| Rechargeable Zn-air batteries have drawn strong recent interest because theoretically they can combine rechargeability with the high specific energy (energy stored per unit mass) of fuel cell systems. Part of the high specific energy is due to the cathode active material (i.e. oxygen) being drawn from the surrounding air and not stored in any form in the cell like traditional rechargeable batteries (the other reason is the use of a highly condensed "fuel" in the form of an oxidizable zinc metal as the anode). However, the reactions in the air electrode are kinetically challenged, resulting in a significant lowering of the round-trip efficiency. Effective catalysts are needed to reduce the high overpotentials in these reactions, i.e. oxygen reduction reaction (ORR) during discharge process and oxygen evolution reaction (OER) during recharge process. While catalysts based on the platinum group metals (PGM) have a long developmental history and some success with fuel cells and water electrolyzers, their prohibitively high cost is disincentive to any large-scale deployment (which is however the target market for rechargeable Zn-air batteries). The need for non-PGM catalyst alternatives is therefore clear and present.;The thesis presents several designs of non-PGM electrocatalysts which have shown high activity for the oxygen reactions in alkaline solution. (Abstract shortened by UMI.). |
