联系我们  |  网站地图  |  English   |  移动版  |  中国科学院 |ARP
站内搜索:
首页 简介 管理部门 科研部门 支撑部门 研究队伍 科研成果 成果转化 研究生教育 党建与创新文化 科普 信息公开 办公内网
科技信息
Low-cost wearables manuf...
Researchers develop 3-D-...
硫化钴能用来制作超级电容
青岛能源所在石墨炔能源存...
二维非铅钙钛矿动力学机理...
Scientists fine-tune sys...
Amorphous diamond synthe...
化学耦合的硫化镍和碳空心...
全无机钙钛矿光电探测器动...
科研人员提出纳米催化医学...
Newly-discovered semicon...
Molecular nanoparticles ...
碳纳米点固态高效发光新方法
基于甲胺气体的钙钛矿薄膜...
新型镁电池可使储能技术更...
现在位置:首页>新闻动态>科技信息
Chemical 'dance' of cobalt catalysis could pave way to solar fuels
2017-07-06 09:11:12 | 编辑: | 【 【打印】【关闭】

  By splitting a water molecule into two atoms of hydrogen and one of oxygen, scientists can use the boundless energy of the sun to make a clean fuel. In a new study from the U.S. Department of Energy's (DOE) Argonne National Laboratory and Harvard University, scientists have for the first time been able to see an especially important step in the water-splitting process, which may bring us closer to abundant solar energy for all.

  Splitting a water molecule requires a metal catalyst to get the reaction going. Recently, much scientific attention has focused on cobalt, a relatively abundant and inexpensive catalyst that - in the right circumstances - can serve as an escort to an electronic dance between hydrogens and oxygens.

  "Essentially, it allows you to have a focused snapshot, as opposed to just seeing a chemical blur. It's important that we determine the characteristics of the catalyst on the timescale the electrons are moving."

  "Cobalt oxygen-evolving catalysts are the active components in technologies like artificial leaves and other materials in which you can harvest light to drive the synthesis of solar fuels," said Argonne postdoctoral researcher Ryan Hadt, a co-first author of the study.

  The overall water-splitting reaction actually has two halves. The researchers focused on the first half, called water oxidation, which requires the transfer of four protons and four electrons and eventually results in the formation of an oxygen-oxygen bond. For this process, the oxygens need a temporary dance partner, which is played by the cobalt catalyst.

  But the reason this dance isn't yet well understood is that the transfers and the formation of the bond happen in a flash - the whole process takes less than a billionth of a second. To understand the nuances of the bonding action, the researchers needed to perform X-ray absorption spectroscopy measurements at Argonne's Advanced Photon Source.

  In their analysis, the researchers focused on a particularly intriguing chemical twist. At the beginning of the process, a bridge of two oxygen atoms connects two cobalt ions. Each of the cobalt ions, in turn, is connected to its own water molecule. At this point, things are pretty stable.

  The electronic dance is ready to begin when a cobalt ion adds an additional positive charge, temporarily increasing a characteristic number that scientists term an "oxidation state." In the case of cobalt, the oxidation state changes, just for an instant, from three to four.

  When two cobalt ions with an oxidation state of four come into contact, the process begins in earnest. The charge transfers cause the hydrogen atoms of the water molecules to dissociate from their oxygen bonds, leaving the cobalt atoms bonded just to oxygen ions.

  The key moment follows immediately afterwards, when the cobalt centers each receive an extra electron from the newly exposed oxygen atoms. When this happens, a bond is formed between the two oxygens, creating a molecular intermediate stage called a peroxide, which can be rapidly oxidized to release a dioxygen molecule. The electrons obtained from water during this process can be used to make solar fuels.

  By using the Advanced Photon Source, a DOE Office of Science User Facility, the researchers were able to directly measure cobalt oxidation states and then use theory to a calculate a quantity known as "exchange coupling," a quantum mechanical value that identifies the relationship between the spins of the electrons that are shuttled between the oxygen and cobalt atoms. The researchers found that these electrons spins are in opposite directions - in scientific parlance, they are antiferromagnetically coupled.

  "Antiferromagnetism plays an important role in the formation of the oxygen-oxygen bond," said Hadt, "as it provides a way to simultaneously transfer two electrons to make a chemical bond."

  Argonne postdoctoral researcher and study author Dugan Hayes also pointed to the unique ability of the Advanced Photon Source to resolve the location of the extra-oxidized cobalt atoms. "Essentially, it allows you to have a focused snapshot, as opposed to just seeing a chemical blur," he said. "It's important that we determine the characteristics of the catalyst on the timescale the electrons are moving."

  A paper based on the research, "In situ characterization of cofacial Co(IV) centers in Co4O4 cubane: Modeling the high-valent active site in oxygen-evolving catalysts," appeared in the March 27 edition of the Proceedings of the National Academy of Sciences.

  Explore further: Three-layer nanoparticle catalysts improve zinc-air batteries 

  More information: Casey N. Brodsky et al, In situ characterization of cofacial Co(IV) centers in CoOcubane: Modeling the high-valent active site in oxygen-evolving catalysts, Proceedings of the National Academy of Sciences (2017). DOI: 10.1073/pnas.1701816114   

版权所有 中国科学院上海硅酸盐研究所 沪ICP备05005480号
长宁园区地址:上海市长宁区定西路1295号 电话:86-21-52412990 传真:86-21-52413903 邮编:200050
嘉定园区地址:上海市嘉定区和硕路585号  电话:86-21-69906002 传真:86-21-69906700 邮编:201899