Phosphorus Vacancy Molybdenum Phosphide Material and Its Preparation and Application in HER Catalysis

Abstract

The present invention relates to the field of catalytic materials, and particularly to a molybdenum phosphide material with phosphorus vacancies, which is a molybdenum phosphide material having phosphorus vacancies on its surface. The present invention also relates to the preparation of the said material and its application in HER catalysis. The molybdenum phosphide material with phosphorus vacancies of the present invention has abundant electroactive sites and fast charge transfer ability, and shows low overpotential and high TOF value in both alkaline and acidic media, and can exhibit excellent HER catalytic activity.

Description

Technical Field

[0001] This application belongs to the field of catalytic materials, specifically relating to the field of HER catalytic materials. Background Art

[0002] As a renewable clean energy source, hydrogen energy plays a key role in the production of hydrogen as its demand continues to increase. To date, many raw materials can be used to produce hydrogen, such as biomass, natural gas, water, etc. Among them, the electrochemical splitting of water using renewable electricity to generate hydrogen is a clean and renewable method. As the cathodic half-reaction, the hydrogen evolution reaction (HER) requires highly efficient and inexpensive electrocatalysts. As the most advanced electrocatalyst, Pt / C has excellent catalytic performance, but its high cost and scarce resources limit its use. It is necessary to develop highly efficient, low-cost, and resource-rich non-precious metal electrocatalysts to promote HER to replace Pt / C.

[0003] Some novel HER catalytic materials have been reported in the prior art, mainly including molybdenum-based catalysts and transition metal phosphides, such as MoS2 [1] 、MoS2 / NiCo-LDH [2] 、Mo2N@NC [3] 、NiS / Ni2P / CC [4] 、NiCo2P x [5] 、MoS2-MoP / NC [6] 、MoP / MoS2-8 [7] 、MoS 2(1-x) Se 2x / NiSe2 [8] and other materials. The existing materials are difficult to balance the application scenarios in both acidic and alkaline systems. In addition, the catalytic performance and stability of HER need to be improved.

[0004] References

[0005] [1]L.Li, Z.Qin, L.Ries, S.Hong, T.Michel, J.Yang, C.Salameh, M.Bechelany, P.Miele, D.Kaplan, M.Chhowalla, D.Voiry, Role of Sulfur Vacancies and Undercoordinated Mo Regions in MoS2 Nanosheets toward the Evolution of Hydrogen, ACS Nano 13(2019)6824-6834.

[0006] [2] J. Hu, C. Zhang, L. Jiang, H. Lin, Y. An, D. Zhou, M. K. H. Leung, S. Yang, Nanohybridization of MoS2 with Layered Double Hydroxides Efficiently Synergizes the Hydrogen Evolution in Alkaline Media, Joule 1 (2017) 383 - 393.

[0007] [3] Z. Lv, M. Tahir, X. Lang, G. Yuan, L. Pan, X. Zhang, J.-J. Zou, Well-Dispersed Molybdenum Nitrides on a Nitrogen-Doped Carbon Matrix for Highly Efficient Hydrogen Evolution in Alkaline Media, J. Mater. Chem. A 5 (2017) 20932 - 20937.

[0008] [4] X. Xiao, D. Huang, Y. Fu, M. Wen, X. Jiang, X. Lv, M. Li, L. Gao, S. Liu, M. Wang, C. Zhao, Y. Shen, Engineering NiS / Ni2P Heterostructures for Efficient Electrocatalytic Water Splitting. ACS Appl. Mater. Interfaces 10 (2018) 4689 - 4696.

[0009] [5] R. Zhang, X. Wang, S. Yu, T. Wen, X. Zhu, F. Yang, X. Sun, X. Wang, W. Hu, Ternary NiCo2P x Nanowires as pH-Universal Electrocatalysts for Highly Efficient Hydrogen Evolution Reaction. Adv. Mater. 29 (2017) 1605502.

[0010] [6]X.Huang,H.Xu,D.Cao,D.Cheng,Interface Construction of P-SubstitutedMoS2 as Efficient and Robust Electrocatalyst for Alkaline Hydrogen EvolutionReaction,Nano Energy 78(2020)105253.

[0011] [7]A.Wu,Y.Gu,Y.Xie,C.Tian,H.Yan,D.Wang,X.Zhang,Z.Cai,H.Fu,EffectiveElectrocatalytic Hydrogen Evolution in Neutral Medium Based on 2DMoP / MoS2Heterostructure Nanosheets,ACS Appl.Mater.Interfaces 11(2019)25986-25995.

[0012] [8]H.Zhou,F.Yu,Y.Huang,J.Sun,Z.Zhu,R.J.Nielsen,R.He,J.Bao,W.A.GoddardIII,S.Chen,Z.Ren,Efficient Hydrogen Evolution by Ternary MolybdenumSulfoselenide Particles on Self-Standing Porous Nickel Diselenide Foam,NatCommun 7(2016)12765. Summary of the Invention

[0013] Aiming at the problem of unsatisfactory catalytic performance of existing HER catalytic materials, the first object of the present invention is to provide a phosphorus-vacancy molybdenum phosphide material, aiming to provide a new material that can exhibit excellent HER catalytic performance in both acidic and alkaline systems.

