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Four basic elements of a PEM fuel cell
When hydrogen comes in contact with the catalyst, the hydrogen splits into protons and electrons. The protons pass through the proton exchange membrane unimpeded and proceed to the cathode side, while the electrons are blocked and forced to travel through an external circuit. As they travel along the external circuit, they provide the electricity needed to illuminate a lightbulb or drive a motor. Eventually the hydrogen protons and electrons reunite and combine with oxygen to produce water.
The negative post of the fuel cell has several jobs. It has channels etched into it that disperse hydrogen gas equally over the surface of the catalyst. It also conducts the electrons freed from the hydrogen molecules, so that they can be used in an external circuit.
The positive post of the fuel cell, also has channels etched into it that distribute the oxygen to the surface of the catalyst. The cathode also conducts the electrons back from the external circuit to the catalyst, where they can recombine with the hydrogen ions and oxygen to form water.
This is the proton exchange membrane. This specially treated material, which looks something like ordinary kitchen plastic wrap, conducts only positively charged ions and blocks electrons. For a PEMFC, the membrane must be hydrated in order to function and remain stable
This is a special material that facilitates the reaction of oxygen and hydrogen. It is usually made of platinum nanoparticles very thinly coated onto carbon paper or cloth. The catalyst is rough and porous so the maximum surface area of the platinum can be exposed to the hydrogen or oxygen.
Hydrogen gas enters the fuel cell on the anode side, where the electrochemical potential pulls it through the catalyst
When hydrogen molecules come in contact with the platinum on the catalyst, they split into two protons (H+ ions) and two electrons (e-).
Meanwhile, on the cathode side of the fuel cell, oxygen gas is being forced through the catalyst, where it forms two oxygen atoms. These atoms have a strong negative charge, which pulls the two hydrogen protons through the exchange membrane.
The electrons simultaneously travel through the anode and make their way through an external circuit generating electricity, eventually returning to the cathode side of the fuel cell.
Fuel Cell Module
All these reactions occur in a cell stack. Cell stacks are contained within a larger system that includes fuel, water and air management, coolant control, hardware, and software. The systems vary in size and use according to their different applications, from transportation to industrial machinery to backup power that can supplement the electric grid.
Advantages of fuel cell technology
- By converting chemical potential energy directly into electrical energy, fuel cells avoid a thermal bottleneck (a consequence of the second law of thermodynamics) and are therefore inherently more efficient than combustion engines, which must first convert chemical potential energy into heat, and then mechanical work.
- The absence of tailpipe emissions provides an environmental advantage compared to an internal combustion engine.
- Fuel cells has few moving parts, which increases reliability and reduces maintenance compared to an internal combustion engine.
- When hydrogen is generated from renewable electricity—like solar—wind, or hydropower—it is a completely decarbonized and renewable fuel with zero emissions.