CN112563517B - Preparation method of rare earth metal doped carbon-based oxygen reduction electrocatalyst - Google Patents
Preparation method of rare earth metal doped carbon-based oxygen reduction electrocatalyst Download PDFInfo
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Abstract
A preparation method of a rare earth metal doped carbon-based oxygen reduction electrocatalyst belongs to the technical field of new energy materials and electrocatalysis, and can solve the problem of the existing oxygen reduction electrocatalystThe activity and stability of the catalyst are determined by reacting aromatic compound containing carboxyl/aldehyde group/amino/hydroxyl functional group as carbon source, nitrogen-containing organic compound as nitrogen source, rare earth metal salt and Fe/Co/Ni transition metal salt as metal precursor in proper solvent to form stable metal complex, polymerizing the material in N solvent by means of solvent-thermal method, and final polymerizing2And roasting and carbonizing at high temperature under the protection of atmosphere, and then carrying out acid washing, washing and centrifuging to obtain the rare earth metal doped carbon-based oxygen reduction electrocatalyst. The rich 4f electrons of the rare earth elements can effectively regulate and control the electronic structure of the catalyst, and the rare earth elements and the Fe/Co/Ni main metal have synergistic effect, so that the activity and the stability of the carbon-based oxygen reduction electrocatalyst are improved.
Description
Technical Field
The invention belongs to the technical field of new energy materials and electrocatalysis, and particularly relates to a preparation method of a rare earth metal doped carbon-based oxygen reduction electrocatalyst.
Background
With the rapid development of society, the demand of people for clean energy is more and more urgent due to the non-regenerability and pollution of the traditional fossil energy. A clean and efficient energy conversion device such as a fuel cell or a metal-air battery has higher conversion efficiency than a conventional device for converting energy by combustion, and is therefore favored by the academic world and the industry and is one of key technologies for the future widespread use of clean energy. However, the poor activity and stability of the cathode oxygen reduction electrocatalyst have been the core factors that prevent the popularization and application of such technologies, and commercial application still depends on the Pt/C catalyst at present. The scale of energy utilization is huge, and the Pt/C catalyst still cannot support the large-scale development of technologies such as fuel cells and the like due to the defects of low natural reserves, high price, poor stability, easiness in CO and methanol poisoning and the like of precious metal Pt. Therefore, suitable efficient and inexpensive alternative catalysts are still being sought.
Non-noble metal catalysts (NPMCs) are ideal materials for replacing Pt/C catalysts, and common NPMCs comprise pure carbon materials doped with nonmetal S, P, O, N, B and the like, carbon-based transition metal materials, and non-noble metal catalysts such as transition metal sulfides, phosphides, oxides, nitrides and the like. The carbon-based transition metal catalyst forms active sites capable of regulating and controlling an internal electronic structure of the catalyst with a carbon structure by means of electron-rich or electron-deficient elements such as metal-N-C, S, P, O, N, B and the like, so that the activation energy of the oxygen electrocatalytic reduction reaction can be remarkably reduced, and the catalytic performance and the stability of the oxygen electrocatalytic reduction reaction are enhanced. The 4f orbit filled with the rare earth element can improve the electronic environment, so that the rare earth metal is introduced into the carbon-based catalytic material, the oxygen electrocatalytic reduction activity of the carbon-based catalytic material is hopeful to be improved, and meanwhile, the valence-variable characteristic of the rare earth element can enable the rare earth element to become a reaction site of a peroxide intermediate, so that the stability of the catalyst is improved.
Disclosure of Invention
The invention provides a method for preparing a rare earth metal doped carbon-based oxygen reduction electrocatalyst with high catalytic activity and good stability, aiming at the problems of activity and stability of the existing oxygen reduction electrocatalyst.
The invention adopts the following technical scheme:
a preparation method of a rare earth metal doped carbon-based oxygen reduction electrocatalyst comprises the following steps:
firstly, putting a nitrogen source, a carbon source, a rare earth metal salt and a Fe/Co/Ni transition metal salt into a container, adding a solvent, sealing and heating to 40-80 ℃, stirring for 4-12h, adding formaldehyde, and continuously stirring for 10-16h to obtain a metal-organic complex precursor;
secondly, transferring the metal-organic complex precursor obtained in the first step into a reaction container, and carrying out solvothermal reaction for 20-24h at the temperature of 100-200 ℃;
thirdly, placing the product obtained in the second step in a muffle furnace, and heating and oxidizing in air at the temperature of 150-;
fourthly, placing the product obtained in the third step into a tubular furnace, and carbonizing at the temperature of 800-1000 ℃ for 1-3h under the nitrogen atmosphere;
and fifthly, washing the carbonized product obtained in the fourth step by 0.5M sulfuric acid and deionized water to be neutral, and centrifugally drying to obtain the rare earth metal doped carbon-based oxygen reduction electrocatalyst.
