Catalyst based on nickel base and preparation method and application thereof

Abstract

The invention discloses a catalyst Cr, Co-Ni (OH) 2 (at) NF based on a nickel base. The catalyst is prepared by taking foamed nickel (NF) as a carrier and doping Cr and Co elements, has efficient urea oxidation reaction (UOR) performance, and can be used for hydrogen production by electrolysis of water and urea pollution treatment. The preparation method comprises the following steps: soaking nickel foam in an HCl solution, soaking the nickel foam in a nickel salt solution with a specific concentration for reaction to generate nickel-based hydroxide, and soaking the nickel-based hydroxide in a solution containing chromic nitrate and cobalt potassium cyanide for reaction to finally generate the catalyst doped with Cr and Co. The catalyst shows low overpotential and good stability in a 1M KOH + 0.33 M urea solution, the overpotential of an anode for hydrogen production through electrolysis of water is remarkably reduced, and meanwhile efficient degradation of urea is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy materials, and in particular to a nickel-based catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of the global economy, the extensive use of traditional fossil fuels has triggered serious environmental problems and energy crises. The greenhouse gases and pollutants produced by the combustion of fossil fuels pose a significant threat to the ecological environment and human health. At the same time, the ever-increasing global energy demand has also posed a serious challenge to the supply of traditional energy. Therefore, the development of clean, renewable, and efficient energy technologies has become a key focus of global scientific research.

[0003] As a clean and efficient energy carrier, hydrogen has the advantages of good combustion performance, high calorific value and no pollution. It is considered to be one of the most promising clean energy sources to replace traditional fossil fuels in the future. Electrocatalytic water splitting is an efficient method for producing high-purity hydrogen. It uses electrical energy to decompose water into hydrogen and oxygen. This method can not only utilize electricity generated by renewable energy sources (such as solar energy, wind energy, etc.), but also achieve environmental friendliness during the electrolysis process. However, the efficiency of electrocatalytic water splitting is limited by the anodic oxygen evolution reaction (OER), because the kinetics of OER are slow and require a high overpotential, which increases the energy consumption of the entire water electrolysis process.

[0004] To improve the efficiency of hydrogen production from water electrolysis, researchers have begun to explore alternative anode reactions to OER. As an alternative reaction, urea oxidation reaction (UOR) has attracted attention due to its lower theoretical potential (0.37 V vs. RHE). Urea is a common biological waste and pollutant, widely present in industrial wastewater and domestic sewage. Using urea oxidation to assist electrocatalytic water splitting can not only reduce the overpotential required at the anode, but also achieve urea degradation, thereby achieving the dual goals of waste treatment and energy production.

[0005] In the study of catalysts, precious metal-based catalysts (such as Ru, Ir and their complexes) have shown excellent activity and stability in urea oxidation, but due to their scarcity and high cost, they are difficult to apply on a large scale. Therefore, researchers have turned their attention to non-precious metal-based catalysts, especially nickel-based catalysts. Nickel-based catalysts have attracted widespread attention due to their low cost, high reserves and good UOR activity. Research on nickel-based catalysts mainly focuses on metallic nickel, nickel-based hydroxides, oxides, nitrides, phosphides and sulfides. Through various design and regulation strategies, such as porous structure design, surface engineering, heterogeneous interface effects and bimetallic synergistic effects, the number of active sites can be increased and the intrinsic catalytic activity of the catalyst can be improved, thereby improving the UOR performance.

[0006] Although nickel-based catalysts have made some progress in UOR catalytic activity, the catalysts synthesized at room temperature are still not suitable for high current density (>100 mA cm -2 Reports on urea oxidation anode catalysts with high catalytic activity and long-term stability (>50h) are still relatively rare. Therefore, the development of a nickel-based catalyst that can be prepared at room temperature and exhibits high catalytic activity and good stability is of great scientific significance and practical application value for reducing the overpotential at the anode end of water electrolysis for hydrogen production and achieving efficient urea degradation. Summary of the Invention

[0007] The present invention aims to provide a nickel-based catalyst to solve the problems of high anode overpotential and difficult urea pollution control in existing water electrolysis hydrogen production, and discloses a preparation method thereof.

