A grid-like porous structure carbon-supported nickel oxide applied to supercapacitors and a preparation method thereof
Small-sized porous NiO2@C was prepared by salt template method and controlled annealing rate, which solved the problem of preparing large-sized NiO2@C in the prior art and achieved the preparation of electrode material with high efficiency of electrochemical performance and environmental protection.
Patent Information
- Application Number
- CN202410963586.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-18
- Publication Date
- 2025-11-18
- Estimated Expiration
- 2044-07-18
AI Technical Summary
Existing technologies make it difficult to prepare small-sized porous NiO2@C using MOFs as precursors, resulting in low electron transport efficiency inside the electrode material. Furthermore, the use of organic template agents is costly and environmentally unfriendly.
A salt template method was used to create pores in MOFs to form a sea urchin-like porous Ni-MOF precursor, which was then annealed in air with controlled water volume and annealing rate to disperse into a grid-like porous NiO2@C structure.
A grid-like porous structure NiO2@C with a large specific surface area was prepared, which improved electrochemical performance, reduced diffusion resistance between the electrode and the electrolyte, promoted charge transport, and the method is environmentally friendly and low in cost.
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Figure CN118666319B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of materials preparation technology, and relates to a method for preparing grid-like porous carbon-supported nickel oxide and its application in supercapacitors. The chemical formula of the grid-like porous carbon-supported nickel oxide is NiO2@C. Background Technology
[0002] With the rapid development of energy-intensive industries, traditional batteries can no longer meet people's needs. Supercapacitors, a new type of energy storage device between traditional capacitors and rechargeable batteries, possess excellent electrochemical performance and cycle stability. As an electrochemical energy storage device with excellent electrochemical characteristics, low cost, and environmental friendliness, supercapacitors have attracted increasing attention from scientists and industrial researchers. Nickel oxide, due to its high theoretical specific capacitance, low cost, availability, and environmental friendliness, has been successfully used as a supercapacitor electrode. Combining nickel oxide with carbon materials can further improve the conductivity of the composite material and enhance its electrochemical properties. NiO2@C materials can be obtained by carbonizing Ni-based metal framework compounds. Metal-organic frameworks (MOFs) are novel materials with a periodic network structure formed by metal ions or clusters and organic molecules through coordination bonds. Their most significant characteristic is their morphological variability, allowing for the preparation of various NiO2@C morphologies such as spherical and columnar shapes. However, MOF materials are generally large in size and their structure is relatively stable during carbonization and oxidation, resulting in large NiO2@C sizes, typically on the micrometer scale. When used as electrode materials, this hinders the redox reaction at the electrode-electrolyte interface, and the electron transport efficiency within the electrode material is also low. Therefore, obtaining small-sized porous NiO2@C using MOFs as precursors is a key challenge.
[0003] To prepare porous NiO2@C, the pore structure of precursor MOFs can be pre-controlled. In existing techniques for pore formation in MOFs, template methods are commonly used. For example, Guan et al. (Angew. Chem. Int. Ed. 2018, 57, 6176–6180) used a dual-soft template method to form a walnut-shaped porous material with mesopores and macropores induced by an organic template agent. Due to its structural characteristics (large specific surface area), the prepared walnut-shaped porous material exhibited good redox reactivity in electrochemical applications. However, MOFs are generally grown in organic solvents, and template agents are mostly organic materials, which are expensive and environmentally unfriendly. Salt templates are a common pore-forming method, using inorganic salts such as sodium chloride and sodium sulfate as templates. However, inorganic salts are not easily soluble in organic solvents, so the low solubility of inorganic salts in organic solvents in salt template methods significantly hinders MOF pore formation. Therefore, based on the above analysis, our invention can use a salt template to create pores in MOFs. The urchin-like structure created by the salt template can reduce the structural stability of MOFs and enable the cutting of MOFs materials during the subsequent carbonization and oxidation process, thereby obtaining small-sized grid-like porous NiO2@C. Summary of the Invention
[0004] To address the problems existing in the prior art, this invention provides a grid-like porous structure carbon-supported nickel oxide NiO2@C for use in supercapacitors and its preparation method. The preparation method is simple, easy to control, environmentally friendly, and low in cost. The grid-like porous structure of carbon-supported nickel oxide NiO2@C can increase the specific surface area of the material, provide sufficient electroactive centers, reduce the diffusion resistance between the electrode and the electrolyte, and promote charge transport during the electrochemical reaction process. At the same time, it has an interconnected framework, which significantly improves the electrochemical performance of the material.