In the first step, the nitrogen source is a nitrogen-containing organic substance, and comprises at least one of melamine, urea, phenanthroline, dicyandiamide and bipyridine.
In the first step, the carbon source is an aromatic compound containing carboxyl/aldehyde/amino/hydroxyl functional groups, and comprises at least one of 2, 4-dihydroxybenzoic acid, 2, 4-dihydroxybenzaldehyde, aminophenol, aminobenzoic acid, hydroxyquinoline, aminoquinoline, hydroxynaphthalene, aminonaphthalene, hydroxynaphthoic acid, aminonaphthoic acid, hydroxypyridine, carboxypyridine, hydroxypyrrole and carboxypyrrole.
In the first step the rare earth metal salt comprises at least one of hydrated chlorides of lanthanum, cerium, neodymium, samarium, gadolinium, erbium and yttrium.
The Fe/Co/Ni transition metal salt in the first step comprises at least one of hydrated chlorides of Fe/Co/Ni.
The solvent in the first step comprises at least one of water, ethanol and ethylene glycol.
In the first step, the molar ratio of the Fe/Co/Ni transition metal salt to the rare earth metal salt to the carbon source to the nitrogen source to formaldehyde is 1: (0.1-0.5): (1-2): (2-5): (1-1).
In the third step, the oxidation heating rate of the muffle furnace is 1-5 ℃/min.
The carbonization heating rate in the fourth step is 1-3 ℃/min.
The invention has the following beneficial effects:
the rare earth elements have rich 4f electrons, and the excellent oxygen affinity and variable valence thereof can often promote the activity of a main catalytic active site in an oxidation-reduction reaction and are beneficial to the adsorption and migration of oxygen species. Meanwhile, the doping of the rare earth elements can form oxygen vacancies, which is beneficial to stabilizing the catalyst, can effectively regulate and control the electronic structure and the electron transfer performance of the catalyst, and can obviously improve the activity and the stability of the carbon-based oxygen reduction electrocatalyst under the synergistic action with the Fe/Co/Ni main metal.
Drawings
FIG. 1 inventive example 12 ORR Linear sweep polarization curves of cerium doped carbon based Co electrocatalyst (Co (Ce) -61) in 0.1M KOH.
Fig. 2 is an ORR linear scan polarization curve for Ce-only single metal doped catalyst in 0.1M KOH.
FIG. 3 is an ORR linear scan polarization curve for Co-only single metal doped catalysts in 0.1M KOH.
FIG. 4 is an ORR linear scan polarization curve before and after stability test of cerium doped carbon based Co electrocatalyst (Co (Ce) -61) in 0.1M KOH.
Fig. 5 is a Tafel slope plot for a series of cerium doped carbon-based Co electrocatalysts.
FIG. 6 is the calculated electron transfer number from the K-L equation for a series of cerium doped carbon based Co electrocatalysts.
Figure 7 is an XRD diffractogram of a series of cerium doped carbon based Co electrocatalysts.
Detailed Description
Example 1
11.51mmol of 2, 4-dihydroxybenzoic acid, 7.77mmol of melamine, 12.80mmol of cobalt chloride hexahydrate (CoCl)2·6H2O) and 3.20mmol of lanthanum chloride heptahydrate (LaCl)3·7H2O) is placed in a container, 18mL of deionized water and 4mL of absolute ethyl alcohol are added, the mixture is stirred for 10 hours at 50 ℃, 48.9mmol of formaldehyde is added, and the mixture is continuously stirred and reacts for 14 hours; then transferring the mixture into a hydrothermal kettle to react for 24 hours at the temperature of 120 ℃; then moving the mixture into a muffle furnace to be oxidized for 4 hours at 280 ℃ in a stage-by-stage manner at the heating rate of 1 ℃/min; transferring the oxidized product into a tubular furnace, heating to 900 ℃ in a staged manner at the heating rate of 1 ℃/min under the nitrogen atmosphere, carbonizing, and preserving heat for 2 hours; cooling to room temperature, washing with 0.5M dilute sulfuric acid, washing with deionized water to neutrality, centrifuging, and drying to obtain the metal-doped carbon-based oxygen reduction electrocatalyst. The serial number of the catalyst is Co (La) -41, and the loading capacity of the prepared catalyst on a glassy carbon electrode is 0.2018 mg-cm-2The limiting current density at the rotation speed of 2025rpm was 5.85 mA cm-2The initial potential was 0.817V vs. RHE.
