Relationships between Structure and Alkaline Stability of Imidazolium Cations for Fuel Cell Membrane Applications

Anion exchange membranes have substantial potential to be useful in methanol fuel cells due to the viability of non-noble metal electrocatalysts at high pH and increases in the oxidation rate of methanol in alkaline conditions. However, long-term stability of the cationic moiety has been an issue, and imidazoliums have recently attracted attention as candidates for stable cations. The prevailing strategy for increasing the stability of the imidazolium has involved adding sterically hindering groups at the 2 position. Surprisingly, the findings of this study show that steric hindrance is the least effective strategy for stabilizing imidazoliums. We propose that the most important stabilizing factor for an imidazolium is the ability to provide alternative, reversible deprotonation reactions with hydroxide and outline other structure–property relationships for imidazolium cations

Electrochemical Stability of Magnesium Surfaces in an Aqueous Environment

An insight into the electrochemical stability of Mg surfaces is of practical importance for improving the corrosion resistance of Mg as well as its performance as a battery electrode. The present paper employs first-principles density functional theory simulations to study the electrochemical stability of magnesium surfaces in aqueous environments. A number of electrochemical reactions that describe the interactions between the Mg(0001) surface and water were analyzed. It was verified that water dissociation is favored upon the Mg surface, in agreement with recent works; however, it is also shown that the previously unstudied Heyrovsky reaction may play an important role in controlling the surface stability. Furthermore, it was found that the surface stability also crucially depends on the concentration of adsorbed hydroxyl groups. Specifically, the surface work function was determined to vary as the function of hydroxyl coverage, which has ramifications for the catalytic behavior of the Mg surface. The influences of surface doping with Ca (a reactive element) and Fe (a comparatively noble element) were also studied to provide an atomic-level understanding of how the dopants influence surface properties and subsequent electrochemical reactions. With a keen recent empirical interest in Mg surface stability given the industrial relevance of Mg, the present study provides key new insights into the physical processes related to the enhanced catalytic activity of Mg and its alloys