[0014] The second object of the present invention is to provide a preparation method of the phosphorus-vacancy molybdenum phosphide material, aiming to prepare the new material with excellent HER activity.

[0015] The third object of the present invention is to provide the application of the phosphorus-vacancy molybdenum phosphide material as an HER catalyst.

[0016] The fourth object of the present invention is to provide an electrode containing the phosphorus-vacancy molybdenum phosphide material.

[0017] The fifth object of the present invention is to provide an electrolytic water hydrogen production device and a battery including the molybdenum phosphide material with phosphorus vacancies for electrolytic water hydrogen production.

[0018] A molybdenum phosphide material with phosphorus vacancies, which is a single crystal molybdenum phosphide material with phosphorus vacancies on its surface.

[0019] The present invention provides a new single crystal molybdenum phosphide material with surface phosphorus vacancies. This material has abundant electroactive sites and fast charge transfer ability. It shows low overpotential and high TOF value in both alkaline and acidic media, and can exhibit excellent HER catalytic activity.

[0020] The molybdenum phosphide material with phosphorus vacancies described in the present invention includes a hexagonal single crystal molybdenum phosphide core and a phosphorus vacancy rough surface shell compounded thereon, forming a core-shell structure.

[0021] The present invention also provides a preparation method of the molybdenum phosphide material with phosphorus vacancies. MoO2 and a phosphorus source are subjected to the first-stage calcination to obtain MoP, and then the second-stage calcination is carried out under a reducing atmosphere and negative pressure to obtain the molybdenum phosphide material with phosphorus vacancies; wherein, the temperature in the second-stage calcination stage is 630-800 °C.

[0022] In the present invention, to successfully prepare the new material and improve its HER performance, it is necessary to solve the problem that it is difficult to construct surface phosphorus vacancies in molybdenum phosphide, especially single crystal molybdenum phosphide. Aiming at the problems in the preparation of the new material, the present invention innovatively discovers that by carrying out the first-stage calcination with MoO2 and a phosphorus source, and then carrying out the second-stage calcination under negative pressure and reducing atmosphere, and further cooperating with the control of the temperature in the second-stage calcination, it can unexpectedly achieve synergy, be able to construct phosphorus vacancy defects on the surface of MoP, improve the active sites and electron transport ability, and thus can significantly improve the HER catalytic performance of the material.

[0023] In the present invention, the combined control of the first-stage calcination of MoO2 and the phosphorus source, and the negative pressure, reducing atmosphere and temperature in the second stage is the key to synergistically preparing the new material and improving its HER performance.

[0024] In the present invention, the MoO2 can be a commercial product or prepared based on existing methods.

[0025] For example, the MoO2 is obtained by hydrothermal and calcination treatment of an aqueous solution containing a molybdenum source, a surfactant and a carrier;

[0026] Preferably, the molybdenum source is at least one of water-soluble molybdates and polymolybdates;

[0027] Preferably, the surfactant is an anionic surfactant;

[0028] Preferably, the carrier is a carbon carrier;

[0029] Preferably, the temperature of the hydrothermal reaction is greater than or equal to 100 °C, and more preferably 100 - 160 °C;

[0030] Preferably, the calcination atmosphere is at least one of nitrogen and inert gas;

[0031] Preferably, the calcination temperature is 400 - 650 °C.

[0032] In the present invention, MoO₂ and the phosphorus source are subjected to the first-stage calcination and then combined with the subsequent second-stage calcination, which helps to synergistically improve the surface phosphorus vacancies of the prepared material and helps to improve the HER performance.

[0033] In the present invention, there is no special requirement for the phosphorus source, for example, it can be at least one of sodium hypophosphite and red phosphorus.

[0034] Preferably, the Mo / P element ratio in MoO₂ and the phosphorus source is 1 - 2:1 - 2, and more preferably 1:1 - 1.1.

[0035] In the present invention, the atmosphere of the first-stage calcination is a protective atmosphere;

[0036] Preferably, the protective atmosphere is at least one of nitrogen and inert gas;

[0037] Preferably, the temperature of the first-stage calcination is 600 - 700 °C. More preferably 650 - 700 °C. It is found that at the preferred first-stage calcination temperature, it is helpful for further cooperation and synergy with the second calcination process, and helps to further improve the HER performance of the prepared material.

[0038] In the present invention, there is no special requirement for the rate of heating to the first-stage calcination temperature, for example, it is 1 - 20 °C / min, and preferably 5 - 15 °C / min.

[0039] Preferably, the holding time at the first-stage calcination temperature is 0.5 - 3 h, and preferably 1 - 2 h.

