Composition and surface modifications of CuWO4 photoelectrodes for enhancing the efficiency of oxygen evolution reaction

• Grant number: 23/04793-7
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• Start date: September 01, 2023
• End date: August 01, 2024
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Nonmetallic Materials
• Principal Investigator: Jose Humberto Dias da Silva
• Grantee: Lucas Caniati Escaliante
• Supervisor: Frank Erich Osterloh
• Host Institution: Faculdade de Ciências (FC). Universidade Estadual Paulista (UNESP). Campus de Bauru. Bauru , SP, Brazil
• Institution abroad: University of California, Davis (UC Davis), United States
• Associated to the scholarship: 22/06542-9 - Development of CuWO4/CuWO4-x homojunctions and optimization of CuWO4 films for H2 photogeneration and pollutant photodegradation, BP.DR

Abstract

Copper tungstate (CuWO4) is a semiconductor with a 2.3 eV bandgap that is used in lithium batteries, sensors, photoelectrochemical (PEC), and photocatalytic (PC) applications. To successfully use thin films of these materials as PEC photoelectrodes their photocurrent and photovoltage need to be optimized. This optimization involves the knowledge of their surfaces and interfaces with the electrolytes. This highly complex problem is further complicated by the fact that the charge transfer processes at the solid-liquid interfaces occur in the presence of light. In order to address this problem, deposition and optimization of CuWO4 films, and the corresponding tests for PEC applications are proposed here. The aim is to better understand the interfaces of the films with the electrolyte in the presence of light, optimize the composition of materials and evaluate their efficiency in photoelectrochemical processes.The reactive co-sputtering technique, using independent Cu and W metallic targets operating simultaneously, was chosen to deposit the films for providing good control of the stoichiometry, and for allowing the growth over large areas. The oxygen will be introduced using different O2 proportions in the Ar plus O2 mixture of the working gas. Depositions under O2 flow modulation will also be made with the purpose of creating CuWO4/CuWO4-x homojunctions. These oxygen-depleted layers (CuWO4-x) are expected to have donor states and produce changes in the built-in electrical potential of the material at the surface and interface regions, which can favor the separation between photogenerated carriers, increasing the efficiency of the devices.Photoelectrochemical scans will be used to characterize the activity of the CuWO4 films for water oxidation. Surface Photovoltage Spectroscopy with a tool only available in the Osterloh lab at UC Davis will be used to observe the photovoltage of the films under vacuum or in liquid electrolytes as a function of the illumination wavelength. This will provide information about the majority carries, defects, and the internal photovoltage. (AU)