阅读说明：本技术 用于氧还原催化的由离子液体和八面体Pt-Ni-Cu合金纳米颗粒制成的复合物 (Composites made of ionic liquids and octahedral Pt-Ni-Cu alloy nanoparticles for oxygen reduction catalysis ) 是由 黄侃 周丽琴 贾鸿飞 加藤久雄 彭振猛 沈晓晨 于 2019-07-08 设计创作，主要内容包括：本发明涉及用于氧还原催化的由离子液体和八面体Pt-Ni-Cu合金纳米颗粒制成的复合物。改良的氧还原反应催化剂包括与二级离聚物接触的铂-铜-镍合金的八面体纳米颗粒。该合金可具有式Pt<Sub>2</Sub>CuNi,并且该二级离聚物可包括离子液体1-甲基-2,3,4,6,7,8-六氢-1H-嘧啶并[1,2-a]嘧啶-9-鎓1,1,2,2,3,3,4,4,4-九氟丁烷-1-磺酸盐([MTBD][C<Sub>4</Sub>F<Sub>9</Sub>SO<Sub>3</Sub>])。该氧还原催化剂与竞争性催化剂相比具有改良的稳定性以及质量面积和比面积。(The invention relates to a composite made of ionic liquid and octahedral Pt-Ni-Cu alloy nanoparticles for oxygen reduction catalysis. The improved oxygen reduction reaction catalyst comprises octahedral nanoparticles of a platinum-copper-nickel alloy in contact with a secondary ionomer. The alloy may have the formula Pt 2 CuNi, and the secondary ionomer may include an ionic liquid 1-methyl-2, 3,4,6,7, 8-hexahydro-1H-pyrimido [1,2-a ]]Pyrimidin-9-ium 1,1,2,2,3,3,4,4, 4-nonafluorobutane-1-sulfonate ([ MTBD)][C 4 F 9 SO 3 ]). The oxygen reduction catalyst has improved stability and mass and specific area compared to competing catalysts.)

1. An Oxygen Reduction Reaction (ORR) catalyst, the catalyst comprising:

octahedral nanoparticles comprising a platinum alloy having platinum, nickel, and copper (Pt-Ni-Cu); and

and octahedron sodiumA secondary ionomer comprising 1-methyl-2, 3,4,6,7, 8-hexahydro-1H-pyrimido [1,2-a ] in contact with rice particles]Pyrimidin-9-ium 1,1,2,2,3,3,4,4, 4-nonafluorobutane-1-sulfonate ([ MTBD)][C₄F₉SO₃])。

2. The ORR catalyst of claim 1, wherein the octahedral nanoparticles comprise nickel and copper present in a nickel to copper molar ratio ranging from about 1:2 to about 2: 1.

3. The ORR catalyst of claim 2, wherein the octahedral nanoparticles comprise nickel and copper present in a nickel to copper molar ratio of about 1: 1.

4. The ORR catalyst of claim 1, wherein the octahedral nanoparticles comprise platinum and nickel present in a platinum to nickel molar ratio ranging from about 1:1 to about 4: 1.

5. The ORR catalyst of claim 4, wherein the octahedral nanoparticles comprise platinum and nickel present in a platinum to nickel molar ratio of about 2: 1.

6. The ORR catalyst of claim 1, wherein the secondary ionomer is present at a weight ratio relative to platinum alloy in a range of 1.25:1 to 3.85: 1.

7. The ORR catalyst of claim 1, wherein the secondary ionomer is present in a weight ratio in a range of 2:1 to 3:1 relative to the platinum alloy.

8. The ORR catalyst of claim 1, wherein the secondary ionomer is present at a weight ratio relative to platinum alloy in a range of 2.5:1 to 2.6: 1.

9. The ORR catalyst of claim 1, comprising a polymeric ionomer in contact with a platinum alloy.

10. The ORR catalyst of claim 1, wherein the secondary ionomer completely coats the platinum alloy.

11. The ORR catalyst of claim 1, wherein the secondary ionomer partially coats the platinum alloy.

12. The ORR catalyst of claim 1, wherein the secondary ionomer comprises porous particles and the secondary ionomer is at least partially impregnated in the porous particles.