[0008] To achieve the above-mentioned purpose, the present invention provides the following technical solution: a nickel-based catalyst, wherein the catalyst is Cr, Co-Ni(OH)2@NF, wherein Cr and Co are doping elements uniformly dispersed in Ni(OH)2, and the catalyst is grown on a nickel foam (NF) carrier.

[0009] Specifically, the doping ratio of Cr and Co is 1:1.

[0010] A method for preparing the nickel-based catalyst comprises the following steps:

[0011] S1, soaking nickel foam (NF) in HCl solution, washing with ethanol and deionized water and drying;

[0012] S2, immersing the treated nickel foam in an aqueous solution containing NaBH4, reacting at room temperature, and washing with deionized water to generate Ni(OH)2@NF;

[0013] S3. Immerse the generated Ni(OH)2@NF in an aqueous solution containing chromium nitrate and potassium cobalt cyanide, and react at room temperature to generate Co,Cr-Ni(OH)2@NF.

[0014] Specifically, the concentration of NaBH4 is 0.2 M and the reaction time is 2 hours.

[0015] Specifically, the concentrations of chromium nitrate and potassium cobalt cyanide are both 1 mg / mL, and the reaction time is 6.5 hours.

[0016] Specifically, a nickel-based catalyst is used in urea pollution control, wherein the catalyst can achieve efficient degradation of urea through urea oxidation reaction (UOR) and produce hydrogen at the same time.

[0017] Specifically, a nickel-based catalyst is used in renewable energy conversion, wherein the catalyst can reduce the anode overpotential during the process of water electrolysis to produce hydrogen, thereby improving the overall efficiency of water electrolysis to produce hydrogen.

[0018] The principle and beneficial effects of this technical solution:

[0019] The present invention provides a nickel-based catalyst, which mainly addresses the problems of high anode overpotential in water electrolysis for hydrogen production and difficulty in controlling urea pollution. The catalyst uses nickel foam (NF) as a carrier and is doped with Cr and Co elements to prepare a catalyst with high urea oxidation reaction (UOR) performance. The preparation process includes pre-treating the nickel foam to remove surface impurities, then generating nickel-based hydroxide on the surface of the nickel foam through an immersion reaction, and finally uniformly doping Cr and Co into the nickel-based hydroxide through a further immersion reaction. The doping of Cr and Co can significantly change the electronic structure of the catalyst, increase the number of active sites, and thus improve the UOR performance of the catalyst. During the urea oxidation process, the metal oxygen bonds (MO) on the catalyst surface combine with hydroxide ions, further react with urea to generate nitrogen and carbon dioxide, achieving efficient degradation of urea.

[0020] The catalyst achieves efficient degradation of urea through urea oxidation reaction and produces hydrogen at the same time, which not only solves the urea pollution problem but also realizes energy recovery and utilization. In the process of hydrogen production by electrolysis of water, the catalyst can significantly reduce the anode overpotential, improve the overall efficiency of hydrogen production by electrolysis of water, and reduce energy consumption. Through dual doping of Cr and Co, the catalyst shows excellent UOR catalytic performance and good stability in alkaline solution of urea, even at high current density (>100mA cm -2 ) and long-term (>50h) operation conditions can still maintain high performance. Based on nickel-based materials, this catalyst is low-cost and abundant in resources, with a simple preparation process, suitable for large-scale production, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Characterization diagrams of the catalysts of the present invention, wherein (a) is the XRD spectrum of nCr-mCo-Ni(OH)2-z@NF, (be) are SEM images of Cr, Co-Ni(OH)2@NF, Cr-Ni(OH)2@NF, Co-Ni(OH)2@NF, and Ni(OH)2@NF, respectively; (f) is the TEM image and corresponding element imaging of Cr, Co-Ni(OH)2@NF, (g) is the SEM image of Cr, Co-Ni(OH)2@NF, (hl) are SEM images of Co, O, Ni, Cr, and N, respectively; and (mp) are high-resolution XPS spectra of Ni, O, Co, and Cr, respectively;

