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Mixed Conductor
Mixed conductors, also known as mixed ion-electron conductors (MIEC), are a single-phase material that has significant conduction ionically and electronically. Due to the mixed conduction, a formally neutral species can transport in a solid and therefore mass storage and redistribution are enabled. Mixed conductors are well known in conjugation with high-temperature superconductivity and are able to capacitate rapid solid-state reactions. They are used as catalysts (for oxidation), permeation membranes, sensors, and electrodes in batteries and fuel cells, because they allow for rapidly transducing chemical signals and permeating chemical components. Strontium titanate (), titanium dioxide (), , cerium(IV) oxide (), lithium iron phosphate (), and are examples of mixed conductors. Introduction MIEC materials tend to be nonstoichiometric oxides, many of which have perovskite structures with rare earth metals on the A-site and transition metals on the B-site. Substituting variou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cerium(IV) Oxide
Cerium(IV) oxide, also known as ceric oxide, ceric dioxide, ceria, cerium oxide or cerium dioxide, is an oxide of the rare-earth metal cerium. It is a pale yellow-white powder with the chemical formula CeO2. It is an important commercial product and an intermediate in the purification of the element from the ores. The distinctive property of this material is its reversible conversion to a non-stoichiometric oxide. Production Cerium occurs naturally as oxides, always as a mixture with other rare-earth elements. Its principal ores bastnaesite and monazite. After extraction of the metal ions into aqueous base, Ce is separated from that mixture by addition of an oxidant followed by adjustment of the pH. This step exploits the low solubility of CeO2 and the fact that other rare-earth elements resist oxidation.. Cerium(IV) oxide is formed by the calcination of cerium oxalate or cerium hydroxide. Cerium also forms cerium(III) oxide, , which is unstable and will oxidize to cerium ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stoichiometry
Stoichiometry refers to the relationship between the quantities of reactants and products before, during, and following chemical reactions. Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equals the total mass of the products, leading to the insight that the relations among quantities of reactants and products typically form a ratio of positive integers. This means that if the amounts of the separate reactants are known, then the amount of the product can be calculated. Conversely, if one reactant has a known quantity and the quantity of the products can be empirically determined, then the amount of the other reactants can also be calculated. This is illustrated in the image here, where the balanced equation is: : Here, one molecule of methane reacts with two molecules of oxygen gas to yield one molecule of carbon dioxide and two molecules of water. This particular chemical equation is an example of complete combustion. St ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cathode
A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in which positive charges move. Electrons have a negative electrical charge, so the movement of electrons is opposite to that of the conventional current flow. Consequently, the mnemonic ''cathode current departs'' also means that electrons flow ''into'' the device's cathode from the external circuit. For example, the end of a household battery marked with a + (plus) is the cathode. The electrode through which conventional current flows the other way, into the device, is termed an anode. Charge flow Conventional current flows from cathode to anode outside of the cell or device (with electrons moving in the opposite direction), regardless of the cell or device type and operating mode. Cathode polarity with respect to the anode can be positive ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solid Oxide Electrolyser Cell
A solid oxide electrolyzer cell (SOEC) is a solid oxide fuel cell that runs in regenerative mode to achieve the electrolysis of water (and/or carbon dioxide) by using a solid oxide, or ceramic, electrolyte to produce hydrogen gas (and/or carbon monoxide) and oxygen. The production of pure hydrogen is compelling because it is a clean fuel that can be stored, making it a potential alternative to batteries, methane, and other energy sources (see hydrogen economy). Electrolysis is currently the most promising method of hydrogen production from water due to high efficiency of conversion and relatively low required energy input when compared to thermochemical and photocatalytic methods. Principle Solid oxide electrolyzer cells operate at temperatures which allow high-temperature electrolysis to occur, typically between 500 and 850 °C. These operating temperatures are similar to those conditions for a solid oxide fuel cell. The net cell reaction yields hydrogen and oxygen gases. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solid Oxide Fuel Cell
A solid oxide fuel cell (or SOFC) 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. Advantages of this class of fuel cells include high combined heat and power efficiency, long-term stability, fuel flexibility, low emissions, and relatively low cost. The largest disadvantage is the high operating temperature which results in longer start-up times and mechanical and chemical compatibility issues. Introduction Solid oxide fuel cells are a class of fuel cells characterized by the use of a solid oxide material as the electrolyte. SOFCs use a solid oxide electrolyte to conduct negative oxygen ions from the cathode to the anode. The electrochemical oxidation of the hydrogen, carbon monoxide or other organic intermediates by oxygen ions thus occurs on the anode side. More recently, proton-conducting SOFCs (PC-SOFC) are being deve ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solid Oxide Fuel Cell
A solid oxide fuel cell (or SOFC) 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. Advantages of this class of fuel cells include high combined heat and power efficiency, long-term stability, fuel flexibility, low emissions, and relatively low cost. The largest disadvantage is the high operating temperature which results in longer start-up times and mechanical and chemical compatibility issues. Introduction Solid oxide fuel cells are a class of fuel cells characterized by the use of a solid oxide material as the electrolyte. SOFCs use a solid oxide electrolyte to conduct negative oxygen ions from the cathode to the anode. The electrochemical oxidation of the hydrogen, carbon monoxide or other organic intermediates by oxygen ions thus occurs on the anode side. More recently, proton-conducting SOFCs (PC-SOFC) are being deve ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Triple Phase Boundary
