A method for preparing a double transition metal phosphide catalyst

Abstract

The application discloses a preparation method of a double-transition metal phosphide catalyst and belongs to the technical field of electrocatalysts. The method comprises the following steps: dispersing two kinds of transition metal salts, ammonium fluoride and urea in a solvent, and forming a dispersion solution through ultrasonic stirring; immersing foamed nickel after ultrasonic cleaning in the dispersion solution, and obtaining double-transition metal hydroxide after reaction and drying; performing phosphorization reaction on the double-transition metal hydroxide to form a precursor; and placing the precursor in an IC-PECVD device, adjusting parameters, and obtaining a double-transition metal nitrogen phosphide catalyst. Through etching activation and element doping of low-temperature plasma, the catalyst has double hydrolysis functions, the catalytic activity and the cycle stability are improved, and the material cost of the catalyst is greatly reduced.

Description

Technical Field

[0001] This invention discloses a method for preparing a dual transition metal phosphide catalyst, belonging to the field of electrocatalyst technology. Background Technology

[0002] With the continuous depletion of traditional fossil fuels, there is an urgent need to find a new sustainable energy source to address the energy crisis and environmental problems caused by traditional fossil fuels. Electrocatalytic water splitting for hydrogen and oxygen production, powered by green and sustainable energy systems such as wind and tidal power, is considered a promising clean energy production method. The water splitting reaction involves two half-reactions: the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. Currently, Pt group noble metals with high HER catalytic activity and Ru / Ir-based materials with high OER catalytic performance are most widely used; however, their scarcity and high price significantly limit their widespread application. Transition metal phosphides (TMPs) have been widely developed and applied due to their excellent electrocatalytic activity, wide availability, and low cost. However, many TMPs only exhibit excellent catalytic effects for one of the two half-reactions in the water splitting reaction, while showing poor activity for the other half. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention discloses a method for preparing a dual transition metal phosphide catalyst. By employing a low-temperature plasma-assisted method, heteroatoms are doped into the catalyst, enabling it to simultaneously exhibit highly active hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), thereby solving the problems mentioned in the background art. Specifically, the objective of this invention can be achieved through the following technical solution:

[0004] A method for preparing a dual transition metal phosphide catalyst, the method comprising the following steps:

[0005] Two transition metal salts, ammonium fluoride, and urea were dispersed in a solvent and ultrasonically stirred to form a dispersion solution.

[0006] After ultrasonic cleaning, the foamed nickel is immersed in the dispersion solution, and after reaction and drying, a dual transition metal hydroxide is obtained.

[0007] The dual transition metal hydroxide undergoes a phosphating reaction to form a precursor;

[0008] The precursor is placed in an IC-PECVD device, and the parameters are adjusted to obtain a dual transition metal phosphide catalyst.

[0009] Furthermore, the transition metal salt includes any two of iron salts, cobalt salts, and nickel salts.

[0010] Furthermore, the solvent includes deionized water, ethanol, or methanol.

[0011] Furthermore, the ultrasonic cleaning process for the nickel foam includes sequential cleaning in dilute hydrochloric acid, water, and ethanol.

[0012] Furthermore, the ultrasonic stirring time is 0.5 to 2 hours.

[0013] Furthermore, the reaction conditions include a reaction temperature of 90–150°C and a reaction time of 10–12 h, and the drying temperature is 60–100°C.

[0014] Furthermore, the conditions for the phosphating reaction include a temperature of 300–350°C, a phosphating time of 1–2 h, and a heating rate of 5°C / min.

[0015] Furthermore, the conditions for processing the precursor by the IC-PECVD equipment include a discharge power of 100-200W, a gas flow rate of 1:1 N2 / H2, and a gas flow rate of 20-30 sccm.

[0016] The beneficial effects of this invention are:

[0017] (1) The dual transition metal phosphide catalyst prepared by this invention is used for hydrogen evolution, oxygen evolution and total water splitting reactions. Compared with traditional commercial Pt / C||RuO2 and similar electrocatalysts, it has significantly higher catalytic activity and cycle stability, and does not require precious metals. While ensuring efficient and stable catalytic effect, it greatly reduces the cost of the catalyst.

