One-pot synthesis of CoO–ZnO/rGO supported on Ni foam for high-performance hybrid supercapacitor with greatly enhanced cycling stability

Rational synthesis of 3D coral-like ZnCo2O4 nanoclusters with abundant oxygen vacancies for high-performance supercapacitors

Transition metal oxides with high theoretical capacitance are regarded as desired electrode materials for supercapacitors, however, the poor conductivity and sluggish charge transfer kinetics constrain their electrochemical performance. The three-dimensional (3D) coral-like ZnCo2O4 nanomaterials with abundant oxygen vacancies were synthesized through a facile hydrothermal method and chemical reduction approach. The introduced oxygen vacancies can provide more active sites and lower the energy barrier, thereby facilitating the kinetics of surface reactions. Furthermore, the abundant oxygen vacancies in metal oxides can function as shallow donors to facilitate charge carrier diffusion, resulting in a faster ion diffusion rate and superior electrochemical conductivity. The electrochemical performance of ZnCo2O4 was optimized by the introduction of oxygen vacancies. The ZnCo2O4 nanoclusters, reduced by 0.5 M NaBH4 (ZnCo2O4-0.5), exhibit a specific capacitance of 2685.7 F g-1 at 1 A g-1, which is nearly twice that of the pristine ZnCo2O4 (1525.7 F g-1 at 1 A g-1). The ZnCo2O4-0.5 exhibits an excellent rate capacity (81.9% capacitance retention at 10 A g-1) and a long cycling stability (72.6% specific capacitance retention after 10 000 cycles at 3 A g-1). Furthermore, the asymmetric supercapacitor (ASC, ZnCo2O4-0.5 nanoclusters//active carbon) delivers a maximum energy density of 50.2 W h kg-1 at the power density of 493.7 W kg-1 and an excellent cycling stability (75.3% capacitance retention after 3000 cycles at 2 A g-1), surpassing the majority of previously reported ZnCo2O4-based supercapacitors. This work is important for revealing the pivotal role of implementing the defect engineering regulation strategy in achieving optimization of both electrochemical activity and conductivity.

Scalable CNTs/NiCoSe2 Hybrid Films for Flexible All-Solid-State Asymmetric Supercapacitors

The rapidly developing wearable flexible electronics makes the development of high-performance flexible energy storage devices, such as all-solid-state supercapacitors (SCs), particularly important. Herein, we report the fabrication of CNTs/NiCoSe₂ hybrid films on carbon cloth (CC) through a facile co-electrodeposition method based on flexible electrodes for all-solid-state SCs. The NiCoSe₂ sheets grown on CNTs uniformly with a diameter of 50-100 nm act as the active materials. The CNTs in the hybrid films act as the scaffold to offer more deposition sites for NiCoSe₂ and provide a conductive network to facilitate the transfer of electrons. Moreover, the one-step electrodeposition process avoids the usage of any organic binders. Benefiting from the high intrinsic reactivity and unique 3D architecture, the obtained CNTs/NiCoSe₂ electrode delivers high specific capacity (218.1 mA h g^-1) and satisfactory durability (over 5000 cycles). Remarkably, the CNTs/NiCoSe₂//AC flexible all-solid-state (FASS) ASC provides remarkable energy density (112.2 W h kg^-1) within 0-1.7 V and maintains 98.1% of its initial capacity after 10,000 cycles. In addition, this flexible ASC device could be fabricated at a large scale (5 × 6 cm²), and the LED arrays (>3.7 V) can be easily lighted up by three ASCs in series, showing its potential practical application.