NiMoO4 Nanosheets Embedded in Microflake-Assembled CuCo2O4 Island-like Structure on Ni Foam for High-Performance Asymmetrical Solid-State Supercapacitors

Micro/nano-heterostructure with subtle structural design is an effective strategy to reduce the self-aggregation of 2D structure and maintain a large specific surface area to achieve high-performance supercapacitors. Herein, we report a rationally designed micro/nano-heterostructure of complex ternary transition metal oxides (TMOs) by a two-step hydrothermal method. Microflake-assembled island-like CuCo2O4 frameworks and secondary inserted units of NiMoO4 nanosheets endow CuCo2O4/NiMoO4 composites with desired micro/nanostructure features. Three-dimensional architectures constructed from CuCo2O4 microflakes offer a robust skeleton to endure structural change during cycling and provide efficient and rapid pathways for ion and electron transport. Two-dimensional NiMoO4 nanosheets possess numerous active sites and multi-access ion paths. Benefiting from above-mentioned advantages, the CuCo2O4/NiMoO4 heterostructures exhibit superior pseudocapacitive performance with a high specific capacitance of 2350 F/g at 1 A/g as well as an excellent cycling stability of 91.5% over 5000 cycles. A solid-state asymmetric supercapacitor based on the CuCo2O4/NiMoO4 electrode as a positive electrode and activated carbon as a negative electrode achieves a high energy density of 51.7 Wh/kg at a power density of 853.7 W/kg. These results indicate that the hybrid micro/nanostructured TMOs will be promising for high-performance supercapacitors.