The cost of platinum catalysts used in hydrogen fuel cells is very high, which limits their commercialization in electric vehicles. Therefore, scientists are studying alternative catalysts to improve the cost-effectiveness of fuel cells while maintaining the high efficiency of hydrogen fuel cells.
(Source: Argonne National Laboratory)
Because hydrogen fuel cells have a fast hydrogenation rate and high energy density, and will not produce harmful emissions or by-products, more and more researchers are using it as an alternative energy source for vehicles and other applications.
According to foreign media reports, the US Department of Energy (DOE) Argonne National Laboratory (Argonne National Laboratory) recently developed a fuel cell catalyst that does not use platinum, which is a chemical substance that can accelerate important fuel cell reactions. This study has better insights into the mechanisms that make such catalysts more efficient, and helps produce more efficient and cost-effective catalysts.
At present, commercial hydrogen fuel cells all need to rely on the redox reaction (ORR), which will break down oxygen molecules into oxygen ions and combine with protons to form water. Such reactions are part of the entire fuel cell process and can convert hydrogen and oxygen in the air into water and electricity. The ORR reaction is relatively slow, which limits the efficiency of the fuel cell and requires a large amount of platinum catalyst.
The researchers said: "At present, the redox reaction is promoted by platinum alloy catalysts, and platinum alloy catalysts are the most expensive part of fuel cell electrodes. If a large-scale sustainable commercialization of fuel cell vehicles is required, the platinum The amount of use, or the use of iron and other abundant and cheap materials on the earth to make a catalyst to replace the platinum catalyst."
(Source: Argonne National Laboratory)
The most promising platinum-free catalyst in the ORR reaction is based on iron, nitrogen and carbon. To make this kind of catalyst, scientists mixed precursors containing these three elements together and heated them at a high temperature of 900 to 1100 degrees Celsius, called "pyrolysis."
After pyrolysis, the iron atoms in the material will combine with four nitrogen atoms and be embedded in a single-atom thick carbon layer-graphene. Each iron atom constitutes an active site, or a site where an ORR reaction may occur. The greater the density of active sites in the material, the higher the efficiency of the electrode.
The researchers conducted an on-site X-ray absorption spectroscopy study at the MR-CAT of the Aggon National Laboratory Advanced Photon Source (APS) Materials Analysis Interview Team to reveal the atomic behavior of the material during pyrolysis. The researchers let X-rays pass through the precursors of iron, nitrogen, and carbon to see which elements would chemically combine and how.
Scientists have discovered that during the pyrolysis of a mixture of iron, nitrogen, and carbon precursors, nitrogen-graphene sites are first formed, and then gaseous iron atoms are inserted into such sites. They also found that by using a doping process, nitrogen is first inserted into carbon, and then iron is introduced into the system during pyrolysis, instead of heating the three components together, a higher density of activity can be produced in the catalyst Location.
In this process, scientists put nitrogen-doped carbon into the furnace, and gaseous iron atoms were inserted into the vacancies of the central positions of the four nitrogen atoms to form active sites. This method avoids the accumulation and burial of iron atoms in the carbon block and increases the number of active sites on the graphene surface.
This research provides scientists with a way to increase the density of active sites in the material. The team will continue to develop more active and stable platinum-free catalysts for use in hydrogen fuel cells. (Author: Yuqiu Yun)
Cylindrical Roller Bearing,High Temperature Cylindrical Bearing,Precision Cylindrical Roller Bearings,Double Row Cylindrical Roller Bearings
Shanghai Yi Kai Cheng bearing Co., LTD , https://www.ykcbearing.com