阅读说明：本技术 一种碳基非贵金属氧还原催化剂的制备方法及应用 (Preparation method and application of carbon-based non-noble metal oxygen reduction catalyst ) 是由 肖作旭 陈艳丽 游国强 于 2019-09-29 设计创作，主要内容包括：本发明属于能源材料领域,具体涉及一种碳基非贵金属氧还原催化剂及其制备方法,还涉及所述催化剂在燃料电池阴极氧还原反应中的电催化应用。采用阴离子掺杂的方法制备了亚铁氰根掺杂聚吡咯,并且在热解过程中加入升华硫,进一步引入杂原子硫,制备硫、氮共掺杂碳基非贵金属氧还原催化剂。本发明的氧还原催化剂表现出高效的氧还原电化学性能及稳定性,优选的氧还原催化剂其氧还原电化学反应的半波电位为(0.89V vs.RHE),优于商业铂碳(0.84V vs.RHE),其电化学稳定性大大优于商业铂碳；组装成锌空气电池,其最大输出功率为94mW/cm<Sup>2</Sup>,优于20wt％商业铂碳(最大输出功率78mW/cm<Sup>2</Sup>)。(The invention belongs to the field of energy materials, and particularly relates to a carbon-based non-noble metal oxygen reduction catalyst and a preparation method thereof, and further relates to an electrocatalysis application of the catalyst in a cathode oxygen reduction reaction of a fuel cell. The method is characterized in that the polypyrrole doped with ferrocyanide is prepared by adopting an anion doping method, sublimed sulfur is added in the pyrolysis process, heteroatom sulfur is further introduced, and the sulfur and nitrogen co-doped carbon-based non-noble metal oxygen reduction catalyst is prepared. The oxygen reduction catalyst of the invention shows high-efficiency oxygen reduction electrochemical performance and stability, the half-wave potential of the oxygen reduction electrochemical reaction of the preferable oxygen reduction catalyst is (0.89V vs. RHE), which is superior to commercial platinum carbon (0.84V vs. RHE), and the electrochemical stability of the preferable oxygen reduction catalyst is greatly superior to commercial platinum carbon; assembled into a zinc-air battery with the maximum output power of 94mW/cm 2 Is better than 20wt% commercial platinum carbon (maximum output power 78 mW/cm) 2 )。)

1. A preparation method and application of a carbon-based non-noble metal oxygen reduction catalyst are characterized in that the catalyst is prepared by firstly preparing ferrocyanide doped polypyrrole by adopting an anion doping method, and then adding sublimed sulfur to the mixture to perform pyrolysis under the protection of inert gas;

the preparation method of the oxygen reduction catalyst is characterized by comprising the following specific steps of:

(1) preparation of sodium ferrocyanide-doped polypyrrole: adding 0-0.024mol (0-11.626g) of sodium ferrocyanide decahydrate, 0.016mol (3.648g) of ammonium persulfate and 200mL of distilled water into a 500mL three-neck flask under the protection of nitrogen, maintaining the system temperature at 0 ℃ and a fixed stirring speed in a cold machine to dissolve for 10min, dissolving 0.012mol (840 mu L) of pyrrole in 50mL of absolute ethyl alcohol, transferring into a separating funnel, slowly dripping into the three-neck flask, continuously stirring for 6h to obtain a black product, carrying out suction filtration, washing with distilled water for multiple times in the process, and drying in a vacuum drying box at 60 ℃ for 24h to obtain the sodium ferrocyanide doped polypyrrole;

(2) preparation of carbon-based oxygen reduction catalyst: taking 100mg of sodium ferrocyanide doped polypyrrole and 0-500mg of sublimed sulfur, grinding and mixing the mixture in a mortar by using a proper amount of absolute ethyl alcohol as a wetting agent until the mixture is uniform, then placing the obtained product in a clean porcelain boat, placing the porcelain boat in a high-temperature tube furnace, under the protection of nitrogen, firstly raising the temperature to 800-1000 ℃ by a program of 5 ℃/min, maintaining the temperature for 2 hours, and then lowering the temperature to 25 ℃ by a program of 10 ℃/min to obtain the doped carbon material.

2. The carbon-based non-noble metal oxygen reduction catalyst as recited in claim 1, wherein the molar weight of doped sodium ferrocyanide is 0-1.5 times of the molar weight of pyrrole monomer, the mass of doped sulfur is 0-5 times of the mass of pyrrole, and the pyrolysis temperature is 800-.

