METHOD FOR PREPARING ONE-DIMENSIONAL Ni12P5/Ni2P POLYCRYSTALLINE HETEROSTRUCTURE CATALYST USED FOR EFFICIENCY WATER OXIDATION

Abstract

A preparation method for a one-dimensional Ni.sub.12P.sub.5/Ni.sub.2P polycrystalline heterostructure catalyst used for high-efficiency water oxidation is provided. In particular, nickel foam is used as a conductive carrier and a nickel source, sodium phosphite is used as a phosphorus source, and the one-dimensional polycrystalline heterostructure catalyst is synthesized therefrom by means of a two-step hydrothermal-phosphorization method. The combination of the one-dimensional heterostructure and the nickel foam conductive carrier is beneficial for charge transfer and the release of bubbles on the surface of an electrode/electrolyte. The prepared Ni.sub.12P.sub.5/Ni.sub.2P/NF catalyst has a relatively low electrocatalytic water oxidation overpotential and long-term stability in an alkaline solution. After the Ni.sub.12P.sub.5/Ni.sub.2P/NF is loaded with monatomic Ir, the water oxidation overpotential can be further reduced.

Claims

1. A method for preparing a one-dimensional Ni.sub.12P.sub.5/Ni.sub.2P polycrystalline heterostructure catalyst used for high-efficiency water oxidation, comprising the following steps of: S1. putting nickel foam into a HCl solution with a concentration of 1.0-4.0 M for ultrasonic treatment for 20-60 min, then performing ultrasonic washing to the nickel foam in deionized water, ethanol and acetone for 20-40 min in sequence, and drying the washed nickel foam to obtain a clean nickel foam sheet for later use; S2. putting the nickel foam sheet obtained in step S1 into a (NH.sub.4).sub.2HPO.sub.4 aqueous solution for solvothermal reaction at a reaction temperature of 170-190 C. for 10-16 h to obtain a reacted nickel foam sheet, naturally cooling the reacted nickel foam sheet to room temperature, washing the reacted nickel foam sheet, drying the reacted nickel foam sheet after washing for 12 h, putting the reacted nickel foam sheet after drying into a NaOH aqueous solution for solvothermal reaction at 100-130 C. for 4-6 h to obtain a reaction product, and then washing and drying the reaction product to obtain a nickel foam sheet with a rough and defective surface for later use; and S3. mixing NaH.sub.2PO.sub.2.Math.H.sub.2O and the nickel foam sheet with a rough and defective surface obtained in step S2 to obtain a mixture, heating the mixture in a tube furnace at 270-380 C. for 2-3 h under a nitrogen atmosphere to obtain a product after naturally cooling, washing and drying the product to obtain a Ni.sub.12P.sub.5/Ni.sub.2P/NF catalyst.

2. The method according to claim 1, wherein in step S1, a size of the nickel foam is 33 cm.sup.2 to 66 cm.sup.2, and the drying conditions are as follows: vacuum drying at 50-70 C. for 24-36 h.

3. The method according to claim 1, wherein in step S2, the (NH.sub.4).sub.2HPO.sub.4 aqueous solution has a concentration of 1-2 nM, and the NaOH aqueous solution has a concentration of 100-200 nM, and the drying conditions are as follows: vacuum drying at 50-70 C. for 10-16 h.

4. The method according to claim 1, wherein in step S3, a weight ratio of NaH.sub.2PO.sub.2.Math.H.sub.2O to r-NF obtained in step S2 is 9-11:1.

5. The method according to claim 1, wherein in step S3, a flow rate of nitrogen is 100-150 sccm, a heating rate is 5-8 C./min, and the drying conditions are as follows: vacuum drying at room temperature for 12-24 h.

6. The method according to claim 1, wherein potassium hexachloroiridate is dissolved in an ethanol/water mixed solution with a volume ratio of 1:1-2 to prepare an potassium hexachloroiridate solution, the potassium hexachloroiridate solution is drop-coated on the obtained Ni.sub.12P.sub.5/Ni.sub.2P/NF catalyst, then the catalyst is heated at 60-90 C. for 2-4 h, and an IrNi.sub.12P.sub.5/Ni.sub.2P/NF catalyst is obtained after naturally cooling.

7. The method according to claim 6, wherein the potassium hexachloroiridate solution has a concentration of 0.02-0.04 mM, and a mass ratio of Ir to Ni.sub.12P.sub.5/Ni.sub.2P/NF catalyst in the IrNi.sub.12P.sub.5/Ni.sub.2P/NF catalyst is 0.01-0.04:1.

