Cu dopant triggering remarkable enhancement in activity and durability of Fe-N-C electrocatalysts toward oxygen reduction

Abstract

Doping of a second metal has been becoming a valid strategy to further improve the catalytic performance of Fe-N-C catalysts toward oxygen reduction reaction (ORR). A highly efficient Cu-Fe-N-C electrocatalyst for oxygen reduction has been prepared by pyrolyzing the precursor of Cu(OH) 2 -Fe(OH) 3 @ZIF-8 (ZIF = zeolitic imidazolate framework) followed by acid treatment. The impact of Cu dopant on the Cu-Fe-N-C electrocatalysts have been fully investigated through various techniques, demonstrating that the Cu/Fe molar ratio in the feedstock (CuCl 2 /FeCl 3 ) significantly influences the resultant Cu-Fe-N-C catalysts in terms of the morphologies, carbon texture (e.g. surface area, pore structure) as well as the distribution of different types of doped N atoms, which clearly determine the ORR performance (activity and durability) of the Cu-Fe-N-C catalysts. The best-performance Cu-Fe-N-C-1-900-AT exhibits a higher half-wave potential ( E 1/2 ) of 0.88 V (vs. RHE) (30 mV higher than the commercial Pt/C) in alkaline electrolyte, and a half-wave potential of 0.79 V (vs. RHE) comparable to Pt/C in acidic electrolyte. Moreover, an enhanced durability in both alkaline ( ΔE 1/2 = 5 mV after 10,000 cycles) and acidic media ( ΔE 1/2 = 20 mV after 10,000 cycles) is also observed with Cu-Fe-N-C-1-900-AT compared to Fe-N-C-900 and Cu-N-C-900. The zinc-air battery based on Cu-Fe-N-C-1-900-AT as cathode catalyst exhibits a peak power density of 140 mW cm −2 superior to the reference Pt/C catalyst (74 mW cm −2 ), and an impressive durability with only ca. 4.3% decay in the output voltage for 50 h at 20 mA cm −2 . A bimetal-codoped carbon eletrocatalyst of Cu-Fe-N-C exhibits excellent ORR activity as well as long-term stability in both alkaline and acidic electrolytes. • A Cu-Fe-N-C carbon electrocatalyst is derived from Cu(OH) 2 -Fe(OH) 3 @ZIF-8 precursor. • Cu dopant can tune the electronic and structural characteristics of Fe-N-C catalysts. • Cu doping can enhance the ORR activity and long-term stability of Fe-N-C catalysts.