[0005] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:
[0006] A method for preparing a grid-like porous NiO2@C structure for use in supercapacitors is disclosed. The method first involves creating pores in a solid spherical Ni-MOF using a salt template method to obtain a sea urchin-like porous Ni-MOF precursor. Then, the sea urchin-like porous Ni-MOF precursor is annealed in air to obtain a grid-like porous carbon-supported nickel oxide NiO2@C structure. This method consists of two steps:
[0007] The first step is to prepare a sea urchin-like porous Ni-MOF product precursor.
[0008] Solution A is prepared by dissolving nickel nitrate and sodium chloride or sodium sulfate in a DMF solution containing a small amount of water and stirring. Solution B is prepared by dissolving pyromellitic acid, polyvinylpyrrolidone (PVP), and 4,4-bipyridine in a DMF solution and stirring.
[0009] Solution B is slowly added dropwise to solution A over a certain period of time. After thorough mixing, the mixture is reacted at a certain temperature for a certain period of time to obtain a Ni-MOF product precursor with a sea urchin-like porous structure. During this reaction step, the salt template method (using sodium chloride or sodium sulfate as the salt template) for pore formation requires addressing the issue of salt dissolution. Adding a small amount of water can control the amount of salt template dissolved; therefore, strictly controlling the amount of water has a significant impact on the pore formation of the material.
[0010] The second step involves annealing the Ni-MOF precursor obtained in the first step in air to obtain a grid-like porous nickel oxide NiO2@C. During this reaction, the urchin-like structure created by the salt template reduces the stability of the MOF precursor. Furthermore, the rapid heating rate leads to uneven changes in the internal structure of the material, destroying the original crystal structure or morphology. Especially within the phase transition temperature range, the rapid heating rate causes local stress concentration, resulting in a smaller material size.
[0011] Furthermore, in the first step, solution A is prepared at room temperature. For every 15-20 ml of the mixed solution of DMF and deionized water, 0.291-0.873 g of nickel nitrate and 0.1-1 g of sodium chloride or sodium sulfate are added, and the mixture is stirred for 15-20 min.
[0012] Furthermore, in the first step, the volume ratio of DMF to water in the mixed solution of DMF and deionized water is 4:1 to 2:1.
[0013] Furthermore, in the first step, solution B is prepared at room temperature. For every 15-20 ml of DMF solution, 0.254-0.762 g of pyromellitic acid, 0.5-2 g of polyvinylpyrrolidone (PVP), and 0.08-0.64 g of 4,4-bipyridine are added and stirred for 15-20 min.
[0014] Furthermore, in the first step, solution B is slowly added dropwise to solution A over 10-20 minutes, stirred for 30-40 minutes, and then transferred to a reaction vessel. After reacting at 120-160°C for 10-16 hours, post-processing is performed to obtain the urchin-like porous Ni-MOF precursor.
[0015] Furthermore, the post-processing of the first step is as follows: the reaction solution is filtered to obtain the reactants, which are washed several times with water and ethanol, and dried in an oven at 50-70℃ for 5-8 hours to obtain the sea urchin-like porous Ni-MOF product.
[0016] The second step involves annealing 150-300 mg of Ni-MOF precursor in air at high temperature to obtain porous grid-like carbon-supported nickel oxide NiO2@C.
[0017] Furthermore, in the second step, the annealing heating rate is 20-30℃ / min, the annealing temperature is 250-400℃, and the annealing time is 2-4h.
[0018] A grid-like porous carbon-supported nickel oxide NiO2@C structure for use in supercapacitors was prepared using the above-described method. This compound has a density of 1 Ag. -1 At unit values, the specific capacitance is 1320–1630 F / g, and this compound exhibits this characteristic at 20 Ag. -1 At the unit price, the multiplier is 70.2%–76%.
