A palladium-carbon catalyst based on anaerobic reduction of metal palladium by microorganisms and a preparation method and application thereof

Abstract

The application discloses a palladium-carbon catalyst obtained based on microbial anaerobic reduction of metal palladium, and a preparation method and application thereof. On the basis of anaerobic reduction of metal palladium by Shewanella, an electron donor sodium pyruvate and an electron shuttle anthraquinone-2,6-disulfonic acid (AQDS) are added, and the system is placed in an anaerobic incubator to discharge oxygen and then placed in a shaking bed for incubation. After the incubation is completed, a palladium solution discharged of oxygen is added, and the above reaction system is continuously placed in the shaking bed for reaction in the dark. After reduction, the sample is collected by centrifugation and dried, and then the sample is placed in a tube furnace for carbonization, so that the catalyst sample is obtained. The method greatly improves the reduction rate of the palladium source, and the catalyst prepared by the method exhibits excellent electrochemical results and can be applied to fuel cells.

Description

Technical Field

[0001] This invention relates to an electrochemical catalytic material, particularly to a palladium-carbon catalyst obtained by anaerobic reduction of metallic palladium by microorganisms, and also to its preparation method and application, belonging to the field of fuel cell technology. Background Technology

[0002] With the continuous development of industry, the availability of fossil fuels is dwindling, making the development of new, efficient, widely applicable, and environmentally friendly power generation devices an urgent priority. Proton exchange membrane fuel cells (PEMFCs) are, in principle, equivalent to the "reverse" process of water electrolysis. Their reactants are H2 and O2, and the reaction product is H2O. As a green power source that can theoretically replace internal combustion engines, PEMFCs can operate without relying on carbon-containing fossil fuels, thus making their development and application significant. Furthermore, PEMFCs possess advantages such as high conversion efficiency, low noise, low operating temperature, fast start-up, and convenient maintenance, and are considered one of the most promising next-generation energy devices. However, the high cost of catalysts, complex bipolar plate processes, and high manufacturing costs of the diffusion layer have hindered the commercialization and practical application of PEMFCs.

[0003] The membrane electrode assembly (MEA) is a key material in PEMFCs, determining the battery's performance and lifespan. According to a cost analysis report on fuel cells from the U.S. Department of Energy, catalyst costs account for 41% of the total stack cost, and this high cost significantly hinders the mass production and application of proton exchange membrane fuel cells. Platinum (Pt) and palladium (Pd) are currently common and ideal catalyst materials, but their global reserves are limited. Therefore, developing low-cost, highly active, and highly stable catalysts is an urgent problem to be solved in proton exchange membrane fuel cells.

[0004] Among the existing methods for preparing fuel cell catalysts, microbial synthesis of metal nanocatalysts has unparalleled advantages over physical and chemical methods, mainly in the following aspects: (1) Microorganisms grow and reproduce rapidly, have strong environmental adaptability, and diverse metabolic types. (2) Their synthesis conditions are mild and can be carried out at room temperature and neutral pH, making the whole process safe and economical. (3) Because microorganisms contain rich biological components, such as proteins, lipids, and polysaccharides, they have reducing power and often endow the synthesized nanomaterials with unique biological properties, such as better biocompatibility and stability. (4) Microorganisms can biomodify the surface of materials to obtain better biocompatibility, dispersibility, and stability. (5) Microorganisms can synthesize nanomaterials with specific shapes and morphologies (such as spheres, hexagons, triangles, rods, planes, dendrites, decahedrons, icosahedrons, and some irregular shapes) in a controllable and programmable manner. However, the current process of synthesizing metal nanomaterials using microorganisms requires further research on conditions, including microbial characteristics and process conditions, to ensure that microorganisms can achieve the best results. Shewanella, widely distributed in freshwater, marine, and sediment environments, possesses an excellent ability to deposit metal nanoparticles and is a typical dissimilar metal-reducing bacterium. Shewanella possesses a complex, multi-branched electron transport system that promotes reduction by various terminal electron acceptors. This system includes endomembrane-localized dehydrogenases, methaqualone, and various cytochromes, and exhibits strong respiration capabilities. Its versatility in reducing metals extends beyond Fe(III) and Mn(IV) to include U(VI), Cr(VI), Np(V), Tc(VII), Pu(IV), V(V), Se(IV), Te(IV), Au(III), Ag(I), Pd(II), and Cu(II). Electron donors and electron transport pathways are generally considered the two main factors affecting respiration efficiency in microbial anaerobic metabolism and electron transport. Although some regulatory mechanisms have been elucidated, existing biosynthetic methods for metal nanomaterials still suffer from low metal reduction rates and face significant implementation challenges, making them unsuitable for large-scale production. Summary of the Invention

[0005] To address the technical problems such as insufficient metal reduction in existing biological methods for synthesizing metal nanomaterials, the first objective of this invention is to provide a method for preparing palladium-carbon catalysts based on the anaerobic reduction of palladium by microorganisms. This method has a high metal reduction rate, is simple to operate, uses readily available raw materials, and has low production and time costs, which is conducive to large-scale production.

