A hierarchical structure gallium nitride / nitrogen-doped carbon working electrode and supercapacitor thereof

Abstract

The present invention relates to a gallium nitride / nitrogen-doped carbon composite working electrode, which is prepared by the following method: 1) taking appropriate amounts of gallium nitride / nitrogen-doped carbon composite powder, acetylene black, and polyvinylidene fluoride, transferring them to an agate mortar, adding N-methylpyrrolidone dropwise, and grinding thoroughly to prepare a slurry; 2) evenly coating the slurry on a current collector, then drying it in a vacuum drying oven at 70-90°C for 10-14 hours. The gallium nitride / nitrogen-doped carbon composite working electrode is then used to assemble a CR2032-type button-type symmetrical supercapacitor. The gallium nitride / nitrogen-doped carbon composite working electrode and the corresponding capacitor exhibit excellent electrochemical performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical energy storage, and relates to a hierarchical structure gallium nitride / nitrogen-doped carbon composite working electrode and a supercapacitor thereof. Background Art

[0002] Supercapacitors, with their high specific power and high specific energy, are a type of electrochemical energy storage device between traditional dielectric capacitors and batteries (Science, 2008, 321, 651-652). The future development of supercapacitors is to increase specific energy without compromising specific power and cycle life. This requires supercapacitor electrode materials with high electrical conductivity, high ion mobility, a high ion-accessible surface area, and high electrochemical stability (Nature Communications, 2014, 5, 4554).

[0003] As a third-generation semiconductor material, gallium nitride (GaN) has been extensively studied in the field of electrochemical energy storage. To improve the electrochemical performance of GaN-based electrode materials, various methods have been developed. For example, mesoporous membranes have been prepared using electrochemical etching, nanosheets have been prepared using templates, nanowires have been prepared using chemical vapor deposition, and GaN / carbon nanowire composites have been prepared using electrosimulation. However, these methods suffer from the disadvantages of cumbersome preparation processes, difficulty in scalable mass production, small surface area of the resulting GaN-based electrode materials, and low specific interfacial energy storage capacity.

[0004] CN 112624066 A discloses a method for preparing a rod-shaped gallium nitride material. The method uses hydrated gallium nitrate and melamine as gallium and nitrogen sources, respectively, to pre-self-assemble in an aqueous solution to form a coordination complex. The dried coordination complex is then calcined in nitrogen and air, respectively, to obtain the rod-shaped gallium nitride. However, the rod-shaped gallium nitride is relatively large (25–75 μm), lacks a hierarchical structure, and has a small specific surface area, which cannot meet the requirements of high-performance supercapacitor electrode materials. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention provides a working electrode based on a hierarchical structure gallium nitride / nitrogen-doped carbon composite and a supercapacitor thereof, wherein the working electrode and the supercapacitor have excellent electrochemical properties.

[0006] A gallium nitride / nitrogen-doped carbon composite working electrode, characterized in that it is prepared by the following method:

[0007] 1) Take appropriate amounts of gallium nitride / nitrogen-doped carbon composite powder, acetylene black, and polyvinylidene fluoride, transfer them to an agate mortar, add N-methylpyrrolidone dropwise, and grind thoroughly to prepare a slurry;

[0008] 2) The slurry is evenly coated on the current collector, and then placed in a vacuum drying oven and dried at 70-90° C. for 10-14 hours to obtain a working electrode, namely a gallium nitride / nitrogen-doped carbon composite working electrode.

[0009] The gallium nitride / nitrogen-doped carbon composite working electrode, wherein the loading amount of the gallium nitride / nitrogen-doped carbon composite (active material) is 3-9 mg cm -2 .

[0010] The electrochemical performance of the gallium nitride / nitrogen-doped carbon composite working electrode is as follows: -2 Under the condition of high-pressure ionization, the electrode active material loading is 3-4 mg cm -2 When the electrode area discharge capacity is 110-310mF cm -2 .

