Carbon-based metal-free electrocatalysts: Recent progress and forward looking

The advances in research and development of carbon-based electrocatalysts have opened up new areas for metal-free electrocatalysis, including but not limited to oxygen reduction reaction (ORR) in fuel cells; triiodide reduction reaction and Co(bpy) 3 3+ reduction in dye-sensitized solar cells; CO 2 reduction reaction for conversion of greenhouse gas to value-added chemicals; N 2 (NO 3 − ) reduction reaction for the synthesis of NH 3 or urea; two-electron transfer ORR for H 2 O 2 generation; oxygen evolution reaction (OER)/hydrogen evolution reaction in electrocatalytic water-splitting processes; ORR/OER for Li/Na/Zn–air batteries; and multi-reactions for integrated energy devices. This perspective provides an overview on the recent progress and future perspective of carbon-based metal-free electrocatalysts for various energy/chemical-related reactions. Current challenges and future opportunities in this rapidly developing field are also discussed. Challenges and opportunities • The catalytic activities of most metal-based catalysts rely on metal element attributes, while carbon-based metal-free electrochemical catalysts (C-MFECs) are generated by introducing various dopants and defects. As such, C-MFECs show promising tunability and synergistic effects for greatly improved electrochemical performance. • Research on mechanistic understanding of the active sites would provide valuable guidelines for the design of future C-MEFCs. In situ and/or operando sophisticated techniques are required to identify the active sites for developing highly efficient C-MFECs. • Insights gained will provide the blueprint for the design and development of more advanced C-MFECs that should effectively compete with metal-based catalysts in developing green-energy-related technologies for practical applications in the future. The advances in research and development of carbon-based electrocatalysts have opened up new areas for metal-free electrocatalysis. This article provides an overview on the recent progress and future perspective of carbon-based metal-free electrocatalysts for various energy/chemical-related reactions. Current challenges and future opportunities in this rapidly developing field are also discussed.