CN115663210A - Preparation method of carbon-coated platinum oxygen reduction electrocatalyst - Google Patents
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Abstract
The invention discloses a preparation method of a carbon-coated platinum-oxygen reduction electrocatalyst, and aims to solve the problems of thicker coated carbon layer, low platinum particle activity and poor catalytic activity of the coated carbon layer prepared by the existing method for preparing a platinum-based nanoparticle carbon-coated layer. The technical scheme is that a mixed dispersion liquid A containing carrier-loaded platinum ions is prepared; then preparing sol B containing metal ions, and preparing a carbon-coated platinum precursor by adopting A and B; and finally, preparing the carbon-coated platinum-oxygen reduction electrocatalyst by using the carbon-coated platinum precursor. Based on the chemical principle of preparing carbon materials and platinum alloys, the prepared carbon-coated platinum oxygen reduction electrocatalyst has a carbon coating layer, and the prepared carbon-coated platinum oxygen reduction electrocatalyst is very good in activity and durability, low in cost and capable of being produced in a large scale.
Description
Technical Field
The invention relates to the technical field of carbon materials and electrochemistry, in particular to a preparation method and application of a carbon-coated platinum oxygen reduction electrocatalyst.
Background
The oxygen reduction reaction (abbreviated as oxygen reduction reaction) is a reaction necessarily involved in energy storage and conversion devices such as hydrogen fuel cells, methanol fuel cells, metal-air cells and the like, generally occurs at the cathode of a cell, and generally, the process is that oxygen molecules obtain electrons, and the electrons are combined with protons or hydroxyl radicals and are reduced into water. When the oxygen reduction reaction proceeds spontaneously, the reaction rate determined by chemical kinetics is very slow, and thus a catalyst material is required to accelerate the reaction. The speed of the oxygen reduction reaction directly determines the performance of the relevant battery, so that the catalyst material capable of catalyzing the oxygen reduction reaction to rapidly proceed is very important for the development of energy storage and conversion devices such as hydrogen fuel cells, methanol fuel cells, metal-air cells and the like.
Platinum-containing catalyst materials, which can catalyze oxygen reduction reaction rapidly with high efficiency, are commonly called carbon-supported platinum catalyst materials, including carbon-supported pure platinum nanoparticles and carbon-supported platinum alloy nanoparticles, which are well-established commercial materials and have been used in hydrogen fuel cells, methanol fuel cells and metal-air batteries. The actual working environment of hydrogen fuel cells, methanol fuel cells and metal-air cells is very harsh, oxygen and water are generally contained, the temperature field and the electric field function is realized, and the electrolyte is acid or alkaline. The platinum or alloy nanoparticles loaded on the carbon have high surface energy, and can undergo deactivation behaviors such as migration, agglomeration, sintering, growth, dissolution and the like under the action of various factors in the working process, so that the activity of the catalyst material is reduced. The high-stability carbon-supported platinum catalyst material is developed, the deactivation behavior of platinum-based particles is inhibited, and the wide application of new energy technologies such as hydrogen fuel cells, methanol fuel cells and metal-air cells is facilitated.
The preparation of the carbon-supported platinum catalyst with an obvious core-shell coating structure is the main method at present, aiming at relieving the deactivation behavior of platinum and platinum alloy nanoparticles (platinum-based nanoparticles for short) and improving the durability of the carbon-supported platinum catalyst. The carbon-supported platinum catalyst with the core-shell coating structure mainly comprises two types: one is active metal platinum, etc. as shell, coating the core of other structural material; the other is active platinum or other metals as core and coated with other structural material. Wherein, the active material such as platinum is taken as a core, and when the core is coated by another shell material, the deactivation behavior of platinum can be effectively relieved, and the durability of the carbon-supported platinum catalyst is improved. The shell material used to coat the platinum-based nanoparticles mainly includes: polymers, metal oxides, and carbon materials.
Patent [ CN 107851803B]Discloses a preparation method of polydopamine-coated carbon-supported platinum, wherein the polymer has poor conductivity, and the formed coating layer is not beneficial to the rapid conduction of electrons of catalytic reaction. Patent [ CN 103155249B]、[JA-A-2005-135900]Discloses a preparation method of platinum nano-particles coated with oxides, which utilizes the oxide coating to inhibit the agglomeration growth of platinum; however, under acidic or basic conditions, oxides readily elute metal ions. The platinum surface adsorbs the dissolved metal ions, platinum can be poisoned, and the dissolved metal ions have destructive effects on other components of the battery and are not beneficial to the long-term stable operation of the battery, such as: fe 3+ 、Co 2+ 、Mn 2+ 、Ti 4+ The metal ions with high valence state generally have oxidation property, and have the destructive effect of oxidation perforation on a proton exchange membrane in a hydrogen fuel cell. Compared with metal oxides, the carbon material has better stability in acid and alkaline environments.