8. An application of the Ni.sub.12P.sub.5/Ni.sub.2P/NF catalyst prepared by the method according to claim 1 in electrocatalytic oxygen production.

9. An application of the Ir.sub.xNi.sub.12P.sub.5/Ni.sub.2P/NF-T catalyst prepared by the method according to claim 6 in electrocatalytic oxygen production.

10. The application according to claim 8, wherein an electrolyte used in the electrocatalytic water splitting reaction is an alkaline electrolyte, a base used in the alkaline electrolyte is one of KOH, NaOH, LiOH and CsOH, preferably KOH, and a concentration of the alkaline electrolyte is 0.5-10 M, preferably 1M.

Description

DETAILED DESCRIPTION OF DRAWINGS

[0026] FIG. 1 shows a transmission electron microscope (TEM) diagram of a target material Ni.sub.12P.sub.5/Ni.sub.2P/NF-275.

[0027] FIG. 2 shows a high resolution transmission electron microscope (HRTEM) diagram of a target material Ni.sub.12P.sub.5/Ni.sub.2P/NF-275.

[0028] FIG. 3 shows LSV polarization curves of target materials Ni.sub.12P.sub.5/Ni.sub.2P/NF-275, Ni.sub.12P.sub.5/NF, Ni.sub.2P/NF and RuO.sub.2/NF.

[0029] FIG. 4 shows a stability test diagram of a target material Ni.sub.12P.sub.5/Ni.sub.2P/NF-275 at a current density of 50 mA/cm.sup.2 (with a test time of 200 h).

[0030] FIG. 5 shows a high-angle annular dark-fieldscanning transmission electron microscopy (HAADF-STEM) diagram of a target material 3% IrNi.sub.12P.sub.5/Ni.sub.2P/NF-275.

[0031] FIG. 6 shows LSV polarization curves of target materials x % Ni.sub.12P.sub.5/Ni.sub.2P/NF-275.

[0032] FIG. 7 shows a stability test diagram of a target material 3% IrNi.sub.12P.sub.5/Ni.sub.2P/NF-275 at a current density of 50 mA/cm.sup.2 (with a test time of 120 h).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0033] In order to further describe the present invention, the following embodiments are illustrated in combination with the accompanying drawings, but it does not limit the scope of the present invention as defined in the claims.

Embodiment 1

[0034] S1. A nickel foam (NF) was cut into 33 cm.sup.2 and was lightly pressed to thin it, the thinned NF was put into a 3.0 M HCl solution for ultrasonic treatment for 30 min, then the NF was ultrasonic washed in deionized water, ethanol and acetone for 30 min in sequence, the washed NF was put into a vacuum drying oven at 60 C. for 24 h to obtain a clean NF sheet for later use.

[0035] S2. 1 nM of a (NH4).sub.2HPO.sub.4 aqueous solution was prepared, the NF sheet obtained in step S1 was put into the (NH4).sub.2HPO.sub.4 aqueous solution for solvothermal reaction at a reaction temperature of 160 C. for 12 h to obtain a reacted NF sheet. The reacted NF sheet was naturally cooled to room temperature, and then was washed with deionized water and vacuum dried in a vacuum drying oven at 60 C. for 12 h. The dried NF sheet was put into a 100 mM NaOH aqueous solution for solvothermal reaction at 120 C. for 5 h to obtain a reaction product. The reaction product was washed with deionized water, and then put into a vacuum dying oven to dry overnight at room temperature to obtain a NF sheet with rough and defective surface (r-NF) for later use.

[0036] S3. NaH.sub.2PO.sub.2.Math.H.sub.2O and the r-NF obtained in step S2 were mixed with a weight ratio of 10:1 to obtain a mixture, the mixture was put in a porcelain boat, and then the porcelain boat was placed into a quartz tube, and the quartz tube was heated at 275 C. for 2 h in a tubular furnace under a nitrogen atmosphere (with a nitrogen flow rate of 150 sccm and a heating rate of 5 C./min) to obtain a product after naturally cooling to room temperature. The product was washed with deionized water, and then put into the vacuum dying oven to dry overnight at room temperature to obtain a target material Ni.sub.12P.sub.5/Ni.sub.2P/NF-275.

