Fuel Cells is a hot topic among scientists these days thanks to their wide range of applications. Their uses are so diverse that fuel cells have found a place even in the space program. In this blog, let me explain in detail the design, working, types and future scope of fuel cells.
Shall we begin?
What are Fuel Cells?
Fuel cells are electrochemical cells that use a pair of redox reactions to transform the chemical energy of a fuel (typically hydrogen) and an oxidizing agent (usually oxygen) into electricity. It finds various applications, including transportation, industrial/commercial/residential structures, and long-term grid energy storage in reversible systems.
Fuel cells are unique in that they may use a wide range of fuels and feedstocks and can power systems as large as a utility power plant and as small as laptop computers. Now, we are moving on to the design of fuel cells.
Fuel Cells Design
A fuel cell comprises 3 adjacent segments namely the anode, the electrolyte, and the cathode. At the intersections of these segments, redox reactions take place. Fuel is burned, water or carbon dioxide is produced, and an electric current is produced, which can be utilized to power electrical devices, commonly referred to as the load.
A fuel cell’s design elements include:
- An electrolyte – It acts as a medium of transport between the electrodes. Most common electrolytes include potassium hydroxide, salt carbonates, and phosphoric acid, and it usually defines the type of fuel cell.
- A fuel – The fuel undergoes oxidation reaction and supplies the ions. Hydrogen is the most common fuel.
- Anode Catalyst – It breaks down the fuel into electrons and ions. We usually use fine platinum powder as the anode catalyst.
- Cathode catalyst – It reacts with the ions that reach the cathode and transforms them into harmless compounds, the most common of which is water.
- Gas diffusion layers that are resistant to oxidation.
Let me show you how fuel cells produce electricity from the fuel we supply.
Fuel Cells Working
In 1839, Sir William Robert Grove, a physicist invented the first fuel cell. The goal of a fuel cell is to generate an electric current that can do some work outside of the cell, such as powering an electric motor or lighting a city.
A catalyst at the anode promotes oxidation reactions in the fuel. As a result, hydrogen atoms are stripped of their electrons at the anode of a fuel cell. The hydrogen atoms have now become positively charged H+ ions.
At full rated load, a typical fuel cell produces a voltage of 0.6 to 0.7 V. If we require alternating current (AC), we must channel the DC output of the fuel cell via a conversion device called an inverter.
Reactions inside Fuel Cell
When the ions and electrons reach the cathode, they rejoin, and the two react with a third molecule, usually oxygen, to produce water or carbon dioxide. The following are the basic reactions that take place inside a fuel cell:
Anode side: 2H2 => 4H+ + 4e–
Cathode side: O2+ 4H++ 4e–=> 2H2O
Net reaction: 2H2 + O2 => 2H2O
Different types of fuel cells
Depending on the electrolyte in use, there are different types of fuel cells. Here are some of them:
Alkali Fuel Cells
- Alkali fuel cells use compressed hydrogen and oxygen to function.
- Their electrolyte is usually a solution of potassium hydroxide (chemically, KOH) in water.
- The efficiency is around 70%, and the operating temperature is between 150 and 200 degrees Celsius (about 300 to 400 degrees F).
- The output of the cells ranges from 300 watts to 5 kilowatts (kW).
- However, they require pure hydrogen fuel, and their platinum electrode catalysts are costly. They can also leak, just like any other liquid-filled container.
- In the Apollo spacecraft, alkali cells were employed to produce both electricity and drinking water.
Molten Carbonate Fuel Cells
- The electrolyte of molten carbonate fuel cells (MCFC) consists of high-temperature salt carbonates (chemically, CO3).
- The efficiency ranges from 60% to 80%, and the working temperature is around 650°C (1,200 degrees F).
- The high temperature prevents the poisoning of cell by carbon monoxide, and waste heat can be recycled to generate more energy. However, the high temperature limits the materials and applications of MCFCs–they are likely too hot for domestic use.
- In addition, the processes consume carbonate ions from the electrolyte, necessitating the injection of carbon dioxide to compensate.
Phosphoric Acid Fuel Cell
- The electrolyte of PAFCs is phosphoric acid, which is a non-conductive liquid acid that causes electrons to go from anode to cathode via an external electrical circuit.
- Since the anode’s hydrogen ion generation rate is low, we use platinum as a catalyst to boost the ionisation rate.
- The use of an acidic electrolyte is a major disadvantage of these cells. This accelerates the corrosion or oxidation of phosphoric acid-exposed components.
- The operating temperature is between 150 and 200 degrees Celsius, and the efficiency ranges from 40 to 80% (about 300 to 400 degrees F). Phosphoric acid cells now available have outputs of up to 200 kW.
Solid Oxide Fuel Cells
- Solid oxide fuel cells (SOFC) use a hard, ceramic composition of metal oxides such as calcium or zirconium as an electrolyte.
- The efficiency is around 60%, and the output of the cells can reach 100 kW.
- The working temperature is around 1,000 degrees Celsius (about 1,800 degrees F).
- Further energy generation through waste heat recovery is possible. The high temperature, on the other hand, limits the applications of SOFC units, which are typically quite big.
Let’s have a look at the different applications of fuel cells.
Fuel Cells Applications
Fuel cell technology has a variety of applications. Currently, scientists are carrying out extensive research to develop a cost-effective fuel cell-powered automobile. The following are a few examples of the uses of this technology:
- Fuel cell electric vehicles, or FCEVs, use clean fuels and are thus more environmentally benign than vehicles powered by internal combustion engines.
- Many space voyages, like the Appolo space program, have relied on them for power.
- In many rural regions, fuel cells are a major backup source of electricity.
Fuel Cells Advantages
Fuel cells outperform traditional combustion-based technologies, which are now in operation in many power plants and automobiles. They emit fewer greenhouse gases and zero atmospheric pollutants that contribute to smog and health issues. When pure hydrogen is the fuel, the only byproducts are heat and water. Traditional combustion systems use significantly more energy than hydrogen-powered fuel cells.
Fuel Cells Future
Hydrogen is the most abundant element in the universe, and a hydrogen ecosystem focusing on fuel cell technology has enormous promise. Unlike batteries, we can scale up fuel cell technology for passenger vehicles, buses, ships, and trains. Hydrogen will also power urban air mobility in the future.
Fuel cells could power our cars in the future, with hydrogen replacing the petroleum fuel currently used in most vehicles. Many automakers are investigating and developing transportation fuel cell technologies. Hyundai is pioneering hydrogen fuel cell technology in addition to increasing its array of battery, hybrid, and plug-in electric vehicles.
Shall we wrap up?
Due to its non-polluting nature and a vast range of applications, the future looks bright for fuel cells. Once we are able to cut down the cost of fuel cells and devise methods for the safe and long term storage of hydrogen, fuel cells would revolutionize the energy sector.