Low-platinum catalyst based on nitride nanoparticles and preparation method thereof

Abstract

The present invention discloses a low-platinum catalyst based on nitride nanoparticles and a preparation method thereof. A component of an active metal of the catalyst directly clades on a surface of nitride particles or a surface of nitride particles loaded on a carbon support in an ultrathin atomic layer form. Preparation steps including: preparing a transition-metal ammonia complex first, nitriding the obtained ammonia complex solid under an atmosphere of ammonia gas to obtain nitride nanoparticles; loading the nitride nanoparticles on a surface of a working electrode, depositing an active component on a surface of the nitride nanoparticles by pulsed deposition, to obtain the low platinum loading catalyst using a nitride as a substrate. The catalyst may be used as an anode or a cathode catalyst of a low temperature fuel cell, has very high catalytic activity and stability, can greatly reduce a usage amount of a precious metal in the fuel cell, and greatly reduces a cost of the fuel cell. The present invention has important characteristics of being controllable in deposition amount, simple and convenient to operate, free of protection of inert atmosphere, and etc., and is suitable for large-scale industrial production.

Claims

1. A low-platinum catalyst based on transition-metal nitride nanoparticles, comprising: an active component, wherein the active component of the catalyst is transition-metal nitride nanoparticles with an atomic layer cladding of an active metal, and the active metal cladding on a surface of a transition metal nitride serves as a substrate in an ultrathin atomic layer form; wherein the transition metal nitride serves as the substrate and comprises a unary, a binary or a ternary transition metal nitride, an average particle size of the nanoparticles being 5-15 nm; and a mass composition of the catalyst is as follows: the transition metal nitride is 10%-40%, and a component of the active metal is 4%-10%, wherein the low-platinum catalyst based on transition-metal nitride nanoparticles is prepared by the following steps: (1) a preparation of the transition-metal nitride nanoparticles: dissolving one or more transition metal compounds in a non-aqueous solvent, then introducing ammonia gas for 0.5-1 hour, evaporating the solvent at 50-90° C. in a vacuum drying oven to obtain a transition-metal ammonia complex; high temperature nitriding the transition-metal ammonia complex in ammonia gas atmosphere for 3-5 hours to prepare transition-metal nitride nanoparticles; the transition-metal ammonia complex includes an ammonia complex formed by any one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo or Ta, or a binary or ternary ammonia complex formed by two or more of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo or Ta; a temperature of the high temperature nitriding is 500-900° C.; the prepared transition-metal nitride nanoparticle has a diameter of 5-15 nm; the non-aqueous solvent is an alcohol, or a mixture formed by the alcohol with a ketone or an ester; the transition metal compound comprises titanium tetrachloride, tetrabutyl titanate, chromium acetate, manganese chloride, ferric nitrate, cobaltous acetate, copper chloride, niobium chloride, molybdenum chloride or tantalum chloride; (2) a fabrication of a working electrode for a pulse electrodeposition, utilizing a method A or a method B as follows: the method A: weighing an appropriate amount of the transition-metal nitride nanoparticles to add into 1-5 mL of an alcoholic solution containing an adhesive, ultrasonically dispersing to make into a slurry, using a micropipette to take an appropriate amount of the slurry to uniformly coat a surface of a working electrode substrate used, a final loading amount of a catalyst substrate material is 0.1-0.5 mg/cm2, and the working electrode for the pulse electrodeposition is obtained after drying; the adhesive comprises a polytetrafluoroethylene emulsion, a fluorocarbon resin emulsion or a perfluorosulfonate resin emulsion, a mass percent of a usage amount of the adhesive accounts for 0.5%-20% of a total amount of the catalyst substrate material based on a dry polymer resin; the alcoholic solution comprises ethanol, isopropanol or ethylene glycol; the working electrode substrate comprises a glassy carbon, a nickel foam, a titanium sheet, a platinum plated titanium sheet or a platinum sheet; and the drying comprises drying by natural air-drying, radiation drying under infrared light or drying by putting into an oven; or the method B: directly adding the transition-metal nitride nanoparticles that are used as the substrate material into a cathode electrolyte solution containing a required active metal for the pulse electrodeposition, stirring, forming the working electrode by a continuous contact of the particles with a cathode conductor; and a catholyte and an anolyte are isolated using a microporous medium; and (3) the pulse electrodeposition: placing the fabricated working electrode into 0.1-0.5 M H.sub.2SO.sub.4 solution saturated with nitrogen, scanning from an open-circuit voltage to −0.25-0 V at a scan speed of 5-50 mV/s, with a number of scanning laps of 10-50 laps, achieving cleanness and an activating treatment of the substrate material; then transferring the electrode into a nitrogen saturated electrodepositing solution containing a salt of the required active metal, a complexing agent and a conductive aid under an atmosphere of nitrogen, connecting an auxiliary electrode with a reference electrode; setting a pulse frequency, a number of times of pulse deposition, a conduction time and a disconnection time, then opening a pulse electrodeposition program, washing the catalyst out from the surface of the electrode when the electrodeposition is completed to obtain the low-platinum catalyst based on the transition-metal nitride nanoparticles, wherein the ultrathin atomic layer is composed of 1-5 atomic layers.