3. The carbon-based non-noble metal oxygen reduction catalyst according to claim 1, wherein the catalyst is applied to an air electrode catalyst of a hydrogen-oxygen fuel cell, a zinc-air fuel cell, a magnesium-air fuel cell, or an aluminum-air fuel cell.

Technical Field

The invention belongs to the field of energy materials, and particularly relates to a carbon-based non-noble metal oxygen reduction catalyst and a preparation method thereof, and further relates to an electrocatalysis application of the catalyst in a cathode oxygen reduction reaction of a fuel cell.

Background

With the rapid consumption of traditional fossil fuels, it becomes more urgent to explore clean and renewable energy technologies to solve the problems of energy shortage and environmental pollution. In all energy storage and conversion systemsAmong them, the fuel cell is called "green energy for the 21 st century" because of its advantages of high energy density, light weight, abundant material sources, no pollution, and the like. The anode of the fuel cell mainly generates oxidation reaction (H) of hydrogen gas₂→2H⁺+2e^－HOR), the reaction is relatively simple and a fast kinetic process; the cathode mainly generates the reduction reaction of oxygen (1/2O)₂+2H⁺→H₂O, ORR), generally need to be carried out at a higher overpotential, and its slow kinetics severely limit the energy conversion efficiency of the fuel cell. Platinum (Pt) catalysts with good molecular adsorption and dissociation characteristics are currently the most desirable and currently the only commercially available oxygen reduction catalyst material. However, since platinum metal is expensive, it is used in a large amount in a fuel cell (the amount of Pt supported on the cathode side is generally 0.4 mg. cm)^－2) So that the catalyst cost accounts for more than about 50% of the total cell cost. The reliance of fuel cells on platinum-based catalysts is a bottleneck that prevents their large-scale commercial application. In addition, the Pt-based oxygen reduction catalyst has problems of poor stability and being easily poisoned by trace amount of carbon monoxide that may be carried in hydrogen gas. Therefore, the oxygen reduction reaction catalyst with high development efficiency, good stability and low cost replaces a platinum-based catalyst, is a research hotspot in the field and also has important practical application value.

Currently, research on non-platinum based oxygen reduction catalysts has focused primarily on transition metal oxides, transition metal-containing nitrogen-doped carbon materials, and fully non-metallic heteroatom-doped carbon materials. The catalyst has the characteristics of rich raw material sources, low price, methanol permeation resistance and the like, can reach the activity equivalent to that of Pt under the acidic or alkaline condition, and is considered to have the possibility of replacing noble metal Pt as an oxygen reduction catalyst. Of these, pyrolytic Fe/N-C as a non-noble metal ORR catalyst has shown great application potential in recent years and is currently the most promising oxygen reduction catalyst to replace Pt. The synthesis method of the Fe/N-C catalyst has various types, for example, a macrocyclic iron compound and an organic metal framework complex are directly used for pyrolysis, the synthesis efficiency is high, the structure is stable, and the control of the content of effective iron is more rigid because the Fe/N coordination structure and the proportion of a precursor of the catalyst are fixed. The method can also be used for one-pot pyrolysis of small molecular iron compounds and nitrogen-containing compounds, the precursor material source is wide, the structural design is flexible and various, the effective iron load can be improved, but the experimental condition variables are numerous, and the multi-factor process regulation and control is complex and time-consuming.

Disclosure of Invention

Aiming at the defects of the prior art and the requirements of research and application in the field, the invention provides a preparation method and application of a Fe/N-C catalyst which is low in price, simple in preparation process and high in activity and stability.

The preparation method of the oxygen reduction catalyst comprises the following step of preparing polypyrrole as a catalyst precursor by adopting an anion doping method. According to a cationic free radical mechanism of pyrrole polymerization, a polypyrrole chain segment contains a large amount of positive charges, iron-containing anion ferrocyanide is doped into the polypyrrole chain segment through electrostatic action, active sites can be effectively prevented from being aggregated in a pyrolysis process, and the active sites inside can be protected by an externally coated carbon material. And further introducing heteroatom S in a mode of adding sublimed sulfur in the pyrolysis process to prepare the sulfur and nitrogen co-doped carbon-based non-noble metal oxygen reduction catalyst. The catalyst has high-efficiency oxygen reduction catalytic performance, and can be applied to air electrode catalysts of hydrogen-oxygen fuel cells, zinc-air fuel cells, magnesium-air fuel cells and aluminum-air fuel cells.

