Nanostructured electrodes for photoelectrochemical energy conversion

Abstract

Fossil fuel depletion and global warming are significant challenges associated with the development of national economies. To mitigate the environmental impact and reduce greenhouse gas emissions, there is a growing need to transition towards new and renewable energy sources. Hydrogen, with its high energy storage density and transportability, has emerged as a promising alternative to fossil fuels. It can be utilized in various applications such as internal combustion engines and fuel cells, offering the advantage of producing no greenhouse gas emissions, particularly carbon dioxide, during combustion. However, the current predominant method of hydrogen production, which relies on natural gas, still results in carbon dioxide emissions, limiting its environmental benefits. Therefore, the development of nature-friendly hydrogen production methods, such as photoelectrochemical water splitting using sunlight, has gained attention. In this process, a photoelectrochemical electrode absorbs sunlight in an electrolytic cell and facilitates the electrochemical decomposition of water into hydrogen and oxygen. To achieve efficient and stable performance, it is crucial to ensure both a high light absorption rate and electrolyte stability in the photoelectrochemical electrode. This paper presents an effective strategy for fabricating high-efficiency and stable photoelectrochemical electrodes. Specifically, it focuses on the selection of well-studied materials for photoelectrochemical electrodes and the incorporation of nanostructures to enhance performance while mitigating corrosion diffusion. Chapter 1 outlines the importance of developing environmentally friendly hydrogen production methods to address the pressing issue of global warming. It provides a theoretical background and discusses the requirements for photoelectrochemical electrodes and the development of nanostructures to improve performance. Chapter 2 demonstrates the efficiency improvement achieved through the fabrication of well-aligned silicon nano-hole photoelectrodes using the metal-assisted chemical etching method developed in this study. By utilizing an electric field to inhibit hole diffusion during etching, well-aligned nanoholes are formed, reducing light reflectance. The reduced surface porosity effectively lowers the recombination rate of electrons and holes, resulting in improved photoelectrochemical performance. Chapter 3, nanopixelated copper oxide photoelectrodes are fabricated to enhance optical properties and stability by impeding corrosion propagation. A novel electrode structure is introduced, featuring isolated nano-pixelated electrodes that enhance light absorption while minimizing corrosion at defect sites. By employing these strategies, the paper aims to advance the development of high-performance photoelectrochemical electrodes with improved efficiency and stability, contributing to the realization of sustainable hydrogen production.