At the two sessions this year, hydrogen energy was included in the government work report for the first time, which means that the country will vigorously promote the development of new hydrogen energy industries. Clean, efficient and non-polluting hydrogen energy will be the star of tomorrow, such as fuel cells, while the country Will be withdrawn in 2020.
For hydrogen energy, the major problem currently being solved in various countries is how to produce hydrogen cheaply and on a large scale. The most common way at present is to generate oxygen through water cracking to form hydrogen, but this process is not efficient and limits the overall For energy conversion efficiency, there is an urgent need for more efficient catalyst materials.
According to news from Zhejiang University, researcher Hou Yang, who was selected by the “100 Persons Program†of the School of Chemical Engineering and Bioengineering of Zhejiang University, designed and developed a single-atom OER catalyst through the method of bionics to anchor highly dispersed nickel single atoms On the nitrogen-sulfur doped porous nano-carbon substrate, it is used for high-efficiency electro / photoelectric catalytic water splitting to analyze oxygen reaction. This achievement was reported online by the well-known academic journal Nature Communications.
Atomic disperse nickel-nitrogen-sulfur electricity / photoelectric catalytic water splitting to analyze oxygen
To design a new type of catalyst, Hou Yang's group began to analyze the atomic structure of the material. The research team found that there is a metal-nitrogen coordinated porphyrin structure in the chloroplast, which can collect solar energy, use photosynthesis oxidation reaction to decompose water, and release oxygen. "In recent years, carbon materials such as nickel, cobalt, iron and other transition metals coordinated with nitrogen are considered to be strong candidates for catalysts in the OER reaction process." Hou Yang introduced, so they further found nickel-nitrogen coordination Carbon material. In this special structure, the four nitrogen atoms "pull" the metal nickel atoms, attracting hydroxide ion adsorption, reducing the difficulty of conversion in various intermediate links, and thus accelerating the precipitation of oxygen. "Compared with the hydrogen evolution reaction, oxygen evolution is a four-electron reaction, which is relatively more difficult to prepare. When oxygen is produced, the problem of hydrogen production is solved."
In order to further accelerate the catalytic efficiency, Hou Yang's group continued to improve the nickel-nitrogen coordination structure. Hou Yang made an analogy. The structure of the nickel-nitrogen coordinated doped carbon material is relatively stable, as if four people of equal strength each exerted a uniform force in one direction. Therefore, Hou Yang's group proposed whether one of the nitrogen atoms could be replaced, just like a different Hercules, with the proper coordination center for the adsorption of hydroxide ions by nickel atoms and the desorption capacity of subsequent products.
Hou Yang's group used spherical aberration corrected scanning transmission electron microscopy, electron energy loss spectroscopy, X-ray near-edge absorption spectroscopy, and extended X-ray absorption spectroscopy to reveal for the first time that a single nickel atom is anchored in nitrogen-sulfur doped porous nanoparticles. The single-level nickel single atoms dispersed in the carbon catalytic material form a coordination structure with the surrounding 3 nitrogen atoms and 1 sulfur atom and co-doped into the nano-carbon skeleton as the catalytic active site. The theoretical calculation results clarify that the introduction of sulfur atoms optimizes the charge distribution on the surface of nickel-nitrogen-doped nano-carbon, greatly reduces the OER reaction barrier, and thus greatly accelerates the OER reaction kinetics, resulting in its efficient electro / optical Catalytic performance and excellent stability.
"Substituting a single sulfur atom for one nitrogen is just one of the methods. From this, single atoms with different strengths can be selected to enter the nickel-nitrogen coordination structure, breaking the original steady state and forming a new catalyst. A series of catalytic materials laid the foundation. "He said.
Nickel-nitrogen materials are extremely unstable and need to be “anchored†on the carbon substrate. This process is like throwing a heavy anchor from the boat when the boat is docked to prevent the boat from moving. Through process iterations, the nickel monoatomic catalyst supported on the nitrogen-sulfur co-doped porous nanocarbon prepared by the researchers exhibited a unique 2D layered structure with a thickness of approximately 32 nanometers and a length of approximately a few microns. Thanks to the high specific surface area and highly dispersed active sites, this new type of catalyst electrode exhibits excellent electrocatalytic water splitting oxygen activity and stability under alkaline conditions.
The experiment found that the nickel single-atom anchored nitrogen-sulfur doped porous nanocarbon catalyst developed by the research group has a potential reduction of about 5% compared to the commercial iridium-based catalyst widely used in the market. That is to say, the energy to drive the reaction is reduced by 5%, while the cost is reduced by more than 80%, and the stability is greatly improved, showing the potential of industrial-grade electrolytic water to produce hydrogen.
The OER oxygen evolution reaction needs to be driven by electricity or photoelectricity. The research group further selectively deposited the prepared electrocatalyst on the surface of the iron oxide electrode to form an efficient solar-powered water splitting integrated photoanode. "Through this design, the solar energy can be used to generate electrical energy to drive the entire catalytic reaction, saving additional driving power."
OER oxygen evolution reaction is the core process of water cracking devices and metal-air batteries. Talking about future applications, Hou Yang introduced that the new generation of fuel cell vehicles puts an important demand on high energy density, and the hydrogen energy generated by water cracking will play an important role. At the same time, the target of new energy vehicles powered by lithium-sulfur batteries is 500 watt-hours per kilogram (Wh / kg), so that the car can run for a day. To further improve battery efficiency in the future, a new fuel cell, metal-air, is needed, and the OER oxygen evolution reaction is an important part of the oxidation reaction.
Hou Yang also said that this study not only designed and developed an efficient and stable transition metal-nitrogen-sulfur atomic-level electrocatalyst, but also designed how to design low-cost and highly active artificial nitrogen fixation to synthesize ammonia, carbon dioxide high-value utilization and oxygen reduction catalysis The design of the material provides new ideas.
This scientific research work was supported by projects such as the National Natural Science Foundation of China, the Zhejiang Provincial Outstanding Youth Fund, and the Zhejiang University "Hundred People Program" start-up fund. Researchers from the Dresden University of Technology and Central China Normal University also cooperated to complete the work. (Author: Xian Rui)
Bathtub Faucet,Bathtub Faucet Set,Bathtub Shower Faucet,Bathtub Faucet With Hand Shower
AIHUI Sanitary Ware , https://www.fsaihuisanitary.com