N and S Co-doped Carbon Nanofibers with Embedded Candle Soot and Designed Surface Decoration for Efficient Bifunctional Electrocatalysts

Abstract Bifunctional electrocatalysts with high activity, low cost, and excellent durability toward oxygen reduction reactions (ORR) and oxygen evolution reactions (OER) are recognized as promising strategy to cope with the problem of energy crisis. In this work, the electrocatalysts based on N and S co-doped carbon nanofibers with embedded candle soot and designed surface decoration of NiCo and NiCo2S4 nanoparticles (NiCo/NiCo2S4@CNS-800) were fabricated by electrospinning technology and subsequent pyrolysis processes. The obtained NiCo/NiCo2S4@CNS-800 exhibited a positive half-wave potential of 0.80 V and a small Tafel slope of 60 mV dec−1 for ORR. Moreover, it also delivered a low potential of 1.60 V at the current density of 10 mA cm−2 and a small Tafel slope of 85 mV dec−1 for OER. The low potential deviation (△E) of 0.8 V between the half-wave potential for ORR and the potential at the current density of 10 mA cm−2 for OER revealed the outstanding bifunctional electrocatalytic activities of NiCo/NiCo2S4@CNS-800. The superior behaviors of NiCo/NiCo2S4@CNS-800 could be mainly attributed to the synergistic effects of the embedded candle soot, decorated NiCo and NiCo2S4 nanoparticles, continuous fibrous networks and incorporated N and S dopants, which could prevent the aggregation of decorated nanoparticles, increase the active sites, enhance the mass transfer and promote the surface adsorption, respectively. This work will provide a new perspective to design and fabricate the high-performance and low-cost bifunctional electrocatalysts for further promising applications.