[0022] Figure 2 The electrochemical test diagram of the catalyst of the present invention, wherein (a) is the LSV curve, (b) is 100mA cm -2 and 200mA cm -2 (c) Tafel slope, (d) LSV curves of Cr, Co-Ni(OH)2@NF in 1 M KOH solution and different urea concentrations, (e) LSV curves of Cr, Co-Ni(OH)2@NF in different solution concentrations, (f) LSV curves of catalysts with different Co and Cr doping amounts, (g) Cdl, (h) Linear sweep voltammetry curves of Cr, Co-Ni(OH)2@NF electrocatalyst before and after 1000 cycles under OER, (i) Cr, Co-Ni(OH)2@NF at an initial current density of 100 mA cm -2 The it curve when DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments:

[0024] Example:

[0025] Preparation of 1Ni(OH)2@NF

[0026] First, nickel foam (NF) was pressed into 1×3cm 2 The size of the NF (1 × 3 cm) was soaked in HCl (3 M) for 30 min, washed three times with ethanol and deionized water, and dried in vacuum. 2 ) was immersed in a 0.2M NaBH4 aqueous solution and reacted for 2 hours at room temperature (26-28°C), then rinsed with deionized water to produce Ni(OH)2@NF material. To optimize the experimental conditions, the reaction time was fixed and the synthesis of the catalyst was explored at different concentrations of NaBH4 (0.1M, 0.2M, 0.3M, and 0.5M). The products obtained were recorded as Ni(OH)2-x@NF (x = 1, 2, 3, and 5). The products with the best OER performance were studied at 0.5h, 1h, 1.5h, 2h, 2.5h, and 3h, respectively, and recorded as Ni(OH)2-xa@NF, Ni(OH)2-xb@NF, Ni(OH)2-xc@NF, Ni(OH)2-xd@NF, Ni(OH)2-xe@NF, and Ni(OH)2-xf@NF.

[0027] Preparation of 2Cr,Co-Ni(OH)2@NF

[0028] The prepared Ni(OH)2@NF was placed in a beaker, and 20 mL of an aqueous solution containing 20 mg of chromium nitrate and 20 mg of potassium cobalt cyanide was added. The mixture was allowed to react at room temperature (26-28°C) for 6.5 hours. The mixture was then removed, rinsed with deionized water and ethanol, and dried under vacuum to produce the Cr,Co-Ni(OH)2@NF material. To optimize the experimental conditions, similar concentration-time studies were conducted as for Ni(OH)2@NF, designated nCr-mCo-Ni(OH)2-z@NF (n = 10, 15, 20, 25; m = 10, 20, 30; z = 4.5, 5, 5.5, 6, 6.5, 7).

[0029] 3 Electrochemical testing

[0030] The OER electrocatalytic performance of all samples was studied using a three-electrode system in a 1 M KOH (pH = 13.8) + 0.33 M urea electrolyte on a CHI630e instrument. Cr,Co-Ni(OH)2@NF was used as the working electrode, a graphite rod as the counter electrode, and saturated Hg / HgO as the reference electrode. All potentials were calculated according to the Nernst equation: E(RHE) = E(Hg / HgO) + 0.0591 pH + 0.098. OER linear sweep voltammetry (LSV) analysis was performed at a scan rate of 5 mV s. -1 All samples were activated by 20 cycles of cyclic voltammetry (CV) before testing. The samples were activated by increasing the scan rate (20, 40, 60, 80, 100 and 120 mV s) within the appropriate potential in the non-Faraday region. -1 ) to obtain the CV curve for determining the electrochemical double layer capacitance (Cdl). The stability test was measured by the chronoamperometric response (it curve) of current versus time in 1M KOH solution at a current density of 100 mA / cm 2 , continuous testing for 55h.