[0040] In the present invention, under the first-stage calcination of MoO₂ and the phosphorus source, further combined with the second-stage calcination under negative pressure and reducing atmosphere and temperature control, it helps to synergistically construct surface phosphorus vacancies, helps to regulate the microstructure, and helps to further synergistically improve the HER performance of the material.

[0041] In the present invention, during the second-stage calcination process, the reducing atmosphere is a hydrogen-containing atmosphere;

[0042] Preferably, the reducing atmosphere is at least one of hydrogen, hydrogen-nitrogen mixture, and hydrogen-inert gas mixture;

[0043] Preferably, in the reducing atmosphere, the volume content of hydrogen is greater than or equal to 1 v%, preferably 10 - 100 v%; considering the processing cost and preparation value, it is further preferably 5 - 15%;

[0044] Preferably, the negative pressure in the second roasting stage is less than or equal to 250 Pa;

[0045] Preferably, the temperature of the second roasting is 650 - 700 °C. In the present invention, at this preferred temperature, it is helpful to further synergistically improve the HER performance of the prepared material.

[0046] In the present invention, there is no special requirement for the rate of heating up to the second roasting temperature, for example, it is 1 - 20 °C / min, preferably 5 - 15 °C / min.

[0047] Preferably, the heat preservation time at the second roasting temperature is 0.5 - 5 h; it is further preferably 1 - 2 h.

[0048] The present invention also provides an application of the molybdenum phosphide material with phosphorus vacancies, using it as a HER catalyst.

[0049] In the present invention, based on existing means, the molybdenum phosphide material with phosphorus vacancies can be used to prepare the required HER catalytic device. For example, using it as a HER catalyst for the preparation of hydrogen production by electrolyzing water and the preparation of zinc - aqueous batteries.

[0050] The present invention also provides a HER catalytic electrode, which contains the molybdenum phosphide material with phosphorus vacancies of the present invention.

[0051] In the present invention, for the HER catalytic electrode, except for adding the active material of the molybdenum phosphide material with phosphorus vacancies of the present invention, other auxiliary materials and structural components can be well - known.

[0052] The present invention also provides a device (or device) containing the HER catalytic electrode, specifically, it can be a hydrogen production device by electrolyzing water or a device for preparing a zinc - aqueous battery. Similarly, for the device of the present invention, except for containing the active material of the molybdenum phosphide material with phosphorus vacancies of the present invention, other materials and structures can be well - known.

[0053] Beneficial effects

[0054] 1. The present invention provides a new molybdenum phosphide single - crystal material with surface phosphorus vacancies. This material has rich electroactive sites and fast charge transfer ability. It shows low over - potential and high TOF value in both alkaline and acidic media, and can exhibit excellent HER catalytic activity.

[0055] 2. The present invention uses MoO2 and a phosphorus source for the first-stage calcination, and then performs the second-stage calcination under a negative pressure and a reducing atmosphere. Further, by controlling the temperature of the second-stage calcination, it can unexpectedly achieve synergy, construct phosphorus vacancy defects on the surface of MoP, improve the active sites and electron transport ability, and thus significantly improve the HER catalytic performance of the material. Description of the Drawings

[0056] Figure 1 Polarization curves and Tafel slope diagrams of the material prepared in Example 1 under acidic and alkaline conditions, where a / b are the polarization curves and Tafel slopes in 1 M KOH electrolyte; c / d are the polarization curves and Tafel slopes in 0.5 M H2SO4 electrolyte.

[0057] Figure 2 HER performance of MoP and MoP-Pv (Group A) electrocatalysts of Example 1 in 1 M KOH electrolyte. (a) Exchange current density (j0); (b) Impedance Nyquist plots and equivalent circuit diagrams at η = 123 mV; (c) Double-layer capacitance measurement (C dl ); (d) Long-term stability.

[0058] Figure 3 HER performance of MoP and MoP-Pv (Group A) electrocatalysts of Example 1 in 0.5 M H2SO4 electrolyte. (a) Exchange current density (j0); (b) Impedance Nyquist plots and equivalent circuit diagrams at η = 158 mV; (c) Double-layer capacitance measurement (C dl ); (d) Long-term stability.

[0059] Figure 4 Comparison of the intrinsic activities of the material of Example 1 with other electrocatalysts. Among them, (a) TOF curves of MoP and MoP-Pv in 1 M KOH and (b) 0.5 M H2SO4. (1 M KOH: MoS2 / NiCo-LDH, [2] MoS2-7H, [3] Mo2N@NC, [4] NiS / Ni2P / CC, [5] Se-MoP, [6] MoP / MoS2-8, [7] NiCo2P x , [8] MoS2-MoP / NC [9] ; 0.5 M H2SO4: MoP / MoS2-8, [7] P-MoP,

[10] MoS2-7H, [3] MoP@NC,

[11] hH-MoS2,

[12] P-1T-MoS2,

[13] MoP,

[0060]

[14] MoS 2(1-x) Se 2x / NiSe2

[15] ).

