Importance of Support and Interactions with Noble Metal Nanocenters in Electrocatalysis

Recently there has been growing interest in low-temperature fuel cells as alternative sources of energy. The most commonly considered electrocatalytic systems (e.g. for oxygen reduction) utilize precious platinum and, therefore, there is a need to minimize contents of Pt (e.g. by activating it with certain metal oxo-species including polyoxometallates of tungsten) as well as to look for alternate molecular catalysts comprising metalloporphyrins or N-chelates combined with Ru-based chalcogenides, and bifunctional materials inducing reduction of both oxygen and hydrogen peroxide intermediate. Broad utilization of hydrogen-oxygen fuel cells would require development of effective means of hydrogen production and storage. In this context, the visible-light induced photelectrocatalytic water splitting is an important concept that will be addressed in this presentation as well. We have found that modification of a regular mesoporous WO₃ film with colloidal gold nanoparticles resulted in a significant improvement of the delivered photocurrent. Enhanced optical properties of WO₃ implemented with colloidal gold nanoparticles are induced by plasmonic excitation of gold nanoparticles.

The problem of oxygen reduction is even more severe case of alcohol-utilizing fuel cells. In this respect, heat-treated carbon-supported macrocyclic complexes and their derivatives as well as chalcogen modified transition metals are promising and selective (e.g. methanol tolerant) platinum-free catalysts for oxygen reduction.

Our research interests also concern development of electrocatalytic systems for the reduction of carbon dioxide. For example, as catalytic materials commercial palladium nanoparticles and the macromolecular complex of palladium, namely [Pd(C₁₄H₁₂N₂O₃)Cl₂]₂∙MeOH, were considered. The electrochemical data clearly imply that the process of electroreduction of carbon dioxide begins at the less negative potentials when pursued at the palladium complex in addition to the significant enhancement of the net (background-subtracted) CO₂-reduction current densities relative to those observed at conventional nanostructured palladium. Among important issues are specific interactions between nitrogen coordinating centers and electrogenerated metallic palladium sites at the electrocatalytic interface.

We have interest in the better understanding and controlling of electrocatalytic phenomena appearing in the direct alcohol fuel cells as alternative technology to hydrogen based electrochemical energy systems. The most common Pt anodes are readily poisoned by the strongly adsorbed intermediates, namely by CO-type species, requiring fairly high overpotentials for their removal. We have recently demonstrated that catalytic activity of platinum-based nanoparticles towards electrooxidation of ethanol has been significantly enhanced through interfacial modification with ultra-thin monolayer-type films of polyoxometallates  particularly heteropolymolybdates. Also gold in combination with platinum has been demonstrated to produce novel high performance bimetallic catalysts. We are going to describe here a concept of utilization of functionalized or mixed titanium dioxide, tungsten oxide or zirconium oxide matrices for supporting and activating noble metal nanoparticles (Pt, Pt-Ru or Pt-Rh) during electrooxidation of ethanol. We are going to consider protonically/electronically conducting zeolite-type cesium salts of Keggin-type heteropolyacids of molybdenum and tungsten as matrices for Vulcan-supported Pt, PtRu and PtSn nanoparticles during electrooxidation of methanol and ethanol.