A hydrogen fuel cell is an electrochemical conversion device, which uses chemicals like hydrogen and oxygen. It generates electric power, and emits only water and heat as its by-products. In contrast to batteries, this cell is a thermodynamically open system, needs no recharge, and produces electricity as long as it is supplied with fuel and oxygen.
In 1839, the first fuel cell was perceived by Sir William Robert Grove, a Welsh judge, inventor and physicist. He produced electricity and water, by combining hydrogen and oxygen in presence of an electrolyte, but this invention didn't generate enough electricity.
Hence, in 1889, Ludwig Mond and Charles Langer built a working fuel cell by using air and industrial coal gas. It is believed that they were the first to coin the term 'fuel cell'. Earlier, porous platinum electrodes and sulfuric acid electrolyte bath were used, but they were expensive and corrosive.
In 1932, Francis T. Bacon came up with an idea of hydrogen fuel cell, using less corrosive alkaline electrolyte and inexpensive nickel electrodes. In 1959, he developed a five-kilowatt fuel cell that could power a welding machine. This device was later known as the Bacon's cell.
The working of the fuel cell is similar to a battery. It consists of two electrodes; an anode and a cathode, separated by a polymer electrolyte membrane. Oxygen is fed to the cathode, and hydrogen to the anode. At the anode, the hydrogen reacts with platinum catalyst, and splits into negatively charged electrons (e-) and positively charged ions (H+).
The hydrogen ions move through the membrane towards the cathode. The electrons route along the external circuit to the cathode, and create an electric current. They travel externally to the other side of the PME membrane, combine with the oxygen, and merge with the positively charged hydrogen ions.
As a result, pure water and a small amount of heat are formed. A hydrogen cell, at full rated load, can produce voltage ranging from 0.6 V to 0.7 V. This cell can be combined in series or parallel circuits to increase efficiency, as series circuits yield higher voltage, while the latter draws more current.
Types of Hydrogen Cells
Polymer Exchange Membrane Fuel Cell (PEMFC)
It is also known as proton exchange membrane fuel cell, and has a high power density. This cell uses a solid polymer as an electrolyte, and porous carbon electrodes, containing a platinum catalyst.
This device is lightweight, and has an operating temperature ranging from 60° C to 80° C, or 140° F to 176° F. It is mainly used in transportation applications like vehicles, cars, buses, etc.
Solid Oxide Fuel Cell (SOFC)
This device uses a hard, non-porous ceramic compound as its electrolyte. This fuel cell type is suitable for large-scale stationary power generators, and operates at very high temperatures between 700° C and 1,000° C. Due to such temperatures, it produces more steam, which in turn generates more electricity, and hence, this improves the overall efficiency.
Alkaline Fuel Cell (AFC)
It is known as Bacon fuel cell, and is one of the oldest and most reliable fuel cell technologies. It uses a solution of potassium hydroxide in water as an electrolyte, and operates at low temperatures between 100º C to 250º C, or 212º F to 482º F.
As it gets contaminated by carbon dioxide (CO2), it requires pure hydrogen and oxygen. It is a high performance device, and has an efficiency up to 60% in space applications.
Molten Carbonate Fuel Cell (MCFC)
This device is best suited for natural gas and coal-based power plants, and operates at 600º C. It uses an electrolyte that is composed of a molten carbonate salt mixture suspended in a porous, chemically inert ceramic lithium aluminum oxide (LiAlO2) matrix.
Phosphoric Acid Fuel Cell (PAFC)
It uses an electrolyte that is composed of liquid phosphoric acid and porous carbon electrodes, containing a platinum catalyst. This device is used in small stationary power-generation systems. It operates at high temperatures, and hence, it's unsuitable for cars.
Direct Methanol Fuel Cell (DMFC)
It is supplied with pure methanol that is mixed with steam, and directly fed to the anode. It has a same operating temperature as PEMFC. This device is expensive, and uses large amount of platinum as a catalyst. It has no fuel storage problem, and is portable.
Fuel cells uses hydrogen as the fuel, and hence, produce water as an exhaust. Since, there are no other emissions, these cells are an extremely clean renewable source of electricity. As its electrochemical conversion rate is high, it extracts more energy from the fuel, and produces significant amount of power.
Since there are no moving parts, and mechanical inefficiencies are low, this technology is silent and vibration-free. Fuel cells provide high quality DC power for modern electrical applications, and are compatible with fossil fuels, biofuels, and hydrocarbon fuels.
Power fluctuations in National electrical grids can be avoided, by using fuel cell powered distributed generation energy network. They have a high power density, and can operate in variable temperatures.
These devices are not very expensive, and have excellent suitability for hybridization with other technologies. Hence, they are more reliable than any other traditional combustion cells.
Application and Efficiency
Hydrogen fuel cell is compact, lightweight, and is used as an energy source in remote locations, spacecraft, weather stations, large parks, rural locations, and military applications. The efficiency of this device is directly proportional to its voltage, and inversely proportional to the current drawn.
The efficiency of a hydrogen cell operating at standard conditions without reactant leaks, depends on the enthalpy or heating value of the reaction. A typical cell functioning at 0.7 V, has 50% efficiency, as 50% of the energy content of hydrogen is converted into electrical energy, and the remaining is converted into heat.
For better efficiency, a fuel cell should be operated at low power densities, and pure hydrogen and oxygen reactants should be used.
Hydrogen fuel cells provide a wide range of critical benefits over any other power producing technology. They has the potential to solve problems like dependence on petroleum, poor air quality, greenhouse gas emissions, and global warming. Its efficiency and design flexibility makes it one of the most reliable technology.