Monatomic metal-doped few-layer molybdenum disulfide electrocatalytic material, preparing method thereof, and method for electrocatalytic nitrogen fixation

Abstract

The present invention provides a monatomic metal-doped few-layer molybdenum disulfide electrocatalytic material, a preparing method thereof, and a method for electrocatalytic nitrogen fixation. The material has a few-layer ultra-thin and irregular flake-like microstructure with a length and a width of nanometer scale. A doping metal in the monatomic metal-doped few-layer molybdenum disulfide electrocatalytic material is dispersed in a form of single atoms. When the catalyst is used in electrochemical reduction of N.sub.2, a Faradic efficiency in selective reduction of N.sub.2 into NH.sub.4.sup.+ is 18% or above, and stability of the catalyst is better.

Claims

1. A monatomic metal-doped few-layer molybdenum disulfide electrocatalytic material, which has a few-layer ultra-thin and irregular flake-like microstructure with a length and a width of nanometer scale, and wherein the doping metal in the monatomic metal-doped few-layer molybdenum disulfide electrocatalytic material is dispersed in a form of single atoms.

2. The monatomic metal-doped few-layer molybdenum disulfide electrocatalytic material according to claim 1, wherein the monatomic metal in the monatomic metal-doped few-layer molybdenum disulfide electrocatalytic material is for non-substitute doping, and the few-layer ultra-thin and irregular flake has a length and width of 50-200 nm, a thickness of 0.5-3 nm and 1-4 layers on average.

3. The monatomic metal-doped few-layer molybdenum disulfide electrocatalytic material according to claim 1, wherein the monatomic metal comprises iron, ruthenium, platinum, palladium, and lanthanum, and a doped amount is 0.2%-3%.

4. A method for preparing the monatomic metal-doped few-layer molybdenum disulfide electrocatalytic material according to claim 1, comprising the following steps: 1) performing an ultrasonic process to flower-ball-shaped molybdenum disulfide to carry out an exfoliation, to obtain a few-layer molybdenum disulfide solution; 2) adding a nitrate hydrate of the metal to be doped to the few-layer molybdenum disulfide solution, mixing the few-layer molybdenum disulfide solution and the nitrate hydrate fully and uniformly by stirring, hydrothermally reacting for 10-12 h at 180-220 C., naturally cooling a reactor to room temperature after the reaction is completed, carrying out a post-treatment, and collecting a reaction product; and 3) ultrasonicating, centrifuging, and drying the reaction product to obtain a monatomic metal-doped few-layer molybdenum disulfide.

5. The method according to claim 4, wherein in the step 2), a molar ratio of the nitrate hydrate of the metal to be doped, based on the metal to be doped, relative to molybdenum disulfide is 0.5%-5%.

6. The method according to claim 4, wherein an ultrasonication time in the step 1) is 15-20 min, and the centrifuging in the step 3) comprises: centrifuging for 5-10 min at a low rotation speed of 3000-5000 r/min to collect a supernatant; and centrifuging the supernatant for 5-10 min at a high rotation speed of 10000-15000 r/min.

7. A method of using the monatomic metal-doped few-layer molybdenum disulfide electrocatalytic material according to claim 1, comprising: in an electrolytic cell comprising an anode tank and a cathode tank separated by a proton exchange membrane, using a monatomic metal-doped few-layer molybdenum disulfide electrocatalytic material electrode as a working electrode, using a platinum plate as an auxiliary electrode, and using a saturated calomel electrode as a reference electrode; respectively charging an anolyte solution and a catholyte solution to the electrolytic cells of the anode tank and the cathode tank; introducing N.sub.2 into the cathode tank until saturation; and then reducing the N.sub.2 at a constant potential of 0.36-0.04 V while introducing the N.sub.2 continuously.

8. The method according to claim 7, wherein the anolyte solution is a 0.05-0.2 M potassium sulfate solution, and the catholyte solution is a 0.05-0.2 M potassium chloride solution.

9. The method according to claim 7, wherein a load of the electrocatalytic material in the monatomic metal-doped few-layer molybdenum disulfide electrocatalytic material electrode is 1-2 mg/cm.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an XRD pattern of iron-doped few-layer molybdenum disulfide obtained in Example 1, showing that a main component in a synthesized material is molybdenum disulfide.