[0061] Figure 5 XPS diagrams of the materials prepared in Example 1, where (a) XRD spectra of MoP-Pv (Group A), MoP, and MoO2; high-resolution XPS spectra of (b) Mo 3d and (c) P 2p in MoP and MoP-Pv.

[0062] Figure 6 Selected area electron diffraction diagrams of the materials prepared in Example 1, where (a) selected area electron diffraction diagrams of MoP and (b) MoP-Pv (Group A).

[0063] Figure 7 High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images of the materials prepared in Example 1, where (a) HAADF-STEM images of MoP-Pv (Group A) and (d) MoP. Figure 7 b, Figure 7 e is the P structure analysis diagram, Figure 7 c and 7f are the atomic model diagrams.

[0064] Figure 8 Polarization curves and Tafel slopes of the materials prepared in Example 2, where (a, b) polarization curves and Tafel slopes in 1 M KOH electrolyte; (c, d) polarization curves and Tafel slopes in 0.5 M H2SO4 electrolyte.

[0065] Figure 9 Polarization curves and Tafel slopes of the materials prepared in Example 3, where (a, b) polarization curves and Tafel slopes in 1 M KOH electrolyte; (c, d) polarization curves and Tafel slopes in 0.5 M H2SO4 electrolyte.

[0066] Figure 10 Polarization curves and Tafel slopes of the materials prepared in Comparative Example 1, where (a, b) polarization curves and Tafel slopes in 1 M KOH electrolyte; (c, d) polarization curves and Tafel slopes in 0.5 M H2SO4 electrolyte.

[0067] Figure 11Polarization curves and Tafel slopes of the materials prepared in Comparative Example 2, where (a, b) are the polarization curves and Tafel slopes in 1 M KOH electrolyte; (c, d) are the polarization curves and Tafel slopes in 0.5 M H2SO4 electrolyte.

[0068] Figure 12 Polarization curves and Tafel slopes of the materials prepared in Comparative Example 3, where the upper left and upper right figures are the polarization curves and Tafel slopes in 1 M KOH electrolyte; the lower left and lower right figures are the polarization curves and Tafel slopes in 0.5 M H2SO4 electrolyte.

[0069] Figure 13 Polarization curves and Tafel slopes of the materials prepared in Comparative Example 4, where (a, b) are the polarization curves and Tafel slopes in 1 M KOH electrolyte; (c, d) are the polarization curves and Tafel slopes in 0.5 M H2SO4 electrolyte. Detailed implementation manners

[0070] Example 1

[0071] Step (1): Preparation of molybdenum dioxide (MoO2) precursor

[0072] A 2 cm × 5 cm carbon cloth was ultrasonically treated with acetone, deionized water, and ethanol for 20 minutes each to remove surface impurities, and then dried for later use. 1.2977 g of ammonium molybdate tetrahydrate ((NH4)6Mo7·4H2O) and 2.0187 g of sodium dodecyl sulfate (C 12 H 25 SO4Na, SDS) were added to a beaker containing 35 mL of deionized water and stirred for 30 minutes to obtain a uniformly dispersed solution, which was transferred to a 50 mL polytetrafluoroethylene high-temperature and high-pressure hydrothermal reactor. The dried carbon cloth was vertically placed into the hydrothermal reactor, and the hydrothermal reactor was placed in an oven and heated to 100 °C for 18 hours. The obtained carbon cloth was washed several times with deionized water and ethanol, dried in an oven at 60 °C, and calcined in a tubular furnace at 450 °C for 2 hours under an argon atmosphere. The obtained product was the carbon cloth containing MoO2 precursor.

[0073] Step (2): Preparation of molybdenum phosphide (MoP) electrocatalyst

[0074] The carbon cloth containing MoO2 precursor obtained in step (1) was placed downstream of a quartz tube 10 cm away from sodium hypophosphite (NaH2PO2, with a Mo / P element molar ratio of 1: in an argon atmosphere and heated to 650 °C (marked as T1) at a rate of 10 °C per minute and maintained for 1 hour for phosphidation. Subsequently, the obtained product was the MoP sample after cooling to room temperature.

[0075] Step (3): Preparation of molybdenum phosphide (MoP-Pv) electrocatalyst containing phosphorus vacancies

[0076] Under a vacuum state (pressure P, less than or equal to 250 Pa), a 10% H2 / Ar atmosphere was circulated, and the temperature was raised to T2 (Group A: 650 °C, Group B: 700 °C, Group C: 800 °C) at a rate of 10 °C per minute and maintained for 1 hour to reduce MoP to generate Pv. After cooling to room temperature, the obtained samples were MoP-Pv-650 (product of Group A), MoP-Pv-700 (product of Group B), and MoP-Pv-800 (product of Group C).

[0077] (Since MoP-Pv-650 has better performance, subsequent characterizations will be based on it. Hereinafter, "MoP-Pv" will also refer to the MoP-Pv-650 sample).

