The development of inexpensive cocatalysts based on earth-abundant-elements, is highly demanding strategy to produce large-scale photocatalytic H-2 for real-life applications. Herein, we report the utilization of CoSe as a highly efficient cocatalyst to significantly improve the photocatalytic H-2 production on ZnSe/CdS under visible irradiation. The maximum H-2 production rate of 785 mu mol h(-1) was attained under optimized conditions. Furthermore, the current system showed robust stability up to 30 h of irradiation and more than 23 mmol of H-2 was produced. The highest apparent quantum yield of the system was 55.3% at monochromatic 420 nm light. Photocurrent responses, UV-vis diffuse reflectance absorption spectroscopy, electrochemical impedance spectroscopy and photoluminescence (PL) spectroscopy were used to explain the mechanistic roles of CoSe and ZnSe in current photocatalytic system. This work showcased the successful usage of CoSe as cocatalyst and ZnSe as visible light active semiconductor for inexpensive conversion of solar energy to H-2. (C) 2020 Elsevier Inc. All rights reserved.