Water splitting associated with the conversion and storage of renewable energy is considered to be the most significant strategy to create hydrogen. Herein, an efficient self-supported electrode was developed by in-situ growth of interlayer expanded lamellar cobalt diselenide (CoSe2) nanosheets (NS) on carbon paper (CP) substrate (CoSe2 NS@ CP). The analyses of TEM, SEM and XRD confirmed that the CP is homogeneously coated by few stacking layers of interlayer expanded lamellar structured CoSe2. This rationally designed nanostructure can provide more active sites for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The bifunctional electrode exhibits high electrocatalytic performance with -128 mV vs. RHE onset potential for the HER in 0.5 mol dm (3) H2SO4 and + 1521 mV vs. RHE for the OER in 1.0 mol dm (3) KOH. Besides, small electrolysis potentials of -201.1 mV vs. RHE and + 1636 mV vs. RHE are needed to drive the HER and OER at current density of 100 mA cm (2). Finally, a small overall cell voltage (ca. + 1.75 V) was used to drive the water splitting reaction in 1.0 mol dm (3) KOH. The CoSe2 NS@ CP electrode showed both excellent catalytic activity with overall current density of 100 mA cm (2) at 2.13 V and tremendous durability with negligible decrease in potential at a constant current of 20 mA cm (2) for more than 30 hours. Thus this rationally designed electrode material can be readily applied for large-scale water splitting process. (C) 2017 Elsevier Ltd. All rights reserved.