[0018] (2) The synergistic effect between the two transition metal atoms changes the electronic structure of the electrocatalyst, enhances its intrinsic activity, and obtains HER and OER activities superior to those of single metal phosphides.

[0019] (3) Nitrogen is introduced through low-temperature plasma treatment to improve the conductivity of the catalyst and provide additional electrons to the transition metal atoms, thereby improving the electron transfer rate of the electrode.

[0020] (4) High-performance dual transition metal phosphide catalysts can be prepared by plasma-assisted annealing, which is simple to operate and avoids the cumbersome and time-consuming nature of traditional industry. Attached Figure Description

[0021] Figure 1 These are SEM images of the catalysts CoFeP-N and CoP, where a represents the SEM image of CoFeP-N and b represents the SEM image of CoP (scale: 1 μm on the left, 200 nm on the right).

[0022] Figure 2 This is a TEM image of the catalyst CoFeP-N (scale: 100 nm on the left, 10 nm in the middle, and 1 nm on the right).

[0023] Figure 3 This is the LSV curve of HER for catalysts CoFeP-N, CoFeP, CoPN and CoP in 1 MKOH, with a scan rate of 5 mV / s.

[0024] Figure 4 This is a Tafel curve of the HER of catalysts CoFeP-N, CoFeP, CoPN and CoP in 1 MKOH.

[0025] Figure 5 This is the EIS curve of HER for catalysts CoFeP-N, CoFeP, CoPN, and CoP in 1 mM OH, with a voltage of 10 mA / cm. 2 The voltage at that point.

[0026] Figure 6 The catalysts CoFeP-N, CoFeP, CoPN, and CoP in 1 M KOH are HER C dl The image shows a scan rate of 10-50 mV / s.

[0027] Figure 7 The catalysts CoFeP-N, CoFeP, CoPN, and CoP exhibit HER activity at 10 mA / cm in 1 M KOH. 2 The graph shows the change of potential over time at current density, with a frequency range of 0.01-100kHz.

[0028] Figure 8 This is the LSV curve of the OER of catalysts CoFeP-N, CoFeP, CoPN and CoP in 1 MKOH, with a scan rate of 5 mV / s.

[0029] Figure 9 This is a Tafel curve of the OER of catalysts CoFeP-N, CoFeP, CoPN and CoP in 1 MKOH.

[0030] Figure 10 This is the EIS curve of the OER of catalysts CoFeP-N, CoFeP, CoPN, and CoP in 1 mkOH, with a voltage of 10 mA / cm. 2 The voltage at that point.

[0031] Figure 11 The catalysts CoFeP-N, CoFeP, CoPN, and CoP have an OER of 10 mA / cm in 1 M KOH. 2 The curve of potential change over time at current density, with a frequency range of 0.01-100kHz.

[0032] Figure 12This is the LSV curve of the total water splitting of catalysts CoFeP-N||CoFeP-N and Pt / C||RuO2 in 1M KOH, with a scan rate of 5mV / s.

[0033] Figure 13 The catalysts CoFeP-N||CoFeP-N and Pt / C||RuO2 undergo total water splitting in 1 M KOH at 100 mA / cm². 2 The curve of potential change over time at current density, with a frequency range of 0.01-100kHz. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without innovative effort are within the scope of protection of the present invention.

[0035] Example 1:

[0036] A method for preparing a dual transition metal phosphide catalyst specifically includes the following steps:

[0037] A: Weigh 1.2 mmol Co(NO3)2·6H2O, 0.15 mmol Fe(NO3)3·9H2O, 5 mmol CO(NH2)2 and 4 mmol NH4F and dissolve them in 30 mL of deionized water. Stir vigorously for 1 h to obtain a uniform dispersion.

[0038] B: Commercially available nickel foam was ultrasonically cleaned in dilute hydrochloric acid, water, and ethanol for 15 minutes and then dried. It was then immersed in a uniform dispersion and reacted in a reactor at 120°C for 10 hours. The product was then washed with deionized water and dried at 60°C to obtain cobalt iron hydroxide, a dual transition metal.

