The objective of this project is to investigate the influence of reaction - diffusion processes for the design of structured and patterned electrode architectures. This will aid the development of strategies for the synthesis of mesostructured and heterogeneous architectures with relevance to energy materials, for example for electrodes in photoelectrochemical cells (PEC) for solar water splitting. This is a joint PhD project for two PhD students at University of Basel and Empa.
The objective of this project is to investigate the influence of reaction – diffusion processes for the design of structured and patterned electrode architectures. This will aid the development of strategies for the synthesis of mesostructured and heterogeneous architectures with relevance to energy materials, for example for electrodes in photoelectrochemical cells (PEC) for solar water splitting. This is a joint PhD project for two PhD students at University of Basel and Empa.
Solar energy driven splitting of H2O by heterogeneous photocatalysts is a promising green technology for hydrogen fuel production and can be obtained in a single step process in PEC, for which two basic materials criteria must be met: the light harvesting system must have the proper thermodynamics and energetics to effect the decomposition of water, and the system must be corrosion stable in the electrolyte environment. Conventional semiconductor metal oxide catalysts partially possess suitable redox potentials for efficient water splitting. Tuning of the band gap energy is important for the performance of an electrode, but device architecture too plays a crucial role and is increasingly taking centre stage. p-n heterojunctions with pillar architecture can perform better than planar electrodes under certain conditions. Therefore, adding structure to the material is of great interest. Downsizing the structures is also important because nanostructures can offer a very high catalytically active surface area and thus enhanced efficiency. In the extreme case, downsizing may lead to quantum confinement phenomena.
The conventional methods to nanostructure materials are the so called 'top-down' techniques, where structures are produced by fabricating the material by removing parts of it, i.e. lithography methods. Recently considerable attention has been devoted to the so called ‘bottom-up’ techniques where the structure is built from building blocks using self-assembling techniques. Reaction-diffusion-precipitation processes are very promising candidates for building complex structures because the location of the self-organised chemical pattern is locked once it is formed. In the well-known periodic Liesegang pattern (LP), colloidal precipitates form periodically behind a moving reaction front, obeying systematic scaling rules [Liesegang 1896].
We propose the combination of reaction-diffusion processes such as Liesegang phenomena with nanostructuring techniques, for example wet stamping method (PhD student at Basel) or using EHD instability as a driving force (PhD student at Empa) to structure the selected material containing mixed metal ions or nanoparticles.
The PhD student at University of Basel will synthesise, analyse and understand mixed metal reaction-diffusion planar meso- and/or microstructures and transfer them to ceramic systems. Structural and morphological characterization of the patterns with XRD and Microscopy as well as electrochemical characterisation will be carried out. The photoelectrochemical response of the produced electrodes will be compared with conventional non-structured systems. With the experimental data obtained, we will formulate a model which explains the observed changes in performance as a function of geometrical /topological /morphological peculiarities.
The PhD student at Empa will synthesise an array of radial p-n junction nanopillar cell by using EHD lithography with bilayer of polymer/nanoparticle nanocomposite or bilayer sol-gel chemistry. Structural and morphological characterization will be carried out. The photoelectrochemical activity of planar and pillar array electrodes will be compared, explained and implemented in a demonstrator-type device cell.
The quantum mechanical and thermodynamic properties, which are insignificant in larger, everyday materials, cause nanomaterials to display new and interesting properties. We intend to comprehend properties and exploit them for energy applications.