(2) FIG. 2 is an SEM image of flower-ball-shaped molybdenum disulfide synthesized in Example 1.

(3) FIG. 3(a) is TEM image of the iron-doped few-layer molybdenum disulfide.

(4) FIG. 3(b) is TEM image of the iron-doped few-layer molybdenum disulfide.

(5) FIG. 3(c) is TEM image of the iron-doped few-layer molybdenum disulfide.

(6) FIG. 3(d) is HAADF-STEM image of the iron-doped few-layer molybdenum disulfide.

(7) FIG. 3(e) is TEM image of the iron-doped few-layer molybdenum disulfide.

(8) FIG. 4(a) is an EDS spectrum of the iron-doped few-layer molybdenum disulfide, showing that iron is definitely doped onto the molybdenum disulfide.

(9) FIG. 4(b) is a table which shows the mass percentage and atomic percentage of each element present in the material.

(10) FIG. 5 is an XPS spectrum of the iron-doped few-layer molybdenum disulfide.

(11) FIG. 6 compares the nitrogen fixation performances of few-layer molybdenum disulfide doped with different doped amounts of iron.

(12) FIG. 7 shows the nitrogen fixation performances under different atmospheres of molybdenum disulfide and few-layer molybdenum disulfide doped with 1% iron.

(13) FIG. 8 shows the Faradic efficiencies in electrocatalytic reduction of N.sub.2 to NH.sub.4.sup.+ with iron-doped few-layer molybdenum disulfide at various electric potentials.

(14) FIG. 9 shows the Faradic efficiencies obtained with few-layer molybdenum disulfide doped with different metals under the same reaction conditions.

DESCRIPTION OF THE EMBODIMENTS

Example 1

(15) Preparation of Iron-Doped Few-Layer Molybdenum Disulfide Material and Electrocatalytic Reduction of N.sub.2.

(16) At room temperature, 1.236 g of ammonium molybdate tetrahydrate and 1.824 g of thiourea were sequentially added to 50 mL of distilled water and mixed uniformly by stirring for 30 min. The mixed solution was transferred to an 80 mL PTFE liner, and then the liner was placed in a reactor and heated in a constant temperature oven. The reaction temperature and time were controlled to 200 C. and 24 h respectively. After the reaction was completed, the reactor was allowed to naturally cool to room temperature. The solid reaction product was collected by centrifugation, and washed 3 times each with dilute hydrochloric acid, distilled water, and anhydrous ethanol. The washed solid product was collected by centrifugation, and dried in a vacuum oven at 80 C., to obtain a flower-ball-shaped molybdenum disulfide. The SEM image is shown in FIG. 2. FIG. 2 shows that the molybdenum disulfide has a flower-ball-shaped structure consisting of flakes.

(17) 0.1 g of the flower-ball-shaped molybdenum disulfide was added to 50 ml of distilled water, and an ultrasonic process is performed to the flower-ball-shaped molybdenum disulfide for 20 min to carry out an exfoliation.

(18) Ferric nitrate hydrate (Fe(NO.sub.3).sub.3.9H.sub.2O) was added to the solution obtained above, wherein the molar ratio of iron relative to molybdenum disulfide was controlled to 1%. Stirring with a magnetic stirrer was continued for 1 h, such that the iron added was fully mixed with molybdenum disulfide.

(19) The mixed solution thus obtained was transferred to an 80 mL PTFE liner, and then the liner was placed in a reactor and heated in a constant temperature oven. The reaction temperature and time were controlled to 200 C. and 12 h respectively. After the reaction was completed, the reactor was allowed to naturally cool to room temperature. The solid reaction product was collected by centrifugation, and washed 3 times each with dilute hydrochloric acid, distilled water, and anhydrous ethanol. The washed solid product was collected by centrifugation, and dried in a vacuum oven at 80 C.

(20) The ultrasonicated suspension was centrifuged as follows. The ultrasonicated suspension was initially centrifuged for 10 min at a low rotation speed of 5000 r/min, to obtain a supernatant. Then, the supernatant was centrifuged for 5 min at a high rotation speed of 15000 r/min, to collect the solid, which was then dried in a vacuum oven at 80 C., to obtain the iron-doped few-layer molybdenum disulfide.

