As a new generation of clean energy, hydrogen has the advantages of no pollution, high combustion value and wide resources. The most common method of producing hydrogen is to generate oxygen through the cracking of water to form hydrogen. In this electro / photoelectric catalytic oxygen evolution reaction (OER) process, a complex reaction process involving the transfer of four electrons has a slow reaction kinetics and a large overpotential, which limits the overall energy conversion efficiency.
To this end, researchers have developed the precious metal iridium as a catalyst to accelerate the reaction efficiency. But it is undeniable that the cost of iridium is too high, and the unit price per gram is close to twice that of gold.
For a long time, researchers have always wanted to find cheap alternatives. However, the results of research often have low overall catalytic efficiency and elusive catalytic mechanisms and active sites.
Recently, Hou Yang, a researcher in the School of Chemical Engineering and Bioengineering of Zhejiang University, designed and developed a monoatomic OER catalyst through the method of bionics, anchoring highly dispersed nickel monoatoms on a nitrogen-sulfur doped porous nanocarbon substrate On the high-efficiency electro / photoelectric catalytic water splitting analysis oxygen reaction. Related results were published online in "Nature-Newsletter".
Discovery of Ni-Ni coordination doped carbon materials
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. The structure can collect solar energy, use the 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 told China Science Journal that further analysis found that Nickel-nitrogen coordination doped 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. Oxygen is produced, and the problem of hydrogen production is solved."
In order to further accelerate the catalytic efficiency, the research group continued to improve the nickel-nitrogen coordination structure. "The structure of the nickel-nitrogen coordinated doped carbon material is relatively stable, as if four people of equal strength each exert a uniform force in one direction." So, Hou Yang's group proposed whether to replace the nitrogen atoms in it. As with a different Hercules, properly coordinate the adsorption of hydroxide ions by the central nickel atom and the desorption capacity of subsequent products.
After that, the research team 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 single-atom nickel is anchored in nitrogen-sulfur doped porous nanoparticles. In the carbon catalytic material, the atomically dispersed single nickel atoms form a coordination structure with the surrounding 3 nitrogen atoms and 1 sulfur atom, and are co-doped into the nano-carbon skeleton as the catalytic active site. 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, thereby making it efficient in electro / photoelectric Catalytic performance and excellent stability.
"Replacement of a nitrogen with a single sulfur atom 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. "Hou Yang said.
The advantages of the new catalyst
Nickel-nitrogen materials are extremely unstable and need to be “anchored†on a carbon substrate. Hou Yang likens this process to “like throwing a heavy anchor from a boat to keep it from moving when the boat is dockedâ€. Through process iterations, the nickel single-atom catalyst prepared 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 monoatomic anchored nitrogen-sulfur doped porous nanocarbon catalyst developed by the team has a reduction in overpotential of about 5% compared to the commercial iridium-based catalyst widely used in the market, that is, the energy to drive the reaction 5%, at the same time, the cost has been reduced by more than 80%, and the stability has been 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."
Cars running far need to improve battery efficiency
The 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 / kg, so that the car can run for a day. In the future, to further improve the efficiency of the battery, a new fuel cell, metal-air, is needed, and the OER oxygen evolution reaction is an important part of the oxidation reaction.
The reporter learned that the research not only designed and developed an efficient and stable transition metal-nitrogen-sulfur atomic-level electrocatalyst, but also designed how to design low-cost, highly active artificial nitrogen fixation to synthesize ammonia, high-value utilization of carbon dioxide, and oxygen reduction. The design of catalytic materials provides new ideas.
This 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.
HCH Hardware is a bolt manufacturer and provides all kindsof fasteners since 2008. Our main products includestandard Bolts, nuts, Screws, washers, Pins and OEM parts. We have integrated resources from more than 50 top level fastener factories in Jiaxing, Haiyan, Ningbo,Dainan, Qintongareas, and have established long term relationships with them.We arenow serving for over 60 customers in South and North America.We can provide you with one stop services to meet you different needs, which can save your purchasing cost and optimize your efficiency. HCH Hardware was certified by ISO9001-2015 on 02/25/2021.We especially emphasize on products quality,HCH Hardware have necessary conditions for quality control with applicable processes and experienced experts. Appropriate production processes and quality control
actions can meet clients` highexpectation on quality and services.
Ss Nuts,Ss T Nuts,316 Stainless Steel Nuts,Lock Nut
Taizhou Hongchuang Hardware Co., Ltd. , https://www.taizhouhongchuang.com