Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Applied Physics | en_US |
| dc.contributor.advisor | Tsang, Yuen Hong (AP) | en_US |
| dc.creator | Guo, Zongliang | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/13936 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Synthesis and stabilization of 1T' phase transition metal dichalcogenides and hydrogen evolution reaction electrocatalyst application | en_US |
| dcterms.abstract | Research on transition metal dichalcogenides (TMDs) has gained significant attention in recent years, especially Group VI TMDs. The van der Waals gap, which lacks bonding between layers, provides opportunities for homo- or hetero-structure engineering by stacking in specific manners. Moreover, the multiple phases of TMDs represent various distinct structures and unique properties. While the well-known 2H phase is thermodynamically stable, the 1T’ phase of TMDs often exhibits remarkable and distinct properties. However, many TMDs in the 1T’ phase are metastable, which limits their practical applications and reliability. For example, 1T’-phase MoS₂, one of the most extensively studied TMDs, gradually transforms into the 2H phase over several months or instantly when exposed to temperatures above 97 °C. This critical drawback has greatly hindered the applications of 1T’ TMDs, as it leads to performance degeneration and low phase purity in synthesis process. In addition to the inherent disadvantage originating from metastable 1T’ phase structure, the synthesis of phase-pure 1T’ TMDs remains a huge challenge due to the low stability. Therefore, there is a pressing need for a technique to prepare 1T’ TMDs with high phase purity and stabilize them. | en_US |
| dcterms.abstract | This thesis introduces a simple, mass-production-capable method for directly synthesizing phase-pure 1T’ TMDs with alkali metal chalcogenides intercalation. The alkali-metal-chalcogenide-intercalated 1T’ TMDs have been directly grown at carefully controlled temperature, employing a proposed self-intercalation method which involves a strategy of utilizing the structure similarity between intercalated 1T’ TMDs and alkali metal molybdate. Experimental characterizations have confirmed that the as-synthesized 1T’ TMDs possessed nearly 100 % 1T’ phase purity and high crystal quality. This method only requires cheap precursors and a simple tube furnace with few-hour process, making this technique available for mass production. Moreover, various TMDs with multiple kinds of alkali metal chalcogenides intercalation have been successfully synthesized via this self-intercalation method, confirming the versatility of this technique. | en_US |
| dcterms.abstract | Notably, this is the first demonstration of stabilizing the 1T’ phase of TMDs through alkali metal chalcogenide intercalation. This method provides stability against high temperature (750 °C) and aging exposed to air for more than one year. The intercalated 1T’ MoS₂ represents stability against strong acid and usual solvents. Thanks to this stabilization and advanced synthesis process, the synthesized MoS₂ is 1T’ phase pure, avoiding the phase mixture issues common in other synthesis methods. The stabilization mechanism was investigated through theoretical calculations. It has been found that K₂S intercalation reduces the formation energy of 1T’ MoS₂, making it stable without altering the in-plane structure. The calculation results indicate that the N-doping and bonding formation in interlayer are two significant reasons for lowered formation energy. | en_US |
| dcterms.abstract | The 1T’ MoS₂ possess hydrogen evolution reaction (HER) electrocatalytically active sites at edge sites and basal planes, while 2H phase only has active sites at edge. Enhancing performance of 2H-MoS₂-based HER electrocatalysts typically requires doping or exposing more edge sites. However, employing 1T’ MoS₂ would inherently and significantly increases the active sites density for HER electrocatalysis, making it promising candidate for HER electrocatalytic application. The K₂S-intercalated 1T’ MoS₂, prepared by proposed self-intercalation method, exhibits excellent HER electrocatalytic performance, with a Tafel slope of 39.3 mV/dec and an overpotential of -73 mV at 10 mA/cm². It also demonstrates exceptional HER long-term stability, maintaining performance at 50 mA/cm² for 1000 hours and enduring 30000 cycles, outperforming many other TMD-based electrocatalysts. | en_US |
| dcterms.abstract | Self-intercalation method demonstrated in this thesis has proven versatile, enabling the synthesis of various 1T’ TMDs and fostering the exploration of their novel properties and the development of new applications. By eliminating the major disadvantage of the 1T’ phase’s instability, this synthesis and stabilization method opens up new avenues for the use of 1T’ TMDs in various advanced technologies. | en_US |
| dcterms.extent | xx, 139 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2025 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.accessRights | open access | en_US |
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