Research Group - Prof. Jörg Weissmüller

Dealloying and impact of mechanics for catalysis

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.

Schematic of experimental setup for current-strain response to determine the current-strain response parameter upon potential cycling (WE: working electrode, RE: reference electrode, CE: counter electrode, R: shunt resistance, cyclic elastic deformation is carried out by a piezo actor that measures the grip displacement simultaneously). Lower sketch shows the magnified contact between electrolyte an the strained thin film WE by a standing meniscus. Sketches taken from: Q. Deng; M. Smetanin; J. Weissmüller, Mechanical Modulation of Reaction Rates in Electrocatalysis. J. Catal. 2014, 309, 351.

Results from DECMA measurement for hydrogen evolution reaction (HER) on a planar Au surface. Upper curve displays a Tafel plot over the entire adsorption potential regime (note the slope change at a potential Ead where the half of the maximum degree of H coverage is reached). Lower curve: Current response parameter upon elastic strain over the same potential regime. Graphs taken from J. Weissmüller, Electrocapillarity of Solids and Its Impact on Heterogeneous Catalysis. In Electrocatalysis; Wiley, 2013.

Prof. Jörg Weissmüller

UNIVERSITÄT HAMBURG-HARBURG

MATERIALPHYSIK

Email: weissmueller@tuhh.de

Phone: 040 42878 3035


Yong Li, PhD student

Xinyan Wu, PhD student