"Energy can neither be created nor destroyed. It can only be converted from one form to another" is the first law of thermodynamics. Well, this rule is the true for most of the appliances and equipment used in commercial and industrial applications. But when it comes to converting an energy without polluting the environment, fuel cells are the most effective solution. Fuel cell is an electrochemical cell which produces electricity by converting chemical energy (from a source fuel) into electrical energy. It is different from the other cells (which also do the same process) in the utilization of the sources that generate the electricity.
Normal battery cells use metallic compounds like zinc, manganese, and lithium. Therefore, once the chemical reaction is over, the battery life reduces and over a period of time, the battery either needs to be recharged or thrown away. But in a fuel cell, where elements like hydrogen and oxygen are used, the electrical energy is generated from the chemical process as long as the fuel supply is constant. The other difference is that the chemicals used are again utilized as an additional source of fuel, thereby minimizing the wastage of energy.
Most of the fuel cells that are in use today contain hydrogen. The main purpose of a fuel cell is to convert the chemical energy derived from sources of fuel which is a combination of gases (like hydrogen, natural gas, gasoline, methanol etc.) and oxidants (like air and oxygen) into electrical energy. It comprises two electrodes: positively charged anode (which is the fuel) and negatively charged cathode (which is the oxidant). Both are separated by an ion-conducting membrane. Say, the fuel is hydrogen and oxidant is oxygen.
The chemical reaction takes place with the aid of an electrolyte (potassium hydroxide), which is used for ionizing the anode where the hydrogen molecules are split into positive hydrogen ions and negatively charged electrons. The electrolyte further splits the direction of the ions and electrons, with the electrons traveling through an external circuit to cathode, thereby generating an electric current. Meanwhile, the positively charged hydrogen ions on reacting with the oxidant (oxygen) at cathode forms water. So when many cells are stacked, the surface area of each cell signifies current and the number of cells aggregated becomes the voltage. The electric power generated is the product of voltage and electric current.
- No recharging is required as the fuel requirements are simple.
- Constant power can be generated even in remote locations as long as there is an uninterrupted supply of fuel and oxidant.
- These cells exhibit maximum efficiency even at low power levels. Practically, their efficiency is as high as 60%.
- One of the major advantage of using a fuel cell is that, it doesn't pollute the environment. The only by-product that is generated is water which is again a useful source of fuel.
- Unlike batteries (that run on internal combustion), these cells are small and compact thereby fitting conveniently in systems (like power inverters and fuel reformers) which have space constraints.
- Unlike the sound pollution created by batteries used in vehicles and other industrial applications, fuel cells do not create any noise. Pertaining to this attribute and the heightened efficiency they offer, these cells are very much in use in electrical systems in residential areas and automobiles. Hydrogen powered cars are a good example of application of the cells.
- These cells are quite expensive. A fuel cell system for gasoline-powered vehicles approximately costs about USD 35-USD 73 per kilowatt. Also, platinum which is an excellent electrolyte used in such cells, is a costly metal. However, research going on to find an economical substitute for it.
- They are sensitive to variations in temperature. The polymer exchange membranes used in these cells cannot operate at a temperature greater than 100ºC. Tolerance to such high temperature is a requisite for this cell in order to increase the tolerance to impurities. So, durability is a factor which needs to be worked upon as currently they tend to degrade when the operating temperatures rise.
- The major issue with fuel cells is the infrastructure involved in making them. Regular fuel cells run on hydrogen, and the infrastructure involved in hydrogen generation plants, fueling stations, pipelines, and truck transport are way too complex and costly.
- Another hassle faced is the storage. Vehicles powered by these cells are environment friendly, but the parameters like hydrogen storage, vehicle weight, costs incurred in vehicle infrastructure, and safety measures are still being worked upon. Also, the fuel supply needs to be replenished continuously for this cell to work.
Some of the fuel cells worth considering are alkaline fuel cells, molten carbonate fuel cells, and proton exchange membrane fuel cells. The cells are of great use in aerospace applications. They are also used in hybrid applications to provide base power load leveling, and regenerative braking that involves batteries and booster capacitors. With the help of research and development, fuel cells will find a laudable place in automotive applications. Although this avenue has been tried (e.g., hydrogen cars), it is costly. So, there is research going on to reduce the cost of this cell. Currently prototypes of this cell which are fueled by methanol are being studied. Studies are underway to see if they could be used for mobile phones and computers.
Fuel cells are definitely a better alternative to normal battery cells to sustain a pollution free environment. They are the perfect solution for global warming and greenhouse gas emission problems.