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Zinc-air battery From Wikipedia

Zinc-air battery
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Zinc-air battery Energy/weight 470 (practical),1370 (theoretical) Wh/kg[1][2]
Energy/size 1480-9780 Wh/L[citation needed]
Power/weight 100 W/kg[3][4]
Cycle durability 240 to 450 cycles[5]
Nominal cell voltage 1.65 V

Zinc-air batteries (non-rechargeable), and zinc-air fuel cells, (mechanically-rechargeable) are electro-chemical batteries powered by oxidizing zinc with oxygen from the air. These batteries have high energy densities and are relatively inexpensive to produce. They are used in hearing aids and in older cameras that previously used mercury batteries. They may be an important part of a future zinc economy.

In rechargeable configurations, zinc-air has a high energy density, a short cycle life, low power density and low efficiency. The porous carbon cathode absorbs oxygen from the air. The anode is zinc and the electrolyte is typically potassium hydroxide (unusualy, a base).[6]

Zinc particles are mixed with an electrolyte; water and oxygen from the air react at the cathode and form hydroxyls which migrate into the zinc paste and form zincate (Zn(OH)2−4), releasing electrons to travel to the cathode. The zincate decays into zinc oxide and water is returned to the system. The water and hydroxyls from the anode are recycled at the cathode, so the water serves only as a catalyst. The reactions produce a maximum voltage level of 1.65 volts, but this is reduced to 1.4–1.35 V by reducing air flow into the cell; this is usually done for hearing aid batteries to reduce the rate of water drying out.

The term zinc-air fuel cell usually refers to a zinc-air battery in which zinc fuel is replenished and zinc oxide waste is removed continuously. This is accomplished by pushing zinc electrolyte paste or pellets into an anode chamber. Waste zinc oxide is pumped into a waste tank or bladder inside the fuel tank, and fresh zinc paste or pellets are taken from the fuel tank. The zinc oxide waste is pumped out at a refuelling station and sent to a recycling plant. Alternatively, this term may refer to an electro-chemical system in which zinc is used as a co-reactant to assist the reformation of hydrocarbon fuels on an anode of a fuel cell.

Zinc-air batteries have properties of fuel cells as well as batteries: the zinc is the fuel, the reaction rate can be controlled by varying the air flow, and oxidized zinc/electrolyte paste can be replaced with fresh paste. Research is being conducted in powering electric vehicles with zinc-air batteries.

Contents [hide]
1 Reaction formulas
2 Properties
3 Zinc as energy currency
4 See also
5 References
6 External links

[edit] Reaction formulas
Here are the chemical equations for the zinc-air cell[2]:

Anode: Zn + 4OH– → Zn(OH)42– + 2e– (E0 = –1.25 V)
Fluid: Zn(OH)42– → ZnO + H2O + 2OH–
Cathode: O2 + 2H2O + 4e– → 4OH– (E0 = 0.4 V)
Overall: 2Zn + O2 → 2ZnO (E0 = 1.65 V)
Alternatively the reaction is stated without use of zincate, but this is inaccurate:

Anode: Zn + 2OH– → Zn(OH)2 + 2e– (E0 = –1.25 V)
Cathode: O2 + 2H2O + 4e– → 4OH– (E0 = 0.4 V)
Overall: 2Zn + O2 + 2H2O → 2Zn(OH)2 (E0 = 1.65 V)
[edit] Properties
This article is in a list format that may be better presented using prose. You can help by converting this article to prose, if appropriate. Editing help is available. (December 2007)

Stable terminal voltage until 80–85% depletion
Long shelf life when sealed to exclude oxygen
High self-discharge rate under air exposure from spontaneous oxidation
Must be isolated from air (sealed) when not in use
The electrolyte can be maintained in a humidified environment.
Must not be over-saturated or immersed in water
Low-cost materials and inexpensive mass production
Rechargeable configurations are yet to be brought to market[7]
[edit] Zinc as energy currency
This section may contain original research. Please improve it by verifying the claims made and adding references. Statements consisting only of original research may be removed. More details may be available on the talk page. (November 2009)

Metallic zinc could be used as an alternative to hydrogen or fossil fuels as an energy transfer medium (a fuel). It could either be used in a zinc-air battery or to generate electrolyze hydrogen near the point of use.

