2.3. Characterization of materials
The crystal structure and textural properties of the products were investigated on a Bruker D8 Advance X-ray diffractometer (XRD, Bruker Optics, Ettlingen, Germany) with Cu-Kα radiation, operated at 40 kV and 40 mA (scanning step: 0.02°/s) in 2θ = 10-80°. The MgCo2O4 NCAs layer was scraped from the nickel foam and grinded to powder for XRD characterization to avoid the strong interference signal of nickel substrate. Nitrogen adsorption-desorption isotherms were measured at 77 K on a NOVA2000e automated volumetric apparatus (Quantachrome Instruments, USA) to determine the Brunauer–Emmett–Teller (BET) surface area, Barret–Joyner–Halenda (BJH) pore size and size distribution. The micro-morphologies were characterized on a Zeiss Ultra 55 scanning electron microscope (SEM) and a JEM-2010 transmission electron microscope (TEM, JEOL Ltd., Japan) at an acceleration voltage of 200 kV. The X-ray photoelectron spectra (XPS) were recorded on an ESCALAB 250 XPS meter (Thermo Scientific) with Al Kα monochromatization at 250 W.