Romanian

 

To be or not to be… renewable: fuel cells

 

Andreea ISPAS, Alexandru BORCESCU

 

Being student nowadays is definitely more complicated than centuries ago!

For instance imagine us going backward not a century, but only 60 years ago, and having to find out data about Fuel Cells. It would pretty simple: course textbooks on the campus libraries –meaning a limited amount of searchable resources –then, few more data in encyclopedias and that is.

Although presently, even worldwide data stays at our fingertips through laptops and internet, we are accessing virtually infinite resources so we have to face huge filtering, organizing and revealing issues during the learning process itself.

If you will search for the definition of Fuel Cell, for instance, you will reach the performance of having about 404,000 results in only 0.13 seconds. Almost all are saying the same:

A fuel cell is an electrochemical cell that derives its energy from combustible substances (hydrogen, methane, propane, methanol, diesel fuel or gasoline). The most widely discussed type is the hydrogen fuel cell, in which energy is obtained from the oxidation of hydrogen and its only byproducts are water and a small amount of nitrous oxide, if air is used as the oxidizer.

Once more, according with one of the many definitions: Renewable energy is any energy resource that is naturally regenerated over a short time scale and derived directly from the sun (such as thermal, photochemical, and photoelectric), indirectly from the sun (such as wind, hydropower, and photosynthetic energy stored in biomass), or from other natural movements and mechanisms of the environment (such as geothermal and tidal energy). Renewable energy does not include energy resources derived from fossil fuels, waste products from fossil sources, or waste products from inorganic sources.

So obviously, electrochemical cells are not renewable sources, even if they are clean, long lasting energy sources.

It is considered that they have been originally conceived by a German scientist, Christian Schoenbein, in the middle of the 19th century.

Despite this public perception the first records referring to ever burning lamps goes back to the Middle Ages discoveries made on ancient thumbs that were found lightened inside after…few thousand years.

More recently, at the end of 80`s, astonishing discoveries made in Egypt at the Temple of Isis shown that electricity is not so modern as we thought before (fig. 1).

To puzzle us even more at the end of 90` archeological excavations made in Iraq shown that even the principle of functional fuel cell dates from ancient times (fig. 2 a, b) The Bagdad battery is very old, about 2000 years. The jar has been discovered in Khujut Rabu and is composed with a stopper made of asphalt.

It is not known for sure the exact use of the jar, but it is presumed it was used as a battery.

A fuel cell does not exhaust its fuel. A method of recharging the fuel cell is a tank or external supply of fuel

If you combine the cell is series or in parallel they can supply larger amount of energy

Fuel cells have been used in the space missions of the Americans in 60`s

The new and modern fuel cell can provide up to 200 kW at the cars, trucks and space vehicles that are equipped with it.

If at the beginning fuel cells have been used in space missions, later in the oil crisis, have found applicability in different areas such as vehicles. On a large scale vehicles use internal combustion engine uses petroleum hydrocarbons as fuel. Though this type of propulsion polluting and has limited resources problems related to oil. In the context of launching Sputnik (1958) and NASA's desire to catch up to the Soviets, Bacon fuel cell,

which had no moving parts and a specific power and specific energy 2-3 times higher than other sources paves the way for large-scale development of fuel cell.

In 1965, the Gemini V space capsule used the H2/O2 cell with solid polymer electrode and for the Apollo program was used a H2/O2 pressurized alkaline cell. There are several criteria by which is made the classification of fuel cells:

 

After the type of fuel

• using gaseous fuel
• using liquid fuel
• using solid fuel

 

After the type of electrolyte

• liquid electrolyte (AFC - Alkaline Fuel Cell,
• MCFC - Molten Carbonate Fuel Cell (fig. 4a),
• PAFC - Phosphoric Acid Fuel Cell (fig. 4b)
• solid electrolyte (PEMFC - Polymer Electrolyte Fuel Cell, SOFC - Solid Oxide Fuel Cell) (fig. 4c)

 

After operating temperature

• low temperature cells (20-80 °C)
• average temperatures cells (200-300 °C)
• high temperatures cells (400-800 °C)

 

According to the way of the fuel consumption

Indirect

- fuel passes through different turn before entering the cell;

Direct

- For historical perspective among the pioneers of the modern fuel cells is also a Romanian physicist Nicolae Vasilescu-Karpen. In 1922, he patents the thermoelectric cell with uniform temperature also known as Karpen cell which is going to be built in 1950 and will continue working non-stop until today.

