Recent developments in manganese oxide based nanomaterials with oxygen reduction reaction functionalities for energy conversion and storage applications: A review

Abstract In this article, a brief overview of manganese oxide nanomaterials (NMs) potential towards oxygen reduction reaction (ORR) for microbial fuel cell (MFC), bioremediations, and battery applications is discussed. It's known that using non-renewable fossil fuels as a direct energy source causes greenhouse gas emissions. Safe, sustainable and renewable energy sources for biofuel cell (BFC) and metal-air batteries hold considerable potential for clean electrical energy generators without the need for a thermal cycle. In an electrochemical reaction system, the four-electron reduction from molecular oxygen at the air-cathode surface to hydroxide ion or water at a reasonably low overpotential was the ultimate goal of many investigations and plays a vital role in metal-air batteries and fuel cell device systems. Different MnxOy nanostructured materials, from Biofunctional structural catalysts up to their electrocatalytic contributions towards ORR are discussed. Brief descriptions of ORR, principle strategy and mechanism, as well as recent developments of cationic dopants and electrolytic media, effect on the air-cathode surface of manganese oxide nanocatalyst are also discussed. Finally, challenges associated with platinum and carbon support platinum in improving electron and charge transfer between biocatalyst and air-cathode electrode are summarized.