Synthesis and inverse hierarchy effect of NiCo2O4@CoS2 and CoS2@NiCo2O4 nanostructures for electrocatalytic overall water splitting

The various non-precious metal oxides and their hierarchical nanostructures have been synthesized and studied for water-splitting applications. However, the investigation of the inverse hierarchical growth of these nanostructures one over the other and their electrochemical properties is needed to be explored to design the electrocatalyst exhibiting high performance. Herein, we have synthesized CoS2@NiCo2O4 and NiCo2O4@CoS2 and investigated the effect of nanostructures growth in inverse order on their electrocatalytic performance for overall water splitting. The synthesis and inversion of hierarchy is confirmed through XRD, SEM, EDX, TEM and Raman spectroscopy. The interaction of water with the nanostructures is studied through contact angle analysis. The CoS2@NiCo2O4 nanostructure hierarchy exhibited lower overpotential and charge transfer resistance than NiCo2O4@CoS2, while the latter experiences better stability for hydrogen evolution reaction (HER) and a relatively larger electrochemically active surface area (ECSA). This manuscript provides insight to understand how the hierarchy of different components in a composite could be utilized to improve material performance while keeping the same chemical composition.