[0037] Structural characterization of the target material: TEM diagram (FIG. 1) and HRTEM diagram (FIG. 2) show that the target material has a polycrystalline heterostructure. It was observed that the crystal lattice fringe spacing of 0.192 nm corresponds to the (210) crystal face of Ni.sub.2P and the crystal lattice fringe spacing of 0.195 nm and 0.22 nm respectively correspond to the (420) crystal face and (202) crystal face of Ni.sub.12P.sub.5.

[0038] Electrochemical test of Ni.sub.12P.sub.5/Ni.sub.2P/NF-275 catalyst: the electrochemical performance of the target material was tested on an electrochemical workstation, using a graphite rod as counter electrode and an Hg/Hgo electrode (KOH, 1M) as reference electrode. According to the Nernst equation, each of the potentials tested herein was calibrated to reversible hydrogen electrode (RHE), and E(RHE)=0.098+E(HG/HGO)+0.0592pH. A polarization curve was recorded at a scan rate of 1 mV/s in an O.sub.2-saturated KOH (1M) electrolyte. The polarization curve and Tafel slope were applied with 90% iR-compensation. An electrochemical double-layer capacitance was measured in a potential range of 0.9 V-1.02 V (vs. Hg/HgO) at different scan rates by means of cyclic voltammetry (CV). The electrochemical impedance spectroscopy (EIS) test recorded data in a range of 0.1 Hz to 100 KHz at the potential of 1.53 V (vs. RHE). Stability test used chronoamperometry under a condition of I=50 mA/cm.sup.2. The obtained polarization curve, double-layer capacitance diagram, EIS, and stability test are shown as FIGS. 3-4. It can be seen from the polarization curve (FIG. 3) that the corresponding overpotential at the current density of I=50 mA/cm.sup.2 was 254 mV, which is superior to the same kind of materials of Ni.sub.12P.sub.5/NF , Ni.sub.2P/NF and commercial RuO.sub.2/NF; and the corresponding overpotential at the current density of 50 mA/cm.sup.2 was 295 mV. The stability test results show that the catalyst was stable during a test period of 200 h at the current density of 50 mA/cm.sup.2 (FIG. 4).

Embodiment 2

[0039] Preparation process of r-NF was the same as that of Embodiment 1.

[0040] NaH.sub.2PO.sub.2.Math.H.sub.2O and the obtained r-NF were mixed with a weight ratio of 10:1 to obtain a mixture, the mixture was put in a porcelain boat, and then the porcelain boat was placed into a quartz tube, and the quartz tube was heated at 300 C. for 2 h in a tubular furnace under a nitrogen atmosphere (with a nitrogen flow rate of 150 sccm and a heating rate of 5 C./min) to obtain a product after naturally cooling. The product was washed with deionized water, and then put into the vacuum dying oven to dry overnight at room temperature to obtain a target material Ni.sub.12P.sub.5/Ni.sub.2P/NF-300.

[0041] The electrochemical test conditions were the same as those in Embodiment 1, and the electrochemical test performance is shown in FIG. 3. The electrochemical test results show that the corresponding overpotential at the current density of 50 mA/cm.sup.2 was 324 mV.

Embodiment 3

[0042] Preparation process of r-NF was the same as that of Embodiment 1.

[0043] NaH.sub.2PO.sub.2.Math.H.sub.2O and the obtained r-NF were mixed with a weight ratio of 10:1 to obtain a mixture, the mixture was put in a porcelain boat, and then the porcelain boat was placed into a quartz tube, and the quartz tube was heated at 325 C. for 2 h in a tubular furnace under a nitrogen atmosphere (with a nitrogen flow rate of 150 sccm and a heating rate of 5 C./min) to obtain a product after naturally cooling. The product was washed with deionized water, and then put into the vacuum dying oven to dry overnight at room temperature to obtain a target material Ni.sub.12P.sub.5/Ni.sub.2P/NF-325.

[0044] The electrochemical test conditions were the same as those in Embodiment 1, and the electrochemical test performance is shown in FIG. 3. The electrochemical test results show that the corresponding overpotential at the current density of 50 mA/cm.sup.2 was 330 mV.

Embodiment 4

[0045] Preparation process of r-NF was the same as that of Embodiment 1.