(21) FIG. 1 is an XRD pattern of the iron-doped few-layer molybdenum disulfide, showing that a main component in the synthesized material is molybdenum disulfide.

(22) FIG. 3(a) shows that the material has an ultra-thin and irregular flake-like microstructure with a length and a width that are both 50-200 nm, FIG. 3(b) shows that the thickness of the few-layer ultra-thin and irregular flake is 0.5-3 nm, and FIG. 3(c) shows that the material has 1-4 layers on average. Obviously, the HAADF-STEM image of FIG. 3(d) shows that Fe on the surface is dispersed in a form of single atoms that mostly exist at a position right above the underlying Mo, that is, a position central to three sulfur atoms on the surface layer, so non-substitute doping occurs. FIG. 3(e) is TEM image of iron-doped monolayer molybdenum disulfide.

(23) FIG. 4(a) is an EDS spectrum of the iron-doped few-layer molybdenum disulfide.

(24) FIG. 4(a) shows that iron is definitely doped onto the molybdenum disulfide, FIG. 4(b) is a table which shows the mass percentage and atomic percentage of each element present in the material.

(25) FIG. 5 is an XPS spectrum of the iron-doped few-layer molybdenum disulfide, showing that iron is doped onto the molybdenum disulfide.

(26) 10 mg of the iron-doped few-layer molybdenum disulfide was weighed as a precursor, and ultrasonically dispersed in 1 mL of a mixed solution of Nafion (2 wt %) and isopropanol. Then, 150 L of the iron-doped few-layer molybdenum disulfide suspension was dripped onto the surface of a glassy carbon electrode with a surface area of 1 cm.sup.2, and dried under infrared light, to prepare a Fe-FL-MS/GC electrode having a load of catalyst of 1.5 mg/cm.sup.2.

(27) In an electrolytic cell including an anode tank and a cathode tank separated by a proton exchange membrane, an iron-doped few-layer molybdenum disulfide catalyst electrode was used as a working electrode (cathode), a platinum plate was used as an auxiliary electrode (anode), and a saturated calomel electrode was used as a reference electrode; a 0.1 M potassium sulfate solution was used as an anolyte solution, and a 0.1 M potassium chloride solution was used as a catholyte solution; N.sub.2 was bubbled into the cathode tank until saturation was reached; and the N.sub.2 was then reduced into NH.sub.4.sup.+ at a constant potential of 0.16 V while the N.sub.2 was introduced continuously, wherein the Faradic efficiency was 11.73%.

(28) FIG. 6 compares the nitrogen fixation performances of few-layer molybdenum disulfide doped with different doped amounts of iron, wherein the doped amount is the doped amount of raw material.

(29) FIG. 7 shows the nitrogen fixation performances under different atmospheres of few-layer molybdenum disulfide and few-layer molybdenum disulfide doped with 1% Fe at 0.16 V; and the argon atmosphere is realized by introducing argon into the electrolyte solution. Since the electrolyte solution has an amount of nitrogen dissolved therein, a trace amount of ammonia can be detected after electrolytic reduction. Except that the gas introduced into the electrolyte solution is replaced with nitrogen, the experimental conditions under the nitrogen and the argon atmosphere are basically the same.

(30) FIG. 8 shows the Faradic efficiencies in electrocatalytic reduction of N.sub.2 to NH.sub.4.sup.+ with iron-doped few-layer molybdenum disulfide at various electric potentials (0.36-0.04 V). FIG. 8 shows that the optimum electric potential is 0.16 V (relative to standard hydrogen electrode).

Example 2

(31) Preparation of Iron-Doped Few-Layer Molybdenum Disulfide Material and Electrocatalytic Reduction of N.sub.2.

(32) At room temperature, 1.236 g of ammonium molybdate tetrahydrate and 1.824 g of thiourea were sequentially added to 50 mL of distilled water and mixed uniformly by stirring for 30 min. The mixed solution was transferred to an 80 mL PTFE liner, and then the liner was placed in a reactor and heated in a constant temperature oven. The reaction temperature and time were controlled to 200 C. and 22 h respectively. After the reaction was completed, the reactor was allowed to naturally cool to room temperature. The solid reaction product was collected by centrifugation, and washed 3 times each with dilute hydrochloric acid, distilled water, and anhydrous ethanol. The washed solid product was collected by centrifugation, and dried in a vacuum oven at 80 C., to obtain a flower-ball-shaped molybdenum disulfide.

