**2. The fuel cells' principle of work**

The main components of a fuel cell are two electrodes isolated from each other with a membrane (either solid or liquid electrolyte). The added parts are usually to improve the functioning of the cell. According to Eq. (1) [5], the gas fuel (hydrogen) oxidized at the anode to produces electrons and cations during entering of the oxidant from the cathode. These released electrons depart the anode through an external circuit and create an electric current before reaching the cathode. The electrons current can be utilized in working any load [5].

$$2H\_2 \rightarrow 4H^+ + 4e^- \tag{1}$$

The positive hydrogen ions diffuse through the membrane and recombine with the exhausted electrons that reached at the cathode to reproduce H2 gas. Finally, the produced hydrogen atoms combine with the oxygen atoms to generate water as the only waste of the complete reaction. Eqs. (2) and (3) show the reduction of oxygen and the fuel cell reaction, respectively [6, 7].

$$2\text{ O}\_2 + 4\text{ H}^+ + 4e^- \rightarrow 2\text{ H}\_2\text{O}\tag{2}$$

$$2H\_2 + O\_2 \rightarrow 2H\_2O \text{ + heat} \tag{3}$$

**229**

**3.1 The end plates**

**Figure 2.**

**3.2 The bipolar plates**

*Fuel Cells as a Source of Green Energy*

*DOI: http://dx.doi.org/10.5772/intechopen.89736*

of the fuel cell is displayed in **Figure 1**.

*A scheme of oxidization processes at the electrodes [13].*

the oxidization reaction schematically.

**3. The main components of fuel cells**

connection. These parts are shown in **Figure 3**.

through it in one direction only which is the direction of the cathode [8]. To reduce the reaction energy on the two electrodes, a catalyst is added [9, 10]. The structure

Theoretically, the anodic substance could be any material that gives up electrons such as hydrogen, methane, kerosene, or even carbon. But among all, hydrogen is preferred due to its availability, has a high energy density, and good reactivity with catalysts [12]. Also, the best chose of oxidant agent is oxygen gas because it is easily subjected to a reduction reaction and is much available in the air. **Figure 2** illustrates

In addition to the two electrodes and their separator electrolyte, other additional parts are required for specific tasks such as gases flow and electrical insulation or

The outer sides of the anode and the cathode are supported mechanically by plastic plates which are called the endplates. Their main jobs are to save the fuel cell

A fuel cell has two bipolar plates each one consists of a current collector and separator plate. They are manufactured from a metal or a carbon-filled composite (conductive polymer) [16]. Researchers suggested several designs of

component and to prevent the reacting gasses from leaking [15].

Fuel cell' efficiency is greatly influenced by the quality of the electrolyte. It increases with increasing the membrane ability to block electrons generated from the oxidation of the anode from reaching the cathode. Therefore, the electrolyte must be chosen with caution as it acts as a filter that allows only positive ions to pass

**Figure 1.** *The components of fuel cell [11].*

*Fuel Cells as a Source of Green Energy DOI: http://dx.doi.org/10.5772/intechopen.89736*

*Thermodynamics and Energy Engineering*

**2. The fuel cells' principle of work**

electrons current can be utilized in working any load [5].

and the fuel cell reaction, respectively [6, 7].

Fuel cells are zero pollution' power generators. They work as an electrochemical converter to chemically produce electrical energy from gas fuels. The conversion occurs directly by the chemical reactions and without burning of the fuel. Even better, they are not following the thermodynamic laws that limit most of the power plants. This chapter presents the operation principle of fuel cells, their main components, and finally the newer trends in developing these cells for commercial uses.

The main components of a fuel cell are two electrodes isolated from each other with a membrane (either solid or liquid electrolyte). The added parts are usually to improve the functioning of the cell. According to Eq. (1) [5], the gas fuel (hydrogen) oxidized at the anode to produces electrons and cations during entering of the oxidant from the cathode. These released electrons depart the anode through an external circuit and create an electric current before reaching the cathode. The

2 *H*2 → 4 *H*<sup>+</sup> + 4 *e*

*O*<sup>2</sup> + 4 *H*<sup>+</sup> + 4 *e*

The positive hydrogen ions diffuse through the membrane and recombine with the exhausted electrons that reached at the cathode to reproduce H2 gas. Finally, the produced hydrogen atoms combine with the oxygen atoms to generate water as the only waste of the complete reaction. Eqs. (2) and (3) show the reduction of oxygen

−

Fuel cell' efficiency is greatly influenced by the quality of the electrolyte. It increases with increasing the membrane ability to block electrons generated from the oxidation of the anode from reaching the cathode. Therefore, the electrolyte must be chosen with caution as it acts as a filter that allows only positive ions to pass

<sup>−</sup> (1)

→ 2 *H*2*O* (2)

2 *H*<sup>2</sup> + *O*2 → 2 *H*2*O* + *heat* (3)

**228**

**Figure 1.**

*The components of fuel cell [11].*

**Figure 2.** *A scheme of oxidization processes at the electrodes [13].*

through it in one direction only which is the direction of the cathode [8]. To reduce the reaction energy on the two electrodes, a catalyst is added [9, 10]. The structure of the fuel cell is displayed in **Figure 1**.

Theoretically, the anodic substance could be any material that gives up electrons such as hydrogen, methane, kerosene, or even carbon. But among all, hydrogen is preferred due to its availability, has a high energy density, and good reactivity with catalysts [12]. Also, the best chose of oxidant agent is oxygen gas because it is easily subjected to a reduction reaction and is much available in the air. **Figure 2** illustrates the oxidization reaction schematically.
