A new way to keep hydrogen: Plumage power

    Hydrogen has long been touted as the future of energy. It is clean, efficient and the most abundant substance in the universe. It can be used to run an internal combustion engine in a car or power one using a fuel cell, with heat and water as the only emissions. But hydrogen is difficult to store because it is the lightest element. Filling a typical fuel tank of 75 litres-about 20 American gallons-with hydrogen at room temperature and pressure will take a hydrogen-powered car only about a kilometre or so. The gas can be compressed to take up less space, but that can be dangerous. It also uses energy, which removes some of the benefits.

    Another way to store hydrogen is to put something inside the tank which increases the total internal surface area to which the molecules of the gas can cling. This means more hydrogen can then be packed into a smaller volume. There has been some progress with materials that can do this, including specially engineered carbon nanotubes. But carbon nanotubes are very expensive to make, especially in large quantities. Richard Wool, a chemical engineer at the University of Delaware, estimates the cost of fitting a single car with a tank full of carbon nanotubes to be $5.5m. Other materials might do, but they could still end up costing over $20,000 a car.

    Dr Wool and a colleague, Erman Sen?z, think they have found a way to bring the price down to only around $200 a car by using chicken feathers. The fibres in feathers are almost entirely composed of keratin, a protein also found in hair and nails. When heated in the absence of oxygen （a process called pyrolysis）, keratin forms hollow tubular structures six millionths of a metre across and riddled with microscopic pores, much like carbon nanotubes.

    The researchers demonstrated how this can be done at the 13th Annual Green Chemistry and Engineering Conference, held recently in College Park, Maryland. To avoid melting the fibres and depriving them of their desirable structural properties, they first heat-treated the feathers to around 215°C. This strengthened their structure and allowed further heating to 400-450°C. At this point the material becomes more porous, increasing its surface area and its hydrogen-storing capacity.

    The substance they created is capable of holding 1.5% of its weight in hydrogen. Since about 4.5kg of the gas is needed to cover 480km （about 300 miles）, the typical range of a petrol-powered car, this would translate into a rather large 284-litre tank stuffed with some 300kg of carbonised chicken feathers, according to Mr Sen?z. This still falls short of the 6% hydrogen-storage target which has been set by America's Department of Energy to encourage innovation with alternative fuels. But the researchers think they can improve their material further by making it even more porous. And unlike rival technologies theirs is well on the way to meeting the department's cost criteria of a hydrogen system that costs $4 per kilowatt hour stored and less than $700 for installing it. Moreover, it could also help with another environmental problem: reducing the mountains of chicken feathers that the poultry industry has to dispose of every year.

    羽毛的力量：储氢材料新发现

    长久以来氢气一直被标榜为未来能源。氢气洁净、燃烧效率高而且是宇宙中最丰富的物质。氢气可以用在汽车的内燃机引擎，或者以燃料电池的形式为汽车提供能源。使用氢气能源的排放物仅仅是热和水。但是，储存氢气很困难，这是因为氢气是最轻的元素。通常情况下，一辆汽车的油箱容量为75升，约合20加仑，在室温和常压下，用氢气作为能源填满油箱的话，仅仅只需要约1公斤的氢气。可以把氢气压缩以减少所占用的空间，但是这可能会有危险。而压缩氢气也需要能源，这也是它的弊端。

    储氢的另外一种方法就是在油箱中放入一些提高总的内表面积的物质，氢气就附着在这些物质的表面。这就意味着更多的氢气可以压缩到更小的空间里面。对这种材料的研究有了一些进展，其中包括特别加工过的碳纳米管。但是碳纳米管非常昂贵，尤其是大批量生产。Richard Wool是来自特拉华大学（University of Delaware）的一名化工工程师，他估计，单单把一辆汽车的油箱填满碳纳米管，其成本就高达550万美元。其它的材料也许可行，但是仅仅对一辆汽车来说，其成本也超过2万美元。

    Wool博士和他的同事Erman Sen?z认为，他们找到了一种方法使成本降到仅仅只有200美元，那就是使用鸡毛。鸡毛中的纤维几乎全部由角蛋白构成，这种蛋白质在头发和指甲中也有。当在没有氧气的情况下加热（这个过程称为热分解）的时候，角蛋白会形成中空的管状结构，管的宽度只有百万分之六米，同时还形成许多的微孔，这种结构很像纳米管。

    研究者们在第13届年度绿色化学和工程会议上展示了他们的研究成果，会议在马里兰的大学公园举行。为了避免融化纤维以及避免丢失所想要的结构特点，他们首先在约215°C下热处理羽毛。这就强化了羽毛的结构，而且使得随后在400---500°C的热处理成为可能。经过这样的处理，这种材料的孔结构增多，从而提高了表面积以及它的储氢容量。

    Wool博士和他的同事所制备的材料能存储其重量为1.5%的氢气。燃烧石油的汽车在加满油的情况下通常能跑480公里（约合300英里）,如果使用氢气的话，大概需要4.5公斤，根据Sen?z的估计，这就意味着需要一个284升的油箱，在里面塞满约300公斤的碳化鸡毛。为了鼓励替代能源的创新，美国能源部制定的储氢标准是6%,该研究还远远低于这个标准。但是，研究者们认为，他们可以把这种材料的孔结构进一步增多，从而提高其储氢能力。和其它竞争对手的技术不一样的是，他们的技术正在接近能源部的氢气系统成本标准，即每千瓦时4美元，安装成本低于700美元。而且，这项技术还能帮助解决另外一个环境问题：减少每年家禽业必须处理的堆积如山的鸡毛。

    Vocabulary:

    High-capacity:大容量

    Plumage: 羽毛

    Tout: 标榜；吹捧

    Abundant: 丰富的

    Internal: 内部的

    Combustion: 燃烧

    Benefit: 好处

    Cling: 附着

    Nanotube: 纳米管

    Fibre: 纤维

    Keratin: 角蛋白

    Protein: 蛋白质

    Pyrolysis: 热分解

    Tubular: 管状的

    Melt: 融化

    Deprive: 剥夺

    Desirable: 值得要的

    Innovation: 创新

    Alternative: 替代的

    Poultry: 家禽

    Dispose: 处理