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Fuel Cell PEMFC Electric Power from Hydrogen

PEMFC fuel cell or PEFC electric power from hydrogen

Hydrogen atom

One of the fuel cell operation technology PEMFC or PEFC is an acronym for ‘cell proton exchange membrane fuel’. This cell, received its name because its main component is a polymeric membrane which separates the electrodes and allows the passage of protons (ions) and is resistant to the passage of electric current, acting as an electrolyte.

This fuel cell technology is a well-advanced stage of development, it is recognized as the replacement of internal combustion engines in automáveis and buses.

On this page you will meet some of the main components of it and also its operation through animation.

Components of a Fuel Cell PEMFC or PEFC

componentes de uma célula ou pilha a combustível PEMFC ou PEFC

These are some of the main components of a cell to PEMFC fuel (Proton Exchange Membrane Fuel Cells) or PEFC, followed by the description of the roles that act.

Ion exchange membrane

Componentes da PEMFC ou PEFC - Membrana de Troca de Íons

Manufactured from a polymeric material, known commercially as Nafion for example, when hydrated allows the conduction of protons (H +) in its interior, it also acts as an electrical insulator and separating fuel gas and oxidizer.

These features are critical to the operation of the fuel cell if the polymer membrane present electrical conductivity, the electrons migrate through it, rather than by the external circuit, causing a short circuit in the cell.

The conduction of H + ions inside the polymer is achieved thanks to the way it was devised. It has two distinct phases. 1) structural and 2) responsible for ionic conduction. Structural: basically its skeleton consists of Teflon, which is insoluble in water and chemically stable for several substances which interact with them in the pH conditions existing in the cell (i.e., at different levels of acidity) Ion Conduction: Teflon this chain are acidic groups that interact with water. These acidic groups provide free H + ions inside the polymer, and thus easily conduct these ions when the electric potential arises in the operation of the cell.

It is easy to understand the operation of the Nafion. Acidic solutions (dilute acid in water) are good conductors of ions H +. However, a liquid can not separate two volumes of gas without generating new engineering problems. To overcome these technological barriers created a hybrid material, a type of insoluble support containing in its interior acidic groups which form small acid solution cores which maintain the conductive characteristics of H + ions and at the same time providing a physical barrier for the separation of fuel and oxidant gases.

The need to keep the membrane hydrated, limited operating temperature, ambient pressure PEM cell type at 100 ° C. In practical terms it operates in the range between 80 ° C and 90 ° C,

Electro Catalyst (electrode)

Componentes da PEMFC ou PEFC - Eletro-catalizador - Eletrodo

Due to the low operating temperature of the PEM cell (less than 100 ° C) the use of noble metals is needed -As platinum and ruthenium, reduced to nano partículas- as catalysts to achieve high electrical currents. To understand why the use of catalysts or electrocatalysts, you must understand what a catalytic converter does and how hydrogen and oxygen interact.

By definition, a catalyst is any substance that increases the rate of a reaction without, however, be consumed therein. In the fuel cell, the hydrogen arrives at the anode (negative electrode) to be adsorbed on the electrode surface-in this case, they have a broken link, separating the electron-proton ions H + (proton) generated can migrate through the membrane, to the other side and combine with oxygen to form water as a byproduct. If there was not a catalyst in hydrogen bonding would be difficult to be broken and a minor amount of H + ions generated would be in the same time interval. Consequently a much smaller electric current would be produced (as electric current is a direct measure of the speed of the chemical reactions involved generated).

It is known that with increasing temperature there is an exponential increase in the rate of a chemical reaction. Therefore there is great interest in modified membranes to increase the operating temperature of the cell, therefore the power density and thus reduce the amount of noble material required for the generation of high electric currents.

Porous layers diffusing gas and electricity conductive

Componentes da PEMFC ou PEFC - Membrana de Troca de Íons

The electrode is essentially a thin catalytic layer -aplicada by airbrushing, for example- that needs to be supported by some structure. This structure is the gas diffusion layer which, in addition to mechanical support, also acts on the homogeneous distribution of the gases in the catalytic layer. And so it guarantees the supply of fuel and oxidant to all catalytic points.

It is an important part, since the homogeneous distribution of gases is essential for all areas to participate in catalytic chemical reactions. In the current state of the art it is composed of a partially teflonado carbon cloth to prevent soaking and obstructs the pores with water, obstructing the passage of gas. This layer is also responsible for conducting electrons, which originated in breaking the hydrogen bond in the catalytic sites, and are drained by it.

Retainers

Componentes da PEMFC ou PEFC - retentores

Its basic function is to prevent the leakage of reactant gases to the environment and separate the plates of support, if they come into contact, ocasionariam a short circuit.

Support plates and flow of gases

Componentes da PEMFC ou PEFC - Membrana de Troca de Íons

Its main function is to make a first distribution of gas along the diffusion layer. Machined coils have in their faces, in order to maximize the distribution of gas and the removal of water generated in the fuel UnionThe process with the oxidant. They are also responsible for keeping the layers together, sandwiched between them. These parts, although simple in its form, is an engineering challenge of materials and manufacturing processes. The PEMFC cell function leading H + ions, these ions raise the internal acidity of the cell, resulting in a pH atmosphere with close to zero and a metal hardly resist corrosion in this medium. Another need of the plates is to possess high electrical conductivity, since they receive all electrical current from diffusing porous layers. The available technological solution are plates made of very hard carbon, difficult to be worked and extremely fragile impact.

There are special composites and alloys of flexible carbon that are candidates for composition of these parts, however, are still trade secrets.

Engineering operation of a PEMFC fuel cell to

The fuel cell is supplied to the anode side H2 in the form of molecules (hydrogen gas). For a feature that makes it unique, the hydrogen atom, in its most common isotope, has not neutral.

When contacting the catalyst, the hydrogen molecule (H2) is dissociated into its atoms in an exothermic reaction (generating heat) and each of them loses its single electron. The fuel cell electrolyte membrane is resistant to the flow of electrons (electricity) and permeable to hydrogen ion (proton), which migrates to the cathode side of which is supplied with air from the atmosphere rich in oxygen. This migration changes the electrical balance of the cell, forcing the electrons to migrate for a path of least resistance, this flow of electrons is the energy that we use to do work (light bulb), the electric current.

On the side of the cathode, an oxygen molecule dissociates into two atoms of this element. Each oxygen atom joins two hydrogen ions and two electrons forming a water molecule.

Eduardo Stefanelli

Engenheiro por profissão, professor por vocação