HYDROGEN FUEL CELLS

As awareness of the detrimental effects of local pollutants and diminishing fossil energy resources grows, scientists are turning to alternative methods of generating energy. Recent developments in hydrogen fuel cells mark the beginning of a technological revolution in electricity generation. Fuel cells are uniquely advantageous over other alternative energy sources in that they are compatible with both hydrogen - the fuel of the future in the opinion of many experts - as well as today's carbon based energy sources. This allows for a continuous migration from hydrocarbon fuels, such as natural gas, to a renewable based energy system without major technological disruptions.

How does a fuel cell work? The basic premise behind the operation of a fuel cell involves the oxidation of hydrogen to water:

"We've been able to reduce our processor size by a factor of three without sacrificing efficiency," said Larry Burns, GM's vice president for research and development, and planning.

The chemical reaction starts when one side, the anode of each fuel cell, is exposed to hydrogen. The anode allows hydrogen atoms to give up an electron and become positively charged protons. On the opposite side of the cell, the cathode adsorbs oxygen from the air, generating a potential that draws electrons through an external circuit to donate them to the adsorbed oxygen. When the adsorbed oxygen receives two electrons, it forms a negatively charged oxygen anion. These oxygen anions subsequently combine with protons. The positive and negative ions on the two sides of the membrane obviously experience mutual attraction.

The membrane acts as a one way valve which blocks electrons, hydrogen gas, oxygen gas, and oxygen radicals and allows only the positively charged protons to pass through. When two positively charged protons encounter a negatively charged oxygen radical they combine to form water. The cathode expels the water and adsorbs more oxygen to start the reaction over again. In this way, electricity is generated without the aide of moving parts, and the cell operates without making noise. Fuel cells are superior to batteries because a fuel cell's lifetime is proportional to the amount of reactants stored (H2 and O2).

Since each individual fuel cell generates only a small amount of electricity, it is necessary to combine several fuel cells in a housing. The housing contains multiple fuel cells (a stack), hydrogen fuel, and controls. The controls determine the amount of electricity produced by the stack.

One area in which fuel cell research seems most promising is the automobile industry. The average internal combustion engine (as taken from a mid-sized car) achieves a fuel efficiency of roughly 12%. The prototype fuel cell cars being developed by the leading automobile manufacturers have achieved system efficiencies of over 50%, even when operating at low speeds.

Research efforts in several industrialized nations are yielding exciting results. In the United States, General Motors recently introduced their newest fuel cell model, heralded by the company as, "the world's leading fuel cell." According to Larry Burns, GM's vice president for research and development, "This stack is the new benchmark for fuel cell stack power density."

One possible hindrance to the adoption of hydrogen fuel cells is the difficulty inherent in storing hydrogen gas as fuel. Hydrogen in its diatomic form is extremely explosive with air. To combat this problem, Daimer-Benz has developed technology that utilizes methanol as a "hydrogen-carrier." These fuel cells make use of a specialized fuel-processing unit that strips the methanol of its hydrogen atoms. These hydrogen atoms are then used as in the traditional fuel cell described above. The remaining hydrocarbons are then combusted in an expander/compressor unit. The entire system qualifies as an Ultra-Low Emissions Vehicle.

Fuel cells are currently being utilized for power generation in utility power plants, office buildings, hospitals, and schools. Fuel cells are convenient because they are able to operate as stand-alone generators. Research continues to be performed in an effort to develop fuel cells of varying sizes and types. One of the most promising developments in fuel cell technology involves integration with solar cells. As solar cells harvest the sun's energy, fuel cells convert and store the energy in the form of hydrogen. As research efforts continue, it is apparent that fuel cells could be the energy of choice in the future.