Electrocatalyst

[1] Homogeneous electrocatalysts, which are soluble, assist in transferring electrons between the electrode and reactants, and/or facilitate an intermediate chemical transformation described by an overall half reaction.

[6] In other cases, an electrocatalyst can impart selectivity by favoring specific chemical interaction at an electrode surface.

The activity of electrocatalysts can be assessed quantitatively by the current density is generated, and therefore how fast a reaction is taking place, for a given applied potential.

The extra energy required to overcome kinetic barriers is usually described in terms of low faradaic efficiency and high overpotentials.

[9] A homogeneous electrocatalyst is one that is present in the same phase of matter as the reactants, for example, a water-soluble coordination complex catalyzing an electrochemical conversion in solution.

Immobilizing the protein onto an electrode surface and employing an electron mediator greatly improves the efficiency of this process.

[18] The effectiveness of bioelectrocatalysts generally depends on the ease of electron transport between the active site of the enzyme and the electrode surface.

For example, formate dehydrogenase, a nickel-containing enzyme, has inspired the development of synthetic complexes with similar molecular structures for use in CO2 reduction.

[17][20] Microbial-based systems leverage the metabolic pathways of an entire organism, rather than the activity of a specific enzyme, meaning that they can catalyze a broad range of chemical reactions.

[17] Microbial fuel cells can derive current from the oxidation of substrates such as glucose,[20] and be leveraged for processes such as CO2 reduction.

[17] 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.

[7] The nature of the electrocatalyst surface determines some properties of the reaction including rate and selectivity.

[2] Water electrolysis is conventionally conducted at inert bulk metal electrodes such as platinum or iridium.

[21] The activity of an electrocatalyst can be tuned with a chemical modification, commonly obtained by alloying two or more metals.

This is due to a change in the electronic structure, especially in the d band which is considered to be responsible for the catalytic properties of noble metals.

[24]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.

[29] Graphene can also serve as a platform for constructing composites with other kinds of nanomaterials such as single atom catalysts.

[30] Because of their conductivity, carbon-based materials can potentially replace metal electrodes to perform metal-free electrocatalysis.

Electrocatalysts can promote the reduction of carbon dioxide into methanol and other useful fuel and stock chemicals.

Although this process is thermodynamically favored, the activation barrier is extremely high, so in practice this reaction is not typically observed.

However, electrocatalysts can speed up this reaction greatly, making methanol a possible route to hydrogen storage for fuel cells.

A platinum cathode electrocatalyst's stability being measured by chemist Xiaoping Wang
Types of electrocatalyst materials, including homogeneous and heterogeneous electrocatalysts.
Electronic density difference of a Cl atom adsorbed on a Cu(111) surface obtained with a density functional theory simulation. Red regions represent the abundance of electrons, whereas blue regions represent deficit of electrons.
Electronic density difference of a Cl atom adsorbed on a Cu(111) surface obtained with a DFT simulation.
An example of a particle-size effect: the number of reaction sites of different kinds depends on the size of the particle. In this four FCC nanoparticles model, the kink site between (111) and (100) planes (coordination number 6, represented by golden spheres) is 24 for all of the four different nanoparticles, while the number of other surface sites varies.
Some transition metal complexes that exhibit some activity as homogeneous electrocatalysts. [ 10 ] [ 11 ]
A schematic of a hydrogen fuel cell. To supply hydrogen, electrocatalytic water splitting is commonly employed.