Boosting photo(electro)catalytic reactions: solvent organization and electrode design

This thesis deals with two different projects tackled during my PhD program. The goal of both projects is to shed light on the specific aspects involved into the improvement of the performances of two distinct energy related processes, i.e., the hydrogen production from water and the ethanol oxidation reaction (EOR). Namely the first project is a combined theoretical and experimental researc h work and is related to the hydrogen production process by photocatalytic water splitting. Concerning this topic, most of the studies reported in literature are focused on the development of strategies for controlling the photocatalyst’s properties in order to obtain the best performing material. By contrast, limited attention was given to the role of the reaction medium. The main result of this project is that water can not be simply considered a passive medium but rather the water molecules , acting as proton donor or can boost the reaction itself . In particular, it is investigated how the structure of water at the water semiconductor interface influences the rate of water splitting. This first part of this PhD thesis is divided in two chapters. Chapter 1 focuses on the experimental study, specifically we have: 1. Synthetized two photocatalysts (an undoped TiO2 and a B doped TiO2 ) exhibiting a different rate of H2 production, but no significant differences in the physical chemical properties. 2. Demonstrated , by performing Fourier Transform Infrared (FTIR) spectroscopic measurements under controlled relative humidity (RH) conditions, that the main responsible of the different photocatalytic activity is the structure of the interfacial water. These experimental activities were carried out in Laboratory of Catalysis for Sustainable Production and Energy (CASPE/INSTM) of the Department Chemical, Biological, Pharmaceutical and Environmental Science (ChiBioFarAm) and in the Optical Spectroscopic Laboratory of the Department of Mathematical and Computer Sciences, Physical Sciences and Earth Sciences (MIFT) of the University of Messina. Chapter 2 deals with the computational results. Indeed, density functional theory molecular dynamic (DFT MD) simulations were performed in order to better understand how the structural organization of water at the interface with a photocatalyst determines the water splitting performances. To the best of our knowledge, in most of the computational literature published works concerning the water splitting on TiO2, the water is at the best represented as an implicit solvent or using just a single layer of explicit water molecules. In our work, the innovative element that allows to give a more realistic description of the interaction of water with the TiO2 surface is the consideration of an entire liquid water slab (132 water molecules) in direct contact with the photocatalyst , i.e., an explicit solvent scheme. This computational study was conducted in collaboration with Dr. Fabrizio Marco Creazzo (Department of Chemistry, University of Zürich, Zürich, Switzerland) and Dr. Giuseppe Cassone (Institute for Chemical Physical Processes, National Research Council of Italy (IPCF CNR), Messina, Italy). The second research project was developed during my abroad research period at the Institut Català d’Investigació Quimìca (ICIQ, Tarragona, Spain) under the supervision of Professor José Ramón Galán Mascarós in the framework of the European Project DECADE (DistributEd Chemicals And fuels production from CO2 in photoelectrocatalytic DEvices). With respect to the previous project, this one is more applicative and relies on the design, fabrication and testing of an highly performing and stable electrocatalyst for realizing the ethanol oxidation reaction (EOR) under extreme conditions (concentrated ethanol 96%). The final goal is to use this catalyst in a new kind of PEC cell that provides an effective way to harness the solar energy for catalyzing the CO2 reduction and the EOR on the cathodic and anodic sides respectively to selectively produce the same product i.e., ethyl acetate).