Preparation method and application of Mo2C / Mo3P heterojunction catalyst with core-shell structure

Abstract

The invention discloses a preparation method and application of a Mo2C / Mo3P heterojunction catalyst with a core-shell structure, and belongs to the field of hydrogen evolution by water electrolysis. The invention aims to solve the problems of high cost, low catalytic activity, poor stability and easy agglomeration of particles in the catalysis process of the existing catalyst for electrocatalytic hydrogen evolution reaction. The method comprises the following steps: 1, preparing a PMo12atPy precursor; and 2, calcining. The Mo2C / Mo3P heterojunction catalyst with the core-shell structure prepared by the invention can avoid agglomeration of particles in a catalysis process, increase the number of exposed active sites, promote H2O adsorption and optimize Gibbs free energy of hydrogen, shows excellent HER stability and catalytic activity in a 1.0 mol / L KOH solution and a 0.5 mol / L H2SO4 solution, has overpotentials of only 58mV and 82mV under the current density of 10mAcm <-2 >, and can be used for preparing the catalyst with the core-shell structure. And pollution-free and high-efficiency chemical reaction is realized.

Description

Technical Field

[0001] The present invention belongs to the field of hydrogen evolution by water electrolysis, and in particular relates to a preparation method and application of a Mo2C / Mo3P heterojunction catalyst with a core-shell structure. Background Art

[0002] Since the hydrogen evolution reaction (HER) has slow kinetics, the development of highly active and environmentally friendly electrocatalysts is crucial to reduce the potential required for HER and improve the efficiency of water electrolysis. H * ) are considered highly efficient HER catalysts. However, their rarity, high cost, and stability issues limit their industrial application. Therefore, exploring simple, low-cost, non-precious metal electrocatalysts is crucial for promoting the large-scale application of water splitting.

[0003] Mo2C, particularly the β-Mo2C phase, has attracted widespread interest due to its excellent HER activity in both acidic and alkaline electrolytes, due to its similar d-band electronic structure and comparable catalytic performance to Pt. However, the high d-orbital vacancy density of Mo2C leads to a strong Mo-H binding energy, hindering further improvement in HER activity. Furthermore, most Mo2C materials are typically synthesized at high temperatures, which poses challenges such as structural collapse and loss of active sites after high-temperature calcination. To obtain Mo2C catalysts with highly active sites, Mo2C nanoparticles are typically dispersed on the surface of a carbon matrix. However, this approach often results in oxidative dissolution of the Mo2C due to the exposure of the Mo2C nanoparticles to the electrolyte, resulting in poor stability during catalysis. Therefore, it is crucial to find a facile synthesis method to achieve both excellent catalytic activity and good cycling stability in Mo2C. Mo3P, due to its unique structure, possesses a low work function and a high density of Mo active centers, and holds great promise for catalytic applications. However, the surface active sites of Mo3P have less than ideal adsorption / desorption capabilities for hydrogen intermediates (H*), resulting in slow reaction kinetics. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems of high cost, low catalytic activity, poor stability and easy agglomeration of particles in the existing electrocatalytic hydrogen evolution reaction catalysts, and to provide a preparation method and application of Mo2C / Mo3P heterojunction catalyst with a core-shell structure.

[0005] The Mo2C / Mo3P heterojunction catalyst with a core-shell structure prepared by the present invention can avoid particle agglomeration during the catalytic process, increase the number of exposed active sites, promote H2O adsorption and optimize the Gibbs free energy of hydrogen, thereby significantly improving the electrode HER catalytic activity and stability.

[0006] A method for preparing a Mo2C / Mo3P heterojunction catalyst with a core-shell structure is specifically completed by the following steps:

[0007] 1. Preparation of PMo 12 @Py Precursor:

[0008] ① Dissolve phosphomolybdic acid in deionized water and stir magnetically to obtain a phosphomolybdic acid solution;

[0009] ②, dissolving pyrrole in anhydrous ethanol and stirring magnetically to obtain an anhydrous ethanol solution of pyrrole;

[0010] ③. Add the pyrrole anhydrous ethanol solution dropwise to the phosphomolybdic acid solution, stir at room temperature for a period of time, then collect the resulting precipitate by centrifugation, and then dry the precipitate to obtain PMo 12 @Py precursor;

[0011] 2. PMo 12 The @Py precursor is placed in a tubular furnace, hydrogen and argon are introduced into the tubular furnace, and the temperature is raised to 750℃~800℃ in an H2 / Ar mixed gas atmosphere and kept warm for a period of time to obtain a Mo2C / Mo3P heterojunction catalyst with a core-shell structure.

