Efficient light absorption, for which the absorbing substrate should be designed in such a way that it provides as large a specific surface area as possible and good light trapping effect, is a critical point for photovoltaic devices. 3D structures could greatly increase specific surface area and help light absorption. AAO is a low-cost and easily accessible template to build ordered 3D structures, which is undergoing fast development. Many 3D substrates, such as metal nanospike arrays and organic polymer 3D structures, have been fabricated by AAO template-assisted method in recent years for different kinds of applications. However, compared to mostly used commercial FTO planar substrates, those 3D-structured substrates are generally unstable in strong base, acid or high tempe...[ Read more ]

Efficient light absorption, for which the absorbing substrate should be designed in such a way that it provides as large a specific surface area as possible and good light trapping effect, is a critical point for photovoltaic devices. 3D structures could greatly increase specific surface area and help light absorption. AAO is a low-cost and easily accessible template to build ordered 3D structures, which is undergoing fast development. Many 3D substrates, such as metal nanospike arrays and organic polymer 3D structures, have been fabricated by AAO template-assisted method in recent years for different kinds of applications. However, compared to mostly used commercial FTO planar substrates, those 3D-structured substrates are generally unstable in strong base, acid or high temperature environments.

With the growing shortage of fossil fuels, batteries, fuel cells and many kinds of solar-energy conversion devices have emerged as a class of more and more important technologies that increasingly rely on electrodes derived from nanoparticles. Among them, PEC cells have been experiencing fast developments. PEC cells offer the ability to convert the energy from our largest renewable source, the Sun, to stored chemical energy through the splitting of water into molecular oxygen and hydrogen. Among many commonly used PEC active materials, hematite (α-Fe₂O₃) has emerged as a promising photo-electrode material due to its significant light absorption, chemical stability in aqueous environments, and earth abundance. However, up to now, most of the hematite photoanodes were constructed on plane FTO substrate, which provided limited specific surface area and light absorption.

In this study, we have designed and fabricated 3D hexagonal ordered FTO nanocone array on glass substrate by using AAO template assisted method. Compared with planar FTO substrates, the 3D FTO substrate has greatly enlarged specific surface area and light trapping effect, which results in significant enhancement of PEC performance of deposited hematite. Besides, elemental doping also has great impact on PEC performance of hematite. We found that 8.5% Ti doping gave the highest photocurrent in our Ti-Fe2₂O₃ PEC system. In addition, the onset potential was significantly lowered by 360 m V when using cobalt phosphate (Co-Pi) as catalyst.

The thesis is organized as follows. In Chapter 1, I give a general introduction of the development of PEC water splitting, the existing problems and approaches. In Chapter 2, I demonstrate the fabrication process of the 30 FTO nanocone array substrate and discuss the technical details. In Chapter 3, I present the procedures for coating hematite layer onto the 30 FTO substrate by USP method and for fabricating the photoelectrodes for PEC testing together with the results of PEC performance. In Chapter 4, I analyze a series of influential factors on the PEC performance, including film thickness, precursor concentration, carrier gas flowing speed, Ti doping ratio and depositing method of Co-Pi catalyst, etc. At last, I provide a brief conclusion of my thesis in Chapter 5 and present an outlook of the future work with our 3D FTO substrates.