A fuel cell is an electrochemical energy generation device that combines hydrogen with oxygen in the air to produce electricity, with water and heat as the only by-products.
Safe, functional and efficient fuel cell systems, toghether with their supporting infrastructure of electrolyzers and hydrogen refuelling stations (HRS), will play a fundamental role in the transition to sustainable energy.
The scope of today’s fuel cell systems extends from small scale portable applications in the Watt range to large field installations with power supply in the MW scale.
When hydrogen comes into contact with a catalyst, the hydrogen splits into protons and electrons. The protons cross a special membrane without encountering obstacles and proceed towards the cathode, while the electrons are forced through an external circuit.
As the electrons travel through the external circuit, they provide electricity, which can be used to illuminate a light bulb or drive a motor. Eventually, the protons and electrons of hydrogen come back together and combine with oxygen to produce water.
All of these reactions occur within a battery. The batteries are contained within a larger system that contains the fuel, water, air management system, cooling control, mechanics and software.
The systems vary in size and use depending on the different applications: transport, industrial machinery, power grids.
ADVANTAGES OF FUEL BATTERY TECHNOLOGY
By converting potential chemical energy directly into electrical energy, fuel cells help 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 the potential chemical energy into heat, hence into mechanical work.
Pure water flows out of the system’s exhaust duct, with no emissions of particulates or other gases, with a significant environmental advantage over an internal combustion engine.
Fuel cells have few moving parts, which increases their reliability and reduces maintenance, compared to an internal combustion engine.
When hydrogen is generated from renewable electricity sources, such as wind, solar or hydroelectric power, the related CO2 emissions are extremely low.
The ability of hydrogen to combine with oxygen was first discovered by Henry Cavendish in 1766. The first electrolyzer appeared later, in the 1800s, when Nicholson and Carlisle induced a static charge in the water.
Electrolysis cells are characterized by their electrolytic type. There are two types of low-temperature electrolysis: alkaline and proton exchange membrane (PEM).
In alkaline electrolysis, a reaction takes place between two electrodes in a solution of water and a molten electrolyte. When sufficient voltage is applied, the water molecules use electrons to produce OH ions and a H2 molecule. OH ions travel through the solution to an anode, where they combine and lose their additional electrons to produce water, electrons and O2.
The recombination of hydrogen and oxygen, in this phase, is avoided by means of special ion exchange membranes. The electrolyte remains in the system due to a closed-loop recirculation process without a pump.
PEM electrolysis creates a reaction using an ionically conductive solid polymer, instead of a liquid one. When voltage is applied between the two electrodes, the negatively charged oxygen in the water molecules releases its electron, which translates into protons, electrons and O2 at the anode. H+ ions travel through the conductive polymer proton to the cathode, where they take on an electron and become neutral H atoms. The latter combine to produce H2 at the cathode. The electrolyte and the two electrodes are enclosed between two bipolar plates, which transport water towards them, transport gaseous products away from the cell, conduct electricity and circulate a refrigerant fluid to cool the process.
Alkaline and PEM technologies have the ability to provide:
Just like with fuel cells, single-cell electrolyzers can be connected in series, creating a battery – the main component of the electrolyzer system – where hydrogen and oxygen are produced.