Fact-checked by Grok 2 weeks ago

Cathode

A cathode is the electrode in a polarized electrical device, such as an electrochemical cell or vacuum tube, through which conventional (positive) electric current flows outward from the device. In electrochemistry, it is the electrode at which reduction reactions predominate, involving the gain of electrons by chemical species.^[1] In electronic devices, it typically serves as the source of electrons, such as in diodes or cathode-ray tubes where thermionic emission from a heated surface generates the electron flow.^[2]^[3] The term "cathode" originates from the Greek káthodos, meaning "descent" or "way down," reflecting the early understanding of current as a flow of positive charge toward the electrode.^[4] It was coined in 1834 by the mathematician William Whewell at the request of Michael Faraday, who was developing terminology for electrolysis experiments, with "anode" (from anodos, "way up") as its counterpart.^[4] This naming convention persists despite the later discovery of electrons in 1897 by J.J. Thomson, which revealed that actual electron flow is opposite to conventional current, making the cathode the entry point for electrons in the device.^[5] Cathodes play essential roles across electrochemistry and electronics. In galvanic cells like batteries, the cathode is the positive terminal where reduction occurs, enabling energy release as in lithium-ion batteries where materials such as lithium cobalt oxide accept electrons.^[6] In electrolytic cells, it is the negative terminal attracting cations for processes like electroplating, where metals deposit via reduction.^[7] In vacuum electronics, cathodes—often oxide-coated or field-emission types—emit electrons for applications in cathode-ray tubes (CRTs) for displays, X-ray tubes, and early computing devices.^[8] Modern advancements include nanostructured cathodes in batteries to enhance energy density and efficiency.^[9] As of 2025, developments include advanced cathode materials for all-solid-state batteries to improve safety and energy density.^[10]

Etymology and History

Etymology

The term "cathode" originates from the Greek word kathodos (κάθοδος), meaning "a going down" or "descent path." It was coined in 1834 by British scholar William Whewell, who had been consulted by Michael Faraday to devise precise nomenclature for the electrodes in electrolytic processes.^[4]^[11] Whewell selected kathodos to describe the path by which positive charges or conventional electric current were thought to descend into the electrolyte at this electrode, aligning with the prevailing view of current flow from positive to negative.^[12] The term first appeared in print in Faraday's paper "On Electrical Decomposition" published that year in the Philosophical Transactions of the Royal Society, where Faraday acknowledged assistance from unnamed scholars in refining the vocabulary.^[11] In early 19th-century electrochemistry texts, "cathode" quickly supplanted vaguer designations such as "negative pole" or "decomposing electrode," becoming standardized by the mid-century in works by figures like Humphry Davy and later chemists exploring electrolysis.^[13] This adoption facilitated clearer discourse on electrochemical phenomena, with the paired term "anode" (anodos, "way up") similarly established for the opposite electrode.

Historical Development

The concept of the cathode emerged in the early 19th century amid pioneering electrochemical experiments, though the term itself was coined by William Whewell at the request of Michael Faraday in 1834, derived from Greek roots meaning "descent," to describe the electrode through which conventional electric current enters the electrolyte.^[14] A foundational milestone came in 1800 with Alessandro Volta's invention of the voltaic pile, the first device to produce a continuous electric current through stacked discs of zinc and copper separated by brine-soaked cardboard, implicitly featuring a cathode as the positive terminal where current entered the electrolyte, even though the nomenclature was not yet established.^[14] This apparatus marked the birth of galvanic cells and enabled sustained electrochemical reactions, laying the groundwork for cathode applications in energy generation.^[15] In 1807, Humphry Davy advanced cathode technology through electrolysis experiments at the Royal Institution, using voltaic piles to isolate alkali metals such as sodium and potassium by applying high currents to molten salts, where these elements were deposited at the cathode via reduction reactions.^[16] Davy's work not only demonstrated the cathode's role in element discovery but also highlighted its practical utility in breaking down compounds, influencing subsequent industrial electrolysis processes.^[17] The late 19th century saw further evolution with William Crookes' investigations in the 1870s using low-pressure gas discharge tubes, where he observed "cathode rays" emanating from the cathode, describing their properties and sparking interest in their nature.^[18] Building on this, J.J. Thomson's 1897 experiments with modified Crookes tubes definitively identified cathode rays as streams of negatively charged particles, later named electrons, revolutionizing atomic theory and confirming the cathode as a source of electron emission.^[19] Concurrently, the development of vacuum tube cathodes accelerated in the late 19th century, notably through Thomas Edison's 1883 observation of the "Edison effect," where heated filaments in evacuated bulbs emitted electrons toward an anode, forming the basis for thermionic cathodes in early electronic devices.^[20] This innovation, refined by inventors like John Ambrose Fleming in the early 1900s, enabled the creation of diodes and amplifiers, transitioning cathodes from electrochemical to electronic roles.^[21]