(33) 0.1 g of the flower-ball-shaped molybdenum disulfide was added to 50 ml of distilled water, and an ultrasonic process is performed to the flower-ball-shaped molybdenum disulfide for 20 min to carry out an exfoliation.

(34) Ferric nitrate hydrate was added to the solution obtained above, wherein the molar ratio of iron relative to molybdenum disulfide was controlled to 1%. Stirring with a magnetic stirrer was continued for 1 h, such that the iron added was fully mixed with molybdenum disulfide.

(35) The mixed solution thus obtained was transferred to an 80 mL PTFE liner, and then the liner was placed in a reactor and heated in a constant temperature oven. The reaction temperature and time were controlled to 200 C. and 10 h respectively. After the reaction was completed, the reactor was allowed to naturally cool to room temperature. The solid reaction product was collected by centrifugation, and washed 3 times each with dilute hydrochloric acid, distilled water, and anhydrous ethanol. The washed solid product was collected by centrifugation, and dried in a vacuum oven at 80 C.

(36) The ultrasonicated suspension was centrifuged as follows. The ultrasonicated suspension was initially centrifuged for 8 min at a low rotation speed of 4000 r/min, to obtain a supernatant. Then, the supernatant was centrifuged for 5 min at a high rotation speed of 12000 r/min, to collect a solid, which was then dried in a vacuum oven at 80 C., to obtain an iron-doped few-layer molybdenum disulfide. As characterized by XRD, TEM, and HAADF-STEM, the material has an ultra-thin and irregular flake-like microstructure with a length and a width that are both 50-200 nm, the thickness of the few-layer ultra-thin and irregular flake is 0.5-3 nm, and the material has 1-4 layers on average over the thickness. Fe on the surface is dispersed in a form of single atoms that mostly exist at a position right above the underlying Mo, that is, a position central to three sulfur atoms on the surface layer, so non-substitute doping occurs.

(37) 10 mg of iron-doped few-layer molybdenum disulfide was weighed as a precursor, and ultrasonically dispersed in 1 mL of a mixed solution of Nafion (2 wt %) and isopropanol. Then, 200 L of the iron-doped few-layer molybdenum disulfide suspension was dripped onto the surface of a glassy carbon electrode with a surface area of 1 cm.sup.2, and dried under infrared light, to prepare a Fe-FL-MS/GC electrode having a load of catalyst of 2 mg/cm.sup.2.

(38) In an electrolytic cell including an anode tank and a cathode tank separated by a proton exchange membrane, an iron-doped few-layer molybdenum disulfide catalyst electrode was used as a working electrode (cathode), a platinum plate was used as an auxiliary electrode (anode), and a saturated calomel electrode was used as a reference electrode; a 0.1 M potassium sulfate solution was used as an anolyte solution, and a 0.1 M potassium chloride solution was used as a catholyte solution; N.sub.2 was introduced into the cathode tank until saturation was reached; and the N.sub.2 was then reduced into NH.sub.4.sup.+ at a constant potential of 0.16 V while the N.sub.2 was introduced continuously, wherein the Faradic efficiency was 11.7%.

Example 3

(39) Preparation of Iron-Doped Few-Layer Molybdenum Disulfide Material and Electrocatalytic Reduction of N.sub.2.

(40) At room temperature, 1.236 g of ammonium molybdate tetrahydrate and 1.824 g of thiourea were sequentially added to 50 mL of distilled water and mixed uniformly by stirring for 30 min. The mixed solution was transferred to an 80 mL PTFE liner, and then the liner was placed in a reactor and heated in a constant temperature oven. The reaction temperature and time were controlled to 180 C. and 24 h respectively. After the reaction was completed, the reactor was allowed to naturally cool to room temperature. The solid reaction product was collected by centrifugation, and washed 3 times each with dilute hydrochloric acid, distilled water, and anhydrous ethanol. The washed solid product was collected by centrifugation, and dried in a vacuum oven at 80 C., to obtain a flower-ball-shaped molybdenum disulfide.

(41) 0.1 g of the flower-ball-shaped molybdenum disulfide was added to 50 ml of distilled water, and an ultrasonic process is performed to the flower-ball-shaped molybdenum disulfide for 20 min to carry out an exfoliation.

