Browsing by Author "Feng, Yaying"
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Item Open Access Characterization of Bacterially Precipitated Cadmium Sulfide Nanoparticles for Photoelectrochemical Applications(2015) Feng, YayingCadmium sulfide (CdS) is one of the most commonly used II/VI semiconductor materials because of its electron energy band edge positions. CdS nanoparticles (NPs) are widely used in applications such as photodegradation of organic molecules, photocatalysis of water splitting, and as building blocks of photovoltaic devices. Bacterial precipitation of CdS NPs provides an innovative, environmentally friendly route for the synthesis of NPs with controllable electronic properties. Our previous research shows that CdS NPs can be extracellularly precipitated with tunable CdS crystallite sizes ranging from 5 nm to over 15 nm in diameter. In this thesis, I investigated the potential application of these bacterially precipitated CdS NPs for photodegradation of organic molecules, photocurrent generation, and for photoelectrochemical (PEC) hydrogen evolution. The results show that the bacterially precipitated CdS NPs and their devices performed competitively when compared with their counterparts that were synthesized via chemical bath deposition (CBD). In photodegradation experiments, the bacterially precipitated CdS NPs showed a slower rate of degradation than CBD CdS. In transient photocurrent response experiments, the devices incorporating bacterially precipitated CdS NPs showed a higher current response to visible light. Furthermore, in electrochemical hydrogen generation experiments, the bacterially precipitated CdS NP device showed a lower onset potential to trigger the reaction when irradiated with light. Collectively, the preliminary results show that biosynthesized CdS NPs have potentially promising applications for the photodegradation of organic molecules and for the photoelectrochemical hydrogen generation.
Item Open Access Stretchable and high-performance supercapacitors with crumpled graphene papers.(Scientific reports, 2014-10) Zang, Jianfeng; Cao, Changyong; Feng, Yaying; Liu, Jie; Zhao, XuanheFabrication of unconventional energy storage devices with high stretchability and performance is challenging, but critical to practical operations of fully power-independent stretchable electronics. While supercapacitors represent a promising candidate for unconventional energy-storage devices, existing stretchable supercapacitors are limited by their low stretchability, complicated fabrication process, and high cost. Here, we report a simple and low-cost method to fabricate extremely stretchable and high-performance electrodes for supercapacitors based on new crumpled-graphene papers. Electrolyte-mediated-graphene paper bonded on a compliant substrate can be crumpled into self-organized patterns by harnessing mechanical instabilities in the graphene paper. As the substrate is stretched, the crumpled patterns unfold, maintaining high reliability of the graphene paper under multiple cycles of large deformation. Supercapacitor electrodes based on the crumpled graphene papers exhibit a unique combination of high stretchability (e.g., linear strain ~300%, areal strain ~800%), high electrochemical performance (e.g., specific capacitance ~196 F g(-1)), and high reliability (e.g., over 1000 stretch/relax cycles). An all-solid-state supercapacitor capable of large deformation is further fabricated to demonstrate practical applications of the crumpled-graphene-paper electrodes. Our method and design open a wide range of opportunities for manufacturing future energy-storage devices with desired deformability together with high performance.Item Open Access Transition Metal Chalcogenide (Cadmium Sulfide) Nanoparticles: (Bio)synthesis, Characterization and Photoelectrochemical Performance(2019) Feng, YayingCadmium sulfide (CdS) is one of the most commonly used and studied II/VI semiconductor materials due to its electron energy band structure with desirable band edges and direct band gap. CdS nanoparticles (NPs) are widely applied in different areas such as biosensing, antibacterial agents, photocatalytic hydrogen evolution, photoelectrochemical (PEC) energy conversion, and photovoltaic devices. Biosynthesis is an innovative, environmentally friendly route for the synthesis of CdS NPs. Specifically, bacterial precipitation of CdS NPs provides a simple, scalable production method. Our previous research shows that CdS NPs can be extracellularly precipitated with tunable CdS crystallite sizes ranging from 5 nm to over 15 nm in diameter. In this dissertation, I investigated the potential PEC application of bacterially precipitated NPs and the engineering of their band structure. The results show that i) bacterially precipitated CdS NPs and their devices performed competitively when compared to chemical bath deposited (CBD) CdS NPs and their devices; ii) the performance difference is likely due to a layer of organic ligands that cap the bacterially precipitated CdS NPs and changed the carrier dynamics; and iii) the band structure of bacterially precipitated CdS NPs can be tuned by using different capping ligands. Collectively, my research demonstrates a promising approach for the biosynthetic precipitation of CdS NPS with tunable electronic properties and their application potential in photoelectrochemical devices.