Fundamental Concepts

Charge Flow Conventions

In electrochemistry, the cathode is the electrode where reduction occurs, and conventional current—defined as the flow of positive charge—is directed toward the cathode within the electrolyte due to the migration of cations. This flow represents the movement of positive ions toward the cathode, where in electrolytic cells they are attracted to the negatively charged cathode surface, while in galvanic cells the potential difference drives their migration to the positively charged cathode. In the external circuit, the direction of conventional current relative to the cathode varies by cell type: in electrolytic cells, it exits the cathode toward the power source, while in galvanic cells, it exits the cathode as the positive terminal. Electron flow, being opposite to conventional current, moves from the anode to the cathode externally in both cases, supplying electrons for reduction at the cathode.^[22]^[23] A useful mnemonic for recalling ion attraction in electrolysis is "CAT-ODE," denoting Cations Attracted To the cathode (Odd Definition for Electrolysis), highlighting how positive ions are drawn to this electrode. In contrast, for batteries (galvanic cells), electrons flow into the cathode from the external circuit, where they participate in reduction, emphasizing the cathode's role as the positive terminal that receives returning electrons. These conventions ensure consistency in describing charge movement across electrochemical systems, regardless of whether the focus is on ionic or electronic carriers.^[24]^[6] The origins of these charge flow conventions trace back to pre-1900 chemical experiments, which emphasized positive ion behavior and defined current based on observable electrolytic effects, such as in Volta's pile where positive charge appeared to flow from anode to cathode. The 1897 discovery of the electron by J.J. Thomson using cathode ray tubes shifted emphasis in physics and electronics toward negative charge carriers, yet the conventional current direction—established earlier by Benjamin Franklin's arbitrary assignment of positive to one charge type—remained unchanged to preserve compatibility in engineering and circuit analysis. This historical persistence explains why electron flow is often described as outgoing from the cathode in vacuum tube devices, contrasting with the incoming electron flow in batteries.^[25]^[26] In a typical direct current (DC) circuit diagram for an electrolytic cell, the cathode is depicted as the negative terminal connected to the power source's negative pole and the anode as the positive terminal connected to the power source's positive pole; conventional current flows from the positive pole to the anode, through the electrolyte to the cathode, and then to the negative pole, while electron flow arrows reverse this path—from the negative pole to the cathode, through the electrolyte (effectively) to the anode, to the positive pole—illustrating the cathode's role as the electron sink.^[27]

Reduction Processes

In electrochemistry, the cathode serves as the electrode where reduction reactions occur, involving the gain of electrons by chemical species in both electrolytic cells, where an external voltage drives the process, and galvanic cells, where the reaction proceeds spontaneously.^[28] This reduction process transforms an oxidizing agent into a reduced species, contrasting with oxidation at the anode. A general representation of a cathodic half-reaction is given by the equation: Oxidizing agent + ne⁻ → reduced species For example, the reduction of copper(II) ions to metallic copper follows: Cu²⁺ + 2e⁻ → Cu This half-reaction exemplifies how cations in solution accept electrons to deposit as neutral metal on the cathode surface.^[29] Several factors influence the efficiency and kinetics of reduction at the cathode interface. Overpotential, the additional voltage beyond the thermodynamic potential required to drive the reaction, arises primarily from kinetic barriers such as slow electron transfer rates and is influenced by the electrode's surface properties.^[30] The choice of electrode material, such as platinum or carbon, affects catalytic activity and selectivity by altering adsorption energies of intermediates, thereby modulating overpotential and reaction pathways.^[31] Additionally, electrolyte composition plays a critical role; the concentration, pH, and nature of supporting ions impact ion transport, solubility of species, and the local reaction environment, potentially suppressing side reactions or enhancing mass transfer.^[31] The cathodic reduction contributes to the overall cell potential, which determines the driving force for the electrochemical process. According to the Nernst equation, the potential for the cathode half-reaction under non-standard conditions is expressed as: E = E^0 - \frac{RT}{nF} \ln Q where E^0 is the standard reduction potential, R is the gas constant, T is temperature, n is the number of electrons transferred, F is Faraday's constant, and Q is the reaction quotient reflecting concentrations of reactants and products. This equation illustrates how deviations from standard conditions, such as changes in species concentrations, shift the cathode potential and thus the cell voltage.^[32] Electrons flow into the cathode from the external circuit to support this reduction.^[28]

