Catalytic material containing porous ordered PtCu octahedron as well as preparation and application of catalytic material in fuel cell

Abstract

The invention belongs to the field of fuel cells, and particularly relates to a catalytic material containing porous ordered PtCu octahedrons, preparation of the catalytic material and application of the catalytic material in the fuel cells, and a preparation method of the catalytic material comprises the steps that solvent heat treatment is conducted on a mixed solution composed of a copper chloride raw material with crystal water, platinum acetylacetonate and DMF, then solid-liquid separation is conducted, and the catalytic material is prepared; the molar ratio of Cu / Pt in the copper chloride raw material with crystal water to the platinum acetylacetonate is (1-3): (1-3); the concentration of the Cu element in the mixed solution is 3-5 mM; the temperature of the solvent heat treatment is 150-250 DEG C. The porous PtCu octahedron in an ordered state is synthesized for the first time in the industry, and the porous PtCu octahedron accidentally has excellent mass ratio activity and long-acting stability under an acidic condition.

Description

Technical Field

[0001] The present invention belongs to the field of battery materials, and in particular relates to the technical field of fuel cell catalysts. Background Art

[0002] In recent years, proton exchange membrane fuel cells, as a green, clean energy conversion device that can directly utilize hydrogen energy, have attracted much attention from researchers, and some hydrogen fuel cell vehicles have been industrialized. Currently, commercial fuel cell catalysts are usually Pt / C, but the scarcity of platinum resources and high costs directly restrict the promotion of fuel cell technology and hinder its global commercialization process.

[0003] Cu is a non-precious metal with a wide range of sources, easy to obtain and low price. After forming an alloy with Pt, it can adjust the crystal structure and electronic structure of Pt through lattice strain and ligand effect to improve the performance of Pt catalyst. In addition, replacing some Pt ​​atoms with Cu can reduce the cost of the catalyst.

[0004] The prior art also discloses some reports on PtCu octahedral catalysts. For example, the Chinese patent document with publication number CN114883588A discloses an ultra-high stability oxygen reduction catalyst for room temperature hydrogen fuel cells, which uses copper-rich octahedral PtCu as a seed, epitaxially grows PtCu clusters on an octahedral PtCu / Pt core-shell structure, and the size of the PtCu clusters is 0.8~2.1nm. For another example, the Chinese patent document with publication number CN111048793A discloses a method for preparing a platinum-based octahedral catalyst, the steps of which include: mixing an acetylacetone transition metal salt with a carbon carrier, followed by reduction in a reducing atmosphere to obtain a Pt transition metal octahedral material.

[0005] In summary, although there are some solutions for PtCu octahedral catalytic materials in the prior art, the materials obtained by the existing solutions are disordered low-surface activity materials, and the mass specific activity (A / mg Pt ) is not high. In addition, the dissolution and precipitation of Cu element are easy to occur under strong acid, and the long-term cycle stability under acidic conditions is not ideal. Summary of the invention

[0006] In view of the problems that the existing PtCu octahedron preparation method can only obtain disordered non-porous materials, and the mass specific activity and long-term cycle stability of such materials under acidic conditions are not ideal, the first object of the present invention is to provide a method for preparing a catalytic material containing porous ordered PtCu octahedrons (also referred to as catalytic material in the present invention), aiming to prepare a PtCu octahedron catalytic material with special ordered pores, high mass specific activity and long-term stability.

[0007] The second object of the present invention is to provide a catalytic material containing porous ordered PtCu octahedrons obtained by the preparation method and its application in fuel cells.

[0008] The third object of the present invention is to provide a fuel cell comprising the catalytic material containing porous ordered PtCu octahedrons.

[0009] A method for preparing a catalytic material containing porous ordered PtCu octahedrons, comprising subjecting a mixed solution consisting of a copper chloride raw material having crystal water, platinum acetylacetonate, and DMF to solvothermal treatment, followed by solid-liquid separation, to obtain the catalytic material; The molar ratio of Cu / Pt in the copper chloride raw material with crystal water and platinum acetylacetonate is 1-3:1-3; In the mixed solution, the concentration of Cu element is 3~5 mM; The temperature of the solvent thermal treatment is 150℃~250℃.

