# cathode

(noun)

## Definition of cathode

The electrode of an electrochemical cell at which reduction occurs.

Source: Wiktionary - CC BY-SA 3.0

## Examples of cathode in the following topics:

• ### Cathode Rays

• Cathode Rays Cathode rays (also called an electron beam or e-beam) are streams of electrons observed in vacuum tubes.
• Electrons were first discovered as the constituents of cathode rays.
• Cathode rays are so named because they are emitted by the negative electrode, or cathode, in a vacuum tube.
• These were the cathode rays.
• Eugene Goldstein named them cathode rays.
• Cathode rays are electron beams or streams of electrons that were observed for the first time in Crookes tubes (vacuum tubes).
• ### Voltaic Cells

• Electrochemical cells have two conductive electrodes (the anode and the cathode).
• The cathode is the electrode where the reduction takes place.
• At the cathode, the metal ion in the solution will accept one or more electrons from the cathode and the ion's oxidation state is reduced to 0.
• This forms a solid metal that electrodeposits on the cathode.
• The cathode attracts cations.
• ### Electrochemical Cell Notation

• The reaction conditions (pressure, temperature, concentration, etc), the anode, the cathode, and the electrode components are all described in this unique shorthand.
• Recall that oxidation takes place at the anode and reduction at the cathode.
• When the anode and cathode are connected by a wire, electrons flow from anode to cathode.
• The anode reaction is: $Cd (s) \rightleftharpoons Cd^{2+} (aq) + 2e^-$ and the cathode reaction is: $2Ag^+ (aq) + 2e^- \rightleftharpoons 2Ag (s)$ Cell Notation Rules 1.
• The anode half-cell is described first; the cathode half-cell follows.
• ### Electrolytic Properties

• Lone electrons normally cannot pass through the electrolyte; instead, a chemical reaction occurs at the cathode that consumes electrons from the anode.
• Another reaction occurs at the anode, producing electrons that are eventually transferred to the cathode.
• As a result, a negative charge cloud develops in the electrolyte around the cathode, and a positive charge develops around the anode.
• The positively charged sodium ions Na+ will react towards the cathode neutralizing the negative charge of OH− there, and the negatively charged hydroxide ions OH− will react towards the anode neutralizing the positive charge of Na+ there.
• Here the electrode reactions convert chemical energy to electrical energy.Oxidation and Reduction at the ElectrodesOxidation of ions or neutral molecules occurs at the anode, and the reduction of ions or neutral molecules occurs at the cathode.
• ### The Lithium-Ion Battery

• Charging and Discharging The three participants in the electrochemical reactions in a lithium-ion battery are the anode, the cathode, and the electrolyte.
• Both the anode, which is a lithium-containing compound, and the cathode, which is a carbon-containing compound, are materials into which and from which lithium ions can migrate.
• When a lithium-based cell is discharging, the positive lithium ion is extracted from the cathode and inserted into the anode, releasing stored energy in the process.
• The most commercially popular cathode material is graphite.
• In a lithium-ion battery, the lithium ions are transported to and from the cathode or anode.
• ### Predicting the Products of Electrolysis

• Positively charged ions (cations) move toward the electron-providing (negative) cathode, whereas negatively charged ions (anions) move toward the positive anode.
• You may have noticed that this is the opposite of a galvanic cell, where the anode is negative and the cathode is positive.
• Oxidation and Reduction Oxidation of ions or neutral molecules occurs at the anode, and reduction of ions or neutral molecules occurs at the cathode.
• For example, it is possible to oxidize ferrous ions to ferric ions at the anode: $Fe^{2+} (aq) \rightarrow Fe^{3+} (aq) + e^-$ It is also possible to reduce ferricyanide ions to ferrocyanide ions at the cathode: $Fe(CN)^{3-}_6 + e^- \rightarrow Fe(CN)^{4-}_6$ Neutral molecules can also react at either electrode.
• This is because Cu2+ ions are attracted to the negatively charged cathode, and since the the cathode is putting out electrons, the Cu2+ becomes reduced to form copper metal, which is deposited on the electrode.
• ### Free Energy and Cell Potential

• Free Energy and Cell PotentialThe basis for an electrochemical cell, such as the galvanic cell, is always a redox reaction that can be broken down into two half-reactions: oxidation at anode (loss of electron) and reduction at cathode (gain of electron).
•  As such, the following rules apply:If E°cell > 0, then the process is spontaneous (galvanic cell)If E°cell < 0, then the process is nonspontaneous (electrolytic cell)Therefore, in order to have a spontaneous reaction, E°cell must be positive, where:E°cell = E°cathode − E°anodewhere E°anode is the standard potential at the anode and E°cathode is the standard potential at the cathode as given in the table of standard electrode potentials.
• ### Electrolysis of Molten Sodium Chloride

• Let's go through each of the methods to understand the different processes.If sodium chloride is melted (above 801°C) and two electrodes are inserted into the melt as shown in and an electric current is passed through the molten salt, then chemical reactions take place at the electrodes.Sodium ions migrate to the cathode, where electrons enter the melt and are reduced to sodium metal:${Na}^{+} + {e}^{-} \rightarrow Na$Chloride ions migrate the other way, toward the anode, give up their electrons to the anode, and are oxidized to chlorine gas:${Cl}^{-} \rightarrow \frac{1}{2}{Cl}_{2} + {e}^{-}$The overall reaction is the breakdown of sodium chloride into its elements:$2NaCl \rightarrow Na(s) + {Cl}_{2}(g)$Now what happens when we have an aqueous solution of sodium chloride as shown here ?
• The reaction at the cathode is:${H}_{2}O (l) + 2 {e}^{–} \rightarrow {H}_{2}(g) + 2{ OH}^{–}$and at the anode:${Cl}^{–} \rightarrow \frac{1}{2} {Cl}_{2}(g)$The overall reaction is as follows:$NaCl(aq) + {H}_{2}O(l) \rightarrow {Na}^{+}(aq) + {OH}^{-}(aq) + {H}_{2}(g) + \frac{1}{2}{Cl}_{2}(g)$Reduction of Na+ (E° = –2.7 v) is energetically more difficult than the reduction of water (–1.23 v), so in aqueous solution the latter will prevail.
• ### The Effect of pH on Solubility

• The gels are set in a buffer in a container with a negatively charged electrode (cathode) on one end and a positively charged electrode (anode) on the other.
• For example, a protein that is in a pH region below its isoelectric point will be positively charged and so will migrate towards the cathode.
• ### Fuel Cells

• Fuel Cell Structure and Function There are many types of fuel cells, but they all consist of an anode (the negative side), a cathode (the positive side), and an electrolyte that allows charges to move between the two sides of the fuel cell, as diagrammed below.
• Electrons are drawn from the anode to the cathode through an external circuit, producing direct-current electricity.
• They are made up of three adjacent segments: the anode, the electrolyte, and the cathode.
• The ions travel through the electrolyte to the cathode.