Synergistic Role of Gemini Surfactants and Carbon Dots in Layer Stacking Engineering of Mixed α/β-Ni(OH)2 for Hybrid Supercapacitors

Abstract Precise control over the stacking order and phase configuration in layered Ni(OH)2 remains a significant challenge for maximizing its electrochemical activity in hybrid supercapacitors. Herein, we report a synergistic stacking-engineering strategy integrating glutathione-derived carbon dots (CDs) and a gemini surfactant (GS) to regulate the interlayer structure and morphology of Ni(OH)2 for enhancing its supercapacitor behavior. The GS with a dual head-group structure provides stronger adsorption and superior structure-directing capability compared to conventional single-head surfactants, facilitating effective modulation of layer stacking. X-ray diffraction of pristine Ni(OH)2 suggests dominating β-phase stacking. However, CDs promote α-phase formation and disrupt long-range β-phase ordering. Subsequent GS incorporation further expands the interlayer structure and weakens face-to-face compact β-layer stacking. FESEM analysis demonstrates the interconnected nanosheet assemblies for Ni(OH)2−CDs−GS. Ni(OH)2−CDs−GS delivers a 65% higher specific capacity than Ni(OH)2−CDs, attributed to the increased proportion of electrochemically active α-phase domains, expanded interlayer galleries, disruption of compact β-layer stacking, reduced stacking constraints, and an interconnected nanosheet morphology that facilitates electrolyte transport and improves ion diffusion. Dunn’s analysis confirms a dominant diffusion-controlled contribution associated with enhanced Faradaic redox kinetics. A hybrid supercapacitor assembled using Ni(OH)2−CDs−GS and guanosine monophosphate-modified graphene oxide (GO−GMP) in a 1.8 V potential window corresponds to an energy density of 63 Wh kg−1 at a power density of 896 W kg−1. This work benefits from the synergistic integration of CDs and the GS, providing a multifunctional stacking-engineering approach that simultaneously tailors phase composition, stacking order, and interlayer architecture beyond conventional phase- or morphology-engineering strategies.