[0010] The existing preparation method of PtCu octahedron basically needs to realize the morphology and alloying preparation of PtCu octahedron by means of surfactant and reducing agent. However, the present invention unexpectedly studies that the mixed solution composed of copper chloride raw material with crystal water, acetylacetonate platinum, and DMF, which does not contain surfactant and reducing agent, is innovatively subjected to solvothermal treatment, which can be based on the combination of chloride ions, highly active crystalline water, acetylacetonate platinum, and DMF system in the raw material. In this way, synergy can be achieved, and a new ordered porous PtCu octahedron can be unexpectedly prepared on the premise of omitting necessary surfactants and reducing agents, and the material with special physicochemical characteristics obtained by the preparation method can provide a large number of pore defects and step atoms, promote the adsorption and transmission of oxygen molecules, reduce the coordination number of PtCu alloys, thereby accelerating the kinetic process of fuel cells and greatly improving catalytic activity; for example, its mass specific activity and long-term stability under acidic conditions can be effectively improved. That is, the preparation method of the present invention, under the premise of eliminating simplification of the preparation process, can unexpectedly synthesize PtCu octahedrons with an ordered porous structure for the first time in the industry. Not only that, the PtCu octahedrons with the special ordered porous characteristics obtained by the preparation method can unexpectedly have high mass activity, and in addition, they also have excellent acid resistance and long-cycle stability.

[0011] In the present invention, the combined control of the copper chloride raw material with crystal water and platinum acetylacetonate is the key to synergistically constructing the porous ordered PtCu octahedron and significantly improving its mass specific activity and long-term stability under acidic conditions. As an optional scheme, the copper chloride raw material with crystal water is copper chloride dihydrate.

[0012] The research of the present invention also shows that under the synergistic joint innovation of the copper chloride raw material of the crystallization water and platinum acetylacetonate, further controlling the molar ratio of Cu / Pt is expected to further improve the synergy of the reaction between the two, which will help to further improve the mass specific activity of the material and the long-term stability under acidic conditions.

[0013] Preferably, the molar ratio of Cu / Pt in the copper chloride raw material with crystal water and acetylacetonate platinum is 1-2:1-2; more preferably 1:0.9-1.1; and more preferably 1:0.95-1.05. The present invention shows that the preferred Cu / Pt molar ratio is helpful to further enhance the combined synergy of the copper chloride raw material with crystal water and acetylacetonate platinum, to further improve the porous ordered characteristics of the material, and to improve the mass specific activity of the material and the long-term stability under acidic conditions.

[0014] In the present invention, the concentration of Cu element in the solvothermal starting solution (mixed solution after slurrying) can be 3.8~4.2mM (the mM is mmoL / L); more preferably 3.8~4.2mM. Studies have shown that at the preferred concentration, a better process combination effect can be obtained, which helps to further optimize the octahedral material with porous ordered physical and chemical structure, and helps to further improve the activity and long cycle performance of the prepared material under acidic conditions.

[0015] In the present invention, the temperature of the solvent thermal treatment is 175-185° C. Studies have shown that at the preferred solvent thermal temperature, the ordered porous characteristics of the prepared material can be further synergistically optimized, which helps to further improve the activity and long cycle performance of the prepared material under acidic conditions.

[0016] In the present invention, the solvent thermal treatment time is 5 to 10 hours, and can further be 7 to 9 hours.

[0017] In another embodiment of the present invention, the catalytic material is a supported catalyst further comprising a carrier. The supported catalyst of the present invention comprises a carrier and porous ordered PtCu octahedrons supported thereon.

[0018] In the present invention, the carrier may be a carrier component known in the industry, for example, a carbon-based carrier, and further may be carbon black.

[0019] In the present invention, the supported catalyst is obtained by compounding the porous ordered PtCu octahedron and the carrier. Further, the carrier can be purified and / or surface modified based on known processes before compounding. For example, when the carrier is a carbon-based material, the carrier can be pre-oxidized with an oxidizing component, and then compounded with the porous ordered PtCu octahedron to obtain the supported catalyst.

[0020] In the present invention, in the supported catalyst, the particle size of the porous ordered PtCu octahedron can be between 20 and 30 nm.

[0021] In the present invention, in the supported catalyst, the content of the porous ordered PtCu octahedron can be adjusted as required, for example, it can be 20-80 wt.%.