[0012] A Mo2C / Mo3P heterojunction catalyst with a core-shell structure is used in the field of hydrogen evolution by water electrolysis.

[0013] Advantages of the present invention:

[0014] The present invention synthesizes a Mo2C / Mo3P heterojunction catalyst with a core-shell structure through polymerization reaction and heat treatment. The heterojunction constructed by Mo3P and Mo2C enhances the HER activity of Mo2C and Mo3P through electronic interaction, thereby providing additional electrons to fill the antibonding orbital of Mo, weakening the strength of the Mo-H bond, and promoting the desorption of H. In addition, the carbon shell provides a physical barrier to prevent particle agglomeration during the electrocatalytic process and slow down the electrochemical oxidation on the surface. The thermal decomposition of polypyrrole produces a porous structure in the nanospheres, thereby exposing a sufficient number of active sites. In addition, the constructed heterojunction can change the electronic structure of the catalyst, accelerate the transfer of electrons at the interface, increase the adsorption energy of water, optimize the hydrogen Gibbs free energy, and further improve the HER catalytic performance. The catalyst exhibits excellent HER stability and catalytic activity in 1.0 mol / L KOH solution and 0.5 mol / L H2SO4 solution, and exhibits excellent HER stability and catalytic activity at 10 mA cm -2 The overpotential at the current density is only 58mV and 82mV;

[0015] 2. The preparation method of the present invention is simple, low in cost, and has excellent electrocatalytic activity and stability; the present invention can convert electrical energy into clean hydrogen energy with a high calorific value, thereby achieving a pollution-free and highly efficient chemical reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is an SEM image of the Mo2C / Mo3P heterojunction catalyst with a core-shell structure prepared in Example 1;

[0017] Figure 2 HRTEM image of the Mo2C / Mo3P heterojunction catalyst with a core-shell structure prepared in Example 1;

[0018] Figure 3 SEM, TEM, and HRTEM images of the Mo2C catalyst prepared in Comparative Example 1;

[0019] Figure 4 The SEM, TEM and HRTEM images of the Mo / Mo3P heterojunction catalyst prepared in Comparative Example 2;

[0020] Figure 5 XRD pattern of the Mo2C / Mo3P heterojunction catalyst with a core-shell structure prepared in Example 1;

[0021] Figure 6 LSV plots of the Mo2C / Mo3P heterojunction catalyst with a core-shell structure prepared in Example 1 before and after 3000 CV cycles in 1M KOH electrolyte;

[0022] Figure 7LSV plots of the Mo2C / Mo3P heterojunction catalyst with a core-shell structure prepared in Example 1 before and after 3000 CV cycles in 0.5M H2SO4 electrolyte;

[0023] Figure 8 LSV plots of the Mo2C / Mo3P heterojunction catalyst with a core-shell structure prepared in Example 1, the Mo2C catalyst prepared in Comparative Example 1, and the Mo / Mo3P heterojunction catalyst prepared in Comparative Example 2 in 1 M KOH electrolyte;

[0024] Figure 9 LSV diagrams of the Mo2C / Mo3P heterojunction catalyst with a core-shell structure prepared in Example 1, the Mo2C catalyst prepared in Comparative Example 1, and the Mo / Mo3P heterojunction catalyst prepared in Comparative Example 2 in 0.5 M H2SO4 electrolyte. DETAILED DESCRIPTION

[0025] Specific embodiment 1: This embodiment is a method for preparing a Mo2C / Mo3P heterojunction catalyst with a core-shell structure, which is specifically completed by the following steps:

[0026] 1. Preparation of PMo 12 @Py Precursor:

[0027] ① Dissolve phosphomolybdic acid in deionized water and stir magnetically to obtain a phosphomolybdic acid solution;

[0028] ②, dissolving pyrrole in anhydrous ethanol and stirring magnetically to obtain an anhydrous ethanol solution of pyrrole;

