Hydrogen and fuel cells the future system for road transport

The long term future for transport lies in part by the development of a (no CO2 emission) clean hydrogen fuel system to replace gasoline/petrol. It has been forecast that in the US by 2030 hydrogen could replace gasoline as the most favorite fuel for cars and use will be made of intermittent sources such as wind and solar generated electrical power and eventually steam from High Temperature Reactors (HTRs) to create it.

There are however many problems to overcome, the cost of platinum used as a catalyst in fuel cells, reliability, durability, safety and introduction of fueling infrastructures. Also hydrogen storage is more bulky even under pressure or at low temperature.

Hydrogen fuel cells.

Hydrogen can be burned in an internal combustion engine producing only water with no other byproducts. ATM have developed an electrolyser for ones garage to supply hydrogen for a modified duel fuel car or van; 25 miles range and overnight charge. See bifuel car and van www.itm-power.com/

The long term solution to transport however is likely to be the hydrogen fuel - fuel cells system to generate electrical power (ref 144) to drive the vehicle (ref 111)(ref 114) (ref 124 hybrid fuel cell-battery for transport). Some city bus services already use hydrogen-fuel cells for propulsion and recharging can be concentrated at the depots.

The efficiency of converting the chemical energy (in hydrogen) to electrical energy in a fuel cell is around 30% but 60% might in future be achieved (p94 ref 6).

The most promising fuel cell for transport is the Polymer Exchange Membrane Fuel Cell (PEMFC) shown below.

Cross section of PEMFC fuel cell

The fuel cell operating temperature is 60 - 80C. It produces DC from a constant stream of fuel/ gas into it.

Some other fuel cells:-

Hydrogen storage, liquid, high pressure, solid form.

Hydrogen is stored either under pressure in a cylinder for easy transport or liquefied at a low temperature (cryogenically).

Probably a better alternative under development for transport is solid storage where hydrogen atoms can be absorbed at normal temperatures in certain light metals. A catalyst effects release. If stored as sodium borohydride (NaBH4) which has a high energy density a catalist yields hydrogen leaving NaBO2 to be reprocessed.

Producing Hydrogen (H2) by electrolysis or thermo-chemistry (or bacteria?)

Two methods of producing hydrogen are 1) 'electrolysis' of steam over 800 C (ref 112) using heat and energy ( off peak or surplus intermittent wind or solar energy ) and 2) extraction from water by thermo-chemistry. The efficiency of heat to hydrogen varies from 25% electrolysis to 45% high temperature electrolysis, to 50% plus for thermo chemical production (p 95 ref 6).

In thermo chemical production water is heated to a high temperature (800 to 1000 C).

Low pressure endothermic (heat absorbing) decomposition of Sulphuric acid (H2SO4) produces oxygen and sulphur dioxide. H2SO4 >> H2O + SO2 + 1/2 O2
In the IS (Iodine) process I2 + SO2 + H2O >>2HI + H2SO4 exothermic at 120 C
2HI >> H2 +I2 at 350 C endothermic. I2 and H2SO4 are recycled with no waste products.
Overall therefore the process results in H2O >> H2 + 1/2 O2

A High Temperature Reactor HTR would in future be suitable for generating gas at 750 to 1000 C for this process, the efficiency at 1000 C being 3 times that at 750 C.

There is a possibility that Hydrogen could be produced by artificial bacteria ( J Craig Venter Institute Rockville Maryland are working on this development.)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Useful sites on fuel cells
California introduction to fuel cell vehicles
Fuel cell - how it works
More on fuel cells
Hydrogen commerce
 

     

 

 

 

 

 

 

 

Solid state storage of hydrogen for cars.
Chrysler are testing a solid storage device in sodium boron hydride. This recycles to borax which is used again.
The Technical University of Denmark (TDU) claims a hydrogen technology where tablets taking up the same space as a petrol tank could fuel a car for 600 miles. The tablets effectively store the hydrogen in solid form. They consist of ammonia absorbed in sea salt, ammonia being a combination of hydrogen and nitrogen from the air. When the hydrogen is needed the ammonia is released through a catalyst that decomposes it back to free the hydrogen. When the tablet is empty it needs a new shot of ammonia to recharge.
A team from the universities of Birmingham and Oxford and the Rutherford Appleton laboratory under the auspices of the UK Sustainable Hydrogen Energy Consortium (UK-SHEC) have produced a fuel cell where hydrogen storage is achieved at normal temp & pressure by 'chemisorbtion.' Atoms of gas are absorbed into the crystal structure of Lithium hydride (Li4BN3H10).