[0022] The invention also provides a catalytic material containing porous ordered PtCu octahedrons prepared by the preparation method.

[0023] The preparation method of the present invention can unexpectedly give the product special ordered porous octahedral physicochemical characteristics, and the material with the physicochemical characteristics prepared by the preparation method can unexpectedly have excellent mass specific activity and long-term stability under acidic conditions.

[0024] The present invention also provides an application of the catalytic material containing porous ordered PtCu octahedrons, which is used as a catalyst for preparing a fuel cell.

[0025] In the present invention, the catalytic material of the present invention can be used to prepare the required fuel cell and its components based on known processes and means.

[0026] In the application of the present invention, the catalyst material containing the porous ordered PtCu octahedron can be used as an electrode to prepare a fuel cell with an acidic solution as an electrolyte. The catalyst material of the present invention can adapt to acidic application requirements and can obtain good electrochemical performance under acidic conditions.

[0027] In the present invention, the acidic solution may be, for example, a 0.05-0.5 M HClO4 aqueous solution.

[0028] In the present invention, the fuel cell may be any type of fuel cell known in the industry. For example, as an optional solution, it may be a proton exchange membrane fuel cell.

[0029] The present invention also provides a fuel cell, which comprises the catalytic material containing porous ordered PtCu octahedrons, or is prepared by the catalytic material containing porous ordered PtCu octahedrons.

[0030] The fuel cell of the present invention, in addition to comprising the catalytic material of the present invention or being prepared based on the catalytic material, may have other components, structural parts and principles that are known.

[0031] Beneficial Effects

[0032] The present invention innovatively uses copper chloride with crystal water as the copper source and platinum acetylacetonate as the platinum source for solvothermal reaction. Based on the special interaction between the components in the ternary system, PtCu octahedron with an ordered structure can be prepared for the first time without surfactants and reducing agents. That is, the preparation system described in the present invention can unexpectedly achieve synergy under the premise of excluding other components, and the preparation of ordered morphological materials is realized for the first time in the industry.

[0033] More importantly, the ordered PtCu octahedron prepared by the preparation method of the present invention can unexpectedly improve its mass specific activity and improve the long-term stability of the material under acidic conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a transmission electron microscopy image of the porous ordered PtCu octahedron (abbreviated as PO-PtCu NOs) prepared in Example 1.

[0035] Figure 2 This is the HAADF-STEM image of PO-PtCu NOs prepared in Example 1.

[0036] Figure 3 This is a high-resolution transmission electron microscopy image of PO-PtCu NOs prepared in Example 1.

[0037] Figure 4 This is the XRD pattern of PO-PtCu NOs prepared in Example 1.

[0038] Figure 5 This is a comparison chart of LSV obtained by testing the PO-PtCu NOs / C prepared in Example 1 and the commercial Pt / C catalyst in an acidic system.

[0039] Figure 6 This is a comparison of the LSV of commercial Pt / C fuel cell catalysts before and after 30,000 ADTs in an acidic system.

[0040] Figure 7 This is a comparison diagram of the LSV of PO-PtCu NOs / C prepared in Example 1 before and after 30,000 cycles of ADTs in an acidic system.

[0041] Figure 8 This is a transmission electron microscope image of the material prepared in Comparative Example 6. DETAILED DESCRIPTION

[0042] The following specific embodiments are intended to further illustrate the present invention in detail, rather than to further limit the scope of protection of the claims of the present invention.

[0043] The reagents involved in the following examples, unless otherwise specified, are commercial reagents purchased directly from the market.

[0044] Example 1

[0045] Step 1. Preparation of porous ordered PtCu octahedral catalyst (PO-PtCu NOs):

[0046] Weigh 20 mg of platinum acetylacetonate (platinum source) and cupric chloride dihydrate (copper source; Pt / Cu molar ratio is 1:1) in a beaker, then add DMF to the beaker, stir magnetically for 2 h, transfer the transparent yellow solution (the copper concentration in the yellow solution is 4 mM) to a stainless steel pressure cooker with a Teflon liner, and place it in an oven and heat from room temperature to 180 o C (solvothermal temperature) and kept at this temperature for 8 h. After the reaction was completed and cooled to room temperature, the black product was collected by centrifugation (5000 rpm, 5 min) and washed 6 times with a mixture of ethanol / cyclohexane (volume ratio of 1:1) to obtain PO-PtCu NOs product.

