An efficient self-supported 3D structured catalyst is developed by combining simple electro-deposition and hydrothermal route for hydrogen and oxygen evolution reactions (HER and OER). The as-obtained Ni/Co-S electrodes show exceptional HER performance with excellent durability in both acidic and alkaline solutions, acquiring a hydrogen evolving current density of 10 mA cm(-2) at overpotentials of merely 85 mV and 102 mV in 0.5 M H2SO4 and 1.0 M KOH, respectively. For the OER, the as-designed electrocatalyst can afford an oxygen evolving current density of 10 mA cm(-2) at an overpotential as low as 170 mV in 1.0 M KOH solution. Furthermore, an alkaline water splitting electrolyzer constructed with two pieces of Ni/Co-S electrodes can deliver a full water splitting current density of 10 mA cm(-2) at a voltage of 1.47 V. Moreover, a Faradic efficiency close to 100% is obtained. The as-revealed simple design, easiness to large-scale preparation and superior electrocatalytic performance enable the bifunctional Ni/Co-S act as promising electrode materials for overall water splitting. (C) 2017 Elsevier Ltd. All rights reserved.