Catalyst for solid polymer fuel cell and method for manufacturing the same
09960431 ยท 2018-05-01
Assignee
Inventors
Cpc classification
Y02E60/50
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
H01M4/8892
ELECTRICITY
H01M4/8842
ELECTRICITY
International classification
Abstract
Provided is a catalyst for solid polymer fuel cell that exhibits excellent initial activity and favorable durability and a method for manufacturing the same. The invention is a catalyst for solid polymer fuel cell which is formed by supporting catalyst particles including platinum, cobalt and manganese on a carbon powder carrier, wherein a composition ratio (molar ratio) among platinum, cobalt and manganese in the catalyst particles is Pt:Co:Mn=1:0.06 to 0.39:0.04 to 0.33, a peak intensity ratio of a CoMn alloy appearing in the vicinity of 2=27 is 0.15 or less with respect to a main peak appearing in the vicinity of 2=40 in X-ray diffraction analysis of the catalyst particles, and a fluorine compound having a CF bond is supported at least on the surface of the catalyst particles. The amount of the fluorine compound supported is preferably from 3 to 20% with respect to the entire mass of the catalyst.
Claims
1. A catalyst for solid polymer fuel cell having catalyst particles comprising platinum, cobalt and manganese supported on a carbon powder carrier, wherein a composition ratio (molar ratio) among platinum, cobalt and manganese in the catalyst particles is Pt:Co:Mn=1:0.06 to 0.39:0.04 to 0.33, a peak intensity ratio of a CoMn alloy appearing in the vicinity of 2=27 is 0.15 or less with respect to a main peak appearing in the vicinity of 2=40 in X-ray diffraction analysis of the catalyst particles, and a fluorine compound having a CF bond is supported at least on a surface of the catalyst particles, wherein a peak ratio of a CoPt.sub.3 alloy and a peak ratio of a MnPt.sub.3 alloy appearing in the vicinity of 2=32 are each 0.13 or more with respect to a main peak appearing in the vicinity of 2=40 in X-ray diffraction analysis of the catalyst particles.
2. The catalyst for solid polymer fuel cell according to claim 1, wherein the fluorine compound is supported from 3 to 20% by mass with respect to the entire mass of the catalyst.
3. The catalyst for solid polymer fuel cell according to claim 1, wherein the fluorine compound is a fluorine resin or a fluorine-based surface active agent.
4. The catalyst for solid polymer fuel cell according to claim 1, wherein a supporting density of the catalyst particles is from 30 to 70%.
5. The catalyst for solid polymer fuel cell according to claim 2, wherein the fluorine compound is a fluorine resin or a fluorine-based surface active agent.
6. The catalyst for solid polymer fuel cell according to claim 2, wherein a supporting density of the catalyst particles is from 30 to 70%.
7. The catalyst for solid polymer fuel cell according to claim 3, wherein a supporting density of the catalyst particles is from 30 to 70%.
8. A method for manufacturing a catalyst for solid polymer fuel cell, the catalyst defined in claim 1, comprising the steps of: supporting cobalt and manganese on a platinum catalyst having platinum particles supported on a carbon powder carrier; subjecting the platinum catalyst that is formed by the supporting step and supports cobalt and manganese to a heat treatment at from 700 to 1100 C.; and forming a water-repellent layer including a fluorine compound on the catalyst by bringing the catalyst after the heat treatment step into contact with a solution containing the fluorine compound.
9. The method for manufacturing a catalyst for solid polymer fuel cell according to claim 8, comprising the step of: eluting cobalt and manganese on the surface of the catalyst particles by bringing the catalyst after the heat treatment into contact with an oxidizing solution at least one time.
10. The method for manufacturing a catalyst for solid polymer fuel cell according to claim 9, wherein the oxidizing solution is sulfuric acid, nitric acid, phosphorous acid, potassium permanganate, hydrogen peroxide, hydrochloric acid, chloric acid, hypochlorous acid and chromic acid.