[0029] ③. Add the pyrrole anhydrous ethanol solution dropwise to the phosphomolybdic acid solution, stir at room temperature for a period of time, then collect the resulting precipitate by centrifugation, and then dry the precipitate to obtain PMo 12 @Py precursor;

[0030] 2. PMo 12 The @Py precursor is placed in a tubular furnace, hydrogen and argon are introduced into the tubular furnace, and the temperature is raised to 750℃~800℃ in an H2 / Ar mixed gas atmosphere and kept warm for a period of time to obtain a Mo2C / Mo3P heterojunction catalyst with a core-shell structure.

[0031] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the mass ratio of the phosphomolybdic acid described in step 1 (1) to the volume ratio of deionized water is (0.5 g to 1.5 g): 50 mL. The other steps are the same as those in specific embodiment 1.

[0032] Specific embodiment 3: This embodiment differs from specific embodiments 1 or 2 in that the magnetic stirring time in step 1 (1) is 10 to 15 minutes, and the magnetic stirring time in step 1 (2) is 3 to 5 minutes. The other steps are the same as those in specific embodiments 1 or 2.

[0033] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the volume ratio of pyrrole to anhydrous ethanol in step 1 ② is (125 μL to 500 μL):12 mL. The other steps are the same as specific embodiments 1 to 3.

[0034] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the volume ratio of the pyrrole anhydrous ethanol solution to the phosphomolybdic acid solution in step 1 (3) is (10 mL to 15 mL):50 mL. The other steps are the same as specific embodiments 1 to 4.

[0035] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the drying temperature in step 1 (3) is 50°C to 70°C and the drying time is 10 to 12 hours; the stirring time at room temperature in step 1 (3) is 10 to 48 hours. The other steps are the same as specific embodiments 1 to 5.

[0036] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that the heating rate in step 2 is 2°C / min to 5°C / min and the holding time in step 2 is 2h to 4h. The other steps are the same as specific embodiments 1 to 6.

[0037] Specific Embodiment 8: This embodiment differs from Specific Embodiments 1 to 7 in that the volume ratio of hydrogen to argon in the H2 / Ar mixed gas in step 2 is 1:9, and the flow rate of the H2 / Ar mixed gas in step 2 is 25 mL / min to 75 mL / min. The other steps are the same as Specific Embodiments 1 to 7.

[0038] Specific embodiment 9: This embodiment is a Mo2C / Mo3P heterojunction catalyst with a core-shell structure used in the field of hydrogen evolution by electrolysis of water.

[0039] Specific embodiment 10: The difference between this embodiment and specific embodiments 1 to 9 is that a Mo2C / Mo3P heterojunction catalyst with a core-shell structure shows excellent HER stability and catalytic activity in 1.0 mol / L KOH solution and 0.5 mol / L H2SO4 solution. -2 The overpotential at the current density of 100 nm is only 58 mV and 82 mV. The other steps are the same as those in the first to ninth embodiments.

[0040] The following examples are used to verify the beneficial effects of the present invention:

[0041] Example 1: A method for preparing a Mo2C / Mo3P heterojunction catalyst having a core-shell structure is specifically completed by the following steps:

[0042] 1. Preparation of PMo 12 @Py Precursor:

[0043] ①, 1g phosphomolybdic acid (H3PMo 12 O 40 ) was dissolved in 50 mL of deionized water and magnetically stirred for 10 min to obtain a phosphomolybdic acid solution;

[0044] ② Dissolve 250 μL of pyrrole in 12 mL of anhydrous ethanol and stir magnetically for 3 minutes to obtain an anhydrous ethanol solution of pyrrole;

[0045] ③. Add the pyrrole anhydrous ethanol solution dropwise to the phosphomolybdic acid solution, stir at room temperature for 20 hours, then collect the resulting precipitate by centrifugation, and then dry the precipitate to obtain PMo 12 @Py precursor;

[0046] The drying temperature in step 1 (3) is 60°C and the drying time is 12 hours;

[0047] 2. PMo 12 The @Py precursor was placed in a tube furnace, hydrogen and argon were introduced into the tube furnace, and the temperature was raised to 750°C in an H2 / Ar mixed gas atmosphere and kept at this temperature for 2 hours to obtain a Mo2C / Mo3P heterojunction catalyst with a core-shell structure.