[0006] A method for obtaining palladium-on-carbon catalysts based on microbial anaerobic reduction of metallic palladium includes the following steps:

[0007] 1) Add the electron shuttle to a mixed solution containing an electron donor, culture medium, and microorganisms;

[0008] 2) Incubate the mixed solution after removing oxygen;

[0009] 3) After incubation, add an oxygen-removed palladium solution for reduction;

[0010] 4) After reduction, the collected material is dried and carbonized sequentially to obtain the final product.

[0011] This invention utilizes small-molecule electron shuttles to enhance extracellular electron transport in Shewanella. It is generally believed that under anaerobic conditions, Shewanella first oxidizes organic electron donors to formic acid. Formic acid is further oxidized by formic acid dehydrogenase (FAD) to produce CO2 and electrons. The electrons are then transported extracellularly via hydrogenase or the Mtr pathway. Electrons transported extracellularly can directly contact electron acceptors for reduction, or they can be transferred over longer distances via "nanowires" and electron mediators. However, since palladium adsorption and reduction in Shewanella typically occur in solution, it is difficult to form a "nanowire" electron transport network under these conditions. Therefore, small-molecule electron shuttles may be the most effective way to enhance extracellular electron transport in Shewanella. Based on this, the technical solution of this invention first screened the optimal electron donor from several common organic electron donors (sodium lactate, sodium pyruvate, and sodium formate) under anaerobic conditions in Shewanella, and then selected three common electron transporters (humic acid, anthrone-2,6-disulfonic acid (AQDS), and riboflavin) and explored their effects on palladium reduction rate. Finally, the optimal electron transporter and concentration, as well as the optimal bacterial concentration OD value for effective function, were determined. Under optimal conditions, the palladium source was reduced, and the bacterial cells were collected and carbonized. Nano-sized palladium was generated in situ on the surface of the bacterial cells, achieving stable and dispersed loading with more uniform and smaller particle size, thus enabling the overall catalytic material to exhibit high catalytic activity.

[0012] The electron shuttle in step 1) comprises at least one of anthrone-2,6-disulfonic acid, humic acid and riboflavin, preferably anthrone-2,6-disulfonic acid; the electron donor comprises at least one of sodium pyruvate, sodium lactate and formic acid, preferably sodium pyruvate.

[0013] In step 1), the concentration of the electron donor in the mixed solution containing the electron donor, culture medium, and microorganisms is 15–25 mmol / L, and the volume ratio of the culture medium to the electron donor solution and microbial solution is 30:0.405:0.25–30:0.405:0.35. The content of microorganisms in the total system is [OD value missing]. 600 =0.55~0.65; the concentration of the electron shuttle in the total system solution is 0.05~0.15mmol / L.

[0014] Step 1) The volume ratio of the electron shuttle solution to the mixed solution containing the electron donor, culture medium and microorganisms is 0.0010:1 to 0.0009:1.

[0015] Step 1) The culture medium contains 0.2–0.25 g / L potassium dihydrogen phosphate, 0.2–0.25 g / L dipotassium hydrogen phosphate, 0.02–0.03 g / L magnesium sulfate heptahydrate, 0.25–0.3 g / L ammonium sulfate, 0.45–0.5 g / L sodium chloride, and 4.7–4.8 g / L sodium sulfate. 4-Hydroxyethylpiperazine ethanesulfonic acid, 1.4–1.6 g / L aminotriacetic acid, 2.9–3.1 g / L magnesium sulfate, 0.7–0.8 g / L anhydrous calcium chloride, 0.9–1.1 g / L sodium chloride, 0.4–0.6 g / L manganese sulfate, 0.16–0.2 g / L zinc sulfate heptahydrate, 0.05–0.15 g / L ferrous sulfate heptahydrate, 0.15–0.2 g / L cobalt sulfate heptahydrate, 0.02–0.03 g / L nickel chloride hexahydrate, 0.01–0.03 g / L potassium aluminum sulfate dodecahydrate, 0.005–0.015 g / L copper sulfate pentahydrate.

