CN110433810B - Preparation method of copper oxide doped nickel-iron hydrotalcite nanosheet/graphene bifunctional water decomposition catalyst - Google Patents

Preparation method of copper oxide doped nickel-iron hydrotalcite nanosheet/graphene bifunctional water decomposition catalyst Download PDF

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CN110433810B
CN110433810B CN201910753019.6A CN201910753019A CN110433810B CN 110433810 B CN110433810 B CN 110433810B CN 201910753019 A CN201910753019 A CN 201910753019A CN 110433810 B CN110433810 B CN 110433810B
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詹天荣
谭磊
孙源
王海燕
周长志
刘颖
王磊
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Hunan Lushao Technical Service Co ltd
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Abstract

本发明涉及一种氧化铜掺杂的超薄镍铁类水滑石纳米片/石墨烯双功能水分解催化剂的制备方法及其在碱性介质中对析氧反应和析氢反应的电催化应用。本发明以氧化石墨烯为基底,在甲酰胺和水的混合溶液中原位生长氢氧化铜掺杂的超薄镍铁类水滑石纳米片,再通过热处理及化学还原制备氧化铜掺杂的超薄镍铁类水滑石纳米片/石墨烯复合物催化剂,该方法避免了类水滑石的剥离及氧化铜后掺杂等步骤,抑制了石墨烯、氧化铜和类水滑石纳米片的聚集,增加了活性位点,提高了导电性,所得催化剂降低了传质阻力,加快了电子传递速率,提高了其碱性条件下析氧和析氢的催化性能,为开发新型双功能水分解催化剂提供了重要方法。The invention relates to a preparation method of a copper oxide-doped ultrathin nickel-iron hydrotalcite nanosheet/graphene bifunctional water splitting catalyst and its electrocatalytic application to oxygen evolution reaction and hydrogen evolution reaction in alkaline medium. The invention uses graphene oxide as a substrate, grows copper hydroxide-doped ultra-thin nickel-iron hydrotalcite nanosheets in-situ in a mixed solution of formamide and water, and then prepares copper oxide-doped ultra-thin nanosheets through heat treatment and chemical reduction. Nickel-iron-like hydrotalcite nanosheet/graphene composite catalyst, the method avoids the steps of hydrotalcite-like exfoliation and post-doping of copper oxide, inhibits the aggregation of graphene, copper oxide and hydrotalcite-like nanosheets, and increases the Active sites, improved electrical conductivity, the resulting catalyst reduced mass transfer resistance, accelerated electron transfer rate, and improved its catalytic performance for oxygen evolution and hydrogen evolution under alkaline conditions, providing an important method for the development of new bifunctional water splitting catalysts .

Description

Preparation method of copper oxide doped nickel-iron hydrotalcite nanosheet/graphene bifunctional water decomposition catalyst
The technical field is as follows:
the invention belongs to the technical field of new energy materials and electrocatalysis, and particularly relates to a preparation method of a copper oxide-doped ultrathin nickel-iron hydrotalcite nanosheet/graphene bifunctional water decomposition catalyst, which further comprises electrocatalysis application of the catalyst in oxygen evolution reaction and hydrogen evolution reaction of water electrolysis in an alkaline medium
Background art:
with the environmental issues such as global warming caused by fossil fuels becoming prominent, hydrogen energy has attracted considerable attention as an ideal new energy source for researchers, including efficient storage and conversion of hydrogen energy. The slow progress of Oxygen Evolution Reaction (OER) and Hydrogen Evolution Reaction (HER) involved in the hydrogen energy storage process is one of the main problems hindering the application and popularization of the electrolyzed water. In the apparatus for electrolyzing water, noble metals Pt and alloys thereof are commonly used as the catalyst for HER, and noble metals Ru, Ir and oxides thereof are used as the catalyst for OER. The noble metal catalyst has limited application in new energy due to its small earth reserve, high price and other factors. And these noble metal catalysts can only catalyze either OER or HER singly. Therefore, research and development of a bifunctional electrocatalyst which can be easily produced and used as a non-noble metal and can simultaneously act on HER and OER becomes a hot research point.