Electrochemistry Applications

Electrolytic Cells

In electrolytic cells, an external power source supplies electrical energy to drive non-spontaneous redox reactions, where the cathode serves as the site of reduction, attracting cations and facilitating reduction by accepting electrons from the power supply.^[33] Unlike galvanic cells, these setups require continuous voltage input to sustain the process, with the cathode typically connected to the negative terminal of the source.^[34] A classic example is the electrolysis of water in an alkaline medium, where the cathode reaction is $2H_2O + 2e^- \rightarrow [H_2](/page/Hydrogen) + 2OH^-, producing hydrogen gas and hydroxide ions.^[35] Cathode materials in electrolytic cells are selected based on the desired reaction kinetics and stability, often favoring inert electrodes to avoid interference with the target reduction. Platinum is a common inert material due to its high corrosion resistance and catalytic activity for reductions like hydrogen evolution, ensuring minimal side reactions.^[36] For hydrogen evolution specifically, reactive metals such as nickel or nickel-based alloys are used in industrial settings to lower activation barriers, though they may require protective coatings to prevent degradation.^[37] Key applications of electrolytic cells highlight the cathode's role in industrial production, particularly for hydrogen generation via water electrolysis, which yields pure H₂ at the cathode for use in fuel cells and chemical synthesis.^[38] In the chlor-alkali process, the cathode enables the reduction of water to hydrogen and hydroxide ions in a brine solution, supporting the co-production of caustic soda while the anode generates chlorine.^[39] Energy efficiency in these systems is limited by overpotentials, where the cathode's hydrogen evolution reaction requires additional voltage beyond the theoretical minimum of 1.23 V for water splitting, often adding 0.1–0.3 V due to kinetic barriers at the electrode surface.^[40]^[41] This overpotential increases operational costs, prompting research into advanced cathode catalysts like transition metal phosphides to minimize it.^[35]

Galvanic Cells

In galvanic cells, also known as voltaic cells, the cathode functions as the positive terminal where the spontaneous reduction half-reaction takes place, accepting electrons from the external circuit to drive the overall electrochemical process that generates electrical energy from chemical potential differences.^[42] This reduction process contrasts with the oxidation occurring at the anode, the negative terminal, ensuring a net flow of electrons through the circuit to power external devices.^[43] The cathode's role is critical for the cell's efficiency, as it determines the upper limit of the cell's electromotive force based on the standard reduction potential of the species involved.^[7] A classic example is the Daniell cell, which consists of a zinc anode in zinc sulfate solution and a copper cathode in copper sulfate solution, separated by a porous barrier or salt bridge. At the cathode, copper(II) ions are reduced to metallic copper according to the half-reaction:

\text{Cu}^{2+}(aq) + 2e^- \rightarrow \text{Cu}(s)

This yields a standard cell potential of approximately 1.10 V, making it a foundational demonstration of spontaneous energy generation.^[2] In cell notation, the cathode half-cell is conventionally written on the right side, as in Zn(s)|Zn²⁺(aq) || Cu²⁺(aq)|Cu(s), with the double vertical line representing the salt bridge or phase boundary.^[44] Modern applications extend this principle to rechargeable batteries, such as the lead-acid battery used in automotive starting systems. Here, the cathode is typically made of lead(IV) oxide (PbO₂) coated on a lead grid, where the reduction reaction during discharge is:

\text{PbO}_2(s) + 4\text{H}^+(aq) + \text{SO}_4^{2-}(aq) + 2e^- \rightarrow \text{PbSO}_4(s) + 2\text{H}_2\text{O}(l)

This reaction, paired with oxidation at the lead anode, produces about 2.04 V per cell and enables high current output for short bursts.^[45] Cathode materials in galvanic cells are selected for their high standard reduction potentials—such as copper (E° = +0.34 V) or PbO₂ (E° ≈ +1.69 V vs. SHE)—to maximize the cell voltage and energy density while ensuring stability and compatibility with the electrolyte.^[6] These choices prioritize noble metals or oxides that favor efficient electron acceptance without excessive corrosion or side reactions.^[46]

Electrodeposition Processes

Electroplating

In electroplating, the cathode serves as the substrate onto which metal ions from the electrolyte are reduced and deposited as a thin, adherent coating through an electrolytic process. The object to be plated, such as a steel component, is connected as the cathode in an electrolytic cell, where direct current drives the reduction reaction at its surface. For instance, in nickel plating, the reaction \ce{Ni^{2+} + 2e^- -> Ni} occurs on the steel cathode, forming a uniform metallic layer.^[36]^[47]^[48] The electrolyte bath typically consists of an aqueous solution containing soluble metal salts (e.g., nickel sulfate for Ni²⁺ ions), conductive acids or bases to enhance ion mobility, and proprietary organic additives to improve coating quality. Additives such as brighteners (e.g., sulfonium-alkane-sulfonates in acid copper baths) and levelers promote uniform deposition, reduce surface roughness, and prevent defects like pitting or dendritic growth on the cathode. Bath pH, temperature, and agitation are controlled to maintain optimal ion transport and minimize side reactions at the cathode surface.^[49]^[50]^[36] Electroplating finds diverse applications where the cathode substrate requires enhanced properties. For decorative purposes, chrome plating deposits a thin, shiny chromium layer on automotive trim or household fixtures, providing aesthetic appeal and mild tarnish resistance. Protective coatings, such as zinc plating on steel (galvanizing via electrolysis), act as a sacrificial anode to prevent rust by corroding preferentially in humid environments. In electronics, gold electroplating on connectors and contacts ensures low electrical resistance, high conductivity, and corrosion protection for reliable performance in devices like circuit boards.^[51]^[52]^[53]^[54]^[55]^[56]^[57] Key factors influencing cathode deposition include current density, throwing power, and hydrogen embrittlement. Higher current densities accelerate plating rates but can lead to uneven coatings or burning if exceeding the bath's limiting value (e.g., 20–50 A/dm² in nickel baths), while lower densities promote smoother films. Throwing power, the bath's ability to deposit metal uniformly on irregular cathode geometries, depends on electrolyte conductivity and ion concentration, with acid baths typically offering 10–20% efficiency for recessed areas. Hydrogen embrittlement occurs when atomic hydrogen generated at the cathode during water reduction diffuses into the substrate, reducing ductility in high-strength steels; mitigation involves additives or pulsed currents to desorb hydrogen.^[58]^[55]^[59]^[60]^[61]

