Browsing by Author "Li, Jialang"

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    Cell Design and Electrode Material for All Vanadium Redox Flow Battery
    (2018-03-09) Li, Jialang; Roberts, Edward P. L.; Ponnurangam, Sathish; Mahinpey, Nader; Roberts, Edward
    The all-vanadium redox flow battery (VRFB) is one of the most promising renewable energy storage systems due to its high energy efficiency, reliability, design flexibility and environmental friendly. In order to improve the performance of VRFB, cell design and electrode materials were studied in this project. A novel flow field design using a flow going through the porous electrode for the VRFB has been evaluated. By dividing the flow between flow-by and a portion of the flow going through the electrode, a significant improvement in the performance was obtained. A vanadium electrolyte system was used and charging and discharging cycles were performed and compared with the flow-by design. With a portion of flow going through the electrode, the voltage efficiency was increased from 74% to 80% and the voltage loss was decreased by 23%. The results indicate that the “flow through” condition can enhance the mass transfer rate at the surface of electrode. A templated nano-carbon scaffold (NCS) electrode material was evaluated for using in the VRFB. Scanning electron microscopy (SEM) was used to characterize the morphology of the electrode materials. This material has an organized nanoporous structure and the pore size can be as small as 22 nm. To investigate the performance of NCS as an electrode material, the NCS was attached to the surface of conventional carbon paper electrodes. The charge discharge performance of the VRFB was determined using a flow through mode of operation. The performance of nano carbon scaffold (NCS) with different pore size and thickness was compared with a conventional heat-treated carbon paper. The results show that by using nano carbon scaffold (NCS-85-HT), the voltage efficiency increased from 74% to 91% at 10 mA cm-2. The energy efficiency also increased from 56% to 70% at 10 mAcm-2 due to the increased voltage efficiency. The results indicate that the large surface area of the NCS, associated with its nano structure, lead to a reduction in overpotential of around 65%, and thus higher battery efficiencies. Cell performance under different current density was also explored and the improved efficiencies for NCS were maintained at all the current densities studied.
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    Tuning the Catalytic Performance of Nitrogen- and Iron-Nitrogen-Doped Mesoporous Carbons for CO2 Reduction
    (2024-09-20) Li, Jialang; Birss, Viola; Heyne, Belinda; Roesler, Roland; Thangadurai, Venkataraman; Kibria, Md; Aicheng, Chen
    This thesis systematically explores the catalytic performance of nitrogen-doped and iron-nitrogen co-doped mesoporous carbon materials for electrochemical CO2 reduction (CO2RR). It particularly examines the effects of nitrogen doping speciation, structural disorder, various pore sizes, and single iron atom incorporation on catalytic performance. First, this research compares the CO2RR performance of N-doped mesoporous carbon materials in both powder (CIC) and self-supported film (NCS). These two materials were prepared using the same process except that the CICs are powder and the NCS is tape-casted into a film. Physical characterization revealed that the N-doped carbon powders possess a more disordered carbon wall structure and more micropores than the sheets, while X-ray photoelectron spectroscopy indicates a higher content of pyridinic nitrogen in the powder (53% of the total nitrogen content). The CO2RR experiments showed that the N-doped CIC-12 exhibits the highest FECO of 97%, higher than the 50% FECO shown by the N-NCS-12, attributed to the higher pyridinic N content and more structural disorder providing more active sites. Then the effect of varying pore sizes in N-doped CIC powders was explored, comparing with another method of templating carbon synthesized via aniline pyrolysis and having 22 nm pores (AD-22), containing 6 at% graphitic nitrogen and exhibiting lower structural disorder due to the absence of NH3 etching. N-doped CIC-12, with the highest structural disorder and pyridinic nitrogen, achieved 97% FECO at -0.45 V vs. RHE, while CIC-85 and CIC-22 gave lower FECO values. AD-22, containing only graphitic nitrogen, showed no CO2RR activity, confirming the inactivity of graphitic N towards CO2RR. This part of the work resulted in a first-time structure-property-performance relationship for CO2RR at N-doped carbons. Finally, the medium-performing N-CIC-85 powder was used to introduce single iron atoms to further enhance the CO2RR performance. The Fe-NCIC-85 catalysts, synthesized at 900 °C, achieved an excellent FECO of 97% at -0.45 V vs. RHE and maintained this high selectivity for over 100 hours without any signs of loss of stability beyond that. This enhancement was attributed to single-atom iron stabilization by the nitrogen doped onto the CIC powder surface during preparation through NH3 exposure.