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Title: Binary clusters produced with cluster beam deposition for electrochemistry and heterogeneous catalysis
Author: Niu, Yubiao
ISNI:       0000 0004 7967 9422
Awarding Body: University of Birmingham
Current Institution: University of Birmingham
Date of Award: 2019
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This thesis describes the production, characterisation and catalytic performance of nanoclusters fabricated by cluster beam deposition using the magnetron sputtering, gas condensation technique. \(MoS_{2}\)-based clusters and Au-based clusters are demonstrated in electrochemistry (HER) and gas phase heterogeneous catalysis (CO oxidation), respectively. The atomic structure analysis of the clusters was performed with aberration-corrected scanning transmission electron microscope with high angle annular dark field (HAADF-STEM). Size-controlled \((MoS_{2}\)\()_{300}\) clusters deposited on amorphous carbon present an incomplete multi-layer structure with the absence of extended crystalline order. Such a layered structure was also found in \(Ni-MoS_{2}\) hybrid clusters [with a mass corresponding to \((MoS_{2}\)\()_{1000}\)] produced by dual target magnetron sputtering. Compared with \(MoS_{2}\) clusters, a significant enhancement in HER activity by \(Ni-MoS_{2}\) hybrid clusters was found. However, both \(MoS_{2}\) clusters (Mo:S = 1:0.9) and \(Ni-MoS_{2}\) clusters (Mo:S = 1:1.8) present a sulphur-deficient composition. In order to overcome the sulphur deficiency of the \(MoS_{2}\) clusters, a sulphur-enrichment technique based on a combination of sulphur addition (by sublimation) and annealing inside the cluster beam vacuum chamber was performed on size-selected \((MoS_{2}\)\()_{1000}\) clusters. This process led to a notable increase in extended crystallinity and a moderate increase in size (from 5.5 nm to 6.0 nm in diameter). Compared with \(Ni-MoS_{2}\) clusters, the sulphur-enriched \(MoS_{2}\) clusters show even more enhancement on the HER activities with more than 30-fold increases in exchange current densities. We have demonstrated a method of inhibiting the sintering of Au clusters in Au-based catalysis by exploring the stabilisation of supported Au clusters against sintering by alloying with Ti. Size-selected \(Au_{2057}\) (405, 229 amu) clusters and similar mass Au/Ti nanoalloy clusters (400, 000 amu) were produced by cluster beam deposition onto thin silica films. A strong anchoring effect was found in the case of Au/Ti clusters by HAADF-STEM experiments, consistent with DFT calculations by collaborators. Different sintering mechanisms were revealed between Au cluster dimers and Au/Ti cluster dimers. Preliminary CO oxidation measurements on Au and Au/Ti clusters indicates that Au/Ti clusters are promising as catalysts. Au/Ti clusters show catalytic activity on CO oxidation while Au clusters are non-active due to the serious sintering and the support effect.
Supervisor: Not available Sponsor: European Commission
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics