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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.
The platinum electrode common to much of electrochemistry is electrocatalytically involved in many reactions. For example, hydrogen is oxidized and protons are reduced readily at the platinum surface of a standard hydrogen electrode in aqueous solution, in a Hydrogen Evolution Reaction.
A schematic of a hydrogen fuel cell. To supply hydrogen, electrocatalytic water splitting is commonly employed. Hydrogen and oxygen can be combined through by the use of a fuel cell. In this process, the reaction is broken into two half reactions which occur at separate electrodes.
The catalytic performance of Mo3P nanoparticles is tested in the hydrogen evolution reaction (HER), indicating an onset potential of as low as 21 mV, H2 formation rate, and exchange current density of 214.7 μmol/(s·g) cat (at only 100 mV overpotential) and 279.07 μA/cm 2, respectively, which are among the closest values yet observed to platinum.
To focus on the reaction at the working electrode, the reference electrode is standardized with constant (buffered or saturated) concentrations of each participant of the redox reaction. [1] There are many ways reference electrodes are used. The simplest is when the reference electrode is used as a half-cell to build an electrochemical cell.
For example, in aqueous conditions the competing reactions in the cell are the formation of oxygen at the anode and hydrogen at the cathode. In this case a graphite anode and lead cathode could be used effectively because of their high overpotentials for oxygen and hydrogen formation respectively. Many other materials can be used as electrodes.
Electrochemical cells – generates electrical energy from chemical reactions; Electrotyping – a process used to create metal copies of designs by depositing metal onto a mold using electroplating; Electrowinning – a process that extract metals from their solutions using an electric current
During the early development of electrochemistry, researchers used the normal hydrogen electrode as their standard for zero potential. This was convenient because it could actually be constructed by "[immersing] a platinum electrode into a solution of 1 N strong acid and [bubbling] hydrogen gas through the solution at about 1 atm pressure".