The nickel-iron-based material comprises nickel-iron hydroxide and oxide, and has good OER catalytic performance. Wherein the nickel-iron hydroxide is also called nickel-iron hydrotalcite, which is a two-dimensional layered material with a general formula of [ Ni ]1-x 2+Fex 3+(OH)2]x+(An-)x/n·mH2O, consisting of a positively charged hydroxide layer and an interlayer anion in charge balance therewith. The earth element reserves are abundant, so the method has good prospect in practical application. In the practical application process, the NiFe-LDH catalyst material also has the defects of small specific surface area, poor conductivity, easy aggregation, poor stability and the like. In order to overcome the defects, researchers peel LDH into single-layer or multi-layer hydrotalcite-like nano-sheets (LDHNS) to improve the specific surface area and the active site of the LDHNS, and simultaneously compound materials such as some carbon materials including Graphene (GR) and Carbon Nano Tubes (CNT) with the LDHNS to improve the conductivity of the composite material, prevent the LDHNS from aggregating and improve the performance of the composite material. GR is an sp2Two-dimensional material with one carbon atom thickness and formed by hybridization of carbon atoms and with ultrahigh specific surface area (2600 m)2Per gram) and excellent conductivity (-10)6S/cm) can greatly improve charge transfer and mass transfer efficiency in electrocatalytic reactions. And negatively charged oxidized stoneThe electrostatic accumulation of Graphene (GO) and LDH nano-sheets with positive charges at the face-to-face molecular level can enable transition metal catalytic centers in the LDH nano-sheets to be in contact with conductive sp2The hybridized carbon atoms are in close contact, and the diffusion distance of the electrolyte is greatly shortened. Although the problems of poor conductivity, aggregation and the like of the LDH material can be solved by compounding LDH and GR by electrostatic assembly, the efficiency of electrolytic oxygen evolution at high potential has a certain limit, i.e. the response current density of the catalyst at high potential is small. In recent years, many reports have been made on obtaining a water-decomposing catalyst by electrodeposition on a copper foil, a copper mesh, or a copper sheet, and the response current density at a high potential is large. Therefore, copper is uniformly doped in the crystal lattice of the nickel-iron hydrotalcite in the form of copper oxide, and an unexpected effect can be achieved on the electrocatalytic water decomposition of the nickel-iron hydrotalcite.
In order to simplify the preparation method of the catalyst and improve the performability of industrial production, divalent nickel, divalent copper and trivalent iron are dissolved in a mixed solution of formamide and water of GO, diluted alkali is used for direct titration, ultrathin CuNiFe-LDHNS grows in situ on a GO substrate, and the copper oxide doped ultrathin nickel-iron-nickel-like hydrotalcite nanosheet/graphene (CuO-NiFe-LDHNS/rGO) water decomposition catalyst is prepared through thermochemical reduction treatment. At present, the CuO-NiFe-LDHNS/rGO water decomposition catalyst prepared by the method and the research of the catalyst used for the water electrolysis reaction under the alkaline condition are not reported.
According to the method, the graphene oxide is used as a substrate, the ultrathin CuNiFe-LDHNS grows in situ in a mixed solution of formamide and water, and the CuO-NiFe-LDHNS/rGO catalyst is prepared by thermal chemical reduction, so that the complex steps of LDH stripping, doping CuO after LDH synthesis and the like are avoided, the specific surface area of the catalyst is increased, the active catalytic sites of the catalyst are enriched, and the overpotentials of OER and HER are reduced, so that the electrocatalytic performance of the catalyst on water decomposition is improved. The electrocatalyst prepared by the method fully exerts the synergistic effect of CuO, ultrathin NiFe-LDHNS and rGO on the aspect of electrocatalysis, and has important significance for developing a novel bifunctional water-splitting electrocatalyst.