[0078] As Figure 1 shown in a, in 1 M KOH, MoP-Pv-650, MoP-Pv-700, and MoP-Pv-800 only require overpotentials of 151 mV, 173 mV, and 188 mV respectively to reach a current density of 10 mA·cm -2 . These are all lower than the 221 mV required for MoP; similarly, as shown in Figure 1 c, in 0.5 M H2SO4, MoP-Pv-650, MoP-Pv-700, and MoP-Pv-800 only require overpotentials of 186 mV, 203 mV, and 218 mV respectively to reach a current density of 10 mA·cm -2 . These are all lower than the 248 mV required for MoP. In addition, calculating the Tafel slope (η vs. log(j)) is also of great significance for evaluating the HER catalytic kinetics of the catalyst. As shown in Figure 1 b and 1d, the Tafel slopes were derived from the polarization curves. In 1 M KOH, the Tafel slopes of MoP-Pv-650, MoP-Pv-700, and MoP-Pv-800 were 71.36 mV·dec -1 , 59.44 mV·dec -1 , and 61.52 mV·dec -1 respectively, all of which are less than that of MoP (93.76 mV·dec -1 ); in 0.5 M H2SO4, the Tafel slopes of MoP-Pv-650, MoP-Pv-700, and MoP-Pv-800 were 58.55 mV·dec -1 , 60.89 mV·dec -1 , and 60.33 mV·dec -1 respectively, all of which are less than that of MoP (67.85 mV·dec -1)。The smaller the value of the Tafel slope, the smaller the overpotential required to increase the same current density, indicating that the charge transfer kinetics is faster. That is to say, the HER performance of MoP-Pv-650 / 700 / 800 is better than that of MoP, which is due to the presence of Pv.

[0079] The exchange current density (j0) was determined by the Tafel slope and intercept, and the intrinsic HER activity of MoP-Pv and MoP was studied in 1 M KOH ( Figure 2 ) and 0.5 M H2SO4 ( Figure 3 ). As Figure 2 shown in a, the j0 value of MoP-Pv is 0.072 mA·cm -1 , which is 35.8% higher than that of MoP with a j0 value of 0.053 mA·cm -1 . The larger the exchange current density, the easier it is for MoP-Pv to gain and lose electrons, that is, MoP-Pv has a higher HER catalytic activity. Therefore, electrochemical impedance (EIS) was measured to further compare the charge transfer ability. As Figure 2 shown in b, a semicircle was observed in the low-frequency region, indicating that the electrode reaction process is kinetically controlled rather than mass-transfer controlled. Obviously, the semicircle diameter of MoP-Pv is smaller than that of MoP, indicating that the charge transfer resistance of MoP-Pv is smaller than that of MoP. The results show that phosphorus vacancies promote charge transfer and enrich the electron density of active sites. As Figure 2 shown in c, the C dl value of MoP-Pv is 0.80 mF·cm -1 , which is larger than the C dl value of 0.64 mF·cm -1 for MoP, indicating that MoP-Pv has more electrochemically active sites than MoP. The increase in active sites is attributed to the increase in surface roughness caused by the generation of Pv and / or the decrease in crystallinity from single crystal to polycrystalline (see Figure 6 a and Figure 6 b). From the perspective of practical applications, the long-term stability of the current density change under a stable voltage is an important parameter for evaluating the electrocatalytic performance. As Figure 2 shown in d, the current density of MoP-Pv decays from 10 mA·cm -2 to 8.44 mA·cm -2 after 24 hours of continuous reaction, with a retention rate of 84.4%.

[0080] Similar to the promoting effect of Pv on HER activity in alkaline electrolyte (1 M KOH), Pv can also significantly improve HER activity in acidic electrolyte (0.5 M H2SO4). In short, j0 increases (from 0.0054 mA·cm -1 to 0.0029 mA·cm-1 , Figure 3 a), Compared with MoP, the semicircle diameter of MoP-Pv is smaller, C dl A larger value ( Figure 3 b and 3c). Figure 3 As shown in d, the current density of MoP-Pv increased from 10 mA cm to 10 mA cm after 24 h of continuous reaction. -2 Decayed to 8.65 mA·cm -2 The retention rate was 86.5%. The results showed that the active sites formed by Pv were stable in both alkaline and acidic media.

[0081] To more accurately evaluate the intrinsic catalytic activity, we calculated the turnover frequency (TOF) based on the electrochemically active surface area (ECSA) of the electrode. ECSA can affect the HER activity due to differences in electrode surface roughness. Figure 4 The TOF values of MoP and MoP-Pv as well as other molybdenum-based or phosphorus-containing electrocatalysts reported in the literature are given. It can be seen that in 1M KOH and 0.5MH2SO4 with an overpotential of 200mV, the TOF values of MoP-Pv are 3.14s and 3.6s, respectively. -1 and 1.19s -1 , which are 4.1 and 2.5 times that of MoP, respectively. Moreover, MoP-Pv exhibits good performance compared with most corresponding electrocatalysts, clearly demonstrating the promoting effect of Pv on HER activity.

