New applications and emerging markets in electromobility and large-scale stationary energy storage require the development of new electrochemical systems with higher energy density than current batteries. Rechargeable metal–air batteries, mainly lithium–air and zinc–air systems, are considered one of the most promising candidates. In contrast to lithium, zinc is abundant, inexpensive and its electrodeposition in aqueous electrolytes is relatively easy. Unfortunately, achieving a rechargeable zinc–air battery is still hindered by various technical problems related to the reversibility and lifetime of the electrodes. The most widely used electrolyte in zinc–air batteries has been the classical aqueous alkaline. In this context and with the main objective of providing a complete overview, we studied a wide number of articles starting from the beginning of the development of secondary zinc–air batteries (1970–1980s) to more recent works, with the aim of compiling all available information. It is essential to revise older papers to find relevant information that may get otherwise forgotten and not taken into account to develop new solutions. This information could also be applied in other storage systems based on zinc as nickel–zinc, zinc hybrid or zinc-ion. Copyright © 2016 John Wiley & Sons, Ltd.

Emerging energy storage systems based on abundant and cost-effective materials are key to overcome the global energy and climate crisis of the 21st century.

An efficient, durable and low cost air cathode with low polarization between the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is essential for a high performance and durable secondary zinc-air battery. Different valence states and morphologies of MnxOy catalysts were synthetized via thermal treatment of EMD (generating Mn2O3 and Mn3O4) and acid digestion of synthetized Mn2O3 (producing α-MnO2) in order to develop an efficient Bifunctional Air Electrode (BAE). Change in the ratio H+ to Mn2O3 during the acid digestion affects the sample microporosity, the crystallographic plane distribution, as well as the physical and chemical adsorbed water which was related to defects, i.e. cation vacancies (Mn4+) and Mn3+. These characteristics were discussed and linked to the electrocatalytic activity. The best ORR performing catalyst was that with the higher surface water content (associated to material BET surface area) and a (310) surface as the 2nd more contributing plane (after 211). On the other hand, the catalyst with the higher structural water and with (110) and (200) crystallographic planes being the most intensity contributors (after 211) was the most OER active material. In this work, it was able to find a relationship between catalyst structure and air-efficiency through a volcano-like relationship between air-efficiency and surface water content. Air-efficiency (also take as round-efficiency discharge/charge in battery context) can be taken as a good descriptor of potentially good materials for Zn-Air secondary batteries technology. In this term, we were able to prepare a Bifunctional Air Electrode based on the selected α-MnO2 sample which demonstrated a round-efficiency of 53%, a ΔV around 1V and a neglected loss of the charge potential (about 2.1V) over the entire lifecycle test (more 200 cycles over 30hours) with a capacity retention superior to 95%

Aqueous zinc–air batteries (ZABs) are a low‐cost, safe, and sustainable technology for stationary energy storage. ZABs with pH‐buffered near‐neutral electrolytes have the potential for longer lifetime compared to traditional alkaline ZABs due to the slower absorption of carbonates at nonalkaline pH values. However, existing near‐neutral electrolytes often contain halide salts, which are corrosive and threaten the precipitation of ZnO as the dominant discharge product. This paper presents a method for designing halide‐free aqueous ZAB electrolytes using thermodynamic descriptors to computationally screen components. The dynamic performance of a ZAB with one possible halide‐free aqueous electrolyte based on organic salts is simulated using an advanced method of continuum modeling, and the results are validated by experiments. X‐ray diffraction, scanning electron microscopy, and energy dispersive X‐ray spectroscopy measurements of Zn electrodes show that ZnO is the dominant discharge product, and operando pH measurements confirm the stability of the electrolyte pH during cell cycling. Long‐term full cell cycling tests are performed, and rotating ring disk electrode measurements elucidate the mechanism of oxygen reduction reaction and oxygen evolution reaction. The analysis shows that aqueous electrolytes containing organic salts could be a promising field of research for zinc‐based batteries, due to their Zn²⁺ chelating and pH buffering properties. The remaining challenges including the electrochemical stability of the electrolyte components are discussed.