[0048] The heating rate in step 2 is 2°C / min;

[0049] The volume ratio of hydrogen to argon in the H2 / Ar mixed gas described in step 2 is 1:9;

[0050] The flow rate of the H2 / Ar mixed gas described in step 2 is 50 mL / min.

[0051] Example 2: This example differs from Example 1 in that in step 1 (2), 125 μL of pyrrole was dissolved in 12 mL of anhydrous ethanol and magnetically stirred for 3 minutes to obtain an anhydrous ethanol solution of pyrrole. The other steps and parameters were the same as those in Example 1.

[0052] Example 3: This example differs from Example 1 in that in step 1 (2), 500 μL of pyrrole was dissolved in 12 mL of anhydrous ethanol and magnetically stirred for 3 minutes to obtain an anhydrous ethanol solution of pyrrole. The other steps and parameters were the same as those in Example 1.

[0053] Example 4: The difference between this example and example 1 is that in step 1 (3), the pyrrole anhydrous ethanol solution is added dropwise to the phosphomolybdic acid solution, stirred at room temperature for 10 h, and then the resulting precipitate is collected by centrifugation and then dried to obtain PMo 12 @Py precursor. Other steps and parameters are the same as those in Example 1.

[0054] Example 5: The difference between this example and Example 1 is that in step 1 (3), the pyrrole anhydrous ethanol solution is added dropwise to the phosphomolybdic acid solution, stirred at room temperature for 48 hours, and then the resulting precipitate is collected by centrifugation and then dried to obtain PMo 12 @Py precursor. Other steps and parameters are the same as those in Example 1.

[0055] Comparative Example 1: The difference between this embodiment and embodiment 1 is that in step 2, PMo 12 The @Py precursor was placed in a tube furnace, and hydrogen and argon gases were introduced into the furnace. The temperature was raised to 700°C under a H2 / Ar mixed gas atmosphere and maintained at this temperature for 2 hours to obtain a Mo2C sample with a core-shell structure. The other steps and parameters were the same as in Example 1.

[0056] Comparative Example 2: The difference between this embodiment and embodiment 1 is that in step 2, PMo 12 The @Py precursor was placed in a tube furnace, and hydrogen and argon gases were introduced into the furnace. The temperature was raised to 850°C under an H2 / Ar mixed gas atmosphere and maintained for 2 hours to obtain a Mo / Mo3P heterostructure sample with a core-shell structure. Other steps and parameters were the same as in Example 1.

[0057] Figure 1 This is an SEM image of the Mo2C / Mo3P heterojunction catalyst with a core-shell structure prepared in Example 1;

[0058] Figure 1 The results show that the Mo2C / Mo3P heterojunction catalyst with a core-shell structure prepared in Example 1 is composed of uniform nanospheres with a diameter of about 30 nm.

[0059] Figure 2 HRTEM image of the Mo2C / Mo3P heterojunction catalyst with a core-shell structure prepared in Example 1;

[0060] Figure 2The results show that many nanoparticles with dark contrast and a size of about 10 nm are encapsulated in a shell composed of several layers of carbon. The internal nanoparticles are well crystallized and connected to each other through the carbon matrix. In addition, a heterogeneous interface is formed between Mo2C and Mo3P, proving that the Mo2C / Mo3P heterostructure is successfully synthesized. At the same time, two different lattice fringes can be clearly observed, with lattice spacings of 0.228nm and 0.237nm, corresponding to the (101) crystal plane of Mo2C and the (321) crystal plane of Mo3P, respectively.

[0061] Figure 3 SEM, TEM, and HRTEM images of the Mo2C catalyst prepared in Comparative Example 1;

[0062] Figure 3 The results show that the morphology and size of the Mo2C catalyst obtained by heat treatment at 700℃ are similar to those of the Mo2C / Mo3P heterojunction catalyst, with a diameter of approximately 30 nm. TEM images show that the Mo2C catalyst also has a distinct core-shell structure, with Mo2C nanoparticles of approximately 5 nm in size uniformly distributed in the carbon shell. HRTEM images show that its lattice fringes are 0.228 nm in size, corresponding to the (101) crystal plane of Mo2C.