[0016] As a preferred embodiment, the concentration of sodium pyruvate in the mixed solution containing sodium pyruvate, mineral salt culture medium, and microorganisms is 15–25 mmol / L, and the content of microorganisms is [missing information - likely a percentage] of the total OD [missing information - likely a percentage]. 600 =0.55~0.65. Sodium pyruvate is an electron donor; a suitable electron donor ensures the growth of Shewanella and enhances its metal reduction rate. Mineral salt culture medium provides the necessary nutrients and environment for Shewanella's anaerobic metal reduction. If the proportion of mineral salt culture medium to microorganisms is too low, the microorganisms may not be able to fully utilize their metal reduction ability due to excessive density; conversely, if the proportion of mineral salt culture medium to microorganisms is too high, the microorganisms are susceptible to metal toxicity, also failing to fully utilize their metal reduction ability or even becoming inactive.

[0017] As a preferred embodiment, the concentration of the anthrone-2,6-disulfonic acid (AQDS) solution in the total system is 0.05–0.15 mmol / L. The anthrone-2,6-disulfonic acid (AQDS) solution primarily utilizes AQDS as an electron shuttle to accelerate electron transfer between the donor and acceptor, thereby increasing the reduction rate and enhancing the reduction effect.

[0018] As a preferred embodiment, the volume ratio of the anthrone-2,6-disulfonic acid (AQDS) solution to the mixed solution containing sodium pyruvate, mineral salt culture medium, and microorganisms is 0.0010:1 to 0.0009:1. Even trace amounts of AQDS solution can promote metal reduction. Excessively high AQDS concentrations do not significantly promote metal reduction and increase production costs. Insufficient AQDS concentrations prevent it from fully exerting its effect. The microorganism in step 1) is Shewanella.

[0019] As a preferred embodiment, the microorganism is *Shewanella*. More specifically, the microorganism is *Shewanella onedensis* MR-1 (purchased from the American Type Culture Collection, trade number ATCC 700550). This preferred *Shewanella* strain exhibits good adsorption of palladium sources, contains abundant hydrogenase, demonstrates high tolerance to precious metals, and is particularly effective against Pd. 2+ Shewanella bacteria possesses excellent adsorption capacity and, under certain conditions, also exhibits a certain reducing ability towards metal ions. Therefore, it is highly effective to use Shewanella bacteria to deposit metal nanoparticles. This study selected Shewanella bacteria for the deposition of Pd... 2+ The adsorption characteristics and subsequent carbonization process can synthesize carbonized bacterial-supported noble metal catalysts with good stability and high catalytic activity. Furthermore, the carbon material obtained after carbonization exhibits nitrogen doping, which not only improves the loading stability of palladium but also synergistically enhances its catalytic activity. Shewanella bacteria can effectively adsorb palladium ions, and carbonization allows for the uniform and stable loading of palladium ions within the carbonized Shewanella bacteria.

[0020] The incubation conditions described in step 2) are: 160-200 rpm shaker, 28-30℃ incubation for 1.5-2.5 h.

[0021] As a preferred embodiment, the incubation conditions are: 160–200 rpm shaker, 28–30°C, for 1.5–2.5 h. Incubation with an appropriate concentration of sodium pyruvate for 2 h indicates that Shewanella exhibits multi-level regulation of pyruvate perception and response. This rapid reduction of Pd... 2+ This method protects the bacteria themselves from Pd. 2+ The toxicity of the nanoparticles is greatly reduced, which also greatly enhances the synthesis of palladium nanoparticles, making them more valuable for future practical applications.

[0022] The palladium source in step 3) is sodium tetrachloropalladium; the palladium source is added in the form of a solution with a final concentration of 1.4 to 1.6 mmol / L in the total system.

[0023] As a preferred embodiment, the reduction conditions are: 180 rpm shaker, 30°C, and reaction in the dark for 6 hours. The 6-hour dark-protected reaction is to allow Pd to... 2+ This experiment demonstrates that when the total system contains 0.1 mM electron transporter AQDS solution and the Shewanella bacteria concentration is maintained at OD, the reduction process is complete. 600 When the concentration is 0.6, a reduction rate of 91.53% can be achieved under a total system palladium concentration of 1.5M.

[0024] Step 4) After reduction, centrifuge and collect the samples for freeze drying.

