Glossary of Fuel Cell Terms

  • Adsorption: the process by which a gas or liquid accumulates and chemical binds to the surface of a solid. This is how metal hydrides store hydrogen.
  • Alkali: The opposite of an acid. This is a chemical base, having pH less than 7. An example is potassium hydroxide, which is used as the electrolyte in alkaline fuel cells.
  • Alkaline Fuel Cell: Any Fuel cell that uses an alkaline (usually potassium hydroxide) as its electrolyte.
  • Anion: A negatively charged ion due to having more electrons than protons. Oxygen is combined with hydrogen to forma negatively charged hydride anion, which migrates through molten carbonate fuel cells toward the anode.
  • Anode: One of two electrodes in a battery or fuel cell. It is where oxidation occurs in a fuel cell, leading to electron release. When fuel cells are generating electricity, the anode is positively charged.
  • Atmospheric pressure: The pressure at any given point in the Earth’s atmosphere. It varies with altitude and is 760 mm Hg at sea level. 760 mm Hg is standard pressure.
  • Atom: The smallest unit of an element that retains the chemical and physical properties of the element. It has a nucleus composed of positively charged protons (and neutrons (no charge)in many cases) surrounded by a cloud of electrons (negative charge).
  • Auxiliary Power Unit: Provides energy for purposes other than propulsion. Abbreviated APU.
  • Balance of Plant: All components of a power generating system (such as a fuel cell) other than the primary electricity generating component.
  • Ballard Power Systems: A Canadian-based fuel cell company that develops fuel cells for multiple applications. It is one of the oldest fuel cell companies in existence.
  • Battery: An electrochemical cell which stores electricity in the form of chemical energy.
  • Biofuel: A fuel derived from recently dead biological material.
  • Biogas: The hydrocarbon gas produced by the breakdown of dead organic material. For example, methane.
  • Bipolar plate: Conductive plate in a fuel cell stack that connects the anode of one cell to the cathode of the next
  • British Thermal Unit: A measure of heat energy defined as the1/80 of the amount of heat need to raise the temperature of 1 pound of water from 0 C to 100 C at standard pressure (760 mm Hg). Abbreviated BTU.
  • Carbon dioxide: Chemical made of one carbon and 2 oxygen atoms. Written as CO2. It is a major greenhouse gas.
  • Carbon monoxoide: A carbon combined with one oxygen and written as CO. It is poisonous to humans and renders platinum catalysts useless.
  • Carbon: The sixth atom in the periodic table with 6 protons, 6 neutrons, and 6 electrons. It is found in all hydrocarbon fuels and combines with oxygen to produce carbon monoxide and carbon dioxide.
  • Carnot cycle: The theoretical thermodynamic cycle that relates the relationship between thermal energy and heat. Often used to describe internal combustion engines.
  • Carnot Limit: The maximum efficiency of heat flow between two volumes. Fuel cells are not limited by this, but internal combustion engines are.
  • Catalyst poisoning: The process of rendering a catalyst unusable. It is a problem with carbon monoxide and platinum in many fuel cells.
  • Catalyst: Any substance that increases the rate of a chemical reaction, but which is not used up by the reaction and can thus be used over and over again.
  • Cathode: One of two electrodes in a battery or fuel cell. It is where reduction occurs, meaning electrons are captured rather than released. In fuel cells that are producing electricity the cathode is negatively charged.
  • Cation: A positive ion. The proton liberated from hydrogen is a cation.
  • Celsius: The temperature scale in which 0 is freezing and 100 is boiling. It is the conventional temperature scale used in science.
  • Ceramic: Any inorganic nonmetallic material formed through heating.
  • ClearEdge Power: A fuel cell company that specializes in stationary fuel cells for residential and small commercial applications.
  • Circuit: A closed path through which electrons can flow.
  • Cogeneration: Using waste heat (from any location, but in this case from a fuel cell) for generating electricity, hot water, or heating building space.
  • Combustion: Also known as burning, this is a complex sequence of exothermal chemical reactions between a fuel and oxidant (usually oxygen). The reaction is accompanied by the production of heat and/or light.
  • Compressed hydrogen: Hydrogen in the gaseous state kept under pressure greater than standard atmospheric pressure.