[0031] 4 Results

[0032] 4.1 Material characterization

[0033] Three different Cr and Co doped Ni(OH)2 with different chromium and cobalt concentrations were prepared on Ni(OH)2@NF materials, namely bare Ni(OH)2, nCr-mCo-Ni(OH)2-z@NF. The X-ray diffraction peaks are located at 19.3°, 33.1° and 38.5° of Ni(OH)2 ( Figure 1 a), proving the existence of electrocatalyst. The results show that no phase segregation occurs after doping Ni(OH)2 with Cr and Co. Cr,Co-Ni(OH)2@NF( Figure 1 The scanning electron microscopy (SEM) image of b) clearly shows the vertical nanosheets, which are uniformly dispersed throughout the nickel foam. Figure 1 c) and Co-Ni(OH)2@NF( Figure 1 d) and Ni(OH)2@NF( Figure 1 Comparing the SEM image of (e), it can be seen that Cr and Co are uniformly dispersed on Ni(OH)2, demonstrating the feasibility of the experimental scheme.

[0034] from Figure 1 f and g show that Cr,Co-Ni(OH)2@NF exists in a blocky form, which is beneficial for the catalyst to maintain stability during the UOR process. Figure 1 The corresponding TEM images in hl show that Co, O, Ni, Cr, and N are uniformly dispersed in Cr, Co-Ni(OH)2@NF. In addition, X-ray photoelectron spectroscopy (XPS) was used to characterize the fine structure of the electronic interactions between Co, Cr, and Ni atoms on the surface of the prepared Cr, Co-Ni(OH)2@NF catalysts. Figure 1 The XPS survey spectrum of mp confirmed the presence of Ni, Co, Cr and O elements in the Cr,Co-Ni(OH)2@NF catalyst. Figure 1 In m, the Ni2p spectrum of Cr,Co-Ni(OH)2@NF is dominated by two peaks at 874.2 and 856.6 eV corresponding to Ni2p3 / 2 and Ni2p1 / 2 of Ni2+. Figure 1 In n, compared with CoNi-LDH (798.2, 796.6, 783.0 and 781.0eV), the two pairs of heavy states of Co 2p1 / 2 and Co 2p3 / 2d (796.6 and 780.96eV) and (798.3 and 782.8eV) shifted to the direction of lower binding energy, indicating that the local electronic structure of Co atoms was strongly affected by Cr incorporation. Figure 1 o, the Cr 2p spectra at 587.2eV and 577.3eV correspond to Cr 2p1 / 2 and Cr 2p3 / 2, indicating that Cr in the composite exists in trivalent form. Figure 1 In the O XPS spectrum of Cr,Co-Ni(OH)2@NF (see Figure 1), the three peaks at 530.80, 532.10, and 533.80 eV are attributed to metal-oxygen bonds, oxygen atoms near oxygen vacancies, and surface-adsorbed water, respectively. Previous studies have shown that during alkaline UOR oxidation, metal-oxygen bonds (MO) combine with hydroxide ions to form MOOH, which then reacts with urea to form nitrogen and carbon dioxide. The presence of MO in Cr,Co-Ni(OH)2@NF has a beneficial effect on its performance.

[0035] 4.2 Electrochemical test characterization

[0036] To evaluate the effects of Co atoms, Cr atoms, and O vacancies on the catalytic activity of UOR, we performed electrochemical tests. Figure 2 The linear sweep voltammetry (LSV) curves in (a) and (b) corrected by 95% IR showed that the current density was 100 mA cm -2 When Cr, Co-Ni(OH)2@NF is prepared, the overpotential of the NF relative to RHE (reversible hydrogen electrode) reaches 1.45 V, which is lower than that of Co-doped and Cr-doped Ni(OH)2, indicating that Co and Cr doping can effectively improve the catalytic performance.