11. The method for manufacturing a catalyst for solid polymer fuel cell according to claim 9, wherein a contact treatment with the oxidizing solution is conducted at a treatment temperature of from 40 to 90 C. for a contact time of from 1 to 10 hours.
12. A method for manufacturing a catalyst for solid polymer fuel cell, the catalyst defined in claim 2, comprising the steps of: supporting cobalt and manganese on a platinum catalyst having platinum particles supported on a carbon powder carrier; subjecting the platinum catalyst that is formed by the supporting step and supports cobalt and manganese to a heat treatment at from 700 to 1100 C.; and forming a water-repellent layer including a fluorine compound on the catalyst by bringing the catalyst after the heat treatment step into contact with a solution containing the fluorine compound.
13. A method for manufacturing a catalyst for solid polymer fuel cell, the catalyst defined in claim 3, comprising the steps of: supporting cobalt and manganese on a platinum catalyst having platinum particles supported on a carbon powder carrier; subjecting the platinum catalyst that is formed by the supporting step and supports cobalt and manganese to a heat treatment at from 700 to 1100 C.; and forming a water-repellent layer including a fluorine compound on the catalyst by bringing the catalyst after the heat treatment step into contact with a solution containing the fluorine compound.
14. A method for manufacturing a catalyst for solid polymer fuel cell, the catalyst defined in claim 1, comprising the steps of: supporting cobalt and manganese on a platinum catalyst having platinum particles supported on a carbon powder carrier; subjecting the platinum catalyst that is formed by the supporting step and supports cobalt and manganese to a heat treatment at from 700 to 1100 C.; and forming a water-repellent layer including a fluorine compound on the catalyst by bringing the catalyst after the heat treatment step into contact with a solution containing the fluorine compound.
15. A method for manufacturing a catalyst for solid polymer fuel cell, the catalyst defined in claim 4, comprising the steps of: supporting cobalt and manganese on a platinum catalyst having platinum particles supported on a carbon powder carrier; subjecting the platinum catalyst that is formed by the supporting step and supports cobalt and manganese to a heat treatment at from 700 to 1100 C.; and forming a water-repellent layer including a fluorine compound on the catalyst by bringing the catalyst after the heat treatment step into contact with a solution containing the fluorine compound.
16. The method for manufacturing a catalyst for solid polymer fuel cell according to claim 10, wherein a contact treatment with the oxidizing solution is conducted at a treatment temperature of from 40 to 90 C. for a contact time of from 1 to 10 hours.
Description
BRIEF DESCRIPTION OF THE DRAWING
(1)
DESCRIPTION OF EMBODIMENTS
First Embodiment
(2) A ternary catalyst of PtCoMn having a water-repellent layer was manufactured and subjected to the evaluation on the initial catalytic activity and durability. The basic process for manufacturing the catalyst is as follows.
(3) [Supporting of Catalyst Metal]
(4) A commercially available platinum catalyst was prepared and cobalt and manganese were supported on this. As the platinum catalyst, 5 g (2.325 g (11.92 mmol) in terms of platinum) of a platinum catalyst having a carbon fine powder (specific surface area of about 900 m.sup.2/g) as the carrier and a platinum supporting rate of 46.5% by mass was prepared. This platinum catalyst was immersed in a metal salt solution obtained by dissolving cobalt chloride (CoCl.sub.2.6H.sub.2O) and manganese chloride (MnCl.sub.2.4H.sub.2O) in 100 mL of ion exchanged water and stirred using a magnetic stirrer. Thereafter, 500 mL of a sodium borohydride (SBH) solution having a concentration of 1% by mass was added dropwise to this solution and stirred to conduct the reduction treatment, whereby cobalt and manganese were supported on the platinum catalyst. After that, the catalyst thus obtained was filtered, washed and dried.
