R-020

Iwona A. Rutkowska

ilinek@chem.uw.edu.pl

Anna Chmielnicka, Pawel J. Kulesza 

Faculty of Chemistry, University of Warsaw, Poland

Optimization of electrocatalytic systems toward selective CO2-reduction in acid medium

There has been growing interest in the electrochemical reduction of carbon dioxide (CO2), a potent greenhouse gas and a contributor to global climate change, and its conversion into useful carbon-based fuels or chemicals. To produce highly efficient and selective electrocatalysts, the transition-metal-based molecular materials are often considered. To optimize the conventional copper-based electrocatalytic approach, we explore such a model catalytic matrix as nanostructured tungsten oxide nanowires which are capable to undergo partial reduction to hydrogen-rich nonstoichiometric tungsten oxide bronzes. We demonstrate here that following the intercalation of copper into tungsten(VI)-oxide-nanowires, the resulting electrocatalytic systems exhibits synergistic properties toward electroreduction of carbon dioxide. In particular, evidence has been provided that the hybrid Cu/WO3 catalyst can be successfully utilized to drive reduction of carbon dioxide (saturated solution, concentration, ca. 0.033 mol dm-3) in a fairly strong acid medium of 0.5 mol dm-3 H2SO4. Here formation of the partially reduced tungsten oxides (HxWO3 and WO3-y) is accompanied by consumption of protons and sorption of hydrogen, and it tends to inhibit hydrogen evolution by shifting the proton discharge toward more negative potentials. Our observations are consistent with the view that copper is irreversibly trapped (i.e., it cannot be reoxidized) within the network of WO3 nanowires. On mechanistic grounds, the existence of hydrogen-rich partially-reduced tungsten oxides, HxWO3, which contain large population of delocalized electrons and monoatomic H, are likely to induce hydrogenation of carbon oxo species, followed by protonation, in the vicinity of Cu to form oxo-hydrocarbon-type products. Our research aiming at optimization the material’s activity and selectivity has also concentrated on application of mixed oxides, e.g. WO3-ZrO2. Finally, the present study demonstrates usefulness of certain diagnostic electroanalytical approaches, such as chronocoulometric probing of the diffusional-type charge propagation dynamics, or voltammetric monitoring of small organic or inorganic molecules as electroreduction products.