[0011] The gallium nitride / nitrogen-doped carbon composite working electrode has an active material loading of 3–4 mg cm –2 When 1mAcm -2 At the current density, the area discharge capacity is 181~448mF cm -2 ( Figure 4 b) When the current density increases from 1 mA cm -2 Increased to 200 mA cm -2 The capacity retention rate of the electrode is 58.2-72.7% (the capacity retention rates of S-1, S-2, S-3 and S-4 electrodes are 60.8%, 58.2%, 60.3% and 69.2% respectively). -2 After 10,000 cycles, the capacity retention rate of the electrodes is close to 100% ( Figure 4 d), showing excellent electrochemical cycling stability.

[0012] When the active material loading is 7.6 mg cm –2 When 1mA cm -2 The area discharge capacity is 1076mF cm -2 , at 200mA cm -2 The area discharge capacity is 730mF cm -2 ( Figure 5 ), the capacity retention rate is 67.8%. The active material loading is 9.0 mg cm –2 When 1mA cm -2 The area discharge capacity is 1096mF cm 2 , at 200mA cm 2 The area discharge capacity is 540mF cm 2 , the capacity retention rate is 49.3%.

[0013] A symmetrical supercapacitor is characterized by being assembled using the following method:

[0014] 1) Take appropriate amounts of gallium nitride / nitrogen-doped carbon composite powder, acetylene black, and polyvinylidene fluoride, transfer them to an agate mortar, add N-methylpyrrolidone dropwise, and grind thoroughly to prepare a slurry;

[0015] 2) The slurry is evenly coated on the current collector, and then placed in a vacuum drying oven and dried at 70-90° C. for 10-14 h to obtain a working electrode.

[0016] 3) 1 mol L –1 H2SO4 was used as the electrolyte, a BH5510 sulfonated diaphragm was selected, and a CR2032 button-type symmetrical supercapacitor was assembled using the working electrode in step 2).

[0017] The supercapacitor device (single electrode active material loading of 7.6 mg cm –2 ), at 1050mAcm –2 The current density was continuously changed within the range for 20,000 cycles and then returned to 10 mA cm –2 Loop 500 times ( Figure 6 c), the device’s capacity retention is 98.1%, demonstrating excellent electrochemical cycling stability. The device has a volumetric power of 142.9 mW cm 3 When the volume specific energy is 3.89 mW h cm -3 Specific power is 7142.9mW cm -3 It still has a high volume specific energy (1.98mW h cm 3 ).

[0018] Preferably, the active material loading of the working electrode is 3–9 mg cm –2 .

[0019] Preferably, in step 1), the mass ratio of gallium nitride / nitrogen-doped carbon composite powder, acetylene black and polyvinylidene fluoride is 8:1:1.

[0020] Preferably, in step 2), the current collector is a stainless steel wire mesh.

[0021] Preferably, in step 2), the mixture is dried at 80° C. for 12 h.

[0022] Preferably, the gallium nitride / nitrogen-doped carbon composite is prepared by the following steps:

[0023] a. Grind and mix melamine and GaCl3-benzene solution in a fume hood to obtain mixture A. The molar ratio of gallium trichloride to melamine is 1:11:3.

[0024] b. Transfer mixture A to a reactor lined with graphite paper, purge oxygen with nitrogen, and seal; then transfer to a tube furnace.

[0025] c. Heat the tube furnace to 800-850°C under nitrogen protection at a heating rate of 5-10°C / min -1 , keep warm for 6-9h, and cool naturally to room temperature to obtain gallium nitride / nitrogen-doped carbon composite.

[0026] Preferably, the gallium nitride / nitrogen-doped carbon composites all have a hierarchical structure. The gallium nitride / nitrogen-doped carbon composites are primarily composed of gallium nitride micron-sized clusters (gallium nitride microclusters), which are stacked from gallium nitride nanowires with diameters of 30-70 nm. The gallium nitride microclusters form porous gallium nitride microclusters due to thermal decomposition. The gallium nitride / nitrogen-doped carbon composites have hierarchical pores with pore sizes distributed at 0.8, 1.4, 1.7, 2.8, 3.9, 7.7, and 10.8 nm.

