Proton conductor

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A proton conductor is an electrolyte, typically a solid electrolyte, in which H+ [1] are the primary charge carriers.

An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent, such as water. The dissolved electrolyte separates into cations and anions, which disperse uniformly through the solvent. Electrically, such a solution is neutral. If an electric potential is applied to such a solution, the cations of the solution are drawn to the electrode that has an abundance of electrons, while the anions are drawn to the electrode that has a deficit of electrons. The movement of anions and cations in opposite directions within the solution amounts to a current. This includes most soluble salts, acids, and bases. Some gases, such as hydrogen chloride, under conditions of high temperature or low pressure can also function as electrolytes. Electrolyte solutions can also result from the dissolution of some biological and synthetic polymers, termed "polyelectrolytes", which contain charged functional groups. A substance that dissociates into ions in solution acquires the capacity to conduct electricity. Sodium, potassium, chloride, calcium, magnesium, and phosphate are examples of electrolytes.

In chemistry, a hydron is the general name for a cationic form of atomic hydrogen, represented with the symbol H+
. However, this term is avoided and instead "proton" is used, which strictly speaking refers to the cation of protium, the most common isotope of hydrogen. The term "hydron" includes cations of hydrogen regardless of their isotopic composition: thus it refers collectively to protons (1H+) for the protium isotope, deuterons (2H+ or D+) for the deuterium isotope, and tritons (3H+ or T+) for the tritium isotope. Unlike most other ions, the hydron consists only of a bare atomic nucleus.


Acid solutions exhibit proton-conductivity, while pure Proton Conductors are usually dry solids. Typical materials are polymers or ceramic. Typically, the pores in practical materials are small such that protons dominate direct current and transport of cations or bulk solvent is prevented. Water ice is a common example of a pure proton conductor, albeit a relatively poor one. [2]

Grotthuss mechanism

The Grotthuss mechanism is the process by which an 'excess' proton or proton defect diffuses through the hydrogen bond network of water molecules or other hydrogen-bonded liquids through the formation and concomitant cleavage of covalent bonds involving neighboring molecules.

Proton nucleon (constituent of the nucleus of the atom) that has positive electric charge; symbol p

A proton is a subatomic particle, symbol
, with a positive electric charge of +1e elementary charge and a mass slightly less than that of a neutron. Protons and neutrons, each with masses of approximately one atomic mass unit, are collectively referred to as "nucleons".

Ice water frozen into the solid state

Ice is water frozen into a solid state. Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color.

Solid-phase proton conduction was first suggested by Alfred Rene Jean Paul Ubbelohde and S. E. Rogers. in 1950. [3] , although electrolyte proton currents have been recognized since 1806.

Theodor Grotthuss Chemist, photochemist

Freiherr Christian Johann Dietrich Theodor von Grotthuss was a German chemist known for establishing the first theory of electrolysis in 1806 and formulating the first law of photochemistry in 1817. His theory of electrolysis is considered the first description of the so-called Grotthuss mechanism.

Proton conduction has also been observed in the new type of proton conductors for fuel cells - protic organic ionic plastic crystals (POIPCs), such as 1,2,4-triazolium perfluorobutanesulfonate [4] and imidazolium methanesulfonate. [5] In particular, a high ionic conductivity of 10 mS/cm is reached at 185 °C in the plastic phase of imidazolium methanesulfonate.

A plastic crystal is a crystal composed of weakly interacting molecules that possess some orientational or conformational degree of freedom. The name plastic crystal refers to the mechanical softness of such phases: they resemble waxes and are easily deformed. If the internal degree of freedom is molecular rotation, the name rotor phase or rotatory phase is also used. Typical examples are the modifications Methane I and Ethane I. In addition to the conventional molecular plastic crystals, there are also emerging ionic plastic crystals, particularly organic ionic plastic crystals (OIPCs) and protic organic ionic plastic crystals (POIPCs). POIPCs are solid protic organic salts formed by proton transfer from a Brønsted acid to a Brønsted base and in essence are protic ionic liquids in the molten state, have found to be promising solid-state proton conductors for high temperature proton exchange membrane fuel cells. Examples include 1,2,4-triazolium perfluorobutanesulfonate and imidazolium methanesulfonate.

