An ideal electrocatalyst for the hydrogen evolution reaction of water splitting requires substantial active sites with high catalytic activity, fast electron and mass transfer, low gas adsorption energy, and high stability. However, a single component catalyst usually has only one of the many properties of an ideal electrocatalyst. Herein, for the first time, we synthesize CoxSe/MoSe2 micro-prisms on foam via a hydrothermal and selenization strategy. After selenization, a crystallized CoMoO4 smooth prismatic structure can be converted into a CoxSe/MoSe2 prismatic structure with lamellar morphology. Such synergistic effects lead to CoxSe/MoSe2 superior electrochemical catalytic activity with a 109 mV over-potential at 10 mA cm(-2) and 204 mV over-potential at 100 mA cm(-2), an appropriate Tafel slope of 90 mV dec(-1), and remarkable long-term stability during 20 h of testing for the hydrogen evolution reaction in an alkaline medium. Density-functional calculations reveal the absorption energy of water and Gibbs free-energy of intermediate adsorb hydrogen of CoxSe/MoSe2 is more favorable for hydrogen evolution reaction than single component catalyst. Both experimental and theoretical calculation results reveal that synergistic effect can efficiently reduce energy barrier of both the initial water adsorption step and subsequent H-2 generation on binary catalysts, and improve catalytic activity. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.