The design and fabrication of catalysts with low-cost and high electrocatalytic activity for the oxygen evolution reaction (OER) have remained challenging because of the sluggish kinetics of this reaction. The key to the pursuit of efficient electrocatalysts is to design them with high surface area and more active sites. In this work, we have successfully synthesized a highly stable and active NiCo2S4 nanowire array on a Ni-foam substrate (NiCo2S4 NW/NF) via a two-step hydrothermal synthesis approach. This NiCo2S4 NW/NF exhibits overpotential as low as 275 mV, delivering a current density of 20 mA cm-2 (versus reversible hydrogen electrode) with a low Tafel slope of 89 mV dec-1 and superior long-term stability for 20 h in 1M KOH electrolyte. The outstanding performance is ascribed to the inherent activity of the binder-free deposited, vertically aligned nanowire structure, which provides a large number of electrochemically active surface sites, accelerating electron transfer, and simultaneously enhancing the diffusion of electrolyte.

Abstract
1. Introduction
2. Experimental
    2.1 Synthesis of Nickel cobalt oxide (NiCo2O4/NF)
    2.2 Synthesis of Nickel cobalt sulfide (NiCo2S4 NW/NF)
    2.3 Structural characterization
    2.4 Electrochemical measurements
3. Results and discussion
    3.1 Morphological and structural study
    3.2 Electrochemical activity towards OER
4. Conclusion
References

• Komal Patil(Optoelectronic Convergence Research Center, Department of Materials Science and Engineering, Chonnam National University)
• Pravin Babar(Optoelectronic Convergence Research Center, Department of Materials Science and Engineering, Chonnam National University)
• Jin Hyeok Kim(Optoelectronic Convergence Research Center, Department of Materials Science and Engineering, Chonnam National University) Corresponding author