Preparation of Nickel-Based Thin Film Co-Deposited with Bi2Ru2O7-Z Nano-Particles on Resin for Air Secondary Batteries

Abstract

A metal hydride/air secondary battery consists of a gas diffusion electrode as the positive electrode, a hydrogen storage alloy as the negative electrode, and a high concentration of alkaline solution as the electrolyte. In this battery, oxygen reduction occurs at the three-phase boundary of catalyst/air/alkaline solution during discharge and oxygen is evolved during charge, so that the positive electrode needs a high catalytic activity for the oxygen reactions and a high durability in the alkaline solution. Among the materials for the positive electrode, we have developed a novel electrode comprising pyrochlore-type oxide loaded on nickel coated silica particles with PTFE binder [1]. The electrode worked for oxygen evolution and reduction and was stable in 6 mol/L KOH solutions. From the results, we have been also trying to develop a new concept of positive electrode, which is based on resin substrate coated with conductive nickel-based thin film with oxide catalyst prepared by electroless plating in order to reduce the weight of the positive electrode. In this paper, we present the preparation method of the novel air electrode’s material, i.e., nickel-based coating with Bi2Ru2O7-zparticles formed on resin, and the results on polarization measurements for oxygen evolution and reduction in KOH solutions.The electroless plating of nickel-based thin film was carried out by the method with some modification from the reported one [2]. Three kinds of resin plates, ABS, PE, and PP, were used and were pre-treated before the electroless plating consisting of sensitization, activation, and finally deposition of nickel-based coating. The oxide catalyst, Bi2Ru2O7-z, was prepared through co-precipitation and calcination process, in which the precipitates obtained from the metal salt solution containing Bi(III) and Ru(III) after adding NaOH solution was calcined. The co-deposition of the oxide particles into nickel-based film was performed by adding the oxide into the nickel plating solution. A variety of parameters in the above procedure such as the pretreatment method of the resin, the temperature and time in sensitization, activation, and deposition processes of electroless plating, and the concentration of the oxide particles in the plating solution were examined. The obtained samples were analyzed by SEM and EDX, and the electrochemical measurements were done by cyclic voltammetry using a conventional three-electrode cell with 6 mol/L KOH solutions.All the resins were possible to create nickel-based thin film by electroless plating, although the most uniform and thin film was obtained on and was well adherent to ABS resin. With the preparation conditions to make such a uniform and adhesive film on ABS, the co-deposition of the oxide particles was tried, resulting in the surface morphology of the obtained sample as shown in Fig. 1. Although the oxide particles seemed to be partly aggregated compared to those before co-deposition, the particles were found on the outermost surface of the film. This coated resin plate was used as the working electrode and the cyclic voltammograms in 6 mol/L KOH solution were measured. The results indicated that the currents for oxygen evolution and reduction were obtained with the co-deposited film, which were apparently higher than those obtained the nickel-based film without the oxide catalyst. In this paper, the details of the optimum preparation conditions are presented. The authors acknowledge “Advanced Low Carbon Technology Research and Development Program (ALCA)” of Japan Science and Technology Agency (JST).