Electrocatalyst is a catalyst that participates in electrochemical reactions. Electrocatalysts are a specific form of catalysts that function at electrode surfaces or, most commonly, may be the electrode surface itself. An electrocatalyst can be heterogeneous such as a platinized electrode.
Homogeneous electrocatalysts, which are soluble, assists in transferring electrons between the electrode and reactants, and/or facilitates an intermediate chemical transformation described by an overall half reaction. Major challenges in electrocatalysts focus on fuel cells.
A heterogeneous electrocatalyst is one that is present in a different phase of matter from the reactants, for example, a solid surface catalyzing a reaction in solution.
Since heterogeneous electrocatalytic reactions need an electron transfer between the solid catalyst (typically a metal) and the electrolyte, which can be a liquid solution but also a polymer or a ceramic capable of ionic conduction, the reaction kinetics depend on both the catalyst and the electrolyte as well as on the interface between them. The nature of the electrocatalyst surface determines some properties of the reaction including rate and selectivity.
Electrocatalysis can occur at the surface of some bulk materials, such as platinum metal. Bulk metal surfaces of gold have been employed for the decomposition methanol for hydrogen production. Water electrolysis is conventionally conducted at inert bulk metal electrodes such as platinum or iridium.
A variety of nanoparticle materials have been demonstrated to promote various electrochemical reactions, although none have been commercialized. These catalysts can be tuned with respect to their size and shape, as well as the surface strain.
Also, higher reaction rates can be achieved by precisely controlling the arrangement of surface atoms: indeed, in nanometric systems, the number of available reaction sites is a better parameter than the exposed surface area in order to estimate electrocatalytic activity.
Sites are the positions where the reaction could take place; the likelihood of a reaction to occur in a certain site depends on the electronic structure of the catalyst, which determines the adsorption energy of the reactants together with many other variables not yet fully clarified.
The interest in reducing as much as possible the costs of the catalyst for electrochemical processes led to the use of fine catalyst powders since the specific surface area increases as the average particle size decreases.
The chloralkali process is a large scale application that uses electrocatalysts. This technology supplies most of the chlorine and sodium hydroxide required by many industries. The cathode is a mixed metal oxide clad titanium anode.
Many organofluorine compounds are produced by electrofluorination. One manifestation of this technology is the Simons process, which can be described as:
R3C–H + HF → R3C–F + H2
In the course of a typical synthesis, this reaction occurs once for each C–H bond in the precursor. The cell potential is maintained near 5–6 V. The anode, the electrocatalyst, is nickel-plated.
Acrylonitrile is converted to adiponitrile on an industrial scale via electrocatalysis.