The invention content is as follows:
aiming at the defects of the prior art and the requirements of research and application in the field, one of the purposes of the invention is to provide a preparation method of a copper oxide doped ultrathin nickel-iron hydrotalcite nanosheet/graphene bifunctional catalyst, which is characterized in that the catalyst is prepared by a coprecipitation method in a formamide-water mixed solution containing graphene oxide, and comprises the following specific steps:
taking a certain amount of graphene oxide GO to be ultrasonically dispersed in 100mL of mixed solvent of formamide and water to enable the concentration of the graphene oxide GO to be 0.3mg/mL, adding ferric nitrate nonahydrate, nickel nitrate hexahydrate and copper nitrate hexahydrate according to a certain molar ratio to enable the concentration of total metal ions of ferronickel to be 0.03mol/L and the concentration of copper metal ions to be 1-5% of the concentration of ferronickel metal ions, stirring for 1h to enable the metal salts to be completely dissolved, slowly titrating by using a formamide-containing sodium hydroxide aqueous solution with the concentration of 0.7mol/L under the condition of vigorous stirring until the pH value of a reaction liquid is 8.5-9.5, adding 100 mu L of 80% hydrazine hydrate into the mixed liquid, gradually heating to 100 ℃ for reaction for 2h, cooling, centrifugally separating the reaction liquid, washing precipitates for 3 times by using deionized water and ethanol respectively, drying to obtain the copper oxide-doped ultrathin ferronickel nanosheet/graphene composite, is marked as CuO-NiFe-LDHNS/rGO;
wherein the molar ratio of the ferric nitrate nonahydrate to the nickel nitrate hexahydrate to the copper nitrate hexahydrate is 1: 2; the volume percentage of formamide in a mixed solvent or solution of formamide and water is 40-100%; the size of LDHNS in the CuO-NiFe-LDHNS/rGO composite catalyst is 20-50 nm, and the thickness is less than 3 nm; the particle size of CuO is 3-15 nm, and the CuO is uniformly doped in an LHDNS matrix.
The invention also aims to provide application of the copper oxide-doped ultrathin nickel-iron hydrotalcite nanosheet/graphene bifunctional catalyst in oxygen evolution reaction and hydrogen evolution reaction of water electrolysis in an alkaline medium.
According to the method, graphene oxide is used as a substrate, ultrathin CuNiFe-LDHNS grows in situ in a mixed solution of formamide and water, and then chemical reduction is performed to prepare the CuO-NiFe-LDHNS/rGO water decomposition catalyst, so that the steps of LDH stripping, doping CuO after LDH synthesis and the like are avoided, the active sites of the catalyst are increased, the overpotentials of OER and HER are reduced, and the electrocatalytic performance of the catalyst is improved.
Compared with the prior art, the invention has the following main advantages and beneficial effects:
1) the bifunctional water decomposition catalyst is a non-noble metal composite material, the used raw materials are easy to purchase and prepare, the resources are rich, the price is low, the operation is easy, and the large-scale production is facilitated;
2) avoids the complex steps of LDH stripping, doping CuO after LDH synthesis and the like, increases the specific surface area of the catalyst, and enriches the active catalytic sites
3) The bifunctional water decomposition catalyst has good stability, and the response current of the catalyst is hardly attenuated in a constant voltage test lasting for 12 hours in 0.1mol/L KOH electrolyte;
4) the bifunctional water decomposition catalyst has better OER and HER activities, and has remarkable advantages compared with unilateral catalytic activities of non-noble metal/nonmetal catalysts reported in current researches;
5) compared with commercial noble metal catalysts, the bifunctional water decomposition catalyst provided by the invention has the advantages that the stability is obviously improved, and the catalyst can keep good catalytic activity in long-term use of water electrolysis.
Description of the drawings:
FIG. 1 is a TEM image of a 2.5% CuO-NiFe-LDHNS/rGO composite obtained in example 1 and a NiFe-LDHNS/rGO obtained in comparative example 2, and a mapping profile (c) of Cu in the CuO-NiFe-LDHNS/rGO composite obtained in example 1.
FIG. 2 is an XRD spectrum of a 2.5% CuO-NiFe-LDHNS/rGO composite obtained in example 1 and a NiFe-LDHNS/rGO obtained in comparative example 2.
FIG. 3 is an OER linear voltammogram of a glassy carbon electrode modified with 2.5% CuO-NiFe-LDHNS/rGO composite obtained in example 1, 1% CuO-NiFe-LDHNS/rGO composite obtained in example 3, and 5% CuO-NiFe-LDHNS/rGO composite obtained in example 4.
