Fuel cells are becoming more and more popular in the production of fuel cell vehicles (FCV), such as automobiles, forklifts, buses, and airplanes, due to their high efficiency and environmental protection characteristics in the power generation process. However, the high cost of producing fuel cell catalysts hinders the large-scale production and large-scale application of fuel cell vehicles.
The fuel cell catalyst is usually made of platinum (Pt) or Pt alloy, and the transition metal is thinly coated on the porous carbon support. Pt is an ideal catalytic material because it can withstand acidic conditions and effectively increase the rate of chemical reactions. But the price is expensive and the resource reserves are insufficient. Therefore, there is an urgent need to develop and screen new catalysts with low Pt content and high catalytic activity for the commercialization of fuel cells.
In a scientific paper published on October 22, 2021, researchers from the Chinese Academy of Sciences (CAS) University of Science and Technology of China (USTC) reported a high-temperature sulfur anchoring method that successfully synthesized small-sized Pt intermetallic compounds with Nanoparticle (i-NPs) catalyst with ultra-low platinum loading and high-quality activity. They also established an i-NPs library containing 46 kinds of Pt nanoparticles (NPs) to screen cheap and durable electrode materials and systematically explore the structure-activity relationship of i-NPs.
I-NPs have received extensive attention due to their unique atomic ordering properties and excellent catalytic performance in many chemical reactions. However, during the synthesis of i-NPs, the inevitable metal sintering at high temperatures is undesirable, which can lead to larger crystallites. As a result, the specific surface area is reduced, the catalytic activity of the material is reduced, and finally the utilization rate of platinum is reduced, thereby greatly increasing the cost of the fuel cell.
The research team led by Liang Haiwei cleverly used the powerful platinum-sulfur chemical interaction. They prepared Pt intermetallic compounds on a sulfur-doped carbon (SC) support to inhibit the sintering of NPs at high temperatures, and they were able to obtain atomically ordered i-NPs with an average size of <5 nm. The SC carrier exhibits such excellent anti-sintering ability. The researchers obtained Pt NPs with an average diameter of <5 nm after annealing at a high temperature of up to 1000°C. However, after performing the same annealing process on a commercial carbon black support, severe Pt sintering was observed.
In order to take advantage of the anti-sintering properties, the researchers synthesized 46 kinds of small Pt-based i-NPs on the SC carrier and established an i-NPs library. The spectral characterization was measured, and the results confirmed the strong chemical interaction of the Pt-S bond. In addition, X-ray diffraction (XRD) results show that the i-NPs catalysts in the library have a high degree of order and small size, which is consistent with the statistical analysis observed by the high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM).
"Based on the i-NPs library, we can systematically study the relationship between the structure and performance of the catalyst," Liang said. "Sufficient samples help us screen out highly efficient catalysts that are expected to greatly reduce the cost of fuel cells." The researchers screened i -NP and applied it to the Proton Exchange Membrane Fuel Cell (PEMFC). These catalysts exhibit excellent electrocatalytic performance for oxygen reduction reactions (ORR). Especially in the H2-air PEMFC, although the Pt loading of i-NPs is 11.5 times lower than that of the Pt/C cathode, the i-NPs catalyst cathode exhibits similar capabilities to the Pt/C cathode.
This work provides a general method for synthesizing platinum alloy catalysts for hydrogen fuel cells. This method brings hope for reducing the amount of Pt used, thereby reducing the cost of fuel cells. "By designing the porous structure and surface functions of the carbon support, the efficiency of the fuel cell can be further improved, thereby accelerating its transition from the laboratory to the public," Liang said.
-This press release is provided by the University of Science and Technology of China
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