Design of Hierarchical NiCo2O4 Nanocages with Excellent Electrocatalytic Dynamic for Enhanced Methanol Oxidation

Although sheet-like materials have good electrochemical properties, they still suffer from agglomeration problems during the electrocatalytic process. Integrating two-dimensional building blocks into a hollow cage-like structure is considered as an effective way to prevent agglomeration. In this work, the hierarchical NiCo2O4 nanocages were successfully synthesized via coordinated etching and precipitation method combined with a post-annealing process. The nanocages are constructed through the interaction of two-dimensional NiCo2O4 nanosheets, forming a three-dimensional hollow hierarchical architecture. The three-dimensional supporting cavity effectively prevents the aggregation of NiCo2O4 nanosheets and the hollow porous feature provides amounts of channels for mass transport and electron transfer. As an electrocatalytic electrode for methanol, the NiCo2O4 nanocages-modified glassy carbon electrode exhibits a lower overpotential of 0.29 V than those of NiO nanocages (0.38 V) and Co3O4 nanocages (0.34 V) modified glassy carbon electrodes. The low overpotential is attributed to the prominent electrocatalytic dynamic issued from the three-dimensional hollow porous architecture and two-dimensional hierarchical feature of NiCo2O4 building blocks. Furthermore, the hollow porous structure provides sufficient interspace for accommodation of structural strain and volume change, leading to improved cycling stability. The NiCo2O4 nanocages-modified glassy carbon electrode still maintains 80% of its original value after 1000 consecutive cycles. The results demonstrate that the NiCo2O4 nanocages could have potential applications in the field of direct methanol fuel cells due to the synergy between two-dimensional hierarchical feature and three-dimensional hollow structure.

Ultrathin and porous NiCo2O4 nanosheets based 3D hierarchical electrode materials for high-performance asymmetric supercapacitor

It is well-known that designing unique morphology and structure of electrode materials is an effective strategy to achieve high performance supercapacitors. Herein, the ultrathin and porous NiCo2O4 nanosheets based 3D hierarchical electrode materials were synthesized via a simple and cost effective solvothermal method and subsequent annealing prosses. Since the ultrathin and porous nanosheets could accelerate the transmission of ions and provide numerous active sites, the obtained NiCo2O4 nanosheets based electrode exhibited excellent electrochemical performance with a high area capacity of 5.38 F cm−2 (2690 F g−1) at a current density of 10 mA cm−2 and a good rate performance of 41% capacitance retention at 50 mA cm−2. Furthermore, the corresponding asymmetry supercapacitor was assembled by using the resulted NiCo2O4 nanosheets and active carbon as positive electrode and negative electrode respectively. As expected, the corresponding supercapacitor delivered superior energy density of 52.6 Wh kg−1 at power density of 1.1 kW kg−1 and an extraordinary capacitive retention of 80.9% after 3,000 cycles at 20 mA cm−2. The high energy storage performances suggested that the obtained ultrathin and porous NiCo2O4 nanosheets based 3D hierarchical electrode materials could be prospective candidate in the field of energy storage.

NiCo2O4 Nanosheets for High Performances Formaldehyde Gas Sensing Performances

The advancements in gas sensors application with maximum performances in selectivity, response, accuracy in resistance measurements and inexpensive fabrication cost has led researcher to develop and new outstand nanomaterials for environmental safety. In this study, we followed a simple hydrothermal route to synthesize ultrathin NiCo2O4 nanosheets used in gas sensing applications. The wide surface area of nanosheets provides plenty of surface area for the adsorption of HCHO gas molecules. The nanostructures are testified using XRD, XPS, SEM and TEM, respectively. The nanosheets are tested for diverse gases at assorted effective temperature ranges, and shows high response and selectivity towards formaldehyde gas. The outstanding gas-sensing properties of ultrathin NiCo2O4 nanosheets based sensor make it a potential candidate in industrial applications.