咋一看，还以为水变油呢，吓一跳，呵呵！

04 October 2007

UK chemists have overcome the shortcomings of a promising hydrogen storage material by simply converting it into nanofibres.

The lithium nitride fibres, created by Duncan Gregory and colleagues at the University of Glasgow, UK, can store and release hydrogen in minutes - rather than the hours required by bulk lithium nitride. And they do it without compromising on the amount of hydrogen that can be stuffed into the material - the key advantage of the lithium nitride system.



Gregory presented his work at an RSC conference, 'Future Energy - Chemical Solutions', held in Nottingham, UK. As he explained, lithium nitride (Li3N) has been earmarked as an excellent hydrogen absorber since 2002, when Ping Chen of the National University of Singapore and colleagues discovered that hydrogen readily binds to nitrogen atoms in the structure, displacing lithium, to form first the imide Li2NH, then the amide LiNH2. Lithium hydride (LiH) is kicked out during the reaction.

Li3N's sheet-like structure is similar to graphite, which forms carbon nanotubes © Duncan Gregory

By cycling from imide to amide and back again - storing and releasing hydrogen many times - other researchers have shown that the system can, in practice, store about 6 per cent of its own weight in hydrogen. That is not far short of targets demanded by the US Department of Energy to show that a solid material can reversibly store enough hydrogen to keep conventional cars running for hundreds of miles.

But bulk lithium nitride has snags: the temperatures required for the desorption, at 260°C, are rather high for practical purposes; and the absorption/desorption cycle is painfully slow (around 5 hours).

Gregory's Li3N fibres, which are 50-400 nm in diameter, absorb hydrogen much faster. The idea came from the similarity of Li3N's sheet-like structure to graphite, which forms carbon nanotubes. Thanks to their large surface area, carbon nanotubes have been tried before as fast hydrogen absorbers, but the results were poor: only 1 per cent hydrogen by weight can be accommodated because the nanotubes only form weak, physisorbed attractions to the hydrogen. But lithium nitride forms strong chemical bonds, so Gergory's fibres can pack in much more hydrogen.

"It seems we combine the benefits of slow but high capacity chemical storage of hydrogen in bulk Li3N, with a fast physisorption-mediated mechanism in nanofibres"
- Duncan Gregory

'It seems we combine the benefits of slow but high capacity chemical storage of hydrogen in bulk Li3N, with a fast physisorption-mediated mechanism in nanofibres,' said Gregory.

Paul Anderson, who has developed related lithium-boron nitride hydrogen storage systems at the University of Birmingham, UK, said it was impressive that Gregory could alter the storage kinetics by changing the form of the starting material. But he added, 'For a viable store, a question for any nanomaterial is whether you can make enough of it.'

Gregory won't divulge how he makes the nanofibres; his work is yet to be published but has been patented in the US. He suggested that as Li3N is a good conductor of lithium ions, the strong fibres might also make promising battery materials.

Richard Van Noorden


References
P Chen et al, Nature, 2002, 420, 302 (DOI: 10.1038/nature01210)

Source: Chemistry World.

Turning Water Into Fuel

Silicide compound and sunlight convert water to H2 and O2
Mitch Jacoby
In a two-for-one deal that may give the solar energy field a shot in the arm, researchers have discovered a semiconducting silicide that functions effectively as a water-splitting photocatalyst and doubles as a gas separator (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200701626).

Courtesy of Martin Demuth

SPLIT UP Sunlight and residual oxygen form active domains of oxide species (purple and green regions) on the surface of TiSi2 particles. These species catalyze formation of H2 and O2 from water

Using sunlight to liberate hydrogen from water is an appealing way to generate a clean-burning fuel from a renewable energy source. As a result, scientists have examined a variety of materials over the years in search of a suitable catalyst to accelerate the water-splitting reaction. Several candidates show some level of promise, yet each material suffers from shortcomings that would limit its applications. For example, some catalysts absorb solar radiation inefficiently, exhibit low activity, or are unstable or costly.

Now, a team of researchers at the Max Planck Institutes for Bioinorganic Chemistry and for Coal Research, in Germany, report that titanium disilicide (TiSi2)—an abundant and inexpensive semiconductor not known previously to be a water-splitting catalyst—separates water into hydrogen and oxygen when reactors containing the powdered catalyst are illuminated with simulated sunlight.

