Question

A zinc air battery has the following reactions at the two electrodes:

1⁄2 O2 + H2O + 2e- -> 2OH-

Zn -> Zn2+ +2e-
Zn&2+ + 2OH- -> Zn(OH)^2

a) Which of these reactions occurs at the anode and which at the cathode? Explain your answer.

b) Determine the two half-cell potentials at the electrode-electrolyte interfaces using standard Gibbs free energy values (Note: Assume the phase of the Zn(OH)2 is the epsilon phase.)

c) A zinc air battery is typically used in a button configuration for hearing aids. Describe the cell construction for the air electrode and how the air flow is guided into the cell.

d) What is the typical current draw range for this battery in the hearing aid application and how long can the battery typically last in this application?

Answer 1

A)(a) In anode the oxidation Reaction happened on electrons are lost, so fos zine air battery the anode Reaction is, Anode: Zn → Zn2+ +2e- - In cathode the o Reduction Reaction happened and electrons are gained, so for zine air battery the cathode Reaction is, Cethode: 4202 +H20 +2e- →204 ( Emulanzt => -0.76. (from standard table). .: E° = 0.059110g K. = -0.76 2 .. K: 1.9 x10-26 · - Ea - F° - 0.059 lagk.. En = + 0*76 +0.76 = 1·52 V. E°ozloh- -040., 3° -0.0591@gk 2-0.40 K = 2.9 X10-4 .. Ec=0:40+0.42 =0.82 V (© Here, two types of cells are use. primary cell or non rechargeable and secondary eеll ar recharge- ble. Button cells are highly effective but it is Idifficult to extend the same coristrauction to large size due to air diffusion performance, leakrige problems. Parsis matic aud cylindrical cell designs address these problems.stacking prismatic cells requires air channel air in the battery and may require a fan to force through the stack. . d) the typical current draw rouge for this application is up to battery in the hearing aid 2000 ampere , hours and the battery typically last in the applications is I hour.