[0027] The relative contents of gallium nitride and carbon components in the gallium nitride / nitrogen-doped carbon composite are such that the mass percentage of the carbon component in the composite is 8-14%.

[0028] Beneficial effects

[0029] The present invention provides a working electrode based on a hierarchical gallium nitride / nitrogen-doped carbon composite. The preparation method of the working electrode is simple, environmentally friendly, and easy to scale up for industrial production.

[0030] The electrode material based on hierarchical porous gallium nitride / nitrogen-doped carbon has excellent electrochemical performance, not only at a low loading of electrode active material (3–4 mg cm –2 ), and the electrode rate performance is also excellent when the active material loading is high.

[0031] The sample electrode not only has a high specific capacity at low current density, but also has good rate performance ( Figure 4 c, Table 3). When the current density is increased from 1 mA cm -2 Increased to 200 mA cm -2 , the capacity retention rates of S-1, S-2, S-3 and S-4 electrodes are 60.8%, 58.2%, 60.3% and 69.2%, respectively.

[0032] The electrode provided by the present invention has a low loading amount of active material (3-4 mg cm –2 ), and the electrode rate performance is also excellent when the active material loading is high.

[0033] Supercapacitor devices have excellent rate performance. –2 The current density was continuously changed within the range for 20,000 cycles and then returned to 10 mA cm –2 Loop 500 times ( Figure 6 c), the device’s capacity retention is 98.1%, demonstrating excellent electrochemical cycling stability. The device has a volumetric power of 142.9 mW cm -3 When the volume specific energy is 3.89 mW h cm -3 Specific power is 7142.9mW cm -3 It still has a high volume specific energy (1.98mW h cm -3 ). BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Spectra of the sample: (a) XRD; (b) Raman; (c) FT-IR; (d) electron energy spectrum N1s.

[0035] Figure 2 SEM images of samples: (a) S-1; (b) S-2; (c) S-3; (d) S-4.

[0036] Figure 3 (a) Nitrogen adsorption-desorption isotherm; (b) pore distribution curve.

[0037] Figure 4 The loading capacity is 3-4 mg cm -2 Electrochemical performance of the lower electrode: (a) CVs; (b) GCD curves; (c) rate; (d) cycling performance.

[0038] Figure 5 S-3 has a loading of 7.6 mg cm -2 Electrochemical performance of the lower electrode: (a) GCD curve; (b) rate.

[0039] Figure 6 Electrochemical performance of the S-3∥S-3 symmetric supercapacitor device: (a) CVs; (b) GCD curves; (c) cycling performance; (d) volumetric energy-to-power diagram; single-electrode active material loading of 7.6 mg cm -2 . DETAILED DESCRIPTION

[0040] The technical solution of the present invention will be further described below through specific embodiments in conjunction with the accompanying drawings. These embodiments are only for illustrating the technical solution of the present invention and cannot be regarded as limiting the content of the claims of the present invention.

[0041] Benzene and N-methylpyrrolidone in the examples were purchased from Shanghai Sinopharm Chemical Reagent Co., Ltd.; stainless steel mesh, acetylene black, and polyvinylidene fluoride were purchased from Taobao Jinghong New Energy; BH5510 sulfonated diaphragm was purchased from Shenzhen Gebang Technology Co., Ltd.; gallium trichloride was homemade by the combustion reaction of metallic gallium and chlorine.

[0042] X-ray powder diffraction (XRD) spectra were obtained by Bruker D8 Advance powder diffractometer (Germany); scanning electron microscopy (SEM) images and element distribution maps were obtained by Hitachi Regulus8220 field emission scanning electron microscope (Japan); Raman spectra were obtained by HORIBA Scientific LabRAM HR Evolution Raman spectrometer (France); infrared spectra (FT-IR) were obtained by Nicolet 10 infrared spectrometer (USA); X-ray photoelectron spectroscopy (XPS) was obtained by Fisher Scientific ESCALAB Xi + The results were obtained by X-ray photoelectron spectrometer detection; the nitrogen adsorption-desorption isotherm and pore size distribution were obtained by American Micromeritics ASAP 2460 fully automatic specific surface area and pore size analyzer detection.

