Advances in research and development of carbon-based metal-free electrocatalysts (C-MFECs) have provided potential alternatives to precious metal catalysts for various reactions important to renewable energy and environmental remediation. This timely but critical review provides an overview of recent breakthroughs (within the past 5 years or so) on C-MFECs in all aspects, including the design and regulation of intrinsic catalytic active sites, design and synthesis of carbon composite and hybrid carbon catalysts, mechanism understanding, and potential applications in clean energy storage and energy/chemical conversion. Current challenges and future opportunities in the field of metal-free carbon electrocatalysis are also discussed to provide forward-looking opportunities for their potential applications in various catalytic processes of practical significance.

Atomically dispersed metals stabilized by nitrogen elements in carbon skeleton hold great promise as alternatives for Pt-based catalysts towards oxygen reduction reaction in proton exchange membrane fuel cells. However, their widespread commercial applications are limited by complicated synthetic procedures for mass production. Herein, we are proposing a simple, green mechanochemical approach to synthesize zeolitic imidazolate frameworks precursors for the production of atomically dispersed “Fe-N₄” sites in holey carbon nanosheets on a large scale. The thin porous carbon nanosheets (PCNs) with atomically dispersed “Fe-N₄” moieties can be prepared in hectogram scale by directly pyrolysis of salt-sealed Fe-based zeolitic imidazolate framework-8 (Fe-ZIF-8@NaCl) precursors. The PCNs possess large specific surface area, abundant lamellar edges and rich “Fe-N₄” active sites, and show superior catalytic activity towards oxygen reduction reaction in an acid electrolyte. This work provides a promising approach to cost-effective production of atomically dispersed transition metal catalysts on large scale for practical applications.