Quantized Electrodes: Atomic Palladium and Gold in Polyaniline

Abstract

Electrochemically deposited Pd m Au n metal clusters on a polyaniline-coated Pt electrode have been shown to exhibit an "ordering effect", in which the catalytic activity for n-propanol oxidation depends sensitively on the precise order that the metal atoms are deposited. For example, tri-atomic Pd 2 Au clusters exhibit different catalytic activity for electrodeposition order PdÀ PdÀ Au compared to PdÀ AuÀ Pd on the polyaniline (PANI)/Pt matrix. In this work, we utilize density functional theory (DFT) to elucidate the structure and energetics of triatomic Pd m Au n clusters attached to a model PANI support. We provide a rationale for the experimentally observed "ordering effect" in terms of specific covalent interactions between the metal atoms and PANI framework that alter the net stability of the metal catalyst. We find that hydroxyl radical binding energies computed for the model catalytic systems provide a good descriptor for the experimentally measured catalytic activity for n-propanol oxidation. In addition, the good correlation between experiment/theory serves as additional confirmation of our proposed catalytic structures and rationale of the previously unexplained "ordering effect". Our study highlights the important role of the PANI support in determining the activity of uniquely-defined, atomic metal catalysts.

Two-Step Electrochemical Au Nanoparticle Formation in Polyaniline

“…It will be demonstrated that the PANI/AuCl 4 − complex is stable prior to the reduction process. However, in contrast to the work of Janata et al [ 11 , 12 , 15 ], we do not see any signs of atomic Au species after the controlled reduction of these PANI/AuCl 4 − complexes. Instead, we do clearly observe the formation of Au NPs.…”

“…The latter even showed electrochemical activity towards the oxidation of alcohols with respect to their order of deposition [ 14 ]. Recently, these results were backed up by density functional theory calculations [ 15 ]. It was shown that such triatomic clusters of Au and Pd are indeed stabilized on the quinone ring by a large interaction energy.…”

Two-Step Electrochemical Au Nanoparticle Formation in Polyaniline

“…While the calculated curve also indicates a linear increase, there is a concentration difference of around 9×10 [17][18][19][20]. A different view is advocated by Janata and co-workers in their work on atomic metals [7,8,11,21,22]. Here, AuCl 4 − is reduced at its initial imine site resulting in a single Au atom which becomes stabilized in the PANI framework.…”

“…The latter even showed electrochemical activity towards the oxidation of alcohols with respect to their order of deposition [10]. Recently, these results were backed up by density functional theory calculations [11]. It was shown that such triatomic clusters of Au and Pd are indeed stabilized on the quinone ring by a large interaction energy.…”

Two-Step Electrochemical Au Nanoparticle Formation in Polyaniline

“…Besides Au, also Cl, F, O and N have been detected with the following average quantities across all measured samples: Cl=(1.12±0.49)×10 17 atoms/cm 2 , F=(4.22±3.76)×10 15 atoms/cm 2 , O= (3.06±0.53)×10 17 atoms/cm 2 , and N=(4.29±0.37)×10 17 atoms/cm 2 . The residual amounts of F must stem from the PANI deposition process which is carried out in HBF 4 .…”