The Brunauer-Emmett-Teller (BET) surface area of the NiCo2O4 nanoneedles was determined through nitrogen sorption measurement at 77K. Electrochemical measurements were carried out by electrochemical workstation (CHI 660E, CH Instruments

Inc., Shanghai, China) using three-electrode configuration in 2 M KOH aqueous solution. Both the pristine carbon cloth (≈1.5 × 4.0 cm2) and NCONAs (NiCo2O4 mass, ≈5 mg) were directly used as the working electrode. The value of specific capacitance (F g-1) and current rate (A g-1) was https://www.selleckchem.com/products/jq-ez-05-jqez5.html calculated based on the total mass of the active materials. The reference and counter electrodes were standard calomel electrode (SCE) and platinum foil, respectively. Cyclic voltammetry (CV) measurements were performed at a scanning rate of 2 to 40 mV s-1 www.selleckchem.com/products/VX-680(MK-0457).html from -0.2 to 0.6 V at room temperature. Galvanostatic charge-discharge measurements were carried out from -0.1 to 0.5 V at a current density of 2 to 16 A g-1, under opens circuit potential. Electrochemical impedance spectroscopy (EIS) measurements were performed by applying an alternate current (AC) voltage with 5 mV amplitude in a frequency range from 0.01 Hz to 100 kHz. The specific capacitances were calculated according to equation C = (IΔt)/(ΔV × m),

where I is the constant discharge current, Δt is the discharge time, ΔV is the voltage drop upon discharging (excluding the IR drop), and m is the total mass of the active substance of the electrode material. Results and discussion Figure  1 shows the crystallographic structure and the crystallographic phase of NiCo2O4 with the spinel structure. As depicted in Figure  1a, the

Ni species occupy the octahedral sites and the Co is distributed over both octahedral and tetrahedral sites. Due to the presence of mixed valences of the same cation in such spinel cobaltite, the NiCo2O4 possesses at least 2 orders of magnitude higher electrical conductivity than that of the monometallic nickel and cobalt oxides by electron transfer taking place with relatively low activation energy between cations [12, Florfenicol 26, 27]. The crystallographic phase of the Caspase Inhibitor VI price as-fabricated NCONAs product was studied by the XRD technique, and the typical wide-angle diffraction pattern is shown in Figure  1b (NCONAs were scraped from carbon cloth) and Additional file 1: Figure S2. Seven well-defined diffraction peaks, including not only the peak position but also their relative intensities, can be easily indexed as cubic spinel NiCo2O4 crystalline structure. In order to further understand the composition and structure of these NCONAs samples, Raman analysis was performed and the typical Raman spectrum of the products is shown in Additional file 1: Figure S1. In the Raman spectrum of carbon cloth, the G band (1,590 cm-1) represents the in-plane bond-stretching motion of the pairs of C sp2 atoms (the E2g phonons), while the D band (1,350 cm-1) corresponds to breathing modes of rings or K-point phonons of A1g symmetry [28].