Stable Anion–Cation Layers on Cu(111) under Reactive Conditions

Abstract

Combined voltammetric and in-situ STM studies were employed to gain information about the structure of a sulfate-modified Cu(111) electrode surface exposed to an acidic electrolyte containing a redox-active porphyrin (meso-tetra(N-methyl-4-pyridyl)-porphine, abbreviated as [H 2 TMPyP] 4+ ). A particular focus of this study lies on the characterization of the interfacial structure under reactive conditions, for example, during an ongoing electron transfer reaction. The oxidized form of [H 2 TMPyP] 4+ cannot be stabilized within the narrow potential window of copper. A two-electron transfer reduction affects the central porphine core even at the anodic limit of the copper potential window close to the onset of the oxidative copper dissolution reaction. This porphyrin-related electron transfer reaction can take place even in the presence of a preadsorbed sulfate/ water coadsorption layer. The latter causes a charge inversion at the metal/anion interface with an excess of negative charges within the sulfate/water layer. Enhanced electrostatic interactions between this sulfate/water coadsorption layer and the cationic porphyrin reactants and reaction products are discussed as the physical origin for the formation of a paired anion-cation layer at the interface that retains its structural integrity even during the ongoing electron transfer reaction, at least on the time scale of the STM experiment. It is the starting sulfate desorption at more negative potentials that causes the loss of lateral order within this paired anion-cation layer. Highly water-soluble cationic porphyrin species coadsorb/codesorb together with the sulfate anions onto/from the Cu(111) electrode.

Characterization of Through-Hole Filling by Copper Electroplating Using a Tetrazolium Salt Inhibitor

“…Reaction 2 represents NTBC adsorption on the copper surface via the anchoring effect of the chloride ions, which explains why a high chloride ion concentration results in strong inhibition of NTBC. The tetrazolium rings can lie flat on the copper surface (similar to the adsorption of porphyrin-based molecules on a copper surface 42,43 ) to block the diffusion of copper ions to the cathodic surface, and thus, they can protect the copper surface from corrosion by chloride ions. 44 Hence, they are easily incorporated into the copper deposited in the absence of acid.…”

Organic layers at metal/electrolyte interfaces: molecular structure and reactivity of viologen monolayers

“…The interfacial behavior becomes even more complex when reactants and/or products of the electron transfer process remain adsorbed on the anion-modified electrode surface prior to or during the reaction. Provided the anions retain to a large extent their negative charge upon specific adsorption, the subsequent adsorption of cationic reactants from the electrolyte onto the electrode surface will be facilitated through electrostatic attraction, thus, giving rise to the formation of 'paired'anion-cation layers [6]- [10], which remain stable even during an ongoing electron transfer reaction of the 'bulk' solution species [7,11]. Such an anion-cation layering has recently been reported for the adsorption and subsequent reaction of redox-active viologens [12,13] (1,1 -disubstituted-4,4 -bipyridinium molecules) on a chloridemodified Cu(100) electrode surface [7,8,10].…”

Recent Progresses of Electrochemical Surface Science ∼Importance of Surface Imaging with Atomic Scale∼

“…Another group formed a highly ordered array of TMPyP on a sulfate/bisulfate adlayer on a Cu(111) surface. 76 Highly ordered arrays of various organic molecules can be found on chloride-modified Cu(100), 77,78 I-Cu(111), bromine-modified Au(111), 79 and sulfate adlayers on Au(111). 80 Thus, two-dimensional organization of water-soluble porphyrins has been achieved at electrochemical interfaces.…”