[0082] like Figure 5 As shown in a, MoO2 (with Mark, JCPDF No.78-1069) precursor, after phosphating, a pure hexagonal MoP (with Compared with pristine MoP, MoP-Pv still maintains the hexagonal phase after annealing in hydrogen at 650 °C for 1 h, which indicates that hydrogen only reduces the surface of MoP but not its interior.

[0083] The phosphorus vacancies were further investigated using X-ray photoelectron spectroscopy (XPS). Figure 5 As shown in b, the XPS spectrum of Mo 3d shows two peaks at 228.3eV and 231.4eV, which are attributed to the Mo of Mo-P bond. δ+ Species (0<δ<4). At 235.9eV / 232.8eV (Mo 6+ 3d 3 / 2 / 3d 5 / 2 ) is attributed to Mo in MoO3 6+-O bonds, which are caused by surface oxidation due to the exposure of the sample to air. This seems to be contradictory to the fact that no diffraction peaks of molybdenum oxides (MoO2 or MoO3) are shown in the XRD pattern because XRD mainly detects the bulk phase of substances, while XPS only reflects the surface composition. For MoP-Pv, compared with MoP, two new Mo 3d 3 / 2 and Mo3d 5 / 2 peaks appear at 232.1 eV and 228.9 eV, and these two peaks are attributed to the Mo 4+ -O bonds of MoO2 because part of the surface MoO3 is reduced to MoO2 after hydrogen annealing. Correspondingly, as shown in Figure 5 b, the peak area of Mo 6+ -O on the surface of MoP-Pv is smaller than that of MoP.

[0084] As shown in Figure 5 c, the two P 2p peaks at 129.5 eV and 130.4 eV are attributed to the P 2p 3 / 2 and P2p 1 / 2 of low-valent P in MoP, and the P-O peak at higher binding energy is attributed to PO4 3- or P2O5 existing due to oxidation. According to the semi-quantitative analysis of the XPS results, due to hydrogen reduction, the content of P atoms in MoP-Pv decreased by 45% compared with MoP (from 11.7% to 6.44%), confirming the generation of Pv.

[0085] Phosphorus vacancies are highlighted by yellow dotted circles with a darker background, and orange solid circles with a brighter background represent phosphorus atoms in MoP. (b) Structural analysis of MoP-Pv and (e) MoP. The dimensions along the x-axis in (b) and (e) correspond to the lengths of the cyan lines in (a) and (d) respectively, and the peaks and valleys in (b) and (e) correspond to the Mo sites and P sites of the MoP(001) crystal plane respectively. (c) Atomic model diagrams of the (001) crystal plane of MoP-Pv and (f) MoP, which perfectly match the pink regions in (a) and (d).

[0086] To directly observe phosphorus vacancies, MoP-Pv and MoP electrocatalysts were further characterized by HAADF-STEM. Figure 7 a and 7d are images of the (001) crystal plane in MoP-Pv and MoP, which perfectly match the atomic models shown in Figure 7 c and 7f. In the upper half of Figure 7 a, a large number of phosphorus vacancies are shown in the area highlighted by the yellow dotted circle. In the corresponding MoP-Pv structural analysis in Figure 7 b, the generation of phosphorus vacancies is also proved; Figure 7 the lower half of Figure 7As shown in d-f, there are no phosphorus vacancies in the MoP electrocatalyst. In summary, hydrogen reduction of the MoP electrocatalyst does induce phosphorus vacancies.

[0087] In summary, the combination of physical characterization and in-depth study of electrocatalytic performance verifies that phosphorus vacancy engineering can improve the intrinsic HER activity of MoP-Pv. Among them, the formed Pv either serves as an active site or induces uncoordinated Mo as a hydrogen evolution active site. Since the role of Pv is similar in alkaline and acidic media, it can be known that the improvement of HER activity does not depend much on the pH value. That is to say, HER can proceed through the direct proton adsorption process of H + +e - →H * or through the dissociation process of water molecules: H2O + e - →H * + HO - .

[0088] Example 2

[0089] Compared with Example 1, the only difference is that in step (2), the temperature of transformation T1 is 600 °C or 700 °C respectively. Other operations and parameters are the same as those in Example 1. The MoP prepared in step (2) is labeled as MoP-600 and MoP-700 respectively. The polarization curves and Tafel slopes of the prepared materials are shown in Figure 8 . Note Figure 8 that the MoP-650 described therein is actually the MoP prepared in step 2 of Example 1.

[0090] Example 3

[0091] Compared with Example 1, the only difference is that in step (2), the elemental molar ratios of Mo / P are as follows: Group A: Mo / P = 1:2; the product prepared in step (2) is labeled as MoP-1:2;

[0092] Group B: Mo / P = 2:1. The product prepared in step (2) is labeled as MoP-2:1;

[0093] The polarization curves and Tafel slopes of the prepared materials are shown in Figure 9 . Note Figure 9 that the MoP-1:1 described therein is actually the MoP prepared in step 2 of Example 1.