Example 2
11.51mmol of 2, 4-dihydroxybenzoic acid, 7.77mmol of melamine, 12.80mmol of cobalt chloride hexahydrate (CoCl)2·6H2O) and 3.20mmol gadolinium chloride hexahydrate (GdCl)3·6H2O) into a container, 18mL of deionized water and 4mL of absolute ethanol are added, 50 DEG CStirring for 10h, adding 48.9mmol of formaldehyde, and continuously stirring for reacting for 14 h; then transferring the mixture into a hydrothermal kettle to react for 24 hours at the temperature of 120 ℃; then moving the mixture into a muffle furnace to be oxidized for 4 hours at 280 ℃ in a stage-by-stage manner at the heating rate of 1 ℃/min; transferring the oxidation product into a tubular furnace, gradually heating to 900 ℃ at the heating rate of 1 ℃/min under the nitrogen atmosphere, carbonizing, and preserving heat for 2 hours; cooling to room temperature, washing with 0.5M dilute sulfuric acid, washing with deionized water to neutrality, centrifuging, and drying to obtain the rare earth metal doped carbon-based oxygen reduction electrocatalyst. The serial number of the catalyst is Co (Gd) -41, and the loading capacity of the prepared catalyst on a glassy carbon electrode is 0.2018 mg-cm-2The limiting current density at the rotation speed of 2025rpm was 4.51 mA/cm-2The initial potential was 0.825V vs. RHE.
Example 3
11.51mmol of 2, 4-dihydroxybenzoic acid, 7.77mmol of melamine, 12.80mmol of cobalt chloride hexahydrate (CoCl)2·6H2O) and 3.20mmol of erbium chloride hexahydrate (ErCl)3·6H2O) is placed in a container, 18mL of deionized water and 4mL of absolute ethyl alcohol are added, the mixture is stirred for 10 hours at 50 ℃, 48.9mmol of formaldehyde is added, and the mixture is continuously stirred and reacts for 14 hours; then transferring the mixture into a hydrothermal kettle to react for 24 hours at the temperature of 120 ℃; then moving the mixture into a muffle furnace to be oxidized for 4 hours at 280 ℃ in a stage-by-stage manner at the heating rate of 1 ℃/min; transferring the oxidation product into a tubular furnace, gradually heating to 900 ℃ at the heating rate of 1 ℃/min under the nitrogen atmosphere, carbonizing, and preserving heat for 2 hours; cooling to room temperature, washing with 0.5M dilute sulfuric acid, washing with deionized water to neutrality, centrifuging, and drying to obtain the rare earth metal doped carbon-based oxygen reduction electrocatalyst. The serial number of the catalyst is Co (Er) -41, and the loading capacity of the prepared catalyst on a glassy carbon electrode is 0.2018 mg-cm-2The limiting current density at the rotation speed of 2025rpm was 4.96mA cm-2The initial potential was 0.799V vs. RHE.
Example 4
11.51mmol of 2, 4-dihydroxybenzoic acid, 7.77mmol of melamine, 12.80mmol of cobalt chloride hexahydrate (CoCl)2·6H2O) and 3.20mmol of neodymium chloride hexahydrate (NdCl)3·6H2O) is put into a container, 18mL of deionized water and 4mL of absolute ethyl alcohol are added, the mixture is stirred for 10 hours at 50 ℃, 48.9mmol of formaldehyde is added, and the mixture is stirred continuouslyThe reaction time is 14 hours; then transferring the mixture into a hydrothermal kettle to react for 24 hours at the temperature of 120 ℃; then moving the mixture into a muffle furnace to be oxidized for 4 hours at 280 ℃ in a stage-by-stage manner at the heating rate of 1 ℃/min; transferring the oxidation product into a tubular furnace, gradually heating to 900 ℃ at the heating rate of 1 ℃/min under the nitrogen atmosphere, carbonizing, and preserving heat for 2 hours; cooling to room temperature, washing with 0.5M dilute sulfuric acid, washing with deionized water to neutrality, centrifuging, and drying to obtain the rare earth metal doped carbon-based oxygen reduction electrocatalyst. The serial number of the catalyst is Co (Nd) -41, and the loading capacity of the prepared catalyst on a glassy carbon electrode is 0.2018 mg-cm-2The limiting current density at the rotation speed of 2025rpm was 5.18 mA cm-2The initial potential was 0.868V vs. RHE.
