CoO treated by low temperature quick freezing x / CoP-L nanosheet catalyst and preparation method thereof

Abstract

This work innovatively realizes the effective regulation of the crystalline / amorphous crystal surface by subjecting the phosphide to low-temperature liquid nitrogen quick freezing treatment, and prepares a thin-sheet CoO x / CoP-L catalyst and its preparation method, the preparation method is simple to operate, low cost, and has better economic benefits. x The crystalline / amorphous heterogeneous interface formed by the CoP-L flakes effectively promotes the adsorption and desorption of water during hydrogen evolution, while the lattice distortion optimizes the CoO x The electronic structure of / CoP‑L ultimately achieves improved performance and exhibits excellent performance in hydrogen evolution reactions in both alkaline and acidic media. Under alkaline and acidic conditions, only 56.6mV and 98mV overpotentials are required, respectively, to drive 10mA cm ‑2 It is worth noting that the alkaline HER process has a current density of 68 mA cm ‑2 The catalytic activity begins to exceed that of commercial Pt / C electrode, showing excellent catalytic potential.

Description

Technical Field

[0001] The present invention relates to the field of new energy material technology and electrocatalytic water splitting hydrogen evolution catalysis technology, and in particular to a crystalline / amorphous CoO x / CoP-L nanosheet catalyst; also designed is a preparation method of the catalyst and its application in electrocatalytic hydrogen evolution under alkaline and acidic conditions. Background Art

[0002] With the advocacy and proposal of the "dual carbon" target strategy, the adjustment of the energy structure is imminent, which requires the vigorous development of clean, renewable, and environmentally friendly alternative energy sources. Hydrogen energy has become a hot and ideal energy source. As a green and simple hydrogen evolution technology, the hydrogen evolution reaction (HER) has become a key technology for achieving carbon neutrality and green economic direct energy conversion. Pt-based catalysts, as highly active HER catalysts, have become the first choice for HER, especially under acidic conditions. However, due to its high cost and severe scarcity, researchers are eager to develop an efficient and alternative non-precious metal-based material.

[0003] Low-cost transition metal phosphides (TMPs) have the characteristics of hydrogenase-like catalytic mechanism and high conductivity, and have good prospects for the development of HER. However, their actual catalytic activity is far from comparable to that of platinum-based catalysts. In order to improve the catalytic activity of TMPs, people have proposed the rational use of constructing heterogeneous interfaces to enrich the catalytic function of materials and improve the intrinsic activity of materials. In particular, constructing crystalline / amorphous materials with metal oxides with disordered structures and a large number of vacancies / defects can expose more active sites, better exert the synergistic effect of heterogeneous interfaces, optimize the adsorption / dissociation energy of water, and thus improve the HER activity of catalysts. However, most studies have constructed crystalline / amorphous heterogeneous interfaces through a simple one-step process, and few have conducted further in-depth exploration of this unique interface.

[0004] Previous researchers have discovered that by rapidly freezing or quenching materials at low temperatures, tensile strain can be introduced, causing lattice distortion, or increasing the number of grain boundaries and creating a large number of defect sites. The treated catalysts often have advantages such as improved conductivity, exposure of more active sites, and significant improvement in catalyst stability, which can further optimize the material for high activity. However, according to current reports, liquid nitrogen rapid freezing or quenching processes are optimization treatment steps for metal oxides, and almost no one has studied rapid freezing treatment of phosphides.