[0063] Figure 4 The SEM, TEM and HRTEM images of the Mo / Mo3P heterojunction catalyst prepared in Comparative Example 2;

[0064] Figure 4 The results show that when the pyrolysis temperature is increased to 850 °C, the obtained Mo / Mo3P heterojunction catalyst no longer has the morphology of nanospheres, but still maintains a core-shell structure. The nanoparticles tend to aggregate, and two different lattice fringes can also be observed under HRTEM. The lattice spacing is 0.222 nm and 0.237 nm, corresponding to the (110) crystal plane of Mo and the (321) crystal plane of Mo3P, respectively.

[0065] Figure 5 XRD pattern of the Mo2C / Mo3P heterojunction catalyst with a core-shell structure prepared in Example 1;

[0066] Figure 5The results show that the broad diffraction peak of Mo2C / Mo3P at 2θ = 26° corresponds to the (002) crystal plane of carbon; and the characteristic diffraction peaks (JCPDS NO. 35-0787) are clearly displayed at 2θ = 34.4°, 38.0°, and 39.4°, corresponding to the (100), (002), and (101) crystal planes of the hexagonal β-Mo2C phase, respectively, confirming the existence of β-Mo2C. In addition, the other characteristic peaks of Mo2C / Mo3P are consistent with the standard card of Mo3P (JCPDS NO. 89-5111), indicating that Mo2C and Mo3P are successfully composited.

[0067] Figure 6 LSV plots of the Mo2C / Mo3P heterojunction catalyst with a core-shell structure prepared in Example 1 before and after 3000 CV cycles in 1M KOH electrolyte;

[0068] Figure 6 The results show that when the current density is 10 mA cm -2 The core-shell Mo2C / Mo3P heterojunction catalyst prepared in Example 1 exhibited an overpotential of only 58 mV, demonstrating good catalytic performance in alkaline solutions. Furthermore, the polarization curve after 3000 CV cycles showed a minimal negative potential shift, demonstrating the excellent cycling stability of the core-shell Mo2C / Mo3P heterojunction catalyst in alkaline media.

[0069] Figure 7 LSV plots of the Mo2C / Mo3P heterojunction catalyst with a core-shell structure prepared in Example 1 before and after 3000 CV cycles in 0.5M H2SO4 electrolyte;

[0070] Figure 7 The results show that when the current density is 10 mA cm -2 The overpotential of the core-shell Mo2C / Mo3P heterojunction catalyst was only 82 mV, demonstrating good catalytic performance in acidic solutions. Furthermore, after 3000 CV cycles, the overpotential of the LSV curve showed only a negligible increase, demonstrating the excellent cycling stability of the core-shell Mo2C / Mo3P heterojunction catalyst in acidic media.

[0071] Figure 8 LSV plots of the Mo2C / Mo3P heterojunction catalyst with a core-shell structure prepared in Example 1, the Mo2C catalyst prepared in Comparative Example 1, and the Mo / Mo3P heterojunction catalyst prepared in Comparative Example 2 in 1 M KOH electrolyte;

[0072] Figure 8The results show that in alkaline medium, when the current density is 10 mA cm -2 Under this condition, the overpotential of the Mo2C / Mo3P heterojunction catalyst with a core-shell structure is only 58mV (η 10 =58mV), which has good catalytic performance. However, the Mo2C catalyst with core-shell structure obtained by heat treatment at 700℃ and the Mo / Mo3P heterojunction catalyst with core-shell structure obtained at 850℃ both showed relatively poor HER performance. 10 is 110mV, and the η of Mo / Mo3P 10 The value of Mo3P / Mo2C heterostructure is 87 mV, indicating that the heterostructure constructed by Mo3P and Mo2C plays a key role in improving the catalytic performance of HER.

[0073] Figure 9 LSV diagrams of the Mo2C / Mo3P heterojunction catalyst with a core-shell structure prepared in Example 1, the Mo2C catalyst prepared in Comparative Example 1, and the Mo / Mo3P heterojunction catalyst prepared in Comparative Example 2 in 0.5 M H2SO4 electrolyte.