Compared with a polymer and a metal oxide coating, the carbon coating formed on the surface of the platinum particle can conduct electricity, inhibit the inactivation of the platinum-based nanoparticle and avoid the dissolution of metal ions in the platinum alloy. Patent [ CN 103372467B ] reports a method for coating another structural carbon layer on the surface of a carbon carrier, the coating layer inhibits the corrosion of the carbon carrier, but the stability of platinum particles cannot be improved well without any coating treatment of platinum-based nanoparticles. In order to achieve the purpose of forming a carbon coating layer on the surface of platinum-based nanoparticles, a paper (nat. Nanotechnol.17,968-975 (2022).) adopts platinum acetylacetonate and cobalt acetylacetonate to co-pyrolyze on the surface of carbon black to prepare a graphene-coated platinum-cobalt alloy; in the process, the platinum and the cobalt form a platinum-cobalt alloy, and the carbon-containing acetylacetone group is pyrolyzed to generate a graphene coating layer coating the platinum-cobalt alloy. In the patent [ CN 105609789A ], a carbon material with a special hollow structure is used as a carrier, and the carbon material is repeatedly vacuumized, heated and cooled in the process of dipping chloroplatinic acid, so that the chloroplatinic acid is adsorbed into a cavity of the hollow carbon material, and then the chloroplatinic acid is reduced to obtain carbon-coated platinum; this method relies mainly on a specially structured carrier. In the patent [ CN 104014333B ], graphene and chloroplatinic acid are subjected to hydrothermal reduction to obtain carbon-supported platinum, and then the carbon-supported platinum and sucrose are subjected to co-pyrolysis to form a sucrose pyrolysis carbon coating layer. The surface of the platinum is coated by pure carbon materials such as graphene and the like, so that the contact of reactants and the platinum is hindered, and the pure carbon materials are generally chemical inert and have no oxygen reduction activity, so that the intrinsic activity of the catalyst is reduced.
The surface of the platinum-based nano particles is coated with an active carbon coating layer, so that the inactivation can be relieved, and the intrinsic activity can be improved by the coordination and catalysis of the platinum and the carbon coating layer. The patent [ CN 103495432B ] discloses a method for post-treating carbon-supported platinum, which is used for preparing a nitrogen-doped carbon coating layer. The process method reported in the patent [ CN 107331877A ] is specifically that platinum nanoparticles are prepared firstly, the platinum nanoparticles are continuously mixed with a metal organic framework material, and the mixture of the metal organic framework material and platinum is pyrolyzed to obtain nitrogen-doped carbon coated platinum. In the patent [ CN 110391424A ], the prepared carbon-supported platinum-nickel alloy nanoparticles are immersed in a dopamine hydrochloride solution, and the dopamine hydrochloride is converted into a carbon coating layer through microwave heating treatment, so that nitrogen-doped carbon-coated platinum-nickel is obtained. The nitrogen-doped carbon has the activity of catalyzing oxygen reduction and can play a catalytic role in cooperation with platinum. However, the method for preparing the coating layer by pyrolyzing the organic matter can cause the platinum particles with uniform size to agglomerate and grow under the action of high temperature of pyrolysis, thereby causing the activity of the catalyst to be reduced. Similar patents also include [ CN 110465652B ], [ CN 110814362A ], [ CN 113809344A ].
In summary, the main problems of the current method for preparing the platinum-based nanoparticle-coated carbon coating layer include: the prepared coated carbon layer is thicker (1-3 nm), and the carbon layer is coated on the platinum surface and prevents platinum from contacting with oxygen to influence mass transfer; the preparation of the carbon coating layer needs high-temperature pyrolysis, the platinum particles grow up due to high temperature, and the activity is reduced; the coated carbon layer has no good catalytic activity. How to prepare thin-layer or porous carbon-coated small-size platinum and alloy nano-particles thereof, and the coated carbon layer has better catalytic activity, is a problem which needs to be solved urgently at present in the field.
Disclosure of Invention
The invention aims to solve the technical problems that the coated carbon layer prepared by the existing method for preparing the platinum-based nanoparticle-coated carbon coating layer is thick, the activity of platinum particles growing up is reduced due to high-temperature pyrolysis for preparing the coated carbon layer, and the coated carbon layer does not have good catalytic activity.
