Enhanced energy storage performance of NiCo-LDH nanosheets decorated on biomass-derived carbon microtubes from natural poplar catkins for advanced hybrid supercapacitors

Nickel–cobalt layered double hydroxides (NiCo-LDHs) are promising electrode materials for hybrid supercapacitors (HSCs) due to their high theoretical charge storage capacity and excellent reversibility. However, their practical application is limited by low electrical conductivity and a tendency to agglomerate, which suppress their electrochemical performance. To address these challenges, NiCo-LDH nanosheets (NiCo-LDH NSs)/carbon microtubes derived from poplar catkins (CMT-PC) composite electrode material is synthesized via a hydrothermal method. This composite integrates NiCo-LDH NSs as a coating and CMT-PC with a high specific surface area as the framework. In a three-electrode system, the NiCo-LDH NSs/CMT-PC electrode demonstrated a specific capacity of 228.4 mAh·g⁻¹ (1644.5 F·g⁻¹, 822.2 C·g⁻¹) at a current density of 1 A·g⁻¹, and maintained a specific capacity of 101.7 mAh·g⁻¹ (732.2 F·g⁻¹, 366.1 C·g⁻¹) even at 30 A·g⁻¹. After 5000 cycles, the material exhibited excellent stability, retaining 96.5% of its capacity, with a decrease from 193.6 to 186.9 mAh·g⁻¹. To explore its practical application in HSCs, we assembled NiCo-LDH NSs/CMT-PC//activated carbon (AC) HSCs, using the NiCo-LDH NSs/CMT-PC as the positive electrode and AC as the negative electrode. The assembled device exhibited a specific capacity of 88.3 mAh·g⁻¹ at 1 A·g⁻¹ and an energy density of 72.2 Wh·kg⁻¹ at a power density of 508.6 W·kg⁻¹. Impressively, after 9000 cycles at 3 A·g⁻¹, the specific capacity increased from 64.2 to 66.5 mAh·g⁻¹, demonstrating exceptional cycling stability and suitability for practical applications.