FIG. 4 is the OER linear voltammogram of the 2.5% CuO-NiFe-LDHNS/rGO composite obtained in example 1, the CuNiFe-LDHNS/GO composite obtained in example 2, the NiFe-LDHNS/GO obtained in comparative example 1, and the NiFe-LDHNS/rGO modified glassy carbon electrode obtained in comparative example 2.
FIG. 5 is a plot of the galvanostatic test at 1.53V for the 2.5% CuO-NiFe-LDHNS/rGO composite obtained in example 1.
FIG. 6 is a graph of the HER linear voltammograms of the 2.5% CuO-NiFe-LDHNS/rGO composite obtained in example 1, the CuNiFe-LDHNS/GO composite obtained in example 2, the NiFe-LDHNS/GO obtained in comparative example 1, and the NiFe-LDHNS/rGO modified RDE obtained in comparative example 2.
FIG. 7 is a linear sweep voltammogram of an electrolytic cell assembled with 2.5% CuO-NiFe-LDHNS/rGO composite obtained in example 1, CuNiFe-LDHNS/GO composite obtained in example 2, NiFe-LDHNS/GO obtained in comparative example 1, and NiFe-LDHNS/rGO obtained in comparative example 2 as cathode and anode, respectively, to catalyze the water electrolysis reaction in 0.1M KOH.
The specific implementation mode is as follows:
for a further understanding of the invention, reference will now be made to the following examples and drawings, which are not intended to limit the invention in any way.
Example 1:
taking a certain amount of graphene oxide GO to be ultrasonically dispersed in 100mL of aqueous solution containing 50% formamide to enable the concentration of the graphene oxide GO to be 0.3mg/mL, sequentially adding ferric nitrate nonahydrate, nickel nitrate hexahydrate and copper nitrate hexahydrate to enable the metal ion concentrations of nickel, iron and copper to be 10mmol/L, 20mmol/L and 0.75mmol/L respectively, enabling the metal ion concentration to be 2.5% of the nickel-iron metal ion concentration, stirring for 1h to enable the metal salt to be completely dissolved, slowly titrating the mixture to a pH value of the reaction liquid to be 8.5-9.5 by using 0.7mol/L of aqueous solution of sodium hydroxide containing 50% formamide under the condition of vigorous stirring, adding 100 mu L of 80% hydrazine hydrate into the mixture, gradually heating to 100 ℃ for reaction for 2h, after cooling, centrifugally separating the reaction liquid, washing precipitates for 3 times by using deionized water and ethanol respectively, and drying to obtain the copper oxide doped ultrathin hydrotalcite-like/graphene nickel-iron composite, 2.5% CuO-NiFe-LDHNS/rGO;
example 2:
taking a certain amount of graphene oxide GO to be ultrasonically dispersed in 100mL of aqueous solution containing 60% formamide, the concentration of the iron nitrate nonahydrate, the nickel nitrate hexahydrate and the copper nitrate hexahydrate are added in turn to ensure that the metal ion concentration of the nickel-iron-copper is respectively 10mmol/L, 20mmol/L and 0.75mmol/L, the metal ion concentration of the copper is 2.5 percent of the nickel-iron metal ion concentration, the mixture is stirred for 1 hour to completely dissolve the metal salt, slowly titrating with 0.7mol/L sodium hydroxide aqueous solution containing 60% formamide under the condition of vigorous stirring until the pH value of the reaction solution is 8.5-9.5, centrifugally separating the reaction solution, washing the precipitate with deionized water and ethanol for 3 times respectively, and drying to obtain copper oxide-doped ultrathin nickel iron hydrotalcite nanosheet/graphene composite, which is recorded as CuNiFe-LDHNS/GO;
example 3:
