Controllable construction of porous yolk shell phosphate-functionalized Co/Ni-layered double hydroxides for high-performance supercapacitor

The extensive surface area of porous materials, while beneficial for increasing the specific capacity by exposing more active sites, often comes at the cost of compromised structural stability, which is detrimental to their long-term cycling stability. To address this issue, we capitalized on the ionic self-assembly that occurs during the etching process of metal-organic frameworks (MOFs) to construct a unique porous yolk-shell structure with a robust protective shell, which favors exposure of more active sites and long-term structural stability. By carefully adjusting the ratio of etchant ions, we obtained the optimal yolk-shell Co/Ni-based hydroxide phosphate (YS-CNHP) with an appropriate shell thickness, which exhibited an impressive specific capacity of 1854.6 F g⁻¹ (257.6 mAh g⁻¹) at a current density of 1 A g⁻¹. Moreover, AC//YS-CNHP hybrid supercapacitor with activated carbon (AC) as cathode delivers a significant specific capacity of 143.1 F g⁻¹ (63.6 mAh g⁻¹) and an outstanding energy density of 50.9 Wh kg⁻¹ at the power density of 0.8 kW kg⁻¹. This work provides new ideas and methods for the controllable preparation of porous yolk-shell structures, which is conducive to the wide application of functionalized layered double hydroxides (LDHs) in the field of energy storage.