Fuel cell Glossary

Laboratory Of Research & Development, BAS Inc.
Professor Noriyuki Watanabe

A - C

	Vocabulary	Commentary
	AEM	Abbreviation for anion exchange membrane.It allows the transfer of OH-.
	AFC	Abbreviation for alkaline fuel cell. Alkaline fuel cell. Use an alkaline electrolyte. Carrier ions are hydroxide ion (OH-).
	Agromelate	An aggregate of carbon fine particles dispersed in PEMFC (nano-sized platinum fine particles are supported as catalysts on the surface). Its surface is covered with an electrolyte solution, and there is a hydrophobic part in which the reaction gas passage is partially intertwined in a maze.
	Alkaline fuel cell (AFC)	An alkaline electrolyte is used. Charge carrier ions are hydroxide ion (OH-). Since the oxygen reduction reaction is fast under alkaline conditions, it is possible to use other than Pt electrodes, but on the other hand, there are advantages and disadvantages that the presence of carbon dioxide gas is harmful. It was used in the Apollo program in the early 1960s and proved effective, but was later changed to PEMFC in the Gemini program. The electrolyte is a KOH or NaOH, and the ion that carries the charge is OH-. The difficulty is that the solubility of carbonate generated by the presence of carbon dioxide is low and it causes trouble. The electrode reaction is as follows. the cathodic reaction ½O2 + H2O + 2e → 2OH- the anodic reaction H2 + 2OH- → 2H2O + 2e the total reaction is H2 + ½O2 → H2O It differs from PEMFC in that water is generated on the anode side (in PEMFC, water is generated on the cathode side). OH- from the cathode to the anode, water moves from the anode to the cathode. The electrode activity is high under alkaline conditions, but the major weakness is that the system itself has low CO2 resistance.
	AMFC	Abbreviation for anion exchange membrane fuel cell. Alkaline fuel cell using an anion exchange membrane.
	Anode	An electrode on which an oxidation reaction occurs. Also called the negative electrode. Become a cathode.
	Catalyst poisoning	Impurities (carbon monoxide CO and sulfur) in the fuel bind to the active sites of the catalyst and the activity of the catalyst is lost.
	Cathode	An electrode on which a reduction reaction occurs. Also called the positive electrode.
	CHP	Abbreviation for combined heat and power. A mechanism to improve energy utilization efficiency by effectively utilizing the heat energy generated by power generation. Cogeneration. Also called cogeneration for short. Effectively applied in high temperature fuel cells (SOFC, MCFC and PAFC).
	CO resistance	Platinum electrodes are easily poisoned by CO. When poisoned, the catalytic activity decreases. This is called low CO tolerance.
	Cogeneration	CHP. A direction and mechanism that aims to improve efficiency through the effective use of power generation and the simultaneous generation of heat energy in an integrated manner. Also shortly called cogene. It is effectively applied in high-temperature fuel cells (SOFC, MCFC and PAFC).
	Crossover	In a DMFC, the fuel, methanol, permeates the solid electrolyte membrane from the anode electrode side to the oxygen (cathode) side. In general, it is the permeation of the fuel to the cathode side, causing a reduction in the electromotive force of the battery.

