Synthesis of ultra-high specific surface area trimetallic NiCoMg-LDH hollow cage via bimetallic ion etching for hybrid supercapacitors

A trimetallic layered double hydroxide (LDH), NiCoMg-LDH, was rationally designed and synthesized in this paper by hydrolytic etching of Ni²⁺ and Mg²⁺ using Co-MOF as a conversion template, during which the rhombic dodecahedral structure of Co-MOF was etched to form a hollow cage structure overlaid with nanosheets on the surface. In comparison to the NiCo-LDH prepared by monometallic ion etching, the NiCoMg-LDH prepared in this study has a larger specific surface area and a more stable hollow porous structure, which can provide a large number of active sites for redox reactions as well as ion transport channels. The trimetallic Ni₁Co₁Mg-LDH has a higher specific capacity of 2141.62 F g⁻¹ (208.21 mAh g⁻¹) at 1 A g⁻¹ current density compared to the NiCo-LDH. It also keeps 83.61% of its specific capacity after 5000 cycles at 10 A g⁻¹. It also performs well in rate capacity, with a capacity retention rate of 74.49% at 20 A g⁻¹. With Ni₁Co₁Mg-LDH serving as the positive electrode and AC serving as the negative electrode, the hybrid supercapacitor (HSC) exhibits a high energy density of 61.65 Wh kg⁻¹ at a power density of 800.02 W kg⁻¹. After 10,000 cycles of charge and discharge, 80.17% of the capacity was retained. This study demonstrates that the trimetallic LDH structure generated using bimetallic ion etching with MOF as a template can increase the performance and stability of supercapacitors.