ClimateandFuel

Hydrogen - Fuel cell system for Transport.

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 (ref 215). It has been forecast that in the US by 2030 hydrogen and electricity 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. Storage of hydrogen is at high pressure or at low temperature.

Hydrogen fuel cells.

Hydrogen can be burned in an internal combustion engine producing only water with no other by products. 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 is the hydrogen fuel - fuel cell - electric motor system (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 with recharging concentrated 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.

The fuel cell operating temperature is 60 - 80C. It produces DC from a constant stream of fuel/ gas into it plus heat which could be usefully used.

Some other fuel cells:-

Solid Oxide Fuel Cell (SOFC). Operating temperature 700 to 1000 C. Would be suitable for large scale power generation (50 to 60% efficient fuel to electricity or 80-85% if waste heat captured in cogeneration applications (ref199). In long term could be used for auxiliary power units in large aircraft (ref 176).
• Alkaline Fuel Cell (AFC). Used since 60's in NASA space missions. Operates at 100 C. Unlikely to be used widespread in the future.
• Moltern Carbonate Fuel Cell (MCFC). Unsuitable for cars but could be used for power generation. Operating temperature 650 C. Can be 60% efficient plus if waste heat used.
• Phosphoric Acid Fuel Cell (PAFC). Could be used for small power generating systems. Unsuitable for cars as longer warm up time than PEMFC type. Operating temperature 200 C
• Direct Methanol Fuel Cell (DMFC). Very expensive due to large amount of Platinum. Unsuitable for cars due to longer warm up time but suitable for small power systems.

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 catalyst yields hydrogen leaving NaBO2 to be reprocessed.

Producing Hydrogen (H2) by electrolysis or thermo-chemistry.

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 converting 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

Source of high temperature for thermochemical reaction.

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.

Hydrogen from bacteria.

Artificial organisms are being developed to synthesize new species of bacteria that produce hydrogen as a fuel at the Craig Venter Institute, Rockville, Maryland, more about Venter .The university of Glamorgan UK is developing a plant to produce Hydrogen from biomass and bacteria.

Photo-electrocatalytic hydrogen production

A gold electrode covered with layers of Indium phosphide nanoparticles is submerged in water and irradiated with light - university of East Anglia UK.

Home production system from Honda.

A solar hydrogen system uses 4.5L water to produce 0.5kg hydrogen giving the FCX Clarity a range of 30 miles. Uses a high differential pressure electrolyser.