Chicken feathers could provide a high-capacity store 鸡毛可能作为大容量储氢材料
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 Senöz, 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 Senöz. 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.
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。