"Titanium disilicide has very unusual optoelectronic properties that are ideal for use in solar technology," says research group leader Martin Demuth. Specifically, the material absorbs light over a wide range of the solar spectrum and exhibits a bandgap—an important determinant of semiconductor properties—that varies by nearly 2 eV across that range. Semiconductors typically exhibit a much narrower variation in bandgap.

Another key observation reported by the team, which includes Demuth, Peter Ritterskamp, Andriy Kuklya, and their coworkers, is that hydrogen evolves readily during experiments, but oxygen adsorbs reversibly on the catalyst surface. Raising the temperature above 100 °C rapidly releases the stored oxygen, they say, which provides a convenient way to separate the gases.

On the basis of control experiments, isotope-labeling tests, and other measurements, the researchers propose that exposing commercial TiSi2 to light in the presence of a small amount of oxygen (as found in water that has not been degassed) leads to formation of catalytically active sites. These nanometer-sized domains of oxidized species catalyze the water-splitting and gas-forming reactions, they say.

As news of the findings begins to spread, some scientists are puzzling over the unusual properties reported for TiSi2. At the National Renewable Energy Laboratory, for example, senior research fellow Arthur J. Nozik notes that the "curiously" varying bandgap implies that the material is neither pure nor homogeneous. It is unclear, he says, whether this range represents individual particles with distinct chemical composition or a graded composition for individual particles, which suggests that the mechanism is not well-understood.

Demuth agrees that the behavior is "atypical" but adds that he has founded a start-up company to further study, develop, and possibly commercialize the technology.

From:Chemical & Engineering News

来源：中国科技信息网 发布时间：2007-11-5 13:44:54 小号字 中号字 大号字

据sciencedaily网站2007年11月1日报道，在我们熟悉的高中化学课中，老师首先把液态水电解成成分气体，即氢和氧。然后把两种气体混合在一起，用一个电火花点燃气体，在连续的砰砰声中老师又将气体还原成水。 伊利诺斯大学的科学家发明了一种新的造水方法，不需要点燃气体发出砰砰声。他们的新发明不仅可以从不稳定的原始材料，比如酒精中获取水，而且还可以制造出更好的催化剂和成本并不昂贵的燃料电池。撒迦利亚·赫登说，“我们发现非传统的金属氢化物可以用于一种称之为氧还原的化学反应过程。氧还原是制造水过程的基础部分”。撒迦利亚·赫登是一名博士生，他是该论文的主要撰写人。这篇新造水法论文刊登在了《美国化学会会刊》 (JACS)上，也上传到了该杂志的网站上。 水分子（二氢一氧化合物）由两个氢原子和一个氧原子组成。但是我们不能简单地将二个氢原子粘在一个氧原子上。造水的实际反应要更加复杂一些：2H2 + O2 = 2H2O +能量。 用英语来解释这个等式的意识就是：要制造水（H2O）的两个分子，就必须将两个双原氢与一个双原氧的结合在一起。这一化合过程中会释放出能量。 伊利诺斯大学化学教授托马斯·诺奇夫斯是本篇论文的撰写人之一。他说，“该反应（2H2＋O2＝2H2O＋能量）两个世纪前就为人们所知，但是直到现在也没有一个人能够找到类似的解决方案”。这一著名的反应同样在氢燃料电池中也会发生。 典型的燃料电池，双原氢气体进入电池的一边，而双原氧气体进入另一边。氢分子失去他们的电子，通过氧化过程变成带正电的氢原子，而氧分子获得四个电子，然后通过还原反应过程变成带负电的氧原子。带负电的氧离子与带正电的氢离子结合形成水，释放出电量。 诺奇夫斯说，“燃料电池的不同面发生的是氧还原反应而不是氢氧化反应。然而，我们发现氧还原新催化剂同时还可以引发新的氢氧化化学反应。” 诺奇和赫登最近对新型氢化催化剂进行了研究，该催化剂是用于氧还原的非常传统金属氢化物。在他们发表的论文中，研究人员采用了一种同质非水溶液，专门对铱氢化催化剂的氧化反应进行了研究。 赫登说：“大多数化合反应都是与氢或氧进行的，但是该催化反应却是氢和氧同时也进行化合反应。与氢的反应形成了一种氢化物，然后再与氧反应形成水。这些反应都是在同质非水溶液中进行的。” 赫登称新型催化剂可以促进更具效率的氢燃料电池的发展，充分地降低氢燃料电池的成本。该研究得到了美国能源部的资助。 英文原文链接参见：http://www.sciencedaily.com/releases/2007/10/071031125457.htm

