A Freestanding Single‐Wall Carbon Nanotube Film Decorated with N‐Doped Carbon‐Encapsulated Ni Nanoparticles as a Bifunctional Electrocatalyst for Overall Water Splitting

Noble‐metal free, cost‐effective, and highly stable catalysts with efficient activity for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) have attracted tremendous research interest in recent years. Here, a flexible, self‐standing hybrid film comprising a N‐doped single‐wall carbon nanotube (SWCNT) network on which are anchored Ni nanoparticles encapsulated by a monolayer of N‐doped carbon (NCNi) is reported. The films are prepared by floating catalyst chemical vapor deposition followed by NH(3) treatment. The material obtained at optimum conditions shows excellent bifunctional electrocatalytic activity in alkaline media with low overpotentials of 190 and 270 mV for HER and OER, respectively, to reach a current density of 10 mA cm(−2). A current density of 10 mA cm(−2) at 1.57 V is achieved when this freestanding and binder‐free rod‐shaped NCNi/SWCNT assembly is used as cathode and anode in 1 m KOH solution for overall water splitting, presenting one of the best values reported to date.