Mixed layered WO3/ZrO2 films (with and without rhodium) as active supports for PtRu nanoparticles: enhancement of oxidation of ethanol

Mixed-valent tungsten(VI,V) oxide and zirconium(IV) oxide have been sequentially deposited and integrated through voltammetric potential cycling to form robust sub-microstructured mixed metal oxide (WO3/ZrO2) films on glassy carbon electrode. Attractive interactions between anionic tungstate units (of the inner WO3 layer) and cationic oxo-zirconium surface species (existing in acid media on ZrO2 nanostructures in the outer layer) tend to stabilize the mixed oxide system. By dispersing bimetallic platinum-ruthenium (PtRu) nanoparticles over such active WO3/ZrO2 supports, the activity of PtRu toward the oxidation of ethanol has been enhanced in terms of both increasing the electrocatalytic currents and lowering the onset potential of this reaction. The catalytic effect is more pronounced relative to the performance of PtRu nanoparticles deposited at the same loading of 100 μg cm−2 onto single-component metal oxide films, WO3 or ZrO2. Immobilization of rhodium nanoparticles onto WO3 inner layer (before over-coating with outer ZrO2 layer and deposition of PtRu) has led to further remarkable increases of electrocatalytic (voltammetric, chronoamperometric) currents recorded at the room temperature (22 °C) in 0.5 mol dm−3 H2SO4 containing 0.5 mol dm−3 ethanol. Among important issues is the initial activation of ethanol molecule (presumably by inducing the CC bond breaking) before catalytic electrooxidation at PtRu. Furthermore, the mixed WO3/ZrO2 film (support) is characterized by high acidity and fast charge (electron, proton) propagation during the system's redox transitions. High population of OH reactive groups and good mobility of protons (particularly at zirconia sites) is expected to increase activity of PtRu sites toward the oxidative removal of poisoning (CO) intermediates.