该过程产生氢能的能量是施加电能的288%

作者：任霄鹏 来源：科学网 [url]www.sciencenet.cn[/url] 发布时间：2007-11-13   小号字 中号字 大号字

图片说明：外加电能助力微生物电解池。 （图片来源：Shaoan Cheng, Penn State University） 美国科学家最近开发出一种新型设备，能够让微生物发酵制氢的效率创造新高。而其中的奥秘就是让电流来帮这些小家伙一把。相关论文11月12日在线发表于美国《国家科学院院刊》（PNAS）上。 氢能是一种环境友好型能源，但要找到一种清洁高效的途径来大规模制氢绝非易事。利用微生物对有机原料（比如秸秆中的纤维素）进行发酵是可能的方法之一，不过，较低的转化效率一直是制约该方法的主要因素。 在最新的研究中，美国宾州州立大学环境工程学教授Bruce E. Logan和Shaoan Cheng等人一道，开发出一种新型微生物燃料电池，能够将纤维素和其他可分解有机原料直接转化为氢能。 研究人员利用的是以醋酸为电解液的微生物电解池及其中自发产生的微生物。醋酸也是葡萄糖或纤维素发酵后的主要产物之一。该电解池的阳极是颗粒状的石墨，阴极是带有铂催化剂的碳棒，研究人员同时还利用了一层普通的阴离子交换膜。研究发现，细菌会消耗醋酸并在溶液中产生0.3伏的电压。如果再从外界施加0.2伏多的电压，氢气泡就会从液体中冒出来。 Logan表示：“该过程产生氢能的能量是施加电能的288%。”即使用产出的氢气来制造额外施加的电能，该过程的能量净产出仍然相当可观。（科学网 任霄鹏/编译） 更多阅读（英文） Bruce E. Logan个人主页

Computer graphic representation of a single-walled carbon nanotube (elongated structure) Credit: Courtesy of Michael J. Heben, National Renewable Energy Laboratory


Researchers in Colorado are reporting the first successful “wiring up” of hydrogenase enzymes. Those much-heralded proteins are envisioned as stars in a future hydrogen economy where they may serve as catalysts for hydrogen production and oxidation in fuel cells. Their report, describing a successful electrical connection between a carbon nanotube and hydrogenase, is scheduled for the Nov. issue of Nano Letters.

In the new study, Michael J. Heben, Paul W. King, and colleagues explain that bacterial enzymes called hydrogenases show promise as powerful catalysts for using hydrogen in fuel cells, which can produce electricity with virtually no pollution for motor vehicles, portable electronics, and other devices.

However, scientists report difficulty incorporating these enzymes into electrical devices because the enzymes do not form good electrical connections with fuel cell components. Currently, precious metals, such as platinum, are typically needed to perform this catalysis.

The researchers combined hydrogenase enzymes with carbon nanotubes, submicroscopic strands of pure carbon that are excellent electrical conductors. In laboratory studies, the researchers demonstrated that a good electrical connection was established using photoluminescence spectroscopy measurements.

These new “biohybrid” conjugates could reduce the cost of fuel cells by reducing or eliminating the need for platinum and other costly metal components, they say.