[0046] NaH.sub.2PO.sub.2.Math.H.sub.2O and the obtained r-NF were mixed with a weight ratio of 10:1 to obtain a mixture, the mixture was put in a porcelain boat, and then the porcelain boat was placed into a quartz tube, and the quartz tube was heated at 350 C. for 2 h in a tubular furnace under a nitrogen atmosphere (with a nitrogen flow rate of 150 sccm and a heating rate of 5 C./min) to obtain a product after naturally cooling. The product was washed with deionized water, and then put into the vacuum dying oven to dry overnight at room temperature to obtain a target material Ni.sub.12P.sub.5/Ni.sub.2P/NF-350.

[0047] The electrochemical test conditions were the same as those in Embodiment 1, and the electrochemical test performance is shown in FIG. 3. The electrochemical test results show that the corresponding overpotential at the current density of 50 mA/cm.sup.2 was 340 mV.

Embodiment 5

[0048] Preparation process of r-NF was the same as that of Embodiment 1.

[0049] NaH.sub.2PO.sub.2.Math.H.sub.2O and the obtained r-NF were mixed with a weight ratio of 10:1 to obtain a mixture, the mixture was put in a porcelain boat, and then the porcelain boat was placed into a quartz tube, and the quartz tube was heated at 375 C. for 2 h in a tubular furnace under a nitrogen atmosphere (with a nitrogen flow rate of 150 sccm and a heating rate of 5 C./min) to obtain a product after naturally cooling. The product was washed with deionized water, and then put into the vacuum dying oven to dry overnight at room temperature to obtain a target material Ni.sub.12P.sub.5/Ni.sub.2P/NF-375.

[0050] The electrochemical test conditions were the same as those in Embodiment 1, and the electrochemical test performance is shown in FIG. 3. The electrochemical test results show that the corresponding overpotential at the current density of 50 mA/cm.sup.2 was 351 mV.

Embodiment 6

[0051] An ethanol/aqueous solution (with a volume ratio of 1:1) of potassium hexachloroidate with a concentration of 0.02 nM was prepared, and 100 L of the prepared potassium hexachloroidate solution was drop-coated on the Ni.sub.12P.sub.5/Ni.sub.2P/NF-275 catalyst prepared in Embodiment 1, then the catalyst was heated at 70 C. for 2 h, and a target 1% IrNi.sub.12P.sub.5/Ni.sub.2P/NF-275 catalyst was obtained after naturally cooling to room temperature.

[0052] The electrochemical test conditions were the same as those in Embodiment 1, and the electrochemical test performance is shown in FIG. 6. The electrochemical test results show that the corresponding overpotential at the current density of 10 mA/cm.sup.2 was 230 mV, and the corresponding overpotential at the current density of 50 mA/cm.sup.2 was 274 mV.

Embodiment 7

[0053] An ethanol/aqueous solution (with a volume ratio of 1:1) of potassium hexachloroidate with a concentration of 0.02 nM was prepared, and 200 L of the prepared potassium hexachloroidate solution was drop-coated on the Ni.sub.12P.sub.5/Ni.sub.2P/NF-275 catalyst prepared in Embodiment 1, then the catalyst was heated at 70 C. for 2 h, and a target 2% IrNi.sub.12P.sub.5/Ni.sub.2P/NF-275 catalyst was obtained after naturally cooling to room temperature.

[0054] The electrochemical test conditions were the same as those in Embodiment 1, and the electrochemical test performance is shown in FIG. 6. The electrochemical test results show that the corresponding overpotential at the current density of 10 mA/cm.sup.2 was 210 mV, and the corresponding overpotential at the current density of 50 mA/cm.sup.2 was 258 mV.

Embodiment 8

[0055] An ethanol/aqueous solution (with a volume ratio of 1:1) of potassium hexachloroidate with a concentration of 0.02 nM was prepared, and 300 L of the prepared potassium hexachloroidate solution was drop-coated on the Ni.sub.12P.sub.5/Ni.sub.2P/NF-275 catalyst prepared in Embodiment 1, then the catalyst was heated at 70 C. for 2 h, and a target 3% IrNi.sub.12P.sub.5/Ni.sub.2P/NF-275 catalyst was obtained after naturally cooling to room temperature.

[0056] The target material 3% IrNi.sub.12P.sub.5/Ni.sub.2P/NF-275 has a one-dimensional polycrystalline heterostructure. It can be seen from the HAADF-STEM diagram (FIG. 5) that Ir was monoatomically dispersed in the Ni.sub.12P.sub.5/Ni.sub.2P/NF-275 catalyst.

