Electrochemistry Dictionary - F

F: Symbol and abbreviation of farad, and symbol and abbreviation of the Faraday number. (Often a "bold-face" letter is used for the latter, but this is not a general practice.) It is usually obvious from the context which meaning is appropriate.
Failure: The state in which the performance of a cell or battery does not meet the normal specifications.
farad: Measurement unit of capacitance. Symbol: "F," which is the same as the symbol of the Faraday Number. It is usually obvious from the context which meaning is appropriate. A capacitor has a capacitance of one farad when one coulomb charges it to one volt.
Faraday shield (cage): a network of parallel wires connected to a common conductor at one end to provide electrostatic shielding without affecting electromagnetic waves. The common conductor is usually grounded.
Faraday's Laws: Some of the most fundamental laws of electrochemistry discovered by Faraday in the 1830's. They are usually stated as: (1) In any electrolytic process the amount of chemical change produced is proportional of the total amount of electrical charge passed through the cell. (2) The mass of the chemicals changed is proportional to the chemicals' equivalent weight. The proportionality constant being the Faraday Number.
Faraday Number (Faraday constant): The Faraday Number (or constant) gives the amount of electrical charge needed to change one gram-equivalent of substance by electrochemical reaction. Its value is 96,485.34 coulombs or 26.80 ampere-hours. This charge is often simply called one "Faraday." Symbol: "F," which is the same as the symbol of the farad. It is usually obvious from the context which meaning is appropriate. The Faraday number is the product of Avogadro's number and the electrical charge of a single electron.
Faradic current (density): The current (or current density) that is flowing through an electrochemical cell and is causing (or is caused by) chemical reactions (charge transfer) occurring at the electrode surfaces. Contrast with capacitive current.
Faradaic reaction: See heterogeneous charge-transfer reaction.
Filling solution: See internal electrolyte.
First kind electrode: See electrode of the first kind.
Fixed ion: The permanently attached charged fragment in an ion-exchange resin. Contrast with counterion.
Flade potential: Alternative name for the passivation potential.

Flat-plate array: A photovoltaic array in which the incident solar radiation strikes a flat surface and no concentration of sunlight is involved.
Float charging: A method of maintaining a rechargeable battery in a fully charged condition by continuous, long-term, constant-voltage charging, at a level sufficient to balance self-discharge. See also trickle charging.
Float voltage: The voltage required for retaining a rechargeable battery in fully charged condition. See float charging.
Flow-through electrode: An electrode that permits the electrolyte to flow through it, e.g., a porous electrode or a packed-bed electrode. This type of electrode is especially useful for removing small traces of impurities from the solution by electrolysis (e.g., waste treatment) because the solution contacts a large surface of the electrode material.
Fluidized bed electrode: See packed bed electrode.
Formal electrode potential: Similar to a standard electrode potential except that both the oxidized and the reduced species are present in unit concentration instead of unit activity. It is not as well defined as the standard potential but it is useful in cases when the activities are unknown.
Forming: Electrochemical processing of a rechargeable battery by repeated charging/discharging that converts the electrode materials into usable form. This treatment is needed for some batteries during manufacturing, or when first put into use (and sometime when returned to service after a long storage). Also called "conditioning."
Formula weight: Essentially the same as the molecular weight, but it can be used more generally, e.g., also for ions.

Fresnel lens: A concentrating lens, positioned above and concave to a PV material to concentrate light on the material.
Fuel cell: A device that converts chemical energy into electrical energy. It is different from a battery in that the energy conversion continues till fuel and oxidizing agent are fed to the fuel cell; that is, in principle indefinitely. (A battery is manufactured with a limited amount of chemicals, and it is exhausted when all the chemicals have reacted.) It is a galvanic cell, where spontaneous chemical reactions occur at the electrodes. The fuel is oxidized at the anode, and the oxidizing agent (almost always oxygen or air) is reduced at the cathode. Presently, the most commonly used fuel is hydrogen. More conventional fuels (e.g., gasoline or natural gas) must be converted ("reformed") into hydrogen before they can be utilized in a fuel cell. Fuel cells that can burn hydrocarbon fuels directly are in the development stage. Some fuel cells employ an aqueous solution as electrolyte, that can be either acidic or basic (alkaline), or an ion-exchange membrane soaked in aqueous solution can act as the electrolyte (see PEM) these fuel cells operate at relatively low temperatures (from room temperature to not much above the boiling point of water). Some fuel cells employ molten salts (especially carbonates) as electrolytes and have to operate at many hundreds of ^oC temperature. Others employ ionically conductive solids as electrolyte and must operate close to 1000 ^oC. A single fuel cell has a rather small (typically less then one volt) cell voltage. For practical applications a large number of them are assembled, series coupled, in what is called a "fuel cell stack." (A term essentially analogous to the original meaning of the battery.)
Fugacity: The expression of "activity" for a component in a mixture of gases. It has the same physical meaning as the activity for a component in a solution.