[0039] C: Cobalt iron hydroxide, a dual transition metal, and 1g of sodium hypophosphite were placed in a tube furnace and phosphated at 300℃ and 5℃ / min for 2h to obtain the catalyst precursor cobalt iron phosphide.

[0040] D: Take an appropriate amount of the catalyst precursor cobalt iron phosphide and place it in a ceramic boat. Put the ceramic boat into the discharge chamber of the IC-PECVD equipment, evacuate to about 3 Pa, and introduce a N2 / H2 mixed gas at a ratio of 1:1. The pressure is about 80 Pa and the discharge power is 130 W. After discharging for 15 minutes, turn off the glow discharge equipment and allow it to cool naturally to room temperature to obtain a dual transition metal phosphide catalyst, denoted as CoFeP-N.

[0041] Example 2:

[0042] Steps A, B, and C in this embodiment are the same as in Embodiment 1;

[0043] D: Place an appropriate amount of catalyst precursor in a ceramic boat, put the ceramic boat into the discharge chamber of the IC-PECVD equipment, evacuate to about 3 Pa, introduce only H2 gas with a pressure of about 80 Pa and a discharge power of 130 W, and after discharging for 15 minutes, turn off the glow discharge equipment and allow it to cool naturally to room temperature to obtain a dual transition metal phosphide catalyst, denoted as CoFeP.

[0044] SEM image shows ( Figure 1 The morphology of the catalyst CoFeP-N (Fig. a) is an approximately coral-like, rough nanowire array, while the morphology of the plasma-assisted catalyst CoP (Fig. b) is a very smooth nanowire cluster. This indicates that the etching effect of plasma modifies the morphology of the original catalyst, which is very beneficial to improving the catalyst activity.

[0045] TEM images further show ( Figure 2 The catalyst CoFeP-N has a needle-like nanowire structure. High-resolution transmission electron microscopy (HRTEM) images clearly show the light-colored cobalt phosphide as the main component and the dark-colored iron phosphide as the dopant. The clear lattice stripes of the two correspond to the (211) crystal plane of CoP and the (112) crystal plane of FeP, respectively.

[0046] The LSV curves of the HER of catalysts CoFeP-N, CoFeP, CoP-N and CoP in 1 MKOH are shown. Figure 3 Compared with CoP, CoP-N, and CoFeP, CoFeP-N nanowires exhibit the best HER catalytic activity. At 10 mA / cm², -2 At the given current density, the overpotential of CoFeP-N is only 64mV, which is significantly better than that of CoP (116mV), CoP-N (103mV), and CoFeP (88mV).

[0047] Tafel plots of HER for catalysts CoFeP-N, CoFeP, CoP-N, and CoP in 1 MKOH are shown. Figure 4 CoFeP-N has the smallest Tafel slope (71.8 mV / dec), which is lower than CoP (81.0 mV / dec), CoP-N (75.8 mV / dec), and CoFeP (74.9 mV / dec), and much lower than Pt / C (217.1 mV / dec), indicating that it has a greater advantage in reaction kinetics.

[0048] Electrochemical impedance spectroscopy (EIS) curves of catalysts CoFeP-N, CoFeP, CoP-N, and CoP in 1 mkOH show ( Figure 5 The charge transfer resistance (Rct) of CoFeP-N is significantly lower than that of other materials, which implies a rapid electron transfer rate and dynamic process.

[0049] Electrochemical double-layer capacitance (C0) of catalysts CoFeP-N, CoFeP, CoP-N, and CoP measured by cyclic voltammetry at different scan rates within the non-Radida range. dl The figure shows ( Figure 6 CoFeP-N has the largest C dl (219.5mF / cm 2 (), far exceeding CoP (64.8mF / cm 2 ), CoP-N (95.4 mF / cm) 2 ) and CoFeP (148.1mF / cm 2 This also results in it having the largest ECSA (109.8 cm). 2 This indicates that it has more active sites required for the reaction.

[0050] The HER of catalysts CoFeP-N, CoFeP, CoP-N and CoP in 1 MKOH at 10 mA / cm 2 The curve showing the change of potential over time at a given current density is shown. Figure 7 In addition to its catalytic activity, CoFeP-N also exhibits excellent stability at 10 mA / cm². 2 After working continuously for 100 hours at a current density, the overpotential remains essentially unchanged.

