A chemically modified electrode is an

electrical conductor In physics and electrical engineering, a conductor is an object or type of material that allows the flow of charge (electric current) in one or more directions. Materials made of metal are common electrical conductors. The flow of negatively c ...

that has its surface modified for different

electrochemical Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference and identifiable chemical change. These reactions involve electrons moving via an electronically conducting phase (typi ...

functions. Chemically modified

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas). In electrochemical cells, electrodes are essential parts that can consist of a varie ...

s are made using advanced approaches to electrode systems by adding a

thin film A thin film is a layer of materials ranging from fractions of a nanometer ( monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many ...

or layer of certain chemicals to change properties of the conductor according to its targeted function.Alkire, R., Kolb, D., & Lipkowski, J., Chemically modified electrodes, Germany: Wiley-VCH, Weinheim, 2009 At a modified electrode, an

oxidation-reduction Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

substance accomplishes

electrocatalysis An 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 ca ...

by transferring electrons from the electrode to a reactant, or a reaction

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

.Murray R. W.,Goodenough J. B. and Albery W. J., Modified Electrodes: Chemically Modified Electrodes for Electrocatalysis, The Royal Society, 1981, pp. 253-265, https://www.jstor.org/stable/36940 Modifying electrodes' surfaces has been one of the most active areas of research interest in

electrochemistry Electrochemistry is the branch of physical chemistry concerned with the relationship between Electric potential, electrical potential difference and identifiable chemical change. These reactions involve Electron, electrons moving via an electronic ...

since 1979, providing control over how

s interacts with their environments.

Description

Chemically modified

electrodes An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas). In electrochemical cells, electrodes are essential parts that can consist of a variety ...

are different from other types of electrodes as they have a molecular

monolayer A monolayer is a single, closely packed layer of entities, commonly atoms or molecules. Monolayers can also be made out of cells. ''Self-assembled monolayers'' form spontaneously on surfaces. Monolayers of layered crystals like graphene and molyb ...

or micrometers-thick layers of

film A film, also known as a movie or motion picture, is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, emotions, or atmosphere through the use of moving images that are generally, sinc ...

made from a certain chemical (depending on the function of the electrode). The

is coated on the surface of the electrode. The outcome would be a modified electrode with special new chemical properties in terms of physical, chemical, electrochemical, optical, electrical, transport, and other useful properties.Durst, R., Baumner, A., Murray, R., Buck, R., & Andrieux, C., Chemically modified electrodes: Recommended terminology and definitions, IUPAC, 1997, pp 1317-1323, http://old.iupac.org/publications/pac/1997/pdf/6906x1317.pdf Chemically modified electrodes and electrodes in general heavily depend on

electron transport An electron transport chain (ETC) is a series of protein complexes and other molecules which transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples this ...

: a general term for electrochemical processes where the

charge Charge or charged may refer to: Arts, entertainment, and media Films * ''Charge, Zero Emissions/Maximum Speed'', a 2011 documentary Music * ''Charge'' (David Ford album) * ''Charge'' (Machel Montano album) * '' Charge!!'', an album by The Aqu ...

transports through the chemical films to the electrode. The term "coverage" is used to express the area-normalized in mol/m^2 of a specific type of chemical site in the thin chemical film in on the surface of the chemically modified electrode.

Purpose of developing chemically modified electrodes

Advancements in the field of electrochemical science kept getting more thorough until scientists in the field found no use of bare surfaces to continue their investigations. The reason behind that is that researches that involved electrodes required certain chemical and physical properties that did not naturally exist in the materials used as electrical conductors. To work their way out of the dilemma, they used

chemical modification Chemical modification refers to a number of various processes involving the alteration of the chemical constitution or structure of molecules. Chemical modification of proteins Chemical modification is the change of biomolecular structure and ...

to tailor the materials they used. Atoms, molecules, and nano-particles are attached to the surface of materials to modify their electronic and structural properties, leading to changing their functionality.

Applications of chemically modified electrodes

In their first stages, chemically modified electrodes were merely applied in technologies they were initially made for (tuning

surface A surface, as the term is most generally used, is the outermost or uppermost layer of a physical object or space. It is the portion or region of the object that can first be perceived by an observer using the senses of sight and touch, and is ...

s for electrochemical investigations). After that, chemically modified electrodes provided powerful routes to tune the performance of electrodes. The modification of electrodes facilitated the following processes in electroanalytical chemistry: * Providing selectivity of electrodes * Resisting

fouling Fouling is the accumulation of unwanted material on solid surfaces. The fouling materials can consist of either living organisms (biofouling, organic) or a non-living substance (inorganic). Fouling is usually distinguished from other surfac ...

* Concentrating species * Improving electrocatalytic properties * Limiting access of interferences in complex samples It also provided a route for other purposes, such as: * Researching

energy conversion Energy transformation, also known as energy conversion, is the process of changing energy from one form to another. In physics, energy is a quantity that provides the capacity to perform Work (physics), work (e.g. lifting an object) or provides ...