[0019] Principle analysis of the invention:
[0020] This invention utilizes a simple, controllable, environmentally friendly, and low-cost method to prepare porous, grid-like carbon-supported nickel oxide with a large specific surface area. When used in supercapacitors, it exhibits excellent electrochemical performance. The design of the grid-like porous structure provides a highly usable surface area, exposed active centers, and an interconnected framework, while also preventing undesirable material accumulation, thereby improving the material's electrochemical performance. The amount of salt template plays a decisive role in the formation of the sea urchin-like porous structure. The amount of inorganic salt dissolved has a crucial impact on MOF pore formation. By adding a small amount of water and strictly controlling the amount, the amount of salt dissolved can be expanded and controlled to achieve the desired pore-forming effect without affecting the formation of the MOF material structure (excessive water will affect the organic system for MOF growth, thus affecting the formation of the MOF material). Finally, a sea urchin-like porous structure is formed, which has a certain degree of instability, providing a prerequisite for subsequent dispersion of bulk materials. The relationship between the annealing temperature rise rate and morphological retention is related to the phase transformation and structural stability within the material. Excessively rapid heating rates can lead to uneven changes in the internal structure of materials, disrupting the original crystal structure or morphology, especially within the phase transition temperature range. Rapid heating may cause localized stress concentration, resulting in material dispersion. Dispersing bulk materials into a grid-like porous structure can increase the specific surface area of the material, provide sufficient electroactive centers, reduce diffusion resistance between the electrode and the electrolyte, and promote charge transport during electrochemical reactions, thereby improving electrochemical performance.
[0021] The beneficial effects of this invention are:
[0022] 1) The preparation method is green, environmentally friendly, simple, and low-cost; 2) By strictly controlling the amount of water, the amount of salt template dissolved is controlled, which determines the formation of the porous structure. Furthermore, the urchin-like structure produced by the salt template method can reduce the stability of the MOF precursor, making it easier to segment into smaller materials; 3) A higher heating rate is beneficial for dispersing bulk porous MOFs. By strictly controlling the annealing heating rate, the structural stability of bulk MOFs is reduced, dispersing the bulk porous MOFs into smaller grid-like porous structures; 4) The grid-like porous structure has a large specific surface area, providing a large number of reactive sites, and exhibits high specific capacitance and rate performance. Attached Figure Description
[0023] Figure 1 This is the SEM image of Example 1.
[0024] Figure 2 This is a rate performance diagram of the grid-like porous structure carbon-supported nickel oxide NiO2@C in Example 1.
[0025] Figure 3 This is the SEM image of Example 2.
[0026] Figure 4 This is the SEM image of Comparative Example 1.
[0027] Figure 5 This is a rate performance diagram of rod-shaped carbon-supported nickel oxide NiO2@C in Comparative Example 1. Detailed Implementation
[0028] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.
[0029] Example 1
[0030] The first step, at room temperature, is to prepare (a) a mixed solution of 0.291 g nickel nitrate and 0.15 g sodium chloride dissolved in 12 ml DMF and 3 ml deionized water. Then, prepare (b) a mixed solution of 0.254 g pyromellitic acid, 0.5 g polyvinylpyrrolidone (PVP), and 0.08 g 4,4-bipyridine dissolved in 15 ml DMF. After stirring each solution for 15 min, (b) is slowly added dropwise to (a) over 10 min. After stirring for 30 min, the mixture is transferred to a reaction vessel and reacted at 120 °C for 10 h. The mixture is then washed three times by centrifugation with ethanol and dried in an oven to obtain the sea urchin-like porous Ni-MOF precursor.
[0031] The second step involved annealing 150 mg of the Ni-MOF precursor in air at a high temperature. The annealing rate was 20 °C / min, the annealing temperature was 400 °C, and the annealing time was 2 h, yielding a porous, grid-like carbon-supported nickel oxide NiO2@C. This compound was annealed in 1 Ag... -1At unit temperature, the specific capacitance is 1630 F / g, and at 20 Ag... -1 The multiplier is 76% per unit.
