Enhancement of Activity of Noble Metal Nanoparticles in Oxidative Electrocatalysis through Modification with Mixed-Metal Oxo-Species

Abstract

Platinum has been recognized as the most active catalytic metal towards oxidation of ethanol at low and moderate temperatures. But Pt anodes are readily poisoned by the strongly adsorbed intermediates, namely by CO-type species, requiring fairly high overpotentials for their removal. To enhance activity of Pt catalysts towards methanol and ethanol oxidation, additional metals including ruthenium, tin, molybdenum, tungsten or rhodium are usually introduced as the alloying component. More recently it has been 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 metal oxo species of tungsten, titanium or zirconium. Also gold in combination with platinum has been demonstrated to produce novel high performance bimetallic catalysts.We pursue a concept of utilization of hybrid mixed metal (tungsten(VI)/zirconium(IV), tungsten(VI)/titanium(IV), tungsten(VI)/cerium(IV)) oxides as matrices for supporting and activating noble metal nanoparticles (e.g. Pt, Pt-Ru, Pd, Ru or Rh) during electrooxidation of methanol, ethanol, dimethyl ether and formic acid. Remarkable increases of electrocatalytic currents measured under voltammetric and chronoamperometric conditions have been observed. The most likely explanation takes into account possibility of specific interactions of noble metals with transition metal oxide species as well as existence of active hydroxyl groups in the vicinity of catalytic noble metal sites.The concept of utilization of mixed metal oxide supports to active noble metal catalytic sites will be extended to oxidation of such inert reactants as arsenate(III) and nitrate(III) that of importance to analytical chemistry, namely to electroanalytical determinations of toxic oxoanions. Mechanistic considerations will be provided, and comparison will be made to the behavior of small organic molecules mentioned above.