New technique makes bamboo a safe hydrogen storage for electromobility

Light and small hydrogen storage units made of bamboo could promote the mobile use of fuel cells. Two researchers have developed a special process that enables them to chemically convert bamboo into gas storage.

Batteries or fuel cells: The pendulum of possibilities for generating electricity for electric cars could be turned towards fuel technology by innovative hydrogen storage systems. Two female researchers from the University of Hohenheim in Stuttgart, Germany, tested new chemical processes with which a special activated carbon can be produced from bamboo.

Prof. Dr. Andrea Kruse holds the result, a porous activated carbon cookie, in her hands. “The prepared activated carbon is able to store different gases. At a pressure of 1 bar per 20 grams of weight, it offers an area of around six football fields. This allows more than 60 grams of hydrogen to be stored.” However, there is still a catch: it only works at very low temperatures of minus 196 degrees Celsius.

“With the new storage tanks, we can store three times the amount of gas in the filter weight,” says Prof. Dr. Kruse. “In addition, the storage tanks are much less dangerous because they operate at only 1 bar pressure in conventional gas cylinders instead of 300 bar. The low temperature limits the range of applications, but the results make us very optimistic with regard to new materials for the hydrogen economy.” The findings are important for the development goal: biobased electrodes for fuel cells.

The current prototype is printed with a 3D printer using high-purity carbon powder. “We found out that the activated carbon reservoirs can also be produced using conventional pressing processes,” said Dr. Catalina Rodriguez Correa, also from the Department of Conversion Technology and System Assessment of Renewable Resources at the University of Hohenheim.

Activated carbon  produced during partial chemical combustion

The researchers tested two methods: pyrolysis and hydrothermal carbonisation (HTC) of bamboo. The so-called “slow pyrolysis” is a dry process. Here, the ground bamboo is heated for three hours at 500 degrees Celsius in a nitrogen stream until carbon powder, the carbonisate, is formed.

The other process is hydrothermal carbonization, a so-called wet process. This means that the bamboo is mixed with water and heated in a pressure vessel, the autoclave, for three hours at 250 degrees Celsius.

“In this case, we can use the green leaves at the same time. We were able to produce the coal using relatively common chemical processes, which we applied to renewable organic raw materials,” explains Dr. Rodriguez Correa.

Micropores offer space for three times the amount of gas

Both dry and wet processes produce so-called carbonation products. These are then impregnated with aqueous potash lye. This means that they are mixed with the caustic solution and then filtered. The impregnated coals are then heated to 600 degrees Celsius in a nitrogen stream.

When heated, each potassium ion ultimately produces a very small hole, a so-called micropore. The activated carbon produced in this way is then rinsed with acid water to remove the residues of the caustic potash solution.

After drying, the activated carbon is ready. The micropores form the space in which up to three times the gas weight can be stored.

“We want to produce even better coal and will continue our research,” says Prof. Dr. Kruse. “We hope that together with our industrial partner HTCycle we will be able to develop an economical process from this in a few years.“

Original article: https://doi.org/10.1007/s13399-017-0280-8

Photo credit: Thomas Johansen, flickr/Creative Commons

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