[0047] TEM of PO-PtCu NOs product Figure 1 ;from Figure 1 It can be seen that the single porous ordered PtCu octahedron is evenly distributed, with an average size of about 35 nm, and it can be clearly seen that there are many small white spots on the surface of the single octahedron, which are pore structures.

[0048] The HAADF-STEM image of PO-PtCu NOs product is shown in Figure 2 .from Figure 2 It can be seen that Pt and Cu elements are evenly distributed on the porous octahedron.

[0049] The high-resolution transmission electron microscopy image of PO-PtCu NOs product is shown in Figure 3 ,from Figure 3 It can be seen that the lattice fringe spacing on the surface of the porous octahedron is 0.220 nm, indicating that Cu and Pt form an alloy, and there are many areas where the lattice disappears on the surface of the octahedron (pore structure), and there are many step atoms on the edge defects.

[0050] The XRD pattern of PO-PtCu NOs product is shown in Figure 4 Among them, several XRD diffraction peaks correspond to the ordered PtCu PDF#42-1326 card, indicating that the PO-PtCu NOs catalyst is an ordered alloy structure.

[0051] Step 2: Loading PO-PtCu NOs catalyst on carbon black:

[0052] The purchased carbon black (XC-72R) was pretreated with hydrogen peroxide in advance to obtain modified carbon black. Then the modified carbon black and PO-PtCu NOs prepared in step 1 (mass ratio = 3:2, i.e., loading amount of 40 Wt.%) were weighed and dispersed in anhydrous ethanol (liquid-to-solid ratio of 5-10 mL / g) by ultrasonication, and then ultrasonicated for 1 h under ice bath conditions and dried in an oven to obtain PO-PtCu NOs / C catalyst.

[0053] Step 3: Electrochemical detection

[0054] Take 4 mg of the PO-PtCu NOs / C catalytic material prepared in step 2 and disperse it in a mixture of 500 μL ethanol, 400 μL distilled water, and 100 μL 5 wt% nafion solution. After ultrasonic treatment for half an hour, take 15 μL of the mixed solution and drop it on the rotating disk electrode. After natural drying, the PO-PtCu NOs / C working electrode (also referred to as the working electrode) is obtained. The electrochemical performance of the PO-PtCu NOs / C catalyst is then tested using an electrochemical workstation, where mercurous sulfate is used as the reference electrode, a graphite rod is used as the counter electrode, and 0.1 M HClO4 is used as the electrolyte. The scan rate is 0.01 V / s to test the catalyst activity in an acidic environment. The stability test was scanned at a scan rate of 0.05 V / s for 30,000 cycles. For comparison, commercial Pt / C (a composite material with 40wt.%Pt loaded on a carbon material) was also tested in the same way.

[0055] The LSV diagrams of the PO-PtCu NOs / C and commercial Pt / C catalysts prepared in Example 1 tested in an acidic system are shown in Figure 5 ; It shows that PO-PtCu NOs / C has a higher half-wave potential, indicating higher catalytic activity.

[0056] The cycle diagrams of Pt / C and PO-PtCu NOs / C are shown in Figure 6 and Figure 7 . It shows that after 30,000 cycles of stability test on commercial Pt / C, the half-wave potential of the Pt / C catalyst decreased by 66 mV. However, after 30,000 cycles of stability test on PO-PtCu NOs / C of Example 1 of the present invention, the half-wave potential of the PO-PtCu NOs catalyst decreased by only 15 mV. This shows that the material described in the present invention has better catalytic stability under acidic conditions.

[0057] Example 2

[0058] Compared with Example 1, the only difference is that in step 1, the molar ratio of Pt to Cu is changed to: Pt:Cu=2:1, the total molar amount of Pt / Cu remains unchanged, and other operations, parameters and tests are the same as in Example 1.

[0059] Example 3

[0060] Compared with Example 1, the only difference is that in step 1, the molar ratio of Pt to Cu is changed to: Pt:Cu=1:2, the total molar amount of Pt / Cu remains unchanged, and other operations, parameters and tests are the same as in Example 1.