(5) [Heat Treatment for Alloying]
(6) The catalyst supporting the catalyst metals was subjected to the heat treatment for alloying. In the present embodiment, the heat treatment was conducted at the heat treatment temperature of 900 C. for 30 minutes in 100% hydrogen gas.
(7) [Treatment with Oxidizing Solution]
(8) The catalyst after the heat treatment for alloying was treated with an oxidizing solution. This treatment was conducted as follows. The catalyst after the heat treatment was treated in a 0.2 mol/L aqueous solution of sulfuric acid at 80 C. for 2 hours, then filtered, washed and dried. After that, the catalyst was treated in a 1.0 mol/L aqueous solution of nitric acid (dissolved oxygen of 0.01 cm.sup.3/cm.sup.3 (in terms of STP)) at 70 C. for 2 hours, then filtered, washed and dried.
(9) [Formation of Water-Repellent Layer]
(10) Subsequently, the ternary catalyst of PtCoMn thus manufactured was treated with a fluorine compound solution to form a water-repellent layer. As the fluorine compound solution, a solution obtained by dissolving 20 mL of a commercially available fluorine resin material (trade name: EGC-1700, manufactured by Sumitomo 3M Limited, fluorine resin content of 1 to 3%)) in 20 mL of hydrofluoroether (trade name: HFE-7100 manufactured by Sumitomo 3M Limited) of the solvent was used. In this treatment, 5 g of the catalyst was immersed in the above fluorine compound solution and stirred at 60 C. for 5 hours and then kept at 60 C. in a dryer to evaporate the solvent until the solvent completely disappeared. The fluorine compound was supported on the catalyst by this treatment, whereby a catalyst having a water-repellent layer was manufactured (Example 1).
Example 2
(11) As the fluorine compound solution, a commercially available fluorinated ethylene propylene resin: (trade name: Teflon (registered trademark) FEP-120J, manufactured by Du Pont-Mitsui Fluorochemicals Co., Ltd.) was used. In this treatment, 3.4 g of the catalyst was immersed in the above fluorine compound solution and stirred at 60 C. for the night and then kept at 60 C. in a dryer to evaporate the solvent until the solvent completely disappeared. After that, the catalyst was heated at 340 C. for 30 minutes in N.sub.2. The fluorine compound was supported on the catalyst by this treatment, whereby a catalyst having a water-repellent layer was manufactured.
Reference Example 1
(12) A catalyst in which the ternary catalyst of PtCoMn after the heat treatment was not treated with a fluorine compound solution in the catalyst manufacturing process described above was prepared. In other words, a catalyst on which a water-repellent layer was not formed while in which the composition ratio among platinum, cobalt and manganese and the state of the alloy phases were optimized was prepared.
Comparative Example 1
(13) In addition, as a Comparative Example to Example 1, a conventional PtCo catalyst was manufactured without adding manganese. This Comparative Example was manufactured by immersing a platinum catalyst in a solution containing only a cobalt salt.
Comparative Example 2
(14) A ternary catalyst of PtCoMn was manufactured by simultaneously supporting platinum, cobalt and manganese in the supporting step of the catalyst metals. A carbon carrier (specific surface area of about 900 m.sup.2/g) was prepared by 5 g, and this was immersed in a metal salt solution obtained by dissolving predetermined amounts of a Pt dinitrodiamine nitrate solution (Pt(NO.sub.2).sub.2(NH.sub.3).sub.2), cobalt chloride (CoCl.sub.2.6H.sub.2O) and manganese chloride (MnCl.sub.2.4H.sub.2O) in 100 mL of ion exchanged water and stirred using a magnetic stirrer. Thereafter, 500 mL of a sodium borohydride (SBH) solution having a concentration of 1% by mass was added dropwise to this solution and stirred to conduct the reduction treatment, whereby platinum, cobalt and manganese were supported on the carbon carrier. After that, the catalyst thus obtained was filtered, washed, dried, and alloyed by being subjected to the heat treatment at 900 C. for 30 minutes under a stream of hydrogen.
