Calcination of Porphyrin-Based Conjugated Microporous Polymers Nanotubes As Nanoporous N-Rich Metal-Free Electrocatalysts for Efficient Oxygen Reduction Reaction

The development of non-noble metal electrocatalysts with high-performance and low cost are promising to replace expensive Pt or Pt-based alloy electrocatalysts for the oxygen reduction reaction (ORR). Herein, we demonstrate the fabrication of N-rich metal-free electrocatalysts based on hard carbon nanotubes derived from carbonization of nanotube-like porphyrin-based conjugated microporous polymers (denoted as TPP-CMP) for ORR. Taking advantage of their high specific surface, excellent porosity, and importantly, exposed N–C active site originating from the N-doping carbon nanotubes with unique hollow cylindrical geometry, the as-synthesized TPP-CMP exhibits excellent catalytic activity for ORR in alkaline medium. It shows a half-wave potential of 0.83 V, an onset potential of 0.95 V (vs RHE), a high diffusion limiting current density of 4.6 mA cm–2, which is comparable to the commercial Pt/C catalyst. More importantly, the TPP-CMP manifests higher methanol immunity and long-term stability than that of commercial Pt/C (20 wt %) catalyst for ORR in an alkaline medium. Furthermore, TPP-CMP exhibits a favorable a 4-electron reduction of oxygen (n ≈ 3.95) and lower H2O2 yield. These results make the TPP-CMP promising candidate as efficient electrocatalysts for ORR. In view of the designable flexibility and synthetic diversity of porous organic polymers (POPs), the findings obtained from this study may also open new possibilities for the future tailored design of POPs for creation of high-performance, metal-free ORR electrocatalyst only by a simple calcination process.