When in the form of thin membranes, proton conductors are an essential part of small, inexpensive fuel cells. The polymer nafion is a typical proton conductor in fuel cells. A jelly-like substance similar to nafion residing in the ampullae of Lorenzini of sharks has proton conductivity only slightly lower than nafion. [6]

Nafion chemical compound

Nafion is a brand name for a sulfonated tetrafluoroethylene based fluoropolymer-copolymer discovered in the late 1960s by Walther Grot of DuPont. Nafion is a brand of the Chemours company. It is the first of a class of synthetic polymers with ionic properties that are called ionomers. Nafion's unique ionic properties are a result of incorporating perfluorovinyl ether groups terminated with sulfonate groups onto a tetrafluoroethylene (PTFE) backbone. Nafion has received a considerable amount of attention as a proton conductor for proton exchange membrane (PEM) fuel cells because of its excellent thermal and mechanical stability.

Ampullae of Lorenzini

The ampullae of Lorenzini are special sensing organs called electroreceptors, forming a network of jelly-filled pores. They are mostly discussed as being found in cartilaginous fish ; however, they are also reported to be found in Chondrostei such as reedfish and sturgeon. Lungfish have also been reported to have them. Teleosts have re-evolved a different type of electroreceptors. They were first described by Stefano Lorenzini in 1678.

High proton conductivity has been reported among alkaline-earth cerates and zirconate based perovskite materials such as acceptor doped SrCeO3, BaCeO3 and BaZrO3. [7] Relatively high proton conductivity has also been found in rare-earth ortho-niobates and ortho-tantalates as well as rare-earth tungstates.[ citation needed ]

A zirconate is an oxyanion containing zirconium. Examples include Na2ZrO3, Ca2ZrO4 which can be prepared by fusing zirconium dioxide with e.g. Na2O and CaO respectively.

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Proton-exchange membrane fuel cell

Proton-exchange membrane fuel cells, also known as polymer electrolyte membrane (PEM) fuel cells (PEMFC), are a type of fuel cell being developed mainly for transport applications, as well as for stationary fuel-cell applications and portable fuel-cell applications. Their distinguishing features include lower temperature/pressure ranges and a special proton-conducting polymer electrolyte membrane. PEMFCs generate electricity and operate on the opposite principle to PEM electrolysis, which consumes electricity. They are a leading candidate to replace the aging alkaline fuel-cell technology, which was used in the Space Shuttle.

Solid oxide fuel cell fuel cell that has a ceramic electrolyte

A solid oxide fuel cell is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. Fuel cells are characterized by their electrolyte material; the SOFC has a solid oxide or ceramic electrolyte.

Ionic liquid salt in the liquid state, largely made of ions and short-lived ion pairs (while ordinary liquids such as water and gasoline are predominantly made of electrically neutral molecules)

An ionic liquid (IL) is a salt in the liquid state. In some contexts, the term has been restricted to salts whose melting point is below some arbitrary temperature, such as 100 °C (212 °F). While ordinary liquids such as water and gasoline are predominantly made of electrically neutral molecules, ionic liquids are largely made of ions and short-lived ion pairs. These substances are variously called liquid electrolytes, ionic melts, ionic fluids, fused salts, liquid salts, or ionic glasses. They are known as "solvents of the future" as well as "designer solvents".

A proton-exchange membrane, or polymer-electrolyte membrane (PEM), is a semipermeable membrane generally made from ionomers and designed to conduct protons while acting as an electronic insulator and reactant barrier, e.g. to oxygen and hydrogen gas. This is their essential function when incorporated into a membrane electrode assembly (MEA) of a proton-exchange membrane fuel cell or of a proton-exchange membrane electrolyser: separation of reactants and transport of protons while blocking a direct electronic pathway through the membrane.

Deep eutectic solvents are systems formed from a eutectic mixture of Lewis or Brønsted acids and bases which can contain a variety of anionic and/or cationic species. They are classified as types of ionic solvents with special properties. They incorporate one or more compound in a mixture form, to give a eutectic with a melting point much lower than either of the individual components. One of the most significant deep eutectic phenomenon was observed for a mixture of choline chloride and urea in a 1:2 mole ratio. The resulting mixture has a melting point of 12 °C, which makes it liquid at room temperature.

Protonic ceramic fuel cell

A protonic ceramic fuel cell or PCFC is a fuel cell based on a ceramic electrolyte material that exhibits high protonic conductivity at elevated temperatures.

