NiSe nanoparticles are electrodeposited over a forest of carbon nanotubes (CNTs) to form an intertwined and porous network. The assynthesized composite (denoted as CNT@NiSe/SS) is used as a free-standing and multifunctional electrode for both supercapacitors and overall water splitting applications. For a supercapacitor application, CNT@NiSe/SS exhibits higher specific capacity and improved rate capability compared with individual NiSe and CNTs. A hybrid supercapacitor device consisting of battery-like CNT@NiSe/SS and EDLC-like graphene delivers a maximum energy density of 32.1 Wh kg(-1) at a power density of 823 W kg(-1) and has excellent stability after a floating test of 50 h. On the other hand, CNT@NiSe/SS also serves as a bifunctional electrocatalyst with high activity for overall water splitting. The CNT@NiSe/SS electrode displays excellent hydrogen and oxygen evolution reaction performance with the lowest overpotential of 174 mV at 10 mA cm(-2) and 267 mV at 50 mA cm(-2), respectively. The symmetrical two-electrode system requires an operating potential of 1.71 V to achieve a current density of 10 mA cm(-2). Furthermore, this electrolyzer shows a negligible increment in potential after 24 h of continuous water splitting. The outstanding performances of CNT@NiSe/SS can be attributed to the synergistic effect of NiSe and CNTs. (C) 2020 Elsevier Inc. All rights reserved.