[0032] Example 2
[0033] The first step, at room temperature, is to prepare (a) a mixed solution of 0.873 g nickel nitrate and 0.1 g sodium chloride dissolved in 15 ml DMF and 5 ml deionized water. Then, prepare (b) a mixed solution of 0.762 g pyromellitic acid, 2 g polyvinylpyrrolidone (PVP), and 0.64 g 4,4-bipyridine dissolved in 20 ml DMF. After stirring each solution for 20 min, (b) is slowly added dropwise to (a) over 15 min. After stirring for 40 min, the mixture is transferred to a reaction vessel and reacted at 160 °C for 16 h. The mixture is then washed five times by centrifugation with ethanol and dried in an oven to obtain the sea urchin-like porous Ni-MOF precursor.
[0034] The second step involved annealing 200 mg of the Ni-MOF precursor in air at a high temperature. The annealing rate was 25 °C / min, the annealing temperature was 200 °C, and the annealing time was 3 h, yielding a porous, grid-like carbon-supported nickel oxide NiO2@C. This compound was annealed in 1 Ag... -1 At unit value, the specific capacitance is 1611 F / g, at 20 Ag -1 The multiplier is 72% per unit.
[0035] Example 3
[0036] The first step, at room temperature, is to prepare (a) a mixed solution of 0.291 g nickel nitrate and 0.2 g sodium sulfate dissolved in 17 ml DMF and 3 ml deionized water. Then, prepare (b) a mixed solution of 0.508 g pyromellitic acid, 1 g polyvinylpyrrolidone (PVP), and 0.32 g 4,4-bipyridine dissolved in 20 ml DMF. After stirring each solution for 20 min, (b) is slowly added dropwise to (a) over 20 min. After stirring for 30 min, the mixture is transferred to a reaction vessel and reacted at 140 °C for 13 h. The mixture is then washed three times by centrifugation with ethanol and dried in an oven to obtain the sea urchin-like porous Ni-MOF precursor.
[0037] The second step involved annealing 300 mg of the Ni-MOF precursor in air at a high temperature. The annealing rate was 30 °C / min, the annealing temperature was 300 °C, and the annealing time was 2 h, yielding a porous, grid-like carbon-supported nickel oxide NiO2@C. This compound was annealed in 1 Ag... -1 At unit value, the specific capacitance is 1589 F / g, at 20 Ag -1 At this unit, the multiplier is 71%.
[0038] Example 4
[0039] The first step, at room temperature, is to prepare (a) a mixed solution of 0.632 g of nickel nitrate and 0.5 g of sodium chloride dissolved in 15 ml of DMF and 4 ml of deionized water. Then, prepare (b) a mixed solution of 0.508 g of pyromellitic acid, 1 g of polyvinylpyrrolidone (PVP), and 0.32 g of 4,4-bipyridine dissolved in 18 ml of DMF. After stirring each solution for 10 min, (b) is slowly added dropwise to (a) over 10 min. After stirring for 30 min, the mixture is transferred to a reaction vessel and reacted at 130 °C for 16 h. The mixture is then washed three times by centrifugation with ethanol and dried in an oven to obtain the sea urchin-like porous Ni-MOF precursor.
[0040] The second step involved annealing 150 mg of the Ni-MOF precursor in air at a high temperature. The annealing rate was 22 °C / min, the annealing temperature was 400 °C, and the annealing time was 2 h, yielding a porous, grid-like carbon-supported nickel oxide NiO2@C. This compound was annealed in 1 Ag... -1 At unit temperature, the specific capacitance is 1488 F / g, and at 20 Ag... -1 At the unit level, the multiplier is 71.4%.
[0041] Example 5
[0042] At room temperature, firstly, prepare (a) a mixed solution of 0.592 g nickel nitrate and 0.8 g sodium sulfate dissolved in 10 ml DMF and 5 ml deionized water. Then prepare (b) a mixed solution of 0.508 g pyromellitic acid, 1 g polyvinylpyrrolidone (PVP), and 0.32 g 4,4-bipyridine dissolved in 18 ml DMF. After stirring each solution for 10 min, slowly add (b) dropwise to (a) over 10 min. Then stir for 40 min, transfer to a reaction vessel, and react at 140 °C for 16 h. After washing three times by centrifugation with ethanol, dry in an oven to obtain the sea urchin-like porous Ni-MOF precursor.
