Simple Direct Alternating Current Battery Using Iron Electrodes

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Alternating current (AC) is currently used as a power source for a wide variety of electronic and electrical devices. Direct AC batteries, which generate AC without external devices, are expected to find a variety of applications. Despite the development of various chemical batteries, direct AC batteries with this capability have not been reported. To realize a direct AC battery, the current flow between the two electrodes needs to be spontaneously and repeatedly reversed. In other words, the electrodes of the battery need to alternately undergo oxidation and reduction reactions. On the other hand, electrochemical oscillations are often observed during electrolysis. For example, various metals (e.g., Fe) exhibit current oscillations during dissolution. Typically, these oscillations are observed in anodic currents. Figure 1a shows the current (I)–potential (E) curve of a Fe electrode in a 1.0 M H2SO4 solution. The anode current due to Reaction 1 oscillated at approximately 0.45 V.Fe→ Fe2+ + 2e- (1)When a phosphoric acid solution containing hydrogen peroxide is used as the electrolyte, the oxidation reaction of Fe (Reaction 1) and the reduction reaction of hydrogen peroxide (Reaction 2) proceed alternately at approximately 0.3 V (Figure 1b) [1]. In other words, AC is spontaneously generated.H2O2 + 2H+ + 2e- → 2H2O (2)In this study, we developed a direct AC battery that utilizes the current oscillation. The battery has a simple structure with two Fe electrodes immersed in 0.5 M H3PO4 + 1.5 M H2O2, and an AC is generated by the alternating progression of Reactions 1 and 2 (Figure 2). The amplitude of the AC is approximately 0.05 mA though the amplitude of the current oscillation observed in the I−E curve reaches 10 mA (Fig. 1b). Figure 3 displays the relationship between current (I) and applied voltage (V app) for the direct AC battery, demonstrating that AC behavior is observed over a wide voltage range. It is worth noting that the amplitude of the AC depends on V app. This suggests that the battery can generate considerable amplitudes, possibly reaching several mA.In general, current oscillations are attributed to negative differential resistance (NDR) [2]. In this presentation, the origin of AC will be explained based on the NDR characteristics. The necessary conditions for a direct AC battery will also be explained. References R. Sato and Y. Mukouyama, The 74th Annual Meeting of the ISE, S16-P-026 (2023).M. Orlik, Self-Organization in Electrochemical Systems I, Springer-Verlag Berlin Heidelberg, Berlin (2012). Figure 1