A KCl-assisted pyrolysis strategy to fabricate nitrogen-doped carbon nanotube hollow polyhedra for efficient bifunctional oxygen electrocatalysts

Abstract

The fabrication of stable and low-cost bifunctional electrocatalysts with high activities for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is of vital importance and challenge for regenerative fuel cells and metal–air batteries. Here, we firstly report a simple KCl-assisted pyrolysis strategy to construct hybrid architectures with Co nanoparticles embedded in N-doped carbon nanotube hollow polyhedra (NCNHP) by using ZIF-67 as the precursor. The presence of KCl accelerates the decomposition of ZIF-67 and promotes the in situ formation of carbon nanotubes (CNTs) during the pyrolysis at temperatures as low as 400 °C. The optimal NCNHP-1-500 with a CNT-assembled hierarchical architecture and abundant Co–N_x active sites exhibits excellent OER activity when benchmarked with commercial IrO₂, achieving a needed overpotential of only 310 mV to reach the current density of 10 mA cm⁻². NCNHP-1-500 also displays satisfactory ORR activity with a half-wave potential of 0.828 V vs. RHE that is comparable to that of commercial Pt/C (20 wt% Pt), and superior methanol tolerance and stability to Pt/C. The KCl-assisted pyrolysis strategy might bring new opportunities to fabricate novel hybrid architectures for highly efficient bifunctional OER and ORR electrocatalysts.