[0037] Cr, Co-Ni(OH)2@NF(96mV dec -1 ) has a lower Tafel slope than Co-Ni(OH)2@NF (104mV dec -1 ) and Cr-Ni(OH)2@NF(113mV dec -1 )( Figure 2 c), also demonstrated the superior reaction kinetics of Cr, Co-Ni(OH)2@NF for UOR. Figure 2 In d and 2e, the performance of Cr and Co-Ni(OH)2@NF in different concentrations of KOH solution and urea was compared. Cr and Co-Ni(OH)2@NF showed better performance in UOR than OER. By exploring the effect of the doping amount and ratio of Co and Cr atoms on the performance, according to Figure 2 f research results show that when Co and Cr atoms are doped in a ratio of 1:1 and the content of both is 20mg, the best performance is achieved. Figure 2 It can be clearly seen from g that the Cdl value of Cr, Co-Ni(OH)2@NF is 4.75mF cm-2, which is higher than that of Co-Ni(OH)2@NF (4.21mF cm -2 ) and Cr-Ni(OH)2@NF(4.03mF cm -2 ), which is consistent with the previous speculation that doping Co and Cr provides more active sites for the catalytic reaction. Figure 2 As can be seen from Figure h, the performance of Cr, Co-Ni(OH)2@NF electrocatalyst did not decrease significantly after 1000 cycles under OER. The electrochemical stability of the electrocatalyst was evaluated by IT curve test. Figure 2 As shown in i, the Cr, Co-Ni(OH)2@NF catalysts were heated to 100 mA cm -2 The stability of the product in 1.0 M KOH solution was maintained above 90% for 55 hours.

[0038] 5 Conclusion

[0039] In summary, the Cr,Co-Ni(OH)2@NF obtained by the room temperature synthesis method showed good UOR catalytic performance in 1MKOH+0.33M urea. The current density was 100mA cm -2 The overpotential for the UOR of Cr,Co-Ni(OH)2@NF in 1M KOH + 0.33M urea was 1.45 V. The high catalytic activity of Cr,Co-Ni(OH)2@NF is attributed to the dual doping of Co and Cr into Ni(OH)2, which provides more active sites for the catalytic reaction. The excellent UOR catalytic performance and good stability of Cr,Co-Ni(OH)2@NF in alkaline urea solution have broad application prospects in reducing the overpotential at the anode end of water electrolysis for hydrogen production and in controlling urea pollution.

[0040] The above is only an embodiment of the present invention, and common knowledge such as the specific technical solutions or characteristics in the solution is not described in detail here. For those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the description can be used to interpret the content of the claims.

Claims

1. A nickel-based catalyst, characterized in that: The catalyst is Cr, Co-Ni(OH)2@NF, wherein Cr and Co are used as doping elements and are uniformly dispersed in Ni(OH)2, and the catalyst is grown on a foam nickel (NF) carrier.

2. The nickel-based catalyst according to claim 1, its preparation method and use, characterized in that: The doping ratio of Cr and Co is 1:

1.

3. A method for preparing a nickel-based catalyst according to claim 1, characterized in that: The following steps are involved: S1, soaking nickel foam (NF) in HCl solution, washing with ethanol and deionized water and drying; S2, immersing the treated nickel foam in an aqueous solution containing NaBH4, reacting at room temperature, and washing with deionized water to generate Ni(OH)2@NF; S3. Immerse the generated Ni(OH)2@NF in an aqueous solution containing chromium nitrate and potassium cobalt cyanide, and react at room temperature to generate Co,Cr-Ni(OH)2@NF.

4. The method for preparing a nickel-based catalyst according to claim 3, wherein: The concentration of NaBH4 is 0.2 M and the reaction time is 2 hours.

5. The method for preparing a nickel-based catalyst according to claim 3, wherein: The concentrations of the chromium nitrate and potassium cobalt cyanide were both 1 mg / mL, and the reaction time was 6.5 hours.

6. Use of the nickel-based catalyst according to claim 1 in urea pollution control.

7. Use of a nickel-based catalyst according to claim 1 in renewable energy conversion.

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