The device is composed by two cells connected in series which drives a small galvanometer engine. The small engine sets in motion a palette connected to a switch. Halfway of each rotation, the circuit opens and after the second half of the rotation it closes. The time of rotation of the propeller is calculated so that its cells can be recharged, meaning to be able to restore polarity in the time that the circuit is open.

Uninterrupted working for 60 years of the Karpen cell has determined many to consider it a perpetual motion machine. Since between the initial form of energy (chemical) and final (electrical) there is no other energy form (thermal or mechanical) fuel cells achieve high yields that exceed, in theory, 80%.

 

Areas of fuels cells use

Powering by fuel cells solves the pollution problem, being an alternative at the electric propulsion because there are no limitations regarding the storage of electrical energy in batteries. A main drawback of this method of propulsion is hydrogen storage in pressure tanks, and building a distribution network for hydrogen. One solution would be ethanol-based fuel cells, manufactured from ethanol and vegetable mass waste, representing a renewable source of energy. Another area in which fuel cells are beginning to be used is aeronautical. Thus in 2008, Boeing researchers conducted tests of an airplane powered only by a fuel cell and lightweight batteries. This was called the Fuel Cell Demonstrator, and used a proton exchange membrane and a hybrid system to power an electric motor, which was connected at a conventional propeller. Also 212 type submarines (fig. 6) used by Italian and German navy, use fuel cells to stay under water for several weeks without being forced come to the surface. It is expected that in the coming years fuel cells to increase their presence on the market of power generation devices and equipments.

The most famous fuel cell used in the industry field is PC25 manufactured by UTC (United Technology Corporation) which has an electrical efficiency of 40% and 50% thermal efficiency and delivers 200kW of electricity. It uses natural gas or biogas as fuel.

The fuel cell with alkaline electrolyte, AFC (Alkaline Fuel Cell) comes from Bacon cell and works at low temperatures up to 100 °C making 5-150kW power range. It is used in transportation, space program, military and energy storage systems.

Phosphoric acid electrolyte Fuel Cell, PAFC (Phosphoric Acid Fuel Cell), with porous electrodes made of teflon is used in the production of electricity and heat in decentralized stationary power systems, operating at temperatures between 160-220 °C and reaching a power between 50kW and 11MW. This is the most technologically advanced.

 

Bibliography

• www.ecolife.ro
• www.fuelcells.ro
• www.fuelcelltoday.com
• www.eere.energy.gov
• http://universulenergiei.europartes.eu/articole/energie/pile_de_combustie.pdf

 

Iconography

1. 1.bp.blogspot.com/_reR1GNih3PU/SSjL2YRRupI/AAAAAAAAATU/HgEli8xNORM/s400/dendera-light-bulb+(double).jpg
2. www.greenpacks.org/wp-content/uploads/2009/04/baghdad-battery-components.jpg
3. www.greenpacks.org/wp-content/uploads/2009/04/baghdad-battery-components.jpg
4. galaxywire.net/wp-content/uploads/2009/05/apollo_fuel_cell.jpg
5. www.energobiologie.ro/index.php/Energii/O-sursa-inepuizabila-de-energie-pila-Karpen.html
6. www.naval-technology.com/projects/type_212/type_2122.html
7. upload.wikimedia.org/wikipedia/commons/e/e6/Fuelcell.jpg