2. The low-platinum catalyst according to claim 1, wherein the transition metal nitride comprises one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo or Ta, or the transition metal nitride comprises binary and ternary transition metal nitrides consisting of two or more of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo or Ta.

3. The low-platinum catalyst according to claim 1, wherein a specific preparation process of the transition-metal ammonia complex of the step (1) is as follows: adding a transition metal precursor into a beaker containing the non-aqueous solvent, transferring into a Meng washing bottle after dissolving of the transition metal precursor is completed, introducing ammonia gas for complexation, with a gas flow of ammonia gas being controlled as 30-100 ml/min, and an introducing time of 0.5-1 hour; transferring an obtained mixture containing a complex into a crucible, vacuum drying in the oven at 50-90° C. for 8-24 hours to obtain the transition-metal ammonia complex; wherein the transition metal precursor comprises one or two or three of titanium tetrachloride, tetrabutyl titanate, cobaltous acetate, ferric nitrate, copper chloride, chromium acetate, manganese chloride, niobium chloride, molybdenum chloride or tantalum chloride; and a concentration range of the transition metal precursor in a reaction system solution is 0.1-3 mg/mL.

4. The low-platinum catalyst according to claim 3, wherein the transition metal nitride comprises one of Ti, V, Cr, Mn, Fe, Co, Ni Cu, Nb, Mo or Ta, or the transition metal nitride comprises binary and ternary transition metal nitrides consisting of two or more of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo or Ta.

5. The low-platinum catalyst according to claim 1, wherein in the step (3), the active metal comprises one or more of Pt, Au, Pd, Ru and Ir; a salt of the active metal comprises one or more of tetraammineplatinum chloride monohydrate, chloroplatinic acid, chloroauric acid, palladium dichloride, ruthenium trichloride and iridous chloride; the complexing agent comprises citric acid, EDTA or polyvinylpyrrolidone; the conductive aid is sodium sulfate or potassium sulfate; and a concentration of a component of the active metal in the electrodepositing solution is 5-100 mM.

6. The low-platinum catalyst according to claim 5, wherein the transition metal nitride comprises one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo or Ta, or the transition metal nitride comprises binary and ternary transition metal nitrides consisting of two or more of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo or Ta.

7. The low-platinum catalyst according to claim 1, wherein a way of deposition of the active metal adopted in the step (3) is the pulse electrodeposition, the pulse frequency is 100-10000 s.sup.−1, each pulse contains a turn-on time and a turn-off time, the turn-on time (t.sub.on) is 0.00003 s to 0.001 s, the turn-off time (t.sub.off) is 0.00015-0.01 s, a ratio of the turn-on time to the turn-off time (t.sub.on/t.sub.off) varies depending on a molar concentration of the active metal in an electrolyte and the loading amount of the active metal required, with a value between 0.1 and 100; and a total pulse number is 500-20000.

