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where M is the molar mass of the substance (usually given in SI units of grams per mole) and v is the valency of the ions. For Faraday's first law, M, F, v are constants; thus, the larger the value of Q, the larger m will be.
), and produces chlorine (Cl 2) gas. However, at the cathode, instead of sodium ions being reduced to sodium metal, water molecules are reduced to hydroxide ions (OH −) and hydrogen gas (H 2). The overall result of the electrolysis is the production of chlorine gas, hydrogen gas, and aqueous sodium hydroxide (NaOH) solution.
An electrolytic process is the use of electrolysis industrially to refine metals or compounds at a high purity and low cost. Some examples are the Hall-Héroult process [1] used for aluminium, or the production of hydrogen from water.
The chemical reactions in the cell involve the electrolyte, electrodes, and/or an external substance (fuel cells may use hydrogen gas as a reactant). In a full electrochemical cell, species from one half-cell lose electrons ( oxidation ) to their electrode while species from the other half-cell gain electrons ( reduction ) from their electrode.
The National Renewable Energy Laboratory estimated in 2006 that 1 kg of hydrogen (roughly equivalent to 3 kg, or 4 liters, of petroleum in energy terms) could be produced by wind powered electrolysis for between US$5.55 in the near term and US$2.27 in the longer term.
The applied voltage which is just sufficient to overcome the back EMF due to polarization and also to bring about the electrolysis of an electrolyte without any hindrance is known as decomposition potential. The decomposition potential Ed is composed of various potentials and is given by: Ea (min)= Ed= Eb+ Es+ Ev. where: Ea = applied potential
A particularly efficient way of generating hydrogen (10 kWh/kg H2) is the methane plasmalysis. [8] In this process, methane (e.g. from natural gas) is decomposed in the plasma under oxygen exclusion, forming hydrogen and elemental carbon, as in the following reaction equation:
Usually, the electricity consumed is more valuable than the hydrogen produced, so this method has not been widely used. In contrast with low-temperature electrolysis, high-temperature electrolysis (HTE) of water converts more of the initial heat energy into chemical energy (hydrogen), potentially doubling efficiency to about 50%.