Electrocatalytically Active Hollow Carbon Nanospheres Derived from PS-b-P4VP Micelles

A facile method using polystyrene-b-poly(4-vinyl pyridine) (PS-b-P4VP) micelles is demonstrated to synthesize N/FeN₄-doped hollow carbon nanospheres (N/FeN₄-CHNS) with high electrocatalytic activity for oxygen reduction reactions (ORRs). Uniform spherical micelles with PS core and P4VP shell are prepared by exposing PS-b-P4VP in a mixture of ethanol/tetrahydrofuran. Pyridinic N in shell cooperates with Fe³⁺ to induce an in situ polymerization of pyrrole. Tuning molecular composition of PS-b-P4VP can form hollow carbon spheres with controlled size down to sub-100 nm that remains challenge using traditional hard template strategies. N/FeN₄-CHNS possesses a series of desirable properties as electrode materials, including easy fabrication, high reproducibility, large surface area, and highly accessible porous surface. This electrocatalyst exhibits excellent ORR activity (onset potential of 0.976 V vs reversible hydrogen electrode (RHE) and half-wave potential of 0.852 V vs RHE), higher than that of commercial Pt/C (20 wt%) in an alkaline media, and shows a good activity in an acidic media as well. In addition to its higher stability and methanol tolerance than Pt/C in both alkaline and acidic electrolytes, highly competitive single cell performance is achieved in a proton exchange membrane fuel cell. This work provides a general approach to preparing functionalized small hollow nanospheres based on self-assembly of block copolymers.