[0043] The electrochemical performance of the sample electrode was measured by Shanghai Chenhua CHI760E electrochemical analyzer. The active material loading of the sample electrode was 3–9 mg cm –2 The current collector is stainless steel wire mesh, the diaphragm is BH5510 sulfonated diaphragm, and the electrolyte is 1 molL –1 H2SO4; in the three-electrode system, the counter electrode is platinum and the reference electrode is Hg / Hg2SO4.

[0044] Example 1

[0045] A hierarchical structure gallium nitride / nitrogen-doped carbon composite is prepared by the following steps:

[0046] a. Mix 1.51 g of melamine with 4 mL of 1 mol L -1 The GaCl3-benzene solution was ground and mixed in a fume hood to obtain mixture A. Benzene was used to dissolve gallium chloride for ease of use, and there was no particular limitation on the solution concentration.

[0047] b. Transfer Mix A to a stainless steel reactor lined with graphite paper, purge with nitrogen, and seal. Then, transfer the mixture to a tube furnace. The graphite paper serves as a backing to prevent direct contact between the reactants and the reactor walls.

[0048] c. Heat the tube furnace to 800°C under nitrogen protection at a heating rate of 10°C min –1, kept at 800℃ for 8h, and naturally cooled to room temperature to obtain sample S-3.

[0049] By changing the reaction conditions, samples S-1 to S-6 were obtained. The reaction conditions are shown in Table 1.

[0050] Table 1 Sample preparation conditions

[0051]

[0052] Result Analysis

[0053] Figure 1 a is the XRD pattern of the sample. Figure 1 a It can be seen that S-1 and S-2 have good crystallinity. The diffraction peaks in S-1 and S-2 correspond to the (100), (002), (101), (102), (110), (103), (200), (112) and (201) crystal planes of hexagonal GaN (PDF#50-0972), respectively. The intensity of the diffraction peak related to GaN in S-3 is significantly reduced, while the diffraction peak related to carbon (the diffraction peak at 26.4° corresponds to the (002) crystal plane of hexagonal graphite PDF#14-1487) is significantly enhanced. The diffraction peak related to GaN in S-4 almost disappears, while the carbon peak at 26.4° is clearly discernible. The above results indicate that the crystallinity of GaN gradually decreases with the extension of heat treatment time, which is attributed to the structural destruction caused by the thermal decomposition of GaN; while the relative increase in the intensity of the carbon diffraction peak is attributed to the gradual increase in the degree of graphitization of the carbon component.

[0054] Raman spectroscopy can reveal more structural information of the sample ( Figure 1 b) Raman spectrum located between 100-900 and 1000-1800 cm -1 The peaks at 145, 532, 561 and 711 cm -1 The peaks are attributed to the E2(low), A1(TO), E1(TO) and A1(LO) Raman vibration modes of GaN (Chemical Physics Letters, 2001, 345, 245-251). As the heat treatment time exceeds 7h, the characteristic Raman peaks of GaN gradually weaken, accompanied by the gradual strengthening of the Raman peak of carbon, which is consistent with the results of the sample XRD. In addition, the peaks at 580–680cm –1 The peak at is related to the lattice disorder of GaN (Semicond. Sci. Technol., 2002, 17, 1223-1225). It can be seen that as the heat treatment time exceeds 6 h, the Raman peak at this location gradually becomes obvious; this indicates that as the reaction time increases, the disorder of the GaN lattice increases.

[0055] The coexistence of GaN and carbon components in the sample can be verified by infrared spectroscopy ( Figure 1 c) FT-IR spectrum at 1574, 1400, and 1180–1215 cm –1 The peaks correspond to C=C / C=N stretching vibration, CO–H / CN–H deformation vibration and C–O / C–N stretching vibration (Applied Catalysis A: General, 2012, 439-440, 149-155.); this indicates that the carbon component in the sample is nitrogen-doped carbon. Located at 480–750 cm –1 The peak is attributed to the ω T Phonon mode (Journal of Materials Research, 2000, 15, 267-269), with the extension of heat treatment time, the peak intensity gradually weakened, which was attributed to the gradual thermal decomposition of GaN.

