is an XRD pattern of the Co/MnOx electrode prepared in example 1, showing that Co/MnOx has multiple diffraction peaks, consistent with standard peaks of spinel Co, mnO2 and MnO, and showing that the electrode has high purity and good crystal structure.
And adopting NEWARE battery test system to test the battery performance of Co/MnOx-based liquid zinc-air battery. Fig. 8 is a graph showing the cycle performance of the Co/MnOx electrode obtained in example 1 as an air cathode of a liquid zinc-air cell for constant current discharge test, and after 360 hours of cycle, the charge-discharge potential difference is 0.952V, indicating that the Co/MnOx electrode is used as an air cathode of a zinc-air cell to achieve excellent cell performance and high cycle stability. Fig. 9 is a graph of open circuit voltage of the Co/MnOx-based liquid zinc-air cell of 1.524V, obtained in example 1, as an air cathode of the liquid zinc-air cell for constant current discharge test. Fig. 10 is a power density plot of the Co/MnOx electrode obtained in example 1 as an air cathode for a liquid zinc-air cell for constant current discharge testing, with Co/MnOx achieving power densities up to 111.37mW cm-2, indicating excellent power densities achieved with the Co/MnOx electrode as an air cathode for a zinc-air cell.
Example 2
The preparation method of the cobalt manganese oxide flexible electrode material in the embodiment comprises the following specific preparation steps:
(1) The Co/MnOx electrode is prepared by dissolving 0.36g of urea, 0.19g of ammonium fluoride, 0.58g of cobalt nitrate hexahydrate and 0.18g of manganese nitrate in deionized water, and uniformly stirring to form a mixed solution, wherein the concentration of the manganese nitrate in the mixed solution is 0.9g/L. A portion of the mixture was taken in a reaction vessel, and the pretreated 2 x 2.5cm nickel foam was suspended in 35ml of the mixture and subjected to hydrothermal reaction at 90 ℃ for 6 hours. After the reaction is finished, taking out foam nickel, washing and drying the foam nickel by deionized water and absolute ethyl alcohol, and placing the foam nickel into air which is heated to 400 ℃ at 5 ℃ per minute to calcine the foam nickel for 1 hour, thus obtaining the product MnCo2O4/NF. Subsequently MnCo2O4/NF was placed in a tube furnace and calcined at 450℃for 3 hours in an Ar/H2 atmosphere (H2 volume percent: 8%) to obtain a Co/MnOx electrode.
(2) At room temperature, tests were carried out on an electrochemical workstation with a standard three-electrode system, using a synthetic Co/MnOx electrode (1 x 1cm2 active area) as the working electrode, a platinum sheet (2 x 2cm2) as the counter electrode, and an Ag/AgCl electrode as the reference electrode. The OER and ORR properties of the Co/MnOx electrodes were tested in 1M KOH solution and 0.1M KOH solution, respectively, for the electrolytes.
FIG. 2 is an OER performance graph (a of FIG. 2) and an ORR performance graph (b of FIG. 2) of the Co/MnOx electrode prepared in example 1 under a three electrode system. As can be seen from the graph, the OER performance of MnCoOx electrodes was optimal at a hydrothermal reaction temperature of 110℃and exhibited excellent OER performance at a current density of 10mA cm-2 with a corresponding potential of only 1.52V, and Co/MnOx had a higher half-wave potential (about 0.79V) at a hydrothermal reaction temperature of 110℃and exhibited good ORR performance.
Example 3
The preparation method of the cobalt-manganese oxide-based flexible electrode material comprises the following specific preparation steps:
(1) The Co/MnOx electrode is prepared by dissolving 0.36g of urea, 0.19g of ammonium fluoride, 0.58g of cobalt nitrate hexahydrate and 0.18g of manganese nitrate in deionized water, and uniformly stirring to form a mixed solution, wherein the concentration of the manganese nitrate in the mixed solution is 0.9g/L. A portion of the mixture was taken in a reaction vessel, and the pretreated 2 x 2.5cm nickel foam was suspended in 35ml of the mixture and subjected to a hydrothermal reaction at 110 ℃ for 10 hours. And after the reaction is finished, taking out foam nickel, washing and drying the foam nickel by using deionized water and absolute ethyl alcohol, putting the foam nickel into a muffle furnace, heating to 400 ℃ at 5 ℃ per min, and calcining the foam nickel for 1 hour to obtain the product MnCo2O4/NF. Subsequently MnCo2O4/NF was placed in a tube furnace and calcined at 450℃for 3 hours in an Ar/H2 atmosphere (H2 volume percent: 8%) to obtain a Co/MnOx electrode.
(2) At room temperature, tests were carried out on an electrochemical workstation with a standard three-electrode system, using a synthetic Co/MnOx electrode (1 x 1cm2 active area) as the working electrode, a platinum sheet (2 x 2cm2) as the counter electrode, and an Ag/AgCl electrode as the reference electrode. The OER and ORR properties of the Co/MnOx electrodes were tested in 1M KOH solution and 0.1M KOH solution, respectively, for the electrolytes.