Example 5
11.51mmol of 2, 4-dihydroxybenzoic acid, 7.77mmol of melamine, 12.80mmol of cobalt chloride hexahydrate (CoCl)2·6H2O) and 6.40mmol of samarium chloride hexahydrate (SmCl)3·6H2O) is placed in a container, 18mL of deionized water and 4mL of absolute ethyl alcohol are added, the mixture is stirred for 10 hours at 50 ℃, 48.9mmol of formaldehyde is added, and the mixture is continuously stirred and reacts for 14 hours; then transferring the mixture into a hydrothermal kettle to react for 24 hours at the temperature of 120 ℃; then moving the mixture into a muffle furnace to be oxidized for 4 hours at 280 ℃ in a stage-by-stage manner at the heating rate of 1 ℃/min; transferring the oxidation product into a tubular furnace, gradually heating to 900 ℃ at the heating rate of 1 ℃/min under the nitrogen atmosphere, carbonizing, and preserving heat for 2 hours; cooling to room temperature, washing with 0.5M dilute sulfuric acid, washing with deionized water to neutrality, centrifuging, and drying to obtain the rare earth metal doped carbon-based oxygen reduction electrocatalyst. The serial number of the catalyst is Co (Sm) -21, and the loading capacity of the prepared catalyst on a glassy carbon electrode is 0.2018 mg-cm-2The limiting current density at the rotation speed of 2025rpm was 6.97 mA/cm-2Initial potential of 0.887V vs. RHE, electron transfer number of 3.74, Tafel slope of 47 mV dec-1。
Example 6
11.51mmol of 2, 4-dihydroxybenzoic acid, 7.77mmol of melamine, 12.80mmol of cobalt chloride hexahydrate (CoCl)2·6H2O) and 3.20mmol of samarium chloride hexahydrate (SmCl)3·6H2O) is put into a container, 18mL of deionized water and 4mL of absolute ethyl alcohol are added, the mixture is stirred for 10h at 50 ℃, and 48.9mmol of methanol is addedContinuously stirring the aldehyde for reaction for 14 hours; then transferring the mixture into a hydrothermal kettle to react for 24 hours at the temperature of 120 ℃; then moving the mixture into a muffle furnace to be oxidized for 4 hours at 280 ℃ in a stage-by-stage manner at the heating rate of 1 ℃/min; transferring the oxidation product into a tubular furnace, gradually heating to 900 ℃ at the heating rate of 1 ℃/min under the nitrogen atmosphere, carbonizing, and preserving heat for 2 hours; cooling to room temperature, washing with 0.5M dilute sulfuric acid, washing with deionized water to neutrality, centrifuging, and drying to obtain the rare earth metal doped carbon-based oxygen reduction electrocatalyst. . The serial number of the catalyst is Co (Sm) -41, and the loading capacity of the prepared catalyst on a glassy carbon electrode is 0.2018 mg-cm-2The limiting current density at the rotation speed of 2025rpm was 6.13 mA cm-2Initial potential of 0.880V vs. RHE, electron transfer number of 3.62, Tafel slope of 55 mV dec-1。
Example 7
11.51mmol of 2, 4-dihydroxybenzoic acid, 7.77mmol of melamine, 12.80mmol of cobalt chloride hexahydrate (CoCl)2·6H2O) and 6.40mmol of yttrium chloride hexahydrate (YCl)3·6H2O) is placed in a container, 18mL of deionized water and 4mL of absolute ethyl alcohol are added, stirring is carried out for 10h at 50 ℃, 48.9mmol of formaldehyde is added, and stirring reaction is continued for 14 h; then transferring the mixture into a hydrothermal kettle to react for 24 hours at the temperature of 120 ℃; then moving the mixture into a muffle furnace to be oxidized for 4 hours at 280 ℃ in a stage-by-stage manner at the heating rate of 1 ℃/min; transferring the oxidized product into a tubular furnace, heating to 900 ℃ in a staged manner at the heating rate of 1 ℃/min under the nitrogen atmosphere, carbonizing, and preserving heat for 2 hours; cooling to room temperature, washing with 0.5M dilute sulfuric acid, washing with deionized water to neutrality, centrifuging, and drying to obtain the rare earth/alkaline earth-cobalt-nitrogen co-doped catalyst. The serial number of the catalyst is Co (Y) -21, and the loading capacity of the prepared catalyst on a glassy carbon electrode is 0.2018 mg-cm-2The limiting current density at the rotation speed of 2025rpm was 7.08 mA/cm-2Initial potential of 0.875V vs. RHE, electron transfer number of 3.86, Tafel slope of 50 mV dec-1。