[0057] The electrochemical test conditions were the same as those in Embodiment 1, and the electrochemical test performance is shown in FIG. 6. The electrochemical test results show that the corresponding overpotential at the current density of 10 mA/cm.sup.2 was 199 mV, and the corresponding overpotential at the current density of 50 mA/cm.sup.2 was 239 mV. The stability test results show that the catalyst was stable during a test period of 120 h at a current density of 50 mA/cm.sup.2 (FIG. 7).

Embodiment 9

[0058] An ethanol/aqueous solution (with a volume ratio of 1:1) of potassium hexachloroidate with a concentration of 0.02 nM was prepared, and 400 L of the prepared potassium hexachloroidate solution was drop-coated on the Ni.sub.12P.sub.5/Ni.sub.2P/NF-275 catalyst prepared in Embodiment 1, then the catalyst was heated at 70 C. for 2 h, and a target 4% IrNi.sub.12P.sub.5/Ni.sub.2P/NF-275 catalyst was obtained after naturally cooling to room temperature.

[0059] The electrochemical test conditions were the same as those in Embodiment 1, and the electrochemical test performance is shown in FIG. 6. The electrochemical test results show that the corresponding overpotential at the current density of 10 mA/cm.sup.2 was 200 mV, and the corresponding overpotential at the current density of 50 mA/cm.sup.2 was 240 mV.

Comparative Example 1

[0060] Control experiment on electrochemical water oxidation of non-heterostructure Ni.sub.12P.sub.5/NF catalyst

[0061] Preparation process of r-NF was the same as that of Embodiment 1.

[0062] NaH.sub.2PO.sub.2.Math.H.sub.2O and the obtained r-NF were mixed with a weight ratio of 10:1 to obtain a mixture, the mixture was put in a porcelain boat, and then the porcelain boat was placed into a quartz tube, and the quartz tube was heated at 400 C. for 2 h in a tubular furnace under a nitrogen atmosphere (with a nitrogen flow rate of 150 sccm and a heating rate of 5 C./min) to obtain a product after naturally cooling. The product was washed and dried to obtain a target material Ni.sub.12P.sub.5/NF.

[0063] The electrochemical test conditions were the same as those in Embodiment 1, and the electrochemical test performance is shown in FIG. 3. The electrochemical test results show that the corresponding overpotential at the current density of 10 mA/cm.sup.2 was 288 mV, and the corresponding overpotential at the current density of 50 mA/cm.sup.2 was 358 mV.

Comparative Example 2

[0064] Control experiment on electrochemical water oxidation of non-heterostructure Ni.sub.2P/NF catalyst

[0065] Preparation process of r-NF was the same as that of Embodiment 1.

[0066] NaH.sub.2PO.sub.2.Math.H.sub.2O was placed upstream of the porcelain boat, r-NF was placed downstream of

[0067] the porcelain boat, and the weight ratio of NaH.sub.2PO.sub.2.Math.H.sub.2O to r-NF was 10:1. The flow rate of nitrogen was 150 sccm, the heating rate was 5 C./min, and the heating temperature was 250 C. Then, the material Ni.sub.2P/NF was obtained after naturally cooling, washing and drying.

[0068] The electrochemical test conditions were the same as those in Embodiment 1, and the electrochemical test performance is shown in FIG. 3. The electrochemical test results show that the corresponding overpotential at the current density of 10 mA/cm.sup.2 was 278 mV, and the corresponding overpotential at the current density of 50 mA/cm.sup.2 was 320 mV.

[0069] Comparative Example 3

[0070] Control experiment on electrochemical water oxidation of commercial RuO.sub.2 loaded on NF

[0071] 5 mg of commercial RuO.sub.2 catalyst was dispersed in 450 L of water/ethanol (with a volume ratio of 1:3.5) mixed solvent to obtain a mixed solution, and 50 L of Nafion aqueous solution with a mass fraction of 5% was added into the mixed solution to form a uniform ink-like solution after continuous ultrasonic treatment for 30 min. Then, the prepared catalyst ink-like solution (with an amount of about 1.0 mg/cm.sup.2) was dropped on the NF with a size of 0.50.5 cm.sup.2 as a working electrode.

[0072] The electrochemical test conditions were the same as those in Embodiment 1, and the electrochemical test performance is shown in FIG. 3. The electrochemical test results show that the corresponding overpotential at the current density of 10 mA/cm.sup.2 was 294 mV, and the corresponding overpotential at the current density of 50 mA/cm.sup.2 was 373 mV.