(15) For the catalyst (Example 1) subjected to the treatment with a fluorine compound solution, the amount of the fluorine compound supported was measured as well as for the catalysts manufactured above, the ratio among platinum, cobalt and manganese in the catalyst particles was measured. These measurements were carried out as follows. The ICP analysis of the catalysts was conducted, the mass ratios of the respective metals and the carbon carrier were measured, and the values were calculated based on the measured values of those.
(16) In addition, the X-ray diffraction analysis was conducted for the respective catalysts and the composition of the catalyst particles was investigated. JDX-8030 manufactured by JEOL Ltd. was used as the X-ray diffraction apparatus. The samples were made into a fine powder form and introduced into a glass cell, and the analysis was conducted using a Cu (k ray) as the X-ray source at a tube voltage of 40 kV, a tube current of 30 mA, 2=20 to 90, a scanning speed of 7/min and a step angle of 0.1.
(17)
(18) Next, the catalysts of Examples 1 and 2, Reference Example 1 and Comparative Examples 1 and 2 were subjected to the initial performance test. This performance test was conducted by measuring the mass activity. A single cell was used in the experiment, and a membrane electrode assembly (MEA) in which a proton-conducting polymer electrolyte membrane was sandwiched between a cathode electrode and an anode electrode having an electrode area of 5 cm5 cm=25 cm.sup.2 was fabricated and evaluated. As a pre-treatment, a current/voltage curve was created under the conditions of hydrogen flow rate=1000 mL/min, oxygen flow rate=1000 mL/min, cell temperature=80 C., anode humidification temperature=90 C. and cathode humidification temperature=30 C. After that, the mass activity was measured as the main measurement. The test method was as follows. The current value (A) at 0.9 V was measured, the current value (A/g-Pt) per 1 g of Pt was determined from the weight of Pt coated on the electrode, and the mass activity was calculated. The results are shown in Table 1. Meanwhile, in Table 1, the peak intensity ratio of the CoMn alloy (in the vicinity of 2=27) calculated from the X-ray diffraction patterns of the respective catalysts of
(19) TABLE-US-00001 TABLE 1 Mass Amount of Peak intensity Activity*.sup.1 fluorine ratio*.sup.3 (A/g-pt compound MnPt.sub.3 + PT:Co:Mn at 0.9 V) supported*.sup.2 CoMn CoPt.sub.3 Example 1 1:0.26:0.09 1.16 19.6% 0.10 0.26 Example 2 1:0.29:0.07 1.06 18.7% 0.07 0.13 Reference 1:0.26:0.09 1.13 .sup.0.10*.sup.4 .sup.0.26*.sup.4 Example 1 Compar- 1:0.38:0 1.0 0.11 ative Example 1 Compar- 1:0.25:0.36 0.93 0.33 0.28 ative Example 2 *.sup.1It is a relative comparison when taking Comparative Example 1 (PtCo catalyst) as 1.0. *.sup.2it is a value with respect to the entire mass of catalyst. *.sup.3It is an intensity ratio with respect to the main peak in the vicinity of 2 = 40. *.sup.4Reference Example 1 differs from Example 1 only in the presence or absence of a fluoride and thus there is no difference in the X-ray pattern between them.
(20) From Table 1, all of the ternary catalysts of PtCoMn according to Examples and Reference Example exert favorable initial activity when taking the PtCo catalyst of Comparative Example 1 as the reference. This is considered to be due to the properly adjusted composition (amount of CoMn phase formed) of the catalyst particles as well as addition of manganese. Examples supporting a fluorine compound exhibit a little superior initial activity than Reference Example but the difference is not significant when Examples and Reference Example are compared to each other. In addition, it has been confirmed that the catalyst in a case in which a great amount of the CoMn phase are formed as in Comparative Example 2 is inferior to the PtCo catalyst (Comparative Example 1) in initial activity.