(42) Ferric nitrate hydrate was added to the solution obtained above, wherein the molar ratio of iron relative to molybdenum disulfide was controlled to 1%. Stirring with a magnetic stirrer was continued for 1 h, such that the iron added was fully mixed with molybdenum disulfide.

(43) The mixed solution thus obtained was transferred to an 80 mL PTFE liner, and then the liner was placed in a reactor and heated in a constant temperature oven. The reaction temperature and time were controlled to 180 C. and 12 h respectively. After the reaction was completed, the reactor was allowed to naturally cool to room temperature. The solid reaction product was collected by centrifugation, and washed 3 times each with dilute hydrochloric acid, distilled water, and anhydrous ethanol. The washed solid product was collected by centrifugation, and dried in a vacuum oven at 80 C.

(44) The ultrasonicated suspension was centrifuged as follows. The ultrasonicated suspension was initially centrifuged for 10 min at a low rotation speed of 3000 r/min, to obtain a supernatant. Then, the supernatant was centrifuged for 8 min at a high rotation speed of 10000 r/min, to collect a solid, which was then dried in a vacuum oven at 80 C., to obtain an iron-doped few-layer molybdenum disulfide. As characterized by XRD, TEM, and HAADF-STEM, the material has an ultra-thin and irregular flake-like microstructure with a length and a width that are both 50-200 nm, the thickness of the few-layer ultra-thin and irregular flake is 0.5-3 nm, and the material has 1-4 layers on average over the thickness. Fe on the surface is dispersed in a form of single atoms that mostly exist at a position right above the underlying Mo, that is, a position central to three sulfur atoms on the surface layer, so non-substitute doping occurs.

(45) 10 mg of iron-doped few-layer molybdenum disulfide was weighed as a precursor, and ultrasonically dispersed in 1 mL of a mixed solution of Nafion (2 wt %) and isopropanol. Then, 100 L of the iron-doped few-layer molybdenum disulfide suspension was dripped onto the surface of a glassy carbon electrode with a surface area of 1 cm.sup.2, and dried under infrared light, to prepare a Fe-FL-MS/GC electrode having a load of catalyst of 1 mg/cm.sup.2.

(46) In an electrolytic cell including an anode tank and a cathode tank separated by a proton exchange membrane, an iron-doped few-layer molybdenum disulfide catalyst electrode was used as a working electrode (cathode), a platinum plate was used as an auxiliary electrode (anode), and a saturated calomel electrode was used as a reference electrode; a 0.1 M potassium sulfate solution was used as an anolyte solution, and a 0.1 M potassium chloride solution was used as a catholyte solution; N.sub.2 was introduced into the cathode tank until saturation was reached; and the N.sub.2 was then reduced into NH.sub.4.sup.+ at a constant potential of 0.16 V while the N.sub.2 was introduced continuously, wherein the current efficiency was 11.65%.

Example 4

(47) Electrocatalytic Reduction of N.sub.2 with Lanthanum-Doped Few-Layer Molybdenum Disulfide.

(48) At room temperature, 1.236 g of ammonium molybdate tetrahydrate and 1.824 g of thiourea were sequentially added to 50 mL of distilled water and mixed uniformly by stirring for 30 min. The mixed solution was transferred to an 80 mL PTFE liner, and then the liner was placed in a reactor and heated in a constant temperature oven. The reaction temperature and time were controlled to 200 C. and 24 h respectively. After the reaction was completed, the reactor was allowed to naturally cool to room temperature. The solid reaction product was collected by centrifugation, and washed 3 times each with dilute hydrochloric acid, distilled water, and anhydrous ethanol. The washed solid product was collected by centrifugation, and dried in a vacuum oven at 80 C., to obtain a flower-ball-shaped molybdenum disulfide.

(49) 0.1 g of the flower-ball-shaped molybdenum disulfide was added to 50 ml of distilled water, and an ultrasonic process is performed to the flower-ball-shaped molybdenum disulfide for 20 min to carry out an exfoliation.

(50) Lanthanum nitrate hydrate was added to the solution obtained above, wherein the molar ratio of lanthanum relative to molybdenum disulfide was controlled to 1%. Stirring with a magnetic stirrer was continued for 1 h, such that the lanthanum added was fully mixed with molybdenum disulfide.