[0056] The coexistence of GaN and carbon components in the sample was further confirmed by XPS spectra ( Figure 1 d). The peaks at 394.25±0.15, 397.05±0.05, 398.0, 398.7±0.1, 399.8, and 401.0 eV in the N 1s spectrum are attributed to N defects, N-Ga, pyridinic N, N-Ga-O, pyrrolic N, and graphitic N components, respectively (Advanced Materials, 2016, 28, 3768-3776; Chem. Eur. J., 2015, 21, 324-330; Journal of Materials Chemistry A, 2015, 3, 21257-21268). Due to the thermal decomposition of GaN, with increasing heat treatment time, the content of GaN-related components (N-Ga, N-Ga-O) gradually decreases, while the content of carbon-related components (pyridinic N, pyrrolic N, and graphitic N) gradually increases (Table 1). Pyridinic N and pyrrolic N are different forms of nitrogen in carbon materials.

[0057] The above spectral characterization results indicate that: (1) the composite provided by the present invention is composed of gallium nitride and nitrogen-doped carbon; (2) as the heat treatment time increases, the structure of gallium nitride is gradually destroyed due to thermal decomposition, and the component content gradually decreases, while the degree of graphitization of carbon gradually increases, and the component content gradually increases. Further thermogravimetric analysis determined that the mass percentage of the carbon component in the composites of S-1, S-2, S-3, and S-4 was 8.58%, 8.72%, 9.11%, and 13.55%, respectively.

[0058] Figure 2The SEM images of the samples are shown in Figure 2. As can be seen from the figure, the samples all have a hierarchical structure. S-1 is mainly composed of GaN micron-sized clusters, which in turn are composed of nanowires ( Figure 2 a); the thinner end of the micron cluster is composed of relatively separated nanowires with a diameter of 30–70 nm, while the thicker end of the micron cluster is composed of tightly packed nanowires. The holes caused by the thermal decomposition of GaN are clearly visible in the GaN micron cluster in S-2 ( Figure 2 b). When the heat treatment time is increased to 8h, the GaN microclusters form a honeycomb structure due to thermal decomposition ( Figure 2 c); As the heat treatment time increases to 9 h, the honeycomb structure collapses and a porous stacking structure is formed ( Figure 2 d). SEM results show that the morphology of the sample can be controlled by controlling the heat treatment time.

[0059] By controlling the heat treatment time, not only the morphology and composition of the sample can be regulated, but also the texture characteristics of the sample can be regulated ( Figure 3 ). The nitrogen adsorption and desorption test results of the samples show that ( Figure 3 a), the sample contains micropores, mesopores and macropores, and with the extension of heat treatment time, the S BET Gradually increases. The pore distribution curve of the sample shows that ( Figure 3 b) The sample has hierarchical pores with pore sizes distributed at 0.8, 1.4, 1.7, 2.8, 3.9, 7.7, and 10.8 nm. As the heat treatment time increases from 6 h to 8 h, the mesopores gradually decrease, while the micropores at 1.4 nm gradually increase. When the heat treatment time increases to 9 h, the mesopores with a pore size of 2.8 nm dominate. The nitrogen adsorption and desorption results show that controlling the heat treatment time can regulate the S BET , pore distribution, and pore volume (Table 2).

[0060] Table 2 Texture characteristics of samples

[0061]

[0062]

[0063] Example 2 Preparation of sample electrodes

[0064] 1) Take appropriate amount of sample powder, acetylene black and polyvinylidene fluoride (mass ratio 8:1:1), transfer them to an agate mortar, add appropriate amount of N-methylpyrrolidone dropwise, and grind thoroughly to prepare a slurry;

[0065] 2) The slurry was evenly coated on a stainless steel mesh (current collector), and then placed in a vacuum drying oven and dried at 80° C. for 12 h to obtain a working electrode, namely a gallium nitride / nitrogen-doped carbon composite working electrode.

