Graf, Matthias

Haensch, Mareike

Nefedov, Alexei

Wang, Weijia

Wittstock, Gunther

Wöll, Christof

English

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dp = 6 ± 1 nmaCarl von Ossietzky University of Oldenburg, Institute of Chemistry, Oldenburg, Germany; bKarlsruhe Institute of Technology, Institute of Functional Interfaces, Eggenstein-Leopoldshafen, Germany, cHamburg University of Technology, Institute of Optical and Electronic Materials, Hamburg, Germany;… Nanoporous gold (NPG) is an unsupported bulk material with a bicontinuous poreand ligament structure. The high surface to volume ratio, high chemical flexibilityand tunability as well as high electrical and thermal conductivity makes it interestingas a prototype for a rational design of catalysts.When NPG is prepared by alloy corrosion of a Ag-Au alloy, residual Ag remains inthe otherwise pure gold structure.[1]Because Ag has an influence on the catalytic activity and stability of the NPGcatalyst[2] and Ag tends to segregate to the surface due to its lower free surfaceenergy,[3] XPS with different photon energies was used to determine the distributionof residual Ag in the near-surface regions of NPG.Investigated Nanoporous Gold Samplesdp = 6 ± 1 nm[1] L. V. Moskaleva, S. Röhe, A. Wittstock, V. Zielasek, T. Klüner, K. M. Neyman, M. Bäumer, Phys. Chem. Chem. Phys. 2011, 13, 4529.[2] T. Krekeler, A. V. Straßer, M. Graf, K. Wang, C. Hartig, M. Ritter, J. Weissmüller, Mater. Res. Lett.2017, 5, 314.[3] R. A. Manzhos, A. G. Krivenko, S. V. Doronin, M. A. Choba, V. A. Safonov, J. Electroanal. Chem. 2013, 704, 175.Sample Sample geometry Treatment LB / nmNPG_C_M cylindrical without support 100 CV cycles in a solution of 1 M MeOH + 1 M KOH between -0.5 V and 1.3 V 34.2 ± 8.3NPG_C_0 cylindrical without support 100 CV cycles in a solution of 1 M KOH between -0.5 V and 1.3 V 34.9 ± 8.9NPG_A_M cylindrical without support 5 min at 0.55 V vs. Hg/HgO in 1 M MeOH + 1 M KOH 42.3 ± 12.0NPG_A_0 cylindrical without support 5 min at 0.55 V vs. Hg/HgO in 1 M KOH 36.1 ± 9.2NPG_T cylindrical without support thermal annealing at 300 °C for 10 min 481.6 ± 120.1NPG_P cylindrical without support partial dealloying, stopped at χAg,bulk = 30 at. % 8.0 ± 1.7NPG_F thin film on glass support as dealloyed 10.2 ± 2.0NPG_F_T thin film on glass support thermal annealing at 300 °C for 5 min 12.3 ± 2.6Alloy corrosion or dealloying is the selective leaching of the less noble metal from an alloy, e.g. Ag-Au. In thiswork, NPG was dealloyed in a multistep potential program with increasing dealloying potentials to avoid crackingof the ligaments.Several different NPG samples were investigated towards their distribution of residual Ag.Methanol electrooxidation was chosen as a model electrocatalytic reaction.Exemplary XP spectra of Au 4f and Ag 3d for NPG recorded at Ekin = 145 eV (hν = 234 eV; A and B), 211 eV (hν = 300 eV; C and D) and 311 eV (hν = 400 eV; E and F). XP spectra of NPG at different photon energiesEkin of the emitted photoelectrons:A and B: Ekin = 145 eV, Information depth at Ekin:3 λ = 1.41 nm (Au), 1.59 nm (Ag) and : Ekin = 211 eV, 3 λ = 1.60 nm (Au), 1.71 nm (Ag)E and F: Ekin = 311 eV, 3 λ = 1.89 nm (Au), 2.01 nm (Ag)Fabrication of NPGSEM image of the cross-section of a NPG sampleInvestigation of residual Ag by X-ray photoelectron spectroscopyElemental fraction of Ag (a) and Au (b) in surface-near regions of NPG and elemental fractionnormalized by the bulk fraction as determined byEDX. Values > 1 indicate surface enrichment (Ag)and values < 1 indicate surface depletion (Au).The elemental fractions of Ag and Au were determined for all samples and plotted vs. theinformation depth (3λ) of the analysis.All NPG samples regardless of their treatment show anenrichment of Ag at the surface. The behavior is lesspronounced for high values of bulk residual Ag as in thepartially dealloyed sample.In conclusion, fractions of residual as determined by EDXor XPS with Al Kα radiation are much lower than actuallypresent at the surface of NPG.Residual Silver in Nanoporous Gold prepared by Alloy Corrosion Mareike Haenscha, Matthias Grafc, Weijia Wangb, Alexei Nefedovb Christof Wöllb and Gunther Wittstocka• n 0.1 M H2SO4 at 100 mV/sHESGM beamline of BESSY ǁ

Residual Silver in Nanoporous Gold prepared by Alloy Corrosion

https://publikationen.bibliothek.kit.edu/1000089694/21732424

Residual Silver in Nanoporous Gold prepared by Alloy Corrosion

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