However, solid zinc cannot be moved with the convenience of a liquid. An alternative is to form pellets of a small-enough size to be pumped. Fuel cells using it would have to be able to quickly replace "spent" zinc with fresh zinc.[8] The spent material could be reduced to ionic zinc at a local facility. The zinc-air "battery" cell is a primary cell (non-rechargeable); recycling is required to reclaim the zinc.

Hydrogen generated from zinc and water could be burned in a conventional internal combustion engine, although this would provide less power than traditional hydrocarbon fuel. Electric motors directly use the power produced by a zinc-air battery.

Zinc has a number of advantages over hydrogen as an energy-carrier: zinc-air cell batteries are already efficient enough for practical use in vehicles; pure zinc is non-toxic (although commercially available zinc may be contaminated by toxic metals such as lead); easier to store than hydrogen; and can be processed by water-based electrochemistry.

[edit] See also
Energy portal
Sustainable development portal
Aluminium-air battery
Gas diffusion electrode
Metal-air electrochemical cell
Hydrogen technologies
[edit] References
1.^ power one: Hearing Aid Batteries
2.^ a b Duracell: Zinc-air Technical Bulletin
3.^ greencarcongress: zincair_hybrid
4.^ thermoanalytics: battery types
5.^ thermoanalytics: battery types
6.^ thermoanalytics: battery types
7.^ http://www.revolttechnology.com/
8.^ Science & Technology Review
[edit] External links
Zinc-air powered buses
Military uses of Zinc-air Batteries
Zinc-Air Batteries for UAVs and MAVs (includes half-cell reactions)
Incorrect Zinc-air reaction
Zinc-air fuel cell
Procedure to MAKE a simple Zinc-air fuel cell as a science fair project.
ReVolt Technology developing RECHARGEABLE Zinc-air batteries
Duracell technical bulletin (suppliers of zinc-air hearing aid batteries)
Overview of batteries
Electric Vehicle division
Revolt Introduction
Metal Air Batteries
[show]v • d • eGalvanic cells

Non-rechargeable:
primary cells Alkaline battery · Aluminium battery · Bunsen cell · Chromic acid cell · Clark cell · Daniell cell · Dry cell · Grove cell · Leclanché cell · Lithium battery · Mercury battery · Nickel oxyhydroxide battery · Silver-oxide battery · Weston cell · Zamboni pile · Zinc-air battery · Zinc-carbon battery

Rechargeable:
secondary cells Air-fueled lithium-ion battery · Lead-acid battery · Lithium-ion battery · Lithium-ion polymer battery · Lithium iron phosphate battery · Lithium sulfur battery · Lithium-titanate battery · Nickel-cadmium battery · Nickel hydrogen battery · Nickel-iron battery · Nickel-metal hydride battery · Low self-discharge NiMH battery · Nickel-zinc battery · Rechargeable alkaline battery · Sodium-sulfur battery · Vanadium redox battery · Zinc-bromine battery

Kinds of cells Battery · Concentration cell · Flow battery · Fuel cell · Trough battery · Voltaic pile

Parts of cells Anode · Catalyst · Cathode · Electrolyte · Half cell · Ions · Salt bridge · Semipermeable membrane





[show]v • d • eFuel cells

Types Alkaline fuel cell · Blue energy · Direct borohydride fuel cell · Direct carbon fuel cell · Direct-ethanol fuel cell · Direct methanol fuel cell · Electro-galvanic fuel cell · Enzymatic Biofuel Cell · Formic acid fuel cell · Flow battery · Molten carbonate fuel cell · Microbial fuel cell · Metal hydride fuel cell · Phosphoric acid fuel cell · Protonic ceramic fuel cell · Photoelectrochemical cell · Proton exchange membrane fuel cell · Regenerative fuel cell · Reformed methanol fuel cell · Solid oxide electrolyser cell · Solid oxide fuel cell · Unitized regenerative fuel cell · Zinc-air battery

Hydrogen Economy · Storage · Station · Vehicle

Retrieved from "http://en.wikipedia.org/wiki/Zinc-air_battery"
Categories: Fuel cells | Sustainable technologies | Metal-air fuel cell/batteries

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