Highly Efficient Fe-N-C Electrocatalyst for Oxygen Reduction Derived from Core-Shell-Structured Fe(OH)3@Zeolitic Imidazolate Framework

Fe-N-C electrocatalysts represent one of the most promising oxygen reduction catalysts to replace the expensive platinum (Pt)-based catalysts in fuel cells. Herein, we report a highly efficient zeolitic imidazolate framework (ZIF)-derived Fe-N-C electrocatalyst for the oxygen reduction reaction (ORR) in both alkaline and acidic solutions, which involves the formation of a core-shell-structured Fe(OH)(3)@ZIF-8. The encapsulated Fe(OH)(3) in ZIF-8 gradually evolves into iron oxide with the increasing temperature during the carbonization, which plays several roles including creating Fe-N-x active sites, retaining morphology as a rigid template as well as tuning the carbon microstructure. The best-performing C-Fe(OH)(3)@ZIF-1000 catalyst features a hollow polyhedron (interior cavity: ca. 48 nm) with a thin carbon shell (ca. 5 nm), exhibiting a high Brunauer-Emmet-Teller (BET) surface area of 1021 m(2) g(-1). In alkaline solution, the ORR activity of C-Fe(OH)(3)@ZIF-1000 surpasses the benchmark Pt/C catalyst, with the onset potential (E-onset) of 0.99 V (vs RHE) and the half-wave potential (E-1/2) of 0.88 V (vs RHE). In acidic solution, the difference in E-1/2 between C-Fe(OH)(3)@ZIF-1000 and Pt/C is 60 mV (0.80 vs 0.86 V), ranking it among the best Fe-N-C electrocatalysts in acidic media. The H2O2 proton exchange membrane fuel cell (PEMFC) with C-Fe(OH)(3)@ ZIF-1000 as the cathode catalyst delivers a maximum power density of 411 mW cm(2) at 0.35 V.