Electrostatic force-driven anchoring of Ni(OH)₂ nanocrystallites on single-layer MoS₂ for high-performance asymmetric hybrid supercapacitors

The electrochemical performance of battery-type electrode materials is limited by their diffusive charge storage mechanism in supercapacitors, leading to sluggish electrode kinetics and capacity loss. In this article, we present an electrostatic-induced strategy and rational structural design as a feasible solution to solve this problem. Chemically exfoliated single-layer MoS₂ with negative charges is used as the substrate for the confined growth of Ni(OH)₂. The electrostatic attraction between MoS₂ and Ni²⁺ results in homogeneous distribution of Ni²⁺ and subsequent formation of ultrasmall Ni(OH)₂ crystallites (∼5.5 nm). Due to the smaller size of Ni(OH)₂ and synergetic effect between the components, the graphene coated Ni(OH)₂/MoS₂ heterostructure (G-Ni(OH)₂/MoS₂) exhibits a capacity as high as 890 C g⁻¹ at 2 mV s⁻¹, close to the theoretical capacity of Ni(OH)₂. Moreover, the rapid capacitive surface charge is found to account for 34% of the total charges, ensuring excellent high-rate and cycling performances. As a proof-of-concept demonstration, G-Ni(OH)₂/MoS₂ is assembled into an asymmetric hybrid supercapacitors (AHSC) with active graphene as the counter electrode. The AHSC shows a power density of 3500 W kg⁻¹ at 13 Wh kg⁻¹ and stable cycling performance up to 4000 cycles.