Enhancing the activity and stability of Fe/Co-based nitrogen-doped carbon with richer nitrogen and metal-N active sites towards oxygen reduction reactions

Abstract

Transition metal and nitrogen co-doped carbon (M–N–C) materials possess a broad spectrum of applications in electrocatalysis, particularly in oxygen reduction reactions (ORRs). However, enhancing their stability and further improving their activity continue to be challenging. Herein, based on nitrogen enrichment and coordination effects with Fe/Co of polydopamine (PDA), an efficient and straightforward method was applied to induce dopamine (DA) under alkali-free conditions to generate a PDA shell on a Fe/Co-based zeolitic imidazolate framework (ZIF) surface, and subsequent one-step pyrolysis yielded Fe/Co-based nitrogen-doped carbon with richer nitrogen and metal-N active sites (denoted as Fe/Co-NC RN x, x is the mass ratio of dopamine and Fe/Co-ZIF). Excitingly, the nitrogen content (11.23%) and metal-N active sites content (32.05%) of the resulting material Fe/Co-NC RN III (III refers to 30%, the mass ratio of dopamine and Fe/Co-ZIF) exceeded that of the material Fe/Co-NC without PDA coating (10.11%, 26.36%). The metal-N active site density (SD) of Fe/Co NC RN III was calculated to be 32.51 μmol g⁻¹, which was nearly twice that of Fe/Co-NC (16.48 μmol g⁻¹). Fe/Co-NC RN III achieved a half-wave potential (E_1/2) of 0.90 V in alkaline electrolytes, significantly surpassing that of Pt/C catalysts. Moreover, it retained 91% of its current after 30 000 s of chronoamperometric response (i–t) testing, with a mere reduction of 16 mV in E_1/2 after ten thousand cyclic voltammetry (CV) cycles. In addition to richer nitrogen and metal-N active sites, the excellent ORR activity and outstanding stability can be related to its unique hollow core–shell structure and hierarchical porous structure. The results indicated that this strategy can successfully boost the performance of Fe/Co-based nitrogen-doped carbon with richer nitrogen and metal N active sites, providing a convenient and feasible idea for developing high-activity, long-life M–N–C catalysts.