  • Compressed natural gas (CNG): Natural gas which is kept under pressure. This commonly used as a fuel.
  • Coulomb: The standard international unit of electric charge. Abbreviated as C, it is equal to one ampere of electricity in one second (amp/sec).
  • Desiccant: A substance that induces or sustains a state of dryness. Also known as a hygroscopic compound.
  • Diffusion: The movement of molecules from a region of higher concentration to a region of lower concentration.
  • Direct borohydride fuel cell (DBFC): A subcategory of alkaline fuel cell but uses borohydride as a hydrogen carrier.
  • Direct carbon fuel cell (DCFC): A fuel cell that uses any organic material as a fuel. This includes wood, coal, hydrocarbons, and so forth.
  • Direct formic acid fuel cell (DFAFC): a subcategory of proton exchange membrane fuel cell where to formic acid is injected directly into the fuel cell stack. These fuel cells are commonly used in consumer electronics.
  • Direct Fuel Cell: A fuel cell in which hydrocarbon fuel is not reformed externally, but fed directly into the fuel cell. These generally do not require platinum catalysts, which would be poisoned by the production of carbon monoxide in such fuel cells.
  • Direct methanol fuel cell (DMFC): A subcategory of proton exchange membrane fuel cell where methanol is not reformed before being injected into the fuel cells stack.
  • Direct-ethanol fuel cell (DEFC): A subcategory of proton exchange membrane fuel cell where ethanol is not reformed before being injected into the fuel cell stack.
  • Distributed generation: The production of large quantities of energy from small individual sources. This is also referred to as disbursed generation, decentralized generation, or distributed energy.
  • Doping: the process of intentionally introducing impurities into a pure semiconductor in order to change its electrical properties.
  • Electrical balance of plant (EBOP): All electrical components of a power generating system. This includes such things as the user interface panel and power converter.
  • Electrical conductivity: A measure of how well a material is able to conduct an electric current. In other words, a measure of the resistance to the flow of electrical charged particles.
  • Electricity: A general term that encompasses the flow of charged particles.
  • Electrochemical cell: A device that produces electricity through a chemical reaction.
  • Electrode: A terminal that carries an electric current.
  • Electro-galvanic fuel cell (EGFC): A common device found in scuba diving apparatus and medical equipment that is used to measure the concentration of oxygen gas.
  • Electrolysis: The breakdown of a chemical through the application of an electric charge to it. This process is commonly used to break water into hydrogen and oxygen.
  • Electrolyte: A compound that can conduct electricity or charged particles. In a fuel cell, the electrolyte allows ions to move from one electrode to the other, but is impermeable to electrons.
  • Electron: A sub-atomic particle that is negatively charge and circles the nucleus.
  • Endothermic: a reaction that absorbs heat rather than releasing heat.
  • Energy conversion efficiency: The ratio between the energy obtained from a machine compared to the energy put into the machine.
  • Energy density: The amount of energy stored in a particular volume or mass of a fuel. For instance, a gallon of ethanol will release more energy when burned than a gallon of methanol. Ethanol is said to have a higher energy density.
  • Engine: Any machine that converts heat energy in mechanical energy.
  • Enthalpy: The heat content of a closed system.
  • Ethanol: The scientific term for drinking alcohol. It is composed of two carbon molecules and six hydrogen molecules. It is also known as ethyl alcohol.
  • Exothermic: A reaction that releases heat.
  • Fahrenheit: The temperature scale or water freezes at 32° and boils at 212°.
  • Flow battery: A rechargeable batteries in which the electrolyte flows through a power cell that converts chemical energy to electricity.
  • Formic acid: The simplest carboxyl with acid that the chemical formula CH2O2. It is used to power formic acid fuel cells.
  • Fossil fuel: Any hydrocarbon fuel produced from long dead organic matter.
  • Fouling: The accumulation of unwanted material on a solid surface. This commonly occurs in internal combustion engines were carbon is deposited on services such a spark plugs and cylinder heads.
  • FuelCell Energy: A fuel cell company based in the United States that specializes in stationary fuel cells.