The invention is based on the chemical principle of preparing carbon material and platinum alloy, the prepared carbon-coated platinum oxygen reduction electrocatalyst is provided with a carbon coating layer, platinum coated by carbon has both pure platinum nano particles and platinum alloy nano particles, and the prepared carbon coating layer simultaneously contains C, H, O elements, one or more metal elements of Fe, co, ni, mn, cu, pt, cr, zn, ti, zr, V, mo, ag, au, pt, pd, ru, Y and W metals, and one or more elements of N, P, S; the metal elements exist in a monoatomic form, and the monoatomic metal structure is that each metal atom has a chemical bond with one or more elements in N, P, S, O; the carbon coating layer is provided with a pore structure etched by fused salt and gas, and oxygen can reach the coated platinum surface through the pore structure; the carbon coating layer has a thin layer sheet-like or wire-like structure similar to graphene; the metal monoatomic layer in the carbon coating layer forms a chemical bond with N, P, S, O element, namely has a heteroatom coordination structure, and can be catalyzed by cooperating with coated platinum, and the porous structure of the coating layer is favorable for oxygen to reach the surface of platinum particles and is favorable for mass transfer of reaction, so that the carbon-coated platinum oxygen reduction electrocatalyst prepared by the invention has very high electrocatalytic activity. According to the invention, the carbon-coated layer has a protection and inactivation effect on the coated platinum, so that various inactivation behaviors of the platinum are effectively relieved, and the obtained carbon-coated platinum oxygen reduction electrocatalyst has very good durability.
The technical scheme of the invention is as follows:
firstly, preparing a mixed dispersion liquid A containing carrier-loaded platinum ions; adding a carrier and a platinum precursor into a certain amount of solvent according to a certain proportion, and then uniformly mixing the carrier, the platinum precursor and the solvent;
the carrier comprises one or a combination of several of various carbon black materials, carbon aerogel materials, metal organic framework pyrolytic carbon materials, graphene aerogel, carbon nanotubes, carbon nanotube aerogel, carbon nanocages, fullerene, carbon quantum dots, titanium dioxide nanoparticles, titanium dioxide aerogel, cerium dioxide nanoparticles, cerium dioxide aerogel, tungsten carbide and thallium oxide; the carbon black material comprises the trade marks of XC-72R, EC-300J, EC-600JD and BP-2000;
the platinum precursor is a compound containing platinum ions and comprises chloroplatinic acid (H) 2 PtCl 4 ) And hydrate thereof, platinum acetylacetonate (C) 10 H 14 O 4 Pt), potassium chloroplatinate (K) 2 PtCl 6 ) Sodium chloroplatinate (Na) 2 PtCl 6 ) Platinum tetraamine dichloride (Pt (NH) 3 ) 4 Cl 2 ) Platinum tetraamine bicarbonate ((NH) 3 ) 4 PtC 2 H 2 O 6 ) One or a combination of more of the above;
the platinum precursor is characterized in that the mass of platinum element in the platinum precursor accounts for 1-60% of the total mass of the carrier and the platinum element according to a certain proportion; (platinum element mass = platinum precursor mass × (platinum atomic mass/platinum precursor relative molecular mass));
the mass ratio of the solvent to the carbon carrier is 1-30; the solvent is one or a combination of more of pure deionized water, ethanol, isopropanol, methanol, ethylene glycol, N-dimethylformamide and tetrahydrofuran;
the mixing is uniform, and can be one of ultrasonic dispersion mixing, mechanical stirring mixing and ball milling mixing, or the above steps can be carried out respectively;
secondly, preparing a metal ion-containing sol B; uniformly mixing a certain amount of inorganic metal salt, an organic matter and a solvent according to a certain proportion, and preparing sol B containing metal ions under certain conditions;
the certain amount of inorganic metal salt refers to that the percentage of the atomic mole number of the metal element in the weighed inorganic metal salt to the sum of the atomic mole number of the metal element and the atomic mole number of the platinum element in the platinum precursor is between 1 and 80 percent;
the inorganic metal salt is as follows: fe. One or more of chlorides, acetylacetone compounds, nitrate compounds, acetate compounds and sulfate compounds corresponding to Co, ni, mn, cu, pt, cr, zn, ti, zr, V, mo, ag, au, pt, pd, ru, Y and W elements; such as: manganese chloride tetrahydrate (MnCl) 2 ·4H 2 O), ferrous chloride tetrahydrate (FeCl) 2 ·4H 2 O), iron chloride hexahydrate (FeCl) 3 ·6H 2 O), nickel chloride tetrahydrate (NiCl) 2 ·4H 2 O), cobalt chloride tetrahydrate (CoCl) 2 ·4H 2 O) or a combination of several of O);
the organic matter at least comprises one element of N, P and S elements;
