This review highlights the critical challenges and the corresponding strategies for different metal electrodes in metal–air batteries.

Zn is an important negative electrode material in our battery industry and nextgeneration Zn based batteries are prospective to compete with lithium-ion batteries on cost and energy density. Corrosion is a severe challenge facing Zn electrodes, which can decrease the capacity, cyclability, and shelf life of batteries. More attention should be paid to Zn electrode corrosion in developing rechargeable and high energy density Zn batteries. In this mini review, the fundamental electrochemical behavior and corrosion of Zn electrodes in aqueous environment are retrospected. Then main strategies in recent studies to mitigate Zn electrode corrosion including electrolyte additives usage, electrode composition design and electrode morphology modification are reviewed.

The sponge is one of the oldest multicellular invertebrates in the world. Marine sponges represent one of the extant metazoans of 700-800 million years. They are classified in four major classes: Calcarea, Demospongiae, Hexactinellida, and Homoscleromorpha. Among them, three genera, namely, Haliclona, Petrosia, and Discodemia have been identified to be the richest source of biologically active compounds. So far, 15,000 species have been described, and among them, more than 6000 species are found in marine and freshwater systems throughout tropical, temperate, and polar regions. More than 5000 different compounds have been

As an important alloyed element to improve the localized corrosion resistance of stainless steels, Mo has been widely studied by researchers. This article reviews the mechanisms of the effect of Mo on localized corrosion. Two possible effects and corresponding experimental research are described respectively: Mo exists in the passive film as oxide and enhances the film stability (manifesting as lower nucleation probability of localized corrosion and longer delay time of breakdown of the passive film); Mo affects dissolution kinetics and inhibits active dissolution current density (manifesting as smaller metastable pitting current density and size). Then some contradictory results are discussed by considering the pitting model proposedrecently. Strictly speaking, none of the existing experimental results can deny the effect of Mo on the passive film or on the dissolution kinetics. It is reasonable to believe that Mo affects the entire process of localized corrosion rather than a single reaction. Finally, some possible research suggestions are put forward.