Facile Synthesis of Ni/NiO Composite with Superior Bifunctional Electrocatalytic Activity for Water Electrolysis Under Wide Range of pH

Abstract

Developing potentially viable cost-reductant, highly-efficient, and sustainable bifunctional electrocatalysts with promising activity toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is great significance for water splitting in alkaline media (1M KOH). This work reports a new approach for one-pot synthesis of Ni/NiO composite structure through reduction of NiCl2.6H2O by NaBH4 in octadecyl amine (ODA) followed by thermal treatment. This Ni/NiO composite features as synergistically worthy electrocatalyst that exhibit predominantly enhanced HER and OER kinetics via combining the intrinsic properties of existing components. Ni/NiO exhibited overpotential values of 363 and 437 mV to produce a current density of 10 mA cm-2 for OER and HER, at alkaline medium respectively. The electrochemical OER and HER study also performed in neutral and acidic medium, respectively. The synergistic effect between metallic Ni and NiO leads to a very low charge transfer resistance (Rct) of 8.56 Ω and 18.90 Ω for OER and HER at an applied overpotential of 370 and 500 mV in alkaline medium, respectively. The turn over frequency (TOF) of Ni/NiO composite was calculated to be 6.4×10-2 and 14.98×10-2 s-1 for OER and HER at 350 and 430 mV overpotential, respectively. Ni/NiO also showed superior long-term durability in 1M KOH for both OER and HER activities. The present finding offers an effective strategy to design the bifunctional electrocatalysts for oxygen and hydrogen production under wide range of pH.