taking a certain amount of graphene oxide GO to be ultrasonically dispersed in 100mL of aqueous solution containing 50% formamide to enable the concentration of the graphene oxide GO to be 0.3mg/mL, sequentially adding ferric nitrate nonahydrate, nickel nitrate hexahydrate and copper nitrate hexahydrate to enable the metal ion concentrations of nickel, iron and copper to be 10mmol/L, 20mmol/L and 0.3mmol/L respectively, enabling the metal ion concentration to be 1% of the nickel-iron metal ion concentration, stirring for 1h to enable the metal salt to be completely dissolved, slowly titrating with 0.7mol/L of aqueous sodium hydroxide solution containing 50% formamide under the condition of vigorous stirring until the pH value of reaction liquid is 8.5-9.5, adding 100 mu L of 80% hydrazine hydrate into the mixed liquid, gradually heating to 100 ℃ for reaction for 2h, after cooling, centrifugally separating the reaction liquid, washing precipitates with deionized water and ethanol for 3 times respectively, and drying to obtain the copper oxide doped ultrathin nickel-iron hydrotalcite-like nanosheet/graphene composite, 1% CuO-NiFe-LDHNS/rGO;
example 4:
taking a certain amount of graphene oxide GO to be ultrasonically dispersed in 100mL of aqueous solution containing 50% formamide to enable the concentration of the graphene oxide GO to be 0.3mg/mL, sequentially adding ferric nitrate nonahydrate, nickel nitrate hexahydrate and copper nitrate hexahydrate to enable the metal ion concentrations of nickel, iron and copper to be 10mmol/L, 20mmol/L and 1.5mmol/L respectively, enabling the metal ion concentration to be 5% of the nickel-iron metal ion concentration, stirring for 1h to enable the metal salt to be completely dissolved, slowly titrating with 0.7mol/L of aqueous sodium hydroxide solution containing 50% formamide under the condition of vigorous stirring until the pH value of reaction liquid is 8.5-9.5, adding 100 muL of 80% hydrazine hydrate into the mixed liquid, gradually heating to 100 ℃ for reaction for 2h, after cooling, centrifugally separating the reaction liquid, washing precipitates with deionized water and ethanol for 3 times respectively, and drying to obtain the copper oxide doped ultrathin nickel-iron hydrotalcite-like nanosheet/graphene composite, 5% CuO-NiFe-LDHNS/rGO;
comparative example 1:
taking a certain amount of graphene oxide GO to be ultrasonically dispersed in 100mL of aqueous solution containing 50% formamide to enable the concentration of the graphene oxide GO to be 0.3mg/mL, sequentially adding ferric nitrate nonahydrate and nickel nitrate hexahydrate to enable the concentrations to be 10mmol/L and 20mmol/L respectively, stirring for 1h to enable metal salts to be completely dissolved, slowly titrating the mixture by using 0.7mol/L of aqueous solution containing 50% formamide sodium hydroxide until the pH of the reaction solution is about 8.5-9.5 under the condition of vigorous stirring, washing the reaction solution for 3 times by using deionized water and ethanol after centrifugal separation, and drying to obtain the ultrathin nickel iron hydrotalcite/graphene composite, namely the ultrathin nickel iron hydrotalcite/graphene composite is NiFe nanosheet-LDHNS/GO.
Comparative example 2:
taking a certain amount of graphene oxide GO to be ultrasonically dispersed in 100mL of mixed solution of formamide and water to enable the concentration of the graphene oxide GO to be 0.3mg/mL, and adding ferric nitrate nonahydrate and nickel nitrate hexahydrate according to a certain molar ratio to enable the total metal ion concentration of ferronickel to be 0.03 mol/L. Stirring for 1h to completely dissolve metal salt, slowly titrating with a mixed solution of 0.7mol/L sodium hydroxide formamide and water under the condition of vigorous stirring until the pH of the reaction solution is about 8.5-9.5, adding 100 mu L80% hydrazine hydrate into the mixed solution, gradually heating to 100 ℃ for reaction for 2h, cooling and centrifugally separating the reaction solution, washing with deionized water and ethanol for 3 times, and drying to obtain the ultrathin nickel iron hydrotalcite nanosheet/graphene composite, which is marked as NiFe-LDHNS/rGO.
