• Energy Research

Abstract A complete model of a thermionic generator has been developed in order to optimise the technology for application in the solar thermal generation of electricity. Steady state current densities predicted by the model have been shown to agree with published experimental thermionic data. Two separate genetic algorithm optimisations have been carried out for both power density and efficiency, in which electrode temperatures and work functions, external circuit resistance and electrode separation were varied. The result of these optimisations were two configurations separately exhibiting a maximum power density of 1.66 W/cm 2 , and a maximum efficiency of 7.69% for parameter ranges applicable to concentrating solar thermal power. Examination of the optimum simulation parameters indicated that future developments in lowering collector work functions, increasing emitter service temperature and decreasing attainable electrode separations will all positively impact device performance.

Low energy ion scattering (LEIS) is the study of the composition and structure of a surface by the detection of low energy ions with energies ranging from 100 eV to 10 keV elastically scattered off the surface. The extreme sensitivity to the outermost atomic layer makes it as a unique tool for surface analysis. In this paper, concepts of shadowing, blocking, and also polar and azimuthal scans have been described. Surface order and surface atom spacings are revealed by using these concepts and measuring the intensity of backscattered projectiles as a function of the incident and azimuthal angles.

In this work the role of TiO2 in improving cathode performance has been investigated through the use of electrode imaging, porosity changes, electrochemical characterisation and changes in the chemical composition of constituent γ-MnO2 particles. Time-of-flight secondary ion mass spectrometry studies revealed that TiO2 is mobile in the electrolyte and associates itself with the porous γ-MnO2 surface. This association gives rise to improved electrode performance by allowing electron/proton pairs to more easily (de)intercalate into the MnO2 structure. Depth profiling confirmed that upon cycling surface TiO2 becomes incorporated into the bulk γ-MnO2 structure inhibiting proton diffusion. Refereed/Peer-reviewed