Example 8
11.51mmol of 2, 4-dihydroxybenzoic acid, 7.77mmol of melamine, 12.80mmol of cobalt chloride hexahydrate (CoCl)2·6H2O) and 3.20mmol of Yttrium chloride hexahydrate (YCl)3·6H2O) is placed in a container and addedStirring 18mL of deionized water and 4mL of absolute ethyl alcohol at 50 ℃ for 10h, adding 48.9mmol of formaldehyde, and continuously stirring for reacting for 14 h; then transferring the mixture into a hydrothermal kettle to react for 24 hours at the temperature of 120 ℃; then moving the mixture into a muffle furnace to be oxidized for 4 hours at 280 ℃ in a stage-by-stage manner at the heating rate of 1 ℃/min; transferring the oxidation product into a tubular furnace, gradually heating to 900 ℃ at the heating rate of 1 ℃/min under the nitrogen atmosphere, carbonizing, and preserving heat for 2 hours; cooling to room temperature, washing with 0.5M dilute sulfuric acid, washing with deionized water to neutrality, centrifuging, and drying to obtain the rare earth/alkaline earth-cobalt-nitrogen co-doped catalyst. The serial number of the catalyst is Co (Y) -41, and the loading capacity of the prepared catalyst on a glassy carbon electrode is 0.2018 mg-cm-2The limiting current density at the rotation speed of 2025rpm was 6.80 mA/cm-2Initial potential of 0.885V vs. RHE, electron transfer number of 3.78, Tafel slope of 53 mV dec-1。
Example 9
11.51mmol of 2, 4-dihydroxybenzoic acid, 7.77mmol of melamine, 12.80mmol of cobalt chloride hexahydrate (CoCl)2·6H2O) and 3.20mmol of yttrium chloride hexahydrate (YCl)3·6H2O) is placed in a container, 18mL of deionized water and 4mL of absolute ethyl alcohol are added, the mixture is stirred for 10 hours at 70 ℃, 48.9mmol of formaldehyde is added, and the mixture is continuously stirred and reacts for 14 hours; then transferring the mixture into a hydrothermal kettle to react for 24 hours at the temperature of 120 ℃; then moving the mixture into a muffle furnace to be oxidized for 4 hours at 280 ℃ in a stage-by-stage manner at the heating rate of 1 ℃/min; transferring the oxidation product into a tubular furnace, gradually heating to 900 ℃ at the heating rate of 1 ℃/min under the nitrogen atmosphere, carbonizing, and preserving heat for 2 hours; cooling to room temperature, washing with 0.5M dilute sulfuric acid, washing with deionized water to neutrality, centrifuging, and drying to obtain the rare earth metal doped carbon-based oxygen reduction electrocatalyst. The serial number of the catalyst is Co (Y) -41-70, and the loading capacity of the prepared catalyst on a glassy carbon electrode is 0.2018mg cm-2The limiting current density at the rotation speed of 2025rpm was 6.69 mA cm-2Initial potential of 0.881V vs. RHE, electron transfer number of 3.63, Tafel slope of 47 mV dec-1。
Example 10
11.51mmol of 2, 4-dihydroxybenzoic acid, 7.77mmol of melamine, 12.80mmol of cobalt chloride hexahydrate (CoCl)2·6H2O) and 3.20mmol hexahydrateYttrium chloride (YCl)3·6H2O) is placed in a container, 18mL of deionized water and 4mL of absolute ethyl alcohol are added, stirring is carried out for 10h at 70 ℃, 48.9mmol of formaldehyde is added, and stirring reaction is continued for 14 h; then transferring the mixture into a hydrothermal kettle to react for 24 hours at the temperature of 180 ℃; then moving the mixture into a muffle furnace to be oxidized for 4 hours at 280 ℃ in a stage-by-stage manner at the heating rate of 1 ℃/min; transferring the oxidation product into a tubular furnace, gradually heating to 900 ℃ at the heating rate