Fig. 3 is a graph of the OER (a) performance and ORR (b) performance of example 3 (fig. 3) under a three electrode system, and it can be seen from the graph that the OER performance of Co/MnOx is optimal at 6 hours, and the corresponding potential is only 1.46V at a current density of 10mA cm-2, showing its excellent OER performance. The ORR performance of Co/MnOx exhibits a relatively high half-wave potential of about 0.80V at a hydrothermal reaction time of 10 hours.
Example 4
The preparation method of the cobalt-manganese oxide-based flexible electrode material comprises the following specific preparation steps:
(1) The Co/MnOx electrode is prepared by dissolving 0.36g of urea, 0.19g of ammonium fluoride, 0.58g of cobalt nitrate hexahydrate and 0.18g of manganese nitrate in deionized water, and uniformly stirring to form a mixed solution, wherein the concentration of the manganese nitrate in the mixed solution is 0.9g/L. A portion of the mixture was taken in a reaction vessel, and the pretreated 2 x 2.5cm nickel foam was suspended in 35ml of the mixture and subjected to a hydrothermal reaction at 110 ℃ for 6 hours. And after the reaction is finished, taking out foam nickel, washing and drying the foam nickel by using deionized water and absolute ethyl alcohol, putting the foam nickel into a muffle furnace, heating to 400 ℃ at 5 ℃ per min, and calcining the foam nickel for 1 hour to obtain the product MnCo2O4/NF. Subsequently, mnCo2O4/NF was placed in a tube furnace and calcined at 300℃for 3 hours in an Ar/H2 atmosphere (H2 volume percent: 8%) to obtain a Co/MnOx electrode.
(2) At room temperature, tests were carried out on an electrochemical workstation with a standard three-electrode system, using a synthetic Co/MnOx electrode (1 x 1cm2 active area) as the working electrode, a platinum sheet (2 x 2cm2) as the counter electrode, and an Ag/AgCl electrode as the reference electrode. The OER and ORR properties of the Co/MnOx electrodes were tested in 1M KOH solution and 0.1M KOH solution, respectively, for the electrolytes.
FIG. 4 is a graph of the OER performance of example 4 (FIG. 4 a) and ORR (FIG. 4 b) under a three electrode system, showing that the Co/MnOx electrode exhibits excellent electrochemical performance at a reduction temperature of 300℃and a corresponding potential of only 1.48V at a current density of 10mA cm-2, and that Co/MnOx exhibits a half-wave potential of about 0.76V in the ORR performance test.
Example 5
The preparation method of the cobalt-manganese oxide-based flexible electrode material comprises the following specific preparation steps:
(1) The Co/MnOx electrode is prepared by dissolving 0.36g of urea, 0.19g of ammonium fluoride, 0.58g of cobalt nitrate hexahydrate and 0.18g of manganese nitrate in deionized water, and uniformly stirring to form a mixed solution, wherein the concentration of the manganese nitrate in the mixed solution is 0.9g/L. A portion of the mixture was taken in a reaction vessel and the pretreated 2 x 2.5cm nickel foam was suspended in 35ml of the mixture and subjected to a hydrothermal reaction at 110 ℃ for 6 hours. And after the reaction is finished, taking out foam nickel, washing and drying the foam nickel by using deionized water and absolute ethyl alcohol, putting the foam nickel into a muffle furnace, heating to 400 ℃ at 5 ℃ per min, and calcining the foam nickel for 1 hour to obtain the product MnCo2O4/NF. Subsequently, mnCo2O4/NF was placed in a tube furnace and calcined at 450℃for 1 hour in an Ar/H2 atmosphere (H2 volume percent: 8%) to obtain a Co/MnOx electrode.
(2) At room temperature, tests were carried out on an electrochemical workstation with a standard three-electrode system, using a synthetic Co/MnOx electrode (1 x 1cm2 active area) as the working electrode, a platinum sheet (2 x 2cm2) as the counter electrode, and an Ag/AgCl electrode as the reference electrode. The OER and ORR properties of the Co/MnOx electrodes were tested in 1M KOH solution and 0.1M KOH solution, respectively, for the electrolytes.
Fig. 5 is an OER performance graph (a of fig. 5) and an ORR performance graph (b of fig. 5) of the Co/MnOx electrode prepared in example 5 under a three-electrode system, and it can be seen that there is no significant difference between OER performance at different times, and the ORR performance exhibits a higher half-wave potential (0.79V) at a reduction time of 3h, thereby exhibiting good ORR electrochemical activity.
The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above examples, and any other changes, modifications, substitutions, combinations, and simplifications that do not depart from the spirit and principle of the present invention should be made in the equivalent manner, and the embodiments are included in the protection scope of the present invention.