by Mareike Hänsch
Nanoporous bulk materials have a wide range of applications due to their combination of a very high surface area and an interconnected pore system which is well accessible for reactive species. Therefore they play an important role when the real surface area of the material matters. This applies for catalysis, actuation, energy storage and energy conversion. Nanoporous gold exhibits a bicontinuous structure of nanometer sized ligaments and pores. In contrast to well-defined (e.g. smooth) electrodes which are already well described the understanding of nanoporous electrodes lacks considerably behind. This work, being part of the DFG Research Unit FOR 2213, focuses on transport processes in- and outside the nanoporous network and on the electrocatalysis of methanol oxidation as a model reaction. The aim is to obtain a fundamental understanding of the complex interplay of structure and properties and to use this knowledge to tailor new catalysts on a rational basis. The nanoporous material will be obtained by dealloying a less noble metal (e.g. Ag) from a Ag-Au-alloy. It will be possible to tailor the morphology of the material by using different dealloying processes resulting in distinct ligament and pore sizes. This and starting materials with varying ratios of the two metals can be used to obtain different residual contents of the less noble metal which can have a major influence on electrocatalytic properties and the surface reactivity in general. Another way to tailor the surface composition of the material is through UPD (underpotential deposition) of foreign metals. The final surface composition after a possible segregation of residual atoms or alloy formation of foreign metals can be investigated with XPS. The influence on the transport processes inside the nanoporous gold will be investigated with SECM (scanning electrochemical microscopy) and CLSM (confocal laser scanning microscopy). Since the electrocatalytic reaction of methanol oxidation does not need molecular oxygen as oxidizer, it will be of particular interest to compare the influence of transport behavior and surface reactivity to the catalytic liquid phase methanol oxidation investigated in another sub-project.
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