Fabrication of 3D hierarchically porous Cu-Cr phosphate@MWCNTs nanocomposites for hybrid solid-state energy storage

초록

Transition bimetallic phosphates are promising candidates for supercapacitors owing to their two-metal synergy and multiple oxidation states. However, their electrochemical efficiency is often limited by poor ion/electron transfer rates and insufficient durability. To address this issue, we designed a series of nanocomposites based on in situ growth, in which copper-chromium phosphate nanogranules (CCP-series) were anchored onto multiwalled carbon nanotubes (MWCNTs) using simple and inexpensive chemical processes. This rationally designed hierarchical porous heterostructure, featuring dual-charge storage mechanisms, combines the synergistic benefits of electric double-layer capacitor-based MWCNTs and redox-enriched Cu-Cr phosphate. In addition, MWCNTs offer excellent electrical conductivity and superior endurance to Cu-Cr phosphate by providing continual charge-transfer paths for prolonged electrochemical efficiency, resulting in superior mechanical strength. Notably, the Cu-Cr phosphate/MWCNTs (CCP-4) nanocomposite delivered a superior specific capacity (1575 C/g (437 mAh/g) at 3 A/g current density) and outstanding longevity owing to its expanded surface area of 35.41 m2 g- 1, outperforming earlier reported Cu/Cr phosphate-based electrodes. Furthermore, a hybrid solidstate (HSS) device, incorporating a CCP-4 cathode, a reduced graphene oxide (rGO) anode, and a KOH electrolyte woven into a PVA matrix, achieved an outstanding specific capacity of 135 C/g (37 mAh/g) at a current density of 3.0 A/g. This HSS supercapacitor also exhibited a high energy density of 30.1 Wh/kg at a power density of 2404 W/kg, along with remarkable cycling stability (96.6 % capacity retention after 10,000 cycles), confirming its excellent endurance. In addition, the lighting of differently colored light-emitting diodes (LEDs) using serially coupled HSS devices provides real-world evidence for their application in modern nanoscale technologies.

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