[0066] The sample powders are S-1, S-2, S-3, S-4, S-5 and S-6 prepared in Example 1 respectively; the obtained electrodes are correspondingly recorded as S-1, S-2, S-3, S-4, S-5 and S-6 electrodes.

[0067] The hierarchically structured porous GaN / N-doped carbon samples exhibit excellent electrochemical performance when used as supercapacitor electrode materials ( Figure 4 ). Figure 4 a is the sample electrode at 10 mV s –1 The cyclic voltammetry (CV) graph below shows that the nearly rectangular shape of the CV curve indicates that the interfacial energy storage of the sample electrode is primarily due to the electrochemical double layer (EDLC) capacitance. The redox peaks in the CV curve are attributed to the Faradaic reaction occurring on the electrode surface. The distance between the oxidation and reduction peaks is only 27-58 mV, indicating that the Faradaic reaction on the sample electrode surface is reversible.

[0068] The specific capacity of the sample electrode can be calculated from the constant current charge and discharge (GCD) curve. -2 At the current density, the electrodes of S-1, S-2, S-3 and S-4 samples (active material loading of 3–4 mg cm –2 ) have an area discharge capacity of 129, 275, 448 and 389 mF cm -2 ( Figure 4 b). The sample electrode not only has a high specific capacity at low current density, but also has good rate performance ( Figure 4 c, Table 3). When the current density is increased from 1 mA cm -2 Increased to 200 mA cm -2 The capacity retention rates of S-1, S-2, S-3 and S-4 electrodes were 60.8%, 58.2%, 60.3% and 69.2% respectively. The higher rate performance of S-1, S-2 and S-4 electrodes is attributed to the hierarchical and porous structure of the samples, while the better rate performance of S-3 electrode is attributed to its unique honeycomb structure, which is not only conducive to ion migration, but also conducive to regulating the volume expansion and contraction of the electrode during charge and discharge (Advanced Functional Materials, 2012, 22, 4634-4667). At 10 mA cm -2 After 10,000 cycles, the capacity retention rates of S-1, S-2, S-3 and S-4 electrodes are close to 100% ( Figure 4 d), showing excellent electrochemical cycling stability.

[0069] As can be seen in Table 3, S-3 exhibits the best overall performance. It should be noted that when the molar ratio of gallium trichloride to melamine is 1:1 (S-5) and 1:2 (S-6), the sample electrodes exhibit both ideal specific capacity and rate capability (Table 3). The rate capability is the ratio of the discharge capacity at a high current density to the discharge capacity at the initial low current density; a higher ratio indicates a better rate capability.

[0070] Table 3 Area discharge capacity of sample electrodes at different current densities

[0071]

[0072]

[0073] The electrode provided by the present invention has a low loading amount of active material (3-4 mg cm –2 ), and the electrode rate performance is also excellent when the active material loading is high. Taking the S-3 electrode as an example, when the active material loading is 7.6 mg cm –2 When 1mA cm -2 The area discharge capacity is 1076mF cm -2 , at 200mAcm -2 The area discharge capacity is 730mF cm -2 ( Figure 5 ), the capacity retention rate is 67.8%. The active material loading is 9.0 mg cm –2 When 1mA cm -2 The area discharge capacity is 1096mF cm -2 , at 200mA cm -2 The area discharge capacity is 540mF cm -2 , the capacity retention rate is 49.3%.

[0074] Example 3

[0075] Assembly of S-3∥S-3 symmetrical supercapacitor

[0076] 1) Take appropriate amounts of S-3 powder, acetylene black, and polyvinylidene fluoride (mass ratio 8:1:1), transfer them to an agate mortar, add appropriate amount of N-methylpyrrolidone dropwise, and grind thoroughly to prepare a slurry;

[0077] 2) The slurry was evenly coated on a stainless steel mesh (current collector), and then placed in a vacuum drying oven and dried at 80°C for 12 h to obtain a working electrode. The sample electrode active material loading was 3–9 mg cm –2 .

