Innovative Methods of Hydrogen Storage for use as fossil fuel replacement.

Electric vehicles have been touted as the next step to eliminate reliance on fossil fuels.  The stumbling block on this path is efficient and lightweight storage of enough power to parallel fossil fuel vehicles already in use.  To date, there has been no storage system that can produce enough power to economically and safely power a vehicle for realistic use.      

Hydrogen is the most plentiful element on the planet.  Most alternative energy experts agree that hydrogen is the frontrunner in alternative fuels.  There are several methods that are being explored for hydrogen storage and use in transportation.  These include compressed hydrogen gas, liquid hydrogen, methanol, and solid chemicals from which hydrogen is released (sodium hydride (NaH) and sodium borohydride (NaBH4 )).  

There are several methods that have serious hazards associated with their use.  Compressed hydrogen gas would not be practical for normal transportation methods, since pressurized cylinders of these gases would be bulky, dangerous, and unwieldy to refill.  Liquid hydrogen storage would require cryogenic equipment, which would also create problems in bulk and safety. Extracting hydrogen from methanol via reforming would require complicated reformers which have associated problems, including 10 to 20 minute warm-up times before hydrogen can be generated.  Chemicals such as sodium hydride and sodium borohydride can release hydrogen when reacted with water.  This method using a solid chemical instead of a compressed gas, cryogenic liquid, or methanol, offers several advantages, including storage, safety, and density of hydrogen per unit versus other methods.  

One of the major advantages of this type of hydrogen generation is that the spent fuel is NaOH (Sodium Hydroxide) or NaBO2  (Sodium Borate).  Both of these can be reprocessed into new fuel.  Sodium borohydride is a specialty chemical used in a variety of chemical industries. Sodium hydride is produced by heating waste sodium hydroxide (which is a byproduct of several chemical processes, and also will be the end product of the hydrogen generating process) which removes the oxygen.  This “closed loop” system could prove to be economically and environmentally sound when used. Searching for new deposits of fuel and worries over byproduct disposal will not be an issue with this type of process.

The following chart shows the relative storage capacities of each method:

A fuel cell is an electrochemical device that converts chemical energy directly into electrical energy through the reaction of a fuel with oxygen.  Most fuel cells for hydrogen use a proton exchange membrane (PEM) to produce the electricity.  The PEM is coated with a catalyst on either side.  The electrode assembly consists of the anode and cathode with a PEM separating them.  Hydrogen is supplied to the anode side of the electrode, where the catalyst promotes its separation into electrons and protons.  Air is supplied to the cathode where oxygen in the air attracts the hydrogen protons through the PEM the electrons are captured as electricity through an external circuit and combine with the protons and oxygen on the cathode side to produce water vapor.  

Fuel cells can process the hydrogen from any of these methods and produce electricity.  They are capable of powering cars, buses, houses, boats, homes, and businesses.  Several companies are fielding prototype vehicles using chemical generation of hydrogen. Some are burning the hydrogen to power generators, while most are using the fuel cell approach to generate electric power which is stored in batteries and used to power electric motors.

PEM Fuel Cell Diagram

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