A ''triple phase boundary'' (TPB) is a geometrical class of phase boundary and the location of contact between three different phases. A simple example of a TPB is a coastline where land, air and sea meet to create an energetic location driven by solar, wind and wave energy capable of supporting a high level of biodiversity. This concept is particularly important in the description of electrodes in fuel cells and batteries. For example for fuel cells, the three phases are an ion conductor ( electrolyte), an electron conductor, and a virtual "porosity" phase for transporting gaseous or liquid fuel molecules. The electrochemical reactions that fuel cells use to produce electricity occur in the presence of these three phases. Triple phase boundaries are thus the electrochemically active sites within electrodes. The oxygen reduction reaction that occurs at a solid oxide fuel cell's (SOFC) cathode, can be written as follows: (gas) + 4−(electrode) → 2(electrolyte) Differen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ruddlesden-Popper Phase
Ruddlesden-Popper (RP) phases are a type of perovskite structure that consists of two-dimensional perovskite-like slabs interleaved with cations. The general formula of an RP phase is ''An+1BnX3n+1'', where ''A'' and ''B'' are cations, ''X'' is an anion (e.g., oxygen), and ''n'' is the number of octahedral layers in the perovskite-like stack. Generally, it has a phase structure that results from the intergrowth of perovskite-type and NaCl-type (i.e., rocksalt-type) structures. These phases are named after S.N. Ruddlesden and P. Popper, who first synthesized and described a Ruddlesden-Popper structure in 1957. Crystal structure The general RP formula ''An+1BnX3n+1'' can be written ''An-1A’2BnX3n+1'', where ''A'' and ''A’'' are alkali, alkaline earth, or rare earth metals and ''B'' is a transition metal. The ''A'' cations are located in the perovskite layer and are 12-fold cuboctahedral coordinated by the anions (CN = 12). The ''A’'' cations have a coordination number of 9 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Brownmillerite
Brownmillerite is a rare oxide mineral with chemical formula . It is named for Lorrin Thomas Brownmiller (1902–1990), chief chemist of the Alpha Portland Cement Company, Easton, Pennsylvania. Discovery and occurrence The chemical compound was first recognized in 1932 and named for the chemist who identified it. The naturally occurring mineral form of the compound was first recognized in 1964 for occurrences in the Bellerberg volcano, Ettringen, Mayen-Koblenz, Germany. At the type locality the mineral occurs within limestone blocks that are contained in a volcanic flow. The limestone blocks had undergone thermal metamorphism. The mineral also occurs in the thermally altered strata of the Hatrurim Formation of Israel. Minerals associated with brownmillerite in the Mayen locality include calcite, ettringite, wollastonite, larnite, mayenite, gehlenite, diopside, pyrrhotite, grossular, spinel, afwillite, jennite, portlandite and jasmundite. In an Austrian occurrence near K ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pyrochlore
Pyrochlore () is a mineral group of the niobium end member of the pyrochlore supergroup. The general formula, (where A and B are metals), represent a family of phases isostructural to the mineral pyrochlore. Pyrochlores are an important class of materials in diverse technological applications such as luminescence, ionic conductivity, nuclear waste immobilization, high temperature thermal barrier coatings, automobile exhaust gas control, catalysts, solid oxide fuel cell, ionic/electrical conductors etc. Occurrence The mineral is associated with the metasomatic end stages of magmatic intrusions. Pyrochlore crystals are usually well formed (euhedral), occurring usually as octahedra of a yellowish or brownish color and resinous luster. It is commonly metamict due to radiation damage from included radioactive elements. Pyrochlore occurs in pegmatites associated with nepheline syenites and other alkalic rocks. It is also found in granite pegmatites and greisens. It is characteristical ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron Hole
In physics, chemistry, and electronic engineering, an electron hole (often simply called a hole) is a quasiparticle which is the lack of an electron at a position where one could exist in an atom or atomic lattice. Since in a normal atom or crystal lattice the negative charge of the electrons is balanced by the positive charge of the atomic nuclei, the absence of an electron leaves a net positive charge at the hole's location. Holes in a metal or semiconductor crystal lattice can move through the lattice as electrons can, and act similarly to positively-charged particles. They play an important role in the operation of semiconductor devices such as transistors, diodes and integrated circuits. If an electron is excited into a higher state it leaves a hole in its old state. This meaning is used in Auger electron spectroscopy (and other x-ray techniques), in computational chemistry, and to explain the low electron-electron scattering-rate in crystals (metals, semiconduct ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transition Metal
In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that can use d orbitals as valence orbitals to form chemical bonds. The lanthanide and actinide elements (the f-block) are called inner transition metals and are sometimes considered to be transition metals as well. Since they are metals, they are lustrous and have good electrical and thermal conductivity. Most (with the exception of group 11 and group 12) are hard and strong, and have high melting and boiling temperatures. They form compounds in any of two or more different oxidation states and bind to a variety of ligands to form coordination complexes that are often coloured. They form many useful alloys and are often employed as catalysts in elemental form or in compounds such as coordination complexes and oxides. Most are strongly param ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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