Source: American Chemical Society

来源：新华网 发布时间：2007-11-27   小号字 中号字 大号字

美国科学家近日发现，热带白蚁体内微生物分泌的酶可将植物纤维素转化为糖类，而这些糖类在发酵后能够成为生物燃料。这意味着人们在清洁、可再生燃料的探索上再进一步。 据法国媒体报道，美国一个研究小组日前在英国《自然》杂志上发表论文说，中非一种白蚁的后肠中“可能藏有微生物金矿”，这些微生物能分泌出酶，使白蚁顺利分解食入的木材纤维，将木聚合物转化为糖类，从而获得营养。 研究人员表示，这种藏身于白蚁下半身的酶十分宝贵，可以用来制造新一代生物燃料，替代有污染、价格昂贵并带来地缘政治风险的化石燃料。 目前，研究小组正在将一部分微生物的遗传密码进行排序和分析，希望仿照白蚁的微型生物反应器进行工业生产。 据报道，目前人们所使用的生物燃料主要来自玉米和蔗糖等作物，原理是利用酶、发酵和蒸馏等方式使作物中的淀粉转化为乙醇。新一代生物燃料将使用粮食以外的植物纤维素材料，如木屑和稻草；但是，碍于成本和复杂性，这些新的加工方法很难实现大规模生产。

长见识了，这个发现可是不得了的事情啊

可将汽油、柴油、乙醇和生物柴油等直接转换为氢  

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记者郑晓春  

   本报特拉维夫12月2日电 以色列本•古里安大学与美国埃克森美孚公司、加拿大燃气净化技术公司合作开发出一种车载制氢系统，该系统可直接将汽油、柴油、乙醇和生物柴油等转换为氢供燃料电池使用，从而免去了氢燃料运输和存储的麻烦。研究人员称，这是氢燃料汽车研发上的一大突破。

　　目前，大多数氢燃料汽车通常都使用高压缩或液化氢为燃料，不仅运输和存储不便，而且还要进行大规模的基础设施改造，在各地建许多加氢站，这也是影响氢燃料汽车普及的主要障碍之一。

　　针对这种情况，研究人员认为，既然氢燃料运输和存储困难，为什么不换一种思路，让汽车自带制取装置呢？于是，他们研发了一种将传统制氢装置小型化的方法，可直接安装在汽车上，只要输入汽油、柴油等传统燃料，即可转换为供燃料电池使用的氢。由于该系统不需要改变现有燃料运输、存储的基础设施，因而解决了氢燃料汽车制造商面临的一大难题。

　　埃克森美孚石油公司研发副总裁埃米尔•贾克布斯表示，现他们已成功开发了一种使用该车载制氢系统的吊车，并准备实现其商品化。尽管如此，这只是初步成果，要普及这一技术，仍有很长的路要走。由于该系统的燃料转换率具有比传统内燃机技术高80%%的潜力，并可减少二氧化碳排放45%%，因此从长远的角度看，具有良好的应用前景。

　科技日报　

环球能源网2007年12月12日报道    杜邦公司于2007年12月初作出评测指出，生物燃料在抑制全球变暖和减少美国对烃类燃料的依赖方面将起积极作用。
　　
    预测表明，到2030年，生物燃料将供应车用运输燃料需求量的10%~25%，即达到850亿~1950亿加仑/年。这需要全球投资7000亿美元，即相当于从现在至2030年期间内每5天要建设一套新的1亿加仑/年的乙醇装置。
　　
    按照热能基准，每加仑乙醇的能量比汽油低34%。乙醇工业必须克服与原料来源和生物乙醇性能相关的问题，生物乙醇现主要由食品基原料，如谷物、油籽和甘蔗生产。在生物乙醇性能方面，其为低能量强度燃料，不适宜与大量汽油混配，并且需要新的管道基础设施以用于运输。
　　
    第二代生物燃料，如纤维素乙醇和生物丁醇，从非食用原料生产，将有助于市场发展。然而，解决美国的能源问题需要有多种生物燃料。纤维素生物丁醇仅是考虑的许多替代燃料中的一种。现在需要致力于生物质的发展机遇，以及如何从不同的农业原料来生产生物燃料，但是，也需要着眼于更能可持续发展的燃料及燃料技术。从不断发展的情况来看，纤维素生物燃料作为可再生运输燃料的一种来源，预计将起关键作用。
　　
    美国能源部资助了几个项目，旨在开发有成本竞争性的第二代生物燃料。2007年2月，美国能源部宣布在今后4年内为六座生物炼油厂项目投资3.85亿美元。并将投资3380万美元用于支持开发商业化可行的酶，用于生产纤维素乙醇。
　　
    此外，美国总统布什敦促国会立法，使之在十年内对汽油的依赖度减少20%。也提出需使汽车效率提高1/4，并使替代燃料主要是生物燃料生产量达到350亿加仑。