[0025] As a preferred embodiment, the centrifugation collection conditions are: 8000 rpm, 8 min. The centrifugation speed and time are crucial to the quality and purity of the collected material. Excessive centrifugation speed and time can lead to impurity precipitation; insufficient centrifugation speed and time will result in inadequate material collection.

[0026] The carbonization process described in step 4) is as follows: under a protective atmosphere, the temperature is increased to 750-850℃ at a rate of 3-4℃ / min, and held for 2.5-3.5 hours.

[0027] As a preferred embodiment, the carbonization process is as follows: the carbonization and reduction roasting process involves first heating to 750–850°C at a rate of 3–4°C / min under a protective atmosphere, and holding at this temperature for 2.5–3.5 hours. The reducing atmosphere is such as hydrogen. At the preferred carbonization temperature, complete carbonization of the organic matter and decomposition of the palladium source can be achieved. If the temperature is too high, the porous structure of the carbonized material is easily damaged, and metal agglomeration is likely to occur. If the temperature is too low, carbonization and decomposition of the palladium source will be incomplete.

[0028] A second objective of this invention is to provide a palladium-on-carbon catalyst prepared by the above method. This catalyst exhibits small particle size, good stability, high palladium nanoparticle loading, and uniform distribution, thus demonstrating high catalytic activity.

[0029] The palladium-on-carbon catalyst of this invention, obtained by anaerobic reduction of palladium by microorganisms, uses a porous carbon material as a support, with nano-palladium particles uniformly dispersed and loaded on the surface of the support. The average particle size of the nano-palladium particles is approximately 1.43 nm, and the particle distribution is uniform.

[0030] A third objective of this invention is to provide the application of the aforementioned palladium-on-carbon catalyst in the preparation of fuel cell catalysts.

[0031] Compared with the prior art, the technical solution of the present invention has the following advantages and beneficial effects:

[0032] The present invention incorporates a trace amount of electron shuttle in the preparation process of palladium-carbon catalyst based on microbial anaerobic reduction of palladium. This not only increases the reduction amount of palladium source and reduces production costs, but also accelerates the extracellular electron transfer rate of Shewanella bacteria, greatly improving the reduction rate of palladium source, reducing time costs. Furthermore, the high reduction rate is beneficial to improving the dispersibility of palladium source, avoiding agglomeration, and facilitating the subsequent acquisition of nano-palladium particles.

[0033] The present invention utilizes a technique of incubating with pyruvate for 2 hours before adding the palladium source in the preparation process of palladium-carbon catalyst based on microbial anaerobic reduction of palladium. This technique is based on the sensing and multi-level regulation of pyruvate by Shewanella bacteria, which can greatly improve the reduction rate of the subsequent palladium source and protect the bacteria themselves from Pd. 2+The toxicity of the nanoparticles is reduced, which greatly enhances the synthesis of palladium nanoparticles and makes them more suitable for practical applications.

[0034] The present invention utilizes the optimal reduction process obtained through exploration in the preparation of palladium-carbon catalyst based on the anaerobic reduction of metallic palladium by microorganisms. The sample is collected and carbonized to form highly dispersed and uniformly sized nano-palladium, which is then loaded onto the surface of the support, resulting in high catalytic activity of the overall catalytic material.

[0035] The method for preparing palladium-carbon catalyst based on microbial anaerobic reduction of metallic palladium is simple to operate, uses readily available raw materials, and has low time and production costs, which is conducive to large-scale production.

[0036] The palladium-on-carbon catalyst obtained by the anaerobic reduction of palladium by microorganisms has a large specific surface area, small palladium nanoparticle size, narrow distribution (average particle size of about 1.43 nanometers), and uniform and stable loading in the support, thus improving the overall performance of the catalytic material. Attached Figure Description

[0037] Figure 1 This is the standard curve of Pd(II) in Example 1.

[0038] Figure 2 Figure 1 shows the transmission electron microscope (TEM) images and particle size distribution of the samples in Example 1. Figure 1a is the TEM image of the sample with a scale bar of 200 nm, while Figure 1b is the TEM image of the sample with a scale bar of 20 nm, and Figure 1c is the particle size distribution diagram.

[0039] Figure 3 The electrochemical test results of the palladium-on-carbon catalyst obtained by anaerobic reduction of palladium by microorganisms are shown in Figure a. Figure a is the CV curve of the palladium-on-carbon catalyst, Figure b is the LSV curve of the palladium-on-carbon catalyst, and Figure c is the KL plot of the ORR data of the palladium-on-carbon catalyst at different potentials.

