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In thermolysis, water molecules split into hydrogen and oxygen. For example, at 2,200 °C (2,470 K; 3,990 °F) about three percent of all H 2 O are dissociated into various combinations of hydrogen and oxygen atoms, mostly H, H 2, O, O 2, and OH. Other reaction products like H 2 O 2 or HO 2 remain minor. At the very high temperature of 3,000 ...
In pure water at the negatively charged cathode, a reduction reaction takes place, with electrons (e −) from the cathode being given to hydrogen cations to form hydrogen gas. At the positively charged anode, an oxidation reaction occurs, generating oxygen gas and giving electrons to the anode to complete the circuit.
Since hydrogen can be used as an alternative clean burning fuel, there has been a need to split water efficiently. However, there are known materials that can mediate the reduction step efficiently therefore much of the current research is aimed at the oxidation half reaction also known as the Oxygen Evolution Reaction (OER).
Together with hydrogen (H 2), oxygen is evolved by the electrolysis of water. The point of water electrolysis is to store energy in the form of hydrogen gas, a clean-burning fuel. The "oxygen evolution reaction (OER) is the major bottleneck [to water electrolysis] due to the sluggish kinetics of this four-electron transfer reaction."
The net cell reaction yields hydrogen and oxygen gases. The reactions for one mole of water are shown below, with oxidation of oxide ions occurring at the anode and reduction of water occurring at the cathode. Anode: 2 O 2− → O 2 + 4 e −. Cathode: H 2 O + 2 e − → H 2 + O 2−. Net Reaction: 2 H 2 O → 2 H 2 + O 2
The efficiency of an electrolyser is a measure of the enthalpy contained in the hydrogen (to undergo combustion with oxygen or some other later reaction), compared with the input electrical energy. Heat/enthalpy values for hydrogen are well published in science and engineering texts, as 144 MJ/kg (40 kWh/kg).
In chemistry, the oxygen reduction reaction refers to the reduction half reaction whereby O 2 is reduced to water or hydrogen peroxide. In fuel cells, the reduction to water is preferred because the current is higher. The oxygen reduction reaction is well demonstrated and highly efficient in nature. [1] [2]
Water electrolysis – a process that uses an electric current to split water molecules into hydrogen and oxygen gases Electrolytic capacitors – a type of capacitor that uses an electrolytic solution as one of its plates