[0005] Here, we innovatively achieved effective control of the crystal form / amorphous crystal surface by performing a low-temperature liquid nitrogen quick-freezing treatment on the phosphide, which has good economic benefits. x / CoP-L has excellent electrocatalytic activity and stability under both alkaline and acidic conditions. Specifically, the synthesized crystalline / amorphous CoO with lattice distortion x The / CoP-L catalyst only requires an overpotential of 56.6 mV and 98 mV under alkaline and acidic conditions, respectively, to drive a 10 mA cm -2 It is worth noting that the alkaline HER process has a current density of 68 mA cm -2 The catalytic activity begins to surpass that of commercial Pt / C electrodes, demonstrating excellent catalytic potential. Excellent HER stability is also achieved. This work represents a significant step forward in furthering the activation of phosphides and overcoming the challenges of liquid nitrogen quick-freezing, which has been limited to metal oxides. Summary of the Invention

[0006] In view of the research and application needs of the hydrogen evolution reaction of catalysts in this research field, one of the purposes of the present invention is to disclose a CoO with crystalline / amorphous heterogeneous interface that realizes lattice distortion. x / CoP-L catalyst; CoO was constructed by vapor phase phosphating x / CoP heterostructure, and then subjected to low-temperature liquid nitrogen quick freezing treatment to introduce tensile strain, thereby achieving the distortion of the lattice fringes and obtaining a catalyst material with high HER activity.

[0007] The second purpose of the present invention is to provide a CoO with a crystalline / amorphous heterogeneous interface that realizes lattice distortion. x The preparation method of the / CoP-L catalyst specifically comprises the following steps:

[0008] (a) CoO x Preparation of / CoP-L

[0009] (1) 145.5 mg of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 0.91 g of cetyltrimethylanilinium bromide (CTAB) were ultrasonically dissolved in 20 ml of deionized water to obtain a transparent light pink solution. Then, the prepared NaBH4 solution (47.29 mg of NaBH4 dissolved in 5 ml of deionized water) was added dropwise to the mixed solution under magnetic stirring. The solution was stirred for 12 hours, centrifuged, washed, and dried to obtain green CoO x Powder, set aside;

[0010] (2) Take CoO x and sodium hypophosphite (mass ratio 1:30) in a tube furnace, heated to 350 ° C under nitrogen atmosphere and calcined for 2 hours to obtain CoO x / CoP;

[0011] (3) Take 50ml of liquid nitrogen in a beaker and mix the prepared CoOx / CoP powder is quickly poured into it. After the liquid nitrogen evaporates, the quick-frozen powder sample is quickly taken out and waits for subsequent application processing.

[0012] (b) Preparation of working electrode

[0013] To prepare the working electrode, the synthesized sample was dispersed in a Nafion ethanol solution (volume ratio 9:200) and ultrasonicated for more than 30 minutes to achieve a fully dispersed homogeneous catalyst solution. Then 100 μl of the prepared homogeneous dispersion was dropped onto a 1 cm 2 The samples were deposited on carbon paper and then dried at room temperature for electrocatalytic testing in a conventional three-electrode setup.

[0014] In summary, the present invention innovatively uses ultra-low temperature liquid nitrogen quick freezing method to quickly freeze the synthesized phosphide material to introduce tensile strain, achieves effective control of the crystal form / amorphous crystal surface, and successfully prepares CoO x / CoP-L, which significantly improved the HER activity of the catalyst under alkaline and acidic conditions.

[0015] CoO prepared by the present invention x Compared to other existing technologies, the CoP-L / CoP-L catalytic material offers lower cost and simpler synthesis methods. It exhibits both alkaline hydrogen evolution performance similar to that of Pt / C and excellent acidic hydrogen evolution performance, while also exhibiting exceptional stability. This is due to: 1) its nanosheet-like morphology, which exposes a larger active area and increases the number of exposed active sites; 2) the formation of a crystalline / amorphous heterointerface, which facilitates water adsorption and dissociation; and 3) the resulting lattice distortion, which coordinates the electronic structure and promotes the directional movement of electrons from Co to P atoms. This results in more negatively charged P atoms, promoting H2 release and increasing the reactivity of the active sites. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 CoO obtained in Example 1 x X-ray diffraction pattern (a), transmission electron microscopy (TEM) image (b), and high-resolution transmission electron microscopy (HRTEM) image (c) of the nanosheets.

