The processes of heterogeneous catalysis depend on the local chemical composition, the defect density and the presence of stably adsorbed species such as e.g. Oxygen. For nanoporous gold, the above parameters can be varied by appropriate manufacturing protocols. Preliminary work emphasizes in particular the role of residual content of the sacrificial component of corrosion - usually Ag - for the activity. In the current, first funding period, therefore, the first overall objective of the subproject is the synthesis and characterization of nanoporous metal samples with different composition, adsorbate coverage, and structure size. These samples are provided to all experimental subprojects (TPs) for studies of catalysis (TP1-TP4) and for the characterization of surface composition (TP4) and atomic assembly (TP6).

In the requested second funding period, samples will continue to be produced using the established protocols, as reference conditions for research in all subprojects. However, the focus is on the systematic investigation of nanostructure formation during alloy corrosion and the development of the structure during ligament size adjustment by annealing and in operando during catalysis using atomistic computer simulation. For this purpose, an existing code for kinetic Monte Carlo simulation of alloy corrosion is used. The structural development predictions are carried out in close coordination with experiments in projects TP4 (photoelectron spectroscopy for surface composition) and TP6 (electron microscopy for the distribution of alloying elements). Theory and experiment highlight the crucial role of elastic elongation of the surface for heterogeneous catalysis. The surfaces of nanoporous metals are basically stretched, which can be systematically varied by adjusting the structure size. The experimental documentation and the understanding of the importance of mechanics for the catalytic properties of nanoporous gold form the second overall goal of the subproject. The lattice strain is quantified experimentally in cooperation with TP6. Reference measurements on planar electrodes investigate in situ the mechanical modulation of the electrocatalytic reaction rate during fast mechanical strain cycles. The coupling coefficients determined in this case combine reactivity with elongation and, together with the measured data for the lattice parameter change, allow an estimation of the influence of mechanics in the studies on catalytic and electrocatalytic activity (in TP1 - TP4) of nanoporous metals. The experiments are performed in close consultation and feedback with TP7 and T8 (new), where the influence of strain on the absorption enthalpies of the different species is calculated.

Publications:

C. Mahr, K. Müller-Caspary, M. Graf, A. Lackmann, T. Grieb, M. Schowalter, F.F. Krause, T. Mehrtens, A. Wittstock,
J. Weissmüller and A. Rosenauer
Measurement of Local Lattice Strain in Dealloyed Nanoporous Gold
Materials Research Letters 6 (2018) 84–92.