In the past decade, there have been exciting developments in the fi eld of lithium ion batteries as energy storage devices, resulting in the application of lithium ion batteries in areas ranging from small portable electric devices to large power systems such as hybrid electric vehicles. However, the maximum energy density of current lithium ion batteries having topatactic chemistry is not suffi cient to meet the demands of new markets in such areas as electric vehicles. Therefore, new electrochemical systems with higher energy densities are being sought, and metal-air batteries with conversion chemistry are considered a promising candidate. More recently, promising electrochemical performance has driven much research interest in Li-air and Zn-air batteries. This review provides an overview of the fundamentals and recent progress in the area of Li-air and Zn-air batteries, with the aim of providing a better understanding of the new electrochemical systems.

A composite air electrode consisting of Ketjenblack carbon (KB) supported amorphous manganese oxide (MnOx) nanowires, synthesized via a polyol method, is highly efficient for the oxygen reduction reaction (ORR) in a Zn-air battery. The low-cost and highly conductive KB in this composite electrode overcomes the limitations due to low electrical conductivity of MnOx while acting as a supporting matrix for the catalyst. The large surface area of the amorphous MnOx nanowires, together with other microscopic features (e.g., high density of surface defects), potentially offers more active sites for oxygen adsorption, thus significantly enhancing ORR activity. In particular, a Zn-air battery based on this composite air electrode exhibits a peak power density of ∼190 mW/cm2, which is far superior to those based on a commercial air cathode with Mn3O4 catalysts.

Electrocatalysts facilitating oxygen reduction reaction (ORR) are vital components in advanced fuel cells and metal-air batteries. Here we report Ketjenblack incorporated nitrogen-doped carbon sheets derived from gelatin and apply these easily scalable materials as metal-free electrocatalysts for ORR. These carbon nanosheets demonstrate highly comparable catalytic activity for ORR as well as better durability than commercial Vulcan carbon supported Pt catalysts in alkaline media. Physico-chemical characterization and theoretical calculations suggest that proper combination of graphitic and pyridinic nitrogen species with more exposed edge sites effectively facilitates a formation of superoxide, [O2(ad)](-), via one-electron transfer, thus increasing catalytic activities for ORR. Our results demonstrate a novel strategy to expose more nitrogen doped edge sites by irregular stacked small sheets in developing better electrocatalysts for Zn-air batteries. These desirable architectures are embodied by an amphiphlilic gelatin mediated compatible synthetic strategy between hydrophobic carbon and aqueous water.

Inspired by the tetrapod structures of a breakwater, a highly efficient electrocatalyst for oxygen reduction reaction (ORR) in alkaline solution has been created from low‐cost, commercial melamine foam and ketjenblack. The unique porous architecture greatly facilitates rapid mass transport, while the N‐doped ketjenblack and Fe/Fe3C‐functionalized surface of the framework dramatically enhance the ORR activity.

Die Tetrapodenstruktur eines Wellenbrechers diente als Inspiration für die Synthese eines hocheffizienten Elektrokatalysators der Sauerstoffreduktion (ORR) aus preiswertem kommerziellem Melaminschaum und dem Ruß Ketjenblack. Seine Porosität erleichtert den Stofftransport, und der N‐dotierte Ketjenblack sowie die Fe/Fe3C‐funktionalisierte Gerüstoberfläche verstärken die ORR‐Aktivität drastisch.