  • Fuel cell poisoning: A decrease in a fuel cells efficiency that results from impurities binding to and reducing the function of the catalyst.
  • Fuel cell vehicle (FCV): A vehicle that uses a fuel cell for primary propulsion.
  • Fuel Cell: An electrochemical device for generating electricity.
  • Gadolinium doped ceria (GDC): One of the ceramic materials used in solid oxide fuel cells as the electrolyte.
  • Gasification: A process that converts carbon based material such as coal and petroleum and a carbon monoxide and hydrogen by reacting them up at high temperatures. The process usually involves steam.
  • Gasoline gallon equivalent (GGE): The volume or mass of fuel it takes to equal the energy content of one that liquid gallon of gasoline.
  • Glossary
  • Greenhouse effect: An increase in the temperature of the earth due to the trappings of the sun’s solar energy by gases in the atmosphere.
  • Grid-tied electrical system: A semi-autonomous electrical generating system that links to the main power grid. It can draw energy from the grid when needed and feed energy into the grid when there is an access.
  • Heat of combustion: the energy released as heat when a compound is completely burned in the presence of oxygen. The result of complete combustion of a hydrocarbon with oxygen is carbon dioxide, water, and heat.
  • Horizon Fuel Cell Technologies: A fuel cell company specializing in portable hydrogen fuel cells.
  • Hybrid electric vehicle (HEV): A vehicle which uses a conventional propulsion system as well as a rechargeable energy storage system. This would include such vehicles as the Toyota Prius.
  • Hydride ion: The smallest possible anion. It is made up of two electrons and a proton.
  • Hydride: A negatively charged a hydrogen ion. Metal hydrides are used in certain fuel cells and as hydrogen storage compounds.
  • Hydrocarbon: An organic compound that consists only of hydrogen and carbon atoms.
  • Hydrogen: The smallest of all elements, consisting of a single proton and a single electron. Hydrogen is the fuel for most fuel cells and the most abundant element in the universe.
  • Hydrogen Fuel Cell: A subtype of proton exchange membrane fuel cell in which only hydrogen and oxygen are used as fuels. The only products are water, heat, and electricity. These fuel cells are the main focus for use in automobiles.
  • Internal combustion engine (ICE): An engine in which the combustion of fuel occurs in a confined space in the interior of the engine. The space is called a combustion chamber.
  • Ion: An atom that becomes positively or negatively charged through the loss or gain of an electron.
  • Kilogram: the base unit of mass in the International System of Units. It is equivalent to 2.2 pounds.
  • Kilowatt: 1000 watts. Abbreviated kW.
  • Kilowatt-hour :  1000 watts consumed over 1 hour. Abbreviated kWh.
  • Landfill gas: Gas obtained from the decomposition of organic matter in landfills.
  • Liquefaction: The process of converting the gas into a liquid.
  • Liquefied natural gas (LNG): Natural gas that has been converted to liquid.
  • Liquid hydrogen: This is elemental hydrogen that is in the liquid state. This can only be achieved by calling the hydrogen that to -287 C (-423 F). This is only 20° above absolute zero.
  • Load following power plant: Any power generating facility that adjusts power output in response to demand.
  • Matrix: The framework within a fuel cell that supports the electrolyte.
  • Mechanical balance of plant: All mechanical components of an energy generating system, other than the primary generating component.
  • Mechanical energy: Potential and/or kinetic energy present and a mechanical system.
  • Megawatt: 1 million watts. Abbreviated MW
  • Methane: A chemical compound with the molecular formula CH4. It is the simplest hydrocarbon.
  • Methanol: Also known as a wood alcohol, this is the chemical compound with a formula CH3OH. It is often used in fuel cells.
  • Microbial fuel cell (MFC): A fuel cell that uses biological processes to generate electrical current. Generally bacteria are used.
  • Miles per gallon equivalent: Measurement used to compare alternate energy sources to the traditional fuel efficiency measurement.
  • Molten Carbonate: A high temperature fuel cell that uses a molten carbonate material as its electrolyte. They generally use oxygen and hydrocarbon fuel.
  • Natural gas: A fossil fuel consisting primarily of methane but also including the ethane, propane, butane, and pentane.
