| Popis: |
Compositionally graduated films of a SrTi1-xFexO3-y (STFO) perovskite electrocatalyst were successfully prepared by High Throughput Physical Vapour Deposition (HT-PVD). X-ray diffraction measurements confirmed a cubic perovskite structure for all values of x as well as an increase in the cubic lattice parameter with increasing x from 0.392 ± 0.001 nm for SrTiO3 to 0.386 ± 0.001 nm for SrFeO3 in accordance with Vegard’s Law. A Raman mode corresponding to an O-stretching vibration was observed which is disallowed by symmetry in the cubic structure and suggests a localised lattice distortion. The films were highly resistive, < 7 x 10-8 S cm-1, at low x but conductivity increased with increasing x before reaching a plateau at 0.041 S cm-1 for x > 0.75.High electrocatalytic activity towards the oxygen evolution reaction (OER), characterised by over-potentials below 0.2 V, was found for STFO electrode compositions with x > 0.5. The high OER activity was however found to correlate with low electrode stability, consistent with the participation of lattice oxygen in the OER mechanism. This was supported by the observed redox electrochemistry which showed evidence of reversible oxygen intercalation. An optimal electrode composition of SrTi0.5Fe0.5O3-y is recommended as OER activity showed no significant increase for higher Fe content whilst electrode stability decreases. Low electrocatalytic activity towards the oxygen reduction reaction (ORR) was observed for all compositions. The ORR did not occur until after surface reduction of the films suggesting that the surface reduction is required for the creation of active surface sites.The STFO perovskite system was also investigated on Fe doped STO (110) surfaces. A series of reconstructed surfaces were prepared and characterised by low energy electron diffraction (LEED) in agreement with the literature. X-ray photo-electron spectroscopy (XPS) and low energy ion scattering spectroscopy (LEISS) confirmed that Fe doping was successful in incorporation of Fe into the perovskite structure. Fe incorporation was observed to improve the ORR electrocatalytic activity of the surface however no OER electrocatalytic activity was observed |
