What is the basic principle of the power generation system using fuel cells?

Fuel cells generate electricity through a reaction between hydrogen and oxygen. As they discharge only water, they are a completely clean, promising form of energy.

About FCs

Fuel cells are innovative electricity generators. They differ completely from the conventional batteries in that they generate electricity by a reaction between hydrogen and oxygen (obtained from air). Unlike conventional fossil fuels, fuel cells do not discharge harmful emissions, and they provide higher energy efficiency. Therefore, concentrated efforts are being made on a worldwide basis to develop fuel cells as solutions for global environment and energy problems. This section describes the fuel cells and hydrogen used as fuel.

 

Principles

Simply stated, the fundamental principle of fuel cells is that they use the reverse process to water electrolysis. For water electrolysis,current is supplied to water containing an electrolyte*,thereby generatin hydrogen and oxygen. In a fuel cell with an electrolyte between electrodes, hydrogen is supplied to one electrode and oxygen to the other, thereby causing a chemical reaction which results in generation of water and electricity

* Electrolyte:A substance of which the ions move, causing the substance to conduct electricity. Only ions can pass through an electrolyte. Electrons can scarcely pass through it.

Water Electrolysis,Fuel Cell

Difference between Water Electrolysis and Fuel Cell Process

Features

Clean

Because fuel cells generate electricity directly by chemical reaction between hydrogen and oxygen without burning hydrogen, they do not discharge harmful emissions such as carbon dioxide (CO2). The only emission from them is water. Therefore, they are very clean power sources.

High Efficiency

In theory, fuel cells can convert 83% of hydrogen energy into electrical energy. When fuel cells use hydrogen as their fuel, they are very energy-efficient in comparison with gasoline engines, which provide efficiencies up to about 40%.

Types of Fuel Cells

There are four major types of fuel cells currently under study. They are used in different ways according to their different characteristics, which include working temperature, fuel used and output power. Solid polymer fuel cell batteries are used mainly for fuel cell vehicles. This type of batteries includes a polymer ion exchange film serving as an electrolyte. They work at the relatively low temperature of 80<C to 100<C. They feature high output efficiency even when their size is reduced. They have potential applications for fixed household power systems and vehicles.

Types of Fuel Cells, and Their Output Power and Applications

Solid Polymer Fuel Cells

Like a flat dry battery, solid polymer fuel cells include a solid polymer (electrolyte) film placed between positive and negative electrode plates. There are numerous thin grooves on the positive (oxygen) and negative (hydrogen) electrodes. Oxygen and hydrogen supplied from outside flow along these grooves on both sides of the electrolyte film, thereby causing a chemical reaction which results in electricity generation. Because one cell produces a limited output, as many cells as necessary for the desired output are stacked. A stack of these cells is a fuel cell stack or FC stack, which is called a fuel cell battery.

Cell Configuration

Cell Configuration

Fuel Cell Battery Configuration

Fuel Cell Battery Configuration
  1. Hydrogen molecules (H2), supplied from outside, release two electrons (e-) and become hydrogen ions (H+).
  2. The electrons from the hydrogen pass through the external circuit and flow to the oxygen electrode on the opposite side as current.Generation of Electricity
  3. At the oxygen electrode, oxygen molecules (O2) from the air accept the electrons returned from the external circuit and become oxygen ions (O2-).
  4. The oxygen ions combine with the hydrogen ions (2H+) passed through the electrolyte to form water (H2O).