(Europe Section Alessandro Volta Medal) Structure, Reactivity and Durability of Hybrid Functional Materials in Electrocatalysis: CO2-Reduction Versus N2-Fixation
Authors: Kulesza Pawel , Rutkowska Iwona A. , Chmielnicka Anna , Rytelewska Beata 
Published: December 2024

Our research interests aim at establishing structure/property relations leading to rational designs of functionalized materials for efficient electrocatalysis and electrochemical energy conversion and storage. There has been growing interest in the electrochemical reduction of carbon dioxide, a potent greenhouse gas and a contributor to global climate change. Given the fact that the CO2 molecule is very stable, its electroreduction processes are characterized by large overpotentials. To optimize the hydrogenation-type electrocatalytic approach, we have proposed to utilize nanostructured metallic centers (e.g. Pd, Pt or Ru) in a form of highly dispersed and reactive nanoparticles generated within supramolecular network of distinct nitrogen, sulfur or oxygen-coordination complexes. Among important issues are the mutual completion between hydrogen evolution and carbon dioxide reduction and specific interactions between coordinating centers and metallic sites. We have also explored the ability of biofilms to form hydro-gel-type aggregates of microorganisms attached to various surfaces including those of carbon electrode materials. Upon incorporation of various noble metal nanostructures and/or conducting polymer ultra-thin films, highly reactive and selective systems toward CO2-reduction have been obtained. Another possibility to enhance electroreduction of carbon dioxide is to explore direct transformation of solar energy to chemical energy using transition metal oxide semiconductor materials. We show here that, by intentional and controlled combination of metal oxide semiconductors (titanium (IV) oxide and copper (I) oxide), we have been able to drive effectively photoelectrochemical reduction of carbon dioxide mostly to methanol.

Application of metal oxides as active matrices in electrocatalysis is particular importance. The hydrous behavior, which favors proton mobility and affects overall reactivity, reflects not only the oxide’s chemical properties but its texture and morphology as well. For example, the mixed WO3/ZrO2 systems are characterized by fast charge (electron, proton) propagation during the system’s redox transitions. By dispersing metallic Cu electrocatalytic nanoparticles over such active WO3/ZrO2 supports, the electrocatalytic activities of the respective systems toward the reduction of carbon dioxide have been enhanced even at decreased loadings in acid media. The fact that WO3/ZrO2 nanostructures are in immediate contact with the metallic catalytic sites leads to the specific interactions (via the surface hydroxyl groups) with the reaction intermediates (e.g. CO adsorbates).

Formation of ammonia is one of the most important chemical synthetic processes. Under industrial conditions, ammonia is primarily been synthesized from nitrogen and hydrogen via the Haber-Bosch process which requires pressurizing and heating, despite utilization of catalysts. Consequently, development of low-temperature synthetic methodology is tempting both from the practical and fundamental reasons. An ultimate goal for electrochemistry is to generate NH3 from N2 at temperatures lower than 100ºC, atmospheric pressure, and with use of new generation of catalysts. Currently, most of electrochemical approaches to drive N2-fixation suffer from slow kinetics due to the difficulty of achieving the appropriate adsorption and activation of dinitrogen molecule leading to cleavage of the strong triple N≡N bond. Our recent studies, clearly demonstrate that coordinatively stabilized iron catalytic sites, e.g. iron-centered heme-type porphyrins or iron phosphide, FeP and Fe2P phases, have been found to act as efficient catalysts for the formation of NH3 in alkaline and semi-neutral media.