Tuning the microenvironment of bioinspired Fe-Cu molecular electrocatalysts for efficient oxygen reduction reaction...

Dual-atom catalysts (DACs) with synergistic bimetallic sites are emerging as promising alternatives to the platinum group metal catalysts for the cathodic oxygen reduction reaction (ORR) in advanced energy conversion technologies. However, the rational design of DACs is challenged by the site heterogeneity and structural damage from prevalent pyrolysis methods, while the synthesis process of binuclear complexes with well-defined structures is cumbersome, making them rarely applied in practical devices. Bioinspired by the binuclear heme/Cu center in cytochrome c oxidase, herein we developed a facile stepwise assembly strategy to prepare Fe-Cu binuclear molecular catalysts via coordinating bipyridine (bpy)-derivative-functionalized copper complexes with nitrogen atoms of N-doped carbon substrates, followed by iron phthalocyanine (FePc) incorporation. The microenvironment of the Fe-Cu binuclear molecular catalysts was readily tuned by varying substitutes on bpy (2,2'-bpy-4,4'-R, R = H, Cl, CH₃, COOH), among which the carboxylic acid-functionalized FePc@Cu(bpy^COOH)-NC demonstrated impressive high ORR activity and stability with a half-wave potential (E _1/2) of 0.92 V vs. RHE in 0.1 M KOH and a maximum power density (P _max) of 147 mW cm^-2 in loaded zinc-air batteries, surpassing those of commercial Pt/C (E _1/2 = 0.87 V, P _max = 120 mW cm^-2) under similar experimental conditions. Theoretical calculations suggested that functionalizing the Cu sites with carboxylic acid groups could significantly reduce the overpotential, thus of boosting the intrinsic ORR activity, which could be attributed to the electronic structure modulation of Fe-N₄ sites and the hydrogen-bonding network formation. This work highlights the advantage of bioinspired catalyst design and assembly engineering in advancing the precise construction of DACs for energy conversion applications.