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.