(Invited) Detection of Anodic Partial Current of Mg Dissolution by Gas-Chromatographic Analysis

Magnesium (Mg) and its alloys are attractive materials as the battery electrodes, biomaterials and structural materials because they have high strength-to-weight ratios. However, they actively dissolve in aqueous solution and hydrogen evolution is observed. The hydrogen evolution rate of Mg is increased with increasing anodic polarization above the open circuit potential, which is commonly known as the negative difference effect1,2. The reaction mechanisms of this behavior are unknown and various kinds of electrochemical methods have been developed to clarify them4-7. We have developed an in-situ detection method of hydrogen gas evolved from Mg during electrochemical measurement6. In this method, an electrochemical cell was connected to a gas chromatograph, namely, the hydrogen gas evolved from dissolving Mg is delivered to the gas chromatograph with the argon carrier gas during electrochemical measurement. The hydrogen evolution rate could be determined by calculating from the volume of hydrogen gas estimated by gas-chromatographic analysis. In our previous work6, the hydrogen evolution rate could be determined under potentiostatic polarization of Mg successively. In the present study, we applied the developed method6 to the detection of anodic partial current of Mg dissolution. The cathodic current related to the hydrogen evolution reaction was estimated from the volume of hydrogen gas obtained by gas-chromatographic analysis during anodic polarization measurement of Mg. The partial anodic current at each polarization potential could be estimated by the sum of the measured anodic current and absolute value of cathodic current associated with the hydrogen evolution reaction, namely, the partial anodic polarization curve could be obtained by the plots of partial anodic current at each polarization potential. The characteristics of measured anodic polarization curve of Mg and partial anodic polarization curve obtained by the developed method were discussed. References 1. G. Song, A. Atrens, D. St John, X. Wu and J. Nairn, Corros. Sci., 39, 1981 (1997). 2. G. S. Frankel, A. Samaniego and N. Birbilis, Corros. Sci., 70, 104 (2013). 3. M. Curioni, Electrochim. Acta, 120, 284 (2014). 4. S. Lebouil, A. Duboin, F. Monti, P. Tabeling, P. Volovitch and K. Ogle, Electrochim. Acta, 124, 176 (2014). 5. S. Fajardo and G. S. Frankel, Electrochim. Acta, 165, 255 (2015). 6. Y. Hoshi, R. Takemiya, I. Shitanda and M. Itagaki, J. Electrochem. Soc., 163, C303 (2016). 7. Y. Hoshi, K. Miyazawa, I. Shitanda and M. Itagaki, J. Electrochem. Soc., 165, C243 (2018).