FIG. 1 is a TEM image of a CuO-NiFe-LDHNS/rGO composite (a) obtained in example 1 and a NiFe-LDHNS/rGO (b) obtained in comparative example 2, wherein b shows that the size of LDHNS in the NiFe-LDHNS/rGO is 40-100 nm, while the size of LDHNS in the CuO-NiFe-LDHNS/rGO shows a smaller nano size of 20-40 nm, and CuO particles are doped in LDHNS, and the particle size of the CuO particles is 3-15 nm. And from the mapping graph (c) of copper, CuO is uniformly doped in the LDHNS, so that more edge sites appear in the LDHNS, and the doping of CuO causes the LDHNS to generate more defects, so that CuO-NiFe-LDHNS/rGO has more active sites and catalytic centers, and is more beneficial to the adsorption of water molecules and hydroxide radicals on the surface of the catalyst and the desorption of hydrogen and oxygen in the electrochemical catalysis process, thereby improving the comprehensive water decomposition catalytic performance of the catalyst.
FIG. 2 is an XRD pattern of the CuO-NiFe-LDHNS/rGO composite obtained in example 1 and the NiFe-LDHNS/rGO obtained in comparative example 2. As shown in the figure, both CuO-NiFe-LDHNS/rGO and NiFe-LDHNS/rGO show the characteristic peak of the LDH, which indicates that the NiFe-LDH in the two compounds keeps good crystal characteristics. In addition, the XRD pattern of CuO-NiFe-LDHNS/rGO also shows characteristic peaks of (111), (200) and (202) crystal faces of CuO, but the width of characteristic diffraction peaks of LDHNS and CuO in the composite is widened to some extent, the intensity is also reduced, the ultrathin characteristic of LHDNS and the low crystallinity of CuO are fully explained, and the electrocatalytic activity is favorably exerted.
Example 5:
respectively dispersing 10mg of the catalysts obtained in example 1, example 3, example 4, comparative example 1 and comparative example 2 in 300 muL of ethanol and 30 muL of 0.5 percent Nafion solution, ultrasonically mixing the solutions, dripping 4 muL of slurry on a glassy carbon electrode, tabletting after completely drying the glassy carbon electrode on an electrochemical workstation CHI660D to measure the OER electro-catalytic performance of the glassy carbon electrode;
the electrocatalysis performance tests all use a saturated Hg/HgO electrode as a reference electrode, a Pt electrode as a counter electrode, the sweep rate is 10mV/s, and the electrolyte is 0.1M KOH.
Example 6:
dispersing 10mg of the catalyst (solid content 8.36%) obtained in example 1 in 300. mu.L of ethanol and 30. mu.L of 0.5% Nafion solution, ultrasonically mixing the solution, dripping 3. mu.L of the slurry on a rotating disk electrode, and after the slurry is completely dried, measuring the HER electrocatalytic properties of the slurry on a CHI660D electrochemical workstation at a rotating speed of 1600 rmp;
the electrocatalysis performance tests all use a saturated Hg/HgO electrode as a reference electrode, a carbon rod electrode as a counter electrode, the sweep rate is 10mV/s, the sweep rate direction is from positive potential to negative potential, and the electrolyte is 0.1M KOH.
FIG. 3 is 2.5% CuO obtained in example 1An OER linear voltammogram of a glassy carbon electrode modified by an NiFe-LDHNS/rGO compound, a 1% CuO-NiFe-LDHNS/rGO compound obtained in example 3, and a 5% CuO-NiFe-LDHNS/rGO compound obtained in example 4. As shown in the figure, the OER initial overpotential of the electrode modified by 2.5% CuO-NiFe-LDHNS/rGO compound is 260mV, which is significantly lower than 1% CuO-NiFe-LDHNS/rGO compound (290mV) and 5% CuO-NiFe-LDHNS/rGO compound (300 mV). Meanwhile, when the current density is 10mA/cm2The overpotentials for the 2.5% CuO-NiFe-LDHNS/rGO composite, the 1% CuO-NiFe-LDHNS/GO composite, and the 5% CuO-NiFe-LDHNS/rGO composite were approximately 272, 319, and 301mV, respectively. Obviously, the doping of 2.5% of Cu in the crystal lattice of the ultrathin nickel-iron hydrotalcite is the optimal amount for improving the performance of the catalyst.
