Surface Engineering on Nickel–Ruthenium Nanoalloys Attached Defective Carbon Sites as Superior Bifunctional Electrocatalysts for Overall Water Splitting

Herein, we report a novel catalyst of nickel–ruthenium alloy nanoparticles (NPs) homogeneously enriched in the wall of multiwalled carbon nanotubes (denoted as NiRu@MWCNTs) via a facile plasma reduction method. The NiRu@MWCNTs exhibits remarkable electrocatalytic activity and stability for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The required overpotentials to drive a current density of 10 mA cm–2 (η10) over NiRu@MWCNTs are only 14 and 240 mV, corresponding to Tafel slopes of 32 and 55 mV dec–1 for the HER and OER in alkaline medium, respectively. Furthermore, the NiRu@MWCNTs electrolyzer shows low η10 of 330, 380, and 280 mV in acidic, neutral, and alkaline media, respectively. Density functional theory (DFT) calculations and experimental results reveal that the NiRu alloy NPs attached to the defective and nondefective carbon are the key active sites for the HER and OER, respectively, thus resulting in superior isolated synergistic bifunctional active sites for overall water splitting. Our work provides a promising strategy for efficient synthesis of robust catalysts with specific bifunctional active sites for overall water splitting in a wide pH range, along with deep insight into the catalytic mechanism.