The present study is about the fabrication of an efficient photo-/electrocatalyst, prepared via in-situ hydrothermal coupling of ZnO with g-C3N4. The results prove this electrocatalyst as suitable band structure semiconductor. The crystalline nature and related morphological parameters are controlled by optimized hydrothermal and calcination temperatures conditions. A series of physicochemical characterization are applied to inquire the crystalline structure, surface morphology, optical capabilities and charge transportation properties. Results revealed that the sample acts as excellent electrocatalyst with OER current density at 10 mAcm(-2) @ 335 mV and the HER at 100 mAcm(-2) @ -225 mV. While upon illuminations its catalytic properties further enhance at OER 10 mAcm(-2) @ 326 mV and for HER current density of 100 mAcm(-2) @ 167 mV. It can be seen from the present study that g-C3N4 play gigantic role in enhancing the catalytic property of ZnO and hence it leads to a relationship between hierarchical features and photo-/electrochemical activity for water splitting. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.