FIG. 4 is the OER linear voltammogram of the 2.5% CuO-NiFe-LDHNS/rGO composite obtained in example 1, the CuNiFe-LDHNS/GO composite obtained in example 2, the NiFe-LDHNS/GO obtained in comparative example 1, and the NiFe-LDHNS/rGO modified glassy carbon electrode obtained in comparative example 2. The initial overpotential for 2.5% CuO-NiFe-LDHNS/rGO is 233mV, almost the same as NiFe-LDHNS/rGO, but significantly lower than the overpotentials (248 and 245mV, respectively) for CuNiFe-LDHNS/GO and NiFe-LDHNS/GO. However, the CuO-NiFe-LDHNS/rGO reaches 10mA/cm2The corresponding overpotential is 252mV, which is lower than NiFe-LDHNS/rGO, CuNiFe-LDHNS/GO and NiFe-LDHNS/GO (254, 272 and 275mV respectively); and when the current density reaches 100mA/cm2When the catalyst is used, the overpotential corresponding to CuO-NiFe-LDHNS/rGO is 289mV, which is obviously lower than 322mV corresponding to NiFe-LDHNS/rGO, which shows that the doping of CuO effectively increases the OER catalytic performance of the catalyst.
FIG. 5 is a constant voltage test chart of the 2.5% CuO-NiFe-LDHNS/rGO composite modified glassy carbon electrode obtained in example 1 under 1.53V. As shown in the figure, 12h of test shows that the OER current density of the CuO-NiFe-LDHNS/rGO is only slightly attenuated, which shows that the CuO-NiFe-LDHNS/rGO shows good OER catalytic stability in an alkaline solution and has longer service life.
FIG. 6 is a graph showing 2.5% CuO-NiFe-LDHNS/rGO composite obtained in example 1, CuNiFe-LDHNS/GO composite obtained in example 2, NiFe-LDHNS/GO obtained in comparative example 1, and NiFe-LDHNS/rGO modified in comparative example 2HER linear voltammogram of RDE. As shown in the figure, compared with NiFe-LDHNS/rGO, the HER initial potential of 2.5 percent CuO-NiFe-LDHNS/rGO catalyst is slightly shifted positively to reach-10 mA/cm2The overpotential is reduced from 360mV to 320mV, which is obviously lower than that of samples NiFe-LDHNS/GO and NiFe-LDHNS/rGO which are not doped with CuO, so that the method can be inferred that the CuO is doped into the ultrathin nickel iron hydrotalcite, the mass transfer rate and the electron transfer rate can be obviously improved, and the HER catalytic performance of the composite catalyst is improved.
FIG. 7 is a linear sweep voltammogram of an electrolytic cell assembled with 2.5% CuO-NiFe-LDHNS/rGO composite obtained in example 1, CuNiFe-LDHNS/GO composite obtained in example 2, NiFe-LDHNS/GO obtained in comparative example 1, and NiFe-LDHNS/rGO obtained in comparative example 2 as cathode and anode, respectively, to catalyze the water electrolysis reaction in 0.1M KOH. As shown, the 2.5% CuO-NiFe-LDHNS/rGO complex electrocatalyzed water decomposition with an initial overpotential of 310mV, which is the same as the NiFe-LDHNS/rGO complex but lower than the CuNiFe-LDHNS/GO complex (330mV) and the NiFe-LDHNS/GO (370 mV). Up to 10mA/cm2When the current density is high, the overpotential corresponding to CuO-NiFe-LDHNS/rGO is 362mV, which is obviously lower than the overpotentials (372, 406 and 432mV) corresponding to NiFe-LDHNS/rGO, CuNiFe-LDHNS/GO and NiFe-LDHNS/GO, which indicates that the doping of CuO causes LDHNS to generate more defects, increases CuO-NiFe-LDHNS/rGO active sites and catalytic centers, and the reduction of GO into rGO increases the conductivity of the catalyst, therefore, CuO-NiFe-LDHNS/rGO shows good bifunctional water decomposition catalytic performance.

