Although the authors of several publications say that zinc-air battery is one of the subspecies of the fuel cell, it is not entirely true. Having familiarized with the principle of working of zinc-air battery, even in general terms, you can make a quite unambiguous conclusion that it is more correct to consider it as a separate class of autonomous power sources.
The design of the cell of zinc-air battery includes an anode and a cathode separated by an alkaline electrolyte and mechanical separator. As a cathode is used gas diffusion electrode (GDE). The permeable membrane of cathode allows to obtain oxygen from a circulating air. “Fuel” is a zinc anode, which is oxidized in the process of working of battery, and an oxidizing agent – oxygen obtained from entering air through the “breathing hole”.
At the cathode occurs reaction of electroreduction of oxygen, the products of which are negatively charged hydroxide ions:
O2 + 2H2O + 4e 4OH-.
Hydroxide ions in the electrolyte are moved to the zinc anode, where oxidation occurs zinc with releasing of electrons, which are returned via an external circuit to the cathode:
Zn + 4OH- Zn (OH) 42- + 2e.
Zn (OH) 42- ZnO + 2OH- + H2O.
It is clear that zinc-air battery does not fall under the classification of chemical fuel cells: First, they use a consumable electrode (anode), and secondly, the fuel is initially laid into the cell, and is not supplied from the outside during operation.
The voltage between the electrodes of one cell of zinc-air battery is 1.45 V, which is very close to the same parameter of alkaline batteries. If necessary, to obtain a higher voltage, you can combine a few series-connected cells.
Zinc is a fairly common and inexpensive material, so for the deployment of mass production of zinc-air batteries, manufacturers will not have problems with raw materials. Furthermore, even at the initial stage a cost of such power sources will be competitive.
It is also important that the zinc-air batteries are very eco-friendly products. The materials used for their production, do not poison the environment and can be used again after processing. The reaction products of zinc-air battery (water and zinc oxide) also completely safe for humans and the environment – zinc oxide even is used as the main component of baby powder.
From the operational properties of zinc-air battery is worth noting such advantages, as low self-discharge rate in unactivated state and a small change of the voltage in a process of discharge (flat discharge curve).
A certain drawback of zinc-air battery is the influence of relative humidity of the incoming air on the characteristics of element. For example, a zinc-air battery, designed to operate at a relative humidity 60%, with an increase in moisture content to 90% is reduced battery life on 15%.