8. The low-platinum catalyst according to claim 7, wherein the transition metal nitride comprises one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo or Ta, or the transition metal nitride comprises binary and ternary transition metal nitrides consisting of two or more of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo or Ta.

9. The low-platinum catalyst according to claim 1, wherein a pulse current density of the pulse electrodeposition in the step (3) is 1-50 mA/cm.sup.2.

10. The low-platinum catalyst according to claim 9, wherein the transition metal nitride comprises one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo or Ta, or the transition metal nitride comprises binary and ternary transition metal nitrides consisting of two or more of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo or Ta.

11. The low-platinum catalyst according to claim 1, wherein the non-aqueous solvent comprises an ethanol solution or an isopropanol solution.

12. The low-platinum catalyst according to claim 11, wherein the transition metal nitride comprises one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo or Ta, or the transition metal nitride comprises binary and ternary transition metal nitrides consisting of two or more of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo or Ta.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a TEM image of titanium nitride prepared in Embodiment 1.

(2) FIG. 2 is a TEM image of Pt@TiN prepared in Embodiment 1.

(3) FIG. 3 is transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HR-TEM) images of Pt@TiNiN prepared in Embodiment 2.

(4) FIG. 4 is polarization curves of oxygen reduction of Embodiment 1, Embodiment 2 and a commercial Pt/C catalyst in the case of a same Pt loading amount.

(5) FIG. 5 is a histogram comparing mass activities of Embodiment 1, Embodiment 2 and a commercial Pt/C for oxygen reduction catalysis.

(6) FIG. 6 is a curve chart of performances of Embodiment 1, Embodiment 2 and a commercial Pt/C for methanol oxidation.

(7) FIG. 7 is a comparison chart of change in electrochemically active surface area (ECSA) of Embodiment 1, Embodiment 2 and a commercial Pt/C, cyclically scanned at room temperature in 0.5 M H.sub.2SO.sub.4.

(8) FIG. 8 is a histogram comparing methanol oxidation performances of Embodiment 1, Embodiment 2 and a commercial Pt/C.

(9) FIG. 9 is a (TEM) image of carbon nanotubes-supported titanium nitride (TiN/CNTs) synthesized in Embodiment 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(10) The present invention is further described below in combination with accompanying drawing and embodiments. The embodiments below are just for illustrating the present invention more clearly, but the scope of protection claimed by the present invention is not limited to the scope expressed by the below embodiments, and solutions and effects described in the content of the present invention all can be realized with reference to examples as follows.

Embodiment 1: Pt@TiN Catalyst

(11) (1) Preparation of TiN Nanoparticles Used as a Substrate

(12) In a fuming hood, 60 mL of absolute anhydrous ethanol was added into a Meng washing bottle, and then 2 mL of TiCl.sub.4 was added. After uniformly shocked (stirred), dry ammonia gas was introduced until a number of a formed precipitate did not increase and there were ammonia gas bubbles; ammonia gas was interrupted, the washing bottle was transferred into a vacuum drying oven after the washing bottle was covered, the bottle was uncovered, and was vacuum dried in the oven at 70° C. for solvent evaporation for 16 hours to obtain a titanium ammonia complex solid;

(13) 3 g of the complex solid was taken and put into a quartz boat, and the quartz boat was put into a quartz tube furnace, air in a high purity nitrogen replacement furnace tube was introduced first, and then ammonia water was introduced and a temperature began to increase; a flow rate of the ammonia water was controlled at 10 ml/min, and a heating rate was 5° C./min; the temperature was increased to 750° C., then constant temperature nitriding was performed at this temperature for two hours, and then it was switched to high purity nitrogen gas and the temperature began to decrease, it was taken out after cooled to room temperature, measured by XRD, and the obtained product was pure TiN with a cubic structure (card number: JCPDS NO. 38-1420).

