Leo 1550

Zn_1−xFe_xO (with x = 0.02, 0.04, 0.06, 0.08, 0.10, 0.12) was synthesized according to a previously reported method [15 (link)]. Zinc (II) gluconate (Alfa Aesar, Lancashire, UK) and iron (II) gluconate (Sigma Aldrich, St. Louis, MO, USA) were dissolved in ultra-pure water with respect to the desired dopant ratio (0.2 M total ion concentration). This solution was added dropwise to a second solution comprising 1.2 M sucrose, and the obtained solution was stirred for 15 min. Subsequently, the solvent was evaporated at 160 °C and the obtained material was further heated to 300 °C in order to decompose the sucrose and dry the precursor. Finally, the solid powder was grinded and calcined in a tubular furnace (Nabertherm, L9/12/P330, Lilienthal, Germany) at 450 °C for 3 h (3 K min⁻¹ heating rate). ICP-OES was conducted in order to determine the metal ion concentrations by dissolving the samples in hot hydrochloric acid and via double determination in a Spectro Arcos from Spectro Analytical Instruments (Kleve, Germany) with axial plasma view. Scanning electron microscopy (SEM) was performed by means of a Zeiss LEO 1550 (Zeiss, Oberkochen, Germany).

Scanning electron micrographs were recorded with a LEO1550 field-emission SEM instrument (Zeiss, Oberkochen, Germany) operated at an accelerating voltage of 500 V with an in-lens secondary electron detector. The suspensions of cellulose pulp, pulp-O, and pulp-O-Br obtained after 15 passes at 1000 bar through the homogenizer were diluted and dropped onto silicon wafers. The silicon wafers were dried at ambient temperature and atmosphere overnight. Samples were sputtered with gold/palladium for 40 s to avoid charging effects during SEM detection.

The samples from the CS testing were used to analyze the microstructure. Prior to analysis, the samples were dried in a vacuum for 24 h. The fracture surfaces of dry samples were analyzed with scanning electron microscopy (SEM, LEO 1550, Zeiss, Oberkochen, Germany) under an accelerating voltage of 3.00 kV with an SE2 detector. The samples were previously sputtered with a thin Au/Pd coating for 30 s.

SEM images were recorded using a Carl Zeiss LEO 1550 electron microscope (Carl Zeiss, Jena, Germany) at an accelerating voltage of 30 kV. TEM images were recorded by a Carl Zeiss EM 912 electron microscope (Carl Zeiss, Jena, Germany) at an accelerating voltage of 20 kV. For TEM, the samples were prepared by microtome method.

Scanning electron microscopy (SEM) was conducted with a Zeiss LEO 1550 at 5.00 keV. Raman micro-mapping was performed with a Thermo Fisher DXR microscope (455 nm, 6 mW, 10 s × 3 exposure time, 100× objective, 500 nm step size). X-ray photoelectron spectroscopy (XPS) measurements were performed with a Thermo Fisher Scientific K-alpha XPS system using a Al Kα X-ray source (1486.7 eV).

Raman spectroscopy was performed on a Renishaw inVia Raman microscope using an excitation wavelength of 532 nm from a laser diode with a maximum power of 500 mW. The laser beam was focused on the surface of the as-prepared graphite electrode specimens via a 50× magnification objective. A constant laser power nominally corresponding to 0.5% of its maximum value was utilized for the analyses. A preliminary calibration of the spectrometer was performed by means of a Si wafer to obtain a characteristic reference peak at 520.6 cm⁻¹. 40 cumulative acquisitions with a measuring time of 20 s were run for each spectrum between 200 cm⁻¹ and 3200 cm⁻¹. The exposure to the laser beam was minimized in between subsequent measurements to avoid any possible degradation of the sample surface.
The surface morphologies of the as-prepared electrodes were investigated by means of a Field Emission Scanning Electron Microscope (FE-SEM, Zeiss LEO1550) via a dedicated In-Lens secondary electron detector and employing magnifications of 1000× and 20 000× with an operation voltage of 10 keV. The cast electrode samples were mounted on aluminium stubs using double-sided adhesive conductive copper tape.