D - F

	Vocabulary	Commentary
	DEFC	Abbreviation for direct ethanol fuel cell. A fuel cell that uses the fuel ethanol directly for the anodic oxidation reaction. The carrier ion is a proton. Use the same electrolyte membrane which used for PEMFC.
	DMFC	Abbreviation for direct methanol fuel cell. A fuel cell that uses the fuel methanol directly for the anodic oxidation reaction. The carrier ion is a proton. Use the same electrolyte membrane used for PEMFC.
	Electro-osmotic flow	In solid ion-exchange membrane types (PEMFC, DMFC, etc.), the movement of hydrated water as protons move.
	Energy capacity	The energy that can be obtained from fuel is expressed in terms of weight or volume unit. For example, J/g, Wh/g, Wh/L, kWh/g, kWh/L, etc. (J is joule, W is watt). W is work, h is time, and the product is energy. Also called energy density.
	EOR	Abbreviation for ethanol oxidation reaction. Direct ethanol Oxidation reaction of ethanol at the anode electrode of a fuel cell.
	Ethanol fuel cell (DEFC)	Under acidic conditions, the anodic reaction CH3CH2OH + 3H2O → 2CO2 + 12H+ + 12e the cathodic reaction 3O2 + 12H+ + 12e → 6H2O the total reaction CH3CH2OH + 3O2 → 2CO2 + 3H2O In fact, the reaction cannot be carried through to the end, only to the production of acetic acid and acetaldehyde (4e only). Under alkaline conditions, anodic reaction is CH3CH2OH + 12OH- → 2CO2 + 9H2O + 12e the cathodic reaction 3O2 + 12H+ + 12e → 6H2O the total reaction CH3CH2OH + 3O2 → 2CO2 + 3H2O In fact, the reaction cannot be carried through to the end, only to the production of acetic acid and acetaldehyde (4e only). Under alkaline conditions, anodic reaction is CH3CH2OH + 12OH- → 2CO2 + 9H2O + 12e cathodic reaction is 3O2 + 6H2O + 12e → 12OH- The total reaction CH3CH2OH + 3O2 → 2CO2 + 3H2O However, the current anode catalyst does not complete the above reaction, and just proceeds in below step. CH3CH2OH + 4OH- → CH3COOH + 3H2O + 4e
	Flooding	When water is generated at the cathode, such as in a PEMFC, a flooding condition in which water overflows to the extent that it blocks the gas diffusion pathway. This is why moisture management is so important.
	Fuel cell (FC)	A mechanism or device that converts chemical energy (internal energy of a substance) into electrical energy. A battery composed of a combination of an oxidation reaction of fuel (mainly hydrogen molecules; other methanol, ethanol, formic acid, etc.) that occurs on the anode (negative electrode) side and a reduction reaction of an oxidant (mainly oxygen molecules) that occurs on the cathode (positive electrode) side. The feature is that there is a possibility that the energy utilization efficiency can be increased compared to the heat engine.
	Fuel reforming	The conversion of oil, coal, natural gas, biogas, etc. into molecular hydrogen for fuel through catalysis and chemical reactions.

G - I

	Vocabulary	Commentary
	Gas diffusion electrode (GDE)	In the case of PEMFC, a porous electrode composed of ultrafine particles of catalyst (platinum is a typical example) supported on carbon fine particles. It is believed that a microspace surrounded by a partially covered region of the hydrophilic electrolyte and a hydrophobic region that can serve as a passage for the gas (fuel and oxidant gas) forms an intricate structure. It has an interface where the fuel and oxidizer gas phases, catalysts, and electrodes come into contact. Carbon is responsible for electron conduction, and electrolyte is responsible for ionic conduction.
	GDE	Abbreviation for gas diffusion electrode. A gas diffusion electrode.
	Hydrogen pole	An electrode that causes the oxidation of hydrogen. Anode pole of fuel cell.
	Hydrogen storage	The method of storing hydrogen as fuel and the method of supplying hydrogen (including infrastructure) are major problems for the practical use of fuel cells. There are high-pressure tanks (cylinders), low-temperature liquefaction, occlusion in other compounds, compounding, etc., and the latter is currently being reported in an ongoing manner and mixed with truth.
	ICE	Abbreviation for internal combustion engine. Internal combustion engine. A machine that burns fuel to generate power as rotational energy. It often comes up in the story of fuel cells in comparison with fuel cells.
	Ion exchange membrane	The membrane used in PEMFC is a proton exchange cation exchange membrane. Since it is composed of a polymer membrane based on Teflon (with polyfluoroethylene as a skeleton) and having a sulfonic acid group in the side chain, hydrogen ions (protons) can carry charges. Recently, the development of alkaline and stable anion exchange membranes for alkaline batteries has become active.
	Ionomer	Soluble conductive polymer added as an electrolyte to facilitate the electrode reaction at the cathode and anode in PEMFC.