[0051] The LSV curves of OER for catalysts CoFeP-N, CoFeP, CoP-N, and CoP in 1 MKOH are shown. Figure 8 CoFeP-N exhibits the best OER activity at 10 mA / cm². 2 100mA / cm 2 and 400mA / cm 2 The overpotentials at these locations are 218mV, 264mV, and 315mV, respectively, which are much lower than those of CoP (236mV, 309mV, and 366mV), CoP-N (229mV, 298mV, and 352mV), and CoFeP (224mV, 271mV, and 336mV).

[0052] Tafel plots of OER for catalysts CoFeP-N, CoFeP, CoP-N, and CoP in 1 MKOH are shown. Figure 9CoFeP-N exhibits the smallest Tafel slope (55.0 mV / dec), which is lower than that of CoP (64.9 mV / dec), CoP-N (61.8 mV / dec), and CoFeP (70.4 mV / dec), indicating that it has superior reaction kinetics.

[0053] The EIS curves of the OER of catalysts CoFeP-N, CoFeP, CoP-N and CoP in 1 MKOH are shown. Figure 10 CoFeP-N exhibits the lowest Rct, which means it has a faster charge transport rate during the catalytic process.

[0054] The OER of catalysts CoFeP-N, CoFeP, CoP-N and CoP in 1 M KOH is at 10 mA / cm 2 The curve showing the change of potential over time at a given current density is shown. Figure 11 CoFeP-N exhibits extremely excellent stability at 10 mA / cm². 2 After working continuously for 150 hours at a current density, the overpotential remained essentially unchanged.

[0055] LSV curves of total water splitting of catalysts CoFeP-N||CoFeP-N and Pt / C||RuO2 in 1 MKOH ( Figure 12 The data shows that the current density of the CoFeP-N||CoFeP-N electrolytic cell can reach 100 mA / cm² at a low voltage of 1.636 V. 2 This is superior to the 1.736V of the Pt / C||RuO2 electrolytic cell.

[0056] The catalysts CoFeP-N||CoFeP-N and Pt / C||RuO2 undergo total water splitting in 1 M KOH at 100 mA / cm². 2 The curve of potential change over time at current density ( Figure 13 The results show that the CoFeP-N||CoFeP-N electrolyzer exhibits excellent cycle stability and can operate at 100 mA / cm². 2 It can operate continuously for more than 100 hours at the current density without significant potential deviation.

[0057] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a dual transition metal phosphide catalyst, characterized in that, The method includes the following steps: 1.2 mmol Co(NO3)2·6H2O, 0.15 mmol Fe(NO3)3·9H2O, 5 mmol CO(NH2)2 and 4 mmol NH4F were dissolved in 30 mL of deionized water and then ultrasonically stirred to form a dispersion solution. After ultrasonic cleaning, the foamed nickel is immersed in the dispersion solution, and after reaction and drying, a dual transition metal hydroxide is obtained; the reaction conditions include a reaction temperature of 120°C and a reaction time of 10 h; The dual transition metal hydroxide undergoes a phosphating reaction to form a precursor; The precursor is placed in an IC-PECVD device and processed under conditions of a discharge power of 100-200W, a gas flow ratio of 1:1 for N2 / H2, and a gas flow rate of 20-30 sccm to obtain a dual transition metal phosphide catalyst.

2. The preparation method according to claim 1, characterized in that, The ultrasonic cleaning process for the nickel foam includes sequential cleaning in dilute hydrochloric acid, water, and ethanol.

3. The preparation method according to claim 1, characterized in that, The ultrasonic stirring time is 0.5 to 2 hours.

4. The preparation method according to claim 1, characterized in that, The drying temperature is 60–100°C.

5. The preparation method according to claim 1, characterized in that, The conditions for the phosphating reaction include a temperature of 300–350°C, a phosphating time of 1–2 h, and a heating rate of 5°C / min.

6. A dual transition metal phosphide catalyst prepared by any one of the methods described in claims 1 to 5.

7. The application of the catalyst according to claim 6 in the field of fuel cell technology.

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