(14) (2) Preparing Pt@TiN by a Constant Current Pulse Method

(15) 5 mg of TiN was added into an 1 mL ethanol solution containing 0.25 wt % of a perfluorinated sulfonic acid resin (Nafion), after an ultrasound for 15 minutes into an ink-form slurry, 5 uL of the slurry was taken and was uniformly coated on a glassy carbon electrode served as a working electrode, and was dried naturally. An amount of TiN on the electrode was 75 μg/cm.sup.−2, the working electrode was placed in a 0.5 M H.sub.2SO.sub.4 solution saturated with nitrogen, and was scanned from an open-circuit voltage to −0.2 V for 20 laps at a scan speed of 50 mV/s, to remove a contaminant on a surface of the nitride nanoparticle. The working electrode was then transferred into a chloroplatinic acid salt solution saturated with nitrogen (chloroplatinic acid hexahydrate, with a concentration of 50 mM, containing 0.1 M sodium sulfate and 50 mM polyvinylpyrrolidone), a platinum wire and an Ag/AgCl electrode were served as a counter electrode and a reference electrode, respectively, according to a preset constant current pulse deposition program (a peak current density was 5 mA/cm.sup.2, a turn-on time was 3 ms, a turn-off time was 15 ms, a pulse number was 5200, and an electrodeposition temperature was room temperature), to obtain Pt@TiN catalyst.

(16) Actual compositions of the catalyst can be determined by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-OES). A specific method was as followed: the catalyst was eluted from the surface of the electrode by ethanol, then aqua regia was added for dissolving, its concentration was determined by ICP-OES spectroscopy, and a mass composition of the catalyst was finally obtained by conversion, and the actual loading amount of Pt was determined.

(17) (3) Structure and Morphology Characterization and Performance Testing of the Catalyst.

(18) (A) Structure and Morphology Characterization of the Catalyst:

(19) Morphology of the nitride nanoparticles and morphology of the nitride nanoparticles supporting platinum were observed by transmission electron microscopy (TEM) (FIG. 1), and an average particle size of the titanium nitride prepared in the present embodiment was 8-11 nm, with a relatively uniform particle size distribution. It can be seen from FIG. 2 that, platinum deposited by the pulse electrodeposition method did not form particles at the surface of titanium nitride, while lattice fringes of Pt and titanium nitride can be clearly seen by a high resolution transmission electron microscopy image, and there were also significant differences between the two fringes, proving that Pt was deposited with an atomic layer level thickness. The result of the ICP analysis shows that the catalyst prepared in the present embodiment has a platinum loading of 5.3%.

(20) (B) Cathodic Oxygen Reduction Catalytic Performance Test:

(21) Cyclic voltammetry was performed using a three-electrode system in 0.1 M HClO.sub.4 saturated with oxygen at a scan speed of 10 mV/s and an electrode speed of 1600 r/min. The results are shown in FIG. 3.

(22) (C) Methanol Anodic Oxidation Catalytic Performance Test:

(23) Cyclic voltammetry was performed using the three-electrode system in a 0.5 M H.sub.2SO.sub.4+1 M CH.sub.3OH solution at a scan speed of 50 mV/s. The catalytic activity of the catalyst for methanol anodic oxidation was measured. The results are shown in FIG. 6.

(24) (D) Catalyst Stability Performance Test:

(25) Cyclic voltammetry was performed using the three-electrode system in a 0.5 M H.sub.2SO.sub.4 solution with a scan speed of 50 mV/s and a scan range of 0.3-0.75 V (0.6-1.05 Vs RHE), and a change in electrochemically active surface area (ECSA) was recorded every 2000 laps of scanning. The specific operation was to scan at a scan speed of 50 mV/s with a scan range of −0.2-1.0V, the operation was stopped after the curve was stable, and a scan curve was recorded. The scan range was then resealed to 0.3-0.75V (0.6-1.05 Vs RHE) for the next 2000 cycles of scanning. The change in electrochemically active surface area of the catalyst is shown in FIG. 7.

(26) Activities of the catalyst prepared in the present embodiment for oxygen reduction and methanol oxidation (activity per unit mass of platinum) were 2.8 times and 1.7 times that of the commercial Pt/C catalyst, respectively.