[0094] Comparative Example 1

[0095] Compared with Example 1, the only difference is that the temperature of T2 is changed, which are respectively:

[0096] Group A: T2 is 500 °C, other operations and parameters are the same as those in Example 1, and the product prepared in step (3) is labeled as MoP-H500.

[0097] Group B: T2 was 600 °C, and other operations and parameters were the same as in Example 1. The product prepared in step (3) was labeled MoP-H600.

[0098] The polarization curves and Tafel slopes of the prepared materials are shown in Figure 10 . Note Figure 10 In, MoP-Pv-650 is essentially the product finally prepared in Group A of Example 1, which has surface phosphorus vacancies.

[0099] MoP-Pv-700 is essentially the product finally prepared in Group B of Example 1, which has surface phosphorus vacancies.

[0100] MoP-Pv-800 is essentially the product finally prepared in Group C of Example 1, which has surface phosphorus vacancies.

[0101] No phosphorus vacancies were generated in the two samples of MoP-H500 and MoP-H600.

[0102] Comparative Example 2

[0103] Compared with Example 1, the difference is only that in step (3), the heat treatment in the T2 section was not carried out under vacuum. That is, during the T2 section treatment, the pressure P was 1 atm, and other operations and parameters were the same as in Example 1. The product finally prepared in step (3) was labeled (MoP-H non-vacuum).

[0104] The polarization curves and Tafel slopes of the prepared materials are shown in Figure 11 . Note Figure 11 In, MoP is the product prepared in step 2 of Example 1. The MoP-Pv-vacuum is the product prepared in Group A of step (3) of Example 1.

[0105] The results showed that no surface phosphorus vacancies were formed, the overpotential was similar to that of MoP (prepared in step (2)), and the HER performance was not ideal.

[0106] Comparative Example 3

[0107] Compared with Example 1, the difference is only that the preparation method was changed. The main difference is that MoO3-phosphorus source was used for the first-stage roasting - second-stage roasting. The different steps are:

[0108] Preparation of molybdenum trioxide (MoO3) precursor

[0109] Add 2 g of molybdenum powder to 10 mL of deionized water. While stirring in an ice bath, slowly add 20 mL of 30% hydrogen peroxide (30% H2O2) dropwise thereto. After obtaining a homogeneous solution, hydrothermal react at 200 °C for 12 h in a polytetrafluoroethylene high-temperature and high-pressure hydrothermal autoclave. The solution obtained by hydrothermal reaction is centrifugally washed three times with deionized water and ethanol respectively, and the dried product is MoO3 powder.

[0110] Preparation of molybdenum phosphide electrocatalyst

[0111] The obtained MoO3 precursor is placed downstream of a quartz tube 10 cm away from sodium hypophosphite (NaH2PO2), and phosphidation is carried out under an argon atmosphere. The temperature is raised to 650 °C at a rate of 10 °C per minute and maintained for 1 h. After cooling to room temperature, the obtained product is a molybdenum phosphide sample, named "MoP-MoO3".

[0112] Preparation of molybdenum phosphide electrocatalyst containing phosphorus vacancies

[0113] Under the condition of maintaining a vacuum and flowing a 10% H2 / Ar atmosphere, the temperature is raised to 650 °C at a rate of 10 °C per minute and maintained for 1 h to reduce molybdenum phosphide to generate phosphorus vacancies. After cooling to room temperature, the obtained sample is molybdenum phosphide that may contain phosphorus vacancies, named "MoP-H650-MoO3".

[0114] The polarization curves and Tafel slopes of the prepared materials are shown in Figure 12 . The results show that its HER performance is poor.

[0115] Comparative Example 4

[0116] Compared with Example 1, the main difference is that a phosphidation-reduction one-step roasting preparation process is adopted, specifically:

[0117] Step (1): Preparation of molybdenum dioxide (MoO2) precursor, the same as in Example 1:

[0118] Step (2): Preparation of molybdenum phosphide (MoP) electrocatalyst

[0119] The obtained carbon cloth containing the MoO2 precursor is placed downstream of a quartz tube 10 cm away from sodium hypophosphite (NaH2PO2, with a molar ratio of Mo / P elements of 1:1)), and phosphidation is carried out under a hydrogen-argon mixed atmosphere (10% H2 / Ar). The temperature is raised to 650 °C at a rate of 10 °C per minute and maintained for 1 h. After cooling to room temperature, the obtained product is a molybdenum phosphide sample, and the product is labeled as MoP-H.

[0120] The product performance test is shown in Figure 13 (Note, Figure 13Among them, the MoP-A is the MoP in Step 2 of Example 1). The results show that the overpotentials of MoP-A and MoP-H for electrocatalytic hydrogen evolution are basically equivalent ( Figure 13 a, c), and the Tafel slopes of the two are also basically equivalent ( Figure 13 b, d). This result shows that even if the argon inert gas is replaced with a hydrogen-argon reduction atmosphere in the step of synthesizing molybdenum phosphide, molybdenum phosphide containing phosphorus vacancies cannot be obtained.

