Thema der Dissertation:
A comprehensive study of surface and space charge effects at an operating water splitting iron oxide photoanode
A comprehensive study of surface and space charge effects at an operating water splitting iron oxide photoanode
Abstract: An elegant route to the production of green hydrogen is the immediate utilization and chemical conversion of solar energy at semiconductor electrodes. Haematite is one promising iron oxide electrode material due to its low cost, abundance, harmlessness and outstanding chemical stability. On the downside, water oxidation at haematite photoanodes suffers from low efficiency due to poor catalytic performance and fast charge carrier recombination rates. The work presents an investigation of the haematite electrode/electrolyte interface at an operating sample system using both established photo-electrochemical methods and electric field induced second harmonic (EFISH) spectroscopy. With this, the evolution of the space charge layer into the bulk is tracked as function of the applied potential. Surface charge transfer and accumulation processes are sensed by photocurrent transients and static capacitive load. The experimental findings are analysed in comparison with the materials morphologic and optoelectronic properties.
It was found that the charge separation is limited as the space charge layer of the pristine haematite electrode already reaches the back contact at moderate potentials. A kinetic analysis of the surface charge concentration indicates a third order rate law dependence providing a further explanation of the low water splitting efficiency. Implications and prospects of the EFISH effect as a sensitive and unbiased probe of semiconductor surface voltage are discussed regarding the potential dependence of both intensity and colour of the second harmonic signal. Possible conclusions on electronic structures of the semiconductor electrode material are proposed from the combined spectroscopic and photo-electrochemical findings.
It was found that the charge separation is limited as the space charge layer of the pristine haematite electrode already reaches the back contact at moderate potentials. A kinetic analysis of the surface charge concentration indicates a third order rate law dependence providing a further explanation of the low water splitting efficiency. Implications and prospects of the EFISH effect as a sensitive and unbiased probe of semiconductor surface voltage are discussed regarding the potential dependence of both intensity and colour of the second harmonic signal. Possible conclusions on electronic structures of the semiconductor electrode material are proposed from the combined spectroscopic and photo-electrochemical findings.
Zeit & Ort
18.10.2024 | 13:30
Seminarraum E3 (1.4.31)
(Fachbereich Physik, Arnimallee 14, 14195 Berlin)