13. A cathode for oxygen reduction, the cathode comprising:

a cathode current collector;

octahedral nanoparticles comprising a platinum alloy having platinum, nickel, and copper (Pt-Ni-Cu); and

a secondary ionomer comprising 1-methyl-2, 3,4,6,7, 8-hexahydro-1H-pyrimido [1,2-a ] in contact with octahedral nanoparticles]Pyrimidin-9-ium 1,1,2,2,3,3,4,4, 4-nonafluorobutane-1-sulfonate ([ MTBD)][C₄F₉SO₃])。

14. The cathode of claim 13, wherein the octahedral nanoparticles comprise nickel and copper present in a nickel to copper molar ratio ranging from about 1:2 to about 2: 1.

15. The cathode of claim 14, wherein the octahedral nanoparticles comprise nickel and copper present in a nickel to copper molar ratio of about 1: 1.

16. The cathode of claim 13, wherein the octahedral nanoparticles comprise platinum and nickel present in a platinum to nickel molar ratio ranging from about 1:1 to about 4: 1.

17. The cathode of claim 16, wherein the octahedral nanoparticles comprise platinum and nickel present in a platinum to nickel molar ratio of about 2: 1.

18. The cathode of claim 13, wherein the secondary ionomer is present in a weight ratio relative to platinum alloy in the range of 2:1 to 3: 1.

19. The cathode of claim 13, wherein the secondary ionomer is present in a weight ratio relative to platinum alloy in a range of 2.5:1 to 2.6: 1.

20. A polymer electrolyte fuel cell comprising the cathode of claim 13.

Technical Field

The present disclosure relates generally to fuel cells and, more particularly, to improved catalysts for oxygen reduction reactions in fuel cells.

Background

The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

Fuel Cell Vehicles (FCV) Polymer Electrolyte Membrane Fuel Cells (PEMFCs) provide power. PEMFCs account for a significant portion of the cost of an FCV drivetrain, and therefore an increase in PEMFC power efficiency is an important criterion for improving the economic viability of an FCV.

The Oxygen Reduction Reaction (ORR) occurring at the cathode of the PEMFC has relatively slow chemical kinetics and thus constitutes an obstacle to cell performance. Octahedral platinum alloy catalysts have been shown to have improved performance, at least in part due to the structural manifestation of optimal surface facets. Even with the use of octahedral Pt alloy catalysts, additional improvements are needed.

Ionic liquids have been investigated as non-aqueous reaction media for electrochemical applications because of their low volatility, wide electrochemical window, good ionic conductivity and good chemical stability. The use of ionic liquids as ORR promoters provides a large improvement in specific and mass activity, but additional improvements remain to be developed.

Accordingly, it is desirable to provide an improved combination of ionic liquid and metal catalyst for enhancing the activity of catalyzing ORR in PEMFCs.

Disclosure of Invention

This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

In various aspects, the present teachings provide an Oxygen Reduction Reaction (ORR) catalyst. The ORR catalyst includes octahedral nanoparticles that include a platinum alloy having platinum, nickel, and copper (Pt-Ni-Cu). The ORR catalyst also includes a secondary ionomer (secondary ionomer) in contact with the octahedral nanoparticles, the secondary ionomer comprising 1-methyl-2, 3,4,6,7, 8-hexahydro-1H-pyrimido [1,2-a ]]Pyrimidin-9- ium 1,1,2,2,3,3,4,4, 4-nonafluorobutane-1-sulfonate ([ MTBD)][C₄F₉SO₃])。

In other aspects, the present teachings provide a cathode for oxygen reduction. The cathode includes a cathode current collector. The cathode also includes octahedral nanoparticles comprising a platinum alloy having platinum, nickel, and copper (Pt-Ni-Cu). The cathode additionally includes a secondary ionomer in contact with the octahedral nanoparticles, the secondary ionomer comprising 1-methyl-2, 3,4,6,7, 8-hexahydro-1H-pyrimido [1,2-a ]]Pyrimidin-9- ium 1,1,2,2,3,3,4,4, 4-nonafluorobutane-1-sulfonate ([ MTBD)][C₄F₉SO₃])。

Further areas of applicability, as well as various methods of enhancing the disclosed technology, will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

Drawings

The present teachings will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1A shows [ MTBD ] used in ionic liquids of the present teachings]⁺And [ C₄F₉SO₃]^-A chemical line graph of the ion;

FIG. 1B shows an NMR spectrum of an ionic liquid formed from the ions of FIG. 1A;

