Oxygen reduction reaction electrocatalysis in neutral media for bioelectrochemical systems

The oxygen reduction reaction (ORR) is an electrochemical process of the utmost importance in energy conversion and storage, corrosion and chemical technologies. The ORR plays a major role in biological processes (such as respiratory biochemical chain reactions) and is being incorporated into numerous bioelectrochemical devices and systems, such as microbial and enzymatic fuel cells, microbiosynthesis processes, water desalination and purification technologies and biosensing. Researchers from various backgrounds have come together to address the specifics of the ORR in close-to-neutral environments in light of their possible integration with bioprocesses. Understanding the ORR mechanism in this pH region is complex, as it involves biotic (living systems or components derived thereof) and abiotic (often inorganic materials or composite) catalysts. This review offers a summary of catalyst-class-dependent ORR mechanisms and pathways with the corresponding limitations relevant to their practical use in bioelectrocatalytic systems. We also analyse the technological challenges often caused by the use of oxygen depolarization as the main driving force in practical applications.