ZIF-8/ZIF-67-Derived Co-N-x-Embedded 1D Porous Carbon Nanofibers with Graphitic Carbon-Encased Co Nanoparticles as an Efficient Bifunctional Electrocatalyst

Herein, an approach is reported for fabrication of Co-N-x-embedded 1D porous carbon nanofibers (CNFs) with graphitic carbon-encased Co nanoparticles originated from metal-organic frameworks (MOFs), which is further explored as a bifunctional electrocatalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Electrochemical results reveal that the electrocatalyst prepared by pyrolysis at 1000 degrees C (CoNC-CNF-1000) exhibits excellent catalytic activity toward ORR that favors the four-electron ORR process and outstanding long-term stability with 86% current retention after 40 000 s. Meanwhile, it also shows superior electrocatalytic activity toward OER, reaching a lower potential of 1.68 V at 10 mA cm(-2) and a potential gap of 0.88 V between the OER potential (at 10 mA cm(-2)) and the ORR half-wave potential. The ORR and OER performance of CoNC-CNF-1000 have outperformed commercial Pt/C and most nonprecious-metal catalysts reported to date. The remarkable ORR and OER catalytic performance can be mainly attributable to the unique 1D structure, such as higher graphitization degree beneficial for electronic mobility, hierarchical porosity facilitating the mass transport, and highly dispersed CoNxC active sites functionalized carbon framework. This strategy will shed light on the development of other MOF-based carbon nanofibers for energy storage and electrochemical devices.