Amorphous Fe nanoclusters embedded inside balloon-like N-doped hollow carbon for efficient electrocatalytic oxygen reduction

Rational designs of electrocatalytic active sites and architectures are of great importance to develop cost-efficient non-noble metal electrocatalysts towards efficient oxygen reduction reaction (ORR) for high-performance energy conversion and storage devices. In this paper, active amorphous Fe-based nanoclusters (Fe NC) are elaborately embedded at the inner surface of balloon-like N-doped hollow carbon (Fe NC/Ch sphere) as an efficient ORR electrocatalyst with an ultrathin wall of about 10 nm. When evaluated for electrochemical performance, Fe NC/Ch sphere exhibits decent ORR activity with a diffusion-limited current density of ~5.0 mA cm-2 and a half-wave potential of ~0.81 V in alkaline solution, which is comparable with commercial Pt/C and superior to Fe nanoparticles (NP) supported on carbon sheet (Fe NP/C sheet) counterpart. The electrochemical analyses combined with electronic structure characterizations reveal that robust Fe-N interactions in amorphous Fe nanoclusters are helpful for the adsorption of surface oxygen-relative species, and the strong support effect of N-doped hollow carbon is benefit for accelerating the interfacial electron transfer, which jointly contributes to improved ORR kinetics for Fe NC/Ch sphere.