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Research Project
Reaction-diffusion processes for the growth of patterned structures
and architectures: A bottom-up approach for potoelectrochemical
electrodes
Third-party funded project
Project title Reaction-diffusion processes for the growth of patterned structures and architectures: A bottomup approach for potoelectrochemical electrodes
Principal Investigator(s) Constable, Edwin Charles;
Organisation / Research unit Departement Chemie / Anorganische Chemie (Constable)
Project start 01.11.2011
Probable end 31.05.2015
Status Completed
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.
Keywords self assembly, pattern formation, photo-electrodes, Liesegang pattern, Reaction-Diffusion,
Reaction-Diffusion-Precipitation
Financed by
Swiss National Science Foundation (SNSF)
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