of 1 ℃/min under the nitrogen atmosphere, carbonizing, and preserving heat for 2 hours; cooling to room temperature, washing with 0.5M dilute sulfuric acid, washing with deionized water to neutrality, centrifuging, and drying to obtain the rare earth metal doped carbon-based oxygen reduction electrocatalyst. The serial number of the catalyst is Co (Y) -180-41, and the loading capacity of the prepared catalyst on a glassy carbon electrode is 0.2018mg cm-2The limiting current density at the rotation speed of 2025rpm was 6.99 mA cm-2Initial potential of 0.889V vs. RHE, electron transfer number of 3.87, Tafel slope of 49 mV dec-1。
Example 11
11.51mmol of 2, 4-dihydroxybenzoic acid, 7.77mmol of melamine, 12.80mmol of cobalt chloride hexahydrate (CoCl)2·6H2O) and 6.40mmol of cerium chloride heptahydrate (CeCl)3·7H2O) is placed in a container, 18mL of deionized water and 4mL of absolute ethyl alcohol are added, the mixture is stirred for 10 hours at 50 ℃, 48.9mmol of formaldehyde is added, and the mixture is continuously stirred and reacts for 14 hours; then transferring the mixture into a hydrothermal kettle to react for 24 hours at the temperature of 120 ℃; then moving the mixture into a muffle furnace to be oxidized for 4 hours at 280 ℃ in a stage-by-stage manner at the heating rate of 1 ℃/min; transferring the oxidation product into a tubular furnace, gradually heating to 900 ℃ at the heating rate of 1 ℃/min under the nitrogen atmosphere, carbonizing, and preserving heat for 2 hours; cooling to room temperature, washing with 0.5M dilute sulfuric acid, washing with deionized water to neutrality, centrifuging, and drying to obtain the rare earth metal doped carbon-based oxygen reduction electrocatalyst. The serial number of the catalyst is Co (Ce) -21, and the loading capacity of the prepared catalyst on a glassy carbon electrode is 0.2018 mg-cm-2The limiting current density at the rotation speed of 2025rpm was 6.62mA cm-2Initial potential of 0.888V vs. RHE, electron transfer number of 4.06, Tafel slope of 66 mV dec-1。
Example 12
11.51mmol of 2, 4-dihydroxybenzoic acid, 7.77mmol of melamine and 12.80mmol of cobalt chloride hexahydrate (CoCl)2·6H2O) and 3.20mmol of cerium chloride heptahydrate (CeCl)3·7H2O) is placed in a container, 18mL of deionized water and 4mL of absolute ethyl alcohol are added, the mixture is stirred for 10 hours at 50 ℃, 48.9mmol of formaldehyde is added, and the mixture is continuously stirred and reacts for 14 hours; then transferring the mixture into a hydrothermal kettle to react for 24 hours at the temperature of 120 ℃; then moving the mixture into a muffle furnace to be oxidized for 4 hours at 280 ℃ in a stage-by-stage manner at the heating rate of 1 ℃/min; transferring the oxidation product into a tubular furnace, gradually heating to 900 ℃ at the heating rate of 1 ℃/min under the nitrogen atmosphere, carbonizing, and preserving heat for 2 hours; cooling to room temperature, washing with 0.5M dilute sulfuric acid, washing with deionized water to neutrality, centrifuging, and drying to obtain the rare earth metal doped carbon-based oxygen reduction electrocatalyst. The serial number of the catalyst is Co (Ce) -41, and the loading capacity of the prepared catalyst on a glassy carbon electrode is 0.2018 mg-cm-2The limiting current density at the rotation speed of 2025rpm was 6.46mA cm-2Initial potential of 0.812V vs. RHE, electron transfer number of 4.03, Tafel slope of 82 mV dec-1。
Example 13
