Cathodic polarization behavior of different Mg-rare earth (RE) alloys such as EV31A, WE43C, and ZE10A is being evaluated in different heat treated conditions, and different surface conditions (such as as-polished, and covered by a surface layer) along with volumetric determination of hydrogen gas evolved during cathodic and anodic polarization. The results indicate that presence of Mg(OH)2 layer helped increase the exchange current density for the hydrogen evolution reaction (HER). Enhanced hydrogen evolution on the hydroxide covered magnesium was reported by other researchers also [[2], [3]]. The Tafel slopes are steeper on the surface oxide covered specimens than the Tafel slopes of freshly polished specimens. This implies that the electrodes will be polarized significantly during the hydrogen evolution, and thus the Coulombic efficiency is reduced further.
The hydrogen evolution reaction steps can be given as [[4], [5]]:
Mg + H2O → Mg(OHads) (Hads) (1)
which is similar to Volmer reaction.
Mg(OHads) (Hads) → Mg(Oads) + H2 (2)
Mg(OHads) (Hads) + H2O → Mg(OHads)2 (Hads)2 (3)
Mg(OHads)2 (Hads)2 → Mg(OHads)2 + H2 (4)
This presentation will focus on how the heat treatment conditions (in terms of microstructure, secondary phases, grain size), and the surface conditions influence the hydrogen evolution kinetics. The strategies to minimize the NDE and increase the performance of anode of the Mg-air battery will be discussed based on the experimental results and literature review.
[1] T. Zhang, Z-.L. Tao, J. Chen, Mater. Horiz., 2014, 1, 196
[[2]] S.H. Salleh, S. Thomas, J.A. Yuwono, K. Venkatesan, N. Birbilis, Electrochim. Acta 161 (2015) 144 – 152.
[[3]] G.L. Song, K.A. Unocic, Corros. Sci. 98 (2015) 758 – 765.
[[4]] K.S. Williams, V. Rodriguez-Santiago, J.W. Andzelm, Electrochim. Acta 210 (2016) 261 - 270
[[5]] K.S. Williams, J.P. Labukas, V. Rodriguez-Santiago, J.W. Andzelm, Corrosion 71 (2015) 209 - 223