[0061] Example 4

[0062] Compared with Example 1, the only difference is that in step 1, the solvent thermal temperature is changed to 160 o C, the time is 10 h, and other operations, parameters and tests are the same as those in Example 1.

[0063] Example 5

[0064] Compared with Example 1, the only difference is that in step 1, the solvent thermal temperature is changed to 200 o C. Other operations, parameters and tests are the same as those in Example 1.

[0065] Example 6

[0066] Compared with Example 1, the only difference is that in step 2, the mass ratio of modified carbon black to PO-PtCu NOs is 4:1 (ie, the loading amount is 20 Wt.%), and other operations, parameters and tests are the same as in Example 1.

[0067] Example 7

[0068] Compared with Example 1, the only difference is that in step 2, the mass ratio of modified carbon black to PO-PtCu NOs is 1:4 (ie, the loading amount is 80 Wt.%), and other operations, parameters and tests are the same as in Example 1.

[0069] Example 8

[0070] Compared with Example 1, the only difference is that in step 1, the concentration of copper in the yellow solution is 3 mM, and the Pt / Cu molar ratio, molar amount and other operations, parameters and tests are the same as in Example 1.

[0071] Example 9

[0072] Compared with Example 1, the only difference is that in step 1, the concentration of copper in the yellow solution is 5 mM, and the Pt / Cu molar ratio, molar amount and other operations, parameters and tests are the same as in Example 1.

[0073] Comparative Example 1

[0074] Compared with Example 1, the only difference is that cobalt chloride dihydrate is used to replace the copper source (the molar amount of Co is the same as that of Cu), and other operations, parameters and tests are the same as those in Example 1.

[0075] Comparative Example 2

[0076] Compared with Example 1, the only difference is that ferrous chloride dihydrate is used to replace the copper source (the molar amount of Fe is the same as Cu), and other operations, parameters and tests are the same as Example 1.

[0077] Comparative Example 3

[0078] Compared with Example 1, the only difference is that nickel chloride dihydrate is used to replace the copper source (the molar amount of Ni is the same as that of Cu), and other operations, parameters and tests are the same as those in Example 1.

[0079] Comparative Example 4

[0080] Compared with Example 1, the only difference is that hexahydrated chloroplatinic acid is used to replace the platinum source, wherein the amount of platinum and other operations, parameters and tests are the same as those in Example 1.

[0081] Comparative Example 5

[0082] Compared with Example 1, the only difference is that copper acetylacetonate is used as the copper source, wherein the copper molar amount and other operations, parameters and tests are the same as those in Example 1.

[0083] Comparative Example 6

[0084] Compared with Example 1, the only difference is that copper chloride without crystal water is used as the copper source, wherein the copper dosage, operation, parameters and test are the same as those in Example 1. TEM of the obtained material is shown in FIG. Figure 8 , showing that it is a non-porous disordered octahedral material.

[0085] Comparative Example 7

[0086] Compared with Example 1, the only difference is that copper chloride without crystal water is used as the copper source, and ultrapure water is added to DMF, wherein the amount of ultrapure water used is the same as the amount of crystal water in copper chloride dihydrate in Example 1, and the other operations and parameters are the same as Example 1. The morphology of the material prepared in this case is similar to that of Comparative Example 6, and the octahedral material with an ordered porous morphology of the present invention type is not obtained.

[0087] The electrochemical test results of the catalysts prepared in each example and each comparative example and commercial Pt / C and the subsequent calculation results are listed in Table 1.

[0088]

[0089] Examples 1, 2, 3, 4, 5, 6, 7, 8, and 9 investigated the catalysts prepared using different PtCu molar ratios, solvent thermal temperatures, loading amounts, and concentrations, and their performance tests. The catalyst obtained in Example 1 had the highest mass specific activity (reaching 0.974 A / mg at 0.9 V). Pt , that is, 0.974 amperes of current can be generated per milligram of Pt), which is 9.28 times that of commercial Pt / C. This result shows that the catalyst prepared by the present invention shows excellent fuel cell oxygen reduction catalytic performance. This is because the catalytic material has obtained a platinum-copper octahedron with rich pore defects on the surface and rich step atoms on the edge through morphology design. These defects and step atoms can effectively reduce the coordination number of the PtCu alloy, accelerate the kinetic process of the oxygen reduction reaction at the cathode of the fuel cell, and thus greatly improve the catalytic activity. In addition, from the decay rate of the mass specific activity after 30,000 cycles, it can be seen that the mass specific activity decay of the catalyst in Example 1 is 16.7%, while the commercial Pt / C decays by 59.9%. The high stability of the catalyst in Example 1 is due to the fact that the formed PtCu alloy is ordered, that is, the Pt atoms and Cu atoms in the alloy are arranged in an orderly manner according to a certain rule. This ordered alloy structure can effectively slow down the dissolution and precipitation of Cu atoms in a strong acid environment, thereby improving the structural stability of the alloy and ultimately improving the stability of the catalyst.

