Synergistic effect of nanocrystalline NiCo2S4 and NiCo alloy embedded in N-doped carbon fibers towards high-performance electrocatalysts for oxygen evolution reaction

Abstract

Developing oxygen evolution reaction (OER) electrocatalysts with high efficiency, low cost and good stability for water splitting is significant to relieve the energy crisis and environmental pollution. Herein, NiCo alloy (NC) nanoparticles (NPs) embedded N-doped carbon fibers (NCF) were prepared by electrospinning and carbonization. The surfaces of the NC@NCF were anchored with nanocrystalline NiCo2S4 (NCS) in a following solvothermal process to form NCS-NC@NCF composite. Synergistic effect of the alloy (NC) and the semiconductor (NCS) was successfully stimulated, i.e., rapid charge separation and transfer was achieved during the OER process. In addition, the carbon fibers substrate is beneficial for good dispersion of the NC and NCS NPs as well as the conductivity improvement of the as-prepared NCS-NC@NCF catalyst. The prepared NCS-NC@NCF catalyst electrode owns good OER performances of a low overpotential of 291 mV, 342 mV and 376 mV to respectively deliver current densities of 10 mA cm−2, 50 mA cm−2 and 100 mA cm−2, which are respectively 19 mV, 82 mV and 116 mV lower than those of the RuO2 electrode (310 mV, 424 mV and 492 mV), indicating the great potential of the catalyst in water splitting. Moreover, good durability of current density retention of 90.7 % is observed after 60 h of continuous OER polarization for the catalyst. Additionally, a two-electrode system composed of commercial Pt/C and the NCS-NC@NCF electrodes only needs a driven voltage of 1.51 V to afford 10 mA cm−2 for water splitting, which is superior to that (1.69 V) of the Pt/C||RuO2 system.