the organic matter is organic micromolecules which can generate a high molecular network structure through a polycondensation reaction under the action of metal salt, or micromolecules which can induce the metal salt to generate a gel network structure, or macromolecular compounds which can anchor metal ions to obtain metal ion doping, or one or a combination of a plurality of organic micromolecules which can be complexed with the metal ions; preferably one or a combination of more of aniline, pyrrole, thiophene, acrylonitrile, polystyrene, polyvinylpyrrolidone, melamine, polystyrene sulfonate, polyaniline, polypyrrole, phenanthroline, dopamine, polydopamine, dopamine hydrochloride, propylene oxide, epichlorohydrin, polythiophene, sodium alginate, chitosan, sucrose, glucose, maltose, citric acid, sodium citrate, tannic acid, phytic acid and semi-sulfanilic acid;
the solvent is one or a combination of more of deionized water, ethanol, isopropanol, methanol, ethylene glycol, N-dimethylformamide and tetrahydrofuran; the solvent has no concentration requirement;
the certain proportion means that the mol ratio of the organic matter to the inorganic metal salt is between 1 and 20, and the mol ratio of the solvent to the inorganic metal salt is between 1 and 30;
the certain conditions comprise heating and pH value adjustment, wherein the heating temperature range is 0.5-1 times of the boiling point of the selected solvent, and the pH value is 8-11;
step three, preparing a carbon-coated platinum precursor; uniformly mixing the mixed dispersion liquid A in the first step and the sol B in the second step to prepare a solution C containing a carbon-coated platinum precursor, wherein the solution C contains the carbon-coated platinum precursor and solvents in the dispersion liquid A and the sol B; drying to remove the liquid solvent in the solution C to obtain a carbon-coated platinum precursor;
the mixing is uniform, and can be one of ultrasonic dispersion mixing, mechanical stirring mixing and ball milling mixing, or the above steps can be carried out respectively in sequence, for example, ultrasonic dispersion is carried out firstly, and then ball milling mixing dispersion is carried out; a sol network coated carbon adsorption platinum ion structure is formed in a solution C obtained after the mixed dispersion liquid A and the sol B are mixed, namely the sol network containing metal ions in the sol B is coated or wound on a carbon-loaded platinum ion framework in the mixed dispersion liquid A;
the drying comprises the following steps: freeze drying, heating under normal pressure, and supercritical drying;
the carbon-coated platinum precursor retains a network-coated carbon-supported platinum ion structure formed in the mixed liquid C, and because the drying process only removes the solvent in the mixed liquid C, other chemical reactions which damage the structure do not occur;
fourthly, preparing a carbon-coated platinum-oxygen reduction electrocatalyst; heating the carbon-coated platinum precursor obtained in the third step to 700-1000 ℃ at a certain heating rate in a certain atmosphere, preserving the temperature for 0.5-4 h, and naturally cooling to room temperature under the protection of the atmosphere to obtain a powder mixture; washing the powder mixture by adopting a non-oxidative acid solution, removing unstable metal oxides and the like which are possibly generated in the heating process, filtering the mixture after acid washing to remove acid liquor, then heating and drying the mixture at normal pressure to remove liquid in the mixture, further heating the mixture to a certain temperature in a gas atmosphere, removing unstable substances generated in the washing process of the acid solution and remolding the crystal face of platinum to obtain the final carbon-coated platinum oxygen reduction electrocatalyst;
the carbon-coated platinum oxygen reduction electrocatalyst is obtained by converting carbon-loaded platinum ions coated by a sol network in a carbon-coated platinum precursor in a heating process, organic matters in the sol network are pyrolyzed to form a coated carbon layer, a part of metal ions in the sol network are ionized with platinum to synthesize platinum alloy nano particles, a part of metal ions are coordinated with one or more elements in N, P, S, O in the organic matters to generate a single-atom active site, and a path of the metal ions moving in the carbon network forms a porous structure in the coated carbon layer; in the pyrolysis process, the carbon-supported platinum ions are simultaneously converted into platinum nanoparticles or platinum alloy nanoparticles, and the sol network structure coating the carbon-supported platinum ions has a domain-limiting effect on platinum growth, so that the platinum nanoparticles or platinum alloy nanoparticles have small particle size and are intensively distributed at 2-5 nm;
the atmosphere is preferably one or a combination of more of ammonia, hydrogen, nitrogen and argon; the gas pressure of the certain atmosphere has no special requirements;
the gas atmosphere refers to one or a combination of more of hydrogen, ammonia, nitrogen, argon, carbon dioxide, water vapor, air and oxygen; preferably selecting one or a combination of more of ammonia gas, carbon dioxide, water vapor and air, which have corrosion effect on carbon, so as to be beneficial to thinning the coated carbon layer and leaving an etched pore structure on the surface of the carbon layer;
the certain temperature is 600-800 ℃/min.
