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Glossary

Everything about fuel cells and alternative energy, from A to Z.

A

Alkaline Fuel Cell (AFC) - Also known as the Bacon fuel cell after its British inventor, is one of the most developed fuel cell technologies. NASA has used alkaline fuel cells since the mid-1960s, in Apollo-series missions and on the Space Shuttle. AFCs consume hydrogen and pure oxygen producing potable water, heat, and electricity. They are among the most efficient fuel cells, having the potential to reach 70%.

Alternative Energy - Any energy generating process alternative to the burning of fossil fuels.

Anode - An electrode through which a positive electrical charge flows into a polarized electrical device.

B

Battery - A device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy.

C

Catalyst - An added substance that increases the rate at which a chemical reaction occurs.

Cathode - An electrode through which a negative electrical charge flows into a polarized electrical device. 

Current - The flow of an electrical charge.

D

Direct Borohydride Fuel Cell (DBFC) - A subcategory of alkaline fuel cells which are directly fed by sodium borohydride or potassium borohydride as a fuel and either air/oxygen or hydrogen peroxide as the oxidant. DBFCs are relatively new types of fuel cells which are currently in the developmental stage and are attractive due to their high operating potential in relation to other type of fuel cells.

Direct Ethanol Fuel Cell (DEFC) - A type of fuel cell that where the fuel, ethanol, is fed directly to the fuel cell.

Direct Methanol Fuel Cell (DMFC) - A PEM fuel cell, which uses methanol rather than hydrogen as a fuel. The overall reaction of a DMFC is a redox reaction, reacting with methanol and oxygen to produce electricity, water and carbon dioxide. The anode catalyst used in DMFC's is platinum ruthenium and the cathode catalyst is platinum black.

E

Electrode - An electrical conductor used to make contact with a nonmetallic part within a circuit.

Electrolyte - A substance that ionizes when dissolved in an ionizing solvent such as water.

Electrolyzer - A device that induces electrolysis, the decomposition of water into its elements, hydrogen and oxygen.

F

Flux - Rate of flow per area of a property. Flux can also be referred to as flux density or current density.

Fuel Cell - A device that converts the chemical energy of a fuel to electrical energy. Fuel cells differ from batteries in that they require an external fuel, while batteries contain a finite amount of stored chemical energy to convert to electrical energy.

Fusion - The phenomenon in which two or more atomic nuclei collide, producing energy. Fusion is most likely to occur between two nuclei with very small atomic numbers. In order for fusion to occur, an extremely high temperature must be reached to overcome the repulsion between the two isotopes. Nuclear fusion is the main source of the Sun's energy. Solar energy is actually a form of nuclear energy from far away.

G

Gas Diffusion Electrode (GDE) - Gas diffusion electrodes are essentially gas diffusion layers made into an anode or cathode when painted with a specific catalyst.

Gas Diffusion Layer (GDL) - Thin, porous carbon woven sheets that are conductive, semi-water proof and regulate the flux, or flow per area of gas reactants within the fuel cell.

Generator - A device that is used to convert mechanical energy to electrical energy.

H

Hydrogen - An element in gas form at room temperature with the lowest atomic number, the lowest number of protons at one proton. For hydrogen-oxygen and hydrogen air fuel cells, hydrogen is the fuel of choice to be used in the fuel cell's reverse electrolysis procedure to create energy and water.

I

Isotope - Atoms that of the same element (have the same atomic number or number of protons within the nucleus) but have different mass numbers (different numbers of neutrons within the nucleus). Hydrogen in its normal state, H2 and tritium, H3 are isotopes.

Ion - An atom or molecule that has an uneven amount of protons and electrons, giving the said atom or molecule a net charge. The higher this net charge is, the more reactive the ion is.

J

K

L

M

Membrane Electrode Assembly (MEA) - The meat and potatoes of the fuel cell, the all-in-one MEA consists of a polymer membrane, and two gas diffusion electrodes (anodes and cathodes) that all work in unison to perform the electrochemical process to extract energy from the fuel cell's provided fuel.

Metal Hydride - The anion of hydrogen, hydride or H- is used to properly and effectively store hydrogen. Hydride absorbs H2, allowing the H2 released to be regulated. Because of the chemical storage, small leaks in the metal tank will not result in an abrupt loss or explosion of hydrogen.