* Researching the phenomena that influence electrochemical processes * Storing and protecting

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

* Developing

molecular electronics Molecular electronics is the study and application of molecular building blocks for the fabrication of electronic components. It is an interdisciplinary area that spans physics, chemistry, and materials science. It provides a potential means to ...

* Developing

electrochromic devices An electrochromic device (ECD) controls optical properties such as optical transmission, absorption, reflectance and/or emittance in a continual but reversible manner on application of voltage ( electrochromism). This property enables an ECD to be ...

The research fields where chemically modified electrodes are used include: ;Basic electrochemical investigations:

Electron transfer Electron transfer (ET) occurs when an electron relocates from an atom, ion, or molecule, to another such chemical entity. ET describes the mechanism by which electrons are transferred in redox reactions. Electrochemical processes are ET reactio ...

between electrodes and

electrolytes An electrolyte is a substance that conducts electricity through the movement of ions, but not through the movement of electrons. This includes most soluble salts, acids, and bases, dissolved in a polar solvent like water. Upon dissolving, t ...

. ; Electrostaticity on electrode surfaces: stationary or slow electric charges. ;

Polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

and ionic transport:Movement of electrons from one species or atom to another, with a special focus on polymers. ;Design of electrochemical systems and devices:The creation of systems and devices that use chemically modified electrodes with all the required specifications of the systems or devices.

Approaches to chemically modify electrodes

The surface of electrodes can be modified in the following ways: ;(1)

Adsorption Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a ...

(

Chemisorption Chemisorption is a kind of adsorption which involves a chemical reaction between the surface and the adsorbate. New chemical bonds are generated at the adsorbent surface. Examples include macroscopic phenomena that can be very obvious, like co ...

): A method that uses the same kind of valence forces involved in formation of chemical compounds, where the film is strongly adsorbed, or chemisorbed, onto the surface of the electrode, yielding monolayer coverage. This approach involves substrate-coupled

self-assembled monolayers Self-assembled monolayers (SAM) are assemblies of organic molecules that form spontaneously on surfaces by adsorption and organize themselves into more or less distinct domains (head group, chain/backbone, and tail/end group). In some cases, mole ...

(SAMs), where molecules are spontaneously chemisorbed to the surface of the electrode, resulting in a microscopic

superlattice A superlattice is a periodic structure of layers of two (or more) materials. Typically, the thickness of one layer is several nanometers. It can also refer to a lower-dimensional structure such as an array of quantum dots or quantum wells. Dis ...

structure of layers formed on it. Self-assembled monolayer

;(2)

Covalent bonding A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...

: A method that uses

chemical agents A chemical weapon (CW) is a specialized munition that uses chemicals formulated to inflict death or harm on humans. According to the Organisation for the Prohibition of Chemical Weapons (OPCW), this can be any chemical compound intended as a ...

to create a covalent bond between one or more monomolecular layers of the chemical modifier and the electrode surface. The common agents to use in this method include organosilanes and

cyanuric chloride Cyanuric chloride is an organic compound with the formula (NCCl)3. This white solid is the chlorinated derivative of 1,3,5-triazine. It is the trimer of cyanogen chloride. Cyanuric chloride is the main precursor to the popular but controversi ...

.Colorado State University Fort Collins Department of Chemistry, Chemically modified electrodes, 1994, http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA279821 ;(3) Polymer film coating: A method that uses one of the following to hold electron-conductive and nonconductive polymer films on the electrode surface: * Chemisorption and low solubility in the contacting solution * Physical anchoring in a

porous Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...

electrode This method includes removing chemical species (substrate) from self-assembled monolayers to allow adsorbing molecules on the electrode surface independently of the original substrate structure. The polymer films can be

organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ Chemistry * Organic matter, matter that has come from a once-living organism, is capable of decay or is the product ...

organometallic Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...

inorganic An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemistry''. Inor ...

, and it can either contain the chemical

modifier Modifier may refer to: * Grammatical modifier, a word that modifies the meaning of another word or limits its meaning ** Compound modifier, two or more words that modify a noun ** Dangling modifier, a word or phrase that modifies a clause in an am ...

or have the chemical added to the polymer in a latter process. ;(4) Composite: A method that has the chemical modifier mixed with an electrode matrix material. An example for this method is having an electron-transfer

mediator Mediation is a structured, voluntary process for resolving disputes, facilitated by a neutral third party known as the mediator. It is a structured, interactive process where an independent third party, the mediator, assists disputing parties ...

(the chemical modifier) mixed with carbon particles in a carbon paste electrode (the electrode matrix). Carbon paste, glassy carbon paste, glassy carbon etc. electrodes when modified are termed as chemically modified electrodes. Chemically modified electrodes have been employed for the analysis of organic and inorganic species.{{cite journal, last=Sanghavi, first=Bankim, author2=Srivastava, Ashwini, title=Simultaneous voltammetric determination of acetaminophen, aspirin and caffeine using an in situ surfactant-modified multiwalled carbon nanotube paste electrode, journal=Electrochimica Acta, year=2010, volume=55, issue=28, pages=8638–8648, doi=10.1016/j.electacta.2010.07.093

References

Electrodes