(21) Next, Examples 1 and 2, Reference Example 1 and Comparative Example 1 were subjected to a durability test for the durability evaluation. As the durability test, a cathode electrode (air electrode) was manufactured from the catalyst, a fuel cell was then configured and subjected to the accelerated degradation test to sweep the cell potential of the cathode with a triangular wave, and the power generation properties of the fuel cell after degradation were measured. As the accelerated degradation, the surface of the catalyst particles was cleaned by being swept between 650 and 1050 mV at a sweep rate of 40 mV/s for 20 hours and then degraded by being swept between 650 and 1050 mV at a sweep rate of 100 mV/s for 20 hours, 40 hours and 68 hours. The mass activity was measured for the catalyst after degradation under each condition. The evaluation results after this accelerated degradation test are shown in Table 2.
(22) TABLE-US-00002 TABLE 2 Mass Activity*.sup.1 (A/g-pt at 0.9 V) PT:Co:Mn Initial 20 hours 44 hours 68 hours Example 1 1:0.26:0.09 1.16 1.02 0.62 0.48 Example 2 1:0.26:0.09 1.06 0.82 0.66 0.49 Reference 1:0.26:0.09 1.13 0.67 0.46 0.28 Example 1 Comparative 1:0.38:0. 1.0 0.83 0.59 0.37 Example 1 *.sup.1It is a value obtained by taking the PtCo catalyst (Comparative Example 1) before degradation as 1.0.
(23) From Table 2, in the catalysts on which a water-repellent layer is formed according to Examples 1 and 2, a drop in activity after accelerated degradation is suppressed compared to the conventional PtCo catalyst (Comparative Example 1). Meanwhile, the catalyst which does not have a water-repellent layer according to Reference Example 1 is inferior to the PtCo catalyst according to Comparative Example 1. Upon discussing the factor of this, the reason is considered to be because the elution of the metals (cobalt and/or manganese) more easily proceeds than the elution of the PtCo catalyst under the harsh potential condition (650 to 1050 mV) in this durability test. In this regard, it can be confirmed that the investigation considering not only the initial activity but also the durability is important upon the development of a catalyst since Reference Example 1 exhibits excellent initial activity (Table 1).
Second Embodiment
(24) Here, the catalyst was manufactured by the same process as the first embodiment with the amount of the fluorine compound supported changed and subjected to the evaluation on the initial activity. The amount of the fluorine compound supported was changed by adjusting the amount of the fluorine resin material to be dissolved in the solvent for the fluorine compound solution. The treatment conditions other than that were the same as the first embodiment. Thereafter, the mass activity was measured in the same manner as in the first embodiment. The results are shown in Table 3.
(25) TABLE-US-00003 TABLE 3 Mass Amount of fluorine Activity*.sup.1 (A/g-pt compound PT:Co:Mn at 0.9 V) supported*.sup.2 Example 1 1:0.26:0.09 1.16 19.6% Example 3 1:0.33:0.07 1.18 8.6% Example 4 1:0.31:0.07 0.76 24.5% Example 5 1:0.31:0.07 0.45 36.7% Comparative 1:0.39:0 1.0 Example 1 *.sup.1It is a relative comparison when taking Comparative Example 1 (PtCo catalyst) as 1.0. *.sup.2It is a value with respect to the entire mass of catalyst.
(26) From the first embodiment, it has been confirmed that the effect of supporting a fluorine compound is exhibited to secure durability but not to improve the initial activity. From Table 3, it can be seen that the initial activity decreases when the amount of the fluorine compound supported is more than 20% to be excessive.
INDUSTRIAL APPLICABILITY
(27) According to the invention, it is also possible to achieve an improvement in durability of an electrode catalyst for solid polymer fuel cell while improving the initial power generation properties as the electrode catalyst. The invention contributes to the spread of a fuel cell and is consequently to be a foundation of the environmental problem solution.