An air secondary battery using aqueous alkaline solutions is one of the promising candidates of next-generation energy storage devices, and the bi-functional air electrode for oxygen reduction during discharge and oxygen evolution during charge is the key component for a high energy density and a good cycling performance. The air electrode typically consists of carbon material, catalyst, and PTFE, in which carbon material is light and conductive, but not highly durable for oxygen evolution, so that alternative material with a higher durability is expected. In this work, we aimed to develop a novel air electrode using core-shell structure of resin particles, of which the surface is coated with nickel alloy film by electroless deposition, since this unique material is light and conductive with a high durability for alkaline solutions and oxygen evolution. This paper presents the preparation of the air electrode and the polarization behaviors for oxygen reduction and evolution.

Nickel alloy coated resin (NCR) particles used for the air electrode were prepared by electroless deposition of nickel-phosphorus alloy on the composite resin particles comprising silica and melamine resin. The NCR particles were mixed with Bi_1.87Ru₂O_6.903 nano-partilces as the catalyst and PTFE partilces as the water repellent agent, and the mixture was pressed onto a nickel mesh to form a sheet by roll press at 80℃. For comparison, we prepared the air electrode consisting of NCR and PTFE partilces without the catalyst. Cyclic voltammetry was performed to measure the polarization of the air electrode which faced air on one side and 6 mol/L KOH solution on the other side in a three-electrode cell.

The air electrode using NCR was successfully prepared at the weight ratio of NCR : catalyst : PTFE = 58 : 29 :13 % by roll press at 0.5 MPa. The obtained electrode showed 46% weight reduction compared to that comprising nickel alloy coated silica (NCS) particles with the catalyst and PTFE in our previous study [1]. The polarization curves of the air electrodes with and without the catalyst indicated that oxygen reduction current was quite small at the air electrode without the catalyst, while the reduction current was seen at about 0 V vs. Hg/HgO reference electrode and increased at more negative potentials, indicating that NCR particles work well as the conducting material of the air electrode. In this paper, a comparison in polarization performance between the air electrodes using NCR, NCS, and graphite powders will be presented.

Reference

[1] H. Sano, M. Morimitsu, TMS 2017, San Diego (2017).