Characterisation of Silicon Nanowires Across the Solar Spectrum for Enhanced Photocatalysis

Abstract

Nanowires are promising structures for improving light absorption due to their enhanced optical properties compared to bulk materials. Silicon is a suitable semiconducting material for driving water splitting in a photoelectrochemical (PEC) cell, and is particularly attractive due to its small bandgap as well as its relative abundance and low cost. PEC cells can be enhanced by including silicon nanowires to harness most of the solar spectrum and split water more efficiently, and this will be investigated in this report. Absorption properties of various silicon-based samples are evaluated. For applications in a PEC cell however, additional protective layers are required to improve the stability of silicon in an aqueous environment. TiN and NiOx are investigated for their effects on absorption as well as PEC performance of the nanowires. TiN results in much improved absorption and water-splitting efficiencies, particularly in the near-infrared region of the solar spectrum. NiOx results in further improved absorption and PEC performance. Comparisons between different silicon-based samples are made and performance is examined at individual wavelengths of light across the solar spectrum. Further analyses of performance are recommended, including stability assessments for PEC cells.

Popular Abstract

Photo-electrochemical (PEC) cells can harness energy from the sun to produce ‘green hydrogen’ from water, combining two abundant natural resources on earth to make a fuel that produces zero carbon emissions when burned. Currently, hydrogen gas is mostly produced from natural gas as well as oil and coal, with only about 4% of hydrogen produced by the chemical reaction known as water splitting. Using PEC cells to capture solar energy and split water could potentially reduce the global reliance on carbon-intensive activities for producing hydrogen. The process involves sunlight falling on a semiconductor (a material with conductivity between an insulator and a metal) in contact with water, and the energy from sunlight being used to split water (H2O) into hydrogen gas (H2) and oxygen gas (O2). This process is advantageous for energy storage, as solar energy is intermittent and can’t be easily stored whereas H2 and O2 store energy in their chemical bonds. Silicon is the most widely used semiconductor in the electronics industry because it is cheap, abundant, and has interesting properties. One of the most interesting properties is that silicon absorbs sunlight better than most semiconductors, which makes it suitable for use in a PEC cell. Nanowires (wires with a diameter of a few nm) grown on the surface of silicon allow it to absorb
even more sunlight. This project experimentally determined how efficiently silicon nanowires could perform in a PEC cell under different light conditions. Catalysts were also added to silicon which further improved the water splitting efficiency of the cell. The catalysts also protected silicon from experiencing corrosion, or degradation, in the water while the cell was operating. Stable performance of a PEC cell over time is required for a cell to operate in the long term without significant degradation. Tests to determine the stability of these silicon nanowire-based PEC cells are recommended as future work.

• author: Buttimer, Alexandra Nolan
• supervisor: Jens Uhlig
• organization: Atomic Physics; Department of Physics
• course: PHYM03 20241
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry
• keywords: Photocatalysis, water splitting
• language: English
• id: 9175952
• date added to LUP: 2024-11-05 07:58:57
• date last changed: 2024-11-05 07:58:57