Carbon dot engineered trimetallic hydroxyl carbonates: a strategy for enhanced redox-diffusion coupled charge storage

Abstract

Transition metal oxides have long been vital in energy storage due to their high theoretical capacitance and synergistic redox mechanisms. This study introduces a unique, binder-free synthetic approach to synthesize nickel–cobalt–zinc metal hydroxyl carbonate (MHC) with a flower-like morphology, ensuring efficient electrolyte access. These MHCs achieved an impressive specific capacitance of 1304 C g⁻¹ (3261 F g⁻¹) at 5 A g⁻¹, attributed to trimetallic synergy. Incorporating carbon dots derived from ajwain leaves further boosted the specific capacitance by 9.3%, as these dots acted as efficient conductive channels. A hybrid asymmetric device, pairing the carbon dot-incorporated MHC as a positive electrode with activated carbon as a negative electrode, delivered 93 F g⁻¹ at 1 A g⁻¹, alongside excellent energy and power densities of 33.5 W h kg⁻¹ and 16 200 W kg⁻¹, respectively. This device demonstrated remarkable stability, retaining 77% capacitance with 100% coulombic efficiency over 5000 cycles at 5 A g⁻¹. Dunn's method confirmed diffusion-controlled charge storage as predominant. These findings highlight carbon dot-modified MHCs as highly promising electrodes for future energy storage applications.