Hydrogen Fuel Cells . . . How Do They Work?

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Hydrogen Fuel Cells . . . What is a PEM Membrane?

It depends on who you ask.

Proton Exchange Membrane is the more commonly used term, but technically it is a polymer electrolyte membrane. It is also known as a Solid Polymer Electrolyte (SPE).

In a PEM fuel cell, sometimes referred to as PEMFC, the critical exchange takes place through a thin water-swollen co-polymer film that typically contains sulfonic acid groups. This membrane transforms chemical energy through an electrochemical reaction of hydrogen and oxygen to create electrical energy, whereas if the hydrogen was combusted, it would generate thermal energy.

A membrane electrode assembly (MEA) is made of a thin PEM having a pair of electrodes. The MEA can also be assembled in a plurality of individual PEM fuel cells to create a multi-cell stack. These MEA's are aligned face to face in electrical series while being separated one from the next by an impermeable, electrically conductive electrode plate. When stacked in series, only a single pair of opposite polarity electrodes are needed. When assembled in a fuel cell stack, each flow field plate functions as a current collector. The inlet is connected to a source of fuel in the case of an anode flow field plate, or a source of oxidant in the case of a cathode flow field plate. Oftentimes, the electrodes also function as the gas diffusion layer (“GDL”) of the fuel cell.

With the typical PEMFC, hydrogen is carried to the anode side of the membrane electrode assembly (MEA). At the anode side, it is transformed catalytically into protons and electrons. These protons are able to penetrate this membrane and end up on the cathode side of the MEA. The electrons, on the other hand, cannot penetrate the membrane and are carried to the cathode side by an external circuit, thus the electrical energy.

Hydrogen fuel cells differ from batteries in that they are designed for continuous replenishment of the reactants consumed; they produce electricity from an external supply of fuel, typically hydrogen, and an oxidant, typically oxygen.

One of the technical problems long associated with hydrogen fuel cells, is membrane hydration. In this type of fuel cell, the membrane must be hydrated, requiring water to be evaporated at precisely the same rate that it is produced. If water is evaporated too quickly, the membrane dries, resistance across it increases, and eventually it will crack, creating a gas 'short circuit' where hydrogen and oxygen combine directly, generating heat that will damage the fuel cell membrane. Just as in a combustion engine, a steady ratio between the reactant and oxygen is necessary to keep the fuel cell operating efficiently.

Hydrogen fuel cells which power transportation vehicles are subject to start/stop cycles which reduce the durability of the system. Very cold temperatures have also typically been problematic for PEM fuel cells. Even though the fuel cells are operational when temperatures drop, they need an external heat source to keep the membranes from freezing in a cold snap.

The principle of the fuel cell was discovered by German scientist Christian Friedrich Schönbein in 1838 and published in the January 1839 edition of the "Philosophical Magazine". The fuel cell he made used similar materials to today's phosphoric-acid fuel cells.

It wasn't until 1959 that British engineer Francis Thomas Bacon successfully developed a 5 kW stationary fuel cell. In 1959, a team led by Harry Ihrig built a 15 kW fuel cell tractor for Allis-Chalmers which was demonstrated across the US at state fairs.

Significant R&D efforts in the fuel cell area are being directed towards the science of fuel cell technology as well as in the areas of engineering and systems integration. Effectiveness and efficiency of a PEMFC is dependent upon the operating parameters. Some of these are temperature, fuel to air ratios, voltage, current, fuel, or air humidity. The useful life of such systems can be limited by damage including membrane thinning, weight loss, and redistribution of catalyst materials during fuel cell operation.

Hydrogen peroxide remains the most likely culprit for membrane degradation, being readily produced as a by-product under fuel cell catalysis conditions. As this technology improves, critical questions will need to be answered about the impact of polymer degradation in order to prolong PEM fuel cell lives.

Similarly, the alkaline fuel cell (AFC) was successfully developed and used by NASA's manned space missions, but its inherent intolerance to carbon dioxide makes it not effective for most of today's applications.

Now, Put your hat on backwards, and think about this . . .

The hydrogen fuel cells that I have been discussing up to this point are in simple terms a reversal of an electrolyzer. By reversing the direction of operation, water and electricity are converted into hydrogen and oxygen. Many times electrolyzer fuel cells are referenced as hydrogen fuel cells, which causes some confusion.

In the case of an electrolyzer fuel cell, electricity and distilled water are fed into the cathode side of the cell with the electricity giving up electrons, the water is split into hydrogen and oxygen.

Actually, this seems like a really nice idea for using hydrogen as a way to power a car or truck. Overall, this idea overcomes the major problems with hydrogen storage and production. Using this hydrogen from the electrolyzer cell as a fuel assist device gives the engine significantly more power. The relatively small amount of H2 generated by the electrolyzer cell is then fed directly into the air intake of the internal combustion engine (ICE). It increases the density of hydrogen associated with the ammonia in the fuel provided to the engine.

Not only do we see significant increases in horsepower, but also, depending on the engine, a huge increase in fuel efficiencies and significant reductions in emissions.

Hydrogen fuel cells are one of the most promising up-and-coming clean power sources. The Hydrogen Fuel Cell has been proposed as a power source for electric vehicles and as an alternative energy source for portable, stationary, and industrial applications.

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