[0017] Figure 2 CoO obtained in Example 1 x X-ray diffraction pattern (a), scanning electron microscopy (b), transmission electron microscopy (c) and high-resolution transmission electron microscopy (d) of the Mg / CoP nanosheets.

[0018] Figure 3 CoO obtained in Example 1 xX-ray diffraction pattern (a), scanning electron microscopy (b), transmission electron microscopy (c), atomic force microscopy (d), and high-resolution transmission electron microscopy (e, f) of the Mg / CoP-L nanosheet catalyst.

[0019] Figure 4 CoO obtained in Example 1 x / CoP-L and CoO x XPS characterization of / CoP catalyst.

[0020] Figure 5 CoO obtained in Example 1 x LSV curves of / CoP-L flake catalyst and comparative sample in 1.0M KOH electrolyte (a), comparison diagram at different current densities (b), CoO x / IT test diagram of CoP-L (c).

[0021] Figure 6 CoO obtained in Example 1 x CV curves (ac) of / CoP-L flake catalyst and comparative sample in 1.0 M KOH electrolyte, C dl Figure (d).

[0022] Figure 7 CoO obtained in Example 1 x LSV curves of / CoP-L flake catalyst and comparative sample in 0.5M H2SO4 solution (a), comparison diagram at different current densities (b), CoO x / IT test diagram of CoP-L (c).

[0023] Figure 8 CoO obtained in Example 1 x CV curves (ac) of / CoP-L flake catalyst and comparative sample in 0.5M H2SO4 electrolyte, C dl Figure (d). DETAILED DESCRIPTION

[0024] For a further understanding of the present invention, the present invention will be further described below with reference to the accompanying drawings and embodiments, but the present invention is not limited in any way.

[0025] Example 1

[0026] (a) CoO x Preparation of / CoP-L

[0027] (1) 145.5 mg of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 0.91 g of cetyltrimethylanilinium bromide (CTAB) were ultrasonically dissolved in 20 ml of deionized water to obtain a transparent light pink solution. Then, the prepared NaBH4 solution (47.29 mg of NaBH4 dissolved in 5 ml of deionized water) was added dropwise to the mixed solution under magnetic stirring. The solution was stirred for 12 hours, centrifuged, washed, and dried to obtain green CoO x Powder, set aside;

[0028] (2) Take CoO x and sodium hypophosphite (mass ratio 1:30) in a tube furnace, heated to 350°C under nitrogen atmosphere and calcined for 2 hours to obtain CoO x / CoP;

[0029] (3) Take 50ml of liquid nitrogen in a beaker and mix the prepared CoO x / CoP powder is quickly poured into it. After the liquid nitrogen evaporates, the quick-frozen powder sample is quickly taken out and waits for subsequent application processing.

[0030] (b) Preparation of working electrode

[0031] To prepare the working electrode, the synthesized sample was dispersed in a Nafion ethanol solution (volume ratio 9:200) and ultrasonicated for more than 30 minutes to achieve a fully dispersed homogeneous catalyst solution. Then 100 μL of the prepared homogeneous dispersion was added to a 1 cm 2 The samples were deposited on carbon paper and then dried at room temperature for electrocatalytic testing in a conventional three-electrode setup.

[0032] Figure 1 CoO obtained in Example 1 x X-ray diffraction pattern (a), transmission electron microscopy (b), and high-resolution transmission electron microscopy (c) of the nanosheet. As can be seen from Figure (a), CoO x The nanosheets are amorphous. As can be seen from Figure (b), CoO x The morphology belongs to the ultra-thin nanosheet structure. As can be seen from Figure (c), there are no obvious lattice fringes, which confirms that CoO x amorphous structure.

[0033] Figure 2 CoO obtained in Example 1 x X-ray diffraction pattern (a), scanning electron microscopy (b), transmission electron microscopy (c) and high-resolution transmission electron microscopy (d) of CoP nanosheets. As can be seen from Figure (a), CoO x / CoP can match the crystal phase of CoP without any extra crystals. As can be seen from Figure (b) and Figure (c), after phosphating, the crystal phase of CoO x Compared with the morphology, the nanosheets are slightly thicker, but the thickness is negligible. As can be seen from Figure (d), the catalyst has a crystalline / amorphous heterogeneous interface, and the crystalline region has lattice fringes of 0.283nm and 0.189nm.

