Dear Colleagues,

The increasing demand for the clean forms of energy has motivated researchers to search for new sustainable energy resources and the corresponding energy conversion and storage devices, such as electrolyzers, fuel cells, and metal–air batteries. Electrolyzer devices can split water to produce hydrogen and oxygen via electrochemical reaction. This oxygen evolution reaction (OER) happens on the anode side. On the other hand, fuel cells convert chemical energy into electricity via a chemical reaction with oxygen and hydrogen to produce water, which is completely harmless. In this case, oxygen gets reduced on the cathode side and hence it is called an oxygen reduction reaction (ORR). In metal–air batteries, the ORR and OER take place on the cathode side and anode side, respectively. These devices could be regarded as the next generation of electrochemical energy storage systems due to their high theoretical energy density. It is thus a critical requirement for catalysts to be bifunctional. It is also important to note that both the OER and ORR are kinetically sluggish, and require extra energy (overpotential) to overcome the kinetic barrier of these reactions, leading to a substantial reduction of the energy efficiency of these devices, thus limiting the commercialization of these energy devices. Hence, developing efficient bifunctional (i.e., oxygen evolution reaction (OER) and oxygen reduction reaction (ORR)) electrocatalysts is vital to the new generation of electrochemical energy storage and conversion devices, including metal–air batteries. Efforts have also to be made to develop of bifunctional catalysts based on both noble and non-noble metals with low cost and high activity and stability. In the pursuit of efficient bifunctional oxygen electrocatalysts, both experimental and theoretical calculations have important roles to play in the rational design and analysis of electrocatalysts as well as their performance, including reaction mechanisms both in alkali and acidic media for the OER/ORR reactions. The utilization of any of the above phenomena in oxygen electrocatalysts is of interest to this Special Issue, and such contributions are invited.

Prof. Dr. Pabitra Choudhury
Guest Editor

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• electrocatalysts
• ORR
• OER
• reaction mechanism
• acidic and alkali media
• overpotential
• stability
• current density
• kinetics
• surface characterization
• catalytic performance