[0043] The second step involved annealing 300 mg of the Ni-MOF precursor in air at a high temperature. The annealing rate was 23 °C / min, the annealing temperature was 300 °C, and the annealing time was 2 h, yielding a porous, grid-like carbon-supported nickel oxide NiO2@C. This compound was obtained in 1 Ag... -1 At unit value, the specific capacitance is 1455 F / g, at 20 Ag -1 At the unit level, the multiplier is 72.8%.
[0044] Example 6
[0045] At room temperature, firstly, prepare (a) a mixed solution of 0.792 g nickel nitrate and 0.5 g sodium chloride dissolved in 13 ml DMF and 5 ml deionized water. Then prepare (b) a mixed solution of 0.508 g pyromellitic acid, 1.5 g polyvinylpyrrolidone (PVP), and 0.32 g 4,4-bipyridine dissolved in 15 ml DMF. After stirring each solution for 10 min, slowly add (b) dropwise to (a) over 10 min. Then stir for 40 min, transfer to a reaction vessel, and react at 140 °C for 16 h. After washing three times by centrifugation with ethanol, dry in an oven to obtain the sea urchin-like porous Ni-MOF precursor.
[0046] The second step involved annealing 300 mg of the Ni-MOF precursor in air at a high temperature. The annealing rate was 25 °C / min, the annealing temperature was 300 °C, and the annealing time was 3 h, yielding a porous, grid-like carbon-supported nickel oxide NiO2@C. This compound was annealed in 1 Ag... -1 At unit temperature, the specific capacitance is 1465 F / g, and at 20 Ag... -1 At the unit level, the multiplier is 71.8%.
[0047] Example 7
[0048] At room temperature, firstly, prepare (a) a mixed solution of 0.732 g nickel nitrate and 1 g sodium chloride dissolved in 15 ml DMF and 5 ml deionized water. Then prepare (b) a solution of 0.558 g pyromellitic acid, 1 g polyvinylpyrrolidone (PVP), and 0.64 g 4,4-bipyridine dissolved in 20 ml DMF. After stirring each solution for 10 min, slowly add (b) dropwise to (a) over 10 min. Then stir for 30 min, transfer to a reaction vessel, and react at 140 °C for 16 h. After washing three times by centrifugation with ethanol, dry in an oven to obtain the sea urchin-like porous Ni-MOF precursor.
[0049] The second step involved annealing 350 mg of the Ni-MOF precursor in air at a high temperature. The annealing rate was 25 °C / min, the annealing temperature was 350 °C, and the annealing time was 3 h, yielding a porous, grid-like carbon-supported nickel oxide NiO2@C. This compound was annealed in 1 Ag... -1 At unit value, the specific capacitance is 1320 F / g, at 20 Ag -1 The multiplier is 70.2% per unit.
[0050] Comparative Example 1
[0051] The first step, at room temperature, is to prepare (a) a mixed solution of 0.291 g nickel nitrate and 0.15 g sodium chloride dissolved in 10 ml DMF and 20 ml deionized water. Then, prepare (b) a mixed solution of 0.254 g pyromellitic acid, 0.5 g polyvinylpyrrolidone (PVP), and 0.08 g 4,4-bipyridine dissolved in 15 ml DMF. After stirring each solution for 15 min, (b) is slowly added dropwise to (a) over 10 min. After stirring for 30 min, the mixture is transferred to a reaction vessel and reacted at 120 °C for 10 h. The mixture is then washed three times by centrifugation with ethanol and dried in an oven to obtain the rod-shaped Ni-MOF precursor.
[0052] The second step involved annealing 150 mg of the Ni-MOF precursor in air at a high temperature. The annealing rate was 20 °C / min, the annealing temperature was 400 °C, and the annealing time was 2 h, yielding rod-shaped carbon-supported nickel oxide NiO2@C. This compound was used in 1 A g... -1 At unit value, the specific capacitance is 667 F / g, at 20 Ag -1 The multiplier is 45.2% per unit.
[0053] Compared with Example 1, Comparative Example 1 shows that in the case of adding excess water, no urchin-like porous precursor was formed, and the rod-shaped nickel oxide NiO2@C formed was not dispersed after annealing at a high heating rate, resulting in unsatisfactory rate capability and specific capacitance of the product.
