Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS): SEM images and EDS maps of the SE powders were obtained with a Gemini SEM 560 highresolution scanning electron microscope (Carl Zeiss AG, Germany) at an acceleration voltage of 15 kV. A working distance between 8 mm to 9 mm and an aperture size of 120 µm were chosen. All images were collected with the in-lens detector and the mapping was carried out by using an X-Max50 detector (Oxford Instruments, UK). To avoid air contamination, the samples were transferred from the glove box with a Leica EM VCT500 (Leica Microsystems Germany) shuttle.