Neutral Red: The Synthetic Phenazine Full of Electrochemical Surprises

Neutral red (NR) is a synthetic phenazine that continues to generate significant interest because of its widespread applications. Its ability to form a conducting polymer and participate as a redox mediator has brought about an unprecedented upsurge of research publications internationally. The recent discovery that it can also enhance coal seam methane production for meeting energy scarcity represents yet another unexpected application. Despite this, no recent attempt to summarize the experimental findings relating to this compound has been made. As such, this review aims to discuss the current state of knowledge on the electrochemical properties of NR, its structure and synthesis, proposed mechanisms of NR-mediated electron shuttle, and application of solvated and crystalline NR. Moreover, the environmental implications of its wide-scale usage are also addressed.