(51) The mixed solution thus obtained was transferred to an 80 mL PTFE liner, and then the liner was placed in a reactor and heated in a constant temperature oven. The reaction temperature and time were controlled to 200 C. and 12 h respectively. After the reaction was completed, the reactor was allowed to naturally cool to room temperature. The solid reaction product was collected by centrifugation, and washed 3 times each with dilute hydrochloric acid, distilled water, and anhydrous ethanol. The washed solid product was collected by centrifugation, and dried in a vacuum oven at 80 C.

(52) The ultrasonicated suspension was centrifuged as follows. The ultrasonicated suspension was initially centrifuged for 10 min at a low rotation speed of 5000 r/min, to obtain a supernatant. Then, the supernatant was centrifuged for 5 min at a high rotation speed of 15000 r/min, to collect a solid, which was then dried in a vacuum oven at 80 C., to obtain a lanthanum-doped few-layer molybdenum disulfide.

(53) 10 mg of lanthanum-doped few-layer molybdenum disulfide was weighed as a precursor, and ultrasonically dispersed in 1 mL of a mixed solution of Nafion (2 wt %) and isopropanol. Then, 150 L of the lanthanum-doped few-layer molybdenum disulfide suspension was dripped onto the surface of a glassy carbon electrode with a surface area of 1 cm.sup.2, and dried under infrared light, to prepare a La-FL-MS/GC electrode having a load of catalyst of 1.5 mg/cm.sup.2.

(54) In an electrolytic cell including an anode tank and a cathode tank separated by a proton exchange membrane, a lanthanum-doped few-layer molybdenum disulfide catalyst electrode was used as a working electrode (cathode), a platinum plate was used as an auxiliary electrode (anode), and a saturated calomel electrode was used as a reference electrode; a 0.1 M potassium sulfate solution was used as an anolyte solution, and a 0.1 M potassium chloride solution was used as a catholyte solution; N.sub.2 was introduced into the cathode tank until saturation was reached; and the N.sub.2 was then reduced into NH.sub.4.sup.+ at a constant potential of 0.16 V while the N.sub.2 was introduced continuously, wherein the Faradic efficiency was 18.15%.

Example 5

(55) Electrocatalytic Reduction of N.sub.2 with Platinum-Doped Few-Layer Molybdenum Disulfide.

(56) At room temperature, 1.236 g of ammonium molybdate tetrahydrate and 1.824 g of thiourea were sequentially added to 50 mL of distilled water and mixed uniformly by stirring for 30 min. The mixed solution was transferred to an 80 mL PTFE liner, and then the liner was placed in a reactor and heated in a constant temperature oven. The reaction temperature and time were controlled to 200 C. and 24 h respectively. After the reaction was completed, the reactor was allowed to naturally cool to room temperature. The solid reaction product was collected by centrifugation, and washed 3 times each with dilute hydrochloric acid, distilled water, and anhydrous ethanol. The washed solid product was collected by centrifugation, and dried in a vacuum oven at 80 C., to obtain a flower-ball-shaped molybdenum disulfide.

(57) 0.1 g of the flower-ball-shaped molybdenum disulfide was added to 50 ml of distilled water, and an ultrasonic process is performed to the flower-ball-shaped molybdenum disulfide for 20 min to carry out an exfoliation.

(58) Platinum nitrate was added to the solution obtained above, wherein the molar ratio of platinum relative to molybdenum disulfide was controlled to 1%. Stirring with a magnetic stirrer was continued for 1 h, such that the platinum added was fully mixed with molybdenum disulfide.

(59) The mixed solution thus obtained was transferred to an 80 mL PTFE liner, and then the liner was placed in a reactor and heated in a constant temperature oven. The reaction temperature and time were controlled to 200 C. and 12 h respectively. After the reaction was completed, the reactor was allowed to naturally cool to room temperature. The solid reaction product was collected by centrifugation, and washed 3 times each with dilute hydrochloric acid, distilled water, and anhydrous ethanol. The washed solid product was collected by centrifugation, and dried in a vacuum oven at 80 C.