[0078] 3) 1 mol L–1 H2SO4 was used as the electrolyte, BH5510 sulfonated diaphragm was selected, and R2032 button-type symmetrical supercapacitor was assembled.

[0079] Result Analysis

[0080] Figure 6 a is a supercapacitor device (single electrode active material loading is 7.6 mg cm –2 ) CV graph, when the scan rate reaches 500mV s -1 , CV can still remain rectangular. Figure 6 b is the GCD curve of the device at a current density of 50 mA cm –2 The GCD curve of the device still maintains an isosceles triangle. The CV and GCD test results show that the device has excellent rate performance. –2 The current density was continuously changed within the range for 20,000 cycles and then returned to 10 mA cm –2 Loop 500 times ( Figure 6 c), the device’s capacity retention is 98.1%, showing excellent electrochemical cycling stability. The device has a volume power of 142.9 mW cm -3 When the volume specific energy is 3.89 mW h cm -3 Specific power is 7142.9mW cm -3 It still has a high volume specific energy (1.98mW h cm -3 ).

[0081] The hierarchical structure gallium nitride-based symmetrical supercapacitor provided by the present invention has better volumetric energy and specific power than TiN (Advanced Science 2016, 3, 1500299), TiN-Fe2N (Advanced Materials, 2015, 27, 4566-4571), GON@carbon cloth (Chemical Engineering Journal, 2021, 411, 128481), GaN nanowire@graphite paper (Small, 2017, 13, 1603330) and GaN mesoporous film (Advanced Materials, 2016, 28, 3768-3776) based supercapacitors reported in the literature ( Figure 6 d).

[0082] In summary, the present invention utilizes a carbon thermal reduction reaction in a closed system to prepare a hierarchical GaN / nitrogen-doped carbon composite. This composite is used as a supercapacitor electrode material and exhibits excellent area specific capacity, rate capability, and electrochemical stability. Symmetrical supercapacitors based on the hierarchical GaN / nitrogen-doped carbon composite exhibit superior volume specific energy and specific power. The hierarchical GaN / nitrogen-doped carbon composite has attractive application prospects in the field of electrochemical energy storage and fast charging.

Claims

1. A gallium nitride / nitrogen-doped carbon composite working electrode, characterized in that: Prepared by the following method: 1) Take appropriate amount of GaN / N-doped carbon composite powder, acetylene black and polyvinylidene fluoride, transfer them to an agate mortar, and add N -Methylpyrrolidone, after thorough grinding, to prepare a slurry; 2) The slurry is evenly coated on the current collector, and then placed in a vacuum drying oven and dried at 70-90 °C for 10-14 hours to obtain a working electrode; i.e., a gallium nitride / nitrogen-doped carbon composite working electrode; The preparation steps of the gallium nitride / nitrogen-doped carbon composite are as follows: a. Grind and mix melamine and GaCl3-benzene solution in a fume hood to obtain a mixture A; the molar ratio of gallium trichloride to melamine is 1:1-1:3; b The mixture A was transferred to a reactor lined with graphite paper, sealed with nitrogen purge, and then transferred to a tube furnace; c. Heat the tube furnace to 800-850°C under nitrogen protection at a rate of 5-10°C min -1 , keep warm for 6-9 hours, and cool naturally to room temperature to obtain a gallium nitride / nitrogen-doped carbon composite.

2. The gallium nitride / nitrogen-doped carbon composite working electrode according to claim 1, wherein The loading of GaN / N-doped carbon composites is 3–9 mg cm -2 .

3. The gallium nitride / nitrogen-doped carbon composite working electrode according to claim 1, wherein: The electrochemical performance of the GaN / N-doped carbon composite working electrode is shown in Figure 2 at 200 mA cm -2 Under the condition of high-pressure ionization, the electrode active material loading is 3-4 mgcm -2 When the electrode area discharge capacity is 110-310 mF cm -2 .