The invention can achieve the following beneficial effects:
1. the preparation method disclosed by the invention is simple in process, raw materials are easy to obtain, the obtained catalyst material is low in cost, and the method can be expanded to large-scale industrial production;
2. the invention is based on the chemical principle of preparing carbon materials, and prepares a carbon-coated platinum-oxygen reduction electrocatalyst, wherein metal elements in the carbon-coated layer exist in a monatomic form; the carbon coating layer has a relatively open pore structure etched by fused salt and gas; the carbon-coated platinum oxygen reduction electrocatalyst can be cooperatively catalyzed with coated platinum, and the porous structure is favorable for mass transfer of reaction, so that the carbon-coated platinum oxygen reduction electrocatalyst prepared by the method has very high activity and durability;
3. based on a sol-gel chemical principle and a limited domain principle, a sol network is used for coating carbon-loaded platinum ions to serve as a precursor of carbon-coated platinum, and in the process of obtaining a carbon coating layer through pyrolysis, the sol network well relieves the agglomeration of high-temperature platinum nanoparticles to obtain carbon-coated platinum and platinum alloy nanoparticles with the particle sizes uniformly distributed between 2 nm and 5nm, and the activity of the carbon-coated platinum and platinum alloy nanoparticles is very high when the carbon-coated platinum and platinum alloy nanoparticles are used as a catalyst;
therefore, the method is suitable for large-scale industrial production, and the prepared carbon-coated platinum oxygen reduction electrocatalyst has low cost, high activity and good durability, meets the urgent requirements of the field of electrocatalysis on large-scale preparation of carbon-supported platinum oxygen reduction electrocatalysts with low cost, high activity and high durability, and particularly meets the urgent requirements of hydrogen fuel cells, metal-air fuel cells, methanol fuel cells and the like on oxygen reduction reaction electrocatalysts.
Drawings
FIG. 1 is a general flow diagram of a process for preparing a carbon-coated platinum catalyst according to the present invention;
FIG. 2 is a linear cyclic voltammetry characteristic curve of a carbon-coated platinum-iron alloy electrocatalyst prepared in example 1 of the present invention in a 0.1mol/L aqueous solution of perchloric acid; the abscissa is the collected voltage in the reaction process, the ordinate is the generated current density, and the activity of the catalyst can be calculated from the graph according to the electrochemical knowledge;
FIG. 3 is a transmission electron micrograph of a carbon-coated platinum-iron alloy prepared in example 1 of the present invention.
Detailed Description
In order to more clearly illustrate the present invention, the present invention will be described in detail below with reference to the following examples and the accompanying drawings. It is to be understood by persons skilled in the art that the following detailed description is illustrative and not restrictive, and is not to be taken as limiting the scope of the invention.
As shown in fig. 1, preparation example 1 using the present invention includes the following steps:
firstly, preparing a mixed dispersion liquid A containing carrier-loaded platinum ions; adding 5g of commercial carbon black EC-300J and 3g of chloroplatinic acid hexahydrate into 50g of deionized water, mechanically stirring by magnetons for 2 hours, ultrasonically dispersing and mixing for 30 minutes, and then transferring into a planetary ball mill for ball milling for 18 hours at the speed of 400 r/min;
secondly, preparing sol B containing metal ions; mixing 5g of ferric trichloride hexahydrate, 10g of epichlorohydrin, 5g of phenanthroline and 20g of ethanol, and stirring for 2 hours by using magnetons;
step three, preparing a carbon-coated platinum precursor; mixing the dispersion liquid A in the first step with the sol B in the second step, stirring for 2 hours by magnetons, carrying out ultrasonic treatment for 30 minutes, and then transferring the mixture into a planetary ball mill to carry out ball milling for 30 minutes at the speed of 400r/min to prepare a solution C containing a carbon-coated platinum precursor; removing the solvent from the freeze-dried solution C to obtain a carbon-coated platinum precursor;
step four, preparing carbon-coated platinum; heating the carbon-coated platinum precursor obtained in the third step to 900 ℃ at a heating rate of 2 ℃/min in a hydrogen atmosphere, preserving heat for 0.5h, and naturally cooling to room temperature under the protection of gas to obtain a powder mixture; washing the powder mixture with 2mol/L hydrochloric acid solution, removing unstable metal oxides possibly generated in the process, carrying out suction filtration to remove acid solution, heating and drying, further heating to 900 ℃ at the heating rate of 5 ℃/min in the ammonia atmosphere, keeping the temperature for 0.5h, and cooling to room temperature in the argon atmosphere to obtain the final carbon-coated platinum oxygen reduction electrocatalyst.
