Nanocatalitzadors híbrids i funcionalitzats a la superfície per a la divisió d’aigua
- Autores: Laura Mallón Pernia
- Directores de la Tesis: Xavier Sala Román (dir. tes.), Roger Bofill Arasa (codir. tes.), Karine Ecard Philippot (codir. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2021
- Idioma: catalán
- Tribunal Calificador de la Tesis: Romuald Poteau (presid.), Pierluca Galloni (secret.), Andrea Sartorel (voc.), Karine Ecard Philippot (voc.), Sara Cavaliere (voc.)
- Programa de doctorado: Programa de Doctorado en Química por la Universidad Autónoma de Barcelona
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
One solution to achieve a carbon free energy source is the photoproduction of H2 by the catalytic water splitting (WS, Eq. 1) using sunlight.
2H2O + hv --> 2H2 + O2 (Eq. 1) WS is a process in which water is oxidized to dioxygen in the anode (oxygen evolution reaction, OER, Eq. 2), thus constituting the source of electrons to reduce protons to H2 in the cathode (hydrogen evolution reaction, HER, Eq. 3).
2H2O --> O2 + 4H+ + 4e- (Eq. 2) 2H+ + 2e- --> H2 (Eq. 3) Developing highly efficient and active WS catalysts is essential for the proper kinetics of these two reactions. Nanoparticles (NPs) are true potential catalysts due to their high stability and surface per volume ratio, exposing high amounts of active sites. In this PhD, different nanoelectrocatalysts have been synthesized by following the organometallic approach which is advantageous for obtaining clean-surface nanomaterials compared to other synthesis methodologies.
To understand the factors affecting the electrocatalytic activity of the nanomaterials, theoretical DFT calculations have been performed on the basis of well accepted concepts (hydrogen adsorption free energy, ΔGH*, and volcano plots). Given that the ligands present on the surface of metal NPs can influence the electrocatalytic activity, DFT calculations were performed to determine the most favorable coordination modes of different ligands and to obtain the ΔGH* values of the resulting NPs. Successful correlations between experimental and DFT data have been obtained.
Conductive C-based supports are known to enhance the electrocatalytic activity by restraining the aggregation of the nanocatalysts and improving the electron transfer from the metal nanocatalyst to the electrode. In this PhD, two different carbon materials, reduced graphene oxide (rGO) and carbon microfibers (CF) have been used as supports for metal NPs. Furthermore, the effect of N and P doping onto rGO has been studied towards the HER, obtaining a positive synergistic effect between the heteroatoms and Ru NPs. In contrast to graphene, CF are easier to handle and can be directly used as electrodes, thus avoiding the issues related to the NPs deposition onto macroscopic electrodes (GC, FTO). Thus, Ru and Co NPs have been synthesized on top of two different CF, differing in the presence or not of –COOH moieties onto the surface. Two different methodologies, in-situ and ex-situ, have been employed in order to tune the interface between the NPs and the C support by adding different solvents (THF or 1-heptanol) for Co NPs or ligands (4-phenylpyridine, 4PP) for Ru NPs. The results evidence that a proper interaction between the NPs and the support surface is key for an improved catalytic activity of the hybrid materials, obtaining better results in the systems where π-π interactions between Ru-4PP NPs/C structures or H-bonds between Co(OH)2 and COOH moieties in the CF take place.
Another promising strategy is the addition of another metal onto a metallic nanostructure, leading to beneficial synergistic electronic effects by changing the chemical environment of the metal centers and decreasing the adsorption energy of the reactants. In this sense, bimetallic Ru@Ni-foam and RuCo NPs systems were synthesized. The influence on the catalytic activity towards OER of different percentages of Ru-doping in Ru@Ni-foam systems has been studied. Finally, RuCo bimetallic systems were synthesized by using three different ligands, 4’-(4-methylphenyl)-2,2’:6’,2”-terpyridine, 4-PP and 1-heptanol. The influence of the ligand and the Ru/Co metal ratio on the size and morphology of the NPs has been determined. Preliminary electrocatalytic tests have been performed, opening a new door to explore the interest of bimetallic nanocatalysts for the water-splitting and the production of hydrogen.