FIG. 2A is a cyclic voltammogram across a potential window of 0.05V to 1.0V for an electrochemical cell having an octahedral Pt-Cu-Ni/C cathode catalyst, without and with the ionomer of FIG. 1;

FIG. 2B shows a linear sweep voltammogram across a potential window of 0.05V to 1.0V for the electrochemical cell of FIG. 2A;

fig. 2C shows calculated specific and mass activities for the electrochemical cells of fig. 2A and 2B, relative to RHE at 0.9V, and calculated across a potential window of 0.05V to 1.0V;

FIG. 3A is a cyclic voltammogram across a potential window of 0.05V to 1.2V for an electrochemical cell with a cathode catalyst of octahedral Pt-Cu-Ni/C, without and with the ionomer of FIG. 1;

FIG. 3B shows a linear sweep voltammogram across a potential window of 0.05V to 1.2V for the electrochemical cell of FIG. 2A; and

fig. 3C shows the calculated specific activity and mass activity for the electrochemical cells of fig. 2A and 2B, relative to RHE at 0.9V, and calculated across a potential window of 0.05V to 1.2V.

It should be noted that for the purpose of describing certain aspects, the drawings set forth herein are intended to illustrate the general features of the methods, algorithms, and apparatus of the present technology. These figures may not accurately reflect the features of any given aspect, and are not necessarily intended to define or limit particular embodiments within the scope of the present technology. Moreover, certain aspects may include features from combinations of figures.

Detailed Description

The present teachings provide improved fuel cell catalysts for oxygen reduction reactions that are suitable for improving the efficiency of Polymer Electrolyte Membrane Fuel Cells (PEMFCs). The result described below is that PEMFCs utilizing the disclosed catalyst have better activity at the cathode compared to those utilizing prior art catalysts.

The catalysts of the present disclosure include octahedral Pt-Ni-Cu alloys impregnated with Ionic Liquids (IL). In particular, despite having octahedral Pt₂Previous catalysts of CuNi nanoparticles have been shown to be the most stable andone of the active known catalysts, but having impregnation with a hydrophobic ionic liquid (1-methyl-2, 3,4,6,7, 8-hexahydro-1H-pyrimido [1,2-a ]]Pyrimidin-9- ium 1,1,2,2,3,3,4,4, 4-nonafluorobutane-1-sulfonate ([ MTBD)][C₄F₉SO₃]) Pt as Secondary ionomer₂The catalyst of the present invention of CuNi nanoparticles has better specific activity and mass activity.

Accordingly, a catalyst composition for catalyzing ORR (otherwise known as ORR catalyst) in PEMFCs is disclosed. The catalyst composition includes platinum alloy nanoparticles. In some embodiments, nanoparticles of platinum alloys may be mixed with particles of other materials (e.g., carbon). In particular embodiments, the platinum alloy includes an alloy of platinum, nickel, and copper (Pt-Ni-Cu). In some such cases, the molar ratio of nickel to copper in the alloy may be in the range of 1:2 to 2:1, and in some particular cases may be 1: 1. The molar ratio of platinum to nickel in the alloy may be in the range of 1:1 to 4:1 in some cases, and may be 2:1 in some particular cases. In some cases, the molar ratio of platinum to nickel to copper in the alloy may be 2:1:1, represented by the formula Pt₂NiCu. It is understood that formula Pt₂Alloys of NiCu may have some minor variation from the stoichiometric ratio; for example, with the exact formula Pt₅₀Ni₂₅Cu₂₄Can be considered as approximate Pt₂NiCu alloy.

In general, it is preferred that the Pt-Ni-Cu nanoparticles have a uniform distribution of platinum, nickel, and copper throughout the nanoparticles. The uniformity of this distribution can be measured, for example, by using bragg's law and the near equivalence of lattice parameters obtained using vignette's law. In many embodiments, the Pt-Ni-Cu may have a face centered cubic (fcc) unit cell, and the nanoparticles may have an octahedral morphology.

In some embodiments, the particles of catalytic metal may have a specific surface area of at least 10m²Per g, or 20m²Per g, or 30m²Per g, or 40m²Per g, or 50m²Per g, or 60m²Per g, or 70m²Per g, or 80m²Per g, or 90m²Per g, or 100m²(ii) in terms of/g. In some embodiments, the catalystThe particles of metallised metal will be nanoparticles having an average maximum size as follows: less than 100nm, or less than 90nm, or less than 80nm, or less than 70nm, or less than 60nm, or less than 50nm, or less than 40nm, or less than 30nm, or less than 20nm, or less than 10 nm. In some embodiments, the catalyst composition will include platinum alloy nanoparticles having an average largest dimension of 2-5 nm. In some embodiments, the particles of catalytic metal will comprise porous particles.

