PEM fuel cells



Contrary to what people could think, the concept of the fuel cell is not a modern invention. The principle of operation of the fuel cell is actually very old, discovered by Sir William Grove in 1839.

Despite sporadic attempts to develop a practical device, the Grove´s “gas voltaic battery” remained a scientific curiosity for nearly a century. It was another English scientist Francis T. Bacon, who resumed work on these devices in 1937, developing a stack of 6 kW in the late 1950s.

PEM fuel cells are electrochemical devices that produce continuously electric power and heat, while being fed with hydrogen gas and air, and having only pure water as a byproduct. The Stack is made up of cells stacked in series. In each of these cells it is carried out the chemical reaction between hydrogen and oxygen, producing an electrical potential. However the electrical potential or voltage is very small, in the order of 1 V, therefore, it is necessary to stack in series tens or even hundreds of cells to produce higher voltages.

Each one of these cells consists of three main elements: the bipolar plate, MEA and gasket.

PEMFC is an acronyms of Polymer Electrolyte Membrane Fuel Cell and the electrolyte is made of a polymeric membrane contained in the MEA. The Membrane separates the anode and cathode of the cell, and it is a proton conductor, which allows H+ ions pass through it, but with the particularity of being impermeable to other substances.

Basically, a cell consists of three zones: a cathode electrode, an anode electrode and, in the middle, the electrolyte membrane which physically separates the gas of both sides. The fuel, in this case hydrogen, is introduced to the anode side through the channels in the bipolar plate and it is taken to the catalytic layer where the decomposition of hydrogen in protons and electrons occurs.

The generated protons cross the proton exchange polymer membrane, but electrons cannot cross, since membrane is not electrically conductive. Electrons are conducted through an alternative circuit, formed by the bipolar plates and an external circuit, creating an electrical current that can supply electrical power to an external device. On the other side of the cell, air enters through the channels of the bipolar plate and it is taken to the catalytic layer of the cathode, where oxygen is combined with protons passing through the membrane and electrons coming from the external circuit, producing water and heat.
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