(27) Unless otherwise stated, test methods involved in the present invention of the catalyst for cathodic oxygen reduction, anodic methanol oxidation, and catalyst stability are all the same as the above test methods.

Embodiment 2: Pt@TiNiN Catalyst

(28) (1) Preparation of a bi-metal nickel titanium nitride (TiNiN): in the fuming hood, 60 mL of ethanol was added into the Meng washing bottle, then 2 mL of TiCl4 solution and 169.7 mg of nickel acetate tetrahydrate were added and stirred to dissolve sufficiently. An atomic ratio of Ti to Ni was 19:1. Other preparation procedures were the same as Embodiment 1.

(29) (2) Pt@TiNiN was prepared by the constant current pulse method as same as Embodiment 1.

(30) (3) Structure and morphology of the catalyst are shown in FIG. 3.

(31) (4) Oxygen reduction performance test and methanol oxidation performance test of the catalyst are shown in FIG. 4 and FIG. 6, respectively (an abscissa is potential, and an ordinate is current density).

(32) (5) Catalyst stability test is shown in FIG. 7.

(33) Oxygen reduction performance and methanol oxidation performance of the catalyst prepared in the present embodiment were 4 times and 3.3 times that of the commercial Pt/C catalyst.

Embodiment 3: Pt@TiCoN Catalyst

(34) Except that cobaltous acetate tetrahydrate was used instead of nickel acetate tetrahydrate, the other preparation methods and testing methods were completely the same as those of Embodiment 2, and the oxygen reduction performance of the catalyst prepared in the present embodiment was 3.3 times that of the commercial Pt/C catalyst.

Embodiment 4: Pt@TiMoN Catalyst

(35) Except that molybdenum pentachloride was used instead of nickel acetate tetrahydrate, the other preparation methods and testing methods were completely the same as those of Embodiment 2, and the oxygen reduction performance of the catalyst was 3.1 times that of the commercial Pt/C catalyst.

Embodiment 5: Pt@TiN/CNTs Catalyst

(36) (1) Preparation of TiN/CNTs used as a substrate

(37) In a fuming hood, 60 mL of ethanol was added into a Meng washing bottle, 1 mL of TiCl.sub.4 solution and 3.5 g of carbon nanotubes were added, and then they were stirred to be well blended. A carbon support accounted for 80% of a mass ratio of the substrate. Other processes were the same as Embodiment 1.

(38) (2) Pt@TiN/CNTs was prepared by the constant current pulse method: the same as Embodiment 1 except for several differences as follows:

(39) (A) the salt solution of the active metal (tetraammineplatinum chloride monohydrate, with a concentration of 5 mM, containing 0.1 M sodium sulfate and 0.125 M sodium citrate);

(40) (B) the pulse current was 10 mA/cm.sup.2, the turn-on time was 0.3 ms, and the turn-off time was 1.5 ms, and the oxygen reduction performance of the catalyst prepared in the present embodiment was 3.7 times that of the commercial Pt/C catalyst.

Embodiment 6: Pt@TiCrN/G Catalyst

(41) The same as Embodiment 2 except for several differences as follows:

(42) 1. (1) Chromic chloride hexahydrate was used instead of nickel acetate tetrahydrate.

(43) (2) Graphene was added into the mixed solution, and graphene accounted for 80% of a total mass ratio of the substrate.

(44) (3) Pt@TiCrN/CNTs was prepared by the constant current pulse method as same as Embodiment 1, and

(45) the oxygen reduction performance of the catalyst prepared in the present embodiment was 2.9 times that of the commercial Pt/C catalyst.

Embodiment 7: Pd@TiN Catalyst

(46) The same as Embodiment 1 except for one difference as follows:

(47) (1) Pd@TiN was prepared by the constant current pulse method:

(48) the chloroplatinic acid solution was replaced by a palladium dichloride solution, and a concentration of the metal particles was 100 mM, containing 0.2 M sodium sulfate and 0.05 M polyvinylpyrrolidone, and Pd@TiN catalyst was then continued to be prepared by the constant current pulse method.

