We have prepared a graphitic carbon nitride (g-C 3 N 4 ) composite with MoO 3decorated Co 3 O 4 nanorods (Co 3 O 4 /MoO 3 /g-C 3 N 4 ) via the hydrothermal approach, and this hybrid material acts as a highly active and durable electrocatalyst for water splitting reactions. This material could fundamentally influence the catalytic processes and performance of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The OER and HER activities of Co 3 O 4 -/MoO 3 -based nanorods are enhanced by blending with conducting support, for example, graphitic carbon nitrides (g-C 3 N 4 ). The X-ray diffraction pattern and the attenuated total reflectance-Fourier transform infrared data revealed that the as-synthesized nanorods are highly crystalline in nature and are attached to the g-C 3 N 4 support. Transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy studies also affirm the successful heterointerface formation between Co 3 O 4 /MoO 3 nanorods and g-C 3 N 4 . This Co 3 O 4 /MoO 3 /g-C 3 N 4 rodshaped catalyst is highly stable in comparison to its individual constituent and generates a current density of 10 mA cm −2 at a low overpotential of 206 mV for OER and 125 mV for HER in alkaline and acidic media, respectively. This work could pave the way for developing Co 3 O 4 /MoO 3 /g-C 3 N 4 composite materials as electrocatalysts for overall water splitting reactions. KEYWORDS: Co 3 O 4 /MoO 3 /g-C 3 N 4 , decorated, nanorods, composite, water splitting, OER, HER

Transition-metal sulfide-based composite nanomaterials have garnered extensive interest not only for their unique morphological architectures but also for exploring as a noble-metal-free cost-effective, durable, and highly stable catalyst for electrochemical water splitting. In this work, we synthesized in situ nonstoichiometric Zn0 .76 Co0 .24 S with NiCo 2 S 4 binary composite flowers (Zn 0.76 Co 0.24 S/NiCo 2 S 4 ) in one step by thermal decomposition of Zn 2 [PDTC] 4 and Ni[PDTC] 2 complexes by a solvothermal process in a nonaqueous medium from their molecular precursor, and their potential application in electrochemical oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) was investigated. Field-emission scanning electron microscopy and transmission electron microscopy analyses revealed the flower-shaped morphology of as-synthesized Zn 0.76 Co 0.24 S/NiCo 2 S 4 . Again, the structural and chemical compositions were confirmed through powder X-ray diffraction and X-ray photoelectron spectroscopy studies, respectively. The as-obtained 3D flower-type Zn 0.76 Co 0.24 S/NiCo 2 S 4 nanostructure was further subject to electrochemical OER and HER in alkaline and acidic media, respectively. Zn 0.76 Co 0.24 S/NiCo 2 S 4 showed low overpotential values of 248 mV (Tafel slope, 85 mV dec −1 ) and 141 mV (Tafel slope, 79 mV dec −1 ) for OER and HER activities, respectively, due to the synergistic effects of Zn 0.76 Co 0.24 S and NiCo 2 S 4 . Several long-term stability tests also affirmed that the Zn 0.76 Co 0.24 S/NiCo 2 S 4 composite nanostructure is a highly stable and efficient electrocatalyst toward OER and HER activities as compared to the recently reported superior bifunctional electrocatalysts as well as state-of-the-art materials.

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