Electrowinning

Electrowinning is an electrolytic process used to extract metals from solutions containing dissolved metal ions, where the cathode serves as the site for metal deposition and growth into a solid sheet. In this process, metal ions in the electrolyte are reduced at the cathode, forming a pure metal deposit that builds up over time. For example, in copper electrowinning, copper ions undergo the reaction Cu²⁺ + 2e⁻ → Cu, resulting in the formation of a coherent copper sheet on the cathode surface.^[62]^[63] This reduction at the cathode is driven by an applied direct current, with the deposited metal periodically harvested as cathodes for further refining or use. Industrial electrowinning setups typically employ insoluble anodes, such as lead-antimony or lead-calcium alloys, to minimize anode degradation and maintain process efficiency, paired with cathodes made from materials like stainless steel blanks. The electrolyte is often acidic, such as sulfuric acid solutions derived from ore leachates, or alkaline depending on the metal; in copper production, sulfuric acid leachates from oxide ores provide the electrolyte in large-scale cells containing multiple electrode pairs. These cells operate continuously, with current densities around 200-300 A/m², allowing for the extraction of metals from pregnant leach solutions after solvent extraction purification.^[64]^[65]^[66] One key advantage of electrowinning is the production of high-purity metals, such as 99.99% pure copper cathodes, which meet stringent commercial standards without additional refining steps. Energy consumption for copper electrowinning is typically 2-3 kWh per kg of metal produced, making it an efficient method for bulk recovery compared to pyrometallurgical alternatives.^[67]^[66] In modern applications, electrowinning is widely used for recovering precious metals like gold and silver from cyanide leaching solutions in mining operations, where it selectively deposits these metals onto stainless steel cathodes for subsequent refining. It is also applied in the recovery of base metals such as zinc and nickel from industrial waste streams. For aluminum, the Hall-Héroult process represents a variant of electrowinning in molten salt electrolytes, where aluminum is reduced and collected at the carbon cathode in industrial cells.^[68]^[69]

Electronics Applications

Vacuum Tubes

In vacuum tubes, the cathode serves as the primary source of electrons, emitting them through thermionic emission or field emission mechanisms to flow toward the positively charged anode, enabling the control and amplification of electrical signals in early electronic devices.^[70] Thermionic emission occurs when the cathode is heated, providing sufficient thermal energy to overcome the material's work function and liberate electrons into the vacuum.^[71] This process forms the basis for electron flow in devices such as diodes and triodes, where the emitted electrons create a current that can be modulated by applied voltages.^[72] Cathode rays, consisting of streams of electrons emitted from the cathode, were first systematically observed and studied by William Crookes in the late 19th century using partially evacuated glass tubes.^[73] These rays produce visible fluorescence on tube walls and can be deflected by electric or magnetic fields, a property exploited in cathode ray tubes (CRTs) for applications including oscilloscopes to visualize electrical waveforms and early televisions to generate images by scanning electron beams across phosphor-coated screens.^[73]^[74] Vacuum tube cathodes are broadly classified into hot and cold types based on their emission mechanisms. Hot cathodes, typically constructed from oxide-coated tungsten filaments, are heated to temperatures between 800°C and 1000°C to facilitate thermionic emission, achieving high electron current densities suitable for amplification in radio receivers and transmitters.^[71]^[75] The oxide coating, often barium or strontium compounds on a tungsten base, lowers the work function and enhances emission efficiency at these moderate temperatures compared to uncoated filaments.^[72] In contrast, cold cathodes rely on field emission, where a strong electric field extracts electrons without heating, operating at room temperature but generally offering lower efficiency and current density due to the higher voltages required and sensitivity to surface conditions.^[76] The development of reliable cathodes in vacuum tubes had profound historical impact, underpinning the commercialization of radio broadcasting in the 1920s and television in the mid-20th century by enabling signal amplification and detection essential for these technologies.^[74] Thermionic emission from these cathodes is quantitatively described by the Richardson-Dushman equation, which models the current density J as

J = A T^2 e^{-\phi / kT},

where A is the Richardson constant (approximately 120 A/cm²K²), T is the absolute temperature, \phi is the work function of the cathode material, k is Boltzmann's constant, and the exponential term accounts for the probability of electrons gaining sufficient energy to escape the surface.^[77] This equation, derived from statistical mechanics, guided the optimization of cathode designs for practical devices, balancing emission rates with filament longevity.^[77]

