Facile approach for synthesis of doped carbon electrocatalyst from cellulose nanofibrils toward high-performance metal-free oxygen reduction and hydrogen evolution

Multi-element doped metal-free carbon nanomaterials with a 3D architecture were prepared from inexpensive and naturally abundant cellulose nanofibrils. Compared to the most graphene-based carbons reported in the literature that show only good oxygen reduction reaction (ORR) activity, our N,S-doped carbon nanofiber network coated with N,P-doped carbon nanoparticles showed good bifunctionality toward ORR and hydrogen evolution reaction (HER) activities. The HER performance with doped carbon material exhibited an onset potential of 233 mV (vs. RHE), a current density of 10 mA cm(-2) at 331 mV (vs. RHE), and Tafel slope of 99 mV decade(-1). The same material was also used for ORR, which could deliver an onset potential 10 mV more negative than commercial Pt/C and a cathodic peak of 0.84 V (vs. RHE). These values are better than most reported metal-free electrocatalysts. The superior performance of carbon hybrid may be attributed to the combination of a more exposed highly active N,P-doped carbon, a good integration of N,P-doped carbon with N,S-doped carbon nanofibers, and an accelerated electron transport through N,S-doped carbon nanofibers as good conductivity channels.