A preparation method of a carbon-based non-noble metal oxygen reduction catalyst comprises the following steps:

step 1: preparation of sodium ferrocyanide-doped polypyrrole: adding 0-0.024mol (0-11.626g) of sodium ferrocyanide decahydrate, 0.016mol (3.648g) of ammonium persulfate and 200mL of distilled water into a 500mL three-neck flask under the protection of nitrogen, maintaining the system temperature at 0 ℃ and a fixed stirring speed in a cold machine for dissolving for 10min, dissolving 0.012mol (840 mu L) of pyrrole in 50mL of absolute ethyl alcohol, transferring into a separating funnel, slowly dripping into the three-neck flask, continuously stirring for 6h to obtain a black product, carrying out suction filtration, washing with distilled water for multiple times in the process, and drying in a vacuum drying oven at 60 ℃ for 24h to obtain the sodium ferrocyanide doped polypyrrole.

Step 2: preparation of carbon-based oxygen reduction catalyst: 100mg of sodium ferrocyanide doped polypyrrole and 0-500mg of sublimed sulfur are taken, and a proper amount of absolute ethyl alcohol is used as a wetting agent to be ground and mixed in a mortar until the mixture is uniform. And then placing the obtained product in a clean porcelain boat, placing the porcelain boat in a high-temperature tube furnace, under the protection of nitrogen, firstly raising the temperature to 800-1000 ℃ by a program of 5 ℃/min, maintaining for 2h, and then lowering the temperature to 25 ℃ by a program of 10 ℃/min to obtain the doped carbon material.

The invention discloses application of a carbon-based non-noble metal oxygen reduction catalyst, and the oxygen reduction catalyst is applied to an air electrode catalyst of a hydrogen-oxygen fuel cell, a zinc-air fuel cell, a magnesium-air fuel cell or an aluminum-air fuel cell.

The preparation method of the air electrode comprises the following steps: ethanol and 5% Nafion solution are mixed according to the volume ratio (10-25): 1 obtaining a mixed solution, ultrasonically dispersing a carbon-based composite assembly oxygen reduction catalyst into the mixed solution, spraying the mixture on a carbon paper or carbon cloth electrode, and drying to obtain an air electrode, wherein the loading capacity of the catalyst is 1mg/cm²。

The invention has the beneficial effects that: (1) polypyrrole doped with ferrous cyanide anions is used as a precursor of the carbon-based oxygen reduction catalyst for the first time, and sulfur doping is carried out on the polypyrrole by adding sublimed sulfur in the pyrolysis process to obtain the oxygen reduction catalyst with a microporous and mesoporous combined hierarchical pore structure; the special assembly structure realizes the uniform dispersion and stable loading of the catalytic active sites, and is very beneficial to the diffusion and rapid transportation of oxygen, thereby accelerating the dynamic process of the oxygen reduction catalytic reaction. (2) The oxygen reduction catalyst of the invention shows high-efficiency oxygen reduction electrochemical performance and stability, the half-wave potential of the oxygen reduction electrochemical reaction of the preferable oxygen reduction catalyst is (0.89V vs. RHE), which is superior to commercial platinum carbon (0.84V), and the electrochemical stability of the preferable oxygen reduction catalyst is greatly superior to the commercial platinum carbon; assembled into a zinc-air battery with the maximum output power of 94mW/cm²Better than 20 wt% commercial platinum carbon (maximum output power 78 mW/cm)²)。

Drawings

The invention is further illustrated with reference to the following figures and examples.

FIG. 1 is a scanning electron micrograph of polypyrrole prepared in example 1;

FIG. 2 is a SEM photograph of the C-based oxygen reduction catalyst prepared in example 2;

FIG. 3 is a cyclic voltammogram of the carboxy reduction catalyst prepared in example 3;

FIG. 4 is a linear scan plot of the carboxy reduction catalyst prepared in example 3;

FIG. 5 is a linear scan plot of the carbon-based oxygen reduction catalyst prepared in example 3 at different rotational speeds;

FIG. 6 is a current-time curve of the carboxy reduction catalyst prepared in example 3;

fig. 7 is an open circuit voltage curve of the zinc-air fuel cell made in example 4;

fig. 8 is a polarization curve of the zinc-air fuel cell made in example 3;

Detailed Description