Ten years of carbon-based metal-free electrocatalysts

Since the discovery of the first carbon-based metal-free electrocatalysts (C-MFECs, i.e., N-doped carbon nanotubes) for the oxygen reduction reaction in 2009, the field of C-MFECs has grown enormously over the last 10 years. C-MFECs, as alternatives to nonprecious transition metals and/or precious noble metal-based electrocatalysts, have been consistently demonstrated as efficient catalysts for oxygen reduction, oxygen evolution, hydrogen evolution, carbon dioxide reduction, nitrogen reduction, and many other (electro-) chemical reactions. Recent research and development of C-MFECs have indicated their potential applications in fuel cells, metal-air batteries, and hydrogen generation through water oxidation as well as electrochemical production of various commodity chemicals, such as ammonia, alcohols, hydrogen peroxide, and other useful hydrocarbons. Further research and development of C-MFECs would surely revolutionize traditional energy conversion and storage technologies with minimal environmental impact. In this short review article, we summarize the journey of C-MFECs over the past 10 years with an emphasis on materials development and their structure-property characterization for applications in fuel cells and metal-air batteries. Current challenges and future prospects of this emerging field are also discussed.