11.51mmol of 2, 4-dihydroxybenzoic acid, 7.77mmol of melamine, 12.80mmol of cobalt chloride hexahydrate (CoCl)2·6H2O) and 2.13mmol of cerium chloride heptahydrate (CeCl)3·7H2O) is placed in a container, 18mL of deionized water and 4mL of absolute ethyl alcohol are added, stirring is carried out for 10h at 50 ℃, 48.9mmol of formaldehyde is added, and stirring reaction is continued for 14 h; then transferring the mixture into a hydrothermal kettle to react for 24 hours at the temperature of 120 ℃; then moving the mixture into a muffle furnace to be oxidized for 4 hours at 280 ℃ in a stage-by-stage manner at the heating rate of 1 ℃/min; transferring the oxidation product into a tubular furnace, gradually heating to 900 ℃ at the heating rate of 1 ℃/min under the nitrogen atmosphere, carbonizing, and preserving heat for 2 hours; cooling to room temperature, washing with 0.5M dilute sulfuric acid, washing with deionized water to neutrality, centrifuging, and drying to obtain the rare earth metal doped carbon-based oxygen reduction electrocatalyst. The serial number of the catalyst is Co (Ce) -61, and the loading capacity of the prepared catalyst on a glassy carbon electrode is 0.2018 mg-cm-2The limiting current density at the rotation speed of 2025rpm was 7.15mA cm-2Initial potential of 0.923V vs. RHE, electron transfer number of 4.36, Tafel slope of 67 mV dec-1。
Example 14
11.51mmol of 2, 4-dihydroxybenzoic acid, 7.77mmol of melamine, 12.80mmol of cobalt chloride hexahydrate (CoCl)2·6H2O) and 1.60mmol of cerium chloride heptahydrate (CeCl)3·7H2O) is placed in a container, 18mL of deionized water and 4mL of absolute ethyl alcohol are added and stirred for 10h, 48.9mmol of formaldehyde is added and stirring reaction is continued for 14 h; then transferring the mixture into a hydrothermal kettle to react for 24 hours at the temperature of 120 ℃; then moving the mixture into a muffle furnace to be oxidized for 4 hours at 280 ℃ in a stage-by-stage manner at the heating rate of 1 ℃/min; transferring the oxidation product into a tubular furnace, gradually heating to 900 ℃ at the heating rate of 1 ℃/min under the nitrogen atmosphere, carbonizing, and preserving heat for 2 hours; cooling to room temperature, washing with 0.5M dilute sulfuric acid, washing with deionized water to neutrality, centrifuging, and drying to obtain the rare earth metal doped carbon-based oxygen reduction electrocatalyst. The serial number of the catalyst is Co (Ce) -81, and the loading capacity of the prepared catalyst on a glassy carbon electrode is 0.2018 mg-cm-2The limiting current density at the rotation speed of 2025rpm was 6.59 mA/cm-2Initial potential of 0.875V vs. RHE, electron transfer number of 3.86, Tafel slope of 73 mV dec-1。
Taking the cerium-doped carbon-based Co electrocatalyst (Co (Ce) -61) prepared by the invention as an example, the rare earth metal-doped carbon-based oxygen reduction electrocatalyst prepared by the invention and the electrochemical performance thereof are illustrated.
FIG. 1 is an ORR linear scan polarization curve of a cerium doped carbon based Co electrocatalyst (Co (Ce) -61) in 0.1M KOH with an onset potential of 0.923V vs. RHE and a limiting current density of 5.07 mA-cm-2. Compared with the single metal doped catalyst, the initial potential and the limiting current density are greatly improved, the reaction activity and the conductivity are obviously improved, and the synergistic effect of the rare earth metal and the transition metal cobalt in the catalytic process is proved.
FIGS. 2 and 3 are ORR linear scanning polarization curves of a single-metal Ce-doped catalyst and a single-metal Co-doped catalyst in 0.1M KOH, respectively, the initial potentials of the catalysts are 0.775V vs. RHE and 0.880V vs. RHE, respectively, and the limiting current densities of the catalysts are 3.43 mA-cm-2And 4.45mA · cm-2。
FIG. 4 is an ORR linear scan polarization curve before and after stability test of cerium doped carbon based Co electrocatalyst (Co (Ce) -61) in 0.1M KOH. As can be seen from FIG. 4, after 1500 CV cycles (20 h) of the test, the half-wave potential was shifted only by 23mV negatively, and the limiting current density remained 94.8% of the initial value, showing good stability.
