**1.1.2 Alkaline fuel cell (AFC)**

140 Electrochemical Cells – New Advances in Fundamental Researches and Applications

reactions that involve natural fuels are feasible or not and how they can be efficient. The first experimental studies, conducted after the publication of Ostwald's document, indicated that it was very difficult to build devices for the direct electrochemical oxidation of natural fuels

Ceramic fuel cells came up much later, initially with the discovery of the Nernst solid oxide electrolytes in 1899 [9]. Nearly forty years later, the first ceramic fuel cells began operating at 1000 °C, developed by Baur and Preis in 1937 (Farooque & Maru, 2001). Since 1945, three research groups (USA, Germany and the USSR) made studies on a few main types of generators by improving their technologies for industrial development. This work yielded

Nowadays, the development of fuel cells is being mainly driven by environmental reasons mentioned above. Over the last decades, advances in research made possible for a considerable improvement to happen, regarding the characteristics of the cells, in particular their stability and efficiency. Currently, it is possible to classify the fuel cells into two major groups, which differ by basic operational characteristics: the low-temperature and high

The first large group of fuel cells, the low temperature ones (50 - 250 °C), is characterized by its more focused application on mobile devices and the automotive industry. Within the large group of low-temperature cells, there can also be a division, considering the type of electrolyte used. This classification results in three cell types: proton exchange membrane

PEM fuel cell uses a solid polymer electrolyte, which is an excellent protonic conductor. In this electrolyte the ion exchange occurs between two porous electrodes. The operating

The advantages of PEM fuel cell are its high charge density and its fast startup time, interesting features for automotive applications. The low temperature makes the technology competitive in the transportation sector and in commercial applications such as laptop computers, bicycles and mobile phones. The main disadvantages of PEM fuel cell are its low operating efficiency (40-45%) and the use of a noble catalyst such as platinum, whose CO intolerance ends up limiting the further popularization of this cell type (Farooque & Maru,

Two subcategories of PEM fuel cells are currently being widely studied, for allowing the use of other fuels other than hydrogen directly into the cell: direct methanol (DMFC) and direct

DMFC and DEFC fuel cells use a solid polymer electrolyte for ionic transport. However, they use, respectively, liquid methanol and ethanol as fuel instead of hydrogen. During chemical reactions, the fuel (methanol or ethanol) is directly oxidized in the anode. At the cathode, the reaction occurs with oxygen, producing electricity and water as a byproduct

fuel cell (PEMFC), alkaline fuel cell (AFC); and phosphoric acid fuel cell (PAFC).

temperature of the fuel cell type PEM is about 100 °C (Ellis et al., 2001).

(Wand, 2006).

temperature fuel cells.

2001).

ethanol (DEFC).

(Ellis et al., 2001; Garcia et al., 2004).

**1.1 Low-temperature fuel cells** 

the current concepts on fuel cells (Wand, 2006).

**1.1.1 Proton exchange membrane fuel cell (PEMFC)** 

Initially, it was called Bacon cell, by virtue of its inventor Francis Thomas Bacon. It operates at low temperature around 100 °C and it is able to achieve 60-70% efficiency. It uses an aqueous solution of potassium hydroxide (KOH) as electrolyte solution. This fuel cell has quick startup speed, one of its great advantages. The main disadvantage is that it is very sensitive to CO2 (Farooque & Maru, 2001). It needs an external system to remove CO2 from the air. Furthermore, the use of a liquid electrolyte is also a disadvantage because it reduces the cell lifetime and makes the assembly handling and transport more difficult.