[0034] Figure 3 CoO obtained in Example 1 x X-ray diffraction pattern (a), scanning electron microscopy (b), transmission electron microscopy (c), atomic force microscopy (d), and high-resolution transmission electron microscopy (e, f) of the CoP-L nanosheet catalyst. As can be seen from Figure (a), CoO x / CoP-L can match the crystal phase of CoP. As can be seen from Figure (b) and Figure (c), CoO x / CoP-L nanosheets. As can be seen from Figure (d), CoO x The thickness of the CoP-L nanosheets is about 2 nm. As can be seen from Figure (d), the catalyst has a crystalline / amorphous heterogeneous interface, and the crystalline region has lattice fringes of 0.283 nm and 0.189 nm. At the same time, the lattice fringes at the CoP (011) crystal plane have obvious lattice distortion.

[0035] Figure 4 CoO obtained in Example 1 x / CoP-L and CoO x XPS characterization of CoO / CoP catalyst. x In the Co 2p XPS spectrum of the / CoP-L sample, a pair of peaks at 780.54eV and 795.53eV are attributed to Co δ+ Co 2p 3 / 2 and Co2p 1 / 2 , which is related to the formation of Co-P after phosphating. The peaks at 782.92eV and 798.93eV belong to Co bonded with oxygen. 2+ Co 2p of (Co-O) 3 / 2 and Co 2p 1 / 2 The satellite peaks of Co 2p are located at 787.62eV and 804.41eV. In the XPS spectrum of P 2p, the peaks at 129.44eV and 130.52eV are attributed to the P 2p of phosphide. 3 / 2 and P2p 1 / 2 , this pair of peaks and the XPS peak of Co 2p belong to Co δ+ The peak at 133.49eV belongs to PO43- P 2p. Compared with CoO before quick freezing x Compared with CoP, CoO x The Co 2p peak of the / CoP-L sample shifts toward lower binding energies, while the corresponding P2p peak shifts positively. This suggests that after quick freezing, the strain-induced lattice distortion causes the Co atoms in the phosphide to carry more positive charges. The O1s spectrum decomposes into two peaks at 529.89 eV and 531.35 eV, belonging to OM (M=Co) and OP, respectively.

[0036] Figure 5 CoO obtained in Example 1 x LSV curves of / CoP-L flake catalyst and comparative sample in 1.0M KOH electrolyte (a), comparison diagram at different current densities (b), CoO x / CoP-L IT test diagram (c). As can be seen from Figure (a), CoO x / CoP-L has the best alkaline HER activity at 10 mA cm -2 At a current density of x The overpotential of / CoP-L is only 4.5 mV higher than that of commercial Pt / C electrode. As can be seen from Figure (b), the current density is 10, 50 and 100 mA cm -2 CoO x The overpotentials of CoO / CoP-L were 56.6 mV, 106.6 mV, and 128.6 mV, respectively, which were lower than those of CoO before quick freezing. x / CoP (84mV, 127.4mV, and 149.6mV), and can be compared with the catalytic activity of commercial Pt / C (52.1mV, 101.6mV, and 130.2mV). As can be seen from Figure (c), CoO x / CoP-L can maintain long-term stability for 48 hours.

[0037] Figure 6 CoO obtained in Example 1 x CV curves (ac) of / CoP-L flake catalyst and comparative sample in 1.0 M KOH electrolyte, C dl Figure (d). CV and double layer capacitance (C dl ) is in direct proportion to the electrochemical surface area (ECSA), CoO x / CoP-L C dl The value is 80.3mF cm -2 , much higher than CoO x / CoP(54.3mF cm -2 ) and CoO x(17.7mF cm -2 ). CoO x / CoP-L has a larger ECSA, which means CoO x / CoP-L can expose more electrochemical active sites.