J - M

	Vocabulary	Commentary
	LFFC	Abbreviation for laminar flow fuel cell. Microfluid fuel cell. Development as a small drive power source has recently become active.
	LSM	Abbreviation for lanthanum strontium manganite. Strontium-doped lanthanate manganate (LaMnO3). It is used for the positive electrode of SOFC as an electrode for oxygen reduction. It is an electronic conductor.
	MCFC	Abbreviation for molten carbonate fuel cell. The carrier ion is the carbonate ion (CO32-).
	MEA	Abbreviation for membrane electrode assembly. Membrane-electrode-complex. PEMFC, etc., in which a solid exchange membrane and a catalyst-electrode bonded to it are integrated.
	Methanol fuel cell (DMFC)	Use the same type of ion exchange membrane as that used in PEMFC (acid electrolyte) the cathodic reaction is 3/2O2 + 6H+ + 6e → 3H2O the anodic reaction is CH3OH + H2O → CO2 + 6H+ + 6e the total reaction is CH3OH + 3/2O2 → CO2 + 2H2O The drawbacks are the crossover of methanol and the slow reaction rate. Under alkaline electrolytes, the electrode reaction rate is high, but the presence and formation of carbon dioxide gas is a major drawback in producing carbonates with low solubility. For alkaline fuel cell using an anion exchange membrane the cathodic reaction is &frac32;O2 + 3H2O + 6e → 6OH- the total reaction is CH3OH + &frac32;O2 → CO2 + 2H2O
	Microfluid fuel cell	A small portable fuel cell that utilizes two microscale (anode side and cathode side) laminar flows. There is mixing by diffusion in the direction perpendicular to the laminar flow, but the idea is that if the effect of mixing does not reach the electrodes, there may be no exchange membrane. There is an advantage that the liquid property (pH, fuel, oxidant, etc.) of the flowing fluid can be freely selected according to the purpose.
	Molten carbonate fuel cell (MCFC)	Used at high temperatures (600 - 700 °C). The electrolyte (LiKCO3) is a hot liquid. The reactions at each electrode are the anodic side H2 + CO32- → H2O + CO2 + 2e the cathode side ½O2 + CO2 + 2e → CO32- the total reaction H2 + ½O2 → H2O is the same as other FCs. the charge-carrying ion is carbonate ion (CO32-). The anode is porous metallic nickel, and the cathode is porous nickel oxide (NiO).
	MOR	Abbreviation for methanol oxidation reaction. Direct methanol oxidation reaction at the anode electrode of a methanol fuel cell.

