A study about aqueous reversible air electrode- Catalyst, Electrolyte and Structure

Developing a better high energy density rechargeable battery has becoming critically important for several industries. For building such kind of battery, reversible air electrode has been widely accepted as one of the key components. One of the major challenges for reversible air electrode is finding a good bifunctional catalyst to greatly reduce the recharge overpotential and increase the system efficiency. To achieve this goal, a new air battery chemistry based on cobalt salen modified Au catalyst is proposed in this dissertation as a very promising solution. The unique catalytic activity of this catalyst is found to be a two electron reversible ORR in alkaline electrolyte, which is the most reversible air electrode chemistry system known to date. The reaction mechanism of this catalyst is explained by the surface double layer theory. Cobalt salen is believed to locate in the outer Helmholtz layer, inducing Au surface reconstruction and promoting oxygen chemisorption. Temperature and pH are found to be important environmental conditions for controlling the catalyst ORR reversibility. Electropolymerization is found to be a effective method to stabilize the surface modification without jeopardizing catalytic activity. The nano size Au particles are found to be harmful for ORR reversibility because of the stronger peroxide reduction ability. EDTA, as peroxide stabilizer, is found to be an excellent additive to the electrolyte environment. Three new electrochemical systems are proposed according to the catalyst structure on peroxide production and battery application. An energy storage method and flowing cell structure are discussed in detail for applying this catalyst. The influence of the cation to the ORR catalytic activity on noble metal catalyst is also explained by surface double layer structure, for which the cation proved to have significant influence on the chemisorptions of oxygen containing species.