Electrocatalysis and Bioelectrocatalysis at Network Films of Metal Nanoparticles and Carbon Nanostructures
|Paweł J. Kulesza , Katarzyna A. Karnicka , Barbara Kowalewska , Magdalena Skunik , Beata Baranowska , Andrzej Ernst , Przemysław Ziaja , Krzysztof Miecznikowski , Malgorzata Chojak|
Warsaw University, Faculty of Chemistry, Pasteura 1, Warszawa 02-093, Poland
There has been a growing interest in the fabrication of organized monomolecular (monolayer) and multilayered assemblies at solid surfaces. Most of research concerns alkanothiols and their derivatives that can be successfully employed to obtain monolayer coverages on gold. An interesting alternative originates from the possibility of self-assembling inorganic (e.g. polyoxometallate) monolayers because they provide potentially better stability, and they undergo reversible stepwise electron transfer reactions of importance to such technologies as electrocatalysis, electrochromism, molecular electronics and sensing. We have recently pursued the concept based on multiple formation of two-dimensional arrays composed alternately of a conducting polymer, such as polyaniline or polypyrrole, and a heteropolyanion of molybdenum or tungsten. Monolayers of alkanothiolates are capable of passivating gold nanoparticles and producing alkanothiolate monolayer protected clusters of gold. They combine bulk and molecular properties within a nanometer scale material that is expected to yield novel and promising size-dependent electronic, optical and chemical properties. We have explore the ability of polyoxometallates (phosphotungstate, phosphomolybdate) to form self-assembled monolayers on metal (e.g. Pt or Au) nanoparticles (ca. 2-7 nm) or carbon nanotubes. Such polyoxometallate modified nanostructures can be linked together by ultra thin conducting polymer (polyaniline, polypyrrole, PEDOT) bridges. The formation, morphology, structural transformations and electrochemical properties of the nanoparticle containing three-dimensional network films are examined using cyclic voltammetry, potential step techniques, microgravimmetry, FTIR spectroscopy, STM and scanning electrochemical microscopy. The network films composed of polyoxometallates, ultra-thin conducting polymer layers and platinum or carbon nanostructures can produce interfaces with specific electrocatalytic properties towards reduction of such inert reactants as oxygen, hydrogen peroxide or bromate. Electrocatalytic systems that would be useful in biological media, or the systems utilizing biocatalysts (enzymes), have to operate in neutral solutions. Recently, there has been growing interest in the fabrication of stable highly effective bio-electrocatalytic systems for oxygen reduction, particularly with respect to potential applications in biofuel cells. Unless highly specific and expensive enzymes belonging to a group of proteins with the copper active centers, such as bilirubin oxidase or laccase, are considered, the reduction of oxygen in neutral media is a two-step process suffering from the formation of hydrogen peroxide as undesirable intermediate product. Although the above enzymes are capable of the effective four electron reduction of oxygen to water in neutral media, and significant progress have recently been made in their practical utilization, there is a need to look for alternate bio-electrocatalytic systems. To facilitate electron transfers between the electrode surface and the redox protein centers, the concept of co-deposition of multi-walled carbon nanotubes (CNTs) within the bio-electrocatalytic film has been recently proposed. Good electronic conductivity of CNTs, together with their mechanical stability, have made them attractive for potential applications in electrochemistry and bio-electrochemistry. Representative examples include cases of electrocatalytic reductions of hydrogen peroxide and oxygen. To stabilize composite films, we utilize multi-walled carbon nanotubes, that have been modified with ultra-thin layers of organic (e.g. 4-(pyrrole-1-yl) benzoic acid or ABTS) and inorganic metal oxo compounds. We expect here attractive interactions between anionic adsorbates and positively charged domains of the enzymatic sites. The other important issues are stability and mediating capabilities of adsorbates.
Presentation: Tutorial lecture at SMCBS'2007 International Workshop, by Paweł J. Kulesza
See On-line Journal of SMCBS'2007 International Workshop
Submitted: 2007-09-07 16:37 Revised: 2009-06-07 00:44