[0040] Figure 4 The figures show comparisons of different electron donors and incubated and unincubated samples in Example 2. Figures a and b show the phenomena before and after palladium addition in the unincubated group of sodium lactate, respectively; while figures e and f show the phenomena before and after palladium addition in the unincubated group of sodium pyruvate, respectively; figures i and j show the phenomena before and after palladium addition in the unincubated group of sodium formate, respectively; figures c and d show the phenomena before and after palladium addition in the incubated group of sodium lactate, respectively; while figures g and h show the phenomena before and after palladium addition in the incubated group of sodium pyruvate, respectively; and figures k and l show the phenomena before and after palladium addition in the incubated group of sodium formate, respectively.

[0041] Figure 5 The reduction rate is given by different Pd(Ⅱ) concentrations.

[0042] Figure 6 The reduction rate of Pd(II) under different electron shuttles.

[0043] Figure 7 The reduction rate of Pd(II) is given by different concentrations of AQDS.

[0044] Figure 8 Pd(II) reduction rate under different concentrations of Shewanella oneidensis MR-1 bacteria. Detailed Implementation

[0045] The following specific embodiments are intended to further illustrate the content of the present invention, rather than to limit the scope of protection of the claims.

[0046] Unless otherwise specified, all chemical raw materials used in the following examples are conventional commercially available products. Calcium carbonate powder is analytical grade calcium carbonate from Sinopharm Chemical Reagent Co., Ltd., product model 10005760.

[0047] Example 1

[0048] 1) Pd(II) Standard Curve Construction: Dilute an appropriate amount of sodium tetrachloropalladium stock solution to prepare palladium test solutions with concentration gradients of 0.02 mM, 0.04 mM, 0.06 mM, 0.08 mM, 0.10 mM, 0.12 mM, 0.14 mM, 0.16 mM, 0.18 mM, and 0.20 mM. Take 300 μL of palladium test solution, then add 400 μL of acetate buffer, 80 μL of 4-(2-thiazolylazo)resorcinol solution, 120 μL of hexadecylpyridine bromide solution, and 100 μL of deionized water to prepare the detection system. After thorough mixing, react in the dark for 10 min, and measure the OD value at a wavelength of 540 nm.

[0049] 2) Microbial strain activation and expansion: The microorganism used was Shewanella onedensis MR-1 (purchased from the American Type Culture Collection, trade number ATCC 700550). For activation, the bacteria were first removed from a -80°C freezer, streaked onto LB solid medium, and then incubated at 30°C for 20 hours. A single colony was then inoculated into 100 mL of LB medium and incubated at 180 rpm and 30°C for 18 hours. The activated bacterial solution was then inoculated at a rate of 5% into 1500 mL of LB liquid medium and incubated at 180 rpm and 30°C for 15 hours. OD values ​​were then measured. 600 =1.1. Collect the bacteria after expansion culture by centrifugation, with centrifugation parameters set to 8000 rpm for 8 min.

[0050] 3) Preparation of the reduction system: Add 300 mL of mineral salt culture medium to a 500 mL anaerobic flask to ensure the presence of 20 mM electron donor sodium pyruvate, 0.1 mM AQDS, and an appropriate amount of bacterial solution to achieve OD. 600 =0.6.

[0051] 4) Anaerobic incubation: Place the reduction system in an anaerobic incubator to remove oxygen and then place it in a shaker at 180 rpm and 30°C for 2 hours.

[0052] 5) Palladium ion addition and reduction: After incubation, add sodium tetrachloropalladate solution that has been deoxygenated to make the concentration 1.5mM, and continue to place the above reaction system in a shaker at 180rpm and 30℃ in the dark for 6h.

[0053] 6) Freeze-drying and high-temperature carbonization: After the reduction is completed, the bacterial cells are collected at 8000 rpm for 8 min, frozen overnight at -80℃ and then vacuum freeze-dried. The sample is then placed in a tube furnace for carbonization. The specific steps are as follows: Under an argon atmosphere, the temperature of the tube furnace is increased to 800℃ at a rate of 3℃ / min and held for 3 h. After the program is ended and the tube furnace is cooled to room temperature, the sample is taken out, thus obtaining the palladium carbon catalyst based on the anaerobic reduction of palladium by microorganisms.