Semiconductor Devices

In semiconductor diodes, the cathode serves as the n-type region or the negative terminal connected to the n-type semiconductor material in a p-n junction structure.^[78] Under forward bias, where the cathode is at a lower potential than the anode, electrons are injected from the n-type cathode region across the junction into the p-type anode region via diffusion, while holes move in the opposite direction, enabling current flow. This injection mechanism contrasts with reverse bias conditions, where the depletion region widens, preventing significant current flow and blocking reverse current through the barrier potential.^[79] The standard schematic symbol for a semiconductor diode depicts the cathode as a vertical bar at the end opposite the arrowhead, which points toward the cathode to indicate conventional current direction from anode to cathode under forward bias.^[80] In operation, the diode's behavior is governed by the Shockley ideal diode equation, which models the current-voltage relationship as

I = I_s \left( e^{V / \eta V_T} - 1 \right),

where I is the diode current, I_s is the reverse saturation current, V is the applied voltage (positive for forward bias with cathode at lower potential), \eta is the ideality factor (typically 1-2), and V_T is the thermal voltage (kT/q \approx 25 mV at room temperature). This equation arises from the balance of drift and diffusion currents in the solid-state junction, without reliance on thermionic emission.^[81] Semiconductor cathodes find key applications in rectifiers, where arrays of diodes convert alternating current to direct current by allowing conduction only during positive half-cycles when the cathode is negative relative to the anode.^[79] In light-emitting diodes (LEDs), such as those based on gallium arsenide phosphide (GaAsP), the cathode supplies electrons that diffuse into the active p-n junction region under forward bias, where they recombine with holes to produce photons via electroluminescence, emitting visible light (e.g., yellow-orange in GaAsP structures). Unlike vacuum tube cathodes, semiconductor cathodes operate without thermionic emission or vacuum enclosures, relying instead on carrier drift and diffusion within the solid lattice for efficient, compact performance.^[82] A specialized case is the tunnel diode, or Esaki diode, where the heavily doped p-n junction enables quantum mechanical tunneling of electrons from the valence band of the p-type anode to the conduction band of the n-type cathode across a thin depletion region (typically 2-3 nm), resulting in negative differential resistance for high-speed switching.^[83] This tunneling occurs at the cathode interface under low forward bias, allowing operation at microwave frequencies without the emission processes required in vacuum devices.^[84]

