Phase and Interface Design in Potential Earth-Abundant Multi-Component Photocatalysts

Abstract

Transition metal phosphides are low-cost, earth-abundant semiconductors with promising properties for photocatalysis, including water-splitting. When combined with other semiconductors or noble metals in nanoparticles, their photocatalytic performance can be drastically enhanced. Currently, significant research efforts are aiming to explore the facet and interface evolution and the correlation with their photocatalytic activity. However, the controlled formation of multi-component nanoparticles is not trivial due to the little knowledge of their formation mechanisms.

This thesis aims to provide a fundamental understanding of the Ni-Cu-P nano-system, including its dependence on the synthesis parameters. For that purpose, Ni-Cu nanoparticles reacting with phosphine were investigated under growth conditions using an environmental transmission electron microscope with an integrated gas handling system. The used setup allowed the assessment of dynamic processes during the synthesis and detailed characterisation of the products using power spectra of the acquired high-resolution transmission electron microscopy
images/movies and energy dispersive X-ray spectroscopy. The reaction of Ni-Cu nanoparticles with a relatively low phosphine flow yielded nanoparticles containing the Ni5P4 and Cu3P phases, whereas higher phosphine flows helped stabilise the Ni5P4 and CuP2 phases. Furthermore, annealing under different conditions enabled the nanoparticles’ rearrangement, including forming a single ternary phase and its separation.

This work provides a starting point for studying the Ni-Cu-P nano-system and demonstrates the impact of different parameters, such as the precursor flow and temperature, on forming different phases and their arrangement. Therefore, the obtained results will help progress in developing and designing sustainable photocatalysts to produce clean energy efficiently.

Popular Abstract

Green hydrogen is a potential candidate to be one of the future energy sources. It is a nonpollutant, sustainable and renewable fuel obtained via clean ways from water. However, current ways of producing hydrogen in a sustainable process are inefficient and expensive; therefore, more extensive efforts should be made to progress in green hydrogen production. The process of generating hydrogen from water and solar light using a photocatalyst is called photocatalysis. The photocatalyst is a material that increases the rate of a chemical reaction, and its design is the focus of this work.

An essential factor for efficiently promoting chemical reactions via light is the photocatalyst’s surface interacting with the reactants. Nanoparticles, structures a million times smaller than a metre, have a large surface-volume ratio and are therefore ideal catalysts. There is a wide range of materials used in photocatalysis. However, recent developments highlight the need to create sustainable and efficient materials to progress in this field. Transition metal phosphides are known for their excellent performance in photocatalysis due to their exceptional electronic and physical properties. Moreover, it is well-known in the literature that combining nanomaterials can drastically improve the performance of photocatalysts.

This thesis focuses on the controlled formation of nickel and copper-based phosphides. For this purpose, we created nanoparticles containing the two metals and exposed them to controlled flows of phosphine gas, resulting in the formation of transition metal phosphides. As their photocatalytic activity depends on the shape and structure of the nanoparticles, we investigated those properties in an electron microscope. Specifically, we studied the effect of different parameters, such as temperature and precursor flow, on the shape and structure of the nanoparticles. The obtained results provide a basic understanding of the nickel-copper-phosphorus system and highlight ways to design future photocatalysts with the potential to progress in clean energy production.

• author: Llorens Rauret, David
• supervisor: Michael Seifner
• organization: Department of Chemistry
• course: KEMP30 20221
• year: 2022
• type: L3 - Miscellaneous, Projetcs etc.
• subject: Chemistry
• keywords: Facet control, in-situ TEM, nanoparticle heterostructures, phase transformation, transition metal phosphides, inorganic nanomaterials
• language: English
• id: 9088673
• date added to LUP: 2022-06-17 09:30:18
• date last changed: 2022-06-17 09:30:18