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[[File:Zinc-air-battery-types.gif|thumb|right|Zinc-air hearing aid batteries]]
[[File:Zinc-air-battery-types.gif|thumb|right|Zinc-air hearing aid batteries]]
'''Zinc-air batteries''' (non-rechargeable), and '''zinc-air [[fuel cell]]s,''' (mechanically-rechargeable) are [[Battery (electricity)|electro-chemical batteries]] powered by [[oxidation|oxidizing]] [[zinc]] with [[oxygen]] from the air. These batteries have high [[energy density|energy densities]] and are relatively inexpensive to produce. They are used in [[hearing aid]]s and in older [[camera]]s that previously used [[Mercury battery|mercury batteries]].
'''Zinc-air batteries''' (non-rechargeable), and '''zinc-air [[fuel cell]]s,''' (mechanically-rechargeable) are [[Battery (electricity)|electro-chemical batteries]] powered by [[oxidation|oxidizing]] [[zinc]] with [[oxygen]] from the air. These batteries have high [[energy density|energy densities]] and are relatively inexpensive to produce. They are used in [[hearing aid]]s and in older [[camera]]s that previously used [[Mercury battery|mercury batteries]].

⚫
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]].<ref>[http://www.thermoanalytics.com/support/publications/batterytypesdoc.html thermoanalytics: battery types]</ref>


Zinc particles are mixed with an [[electrolyte]]; water and oxygen from the air react at the [[cathode]] and form [[hydroxyl]]s which migrate into the zinc paste and form [[zincate]] ({{chem|Zn(OH)|4|2-}}), releasing [[electron]]s 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 theoretical 1.65 [[volts]], but this is reduced to 1.4–1.35 V in practical cells.
Zinc particles are mixed with an [[electrolyte]]; water and oxygen from the air react at the [[cathode]] and form [[hydroxyl]]s which migrate into the zinc paste and form [[zincate]] ({{chem|Zn(OH)|4|2-}}), releasing [[electron]]s 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 theoretical 1.65 [[volts]], but this is reduced to 1.4–1.35 V in practical cells.

⚫
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.
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.
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* Low-cost materials and inexpensive mass production
* Low-cost materials and inexpensive mass production
* Rechargeable configurations are yet to be brought to market<ref>http://www.revolttechnology.com/</ref>
* Rechargeable configurations are yet to be brought to market<ref>http://www.revolttechnology.com/</ref>

==Primary cells==
zinc-air batteries are used in disposable form to power hearing aids and other small electronic devices. Large zinc-air batteries, with capacities up to 2000 ampere hours per cell, are used to power navigation instruments and marker lights, oceanographic experiments, and railway signals.

==Secondary rechargeable cells==
Rechargeable zinc-air cells are a difficult design problem since deposition of the zinc must be closely controlled. Electrically reversing the reaction at a bifunctional air cathode, to liberate oxygen from the reaction products of discharge, is difficult and membranes tested have low overall efficiency. If charge and discharge functions are provided by separate uni-functional cathodes, the size, weight, and complexity of the cell are increased.

===Mechanically recharged cells===

⚫
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]].<ref>[http://www.thermoanalytics.com/support/publications/batterytypesdoc.html thermoanalytics: battery types]</ref>

⚫
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 as energy currency==
==Zinc as energy currency==

Revision as of 04:23, 20 January 2010

Zinc–air battery
Specific energy470 (practical),1370 (theoretical) Wh/kg[1][2]
Energy density1480-9780 Wh/L[citation needed]
Specific power100 W/kg[3][4]
Cycle durability240 to 450 cycles[5]
Nominal cell voltage1.65 V
Zinc-air hearing aid batteries

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.

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 theoretical 1.65 volts, but this is reduced to 1.4–1.35 V in practical cells.

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.

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)

Properties

  • 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[6]

Primary cells

zinc-air batteries are used in disposable form to power hearing aids and other small electronic devices. Large zinc-air batteries, with capacities up to 2000 ampere hours per cell, are used to power navigation instruments and marker lights, oceanographic experiments, and railway signals.

Secondary rechargeable cells

Rechargeable zinc-air cells are a difficult design problem since deposition of the zinc must be closely controlled. Electrically reversing the reaction at a bifunctional air cathode, to liberate oxygen from the reaction products of discharge, is difficult and membranes tested have low overall efficiency. If charge and discharge functions are provided by separate uni-functional cathodes, the size, weight, and complexity of the cell are increased.

Mechanically recharged cells

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.[7]

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 as energy currency

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.

See also

Template:EnergyPortal

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. ^ http://www.revolttechnology.com/
  7. ^ thermoanalytics: battery types
  8. ^ Science & Technology Review
  • David Linden, Thomas B. Reddy (ed). Handbook Of Batteries 3rd Edition, McGraw-Hill, New York, 2002 ISBN 0-07-135978-8, chapter 13 and chapter 38

Template:GalvanicCells

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