[0090] It can be seen from Examples 1, 2 and 3 that when the molar ratio of Pt:Cu=1:1, Cu has the best control over the lattice and electrons of Pt, thereby obtaining the highest catalytic activity.

[0091] The mass specific activity of the catalysts obtained in Examples 4 and 5 is somewhat different, but the stability difference is not large. This is because when the solvent thermal temperature changes, the atomic diffusion may change, thereby changing the porous structure, resulting in a decrease in defects and step atoms. When the solvent thermal temperature is 180 o C, the porous ordered structure is optimal, thus obtaining the highest catalytic activity.

[0092] There is a certain difference in the mass specific activity of the catalysts obtained in Examples 6 and 7, but the difference in stability is not large. This is because the modified carbon black can orderly disperse the porous ordered PtCu alloy particles and can exert the best mass specific activity when the loading amount is 40 Wt.%.

[0093] There is a certain difference in the mass specific activity of the catalysts obtained in Examples 8 and 9, but the difference in stability is not large.

[0094] In other comparative examples, since the combined synergistic raw materials of crystal water copper chloride and acetylacetonate platinum described in the present invention are not used, the octahedral and ordered porous structure characteristics of the material are affected, thus affecting its performance.

[0095] The above results indicate that the catalyst prepared by the present invention has excellent catalytic activity and stability, and its preparation is simple and repeatable, and it can be applied on a large scale in proton exchange membrane fuel cells.

[0096] The above describes the specific implementation of the present invention. However, the present invention is not limited to the above implementation. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a catalytic material containing porous ordered PtCu octahedra, characterized in that: The catalytic material is prepared by subjecting a mixed solution consisting of a copper chloride raw material with crystal water, platinum acetylacetonate and DMF to solvothermal treatment, followed by solid-liquid separation; The molar ratio of Cu / Pt in the copper chloride raw material with crystal water and platinum acetylacetonate is 1-3:1-3; In the mixed solution, the concentration of Cu element is 3~5 mM; The temperature of the solvent thermal treatment is 150℃~250℃.

2. The preparation method according to claim 1, characterized in that: The copper chloride raw material with crystal water is copper chloride dihydrate.

3. The preparation method according to claim 1, characterized in that: The molar ratio of Cu / Pt in the copper chloride raw material with crystal water and platinum acetylacetonate is 1-2:1-2.

4. The preparation method according to claim 1, characterized in that: The concentration of Cu element in the starting solution of solvothermal reaction was 3.8~4.2mM.

5. The preparation method according to claim 1, characterized in that: The temperature of solvent thermal treatment is 175~185℃; The solvent thermal treatment time is 5~10h.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The catalytic material is a supported catalyst further comprising a carrier; wherein the loading amount of the porous ordered PtCu octahedron is 20-80 wt.%.

7. The preparation method according to claim 6, characterized in that: The carrier is a carbon-based material, and the carrier is preliminarily subjected to surface oxidation treatment using an oxidizing component, and then composited with the porous ordered PtCu octahedron to obtain the supported catalyst.

8. A catalytic material containing porous ordered PtCu octahedrons obtained by the preparation method according to any one of claims 1 to 7.

9. Use of a catalytic material containing porous ordered PtCu octahedrons obtained by the preparation method according to any one of claims 1 to 7, characterized in that: It is used as a catalyst to prepare fuel cells.

10. A fuel cell, characterized in that: A catalytic material comprising porous ordered PtCu octahedrons prepared by the preparation method according to any one of claims 1 to 7, or prepared by the catalytic material comprising porous ordered PtCu octahedrons.

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