Polyaniline Electrodes Containing Tri-Atomic Au/Pd Clusters: Effect of Ordering

Two-Step Electrochemical Au Nanoparticle Formation in Polyaniline

In this work, we use a two-step cyclic electrochemical process to insert Au into polyaniline (PANI). It was suggested previously that this method would lead to the formation of atomic Au clusters with controlleds number of Au atoms without providing morphological proof. In each cycle, tetrachloroaurate anions (AuCl₄^-) are attached on the protonated imine sites of PANI, followed by a controlled reduction using cyclic voltammetry (CV). In contrast to previous work, we demonstrate that the reduction leads to the nucleation and growth of an Au nanoparticle (NP) whose density and size dispersion depend on the Au loading in PANI. Adding more deposition cycles increases the Au NP density and size. Transmission electron microscopy (TEM) and corresponding energy dispersive X-ray spectroscopy (EDS) indicate a homogeneous distribution of Au elements in the PANI matrix before CV reduction, while Au elements are aggregated and clearly localized in the NPs positions after CV reduction. We further use Rutherford backscattering spectrometry (RBS) to quantify the Au uptake in PANI. The Au distribution is verified to be initially homogeneous across the PANI layer whereas the increasing number of deposition cycles leads to a surface segregation of Au. We propose a two-step growth model based on our experimental results. Finally, we discuss the results with respect to the formation of atomic Au clusters reported previously using the same deposition method.

Developments of the Electroactive Materials for Non-Enzymatic Glucose Sensing and Their Mechanisms

A comprehensive review of the electroactive materials for non-enzymatic glucose sensing and sensing devices has been performed in this work. A general introduction for glucose sensing, a facile electrochemical technique for glucose detection, and explanations of fundamental mechanisms for the electro-oxidation of glucose via the electrochemical technique are conducted. The glucose sensing materials are classified into five major systems: (1) mono-metallic materials, (2) bi-metallic materials, (3) metallic-oxide compounds, (4) metallic-hydroxide materials, and (5) metal-metal derivatives. The performances of various systems within this decade have been compared and explained in terms of sensitivity, linear regime, the limit of detection (LOD), and detection potentials. Some promising materials and practicable methodologies for the further developments of glucose sensors have been proposed. Firstly, the atomic deposition of alloys is expected to enhance the selectivity, which is considered to be lacking in non-enzymatic glucose sensing. Secondly, by using the modification of the hydrophilicity of the metallic-oxides, a promoted current response from the electro-oxidation of glucose is expected. Lastly, by taking the advantage of the redistribution phenomenon of the oxide particles, the usage of the noble metals is foreseen to be reduced.

Effects of Palladium(II) Chlorocomplex Speciation on the Controlled Interaction with a Polyaniline Film in Acid

In this study, we determined the Pd(II) chlorocomplex species that has the most favorable interaction with an electropolymerized and protonated polyaniline (PANI) film. This study was completed with the intent to use this species to electrochemically build atomic palladium clusters in the PANI matrix. Varying amounts of NaCl were added to a K₂PdCl₄/HClO₄ solution to result in three species studied: PdCl₂(H₂O)₂, PdCl₃(H₂O)^-, and PdCl₄^2-. UV-vis spectroscopy was used to confirm the speciation, and Raman spectroscopy, X-ray photoelectron spectroscopy, and cyclic voltammograms were used to probe the interaction between the Pd species and PANI. It was determined that PdCl₃(H₂O)^- most effectively interacts with PANI as a result of the charge balance between the anion and the protonated nitrogen-containing groups in the polymer. It has been also found that some fraction of inserted Pd(II) cannot be reduced to Pd(0).