The catalyst compositions of the present disclosure include a secondary ionomer in contact with platinum alloy nanoparticles. The secondary ionomer comprises ionic liquid, 1-methyl-2, 3,4,6,7, 8-hexahydro-1H-pyrimido [1,2-a ]]Pyrimidin-9- ium 1,1,2,2,3,3,4,4, 4-nonafluorobutane-1-sulfonate ([ MTBD)][C₄F₉SO₃]). FIG. 1 shows Ionic liquid-forming [ MTBD ]]⁺And [ C₄F₉SO₃]^-Line graph of the ions. When contacted with particles of catalytic metal, [ MTFD ]][C₄F₉SO₃]ORR efficiency and catalyst stability are improved, as discussed further below. A catalyst comprising catalytic metal particles in contact with an ionic liquid will be referred to hereinafter as a secondary ionomer catalyst. In certain exemplary embodiments discussed herein, the solid catalyst will comprise a mixture of platinum and carbon particles. When with [ MTBD ]][C₄F₉SO₃]When contacted, such an exemplary catalyst will alternatively be referred to as Pt/C- [ MTBD][C₄F₉SO₃]. In some embodiments, the catalyst composition may also include a polymeric ionomer, such as Nafion, in contact with the solid catalyst^TM。

In some embodiments, the catalyst composition of the present disclosure will have an MTBD][C₄F₉SO₃]Present in a weight ratio relative to the platinum alloy in the range of 1.25:1 to 3.85: 1. In some embodiments, the catalyst composition of the present disclosure will have an MTBD][C₄F₉SO₃]Present in a weight ratio ranging from 2:1 to 3:1 with respect to the platinum alloy. In some embodiments, the catalyst composition of the invention will have an [ MTBD][C₄F₉SO₃]Which isIs present in a weight ratio relative to the platinum alloy in the range of 2.5:1 to 2.6: 1. In some embodiments, the catalytic metal particle will be coated with [ MTBD ]][C₄F₉SO₃]Is completely coated, and in other embodiments, the catalytic metal particles will be coated with [ MTBD ]][C₄F₉SO₃]And (4) partially coating. In some embodiments, the catalytic metal particles will be porous and will be impregnated with MTBD][C₄F₉SO₃]。

[ MTBD ] constituting the disclosed ionic liquids]Cation and [ C₄F₉SO₃]The anion is shown in fig. 1A, while fig. 1B shows the NMR and NMR spectra of the ionic liquid, confirming its synthesis and purity.

Although not shown here, for [ MTBD ]][C₄F₉SO₃]And four comparative ionic liquids: MTBD [ beta]、MTBD[TFSI]、[MTBD][C₂F₅OC₂F₄SO₃]And [ MTBD ]][C₆F₁₃SO₃]And 0.1M HClO₄Measuring O at room temperature at pressures up to 45 bar₂Solubility. A good linear relationship was found between pressure and mole fraction and O at 1 bar was extrapolated from the figure₂Molar fraction ([ O ]₂]). The diffusion coefficient (D) is calculated using one-dimensional mass diffusion according to equation 1.

Wherein the initial conditions are as follows: c ═ C₀When t is 0, and 0<z<L; boundary conditions: c ═ C_sWhen t is>0, z is 0, and

wherein C is O in IL₂Concentration; c₀Is O in IL₂An initial uniform concentration, and an initial value of zero; c_sIs the saturation concentration; l is the depth of the ionic liquid in the sample container; d is the diffusion coefficient assumed to be constant. Determining the spatial average O according to equation 2₂Concentration of (<C>) The analytical solution of (2).