(60) The ultrasonicated suspension was centrifuged as follows. The ultrasonicated suspension was initially centrifuged for 10 min at a low rotation speed of 5000 r/min, to obtain a supernatant. Then, the supernatant was centrifuged for 5 min at a high rotation speed of 15000 r/min, to collect a solid, which was then dried in a vacuum oven at 80 C., to obtain a platinum-doped few-layer molybdenum disulfide.

(61) 10 mg of platinum-doped few-layer molybdenum disulfide was weighed as a precursor, and ultrasonically dispersed in 1 mL of a mixed solution of Nafion (2 wt %) and isopropanol. 150 L of the platinum-doped few-layer molybdenum disulfide suspension was dripped onto the surface of a glassy carbon electrode with a surface area of 1 cm.sup.2, and dried under infrared light, to prepare a Pt-FL-MS/GC electrode having a load of catalyst of 1.5 mg/cm.sup.2.

(62) In an electrolytic cell including an anode tank and a cathode tank separated by a proton exchange membrane, a platinum-doped few-layer molybdenum disulfide catalyst electrode was used as a working electrode (cathode), a platinum plate was used as an auxiliary electrode (anode), and a saturated calomel electrode was used as a reference electrode; a 0.1 M potassium sulfate solution was used as an anolyte solution, and a 0.1 M potassium chloride solution was used as a catholyte solution; N.sub.2 was introduced into the cathode tank until saturation was reached; and the N.sub.2 was then reduced into NH.sub.4.sup.+ at a constant potential of 0.16 V while the N.sub.2 was introduced continuously, wherein the Faradic efficiency was 8%.

Example 6

(63) Electrocatalytic Reduction of N.sub.2 with Palladium-Doped Few-Layer Molybdenum Disulfide.

(64) At room temperature, 1.236 g of ammonium molybdate tetrahydrate and 1.824 g of thiourea were sequentially added to 50 mL of distilled water and mixed uniformly by stirring for 30 min. The mixed solution was transferred to an 80 mL PTFE liner, and then the liner was placed in a reactor and heated in a constant temperature oven. The reaction temperature and time were controlled to 200 C. and 24 h respectively. After the reaction was completed, the reactor was allowed to naturally cool to room temperature. The solid reaction product was collected by centrifugation, and washed 3 times each with dilute hydrochloric acid, distilled water, and anhydrous ethanol. The washed solid product was collected by centrifugation, and dried in a vacuum oven at 80 C., to obtain a flower-ball-shaped molybdenum disulfide.

(65) 0.1 g of the flower-ball-shaped molybdenum disulfide was added to 50 ml of distilled water, and an ultrasonic process is performed to the flower-ball-shaped molybdenum disulfide for 20 min to carry out an exfoliation.

(66) Palladium nitrate hydrate was added to the solution obtained above, wherein the molar ratio of palladium relative to molybdenum disulfide was controlled to 1%. Stirring with a magnetic stirrer was continued for 1 h, such that the palladium added was fully mixed with molybdenum disulfide.

(67) The mixed solution thus obtained was transferred to an 80 mL PTFE liner, and then the liner was placed in a reactor and heated in a constant temperature oven. The reaction temperature and time were controlled to 200 C. and 12 h respectively. After the reaction was completed, the reactor was allowed to naturally cool to room temperature. The solid reaction product was collected by centrifugation, and washed 3 times each with dilute hydrochloric acid, distilled water, and anhydrous ethanol. The washed solid product was collected by centrifugation, and dried in a vacuum oven at 80 C.

(68) The ultrasonicated suspension was centrifuged as follows. The ultrasonicated suspension was initially centrifuged for 10 min at a low rotation speed of 5000 r/min, to obtain a supernatant. Then, the supernatant was centrifuged for 5 min at a high rotation speed of 15000 r/min, to collect a solid, which was then dried in a vacuum oven at 80 C., to obtain a palladium-doped few-layer molybdenum disulfide.

