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

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 degrees 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.