[0074] Figure 9 The results show that in acidic medium, when the current density is 10 mA cm -2 Under this condition, the overpotential of the Mo2C / Mo3P heterojunction catalyst with a core-shell structure is only 82mV (η 10 =82mV), which has good catalytic performance. However, the Mo2C catalyst with core-shell structure obtained by heat treatment at 700℃ and the Mo / Mo3P heterojunction catalyst with core-shell structure obtained at 850℃ both showed relatively poor HER performance. 10 is 150mV, and the η of Mo / Mo3P 10 The value of Mo3P / Mo2C heterostructure is 136 mV, indicating that the heterostructure constructed by Mo3P and Mo2C plays a key role in improving the catalytic performance of HER.

Claims

1. A method for preparing a Mo2C / Mo3P heterojunction catalyst having a core-shell structure, characterized in that The preparation method is specifically completed according to the following steps:

1. Preparation of PMo 12 @Py Precursor: ① Dissolve phosphomolybdic acid in deionized water and stir magnetically to obtain a phosphomolybdic acid solution; ②, dissolve pyrrole in anhydrous ethanol and stir magnetically to obtain an anhydrous ethanol solution of pyrrole; ③. Add the pyrrole anhydrous ethanol solution dropwise to the phosphomolybdic acid solution, stir at room temperature for a period of time, then collect the resulting precipitate by centrifugation, and then dry the precipitate to obtain PMo 12 @Py precursor; 2. PMo 12 The @Py precursor is placed in a tubular furnace, hydrogen and argon are introduced into the tubular furnace, and the temperature is raised to 750℃~800℃ in an H2 / Ar mixed gas atmosphere and kept warm for a period of time to obtain a Mo2C / Mo3P heterojunction catalyst with a core-shell structure.

2. The method for preparing a Mo2C / Mo3P heterojunction catalyst having a core-shell structure according to claim 1, characterized in that The mass ratio of the phosphomolybdic acid described in step 1① to the volume ratio of deionized water is (0.5g~1.5g):50mL.

3. The method for preparing a Mo2C / Mo3P heterojunction catalyst having a core-shell structure according to claim 1, characterized in that The time of magnetic stirring described in step 1① is 10min~15min; the time of magnetic stirring described in step 1② is 3min~5min.

4. The method for preparing a Mo2C / Mo3P heterojunction catalyst having a core-shell structure according to claim 1, characterized in that The volume ratio of pyrrole to anhydrous ethanol described in step 1② is (125 μL~500 μL):12 mL.

5. The method for preparing a Mo2C / Mo3P heterojunction catalyst having a core-shell structure according to claim 1, characterized in that The volume ratio of the pyrrole anhydrous ethanol solution and the phosphomolybdic acid solution described in step 1 ③ is (10mL~15mL):50mL.

6. The method for preparing a Mo2C / Mo3P heterojunction catalyst having a core-shell structure according to claim 1, characterized in that The drying temperature in step 1 (3) is 50°C to 70°C, and the drying time is 10h to 12h; the stirring time at room temperature in step 1 (3) is 10h to 48h.

7. The method for preparing a Mo2C / Mo3P heterojunction catalyst having a core-shell structure according to claim 1, characterized in that The heating rate in step 2 is 2°C / min to 5°C / min; the insulation time in step 2 is 2h to 4h.

8. The method for preparing a Mo2C / Mo3P heterojunction catalyst having a core-shell structure according to claim 1, characterized in that The volume ratio of hydrogen to argon in the H2 / Ar mixed gas described in step 2 is 1:9; the flow rate of the H2 / Ar mixed gas described in step 2 is 25 mL / min~75 mL / min.

9. Use of a Mo2C / Mo3P heterojunction catalyst having a core-shell structure prepared by the preparation method according to claim 1, characterized in that A Mo2C / Mo3P heterojunction catalyst with a core-shell structure is used in the field of hydrogen evolution by water electrolysis.

10. Use of a Mo2C / Mo3P heterojunction catalyst having a core-shell structure according to claim 9, characterized in that A core-shell Mo2C / Mo3P heterojunction catalyst exhibits excellent HER stability and catalytic activity in 1.0 mol / L KOH solution and 0.5 mol / L H2SO4 solution. -2 The overpotential at the current density is only 58mV and 82mV.

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