A slow potentiodynamic method where a porous iron electrode is fully discharged and charged has been used to study the reactions of the alkaline iron electrode. Electrode thickness, temperature, average porosity, number of armor nets, electrolyte concentration, and carbonate contents have been varied. The experiments show that high temperature, porosity, and KOH concentration increases the charge efficiency of the electrodes. High KOH concentration promotes the direct oxidation of Fe to normalFeOOH , and K2CO3 concentrations up to 250 g/liters do not influence the reactions of the electrode considerably.
Anodic oxidation products in 5NKOH of both planar and porous iron electrodes have been investigated with SEM techniques. On the first discharge level well‐defined crystallites of normalFefalse(OH)2 are formed, while on continued discharge the products become sludge formed, probably consisting of hydrated normalFeOOH . The morphologies support the dissolution‐precipitation mechanism during the first discharge step. The second anodic level proceeds probably via migration of ions and electrons in the solid phase. The crystallite size increases with temperature which depends on that the relative supersaturation decreases.
A B S T R A C TIn order to fulfill volume and cost requirements on m e t a l -a i r batteries it is necessary to use bimnctional air electrodes which also serve as counterelectrodes during charge. This twofold duty puts a v e r y high d e m a n d on the electrode, especially the structure and catalyst. In the i r o n -a i r battery prog r a m of S• a 0.6 m m porous Ni-electrode with Ag catalyst has been developed for this purpose with a life of more than 1000 charge/discharge cycles. In this paper design, performance, structural changes, mode of failure etc. are discussed.Secondary m e t a l -a i r batteries are very attractive from the point of view of energy density because the positive electrochemical reactant, oxygen is supplied from outside the battery. Work on this type of power source started in the middle 1960's in the United States, Japan, and Europe. In most cases these activities were based on k n o w -h o w from fuel cell development. A short review on these activities is given in Ref.(1).Swedish National Development Company (SNDC) has been working with an i r o n -a i r b a t t e r y system since 1968. These activities have resulted in full scale batteries tested in vehicles. In 1974 a second generation prototype was tested in a 15 k W -h r -b a t t e r y in a mine vehicle. Based on experience obtained during these tests a third generation was designed and a 30 k W -h r -b a t t e r y built and tested during 1974 and 1975. This b a t t e r y system including auxiliaries is described in Ref. (1).For p r i m a r y and mechanically rechargeable m e t a lair batteries, where zinc dominates the field as negative active electrode material, comparatively simple designs of air electrodes can be used since they only work in discharge mode. Consequently designs ,used in fuel cells are suitable for these applications. For a seconda r y m e t a l -a i r b a t t e r y the application of the air electrode differs somewhat from its use in fuel cells unless a third auxiliary electrode is used during charge. Since volume is a v e r y critical p a r a m e t e r in a m e t a l -a i r b a t t e r y it is necessary to use rechargeable air electrodes which can be used as counterelectrodes during the charge process. This twofold duty puts a v e r y high d e m a n d on the electrode, especially the structure and catalyst. The air electrode used in the prototype b a ttery is of a double layer 0.6 m m thick with nickel as the supporting material. In this paper the structure, limiting factors, as welI as different possibilities to improve performance and life will be discussed. V e r y little has been published on bifunctional air electrodes (2-4). The electrode developed b y Siemens is composed of two layers, one of which is a h y d r ophilic porous nickel sheet adjacent to the electrolyte. The other one bordering the gas phase consists of a hydrophobic carbon layer. During oxygen reduction the carbon layer plays the active part, while the nickel layer catalyzes the electrode process in liberating oxygen. The activity of the ...
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