ABSTRACT
The anion exchange membrane (AEM) in fuel cells requires new, stable, and improved electrocatalysts for large scale commercial production of hydrogen fuel for efficient energy conversion. Fe40Ni20Co20P15C5, a novel metallic glass ribbon, was prepared by arc melting and melt spinning method. The metallic glass was evaluated as an efficient electrocatalyst in water-splitting reactions, namely hydrogen evolution reaction under acidic and alkaline conditions. In addition, oxygen evolution reaction in alkaline medium was also evaluated. In 0.5 M H2SO4, the metallic glass ribbons, after electrochemical dealloying, needed an overpotential of 128 mV for hydrogen evolution reaction, while in 1 M KOH they needed an overpotential of 236 mV for hydrogen evolution. For the oxygen evolution reaction, the overpotential was 278 mV. The electrochemical dealloying procedure significantly reduced the overpotential, and the overpotential remained constant over 20 hours of test conditions under acidic and alkaline conditions. The improved electrocatalytic activity was explained based on the metastable nature of metallic glass and the synergistic effect of metal hydroxo species and phosphates. Based on the excellent properties and free-standing nature of these metallic glass ribbons in electrolyte medium, we propose the current metallic glass for commercial, industrial electrocatalytic applications.
ABSTRACT
The intensity profiles of backscattered and secondary electrons from a pure Mg sample have shown a variation with sample thickness and acceleration voltage in the range of 5-30â¯kV, depending on the specimen holder used. The intensities of backscattered electron (BSE) and secondary electron (SE) signals increases with the sample thickness until saturation when using a scanning transmission electron microscopy (STEM) holder with a closed tube below the sample. However the SE signal increases to the maximum and then decreases with the sample thickness when using a transmission Kikuchi diffraction (TKD) holder with no shielding below the sample whereas the BSE signal again increases until saturation. The influence of the holder on the SE signals is caused by the fact that secondary electrons emitted from the bottom surface could be detected only when using the TKD holder but not the STEM holder. The experimental results obtained are consistent with the Monte Carlo simulation results. Application of the magnitude of the SE and BSE signals to measurement of sample thickness has been considered and the BSE image profile shows a reasonably good accuracy.
