Why electrolysis of water

A ignited wood stick shown to glow more brightly in the presence of concentrated oxygen gas collected in a test tube. Hydrogen gas collected in a test tube is ignited using a bunsen burner. By multiplying the equation for the reaction at the cathode by two and then combining it to the equation for the reaction at the anode you get:. Simplifying the equation by cancelling out the electrons, hydroxide ions, and by reducing the water by two units on both sides gives you the overall equation above.

Skip to main content. 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. 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: High ionic conductivity to promote proton migration and reduce ohmic drop;. Compared to a liquid electrolyte, we can note some behavioral deference resulting from the properties of this assembly: The anionic charges of the membrane are fixed; there can be no concentration gradient in their case.

The gas evolution is done by the back of the electrodes, the ohmic drop is not disturbed by the reactions to the electrodes, in return, it is necessary to make laying electrodes to allow gas release. The nature of the ions also intervenes, but the water content of the membrane, different according to the nature of the ions carried and according to the conditions of preparation and use of the membrane, will condition both its thickness, its mechanical strength, and especially its conductivity.

The appearance of the first ion exchange membranes in the s made it possible to seriously consider industrial applications for this zero-gap concept with immobilized electrolyte. Notably, as early as , 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.

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 2. 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.

Solid oxide fuel cells are electrochemical devices that can operate reversibly in the electrolysis mode. In the solid oxide electrolyzer, water vapor is reduced to H 2. 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 operational efficiencies in the solid oxide electrolyzer. 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 oxygen ions are transported through the ceramic solid electrolyte to the anode, where they are oxidized to form gaseous oxygen.

Hydrogen has a low carbon footprint. It could thus significantly reduce energy-related CO 2 emissions and help limit climate change. 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, transport, and distribution are difficult. Although the first VECFs were developed in the s, it is only in the last 10 years that the technology of using hydrogen as an energy carrier has begun to develop.

Also, some automakers announce the launch of FCEV. Generally, hydrogen station consists of hydrogen production process including desulfurizer, reformer, water gas shift WGS reactor and pressure swing adsorption PSA apparatus, and post-treatment process including a compressor, storage, and distributer [ 45 ]. Research on the development of the hydrogen station is actively conducted in advanced countries such as the United States, Canada, Japan and Europe. An overview of existing and planned hydrogen refueling stations is given in Table 2 [ 46 ].

Existing public hydrogen refueling stations and targets announced by hydrogen initiatives [ 46 ]. Currently, more than 79 hydrogen stations are operating worldwide and others are planned in the future.

Table 3 summarizes the current status of hydrogen station research and development programs and demonstration experiments at home and abroad [ 45 ]. Hydrogen economy is a promising instrument for the transformation of the energy system. Hydrogen, ideal fuel for fuel cells, can have several provenances electrolysis of water, cracking or reforming of petroleum products. The production of hydrogen by the water electrolysis technique gives the concept renewability because it can use a non-greenhouse gas energy source renewable or nuclear energy.

This technique provides applications that require small volumes of high purity hydrogen, including the semiconductor and food industry. Acid solutions are good electrolytes in water electrolyzers because acidic media show high ionic conductivity and are free from carbonate formation, as compared with alkaline electrolytes. But the acid needs the use of noble metals as electrocatalysts for OER.

Consequently, potassium hydroxide is most commonly used in water electrolysis, avoiding the huge corrosion loss caused by acid electrolytes, and the use of noble metals as catalysts.

Nickel is a popular electrode material due to its high activity and availability as well as low cost. PEM electrolyzers are characterized by their very simple construction and their compactness with an electrolyte protons exchange membrane PEM is simple.

It is important to note Today's grid electricity is not the ideal source of electricity for electrolysis because most of the electricity is generated using technologies that result in greenhouse gas emissions and are energy intensive.

Electricity generation using renewable or nuclear energy technologies, either separate from the grid, or as a growing portion of the grid mix, is a possible option to overcome these limitations for hydrogen production via electrolysis.

The U. Department of Energy and others continue efforts to bring down the cost of renewable-based electricity production and develop more efficient fossil-fuel-based electricity production with carbon capture, utilization, and storage. Wind-based electricity production, for example, is growing rapidly in the United States and globally. Reducing the capital cost of the electrolyzer unit and the balance of the system. Improving energy efficiency for converting electricity to hydrogen over a wide range of operating conditions.

Increasing understanding of electrolyzer cell and stack degradation processes and developing mitigation strategies to increase operational life. The electrolysis of water produces hydrogen and oxygen gases. The electrolyte is necessary because pure water will not carry enough charge due to the lack of ions. At the anode, water is oxidized to oxygen gas and hydrogen ions.