N - R

	Vocabulary	Commentary
	Nafion membrane	It is a polymer with a tetrafluoroethylene skeleton, has sulfonic acid group, proton exchange ability, and electrical conductivity.
	ORR	Abbreviation for Oxygene Reduction Reaction. Oxygen reduction reaction that occurs at the positive electrode (cathode).
	Overvoltage	The potential difference that must be applied extra because the charge transfer is too slow at the equilibrium potential is called activation overvoltage (polarization). In addition, there are overvoltages caused by the moving speed of the active ingredient not being able to keep up, and overvoltages caused by ohm resistance. Polarization due to the oxygen reduction reaction at the cathode is generally large in fuel cells, and research is continuing to reduce this to obtain a highly active catalyst.
	Oxygen pole	An electrode that causes the reduction of oxygen in FC. It is the cathode electrode.
	ORR	Reduction of oxygen molecules at the cathode pole, a reaction involving four-electron reduction and cleavage of the oxygen-oxygen bond, which is a major reason for slow reaction rates and large overvoltages, leading to a decrease in the electromotive force. Also, the process of hydrogen peroxide formation occurs partially in the two-electron reduction limit. Hydrogen peroxide can damage the polymer electrolyte membrane, and it is desirable to minimize its formation. Platinum is currently the fastest catalyst for the reaction, but it is a rare and expensive precious metal. Alternative catalysts to platinum are being actively studied.
	PAFC	Abbreviation for phosphoric acid fuel cell. The carrier ion is a proton.
	Parasitic current	Current that does not contribute to the output flowing between different single cells due to the stack structure.
	PEFC	Abbreviation for polymer electrolyte fuel cell.
	PEMFC	Abbreviation for proton exchange membrane fuel cell or polymer electrolyte membrane fuel cell. Proton exchange polymer film type fuel cell. The carrier ion is a proton.
	Phosphate fuel cell (PAFC)	It is the most popular as a distributed portable and stationary fuel cell. Moderate temperature (150°C - 200°C). The charge carrier (H+) and electrode reaction are the same as the solid ion exchange membrane type.
	Polarization	The potential difference that must be applied because the charge transfer reaction is too slow is called the activation polarization. It is also called activation overvoltage. In addition, there is a transport polarization associated with diffusion transport and a resistive polarization caused by ohmic resistance.
	Polarization curve	A curve plotting cell voltage and current values. It shows a voltage drop due to activation polarization, transport polarization, resistance polarization, etc. The first and foremost measurement items required for fuel cell characteristics and performance evaluation.
	Porous electrode	It is used for the purpose of increasing the effective surface area of the electrode. It is important to increase the surface area in order to increase the efficiency of electrode oxidation and reduction reactions. Make it porous for that. Also called a porous electrode. Carbon cloth, carbon fiber, etc. are used for the backbone.
	Proton conduction	In PEMFC and PAFC, the charge is carried by the proton.

S - Z

	Vocabulary	Commentary
	SAFC	Abbreviation for solid alkaline fuel cell. Alkaline fuel cell that uses a polymer electrolyte membrane (anion exchange membrane). Recently, active research has been carried out to reduce the effects of carbon dioxide.
	SOFC	Abbreviation for solid oxide fuel cell. A fuel cell with solid oxide (zirconia and ceria; zirconium and cerium oxides) as the electrolyte. Highest temperature specification (750°C - 1000°C).
	Solid ion exchange membrane fuel cell	Proton exchange membrane type: PEMFC Polymer electrolyte type: PEFC Methanol fuel cell: DMFC The electrolyte is a Teflon-based solid ion exchange polymer membrane having a sulfonic acid group in the side chain (almost the same as PEMFC). The ion that carries the charge is a proton (H+). It is being studied as a power source for automobiles due to its features such as medium and low temperature operation, low temperature startup, and high energy capacity. the cathodic reaction ½O2 + 2H+ + 2e → H2O the anodic reaction H2 → 2H+ +2e However, hydrogen storage of fuel, replenishment, infrastructure development, etc. are still huge challenges.
	Solid oxide fuel cell (SOFC)	Used at high temperatures. Uses an oxygen ion-conducting solid electrolyte (YSZ), which is more stable than MCFCs in that it is solid and does not leak. The reactions at each electrodes are in the anodic side H2 + O2- → H2O + 2e in the cathodic side ½O2 + 2e → O2-
	Stack	A laminated structure in which single cells are stacked to obtain the required electromotive voltage.
	TPB	Abbreviation for three phase boundary. A three-phase interface, a catalyst, a gas phase, and an interface where electrodes are in contact. In the case of SOFC, it means the interface where the three phases of Ni pole, YSZ, and gas phase meet, and it is the place where fuel oxidation proceeds efficiently.
	Water management	In the polymer electrolyte membrane type FC (PEMFC, AMFC, DMFC), water is generated on the cathode or anode side. Therefore, it may become excessive in water. Also, the conductivity of the membrane is highly dependent on the water content. Therefore, proper management of water content is important.
	YSZ	Abbreviation for yttrium stabilized zirconia. Zirconia stabilized by adding yttrium. A solid electrolyte used as an oxygen ion conductor at high temperatures. Due to the large bandgap, its electronic conductivity is negligible. Used for SOFC.