[0038] Figure 7 CoO obtained in Example 1 x LSV curves of / CoP-L flake catalyst and comparative sample in 0.5M H2SO4 solution (a), comparison diagram at different current densities (b), CoO x / CoP-L IT test diagram (c). As can be seen from Figure (a), CoO x / CoP-L exhibits the best acidic electrocatalytic activity, requiring only 98 mV overpotential to reach η 10 As can be seen from Figure (b), CoO x / CoP-L is driven at current densities of 10, 50, and 100 mA cm -2 When , the overpotentials are 98, 148.7 and 174.2 mV, respectively, which are significantly lower than those of CoOx / CoP (117.4 mV, 169.2 mV and 195.6 mV).

[0039] Figure 8 CoO obtained in Example 1 x CV curves (ac) of / CoP-L flake catalyst and comparative sample in 0.5M H2SO4 electrolyte, C dl Figure (d). As can be seen from Figures (ac), CoO x / CoP-L and CoO x / CoP, and CoO x Corresponding CV graph. As can be seen from Figure (d), CoO x / CoP-L C dl The value is 64.4mF cm -2 , much higher than CoO x / CoP(38.1mF cm -2 ) and CoO x (6.8mF cm -2 ). C dl The value of confirms that CoOx / CoP-L has the largest ECAS.

Claims

1. A crystalline / amorphous CoO with a distorted lattice synthesized by a two-step optimization process of phosphating and liquid nitrogen quick freezing x / CoP-L catalyst preparation method, characterized in that, The catalyst uses a low-temperature liquid nitrogen quick-freeze treatment on the phosphide to achieve effective regulation of the crystalline / amorphous crystal surface, and is applied to the electrocatalytic hydrogen evolution reaction under alkaline and acidic conditions. Flake-like crystalline / amorphous CoO x The preparation steps of / CoP-L catalyst are as follows: (a) CoO x Preparation of / CoP-L (1) 145.5 mg of cobalt nitrate hexahydrate and 0.91 g of hexadecyltrimethylanilinium bromide were dissolved in 20 ml of deionized water by ultrasonication to obtain a transparent light pink solution. 47.29 mg of NaBH4 was dissolved in 5 ml of deionized water, and the prepared NaBH4 solution was added dropwise to the mixed solution under magnetic stirring. The solution was stirred for 12 hours, centrifuged, washed, and dried to obtain a green CoO x Powder, set aside; (2) Take CoO with a mass ratio of 1:30 x and sodium hypophosphite in a tube furnace, heated to 350° under nitrogen atmosphere and calcined for 2 hours to obtain CoO x / CoP; (3) Take 50ml of liquid nitrogen in a beaker and mix the prepared CoO x / CoP powder is quickly poured into it, and after the liquid nitrogen evaporates, the quick-frozen powder sample is quickly taken out and waits for subsequent application processing; (b) Preparation of working electrode To prepare the working electrode, the synthesized sample was dispersed in a Nafion ethanol solution with a volume ratio of 9:200 and ultrasonicated for more than 30 min to obtain a fully dispersed homogeneous catalyst solution. Then, 100 μl of the prepared homogeneous dispersion was dropped onto a 1 cm 2 The samples were deposited on carbon paper and then dried at room temperature for electrocatalytic testing in a conventional three-electrode setup.

2. The preparation method according to claim 1, characterized in that In step (b), the catalyst was subjected to electrocatalytic hydrogen evolution in 1M KOH and 0.5M H2SO4 solutions under alkaline and acidic conditions, respectively.

3. CoO prepared by the preparation method according to claim 1 x Application of a / CoP-L catalyst in electrocatalytic hydrogen evolution, characterized in that: The catalyst has lattice distortion and crystalline / amorphous heterogeneous interface, and is used for electrocatalytic hydrogen evolution under alkaline and acidic conditions.

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