References

[1]
MANUAL OF SYMBOLS AND TERMINOLOGY FOR ... - iupac
oxidation. An electrode at which a net negative current flows is called a cathode. The chemical reaction which predominates at a cathode is a reduction ...
[2]
Electrochemical Reactions
The electrode at which reduction occurs is called the cathode. The identity of the cathode and anode can be remembered by recognizing that positive ions, or ...
[3]
Cathode Ray Tube Television - Magnet Academy
A cathode ray tube consists of a glass vacuum tube in which a negatively charged plate (called a cathode) is heated so it emits electrons.Missing: definition | Show results with:definition
[4]
Cathode - Etymology, Origin & Meaning
Cathode, from Greek kathodos meaning "downward path," originated in 1834 to denote the negative electric pole, named for the supposed current path.
[5]
J. J. Thomson 1897 - Cathode Rays - Le Moyne
The rays from the cathode C pass through a slit in the anode A, which is a metal plug fitting tightly into the tube and connected with the earth; after passing ...
[6]
Components of Cells and Batteries
The Cathode is the positive or oxidizing electrode that acquires electrons from the external circuit and is reduced during the electrochemical reaction.
[7]
Electrochemical Cell Parts - Chemistry 302
The electrode for the reduction reaction is called the cathode. The electrons flow from the anode to the cathode. Let's look at a picture of the cell below ...
[8]
General Tube Information - Frostburg State University
In between those two elements different tubes have different components. The cathode is typically a nickel sleeve, coated to increase its electron emission ...Missing: definition | Show results with:definition
[9]
Voltaic Cells
The anode is an electrode where oxidation occurs. The cathode is an electrode where reduction occurs. A salt bridge is a chamber of electrolytes necessary to ...
[10]
Faraday consults the scholars: the origins of the terms of ... - Journals
The words were first published by Michael Faraday, F.R.S. (1791-1867) in 1834, with the barest of acknowledgements to two unnamed friends with whom, he said ...
[11]
Faraday Consults the Scholars: The Origins of the Terms of ... - jstor
Willis then did not do more than draw Faraday's attention to Whewell's interest and ability in scientific nomenclature; but in view of the happy results of ...
[12]
Pillars of modern electrochemistry: a brief history
He also discovered the laws of electrolysis, by which he quantified electrochemistry, and popularized terminology such as anode, cathode, electrode, and ion, ...
[13]
The Etymology and Meaning of Anode and Cathode
Mar 24, 2019 · The word cathode comes from the Greek κάθοδος (kathodos), meaning 'descent' or 'the way downward' [1], which today refers to the movement of ...
[14]
Voltaic Pile – 1800 - Magnet Academy - National MagLab
The voltaic pile, invented by Alessandro Volta in 1800, was the first device to provide a steady supply of electricity. Volta's ongoing disagreement with ...
[15]
Electrochemistry Encyclopedia -- Volta and the "Pile"
The fame of Alessandro Volta (1745-1827) is due to his invention, in late 1799, of the "Pile", the first battery in history. He first named it "artificial ...
[16]
Electrochemical contributions: Sir Humphry Davy (1778–1829) - 2021
May 4, 2021 · Davy is the best known for isolating, by using electrolysis, many elements for the first time: potassium (K) and sodium (Na) in 1807 and calcium (Ca), ...
[17]
Science and Celebrity: Humphry Davy's Rising Star
Dec 23, 2008 · In 1807, using electrochemistry, Davy isolated the metals potassium (from caustic potash, now known to be potassium hydroxide [KOH]) and sodium ...Missing: cathode | Show results with:cathode
[18]
William Crookes - Linda Hall Library
Jun 17, 2016 · Using a Crookes tube, and deflecting the cathode rays by a magnetic field, Thomson discovered that the cathode rays were actually very tiny ...
[19]
Discovery of the Electron: J. J. Thomson - Le Moyne
In 1897 he reported that "cathode rays" were actually negatively charged particles in motion; he argued that the charged particles weighed much less than the ...
[20]
What Is a Vacuum Tube? History, Types, Applications
Aug 20, 2024 · The history of vacuum tube technology starts in the late 19th century with Thomas Edison. While working on light bulbs, Edison noticed a ...
[21]
Historical development and future trends of vacuum electronics
Sep 7, 2012 · Vacuum electronics (VE) have dominated development and industrial growth in their application areas from the end of the 19th century to the ...
[22]
[PDF] Electrochemistry A semi-permeable membrane separates solutions ...
Apr 21, 2021 · The direction of current flow is from cathode to the anode. The electrical work for the electrons in the external circuit is wexternal = – z ...<|separator|>
[23]
[PDF] Lab 9: Electrochemical Cells
Since the anode is the “source” of electrons, it is conventionally given a negative sign while the cathode, being where the electrons are going to, is given a ...
[24]
Ch. 12: Electrochemistry (Complete) Flashcards by Emma Picker
defn + mnemonic: anode + cathode. A. ANODE ... in both: reduction at cathode, oxidation at anode, cations attracted to ... 2 mnemonics for cathode, anode, cations, ...
[25]
History and the electric current convention | IOPSpark
By convention, however, the electric current is taken as flowing in the opposite direction towards the negative terminal.
[26]
October 1897: The Discovery of the Electron
Oct 1, 2000 · JJ Thomson refined previous experiments and designed new ones in his quest to uncover the true nature of these mysterious cathode rays.
[27]
Conventional Versus Electron Flow | Basic Concepts Of Electricity
In conventional flow notation, we show the motion of charge according to the (technically incorrect) labels of + and -. This way the labels make sense, but the ...
[28]
1. Introduction to Electrochemistry - PyRO Lab
In galvanic and electrolytic cells, one electrode always undergoes oxidation (the anode), and the other always undergoes reduction (the cathode).