Metal Hydride Fuel Cell (MHFC) - A subclass of alkaline fuel cells that are in the research and development phase. A notable feature is their ability to chemically bond and store hydrogen within the cell. This feature is shared with direct borohydride fuel cells, although the two differ in that MHFCs are refueled with pure hydrogen.

Microbial Fuel Cell (MFC) - A bio-electrochemical system that drives a current by using bacteria and mimicking bacterial interactions found in nature. MFCs can be grouped into two general categories, those that use a mediator and those that are mediator-less. The first MFCs, demonstrated in the early 20th century, used a mediator: a chemical that transfers electrons from the bacteria in the cell to the anode. Mediator-less MFCs are a more recent development dating to the 1970s; in this type of MFC the bacteria typically have electrochemically active redox proteins such as cytochromes on their outer membrane that can transfer electrons directly to the anode.

Molten-Carbonate Fuel Cell (MCFC) - High-temperature fuel cells that use an electrolyte composed of a molten carbonate salt mixture suspended in a porous, chemically inert ceramic matrix of beta-alumina solid electrolyte (BASE). Since they operate at extremely high temperatures of 650°C (1,202°F) and above, non-precious metals can be used as catalysts at the anode and cathode, reducing costs.

Mylar - A polyester film manufactured by DuPont and used for gasketing (to prevent reactant gas leakage within the fuel cell).

N

O

P

Phosphoric Acid Fuel Cell (PAFC) - A type of fuel cell that uses liquid phosphoric acid as an electrolyte.

Platinum - The staple catalyst of the fuel cell industry. Platinum is combined with carbon to make an ink for electrodes within a fuel cell.

Polymer Electrolyte Membrane - Reference Proton Exchange Membrane.

Proton Exchange Membrane (PEM) - A membrane that allows H+ ions to travel through it while forcing electrons to skip around to the cathode, creating electrical energy.

Proton Exchange Membrane Electrolyzer - The electrolysis of water in a fuel 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 electroyzer was introduced to overcome the issues of partial load, low current density, and low pressure operation currently plaguing the alkaline electrolyzer.

Proton Exchange Membrane Fuel Cell(PEMFC) - A type of fuel cell that uses a water-based, acidic polymer membrane as its electrolyte, with platinum-based electrodes. PEMFC cells operate at relatively low temperatures (below 100 degrees Celsius) and can tailor electrical output to meet dynamic power requirements. Due to the relatively low temperatures and the use of precious metal-based electrodes, these cells must operate on pure hydrogen. PEMFC cells are currently the leading technology for light duty vehicles and materials handling vehicles, and to a lesser extent for stationary and other applications. The PEMFC fuel cell is also sometimes called a polymer electrolyte membrane fuel cell.

Q

R

Redox Flow Battery - A type of rechargeable battery where recharge-ability is provided by two chemical components dissolved in liquids contained within the system and separated by a membrane. Ion exchange (providing flow of electric current) occurs through the membrane while both liquids circulate in their own respective space. A flow battery is technically akin both to a fuel cell and an electrochemical accumulator cell (electrochemical reversibility).

Reversible (Regenerative) Fuel Cell - A fuel cell that runs in reverse mode, which consumes electricity and chemical B to produce chemical A. By definition, the process of any fuel cell could be reversed. However, a given device is usually optimized for operating in one mode and may not be built in such a way that it can be operated backwards. Standard fuel cells operated backwards generally do not make very efficient systems unless they are purpose-built to do so as with high-pressure electrolysers, regenerative fuel cells, solid-oxide electrolyser cells and unitized regenerative fuel cells.

S

Silicon - silicon rubber is used to make air-tight gasketing and tubing for fuel cells.

Solid Oxide Fuel Cell (SOFC) - An electrochemical conversion device that produces electricity directly from oxidizing a fuel. The marking characteristic of a SOFC is its ceramic electrolyte.

T

Turbine - A device that turns current from running water, and pressure from steam and gusts of wind into mechanical energy, which can then be converted into electrical energy by a generator.

U

V

Voltage - The electrical potential difference between two given points.

W

Wind Farm - A group of wind turbines working in unison to convert enough mechanical energy from the wind gusts to electrochemical energy. Wind farms can be onshore, grounded on large patches of land, or offshore, in the ocean.

X

Y

Z

Zinc Air Fuel Cell - Metal-air fuel cells powered by oxidizing zinc with oxygen from the air. These fuel cells have high energy densities and are relatively inexpensive to produce.