[0054] Comparative Example 2
[0055] The first step, at room temperature, is to prepare (a) a mixed solution of 0.873 g nickel nitrate and 0.1 g sodium chloride dissolved in 15 ml DMF and 5 ml deionized water. Then, prepare (b) a mixed solution of 0.762 g pyromellitic acid, 2 g polyvinylpyrrolidone (PVP), and 0.64 g 4,4-bipyridine dissolved in 20 ml DMF. After stirring each solution for 20 min, (b) is slowly added dropwise to (a) over 15 min. After stirring for 40 min, the mixture is transferred to a reaction vessel and reacted at 160 °C for 16 h. The mixture is then washed five times by centrifugation with ethanol and dried in an oven to obtain the sea urchin-like porous Ni-MOF precursor.
[0056] The second step involved annealing 200 mg of the Ni-MOF precursor in air at a high temperature. The annealing rate was 5 °C / min, the annealing temperature was 200 °C, and the annealing time was 3 h, yielding a urchin-like porous carbon-supported nickel oxide NiO2@C. This compound was annealed in 1 Ag... -1 At unit value, the specific capacitance is 868 F / g, at 20 Ag -1 The multiplier is 41.8% per unit.
[0057] Compared with Example 2, Comparative Example 2 shows that when the annealing heating rate is slow, the urchin-like Ni-MOF precursor is not dispersed, and the rate capability and specific capacitance of the product formed after annealing are not ideal.
[0058] The embodiments described above are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.
Claims
1. A method for preparing a grid-like porous carbon-supported nickel oxide structure for use in supercapacitors, characterized in that, The preparation method first involves creating pores in a solid spherical Ni-MOF using a salt template method to obtain a sea urchin-like porous Ni-MOF precursor; then, the sea urchin-like porous Ni-MOF precursor is annealed to obtain a grid-like porous carbon-supported nickel oxide NiO2@C; the method includes the following steps: The first step is to prepare a sea urchin-like porous Ni-MOF product precursor. Nickel nitrate and sodium chloride or sodium sulfate were dissolved in a DMF solution containing a small amount of water and stirred to prepare solution A; pyromellitic acid, polyvinylpyrrolidone (PVP), and 4,4-bipyridine were dissolved in a DMF solution and stirred to prepare solution B; solution B was slowly added dropwise to solution A over a certain period of time, and after thorough stirring, the mixture was reacted at a certain temperature for a certain period of time to obtain a sea urchin-like porous Ni-MOF product precursor. The second step involves annealing the Ni-MOF precursor obtained in the first step in air to obtain a grid-like porous structure nickel oxide NiO2@C, wherein the annealing heating rate is 20-30℃ / min. In the first step, solution A is prepared at room temperature. For every 15-20 ml of the mixed solution of DMF and deionized water, 0.291-0.873 g of nickel nitrate and 0.1-1 g of sodium chloride or sodium sulfate are added and stirred for 15-20 min. In the first step of preparing solution A, the volume ratio of DMF to water in the mixed solution of DMF and deionized water is 4:1 to 2:
1. In the first step, solution B is prepared at room temperature. For every 15-20 ml of DMF solution, 0.254-0.762 g of pyromellitic acid, 0.5-2 g of polyvinylpyrrolidone (PVP), and 0.08-0.64 g of 4,4-bipyridine are added and stirred for 15-20 min. In the first step, solution B is slowly added dropwise to solution A over 10-20 min, stirred for 30-40 min, and then transferred to a reaction vessel. After reacting at 120-160℃ for 10-16 h, post-processing is performed to obtain the urchin-like porous Ni-MOF precursor.
2. The method for preparing a grid-like porous carbon-supported nickel oxide structure for use in supercapacitors according to claim 1, characterized in that, In the second step, the annealing temperature is 250-400 ℃ and the annealing time is 2-4 h.
3. A grid-like porous carbon-supported nickel oxide structure for use in supercapacitors, characterized in that, The aforementioned grid-like porous carbon-supported nickel oxide is prepared using the preparation method described in claim 1 or 2.
4. The grid-like porous carbon-supported nickel oxide structure for use in supercapacitors according to claim 3, characterized in that, The aforementioned grid-like porous structure of carbon-supported nickel oxide at 1 A g -1 At unit values, the specific capacitance is 1320~1630 F / g, and this compound at 20 A g... -1 At the unit price, the multiplier is 70.2% to 76%.