FIG. 5 is a Tafel slope plot for a cerium doped carbon based Co electrocatalyst with a Tafel slope at 70 mV dec-1About, the Tafel slope of the Co (Ce) -61 catalyst is 67 mV dec-1The good dynamic process is demonstrated.
Fig. 6 shows the electron transfer number calculated by the K-L equation for the series of cerium-doped carbon-based Co electrocatalysts, and as can be seen from fig. 6, the electron transfer number catalyzed by the cerium-doped carbon-based Co electrocatalyst is about 4, which indicates that the cerium-doped carbon-based Co electrocatalyst is mainly based on 4 electron paths.
Fig. 7 is an XRD diffractogram of a series of cerium-doped carbon-based Co electrocatalysts, showing a diffraction peak of carbon at 26 ° and no diffraction peaks of Ce and Co, indicating that the particles of the metal element in the catalyst are small or exist in a monoatomic structure.
Claims (8)
1. A preparation method of a rare earth metal doped carbon-based oxygen reduction electrocatalyst is characterized by comprising the following steps: the method comprises the following steps:
firstly, putting a nitrogen source, a carbon source, a rare earth metal salt and a Fe/Co/Ni transition metal salt into a container, adding a solvent, sealing and heating to 40-80 ℃, stirring for 4-12h, adding formaldehyde, and continuously stirring for 10-16h to obtain a metal-organic complex precursor;
the rare earth metal salt comprises at least one of hydrated chlorides of lanthanum, cerium, neodymium, samarium, gadolinium, erbium and yttrium;
the Fe/Co/Ni transition metal salt comprises at least one of hydrated chlorides of Fe/Co/Ni;
secondly, transferring the metal-organic complex precursor obtained in the first step into a reaction container, and carrying out solvothermal reaction for 20-24h at the temperature of 100-200 ℃;
thirdly, placing the product obtained in the second step in a muffle furnace, and heating and oxidizing in air at the temperature of 150-;
fourthly, placing the product obtained in the third step into a tubular furnace, and carbonizing at the temperature of 800-1000 ℃ for 1-3h under the nitrogen atmosphere;
and fifthly, washing the carbonized product obtained in the fourth step by 0.5M sulfuric acid and deionized water to be neutral, and centrifugally drying to obtain the rare earth metal doped carbon-based oxygen reduction electrocatalyst.
2. The method of claim 1, wherein the rare earth metal doped carbon-based oxygen reduction electrocatalyst is prepared by the following steps: in the first step, the nitrogen source is a nitrogen-containing organic substance, and comprises at least one of melamine, urea, phenanthroline, dicyandiamide and bipyridine.
3. The method of claim 1, wherein the rare earth metal doped carbon-based oxygen reduction electrocatalyst is prepared by the following steps: in the first step, the carbon source is an aromatic compound containing carboxyl/aldehyde/amino/hydroxyl functional groups, and comprises at least one of 2, 4-dihydroxybenzoic acid, 2, 4-dihydroxybenzaldehyde, aminophenol, aminobenzoic acid, hydroxyquinoline, aminoquinoline, hydroxynaphthalene, aminonaphthalene, hydroxynaphthoic acid, aminonaphthoic acid, hydroxypyridine, carboxypyridine, hydroxypyrrole and carboxypyrrole.
4. The method of claim 1, wherein the rare earth metal doped carbon-based oxygen reduction electrocatalyst is prepared by the following steps: the solvent in the first step comprises at least one of water, ethanol and ethylene glycol.
5. The method of claim 1, wherein the rare earth metal doped carbon-based oxygen reduction electrocatalyst is prepared by the following steps: in the first step, the molar ratio of the Fe/Co/Ni transition metal salt to the rare earth metal salt to the carbon source to the nitrogen source to formaldehyde is 1: (0.1-0.5): (1-2): (2-5): (1-1).
6. The method of claim 1, wherein the rare earth metal doped carbon-based oxygen reduction electrocatalyst is prepared by the following steps: in the third step, the oxidation heating rate of the muffle furnace is 1-5 ℃/min.
7. The method of claim 1, wherein the rare earth metal doped carbon-based oxygen reduction electrocatalyst is prepared by the following steps: the carbonization temperature rise rate in the fourth step is 1-3 ℃/min.
8. A rare earth metal doped carbon-based oxygen reduction electrocatalyst prepared according to the preparation method of any one of claims 1 to 7.
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