[29]
Table of Standard Electrode Potentials - HyperPhysics
Cathode (Reduction) Half-Reaction, Standard Potential E° (volts). Li+(aq) + e ... Cu2+(aq) + 2e- -> Cu(s). 0.34. ClO3-(aq) + H2O(l) + 2e- -> ClO2-(aq) + ...
[30]
[PDF] ELECTROCHEMICAL METHODS
Apr 5, 2022 · In this new edition, we have sought to update the book in a way that will extend its value as a general introduction to electrochemical methods.
[31]
Electrode Materials in Modern Organic Electrochemistry - PMC - NIH
Aug 24, 2020 · Overpotential is also influenced by supporting electrolyte,93 solvent,99, 111, 112, 113 current density,95, 96 concentration,114 temperature, ...
[32]
Nernst Equation - EdTech Books
... equation relating free energy change to cell potential yields the Nernst equation: − n F E cell = − n F E cell ° + R T ln Q − n F E cell = − n F E cell ° + R T ...
[33]
[PDF] 5.111 Principles of Chemical Science - MIT OpenCourseWare
Electrolytic Cell uses electrical energy provided by an external circuit to carry out nonspontaneous reactions. Summary. Whether the cell operates ...
[34]
17.6 Electrolysis – Chemistry Fundamentals - UCF Pressbooks
An important use for electrolytic cells is in electroplating. Electroplating results in a thin coating of one metal on top of a conducting surface. Reasons for ...
[35]
[PDF] A REVIEW ON WATER ELECTROLYSIS.pdf
Water electrolysis is an electrochemical process where electrical energy decomposes water into hydrogen and oxygen by passing a current through it.<|control11|><|separator|>
[36]
[PDF] Electroplating - IN.gov
Platinum and carbon are usually used as inert anodes. Electrolyte is the electrical conductor in which current is carried by ions rather than by free electrons.
[37]
[PDF] Effectiveness of Different Materials as Catalysts for Alkaline Water ...
Jun 1, 2023 · Molybdenum electrodes were found to be significantly more effective than nickel electrodes in alkaline water electrolysis, with lower ...
[38]
Water electrolysis: from textbook knowledge to the latest scientific ...
Basically Fe, Ni, Co, Cu, W and Mo phosphides were found promising cathode materials for water electrolysis. ... reaction overpotential in turns yielding high ...
[39]
[PDF] The Chlor-Alkali Industry - eere.energy.gov
When a source of direct current is attached to the electrodes, sodium ions begin to move toward the negative electrode. (cathode) and chlorine ions toward the ...
[40]
Electrolysis – Chemistry - UH Pressbooks
The cathode is located on the right and is the spoon, which is made from inexpensive metal. Both electrodes are immersed in a solution of silver nitrate. As the ...<|control11|><|separator|>
[41]
[PDF] Principles and implementations of electrolysis systems for water ...
Feb 12, 2016 · The total kinetic overpotential of an electrolyzer is thus the sum of the overpotentials at each of the electrodes of the electrolysis cell.
[42]
17.2 Galvanic Cells – Chemistry Fundamentals
cathode: electrode in an electrochemical cell at which reduction occurs; information about the cathode is recorded on the right side of the salt bridge in cell ...
[43]
[PDF] 10.626 Lecture Notes, Basic physics of galvanic cells - DSpace@MIT
On the other hand, at cathode, a reduction reaction occurs, consuming electrons on the electrode surface. Since the electrons are not able to move through the ...
[44]
Cell Short Hand
We have developed a short hand notation for a cell. For the cell above we have the anode on the left and the cathode on the right.
[45]
Lead Storage Battery I
A Secondary Battery: The Lead Storage Battery · 2 e– + PbO2 + 4 H+ Pb2+ + 2 H2O · 2 e– + PbO2 + 4 H+ + SO42– PbSO4 (electrode) + 2 H2O.
[46]
Corrosion - galvaniccell
Zinc behaves as the anode (supplying electrons) of the galvanic cell and the copper as the cathode (consuming electrons). The reactions occurring are those ...
[47]
[PDF] Electroplating Lab
These dissolved ions are then reduced at the cathode, which is what plates the metal ions onto the conductive material. This is shown in the figure below. Page ...
[48]
[PDF] 12.20 Electroplating - U.S. Environmental Protection Agency
The essential components of an electroplating process are an electrode to be plated (the cathode or substrate), a second electrode to complete the circuit ...
[49]
[PDF] Acid Copper Sulfate Plating Bath - OSTI.GOV
In the alkaline copper pyrophosphate bath, two addition agents--the dipotassium salt of dimercaptothiadiazole or a similar compound1,2 and anunonia--brightened ...
[50]
[PDF] Brighteners in Acid Copper Plating Baths
The brightener additives generally used for plating copper are members of a class of compounds called sulfo- nium-alkane-sulfonates,' which work in conjunction ...
[51]
Decorative Chromium Electroplating
Chromium electroplating and anodizing operations coat metal parts and tools with a thin layer of chromium to protect them from corrosion and wear. Examples of ...
[52]
National Emission Standards for Hazardous Air Pollutants | US EPA
Hard and decorative chromium electroplating and chromium anodizing tanks have been identified by EPA as significant emitters of chromium compounds to the ...
[53]
[PDF] Effect of zinc coatings on the endurance properties of steel
properties of low carbon open hearth iron and two carbon steels. II. MATERIALS. Zinc coatings were chosen because they are the most commonly used protective ...
[54]
[PDF] Zinc plating from alkaline non-cyanide bath - Scholars' Mine
Organic additives are required for alkaline zincate plating baths to obtain an acceptable coating on steel for corrosion protection. The effects and possible ...
[55]
[PDF] PLATING METHODS - NASA Technical Reports Server (NTRS)
The electrodiffusion process has been used primarily to produce boride coatings for hardness and wear resistance, although many other types of diffusion ...<|control11|><|separator|>
[56]
Facile and Electrically Reliable Electroplated Gold Contacts to p ...
Aug 4, 2021 · This study demonstrates that electroplated gold contacts can be considered as a simple and reliable metallization technology for the electrical-response ...