FIG. 2 is a linear cyclic voltammetry curve and a cyclic voltammetry curve of a carbon-coated platinum-oxygen reduction electrocatalyst prepared in example 1 of the present invention in a 0.1mol/L aqueous solution of perchloric acid; reaction with abscissa of CollectionThe voltage in the process and the ordinate are the generated current density, and according to the knowledge of electrochemistry, the catalyst activity of the carbon-coated platinum-iron alloy nano-particles is calculated to be about 800A/g Pt Is far higher than the activity of the current commercial platinum-on-carbon catalyst (about 100-200A/g) Pt )；
FIG. 3 is a transmission electron micrograph of an iron alloy in the carbon-coated platinum-oxygen reduction electrocatalyst prepared in example 1; the ruler in the figure is 5nm, the nanoparticles with darker colors in the figure are platinum nanoparticles or platinum alloy nanoparticles, the nanoparticles with lighter colors are carbon carriers and carbon coating layers, and the figure shows that the surfaces of the platinum nanoparticles or platinum iron alloy nanoparticles are provided with carbon coating layers with different structures and lighter colors, the thickness of the carbon coating layers is less than 1nm, and the sizes of the platinum nanoparticles or platinum alloy nanoparticles are smaller than the length of a scale and are between 1 and 5nm; examples 2 to 7 provide methods for preparing carbon-coated platinum oxygen reduction electrocatalysts, which have different mass fractions of platinum supported, and the same mass and type of carbon carrier as in example 1, and the specific mass of other raw materials can be converted from the stoichiometric ratio between the carbon carrier and the raw materials, and the other steps and parameters are the same as those in example 1; as can be seen from table 1, the activity of the final oxygen-reducing electrocatalyst increases and then decreases as the mass fraction of platinum increases; the reason is that with the increase of the mass fraction of the platinum, the proportion of the platinum-iron alloy is gradually increased, the activity of the catalyst is increased, and after the activity is increased to a certain amount, the platinum is easy to agglomerate and grow in the heat treatment process, but the activity is reduced; as can also be seen from Table 1, the catalysts with different platinum mass fractions have better durability, the retention rate of the mass activity after aging test after thirty thousand cycles is over 85 percent and is only reduced by less than 15 percent, while the mass activity of thirty thousand cycles is reduced by at least 30 percent in common commercial carbon-supported platinum;
table 1 raw material parameters and performance parameters table (durability means catalyst activity retention after thirty thousand cycles of aging,%)
Examples 8-12 provide methods for preparing carbon-coated platinum oxygen reduction electrocatalysts, which have different inorganic metal salt types and other steps and process parameters consistent with those of example 1, compared with example 1; as can be seen from table 2, the activity of the final oxygen reduction electrocatalyst is affected by the type of the added inorganic metal salt, which is because different platinum alloys are formed by adding different inorganic metal salts, and the intrinsic activities of different types of platinum alloys are different; it can also be seen from table 2 that the carbon-coated platinum prepared from different inorganic salts has better durability, the retention rate of the mass activity after aging test after thirty thousand cycles is over 85%, and is only reduced by less than 15%, while the mass activity of the general commercial carbon-supported platinum is reduced by at least 30%.
Table 2 raw material parameters and performance parameters table (durability means catalyst activity retention after thirty thousand cycles of aging,%)
| Examples | Inorganic metal salt species | Catalyst Activity (A/g) Pt ) | |
| 5 | FeCl 3 ·6H 2 O | 0.88 | 92％ |
| 8 | CoCl 2 ·4H 2 O | 0.84 | 96％ |
| 9 | FeCl 2 ·4H 2 O | 0.86 | 93％ |
| 10 | NiCl 2 ·4H 2 O | 0.92 | 88％ |
| 11 | MnCl 2 ·4H 2 O | 0.78 | 90％ |
| 12 | CuCl 2 ·4H 2 O | 0.96 | 86％ |
Examples 13 to 17 provide methods for preparing a carbon-coated platinum oxygen reduction electrocatalyst, in which, compared with example 1, ferric chloride hexahydrate is still used as an inorganic metal salt, but the content of ferric chloride hexahydrate added to raw materials corresponding to different examples is different, and is shown in the table that the atomic percentages of platinum element and iron element added to the raw materials are different, the mass and the type of a carbon carrier are the same as those in example 1, the specific mass of other raw materials can be converted from the stoichiometric ratio between the raw materials and the carbon carrier, and other steps and process parameters are the same as those in example 1; as can be seen from table 3, the activity of the final oxygen reduction electrocatalyst is affected by the content of added inorganic metal salt; the crystal structure of the final platinum-iron alloy is influenced by the quality of the added inorganic metal salt, when raw materials are added, iron atoms are more than platinum atoms, the alloy structure is more, and the ordered platinum-iron alloy has better activity and durability; when the iron atom is smaller than the platinum atom, the structure of the alloy particle is often disordered platinum-iron alloy with slightly lower activity and durability.