4. The gallium nitride / nitrogen-doped carbon composite electrode according to claim 1, wherein: The gallium nitride / nitrogen-doped carbon composite working electrode has an active material loading of 3-4 mg cm -2 At 1 mA cm -2 At the current density, the area discharge capacity is 181~448 mF cm -2 When the current density is increased from 1 mA cm -2 Increased to 200 mAcm -2 , the capacity retention rate of the electrode is 58.2~72.7%; The active material loading was 7.6 mg cm -2 At 1 mA cm -2 The area discharge capacity is 1076 mF cm -2 , at 200 mA cm -2 The area discharge capacity is 730 mF cm -2 , the capacity retention rate is 67.8%; The active material loading was 9.0 mg cm -2 At 1 mA cm -2 The area discharge capacity is 1096 mF cm -2 , at 200 mA cm -2 The area discharge capacity is 540 mF cm -2 , the capacity retention rate is 49.3%.

5. A symmetrical supercapacitor, characterized in that: Prepared by the following method: 1) Take appropriate amount of GaN / N-doped carbon composite powder, acetylene black and polyvinylidene fluoride, transfer them to an agate mortar, and add N -Methylpyrrolidone, after thorough grinding, to prepare a slurry; 2) The slurry was evenly coated on the current collector, and then placed in a vacuum drying oven at 70-90 ° C for 10-14 h to obtain a working electrode; 3) 1 mol L -1 H2SO4 was used as the electrolyte, and a BH5510 sulfonated diaphragm was selected to assemble a CR2032 button-type symmetrical supercapacitor using the working electrode from step 2; The preparation steps of the gallium nitride / nitrogen-doped carbon composite are as follows: a. Grind and mix melamine and GaCl3-benzene solution in a fume hood to obtain a mixture A; the molar ratio of gallium trichloride to melamine is 1:1-1:3; b The mixture A was transferred to a reactor lined with graphite paper, sealed with nitrogen purge, and then transferred to a tube furnace; c. Heat the tube furnace to 800-850°C under nitrogen protection at a rate of 5-10°C min -1 , keep warm for 6-9 hours, and cool naturally to room temperature to obtain a gallium nitride / nitrogen-doped carbon composite.

6. The supercapacitor according to claim 5, wherein In the range of 10–50 mA cm -2 The current density was continuously changed within the range for 20,000 cycles and then returned to 10 mA cm -2 After 500 cycles, the device's capacity remained at 98.1%; the device's volume power was 142.9 mW cm -3 When the volume specific energy is 3.89 mW h cm -3 ; Volume power ratio is 7142.9 mW cm -3 When the volume specific energy is 1.98 mW h cm -3 .

7. The working electrode according to any one of claims 1 to 4 or the supercapacitor according to any one of claims 5 to 6, characterized in that: In step 1), the mass ratio of gallium nitride / nitrogen-doped carbon composite powder, acetylene black and polyvinylidene fluoride is 8:1:

1.

8. The working electrode according to any one of claims 1 to 4 or the supercapacitor according to any one of claims 5 to 6, characterized in that: In step 2), the current collector is a stainless steel wire mesh; In step 2), the mixture was dried at 80 °C for 12 h.

9. The working electrode or supercapacitor according to claim 8, wherein The gallium nitride / nitrogen-doped carbon composites all have a hierarchical structure; the gallium nitride / nitrogen-doped carbon composites are mainly composed of gallium nitride microclusters, which are stacked by gallium nitride nanowires with a diameter of 30-70 nm. The gallium nitride microclusters form porous gallium nitride microclusters due to thermal decomposition; the gallium nitride / nitrogen-doped carbon composites have hierarchical pores with pore size distributions of 0.8, 1.4, 1.7, 2.8, 3.9, 7.7 and 10.8 nm; The relative contents of gallium nitride and carbon components in the gallium nitride / nitrogen-doped carbon composite are such that the mass percentage of the carbon component in the composite is 8-14%.

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