Electrolysis

In 1800, Sir Humphry Davy, inventor of the miner’s safety lamp, began testing the chemical effects of electricity and found out that decomposition occurred when passing electrical current through substances. This process was later called electrolysis.

He made new discoveries by installing the world’s largest and most powerful electric battery in the vaults of the Royal Institution of London, connecting the battery to charcoal electrodes produced the first electric light.

Voltaic cells use a spontaneous chemical reaction to drive an electric current through an external circuit. These cells are important because they are the basis for the batteries that fuel modern society. But they aren't the only kind of electrochemical cell. It is also possible to construct a cell that does work on a chemical system by driving an electric current through the system. These cells are called electrolytic cells. Electrolysis is used to drive an oxidation-reduction reaction in a direction in which it does not occur spontaneously. Voltaic cells use the energy given off in a spontaneous reaction to do electrical work. Electrolytic cells use electrical work as source of energy to drive the reaction in the opposite direction.

A Galvanic cell converts chemical energy into electrical energy.

Here, the redox reaction is spontaneous and is responsible for the production of electrical energy.

The two half-cells are set up in different containers, being connected through the salt bridge or porous partition.

Here the anode is negative and cathode is the positive electrode. The reaction at the anode is oxidation and that at the cathode is reduction.

An electrolytic cell converts electrical energy into chemical energy.

The redox reaction is not spontaneous and electrical energy has to be supplied to initiate the reaction.

Both the electrodes are placed in a same container in the solution of molten electrolyte.

Here, the anode is positive and cathode is the negative electrode. The reaction at the anode is oxidation and that at the cathode is reduction.

The external battery supplies the electrons. They enter through the cathode and come out through the anode.

Michael Faraday defined the cathode of a cell as the electrode to which cations (positively charged ions, like silver ions Ag⁺  ) flow within the cell, to be reduced by reacting with electrons (negatively charged) from that electrode.

Likewise he defined the anode as the electrode to which anions (negatively charged ions, like chloride ions Cl⁻) flow within the cell, to be oxidized by depositing electrons on the electrode.

An electrolytic cell converts electrical energy into chemical energy and not the other way round.

The ensuing redox reaction in the process is not a spontaneous one and for the reaction to start, electric energy has to be introduced in the apparatus.

 

 

Galvanic cell

The Daniell cell, invented in 1836 by British chemist John Frederic Daniell, was the first practical source of electricity, becoming an industry standard and seeing widespread adoption as a power source for electrical telegraph networks. It consisted of a copper pot filled with a copper sulfate solution, in which was immersed an unglazed earthenware container filled with sulfuric acid and a zinc electrode.

In 1866, Georges Leclanché invented a battery that consisted of a zinc anode and a manganese dioxide cathode wrapped in a porous material, dipped in a jar of ammonium chloride solution. The manganese dioxide cathode had a little carbon mixed into it as well, which improved conductivity and absorption. It provided a voltage of 1.4 volts. This cell achieved very quick success in telegraphy, signalling and electric bell work.

Dry Cell

·         The container of the dry cell is made of zinc which also serves as one of the electrodes.

·         The other electrode is a carbon rod in the centre of the cell.

·         The zinc container is lined with a porous paper.

·         A moist mixture of ammonium chloride, man­ganese dioxide, zinc chloride and a porous inert filler occupy the space between the paper lined zinc container and the carbon rod.

·         The cell is sealed with a material like wax.

·         As the cell operates, the zinc is oxidised to Zn²⁺

·         Anode reaction: Zn → Zn²⁺ + 2e^-   

·         The electrons are utilized at carbon rod (cathode) as the ammonium ions are reduced.

·         Cathode Reaction: 2NH₄⁺+2e →2NH₃ + H₂ 

·         The cell reaction is:  Zn+ 2 NH₄⁺ → Zn²⁺ + 2NH₃ + H₂

·         Hydrogen is oxidized by MnO₂ in the cell:  2MnO₂ + H₂ →2MnO(OH)

·         Ammonia produced at cathode combines with zinc ions to form complex ion.  Zn²⁺ + 4NH₃ →[Zn(NH₃)₄]₂₊ 

·         E_cell is 1.6 volt

The battery History

1800 Voltaic Pile—Alessandro Volta invented the Voltaic Pile and discovered the first practical method of generating electricity. Constructed of alternating discs of zinc and copper with pieces of cardboard soaked in brine between the metals, the Voltaic Pile produced electrical current. The metallic conducting arc was used to carry the electricity over a greater distance. Alessandro Volta's voltaic pile was the first "wet cell battery" that produced a reliable, steady current of electricity.

1836 Daniell Cell—The Voltaic Pile could not deliver an electrical current for a long period of time. Englishman, John F. Daniell invented the Daniell Cell that used two electrolytes: copper sulfate and zinc sulfate. The Daniel Cell lasted longer than the Volta cell or pile. This battery, which produced about 1.1 volts, was used to power objects such as telegraphs, telephones, and doorbells, remained popular in homes for over 100 years

1859 Rechargeable—French inventor, Gaston Plante developed the first practical storage lead-acid battery that could be recharged (secondary battery). This type of battery is primarily used in cars today.

1881—J.A. Thiebaut patented the first battery with both the negative electrode and porous pot placed in a zinc cup.

1881—Carl Gassner invented the first commercially successful dry cell battery (zinc-carbon cell).

1899—Waldmar Jungner invented the first nickel-cadmium rechargeable battery.

1901 Alkaline Storage—Thomas Alva Edison invented the alkaline storage battery. Thomas Edison's alkaline cell had iron as the anode material (-) and nickelic oxide as the cathode material (+)

1949 Alkaline-Manganese Battery—Lew Urry developed the small alkaline battery in 1949. The inventor was working for the Eveready Battery Co. at their research laboratory in Parma, Ohio. Alkaline batteries last five to eight times as long as zinc-carbon cells, their predecessors

Most research activities today revolve around improving lithium-based systems, first commercialized by Sony in 1991. Besides powering cellular phones, laptops, digital cameras, power tools and medical devices, Li-ion is also used for electric vehicles and satellites. The battery has a number of benefits, most notably its high specific energy, simple charging, low maintenance and being environmentally benign.