Table 3 raw material parameters and performance parameters table (durability means catalyst activity retention after thirty thousand cycles of aging,%)
In examples 18 to 22, compared with example 1, the inorganic metal salt is still ferric chloride hexahydrate, but the organic raw materials in different examples are different in addition ratio, the quality and type of the carbon carrier are the same as those in example 1, the specific quality of other raw materials can be obtained by converting the specific quality of the raw materials with the carbon carrier and the stoichiometric ratio of the raw materials, and other steps and process parameters are the same as those in example 1; as can be seen from table 4, the activity of the final oxygen reduction electrocatalyst is affected by the content of the added organic matter, and as the organic matter content increases, the catalyst mass activity tends to increase first and then decrease, and the catalyst durability tends to increase gradually; the reason is that the added amount of organic matters influences the thickness of the final carbon coating layer and the content of metal monoatomic atoms in the coating layer, the content of the metal monoatomic atoms is increased along with the increase of the amount of the organic matters, the activity of the catalyst is enhanced, the content of the organic matters is continuously increased, the thickness of the coated carbon layer is increased, mass transfer is gradually influenced, and the activity is slightly reduced; the durability will gradually increase as the thickness of the carbon coating layer in the catalyst increases.
Table 4 raw material parameters and performance parameters table (durability means catalyst activity retention after thirty thousand cycles of aging,%)
The main factors influencing the activity and durability of the catalyst are the platinum content, the types and the contents of inorganic metal salts and organic matters; the examples given in tables 1-4 demonstrate the effect of several of the above factors on oxygen reduction electrocatalyst performance.
Other technological parameters in the preparation process, the numerical values of which are in the range of the invention, have little influence on the structure of the finally prepared electrocatalyst and only influence other properties of the prepared electrocatalyst, such as density, mechanical strength and the like, which have no great relation with the electrocatalysis performance, so that the other technological parameters have little influence on the activity of the electrocatalyst and are not key technological parameters influencing the effect of the invention. The other parameters are preferably selected as in example 1.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention, and all modifications and equivalents of the present invention, which are made by the contents of the present specification and the accompanying drawings, or directly/indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (11)
1. A preparation method of a carbon-coated platinum oxygen reduction electrocatalyst is characterized by comprising the following steps:
firstly, preparing a mixed dispersion liquid A containing carrier-loaded platinum ions; adding a carrier and a platinum precursor into a certain amount of solvent according to a certain proportion, and then uniformly mixing the carrier, the platinum precursor and the solvent;
the carrier comprises one or a combination of several of various carbon black materials, carbon aerogel materials, metal organic framework pyrolytic carbon materials, graphene aerogel, carbon nanotubes, carbon nanotube aerogel, carbon nanocages, fullerene, carbon quantum dots, titanium dioxide nanoparticles, titanium dioxide aerogel, cerium dioxide nanoparticles, cerium dioxide aerogel, tungsten carbide and thallium oxide;
the platinum precursor is a compound containing platinum ions;
the platinum precursor comprises platinum element in a certain proportion, wherein the mass of the platinum element in the platinum precursor accounts for 1-60% of the total mass of the carrier and the platinum element, and the mass of the platinum element = mass x of the platinum precursor (platinum atomic mass/relative molecular mass of the platinum precursor);
the mass ratio of the solvent to the carbon carrier is 1-30;
secondly, preparing sol B containing metal ions by the following steps: uniformly mixing a certain amount of inorganic metal salt, an organic matter and a solvent according to a certain proportion, and preparing sol B containing metal ions under certain conditions;
the certain amount of the inorganic metal salt refers to that the atomic mole number of the metal element in the weighed inorganic metal salt accounts for 1 to 80 percent of the sum of the atomic mole number of the metal element and the atomic mole number of the platinum element in the platinum precursor;
the inorganic metal salt refers to: fe. One or more of chlorides, acetylacetone compounds, nitrate compounds, acetate compounds and sulfate compounds corresponding to Co, ni, mn, cu, pt, cr, zn, ti, zr, V, mo, ag, au, pt, pd, ru, Y and W elements;
the organic matter at least comprises one element of N, P and S elements;
the organic matter is organic micromolecules which can generate a high molecular network structure through a polycondensation reaction under the action of metal salt, or micromolecules which can induce the metal salt to generate a gel network structure, or macromolecular compounds which can anchor metal ions to obtain metal ion doping, or one or a combination of a plurality of organic micromolecules which can be complexed with the metal ions;
the solvent is one or a combination of more of deionized water, ethanol, isopropanol, methanol, ethylene glycol, N-dimethylformamide and tetrahydrofuran;