[0054] Figure 2 Figure 1 shows the transmission electron microscopy (TEM) images and particle size distribution of the samples. Figure 2a shows the TEM image of the sample with a scale bar of 200 nm, while Figure 3b shows the TEM image of the sample with a scale bar of 20 nm. Figure 4c shows the particle size distribution. In TEM image (a), no obvious particles are visible to the naked eye, indicating that agglomeration has basically disappeared. To facilitate particle size statistics, a higher magnification TEM image (b) was used for counting analysis, and the results are shown in Figure 4c. The palladium particles are distributed in the range of 0-5 nm, with approximately 95% of the particles being within 2.5 nm in size. Statistical analysis shows that the average particle size of the palladium-carbon catalyst synthesized after bioreduction optimization by Shewanella bacteria is 1.43 nm, which can be roughly inferred to be that bioreduction enhances particle distribution and thus improves catalyst performance.

[0055] Catalytic performance test:

[0056] 1) Catalyst Ink Preparation:

[0057] Weigh 4 mg of palladium on carbon catalyst, add 200 μL of ethanol, shake gently, then add 760 μL of distilled water and 40 μL of Nafion (5% wt), and sonicate for 30 min.

[0058] 2) Cleaning and drying of the working electrode:

[0059] The working electrode was polished and cleaned with 0.05-micron polishing powder. After the electrode was dried, 15 microliters of the prepared catalyst ink was pipetted into the sample dropping area of ​​the glassy carbon electrode, and then the sample was allowed to dry completely.

[0060] 3) Preparation for electrochemical detection:

[0061] Add an appropriate amount of freshly prepared 0.1M KOH electrolyte to the electrolyte container, and purge with oxygen for 30 minutes to form an oxygen-saturated electrolyte. Before the formal test, activate the working electrode by performing a 20-cycle voltammetric test at a scan rate of 0.05V / s within the test voltage range. After the working electrode is fully activated, perform voltammetric cyclic testing and linear scan voltammetry testing.

[0062] Voltmeter-ammeter cycle method: Voltage range: -1V—0.2V, scan rate: 0.01V / s

[0063] Linear scanning voltammetry: Voltage range: -0.8V—0.4V, scan rate: 0.01V / s

[0064] 4) Calculation of catalytic activity index

[0065] The calculation of electrochemical activity indicators mainly includes the catalyst's electrochemical surface area (ECSA), mass activity (MA), and specific surface area (SA), as shown in the following formulas:

[0066]

[0067]

[0068]

[0069]

[0070] Where Q represents the integrated area of ​​the oxygen reduction peak, and j represents the instantaneous current at 0.1V at 1600rpm. d This is the limiting current. Pd load The palladium loading is calculated based on the ICP detection results.

[0071] Figure 3 The figures show the electrochemical test results for the samples. Figure a is the CV curve of the palladium-on-carbon catalyst, Figure b is the LSV curve of the palladium-on-carbon catalyst, and Figure c is the KL plot of the ORR data for the palladium-on-carbon catalyst at different potentials.

[0072] Table 1 summarizes the main activity indicators of the above test results. ECSA represents the electrochemical active area. For some nanomaterials, a larger surface area exposes more active sites, thus improving electrochemical performance. MA largely depends on the size of the electrocatalyst particles. Smaller catalysts exhibit higher mass activity because smaller particles have a larger ratio of surface atoms to total atoms per unit mass and a large number of electrocatalytic active sites. Therefore, the electrochemical results are basically consistent with the characterization results in Case Study 1, which also verifies that the surface area and metal distribution of the catalyst are improved after bio-enhanced reduction treatment, thus contributing to better catalytic performance.

[0073] Table 1 Calculation results of electrochemical activity index parameters

[0074]

[0075] Example 2

[0076] 1) The preparation of the Pd(II) standard solution is the same as in Example 1.

[0077] 2) Microbial strain activation and expansion: The microorganism used was Shewanella onedensis MR-1. For activation, the bacteria were first removed from a -80℃ freezer, streaked onto LB solid medium, and then incubated at 30℃ for 20 hours. A single colony was inoculated into 100 mL of LB medium and incubated at 180 rpm and 30℃ for 18 hours. The activated bacterial solution was then inoculated at a rate of 5% into 1500 mL of LB liquid medium and incubated at 180 rpm and 30℃ for 15 hours. OD was measured. 600 =1.1. Collect the bacteria after expansion culture by centrifugation, with centrifugation parameters set to 8000 rpm for 8 min.

[0078] 3) Optimal electron donor selection and comparison between hatched and unhatched electron donors:

[0079] A) Incubation system: Add 30mL of mineral salt culture medium, 20mM sodium lactate / sodium pyruvate / sodium formate, and an appropriate amount of bacterial solution to a 50mL anaerobic flask to achieve OD... 600 =0.2. Then place it in an anaerobic incubator to remove oxygen and incubate it in a shaker at 180 rpm and 30°C for 2 hours. After incubation, add the deoxygenated palladium solution to make the concentration 0.1 mM, and continue to place the above reaction system in a shaker at 180 rpm and 30°C in the dark for 2 hours. Observe the reaction results after 2 hours.

