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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.
Water splitting is the chemical reaction in which water is broken down into oxygen and hydrogen: [1] 2 H 2 O → 2 H 2 + O 2. Efficient and economical water splitting would be a technological breakthrough that could underpin a hydrogen economy. A version of water splitting occurs in photosynthesis, but hydrogen is not produced.
Heat of combustion. The heating value (or energy value or calorific value) of a substance, usually a fuel or food (see food energy), is the amount of heat released during the combustion of a specified amount of it. The calorific value is the total energy released as heat when a substance undergoes complete combustion with oxygen under standard ...
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."
Hydrogenation is a chemical reaction between molecular hydrogen (H 2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic compounds.
In the combustion reaction, oxygen reacts with the fuel, and the point where exactly all oxygen is consumed and all fuel burned is defined as the stoichiometric point. With more oxygen (overstoichiometric combustion), some of it stays unreacted. Likewise, if the combustion is incomplete due to lack of sufficient oxygen, fuel remains unreacted.
Hydrogen evolution reaction (HER) is a chemical reaction that yields H 2. [ 1 ] The conversion of protons to H 2 requires reducing equivalents and usually a catalyst. In nature, HER is catalyzed by hydrogenase enzymes. Commercial electrolyzers typically employ supported platinum as the catalyst at the anode of the electrolyzer.
Appearance. In chemistry, thermochemical cycles combine solely heat sources (thermo) with chemical reactions to split water into its hydrogen and oxygen components. [ 1 ] The term cycle is used because aside of water, hydrogen and oxygen, the chemical compounds used in these processes are continuously recycled.