How does Hydrogen Cell Work

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, hydrogen fuel cell is a thermodynamically open system, needs no recharge, and produces electricity as long as it is supplied with fuel and oxygen.

History
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. So, 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 in the fuel cell, 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 cell was later known as the Bacon's cell.

Working of Hydrogen Fuel Cell
The working of the hydrogen 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 anode, the hydrogen reacts with the 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 Fuel Cell
The fuel cells are mainly classified by the type of electrolyte they use, and their operating temperature. The main types of fuel cells are:

• 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. PEM fuel cell is light in weight, 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 fuel cell uses a hard, non-porous ceramic compound as its electrolyte. Solid oxide fuel cell is suitable for large-scale stationary power generators, and operates at very high temperatures between 700°C and 1,000°C. Due to its high operating temperatures, it produces more steam which in turn generates more electricity and hence, improves the overall efficiency of the system.
• Alkaline Fuel Cell (AFC): It is known as Bacon fuel cell, and is one of the oldest and reliable fuel cell technology. It uses a solution of potassium hydroxide in water as an electrolyte, and operates at low temperatures between 100ºC to 250ºC, or 212ºF to 482ºF. As alkaline fuel cell gets contaminated by carbon dioxide (CO₂), it requires pure hydrogen and oxygen. It is a high performance cell, and has an efficiency up to 60% in space applications.
• Molten Carbonate Fuel Cell (MCFC): This fuel cell is best suited for natural gas and coal-based power plants, and operates at 600ºC. This cell uses an electrolyte, composed of a molten carbonate salt mixture suspended in a porous, chemically inert ceramic lithium aluminum oxide (LiAlO₂) matrix.
• Phosphoric Acid Fuel Cell (PAFC): Phosphoric acid fuel cell uses an electrolyte, composed of liquid phosphoric acid and porous carbon electrodes, containing a platinum catalyst. This cell is used in small stationary power-generation systems. It operates at high temperature and so, it is unsuitable for cars.
• Direct Methanol Fuel Cell (DMFC): It is supplied with pure methanol, mixed with steam and fed directly to the anode. It has a same operating temperature as PEMFC. This fuel cell is expensive and uses large amount of platinum as a catalyst. It has no fuel storage problem and is portable.

Advantage
Fuel cell uses hydrogen as its fuel, hence it produces water as an exhaust. Since, there are no other emissions, fuel cells are extremely clean and 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 in a fuel cell stack, hence it is silent and vibration-free. Fuel cell provides high quality DC power for modern electrical applications, and is compatible with other fuels like, fossil fuels, biofuels and hydrocarbon fuels. Power fluctuations in National electrical grids can be avoided, by using a fuel cells-powered distributed generation energy network. It has a high-power density, and can operate in variable temperatures. Fuel cell is not very expensive and has excellent suitability for hybridization with other technologies. Hence, it is more reliable than any other traditional combustion engines.

Application and Efficiency
Hydrogen fuel cell is compact, lightweight, and used as an energy source in remote locations, such as spacecraft, weather stations, large parks, rural locations, and military applications. The efficiency of the fuel cell 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 50% is converted into heat. For better efficiency, hydrogen cell should be operated at low power density, and pure hydrogen and oxygen reactants should be used.

Hydrogen fuel cell provides a wide range of critical benefits over any other power producing technology. It 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.