Wherein

Disclosed [ MTBD ]][C₄F₉SO₃]O of ionic liquids and of contrast substances₂The diffusion properties are summarized in table 1. Note that [ MTBD ]][C₂F₅OC₂F₄SO₃]、[MTBD][C₆F₁₃SO₃]、[MTBD][C₄F₉SO₃]Is solid at room temperature, so that it is impossible to directly measure O at room temperature₂And (4) diffusion. But due to [ MTBD ]][C₂F₅OC₂F₄SO₃]、[MTBD][C₆F₁₃SO₃]And [ MTBD ]][C₄F₉SO₃]Soluble in [ MTBD ]][TFSI]Thus, the O in the mixed ionic liquid can be measured₂Solubility and diffusion. Calculating respective O according to the lever rule₂Solubility, as shown in equation 3:

X_O2＝X1*X_O2,1+X2*X_O2,2equation 3

Wherein X_O2Is [ O ] in a mixture of ionic liquids₂]X1 and X2 are the mole fractions of the respective IL in the gas-free mixture, X_O2,1And X_O2,2Is [ O ] in pure respective IL₂]. With respect to the diffusion coefficients of those solid IL, elevated temperatures are required to reach the liquid phase, so the diffusion coefficients are reported at 60 ℃.

Fig. 2A and 2B show cyclic voltammetry and linear sweep voltammetry curves for PEMFCs having an exemplary catalyst of the present disclosure across a potential window of 0.05V to 1.0V. The catalysts of the PEMFC of fig. 2A and 2B include octahedral Pt₂CuNi alloy nanoparticles mixed with carbon particles, the alloy nanoparticles either directly with the disclosed ionic liquids [ MTBD][C₄F₉SO₃]Either not in contact with the ionic liquid. Across a potential window (phase) of 0.05V to 1.0VFor reversible hydrogen electrode [ RHE]) The voltammograms of fig. 2A and 2B were measured. The electrochemically active surface area (ECSA) without ionic liquid and with ionic liquid is very similar: 41 and 37m respectively²(ii) Pt in g. Specific Activity (SA) and Mass Activity (MA) increased 67% and 52% respectively after IL incorporation.

Fig. 2C shows the calculated specific and mass activities of the two PEMFCs of fig. 2A and 2B. Relative RHE at 0.9V. It will be noted that use is made of

The Levich equation calculates MA, and MA ═ SA × ECSA. As shown in fig. 2C, ORR catalysts contacted with the disclosed ionic liquids have better specific activity than catalysts without ionic liquids.

Fig. 3A and 3B show cyclic voltammetry and linear sweep voltammetry curves for the same PEMFC as in fig. 2A and 2B, but across a potential window of 0.05V to 1.2V versus RHE. Very similar ECSA values were obtained, 45 and 43m respectively²/gPt, no ionic liquid and with ionic liquid. SA and MA increased 77% and 69% after IL incorporation, respectively.

Figure 3C shows the specific activity and mass activity calculated from the curves of figure 3. SA and MA increased 77% and 69% after IL incorporation, respectively.

It should be understood that equation 4 generally describes the rate of ORR:

where n is the number of electrons transferred, F is the Faraday constant, K is the chemical rate constant, (1- θ) is the available surface, β is the symmetry factor, E is the applied potential, and ω is the energy parameter of the Temkin isotherm. Therefore, equation 4 indicates that the current density is proportional to the oxygen concentration.

Because of [ MTBD ]][C₄F₉SO₃]Ionic liquids have appreciable oxygen solubility and are expected to increase the oxygen concentration at the platinum alloy surface, so it is further expected that this will produce a proportional increase in current density. The results shown in FIGS. 2C and 3C demonstrate the results obtained from the above-described results[MTBD][C₄F₉SO₃]The mass activity resulting from the ionic liquid contacting the platinum alloy nanoparticles is improved. It should be noted that the current density depends not only on the concentration of the reactant (C) near the surface but also on the thickness (δ) and diffusion coefficient (D) of the diffusion layer. Therefore, the product of C and D can be considered as an important parameter for judging the gas diffusion efficiency through the solid electrolyte. As can be seen from Table 1, the oxygen diffusion coefficient (D) is considered to be a factor_O2) Much lower, CxD final product did not show a specific aqueous electrolyte (0.1M HClO in this work)₄) To higher values. Therefore, it can be speculated that comparable oxygen molar fluxes may be one of the factors limiting the significant enhancement of ORR activity caused by the presence of secondary ionomers.

TABLE 1 solubility and diffusion coefficient of oxygen in IL used in this study

Note [ MTBD ]][C₂F₅OC₂F₄SO₃]The melting point of (B) was-59 ℃. Temperatures above 70 ℃ are required to completely melt.

The invention is further illustrated with respect to the following examples. It is to be understood that these examples are provided to illustrate specific embodiments of the present invention and are not to be construed as limiting the scope of the invention.