Plasmonic nano-photocatalysts for light-induced alcohol oxidation

Photocatalytic oxidation of alcohols in the presence of plasmonic metals using oxygen as oxidizing agent is considered as a promising approach for efficient and green chemical transformations under mild conditions. In this direction, this Thesis demonstrates the synthesis of commercially valuable products such as benzaldehyde via the development of plasmonic-based nanomaterials as photocatalysts, along with design of continuous flow reactor, enabling high reaction rate and high selectivity of formed carbonyl compounds. Initially, the current state of photocatalytic oxidation of alcohols is summarized, the importance and fundamentals of plasmonic metal nanoparticles is presented while challenges and research gaps of the field are highlighted. Three experimental strategies were adopted in the Thesis. The first experimental part of the thesis focused on understanding the plasmonic heating effect generated by Au nanoparticles and particularly the surface plasmon resonance of Au nanoparticles by performing a well controlled experiment using a continuous flow system. The results revealed a significant temperature rise of Au-based nanofluids, with different Au loadings, compared to bare TiO2 nanofluid or pure water, which arise from the localized surface plasmon resonance effect of Au nanoparticles. The second experimental part of the thesis aimed to investigate the performance of plasmonic Au nanoparticles decorated on Cr2O3 microspheres towards the photocatalytic oxidation of benzyl alcohol. It has been shown that the amount of Au loading affected significantly the reaction efficiency, with 1.18 wt.% of Au loaded photocatalyst converting 81.4% of benzyl alcohol to benzaldehyde with a selectivity of 98.3% after 3 hours of laser irradiation. Additionally the plasmonic heating effect of Au nanoparticles contributed to a 26% oxidation rate enhancement using 1.18 wt.% Au. In the third experimental part, the effect of incorporating a second noble metal like Ag as well as the fabrication of a continuous flow reactor for comparison with a typical batch reactor were demonstrated. Bimetallic 0.34Ag-1.21Au/Cr2O3 photocatalyst converted 92.4% of benzyl alcohol to benzaldehyde with 98.8 % selectivity, which is 4.5 times that of pure Cr2O3 and 1.3 times of monometallic 1.18Au/Cr2O3. The results showed that the reaction rate under continuous flow conditions was almost an order of magnitude superior to the values achieved using batch reactor. Therefore, the findings of this Thesis highlight the need for development and optimization of continuous flow synthesis of carbonyl compounds in the presence of plasmonic metals, which can favour the conversion of alcohols in terms of reaction rate and selectivity

Techno-economic Assessment of a Hybrid Off-grid DC System for Combined Heat and Power Generation in Remote Islands

Hybrid renewable energy systems that combine heat and electricity generation is an achievable option for remote areas where grid is uneconomical to extend. In this study, a renewable-based system was designed to satisfy the electrical and thermal demands of a remote household in an off-grid Greek island. A hybrid DC system consisted of a combination of photovoltaic modules, wind turbine, electrolyzer-hydrogen tank, fuel cell and batteries were analysed using HOMER Pro software. Based on the optimal obtained system, it is found that such a system can satisfy both electrical and thermal load demand throughout the year in a reliable manner

Understanding improved capacity retention at 4.3 V in modified single crystal Ni-rich NMC//graphite pouch cells at elevated temperature

The capacity retention of commercially-sourced pouch cells with single crystal Al surface-doped Ni-rich cathodes (LiNi0.834Mn0.095Co0.071O2) is examined. The degradation-induced capacity fade becomes more pronounced as the upper-cut-off voltage (UCV) increases from 4.2 V to 4.3 V (vs. graphite) at a fixed cycling temperature (either 25 or 40 °C). However, cycles with 4.3 V UCV (slightly below the oxygen loss onset) show better capacity retention upon increasing the cycling temperature from 25 °C to 40 °C. Namely, after 500 cycles at 4.3 V UCV, cycling temperature at 40 °C retains 85.5% of the initial capacity while cycling at 25 °C shows 75.0% capacity retention. By employing a suite of electrochemical, X-ray spectroscopy and secondary ion mass spectrometry techniques, we attribute the temperature-induced improvement of the capacity retention at high UCV to the combined effects of Al surface-dopants, electrochemically resilient single crystal Ni-rich particles, and thermally-improved Li kinetics translating into better electrochemical performance. If cycling remains below the lattice oxygen loss onset, improved capacity retention in industrial cells should be achieved in single crystal Ni-rich cathodes with the appropriate choice of cycling parameter, particle quality, and particle surface dopants

Understanding improved capacity retention at 4.3 V in modified single crystal Ni-rich NMC//graphite pouch cells at elevated temperature

The capacity retention of commercially-sourced pouch cells with single crystal Al surface-doped Ni-rich cathodes (LiNi0.834Mn0.095Co0.071O2) is examined. The degradation-induced capacity fade becomes more pronounced as the upper-cut-off voltage (UCV) increases from 4.2 V to 4.3 V (vs. graphite) at a fixed cycling temperature (either 25 or 40 °C). However, cycles with 4.3 V UCV (slightly below the oxygen loss onset) show better capacity retention upon increasing the cycling temperature from 25 °C to 40 °C. Namely, after 500 cycles at 4.3 V UCV, cycling temperature at 40 °C retains 85.5% of the initial capacity while cycling at 25 °C shows 75.0% capacity retention. By employing a suite of electrochemical, X-ray spectroscopy and secondary ion mass spectrometry techniques, we attribute the temperature-induced improvement of the capacity retention at high UCV to the combined effects of Al surface-dopants, electrochemically resilient single crystal Ni-rich particles, and thermally-improved Li kinetics translating into better electrochemical performance. If cycling remains below the lattice oxygen loss onset, improved capacity retention in industrial cells should be achieved in single crystal Ni-rich cathodes with the appropriate choice of cycling parameter, particle quality, and particle surface dopants

Understanding improved capacity retention at 4.3 V in modified single crystal Ni-rich NMC//graphite pouch cells at elevated temperature

Acknowledgements: We thank Ieuan Ellis and Paul Malliband from the Battery Scale Up facility at WMG for their assistance. This work is supported by the Faraday Institution under grant no. FIRG060, no. FIRG024, and no. FIRG061. We acknowledge Diamond Light Source for time on beamline I09 under proposal SI25355-5 and SI27494-2.Al-surface doped Ni-rich single crystal material translates into better capacity retention in long-term cycling at higher UCV and cycling temperature.</jats:p