the certain proportion refers to that the mol ratio of the organic matter to the inorganic metal salt is between 1 and 20, and the mol ratio of the solvent to the inorganic metal salt is between 1 and 30;
the certain condition refers to heating and pH value adjustment;
step three, preparing a carbon-coated platinum precursor, which comprises the following steps: uniformly mixing the mixed dispersion liquid A in the first step and the sol B in the second step to prepare a solution C containing a carbon-coated platinum precursor, and drying to remove a liquid solvent in the solution C to obtain a carbon-coated platinum precursor;
a sol network coated carbon adsorption platinum ion structure is formed in a solution C obtained after the mixed dispersion liquid A and the sol B are mixed, namely the sol network containing metal ions in the sol B is coated or wound on a carbon-loaded platinum ion framework in the mixed dispersion liquid A;
the carbon-coated platinum precursor reserves a network-coated carbon-supported platinum ion structure formed in the mixed liquid C;
fourthly, preparing the carbon-coated platinum oxygen reduction electrocatalyst, wherein the method comprises the following steps: heating the carbon-coated platinum precursor obtained in the third step to 700-1000 ℃ at a certain heating rate in a certain atmosphere, preserving the temperature for 0.5-4 h, and naturally cooling to room temperature under the protection of the atmosphere to obtain a powder mixture; washing the powder mixture by adopting a non-oxidative acid solution, removing unstable metal oxides possibly generated in the heating process, filtering the mixture after acid washing to remove acid liquor, then heating and drying the mixture at normal pressure to remove liquid in the mixture, further heating the mixture to a certain temperature in the gas atmosphere, removing unstable substances generated in the washing process of the acid solution and remolding the crystal face of platinum to obtain the final carbon-coated platinum oxygen reduction electrocatalyst;
the carbon-coated platinum oxygen reduction electrocatalyst is obtained by converting carbon-loaded platinum ions coated by a sol network in a carbon-coated platinum precursor in a heating process, organic matters in the sol network are pyrolyzed to form a coated carbon layer, a part of metal ions in the sol network are ionized with platinum to synthesize platinum alloy nano particles, a part of metal ions are coordinated with one or more elements in N, P, S, O in the organic matters to generate a single-atom active site, and a path of the metal ions moving in the carbon network forms a porous structure in the coated carbon layer; in the pyrolysis process, the carbon-supported platinum ions are simultaneously converted into platinum nanoparticles or platinum alloy nanoparticles;
the gas atmosphere refers to one or a combination of more of hydrogen, ammonia, nitrogen, argon, carbon dioxide, water vapor, air and oxygen;
the certain temperature is 600-800 ℃/min.
2. The method of claim 1, wherein the carbon black material of the first step comprises XC-72R, EC-300J, EC-600JD or BP-2000.
3. The method of claim 1, wherein the platinum precursor comprises chloroplatinic acid (H) in the first step 2 PtCl 4 And hydrate thereof, platinum acetylacetonate i.e. C 10 H 14 O 4 Pt, potassium chloroplatinate i.e. K 2 PtCl 6 Sodium chloroplatinate, i.e. Na 2 PtCl 6 Platinum tetraamine dichloride i.e. Pt (NH) 3 ) 4 Cl 2 Tetraamine platinum bicarbonate, i.e. (NH) 3 ) 4 PtC 2 H 2 O 6 One or a combination of several of them.
4. The method of claim 1, wherein the solvent in the first step is one or more selected from the group consisting of pure deionized water, ethanol, isopropanol, methanol, ethylene glycol, N-dimethylformamide, and tetrahydrofuran.
5. The method of claim 1, wherein the mixing step in the first and second steps is one of ultrasonic dispersion mixing, mechanical stirring mixing, and ball milling mixing, or they are performed separately.
6. The method of claim 1, wherein the second step is carried out in the presence of an inorganic catalystThe metal salt refers to manganese chloride tetrahydrate, namely MnCl 2 ·4H 2 O, ferrous chloride tetrahydrate, good FeCl 2 ·4H 2 O, iron chloride hexahydrate FeCl 3 ·6H 2 O, nickel chloride tetrahydrate or NiCl 2 ·4H 2 O, cobalt chloride tetrahydrate i.e. CoCl 2 ·4H 2 O or a combination of several O.
7. The method according to claim 1, wherein the organic material in the second step is one or more selected from aniline, pyrrole, thiophene, acrylonitrile, polystyrene, polyvinylpyrrolidone, melamine, polystyrene sulfonate, polyaniline, polypyrrole, phenanthroline, dopamine, polydopamine, dopamine hydrochloride, propylene oxide, epichlorohydrin, polythiophene, sodium alginate, chitosan, sucrose, glucose, maltose, citric acid, sodium citrate, tannic acid, phytic acid, and cysteine.
8. The method of claim 1, wherein the heating temperature during the second step is in the range of 0.5-1 times the boiling point of the selected solvent, and the pH is adjusted to a pH of 8-11.
9. The method of claim 1, wherein the drying in the third step is any one of freeze-drying, atmospheric pressure heat-drying and supercritical drying.
10. The method according to claim 1, wherein the platinum nanoparticles or platinum alloy nanoparticles of the fourth step have a particle size of 2-5 nm.
11. The method according to claim 1, wherein the atmosphere in the fourth step is one or a combination of ammonia, hydrogen, nitrogen and argon; the gas atmosphere refers to one or a combination of more of ammonia gas, carbon dioxide, water vapor and air.
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