Dinâmica de cargas em semicondutores para fotoeletrólise

Abstract

The present work aims to study the dynamics of charges in nanostructured iron oxide semiconductors in the hematite phase (α-Fe2O3) and hematite modified with Na1+, Zn2+ and Ta5+ used in the generation of hydrogen through photoelectrolysis, a clean, sustainable approach and renewable for fuel production. Photoelectrolysis takes place in a photoelectrochemical (PEC) cell composed of two electrodes, at least one of which is a photoactive semiconductor, immersed in an electrolyte solution and connected by an external circuit. Hematite is studied in this work for use as a photoanode, where the water oxidation reaction occurs, which is the current bottleneck for hydrogen production due to its greater complexity. Recently, an increase in the efficiency of hematite films modified with tetra and pentavalent elements through the method of polymeric precursors with deposition via spin-coating was observed. This increase was induced by the segregation of these elements preferentially on the grain boundaries of the hematite surface. Seeking to assess whether this effect was due to the route of synthesis or to the type of modifier used (Noxidation > 3+), elements with an oxidation number lower than that of Fe3+ were used, as well as a pentavalent element as hematite modifiers by the described method. In order to determine the effects on the load dynamics caused by each element and the position in which each one acted on the photoelectrode structure, measurements of structural, morphological and (photo)electrochemical characterizations were carried out. Although the elements with oxidation numbers lower than Fe3+ have contributed to the increase in the thickness of the films, it was not possible to conclude from the characterizations carried out where these elements acted in the structure of the films and further analyzes are in progress. However, it was observed that these elements worsen or do not modify (Na1+) the hematite charge dynamics processes while the pentavalent element (Ta5+) is responsible for increasing the charge separation efficiency and the external quantum efficiency, reducing the rates surface and bulk recombination as effects of its segregation on the hematite surface.