Our intern Matt Stern is guest blogging on some background research he did at our office on hydrogen fuel before he gets ready to start his junior year at the Bronx High School of Science:
In modern times, we have become accustomed to using fossil fuels as our source of energy for road transportation. But, in Maxi Taxi, we would like to avoid the need of charging up a battery in a car (Tesla) or using gasoline (which is bad for the environment). So, instead we can use hydrogen for fueling the car.
Hydrogen, is a better fuel for a car, since it is more efficient. One gallon of gasoline is roughly equivalent to one kilogram of hydrogen. Hydrogen can either be combusted or used in fuel cells. In combustion, hydrogen is in contact with oxygen. The resulting product of doing so is water. Fuel cells use a chemical reaction where oxygen and hydrogen interact in the presence of an electrolyte to produce electricity also with a resulting product of water.
Overall, at the moment, the fuel cell is more efficient, since heat is lost by combustion.
There are a number of ways to obtain hydrogen for cars, some of which are electrolysis, reforming, photobiologically, and gasification. It becomes most interesting when hydrogen is generated through solar power and this is called photocatalytic water splitting.
Electrolysis, is the usage of electricity to split the water molecule into two, where the oxygen is produced at the anode (positively charged electrode) and the hydrogen is produced at the cathode (negatively charged electrode). In addition, electrolysis can use any source for electricity, such as solar panels or utility generated electricity whether nuclear, hydro or coal. Polymer Electrolyte Membrane (PEM) electrolysis is, at present, the most efficient approach. In PEM electrolysis, the cost of production is about $5.14 for one kilogram of hydrogen, at a production rate of 1,500 kg/day. In the future, it is estimated that the price will drop to $4 and production facilities will increase to 50,000 kg/day.
Reforming is the process of combining steam and methane, ethanol or biodiesel at high temperatures to obtain H2. However, regardless of being one of the more efficient and cheaper ways of obtaining hydrogen today, it is bad for the environment, since it produces green house gasses. Gasification similarly uses steam with burning coal or biomasses.
Photobiological Hydrogen production is the process of using photosynthetic biological organisms (algae) to produce hydrogen in a controlled environment. The environment is made to cause the organism to be deficient in sulfur. This is because of an enzyme (hydrogenase) that will change the organisms output of oxygen to switch to hydrogen. However, at this time, photobiology requires a large amount of space and the cost of one kg of hydrogen at the pump by doing so was $13.53, in 2004.
Lastly, water-splitting solar panels skips the step of first generating electricity for electrolysis, where metals directly absorb the solar energy and release electrons needed to split the water molecule, by using solar power to corrode oxides in order to obtain hydrogen or to convert solar power to electricity to perform electrolysis.
Once obtained, the hydrogen has to be transported. Under the Maxi Taxi concept, it would be best to produce hydrogen locally, that way the cost of transporting it is cheaper. For transporting the fuel, there are three major ways of making it transportable: compression; liquefaction; and binding it to another atom or molecule. Compression is attractive, since not much of the energy is lost. Liquefying takes a lot of energy that cannot be easily recovered. Also, compressed hydrogen is slightly more expensive than liquefied hydrogen to transport and distribute, since liquid hydrogen takes up less space than a gas. But compressed hydrogen is much cheaper to buy at the pump, because the cost to liquefy the hydrogen is higher, and it is more expensive to store ($5/GJ to $1.70/GJ), because liquid hydrogen requires cryogenic storage rather than tanks.
The major ways for transportation are using pipelines, tube trailers or liquid tankers. But transporting the hydrogen can easily add up fast. In addition to the cost of transport, to produce 1,500kg of hydrogen for one day is around $6,000 – $8,700 using PEM.
Overall, under the Maxi Taxi concept, hydrogen is the way to go. As science, production and transportation of hydrogen develop, it will become a less expensive fuel. I feel that the hydrogen production should be done locally, that way the cost of transporting will go down and using local solar panels to obtain electricity for PEM electrolysis will be good, since it can be made relatively cheaply over time and it is an efficient eco friendly method.
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