Facile synthesis of an Ni/NiO composite with superior bifunctional electrocatalytic activity for water electrolysis over a wide range of pH

Abstract

In this work, we report a new approach for the one-pot synthesis of Ni/NiO composite structures through the reduction of NiCl₂·6H₂O by NaBH₄ in octadecyl amine (ODA) followed by thermal treatment. This Ni/NiO composite served as an effective electrocatalyst with predominantly enhanced HER and OER kinetics by synergistically combining the intrinsic properties of Ni and NiO. Ni/NiO exhibited overpotential values of 363 and 437 mV to produce a current density of 10 mA cm⁻² for the OER and HER, respectively, in an alkaline medium. An electrochemical OER and HER study was also performed in neutral and acidic media, respectively. The synergistic effect between metallic Ni and NiO led to very low charge transfer resistance (R_ct) values of 8.56 Ω and 18.90 Ω for the OER and HER at applied overpotentials of 370 and 500 mV in an alkaline medium, respectively. The turn over frequency (TOF) of the Ni/NiO composite was calculated to be 6.4 × 10⁻² and 14.98 × 10⁻² s⁻¹ for the OER and HER at overpotentials of 350 and 430 mV, respectively. Ni/NiO also showed superior long-term durability in 1 M KOH for both the OER and HER activities. This study offers an effective strategy to design bifunctional electrocatalysts for oxygen and hydrogen production over a wide range of pH.