Nanoionics is the study and application of phenomena, properties, effects and mechanisms of processes connected with fast ion transport (FIT) in all-solid-state nanoscale systems. The topics of interest include fundamental properties of oxide ceramics at nanometer length scales, and fast ion conductor /electronic conductor heterostructures. Potential applications are in electrochemical devices for conversion and storage of energy, charge and information. The term and conception of nanoionics were first introduced by A.L. Despotuli and V.I. Nikolaichik in January 1992.

In materials science, fast ion conductors are solids with highly mobile ions. These materials are important in the area of solid-state ionics, and are also known as solid electrolytes and superionic conductors. These materials are useful in batteries and various sensors. Fast ion conductors are used primarily in solid oxide fuel cells. As solid electrolytes they allow the movement of ions without the need for a liquid or soft membrane separating the electrodes. The phenomenon relies on the hopping of ions through an otherwise rigid crystal structure.

Ionic conduction is the movement of an ion from one site to another through defects in the crystal lattice of a solid or aqueous solution.

Yttria-stabilized zirconia

Yttria-stabilized zirconia (YSZ) is a ceramic in which the cubic crystal structure of zirconium dioxide is made stable at room temperature by an addition of yttrium oxide. These oxides are commonly called "zirconia" (ZrO2) and "yttria" (Y2O3), hence the name.

Solid solid object

Solid is one of the four fundamental states of matter. In solids particles are closely packed. It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a gas does. The atoms in a solid are tightly bound to each other, either in a regular geometric lattice or irregularly. Solids cannot be compressed with little pressure whereas gases can be compressed with little pressure because in gases molecules are loosely packed.

Solid state ionics

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Sossina M. Haile is an Ethiopian-American chemist, known for developing the first solid acid fuel cells. She is a professor of Materials Science and Engineering at Northwestern University, Illinois, USA.

Polymer electrolyte membrane electrolysis Polymer electrolyte membrane electrolysis

Proton exchange membrane (PEM) electrolysis is the electrolysis of water in a cell equipped with a solid polymer electrolyte (SPE) that is responsible for the conduction of protons, separation of product gases, and electrical insulation of the electrodes. The PEM electrolyzer was introduced to overcome the issues of partial load, low current density, and low pressure operation currently plaguing the alkaline electrolyzer.

Caesium hydrogen sulfate

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Mixed conductor Mixed ion-electron conductor

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Solid acid fuel cells (SAFCs) are a class of fuel cells characterized by the use of a solid acid material as the electrolyte. Similar to proton exchange membrane fuel cells and solid oxide fuel cells, they extract electricity from the electrochemical conversion of hydrogen- and oxygen-containing gases, leaving only water as a byproduct. Current SAFC systems use hydrogen gas obtained from a range of different fuels, such as industrial-grade propane and diesel. They operate at mid-range temperatures, from 200 to 300 °C.


  1. Traditionally, but not precisely, H+ ions are referred as "protons".
  2. Ramesh Suvvada (1996). "Lecture 12: Proton Conduction, Stoichiometry". University of Illinois at Urbana-Champaign . Retrieved 2009-12-06.
  3. S. E. Rogers & A. R. Ubbelohde (1950). "Melting and Crystal Structure III: Low-melting Acid Sulphates". Transactions of the Faraday Society . 46: 1051. doi:10.1039/tf9504601051.
  4. Jiangshui Luo; Annemette H. Jensen; Neil R. Brooks; Jeroen Sniekers; Martin Knipper; David Aili; Qingfeng Li; Bram Vanroy; Michael Wübbenhorst; Feng Yan; Luc Van Meervelt; Zhigang Shao; Jianhua Fang; Zheng-Hong Luo; Dirk E. De Vos; Koen Binnemans; Jan Fransaer (2015). "1,2,4-Triazolium perfluorobutanesulfonate as an archetypal pure protic organic ionic plastic crystal electrolyte for all-solid-state fuel cells". Energy & Environmental Science . 8 (4): 1276. doi:10.1039/C4EE02280G.
  5. Jiangshui Luo, Olaf Conrad & Ivo F. J. Vankelecom (2013). "Imidazolium methanesulfonate as a high temperature proton conductor". Journal of Materials Chemistry A . 1 (6): 2238. doi:10.1039/C2TA00713D.
  7. K. D. Kreuer (2003). "Proton-conducting oxides". Annual Review of Materials Research . 33: 333. Bibcode:2003AnRMS..33..333K. doi:10.1146/annurev.matsci.33.022802.091825.