(49) The methanol oxidation performance of the catalyst prepared in the present embodiment was 2.5 times that of the commercial Pt/C catalyst.

Embodiment 8: Pd@NbN/CNTs Catalyst

(50) The same as Embodiment 5 except for several differences as follows:

(51) (1) Preparation of NbN/CNTs used as a substrate: columbium pentachloride was used instead of titanium tetrachloride as the metal precursor.

(52) (2) After the tube furnace was cooled to room temperature, NbN/CNTs was not taken out immediately, an exhaust port of the tube furnace was pluck off first, and nitrogen gas was continued to be introduced close to a gas valve side to make NbN/CNTs slowly contact the air and to avoid niobium nitride from being oxidized. After nitrogen gas was continuously introduced for half an hour, the sample was taken out.

(53) (3) The salt solution of the active metal was palladium dichloride, with a concentration of 50 mM, containing 0.1 M sodium sulfate and 0.05 M polyvinylpyrrolidone.

(54) The methanol oxidation performance of the catalyst prepared in the present embodiment was 2.6 times that of the commercial Pt/C catalyst.

Embodiment 9: Ru@TiN Catalyst

(55) The same as Embodiment 1 except for several differences as follows:

(56) (1) The deposited active metal solution was replaced by a ruthenium trichloride solution.

(57) (2) The polytetrafluoroethylene emulsion was replaced by a perfluorinated sulfonic acid resin as the adhesive, ethanol was replaced by isopropanol as the solvent, and a concentration of the resin was changed as 0.15%.

(58) The methanol oxidation performance of the catalyst prepared in the present embodiment was 1.9 times that of the commercial Pt/C catalyst.

Embodiment 10: PtRu@TiN Catalyst

(59) The same as Embodiment 1 except for one difference as follows:

(60) (1) PtRu@TiN was Prepared by the Constant Current Pulse Method:

(61) Electrodeposition of the active metal was implemented by two steps: Ru@TiN was prepared by the constant current pulse method first, and a specific implementation was the same as electrodepositing a shell-layer metal Pt part of Embodiment 1 (except a electroplate liquid was replaced by a ruthenium trichloride solution, with a concentration of 50 mM, containing 0.1 M sodium sulfate and 0.05 M polyvinylpyrrolidone), PtRu@TiN was then continued to be prepared by the constant current pulse method, and a specific implementation was the same as electrodepositing a shell-layer metal Pt part of Embodiment 1.

(62) The oxygen reduction performance and the methanol oxidation performance of the catalyst prepared in the present embodiment were 4.2 times and 3.1 times that of the commercial Pt/C catalyst, respectively.

Embodiment 11: Pd@TiN/G Catalyst

(63) The same as Embodiment 1 except for two differences as follows:

(64) (1) preparation of TiN/G used as a substrate

(65) In a fuming hood, 60 mL of ethanol was added into a Meng washing bottle, 1 mL of TiCl.sub.4 solution was then injected into the ethanol solution slowly, and then 200 mg of graphene was added into the mixed solution, and they were stirred and blended sufficiently.

(66) (2) Pd@TiN/G was prepared by the constant current pulse method:

(67) the electroplate liquid was changed as the palladium dichloride solution replacing the chloroplatinic acid solution, with a concentration of 100 mM, containing 0.1 M sodium sulfate and 0.1 M polyvinylpyrrolidone.

(68) The methanol oxidation performance of the catalyst prepared in the present embodiment was 2.9 times that of the commercial Pt/C catalyst.

(69) As can be seen from the above data, the low-platinum catalyst based on nitride nanoparticles prepared by the pulse electrodeposition method has better catalytic activity and stability than the commercial Pt/C both in the methanol oxidation activity of the anode and the oxygen reduction activity of the cathode.

(70) Any equivalent variation of the implementation used for the technical solution of the present invention by those having ordinary skill in the art by reading the specification of the present invention is covered by the right of the present invention.