(69) 10 mg of palladium-doped few-layer molybdenum disulfide was weighed as a precursor, and ultrasonically dispersed in 1 mL of a mixed solution of Nafion (2 wt %) and isopropanol. 150 L of the palladium-doped few-layer molybdenum disulfide suspension was dripped onto the surface of a glassy carbon electrode with a surface area of 1 cm.sup.2, and dried under infrared light, to prepare a Pd-FL-MS/GC electrode having a load of catalyst of 1.5 mg/cm.sup.2. In an electrolytic cell including an anode tank and a cathode tank separated by a proton exchange membrane, a palladium-doped few-layer molybdenum disulfide catalyst electrode was used as a working electrode (cathode), a platinum plate was used as an auxiliary electrode (anode), and a saturated calomel electrode was used as a reference electrode; a 0.1 M potassium sulfate solution was used as an anolyte solution, and a 0.1 M potassium chloride solution was used as a catholyte solution; N.sub.2 was introduced into the cathode tank until saturation was reached; and the N.sub.2 was then reduced into NH.sub.4.sup.+ at a constant potential of 0.16 V while the N.sub.2 was introduced continuously, wherein the Faradic efficiency was 4.35%.

Example 7

(70) Electrocatalytic Reduction of N.sub.2 with Ruthenium-Doped Few-Layer Molybdenum Disulfide.

(71) At room temperature, 1.236 g of ammonium molybdate tetrahydrate and 1.824 g of thiourea were sequentially added to 50 mL of distilled water and mixed uniformly by stirring for 30 min. The mixed solution was transferred to an 80 mL PTFE liner, and then the liner was placed in a reactor and heated in a constant temperature oven. The reaction temperature and time were controlled to 200 C. and 24 h respectively. After the reaction was completed, the reactor was allowed to naturally cool to room temperature. The solid reaction product was collected by centrifugation, and washed 3 times each with dilute hydrochloric acid, distilled water, and anhydrous ethanol. The washed solid product was collected by centrifugation, and dried in a vacuum oven at 80 C., to obtain a flower-ball-shaped molybdenum disulfide.

(72) 0.1 g of the flower-ball-shaped molybdenum disulfide was added to 50 ml of distilled water, and an ultrasonic process is performed to the flower-ball-shaped molybdenum disulfide for 20 min to carry out an exfoliation.

(73) Ruthenium nitrate hydrate was added to the solution obtained above, wherein the molar ratio of ruthenium relative to molybdenum disulfide was controlled to 1%. Stirring with a magnetic stirrer was continued for 1 h, such that the ruthenium added was fully mixed with molybdenum disulfide.

(74) The mixed solution thus obtained was transferred to an 80 mL PTFE liner, and then the liner was placed in a reactor and heated in a constant temperature oven. The reaction temperature and time were controlled to 200 C. and 12 h respectively. After the reaction was completed, the reactor was allowed to naturally cool to room temperature. The solid reaction product was collected by centrifugation, and washed 3 times each with dilute hydrochloric acid, distilled water, and anhydrous ethanol. The washed solid product was collected by centrifugation, and dried in a vacuum oven at 80 C.

(75) The ultrasonicated suspension was centrifuged as follows. The ultrasonicated suspension was initially centrifuged for 10 min at a low rotation speed of 5000 r/min, to obtain a supernatant. Then, the supernatant was centrifuged for 5 min at a high rotation speed of 15000 r/min, to collect a solid, which was then dried in a vacuum oven at 80 C., to obtain a ruthenium-doped few-layer molybdenum disulfide.

(76) 10 mg of ruthenium-doped few-layer molybdenum disulfide was weighed as a precursor, and ultrasonically dispersed in 1 mL of a mixed solution of Nafion (2 wt %) and isopropanol. 150 L of the ruthenium-doped few-layer molybdenum disulfide suspension was dripped onto the surface of a glassy carbon electrode with a surface area of 1 cm.sup.2, and dried under infrared light, to prepare a Ru-FL-MS/GC electrode having a load of catalyst of 1.5 mg/cm.sup.2.

(77) In an electrolytic cell including an anode tank and a cathode tank separated by a proton exchange membrane, a ruthenium-doped few-layer molybdenum disulfide catalyst electrode was used as a working electrode (cathode), a platinum plate was used as an auxiliary electrode (anode), and a saturated calomel electrode was used as a reference electrode; a 0.1 M potassium sulfate solution was used as an anolyte solution, and a 0.1 M potassium chloride solution was used as a catholyte solution; N.sub.2 was introduced into the cathode tank until saturation was reached; and the N.sub.2 was then reduced into NH.sub.4.sup.+ at a constant potential of 0.16 V while the N.sub.2 was introduced continuously, wherein the Faradic efficiency was 0.75%.