Claims (2)

1.一种氧化铜掺杂的超薄镍铁类水滑石纳米片/石墨烯双功能水分解催化剂的制备方法,其特征在于在含有氧化石墨烯的甲酰胺-水混合溶液中经共沉淀法制得,包括以下具体步骤:1. a preparation method of a copper oxide-doped ultra-thin nickel-iron class hydrotalcite nanosheet/graphene bifunctional water splitting catalyst, is characterized in that in the formamide-water mixed solution containing graphene oxide, through co-precipitation method , including the following specific steps: 取一定量的氧化石墨烯GO超声分散于100mL甲酰胺和水的混合溶剂中,使其浓度为0.3mg/mL,按一定摩尔比加入九水合硝酸铁、六水合硝酸镍和六水合硝酸铜,使镍铁总金属离子浓度0.03mol/L,铜金属离子摩尔浓度为镍铁金属离子总摩尔浓度的1~5%,搅拌1h使金属盐完全溶解,在剧烈搅拌的条件下,用浓度为0.7mol/L的含甲酰胺的氢氧化钠水溶液缓慢滴定至反应液的pH值为8.5~9.5,向该混合液加入100μL 80%的水合肼,逐渐加热至100℃反应2h,冷却后反应液离心分离后,沉淀分别用去离子水和乙醇洗涤3次,干燥后得氧化铜掺杂的超薄镍铁类水滑石纳米片/石墨烯复合物,记为CuO-NiFe-LDHNS/rGO;Take a certain amount of graphene oxide GO and ultrasonically disperse it in a mixed solvent of 100 mL of formamide and water to make its concentration 0.3 mg/mL, and add ferric nitrate nonahydrate, nickel nitrate hexahydrate and copper nitrate hexahydrate in a certain molar ratio, Make the total metal ion concentration of nickel-iron 0.03mol/L, and the molar concentration of copper metal ions to be 1-5% of the total molar concentration of nickel-iron metal ions. Stir for 1 hour to completely dissolve the metal salt. Under the condition of vigorous stirring, use a concentration of 0.7 The mol/L sodium hydroxide aqueous solution containing formamide was slowly titrated to pH 8.5-9.5 of the reaction solution, 100 μL of 80% hydrazine hydrate was added to the mixed solution, gradually heated to 100 °C and reacted for 2 h. After cooling, the reaction solution was centrifuged. After separation, the precipitate was washed three times with deionized water and ethanol, respectively, and dried to obtain a copper oxide-doped ultra-thin nickel-iron-based hydrotalcite nanosheet/graphene composite, denoted as CuO-NiFe-LDHNS/rGO; 其中九水合硝酸铁、六水合硝酸镍的摩尔比为1:2;甲酰胺和水的混合溶剂或溶液中甲酰胺的体积百分比为40~100%;所得CuO-NiFe-LDHNS/rGO复合催化剂中LDHNS的大小为20~50nm,厚度小于3nm;CuO的粒径大小为3~15nm,均匀掺杂于LHDNS基体中。The molar ratio of ferric nitrate nonahydrate and nickel nitrate hexahydrate is 1:2; the volume percentage of formamide in the mixed solvent or solution of formamide and water is 40-100%; in the obtained CuO-NiFe-LDHNS/rGO composite catalyst The size of LDHNS is 20-50 nm and the thickness is less than 3 nm; the particle size of CuO is 3-15 nm, which is uniformly doped in the LHDNS matrix. 2.根据权利要求1所述的一种氧化铜掺杂的超薄镍铁类水滑石纳米片/石墨烯双功能水分解催化剂的制备方法,其特征在于利用该制备方法得到的氧化铜掺杂的超薄镍铁类水滑石纳米片/石墨烯复合物用于碱性介质中电解水的析氧反应和析氢反应中。2. the preparation method of the ultrathin nickel-iron type hydrotalcite nanosheet/graphene bifunctional water splitting catalyst of a kind of copper oxide doped according to claim 1, it is characterized in that utilizing the copper oxide doped that this preparation method obtains The ultrathin nickel-iron-based hydrotalcite nanosheets/graphene composites were used in the oxygen evolution reaction and hydrogen evolution reaction of electrolyzed water in alkaline medium.
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