What is a Fuel Cell? How does it work ?

Today, both the increasing population and the carbon dioxide emitted by vehicles or factories increase the greenhouse gas rate in the atmosphere, and as a result, we feel the effects of global warming more. Especially in the automobile industry, there are promising developments to reduce the effects of global warming. The most important of these developments are vehicles powered by electric and fuel cells. In this article, we have compiled the fuel cell issue, which is a technology that can shape future  technology, for you.

A fuel cell, to be defined in general, is a device that does not have any moving parts that directly converts the chemical energy contained in the fuels into electrical energy and releases water as a waste product as a result of this process. Fuel cells can also be called electrochemical units because they carry out the conversion process with chemical reactions with a certain efficiency.

Fuel cells produce electricity by directly reacting hydrogen with oxygen or hydrogen obtained through fossil fuels, alternative energy sources or chemical products. A single fuel cell produces a voltage of 1 V or less. To obtain a greater amount of electrical energy from these batteries, the batteries must be connected in series with each other. The connection type and the number of fuel cells vary according to the area where the fuel cells will be used. Thanks to this feature, the fuel cell can be used in laptops (50-100W), residences (1-5kW), vehicles (50-1250 kW) and power plants (1-200 MW or more).

 

History of Fuel Cells

In 1838, German chemist Christian Friedrich Schönbein made the first academic study on the fuel cell and published his results in physics journals. On the other hand, Sir William Robert Grove first invented and developed the concept of hydrogen fuel cell. Francis Bacon introduced the first alkaline fuel cell with a power of 5 kW at Cambridge University in 1950. With the development of alkaline fuel cells, NASA has integrated these cells into power supply systems for spacecraft.

Fuel cell used by NASA on Apollo missions

In the first period of the 1960s, various fuel cells were produced for use in R&D studies, stable power applications and transportation sector. By 1970, NASA had produced an alkaline fuel cell with a power of 12 kW that provided energy for space studies without the need for any external power unit such as batteries. Since research on fuel cells requires huge budgets, most countries did not attach much importance to this technology in the beginning. But 50 years later, this technology has become important.

Structure of Fuel Cell

Fuel cells generally consist of three basic processing units. These;

1.       Fuel Processing Unit

2.       Power Generation Unit

3.       Power Conversion Unit

Fuel cells are basically like conventional batteries; It consists of anode, cathode and electrolyte. There is an electrolyte between the two electrodes. The anode electrode can be called the fuel electrode, and the cathode electrode can be called the oxygen electrode. Depending on the electrolyte used, the type and operating temperature range of fuel cells may vary.

 Structure of Fuel Cell

 The following electrolytes can be used in fuel cells;

·         Phosphoric Acid

·         Molten Carbonate

·         Solid Oxide

·         Proton Pass Membrane (PEM)

If the electrolyte is phosphoric acid, they work at 190 0C, in molten carbonate at 650 0C, if it is ceramic, at 1000 0C, and if the polymer is solid, they work at 80 0C.

Electrolyte selection is very important when building fuel cells. For this, there are some points to be considered. The most important of these are the operating temperatures and pressures of fuel cells. The electricity produced by fuel cells alone is very low. The average DC voltage produced by a fuel cell is between 0.5 and 0.9 V. Therefore, a module is formed by connecting more than one fuel cell with each other.

 Working Principle of Fuel Cell

Fuel cells basically react with hydrogen, which is their fuel, and as a result of this reaction, electricity, heat and pure water are produced. Hydrogen fuel is supplied from the anode side of the fuel cell and air is supplied from the cathode side. Hydrogen dissociates into positive and negative ions at the anode. Positive ions reach the cathode tip by passing through the electrolyte, which allows only positively charged ions to pass. Since the electrons remaining at the anode tip tend to recombine with the positively charged ions, they flow to the cathode side with an external circuit. Electricity is produced by this flow of electrons in the external circuit. Electrons passing to the cathode side combine with positive ions and air to form pure water. The reactions of this process are as follows.

Anode reaction:H₂–> 2H⁺+2e^–

Cathode reaction:½ O₂+2H⁺+2e^––> H₂O

Total Reaction:H₂+1/2O₂–>H₂O

 

Fuel Cell Working Diagram

 

If we describe the generation of electricity with a fuel cell in stages;

1.       step : Hydrogen is added to the fuel cell

2.       Step: The hydrogen entering the fuel cell is decomposed into its ions by the catalysts on the anode surface and prevents the electron passage. Only protons pass through the electrode and flow towards the cathode.

3.       Step: These electrons, which cannot pass through the electrolyte, pass to the cathode via a conductive external circuit and form an electric current.

4.       Step: Protons passing through the cathode combine with electrons from the external circuit to form hydrogen again.

5.       Step: In hydrogen, water is formed by combining with the air given by the cathode and the water is transferred to the external environment as exhaust.

 

Types of Fuel Cell

Fuel cells are classified according to the type of fuel used, the type of electrode and electrolyte, and the active operating temperature. The following table lists the operating temperatures of the fuel cell types and the electrolyte types used.

 

Fuel Cell Type	Electrolyte	Operating Temperature (0C)
Alkaline Fuel Cell	KOH (Potasyum Oksit)	50-90
Proton Changing Membrane Fuel Cell	Polymer	0-125
Fuel Cell Directly Using Methanol	Sulfuric Acid or Polymer	50-120
Phosphoric Acid Fuel Cell	Phosphoric acid	190-210
Molten Carbonate Fuel Cell	Li/K carbonate mixture	630-650
Katı Oksit Yakıt Pili	Zirconium	900-1000

 

In the table below, the ideal operating temperatures, efficiency values, the amount of power per cm2 of a cell and the usage areas of these fuel cells are given.

 

Fuel Cell Type	Operating Temperature (0C)	Yield (%)	Power Density (mW/cm2)	Kullanım Alanları
Alkaline Fuel Cell	50-90	50-60	100-200	It is used in space technologies.
Proton Changing Membrane Fuel Cell	50-125	50-60	350	in the aerospace and transportation industries
Fuel Cell Directly Using Methanol	50-120	30-40	40	It is used in the transportation, computer and telephone industries.
Phosphoric Acid Fuel Cell	180-210	55	100	It is used in cogeneration systems and transportation.
Molten Carbonate Fuel Cell	630-650	60-65	100	It is used in cogeneration systems.
Solid Oxide Fuel Cell	900-1000	55-65	240	It is used in cogeneration systems.

 

Although fuel cells are structurally similar to batteries, there are great differences in operation. In terms of both portability and efficiency, it has taken its place in most sectors today and will reach a much more advanced level in the future.