[57]
[PDF] electroplating.pdf - New Mexico Tech
However, new applications for gold electroplating include electrodes in fuel cells for the conductive, circuit board contacts, and protection of electronic ...
[58]
Effects of Chemical Compositions on Plating Characteristics of ... - NIH
Oct 23, 2020 · The coatings produced from baths with a moderate Zn-to-NaOH ratio of 0.067–0.092 appear to provide uniform and compact deposits, moderately high ...
[59]
[PDF] electrodeposition research - NIST Technical Series Publications
hydrogen embrittlement under cathodic conditions, which is being ... densities the shape of the cathode potential-current density curves and the ...
[60]
[PDF] Effect of Hydrogen Pick-up and Release Behavior on the Tensile ...
Jun 6, 2016 · In addition, electroplating allows for a dense and tightly adhered coating whose thickness can be controlled by the current density and length ...
[61]
Guide to Clean Technology: Alternative Metal Finishes - epa nepis
Cathode current ... In chromium plating baths, current efficiency increases with current density, which results in poor throwing power.<|control11|><|separator|>
[62]
Copper Mining and Processing: Processing Copper Ores
The last step is called electrowinning, a type of electrolysis. An electrical current passes through an inert anode (positive eletrode) and through the copper ...
[63]
[PDF] ELECTROWINNING PROCESS FOR COPPER REMOVAL FROM ...
Metal will plate on the cathode when the anode and cathode are powered. Unlike other methods for heavy metal removal, electrowinning is a clean single-step.
[64]
[PDF] DESIGN OF COPPER ELECTROWINNING CIRCUIT USING ...
Copper electrowinning is the recovery of copper metal onto the cathode from electrolyte. The electrolyte may be the leach solution or the purified solution ...
[65]
[PDF] Laboratory Scale Experimental Analysis of the Effect of Surfactants ...
2.2. Anodes used during copper electrowinning are positive inert lead steel plates (Pb-Sn or Pb-Sb alloys) placed Page 21 10 in the electrolyte cell that ...<|control11|><|separator|>
[66]
[PDF] Estimates of Electricity Requirements for the Recovery of Mineral ...
Feb 16, 2011 · Approximately 2.5 kWh is required to recover one kg of copper by electrowinning of copper-laden leach solutions in efficiently operated ...
[67]
[PDF] Understanding Impurities in copper electrometallurgy - Scholars' Mine
Copper electrowinning produces about 99.99% pure copper sheet during a week- long plating cycle using 316L stainless steel cathode blanks. This product is ...
[68]
[PDF] Selective Electrowinning of Silver and Gold From Cyanide Process ...
The U.S. Bureau of Mines investigated the selective electrowinning of Ag and Au from cyanide solu- tions contaminated with Cu with the goal of decreasing the ...
[69]
[PDF] Studies on the Hall-Heroult Aluminum Electrowinning Process
The commercial production of metallic aluminum started in 1889 with electrolysis of cryolite-alumina melt by the Hall-Heroult process. Apart from the ...
[70]
Thermionic Emission: A Comprehensive Guide - Electrical4U
Jun 18, 2023 · Cathode ray tubes: Cathode ray tubes are vacuum tubes that use thermionic emission to produce a beam of electrons that can be deflected by ...
[71]
Thermionic Cathodes - Information and Resource - eBeam, Inc.
Thermionic cathodes use heat to expel electrons from a solid. They are in contrast to cold (field emission) cathodes, which use high electric fields to tear ...
[72]
Hot Cathode - an overview | ScienceDirect Topics
Hot cathodes are based on thermionic phenomena (the emission of charged particles from the surface of a conducting material or compound at high temperature).
[73]
The History of Vacuum Tubes: An Era Away - Technical Articles
Dec 11, 2020 · Vacuum tubes were early tech, enabling radar, radio, TV, and computers. They were replaced by semiconductors due to issues like being easily ...
[74]
Secrets of the Tube Alchemists - Effectrode
The oxide-coated cathode is the prime-mover, the working-end of a vacuum tube: the source of negative ions (electrons) that makes amplification of an electrical ...<|separator|>
[75]
The Quest for the Ultimate Vacuum Tube - IEEE Spectrum
Nov 24, 2015 · The latest generation of traveling-wave tubes can provide up to 180 W at frequencies up to 22 GHz, with efficiencies approaching 70 percent and ...
[76]
Thermionic Emission - an overview | ScienceDirect Topics
The Richardson's constant, A, is given by A = ( 4 πm k 2 e ) / h 3 = 1.20173 × 106 Am−2K−2, where m and e are the mass and charge of electron, respectively, and ...<|separator|>
[77]
4.1 Diode concept and bias - Open Books
The electrode attached to the p-type region is called the anode, while the electrode attached to the n-type region is called the cathode.
[78]
[PDF] Semiconductor Devices: Theory and Application | James M. Fiore
from anode to cathode, the diode will conduct current. If the polarity is reversed, the diode will not conduct. Therefore a simple model of the diode is a ...
[79]
[PDF] Graphic Symbols for Electrical and Electronics Diagrams
Jun 8, 2015 · “D” is now listed as an alternate to the common “CR” for the common semiconductor diode family of devices.
[80]
[PDF] Lecture 18 - Metal-Semiconductor Junction (cont.) March 16, 2007 ...
Mar 16, 2007 · Drift-diffusion theory of current exhibits several dependences observed in devices, but fails temperature dependence. • Thermionic emission ...
[81]
[PDF] Semiconductors
The electron and hole currents therefore add, giving a total diode current density,. Jtotal VD. ( )= Jp VD. ( )+ Jn VD. ( )= Jp diff 0( )+ Jn diff 0( ). (. ) e.
[82]
[PDF] Lateral Processing of Silicon Esaki Tunnel Diode
Current flow is governed by quantum-mechanical tunneling through the thin depletion region, which ranges between 2 and 3 nanometers in high current density ...
[83]
[PDF] Leo Esaki - Nobel Lecture
The rectification direction in this junction is again backward as is the case in the tunnel diode. We might add that, in this treatment, the tunneling ...