(Invited) Application of Metal Oxide Active Supports for Enhancement of Electrocatalytic Reduction of Carbon Dioxide

Abstract

Of particular interest to the preparation of advanced catalytic materials is efficient utilization of catalytic sites (metal and metal oxide nanostructures, their stabilization and intentional activation, as well as organization into two-dimensional arrays, ultra-thin films or three-dimensional networks (e.g. through sequential deposition) on electrode surfaces. They can form nanosized materials with well-defined composition, structure and thickness that exhibit desirable electrocatalytic properties (e.g. toward reduction of CO2). We explore here the ability of polynuclear inorganic metal oxo systems to stabilize and functionalize metal (e.g. copper) nanostructures. Here certain nanostructured metal oxides of zirconium, titanium, zinc or tungsten have been demonstrated to influence supported metal (e.g. Cu, Fe, Ag) centers in ways other than simple dispersion over electrode area. Evidence is presented that the support can modify activity (presumably electronic nature) of the above mentioned catalytic metal nanocenters thus affecting their chemisorptive and catalytic properties. Metal oxide cocatalysts can generate –OH groups at low potentials that induce proton mobility at the photo(electro)chemical interface.Our research interests concern development of systems for the electrocatalytic reduction of carbon dioxide not only in neutral but also in acid media. For example, nanosized Cu or Fe catalytic centers immobilized within ultra-thin films of tungsten oxide or mixed ZrO2-WO3 films have been considered and demonstrated to exhibit synergism during CO2-reduction. Selectivity of the catalytic systems largely depends on the activing adsorptive (CO2) phenomena and the affinity of catalytic centers to the adsorbed carbon monoxide (CO) type intermediates leading to their protonation or hydrogenation. Reduction of carbon dioxide begins now at less negative potentials and is accompanied by significant enhancement of the CO2-reduction current densities relative to the competitive hydrogen evolution. Among other important issues is the ability of certain metal oxides (e.g., WO3) to affect hydrogen via intra-structural sorption of hydrogen molecules or atoms.