[0080] B) Unincubated system: All reagents were added in the same amounts as in the incubation system described above. The difference was that 30 mL of mineral salt culture medium and 20 mM sodium lactate / sodium pyruvate / sodium formate were added first and the mixture was shaken and incubated under anaerobic conditions for 2 h. Then, bacterial culture and palladium solution were added and reacted in the dark, and the reaction results were observed.

[0081] Figure 4 The diagram shows the phenomena of palladium(II) reduction before (ac,eg,ik) and after (bd,fh,jl) reduction in the unincubated group (ab,ef,ij) and the incubated group (cd,gh,kl) when sodium lactate (ad), sodium pyruvate (eh), and sodium formate (il) were used as electron donors. It can be observed that the treatment groups turned black after 2 hours of incubation (d,h,l), indicating that palladium reduction occurred to some extent in all three treatment groups, and that co-incubation accelerated the palladium reduction process in Shewanella. The darker the solution color, the more palladium was reduced. Visual observation showed that the incubated group using sodium pyruvate as the electron donor had the best reduction effect. To further verify this, the palladium concentration after 2 hours of reduction for each of the three treatments was measured spectrophotometrically, and the reduction rates were calculated to be 70.35%, 96.82%, and 71.16%, respectively, further confirming that sodium pyruvate had the best reduction-promoting effect. Therefore, all subsequent studies were conducted under the condition of using 20 mM sodium pyruvate as an electron donor and incubation for 2 hours.

[0082] Example 3

[0083] In Example 1, step 3) was modified by adding 30 mL of mineral salt culture medium, 20 mM sodium pyruvate, and an appropriate amount of bacterial solution to a 50 mL anaerobic bottle to achieve OD... 600 =0.2, the palladium concentration in step 4) is changed to Pd(II) = 0.1mM / 0.5mM / 1mM / 1.5mM / 2mM / 3mM. The Pd(II) content in the sample supernatant is measured at fixed points every 2 hours, and no catalytic performance is measured.

[0084] Figure 5 The reduction rates are shown for different Pd(II) concentrations. It can be seen that all treatment groups experienced rapid and significant reduction within the first 2 hours. After 2 hours, the reduction rate slowed down, and palladium at concentrations of 0.5 mM and below was almost completely reduced. However, as the palladium concentration increased, the reduction rate gradually decreased. When the palladium concentration was 1.5 mM, the reduction rate was significantly higher than that of Shewanella at 20 mM sodium pyruvate and OD500 of Pd(II). 600 Under conditions of 0.2 and co-incubation for two hours, the reduction rate of palladium was still far less than 50% after 24 hours of reaction. This indicates that higher metal concentrations inhibit the metal reduction rate of Shewanella and lead to a decrease in the final metal reduction amount. Based on this, subsequent studies selected a Pd(II) concentration of 1.5 mM for further exploration.

[0085] Example 4

[0086] In Example 1, step 3) is modified by adding 30 mL of mineral salt culture medium, 20 mM sodium pyruvate, AQDS / humic acid / riboflavin concentration of 1 mM, and an appropriate amount of bacterial solution to a 50 mL anaerobic bottle to achieve OD 600 =0.2, and the Pd(II) content in the sample supernatant was measured at fixed points every 4 hours without catalytic performance determination.

[0087] Figure 6 The reduction rates of Pd(II) under different electron shuttles are shown. Targeted sampling results revealed that the reduction rate was rapid in the first 4 hours for all samples, gradually slowing down thereafter. The system with added AQDS showed the best reduction effect, reaching a final reduction rate of 97.47%. The reduction effects of humic acid and riboflavin treatments were similar, both around 83%, while the blank control group without any electron shuttle showed the worst reduction effect, with a reduction rate of only 45.47%. In conclusion, humic acid, AQDS, and riboflavin can all promote palladium reduction in Shewanella, with AQDS showing the best promoting effect. Therefore, AQDS will be selected as the optimal electron shuttle for future research.

[0088] Example 5

[0089] In Example 1, step 3) is modified by adding 30 mL of mineral salt culture medium, 20 mM sodium pyruvate, AQDS = 0 mM / 0.1 mM / 0.5 mM / 0.75 mM / 1 mM / 1.25 mM / 1.5 mM, and an appropriate amount of bacterial suspension to a 50 mL anaerobic bottle to achieve OD... 600 =0.2, and the Pd(II) content in the sample supernatant was measured at fixed points every 4 hours without catalytic performance determination.

