5. PEM electrolyzer

PEM electrolyzers are characterized by their very simple construction and their compactness. The operating principle of electrolysis of water with an electrolyte protons exchange membrane (PEM) is simple. When operating in electrolysis, the water decomposes at the anode into protons and molecular oxygen. The oxygen is evacuated by the water circulation, and the protons migrate to the cathode under the effect of the electric field. There, they are reduced to molecular hydrogen. Each proton carries with it a procession of several molecules of solvation water: it is the electro-osmotic flow.

The appearance of the first ion exchange membranes in the 1940s made it possible to seriously consider industrial applications for this zero-gap concept with immobilized electrolyte. Notably, as early as 1953, at the dawn of the American space program, the US General Electric Company suggested for the first time the use of cation exchange membranes as a solid polymer electrolyte for the production of acid fuel cells. The US solid polymer electrolyte (SPE) concept was born. Applied to the electrolysis of water, it was hoped to be able to operate

for minimizing investment costs and increasing the volume density of production. Unlike fuel cells, the electrolysis of water SPE requires a polymeric material that is very resistant to the

Solid oxide fuel cells are electrochemical devices that can operate reversibly in the electrolysis

Electrolysis at high temperature allows decreasing the electric consumption because with the increase of the temperature offers an additional part of the global energy; which allows high

The main advantage is that a substantial part of the energy required for the electrolysis process is added in the form of heat, which is much cheaper than electrical energy. In addition, the high temperature promotes the conduction of the electrolyte and accelerates the kinetics of the reaction, reducing the energy loss due to the polarization of the electrode. Thus, the efficiency of the electrolysis at high temperature is higher than that obtained at low temperature. The typical high-temperature electrolyzer can achieve an electrical efficiency of 92% while the

The high-temperature system uses oxygen ion conducting ceramics as an electrolyte (ZrO2 stabilized by Y2O3, MgO or CaO). The water is brought to a temperature of 200C to supply steam in the cathode. The electrolysis cell operates at a temperature of 800–1000C, which ensures the conduction of the solid electrolyte. The water vapor is decomposed into hydrogen gases and oxygen ions (O<sup>2</sup>). The oxygen ions are transported through the ceramic solid

Hydrogen has a low carbon footprint. It could thus significantly reduce energy-related CO2 emissions and help limit climate change. Fuel cell electric vehicles (FCEVs) can provide the mobility service of today's conventional cars with potentially very low carbon emissions. Although the potential benefits of hydrogen and fuel cells in end-use applications are promising in terms of environment and energy security, the development of hydrogen production,

). This possibility was interesting

Hydrogen Generation by Water Electrolysis http://dx.doi.org/10.5772/intechopen.76814 13

at a high current density (of the order of an ampere per cm<sup>2</sup>

6. Solid oxide electrolyzer

7. Hydrogen station

oxidizing potential of the anode under the release of native oxygen.

mode. In the solid oxide electrolyzer, water vapor is reduced to H2.

electrolyzers at low temperature reach a maximum of 85% efficiency.

electrolyte to the anode, where they are oxidized to form gaseous oxygen.

operational efficiencies in the solid oxide electrolyzer.

During the twentieth century, several major innovations have significantly increased the energy and faradic efficiencies of electrolyzers. The concept of zero-gap cells has been developed in order to overcome the disadvantages of the electro-osmotic flow. It consists of pressing porous electrodes against the solid separator in order to reduce the interpolar distance and to reject the gas production at the rear of the interpolar space.

The zero-gap concept with immobilized electrolyte goes even further: it consists of maintaining the electrolyte (acid) in the separator so as to be able to electrolyze the water in the acidic medium while avoiding corrosion problems. Of course, this interesting approach was practically limited by the leakage of electrolyte pushed back into the circuit of the electrolyzer.

The membrane thus serves both electrolyte and separator of electrodes and gases. Therefore, the membrane must have certain physicochemical properties, such as:


Compared to a liquid electrolyte, we can note some behavioral deference resulting from the properties of this assembly:


The appearance of the first ion exchange membranes in the 1940s made it possible to seriously consider industrial applications for this zero-gap concept with immobilized electrolyte. Notably, as early as 1953, at the dawn of the American space program, the US General Electric Company suggested for the first time the use of cation exchange membranes as a solid polymer electrolyte for the production of acid fuel cells. The US solid polymer electrolyte (SPE) concept was born. Applied to the electrolysis of water, it was hoped to be able to operate at a high current density (of the order of an ampere per cm<sup>2</sup> ). This possibility was interesting for minimizing investment costs and increasing the volume density of production. Unlike fuel cells, the electrolysis of water SPE requires a polymeric material that is very resistant to the oxidizing potential of the anode under the release of native oxygen.
