Designing NiCoS/CNTs composites for highly efficient bifunctional electrocatalyst in water splitting

Abstract

Electrocatalytic water-splitting holds great promise for the large-scale production of hydrogen as a renewable and environmentally friendly alternative to fossil fuels. However, the exploration of a cost-effective, stable, and active bifunctional electrocatalyst remains a significant challenge in achieving efficient hydrogen (H₂)/oxygen (O₂) production through water electrolysis. Herein, we used nickel-doped cobalt sulfide (NiCoS) supported by carbon nanotubes (CNTs) as a promising candidate for electrocatalytic water splitting. The Ni-Co-based catalyst comprising the redox couples of Ni⁺³/Ni⁺² and Co⁺³/Co⁺² exhibits remarkable efficiency as active sites for both HER as well as OER. The linear sweep voltammetry (LSV) results indicate that the fabricated bifunctional catalyst necessitates overpotentials of just 327 mV for achieving a cathodic current density of 100 mAcm⁻² and 344 mV for the anodic current density of the same value. Additionally, the Tafel slopes for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are 64 mVdec⁻¹ and 70 mVdec⁻¹, respectively. The electrochemical impedance analysis (EIS) was also performed which revealed that NiCoS/CNTs has the lowest charge transfer resistance (R_ct) which is 1.94 Ω as compared to the CoS (7.52 Ω) and NiCoS (4.74Ω). The ECSA value of the prepared NiCoS/CNTs material was observed as 3.47 cm². Such an excellent synergetic effect is due to the interaction of NiCoS with CNTs, which not only provides highly active sites available for faster charge transfer but also increases the electrical conductivity of the fabricated material. This study offers valuable insights into the design of the best electrocatalysts for water splitting.