[0090] Figure 7 The reduction rates of Pd(II) with different concentrations of AQDS were shown. Results indicated that the reduction rates of all treatment groups were relatively rapid in the first 8 hours, then gradually decreased. The group with 0.5 mM AQDS showed the best promoting effect in the first 8 hours; increasing the AQDS concentration did not further increase the reduction rate. However, after 8 hours, 0.1 mM AQDS showed the best reduction effect. Due to the high price of AQDS, the reduction-promoting effects of 0.5 mM and 0.1 mM were not significantly different in the first 8 hours, and showed relatively consistent effects after 8 hours. Therefore, considering all factors, it can be concluded that a small amount of AQDS is sufficient to achieve a good palladium reduction effect in Shewanella; that is, when the palladium concentration is 1.5 mM, 0.1 mM AQDS is sufficient.

[0091] Example 6

[0092] In Example 1, step 3) is modified by adding 30 mL of mineral salt culture medium, 20 mM sodium pyruvate, AQDS of 0.1 mM, and an appropriate amount of bacterial solution to a 50 mL anaerobic bottle to achieve OD... 600=0 / 0.2 / 0.4 / 0.6 / 0.8 / 1.0, samples were taken at fixed points every 4 hours to determine the Pd(II) content in the supernatant of the sample, and catalytic performance was not measured.

[0093] Figure 8 The reduction rate of Pd(II) was determined under different concentrations of Shewanella oneidensis MR-1 bacteria. The results show the OD values ​​without the addition of Shewanella. 600 The =0 treatment group showed only weak reduction, with a reduction rate of 12.27% after 12 hours, while the addition of a small amount of Shewanella (OD) 600 After adjusting for concentrations of 0.2%, the reduction rate significantly increased (to 87.86%), indicating that Shewanella is indispensable in the palladium reduction process. The reduction rate also showed an upward trend with increasing bacterial concentration in the reduction system. It is noteworthy that the reduction rate increased at OD... 600 When the concentration is 0.6, most of the palladium can be reduced within 2 hours, with a reduction rate of 91.53%. Furthermore, increasing the bacterial concentration did not produce a better effect. Therefore, it can be concluded that in a system with 20 mM sodium pyruvate, 0.1 mM AQDS, and 1.5 mM palladium, the addition of OD... 600 Shewanella bacteria with a concentration of 0.6 can exert a good reduction-promoting effect, reducing more than 90% of palladium within 2 hours.

Claims

1. A method for obtaining palladium-on-carbon catalyst based on microbial anaerobic reduction of metallic palladium, characterized in that: Includes the following steps: 1) Add the electron shuttle to a mixed solution containing an electron donor, culture medium, and microorganisms; 2) Incubate the mixed solution after removing oxygen; 3) After incubation, add an oxygen-removed palladium solution for reduction; 4) After reduction, collect the product and successively dry and carbonize it to obtain the final product; The electron shuttle mentioned in step 1) is anthrone-2,6-disulfonic acid; the electron donor is sodium pyruvate. Step 1) The concentration of the electron donor in the mixed solution containing the electron donor, culture medium, and microorganisms is 20 mmol / L. The volume ratio of the culture medium to the electron donor solution and the microbial solution is 30:0.405:0.25 to 30:0.405:0.

35. The content of microorganisms in the total system is [OD value missing]. 600 =0.6; the concentration of the electron shuttle in the total system solution is 0.1 mmol / L; Step 1) The volume ratio of the electron shuttle solution to the mixed solution containing the electron donor, culture medium, and microorganisms is 0.0010:1 to 0.0009:1; The microorganism mentioned in step 1) is Shewanella MR-1; Step 2) The incubation conditions are: 160-200 rpm shaker, 28-30℃ incubation for 1.5-2.5 h; The palladium source in step 3) is sodium tetrachloropalladium; the palladium source is added in the form of a solution with a final concentration of 1.5 mmol / L in the total system. The carbonization process is as follows: under a protective atmosphere, the temperature is increased to 750-850℃ at a rate of 3-4℃ / min, and held for 2.5-3.5 hours.

2. A palladium-on-carbon catalyst, characterized in that: It is prepared by the method described in claim 1.

3. The application of the palladium-on-carbon catalyst according to claim 2, characterized in that: Used to prepare fuel cell catalysts.

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