The starting point for this project is the observation that processes at materials surfaces in heterogeneous catalysis are influenced by the state of the surface through various variables, and specifically through local chemical composition, density of defects such as step edges or kinks, coverage with stable adsorbates such as oxides, and specifically elastic strain.

The first of the two aims to be derived from these assumptions is to synthesize and characterize nanoporous Au samples under systematic and controlled variation of structure size, composition (i.e. remaining Ag content or other ternary alloy metals) and adsorbate coverage. Nanoporous gold samples with different types of metallic impurities will be prepared by dealloying the solid solutions Ag-Au and Cu-Au. Nanoporous Au-Pt alloys will be prepared by dealloying Ag-Au-Pt. The prepared samples will be supplied to the other sub-projects focusing on both, catalysis and material characterization.

The second task to be derived is to clarify how surface stress can influence the electrocatalytic behavior or, contrariwise, how electrochemical reactions at the surface cause mechanical action. Since the oxidative conversion of organics at metal electrodes depends on the presuming adsorbate covering, different adsorption states of planar surfaces besides their modification with secondary metals are in the focus of investigations that connect mechanical deformation with electrochemical measurements. We shall carry out in-situ dilatometry and dynamic electrochemical mechanical analysis (DECMA) experiments during cyclic voltammetry scanning. These experiments – along with the known coupling between surface stress and adsorbate coverage – will then provide a signature of the adsorption processes that allows to link in-gas to in-electrolyte experiments. The conditions of these experiments will be matched to (electro-) catalysis experiments carried out by M. Bäumer, A. Wittstock, and G. Wittstock. In this way the role of stable adsorbates for catalysis as a function of the surface composition and the type and amount of ad-metal, respectively can be clarified.

Publications:

M. Graf, B. Roschning and J. Weissmüller
Nanoporous Gold by Alloy Corrosion: Method-Structure-Property Relationships
Journal of the Electrochemical Society 164 (2017) C194-C200.

A. Lackmann, C. Mahr, M. Schowalter, L. Fitzek, J. Weissmüller, A. Rosenauer and A. Wittstock
A Comparative Study of Alcohol Oxidation over Nanoporous Gold in Gas and Liquid Phase
Journal of Catalysis 353 (2017) 99-106.

M. Graf, B.-N. D. Ngô, J. Weissmüller and J. Markmann
X-Ray Studies of Nanoporous Gold: Powder Diffraction by Large Crystals with Small Holes
Physical Review Materials 1 (2017) 076003.

M. Graf, M. Haensch, J. Carstens, G. Wittstock and J. Weissmüller
Electrocatalytic Methanol Oxidation with Nanoporous Gold: Microstructure and Selectivity
Nanoscale 9 (2017) 17839–17848