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A New Catalyst for Fuel Cell
Reduction of PtRu Catalyst Size to 2nm by Addition of Phosphorus |
Hitachi Maxell Ltd. (President and Chief Executive Officer : Norio Akai) developed a quite new technology reducing size of PtRu catalyst*1 for fuel cell to 2nm and improving its dispersion by addition of phosphorus.
PtRu*2 is widely used in catalyst for fuel cell. In general, increase of reaction area of catalyst by reducing its size is effective to improve catalytic activity. It is well known that the size of catalyst becomes fine by using carbon supports having large specific surface area*3. However, many micropores exist in such carbon supports and the catalysts buried in the micropores can not oxidize methanol and hydrogen. Therefore, there was trade-off between reducing the size of catalyst and improving efficiency in utilization of expensive catalyst.
Maxell developed a quite new technology reducing size of PtRu catalyst to 2nm by addition of non-metallic element of phosphorus, which is based on electroplating technology over 20 years. Phosphorus has large binding energies with Pt and Ru, therefore, metallic bonds of Pt and Ru are terminated by addition of phosphorus resulting in size reduction of PtRu catalyst. The size of PtRuP catalyst is retained in 2nm regardless with the specific surface area of carbon supports.
Sharp size distribution is another characteristics of PtRuP catalyst. In conventional synthesis of catalyst, the size distribution tends to be wide, that is, 2 to 10nm. However, addition of phosphorus suppresses the size dispersion and PtRuP catalyst with the size distribution of 2.0±0.5nm can be obtained.
Maximum power density of direct methanol fuel cell using conventional PtRu catalyst was 38mW/cm2. On the other hand, maximum power density of 64mW/cm2 (about 1.7 times larger than that of conventional PtRu catalyst) was achieved using the new PtRuP catalyst*4.
Maxell advances R&D with the aim of applying PtRuP catalyst to solid polymer fuel cell and direct methanol fuel cell.
| *1: |
Reduces activation energy of chemical reaction and raises reaction speed. |
| *2: |
Pt catalyst is poisoned by CO. In 1960', it was found that addition of Ru was effective to suppress the poisoning and PtRu alloy catalyst is widely used. |
| *3: |
Catalyst used in fuel cell is supported on conductive carbon materials to improve its dispersion. |
| *4: |
Maxell's data. Power density of direct methanol fuel cell was measured using 2nm of PtRuP catalyst supported on conductive carbon black with specific surface area of 254m2/g. |
・Features
| 1. |
Reduction of PtRu catalyst size to 2nm by addition of phosphorus. |
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Size of PtRu catalyst was reduced to 2nm by addition of phosphorus, which raises specific surface area of catalyst and improves catalytic activity. |
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| 2. |
Retaining size of PtRuP catalyst in 2nm regardless with specific surface area of carbon supports. |
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It was difficult to reduce size of catalyst using carbon supports with small specific surface area. In PtRuP catalyst, the size is retained in 2nm regardless with the specific area of carbon supports, which makes it possible to improve efficiency in utilization of catalyst keeping high catalytic activity. |
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| 3. |
Sharp size distribution of 2.0±0.5nm |
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In PtRuP catalyst, sharp size distribution of 2.0±0.5nm is obtained compared with conventional PtRu catalyst of 2 to 10nm. |
・Transmission Electron Micrograph Images of PtRuP and PtRu Catalysts.
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| PtRuP Catalyst |
PtRu Catalyst |
・Power Density Characteristics.
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