  • Oxidant: An oxidizing agent. In a chemical reaction, this component gains electrons.
  • Oxidation: The loss of electrons
  • Oxygen: The eighth chemical element with 8 protons and 8 electrons. One of the primary fuels in all fuel cells. Combines with two hydrogen atoms to create water.
  • Palladium: A rare metal often used as a catalyst in fuel cells. Its atomic number is 46. Abbreviated Pd.
  • Phosphoric Acid: A chemical solution made up of phosphorus, oxygen and hydrogen. The chemical formula is H3PO4.
  • Platinum: A rare metal often used as a catalyst in fuel cells. It has the atomic number 78 and is abbreviated Pt. 80% of the world’s platinum comes from South Africa.
  • Polymer electrolyte membrane fuel cell (PEMFC): A type of acid-based fuel cell that uses the transport of protons from the anode to the cathode through a solid polymer electrolyte membrane. These fuel cells run at temperatures less than 100° C.
  • Polymer electrolyte membrane: a solid polymer membrane used as an electrolyte in certain fuel cells.
  • Polymer: A compound made by linking small subunits (called monomers) together in a repeating pattern.
  • Portable fuel cell: Any fuel cell that can be carried by hand. These are often used for emergency power applications, during camping, and by the military.
  • Potassium Hydroxide: A chemical solution made up of potassium, hydrogen, and oxygen. The chemical formula is KOH.
  • Power: the rate at which the work is performed for energy is transmitted.
  • Proton Exchange Membrane: A thin polymer that is permeable to protons, but not electrons and serves as the electrolyte in many fuel cells, particularly hydrogen fuel cells.
  • Redox: Short for reduction-oxidation reaction. This is a chemical reaction in which atoms undergo a change in the oxidation number, usually gaining or losing electrons.
  • Reformer: A device that extracts hydrogen from hydrocarbons. Part of indirect fuel cell systems in which the fuel is process prior to injection into the fuel cell stack.
  • Regenerative Fuel Cell: Any fuel cell that can be run backward through the application of electricity to reproduce the spent fuel. Very similar to a battery.
  • Renewable energy: Any energy produced from a natural resource, which does not have an immediate, finite limit. This includes such things as sun, wind, water, and geothermal heat.
  • Ruthenium: Ruthenium is a metal that is similar to platinum in many ways. It is often combined with platinum for use as a catalyst. It has the atomic number 44 and is abbreviated Ru.
  • Sainergy: A fuel cell component supply company.
  • Sodium borohydride: A chemical used in certain fuel cells as the fuel. Chemical formula is NaBH4.
  • Sodiuim borohydride fuel cell: A subtype of high-temperature fuel cell that uses sodium borohydride as the hydrogen carrier.
  • Solid Oxide Fuel Cell: A type of high temperature fuel cell that uses a solid oxide like yttria stabilized zirconia as the electrolyte.
  • Stack: Individual fuel cells (anode, electrolyte, and cathode) connected together to create a larger fuel cell.
  • Stationary fuel cell: A fuel cell that is not a movable. These are often used for electrical generation in large applications such as hospitals and supermarkets. They are often phosphoric acid fuel cells, molten-carbonate fuel cells, or solid oxide fuel cells.
  • Steam reforming: A process of producing hydrogen from hydrocarbons in the presence of a metal-based catalyst such as nickel at high temperatures (700-1100° C).
  • Turbine: A rotary engine that extracts energy from the flow of a fluid such as water or steam.
  • Uninterruptible Power Supply (UPS): Also known as a continuous power supply, this is a device which maintains a constant supply of electricity even when energy from the grid is not available.
  • UTC Power: A fully-owned subsidiary of United Technologies Incorporated that produces commercial fuel cells.
  • Voltage: the difference in electrical potential between two points. That is to say, the difference in charge of between two points between which electricity will flow if they are connected.
  • Watt: this is the International standard unit of power. It is equal to one joule of energy per second.
  • Yttria-stabilized zirconia: The most commonly used ceramic in molten carbonate fuel cells.
  • Zinc-air fuel cells: A fuel cell that derives power from the oxidation of zinc with oxygen. The oxidized zinc can be recycled and reused through electrolysis.