Claims

1. A preparation method of a phosphorus vacancy molybdenum phosphide material, characterized in that, The MoO₂ and a phosphorus source are subjected to a first-stage calcination to obtain MoP, and then a second-stage calcination is carried out under a reducing atmosphere and negative pressure to obtain the phosphorus-vacancy molybdenum phosphide material; The temperature in the second-stage calcination is 630-800 °C; The phosphorus-vacancy molybdenum phosphide material is a molybdenum phosphide single-crystal material with phosphorus vacancies on the surface; the phosphorus-vacancy molybdenum phosphide material includes a hexagonal-phase single-crystal molybdenum phosphide core and a phosphorus-vacancy rough surface shell composite thereon, forming a core-shell structure.

2. The preparation method of the phosphorus vacancy molybdenum phosphide material according to claim 1, wherein The MoO₂ is obtained by hydrothermal and calcination treatment of an aqueous solution containing a molybdenum source, a surfactant, and a carrier.

3. The preparation method of the phosphorus vacancy molybdenum phosphide material according to claim 2, characterized in that, The molybdenum source is at least one of water-soluble molybdates and polymolybdates.

4. The preparation method of the phosphorus-vacancy molybdenum phosphide material according to claim 2, wherein, The surfactant is an anionic surfactant.

5. The preparation method of the phosphorus vacancy molybdenum phosphide material according to claim 2, wherein, The carrier is a carbon carrier.

6. The preparation method of the phosphorus-vacancy molybdenum phosphide material according to claim 2, wherein, The hydrothermal temperature is greater than or equal to 100 °C.

7. The preparation method of the phosphorus-vacancy molybdenum phosphide material according to claim 2, wherein, The calcination atmosphere for obtaining MoO₂ is at least one of nitrogen and inert gases.

8. The preparation method of the phosphorus vacancy molybdenum phosphide material according to claim 2, wherein, The calcination temperature for obtaining MoO₂ is 400-650 °C.

9. The preparation method of the phosphorus-vacancy molybdenum phosphide material according to claim 1, characterized in that, The phosphorus source is at least one of sodium hypophosphite and red phosphorus.

10. The preparation method of the phosphorus vacancy molybdenum phosphide material according to claim 1 or 9, characterized in that, The Mo / P element ratio in MoO₂ and the phosphorus source is 1-2:1-2.

11. The preparation method of the phosphorus vacancy molybdenum phosphide material according to claim 1, characterized in that, The atmosphere in the first-stage calcination is a protective atmosphere.

12. The preparation method of the phosphorus vacancy molybdenum phosphide material according to claim 11, characterized in that, The protective atmosphere is at least one of nitrogen and inert gases.

13. The preparation method of the phosphorus-vacancy molybdenum phosphide material according to claim 1 or 11 or 12, characterized in that, The temperature in the first-stage calcination is 60-700 °C.

14. The preparation method of the phosphorus-vacancy molybdenum phosphide material according to claim 13, wherein, The holding time at the first-stage calcination temperature is 0.5-3 h.

15. The preparation method of the phosphorus-vacancy molybdenum phosphide material according to claim 1, characterized in that, During the second-stage calcination, the reducing atmosphere is a hydrogen-containing atmosphere.

16. The preparation method of the phosphorus vacancy molybdenum phosphide material according to claim 1 or 15, characterized in that, The reducing atmosphere is at least one of hydrogen, a hydrogen-nitrogen mixture, and a hydrogen-inert gas mixture.

17. The preparation method of the phosphorus-vacancy molybdenum phosphide material according to claim 1 or 15, characterized in that, In the reducing atmosphere, the volume content of hydrogen is greater than or equal to 1 v%.

18. The preparation method of the phosphorus-vacancy molybdenum phosphide material according to claim 1 or 15, characterized in that, In the reducing atmosphere, the volume content of hydrogen is 10-100 v%.

19. The preparation method of the phosphorus vacancy molybdenum phosphide material according to claim 1, characterized in that, The negative pressure in the second-stage calcination is less than or equal to 250 Pa.

20. The preparation method of the phosphorus vacancy molybdenum phosphide material according to claim 1, wherein, The temperature in the second-stage calcination is 650-700 °C.

21. The preparation method of the phosphorus vacancy molybdenum phosphide material according to claim 1 or 20, characterized in that, The holding time at the second-stage calcination temperature is 0.5-5 h.

22. Use of a phosphorus vacancy molybdenum phosphide material prepared by the preparation method according to any one of claims 1 to 21, characterized in that Use it as a HER catalyst.

23. The application according to claim 22, characterized in that, Use it as a HER catalyst for: electrolytic water for hydrogen production or preparation of a zinc-water battery.

24. A HER catalytic electrode, characterized in that, Containing the phosphorus-vacancy molybdenum phosphide material prepared by the preparation method according to any one of claims 1-21.

25. A device comprising the HER catalytic electrode according to claim 24, characterized in that, It is an electrolytic water hydrogen production device or a zinc-water battery.

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