Hierarchically porous Fe,N-doped carbon nanorods derived from 1D Fe-doped MOFs as highly efficient oxygen reduction electrocatalysts in both alkaline and acidic media

Abstract

Rationally designing low-cost yet highly efficient electrocatalysts for the oxygen reduction reaction (ORR) in both alkaline and acidic media remains highly challenging. Herein, we report the facile synthesis of Fe,N-doped carbon nanorods (denoted as Fe–N/C-NR) with abundant hierarchical pores and highly active sites by the pyrolysis of a one-dimensional (1D) Fe-doped zeolitic imidazolate framework (Fe–ZIF-8) as a self-sacrificing template. The unique 1D nanoarchitecture of the resultant Fe–N/C-NR can provide fast electron and electrolyte transport towards exposed active sites, and their hierarchically porous structures with large surface areas can efficiently facilitate mass diffusion and increase the density of exposed active sites. Furthermore, it is demonstrated that the coexistence of highly dispersed Fe–N_x sites and Fe₃C/Fe nanoparticles (NPs) in these electrocatalysts can provide a large number of desired catalytic centers with highly intrinsic activity and structural stability. As a result, the optimized 5Fe–N/C-NR exhibits excellent catalytic activity for the ORR, with a high half-wave potential (E_1/2) of 0.90 V vs. RHE in alkaline medium, superior to that of commercial Pt/C (0.86 V vs. RHE), and also a high E_1/2 of 0.81 V vs. RHE in acidic medium, comparable to that of commercial Pt/C (0.81 V vs. RHE). Moreover, its robust ORR durability can far surpass that of commercial Pt/C in both acidic and alkaline media, further highlighting the merit of this MOF-templated strategy. Our findings might shed light on the rational design of cost-effective and highly efficient ORR electrocatalysts for practical applications.