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Advanced Carbon-Based Materials for Energy Storage and Conversion Applications.

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Wei, Qiliang (2018). Advanced Carbon-Based Materials for Energy Storage and Conversion Applications. Thèse. Québec, Université du Québec, Institut national de la recherche scientifique, Doctorat en sciences de l'énergie et des matériaux, 261 p.

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The development of electrochemical energy storage and conversion systems with high energy density, low cost and good safety have been at the heart of current research on renewable clean energy technologies. To date, lithium-ion batteries (LIBs) have gained the most successful applications ranging from portable electronic devices to electrical vehicles (EVs). However, they are reaching their limitations in energy density and power density, and facing the cost issues of relative shortage of Li resources. New electrochemical energy systems are therefore being actively sought. From the cost issue, sodium‐ion batteries (SIBs) have gained increasing research interest all over the world, due to the high abundance and low cost of sodium as well as its suitable redox potential (E0(Na+/Na)=−2.71 V versus the standard hydrogen electrode, SHE), which is only 0.3 V above that of lithium, meaning that there is only a small energy penalty to pay. From the energy density and power density point view, recently, Zn-air batteries (ZABs) and hydrogen-powered proton exchange membrane fuel cells (PEMFCs) are attracting significant attention since the oxygen on the cathode being from air and excluded in the system, which significantly increases the energy densities. In these devices, an efficient oxygen electrocatalyst on the cathode is extremely important for the development of high-performance ZABs and PEMFCs. Up to now, the benchmark catalysts for oxygen reduction reaction (ORR) are noble-metal-based materials; however, the high price and scarcity of these catalysts inhibit their extensive commercial reach. Therefore, developing highly efficient and low-cost non-precious-metal catalysts (NPMCs) to facilitate the sluggish cathodic ORR is a key issue in metal-air batteries and fuel cells. In this thesis, the work is focused on the development of various carbon-based ORR electrocatalysts and their applications in ZABs and PEMFCs. Moreover, we also fabricated highly-ordered microporous carbon (MPC) spheres and applied it as high-performance anodes for SIB. In the first part of the thesis, we fabricated spherical phenolic resol-F127 monomicelles (SPRMs) by a simple hydrothermal route based on a soft template. A series of 3D microporous Fe/N/C ORR catalysts were then prepared by employing SPRMs as the carbon host for impregnating FeAc and 1,10-Phen, followed by high temperature pyrolysis in Ar and in NH3, consequently. Through the systematic studies, we found that (i) the content of Fe precursor and pyrolysis time under NH3 have significant impact on the morphology and structure of the final Fe/N/C catalysts; (ii) the pyrolysis temperature in Ar, the Brunauer-Emmett-Teller (BET) surface area, and the content of Fe in the catalysts largely affect the ORR activity; (iii) the optimized Fe content of the Fe/N/C catalysts is around 5.5–8 wt% and the optimized porosity is with 450 m2 g–1 micropore with preferably higher value of mesopores, therefore, only catalysts subjecting within these two ranges exhibit high activity. The optimized 3D Fe/N/C exhibits good ORR performances in both alkaline and acidic conditions. In alkaline solution, it shows excellent activity with a half-wave potential of 0.87 V, excellent stability, and strong methanol tolerance. Moreover, in acidic solution, it also exhibits excellent stability and selectivity. This work provides important reference of key parameters for rational designing high-efficient Fe/N/C electrocatalysts. From the first work described above, we can see that the microporous structure plays an important role on the electrochemical performance of the Fe/N/C catalysts, therefore, in the second part of the thesis, we employed sulfur (S) as the promoter to tune the pore structures of the Fe/N/C catalyst. We discovered that the addition of S not only affords interpenetrating holes leading to a large surface area and pore volume inside the architecture, but also helps the whole carbon framework keep a perfect 3D spherical shape and uniformly dispersed Fe–Nx active sites. Moreover, a higher degree of distortion of the local Fe–N4 structure was observed for the S-treated Fe/N/C sample. Consequently, the optimal S-treated Fe/N/C catalyst shows a litchi-like spherical structure, large surface area (982.1 m2 g−1) with a huge pore volume (1.01 cm3 g−1), and excellent ORR/OER (oxygen evolution reaction) activity. Importantly, it achieves a superior performance (∼250 mW cm−2, double the power density compared to the untreated sample) as an air cathode for a Zn–air battery device. This work may provide a new strategy to develop high performance carbon-based bifunctional electrocatalysts for low cost metal–air batteries and other electrochemical energy conversion/storage applications. It is reported that the additional of a second metal (i.e., bimetallic catalyst) could further improve the catalyst performance due to the synergistic effects, therefore in the third part of the thesis, we developed highly porous (Fe-Cu)/N/C based on metal organic framework (MOF). We found that compared with the Fe/N/C, the as-synthesized (Fe-Cu)/N/C possesses higher surface area, longer Fe-N bond, and lower H2O2 yield, which are all favorable for the catalytic activity and stability. Indeed, when applied in a membrane electrode assembly (MEA) in the H2-air PEMFC, the (Fe-Cu)/N/C catalyst demonstrates a higher power density (0.4 W cm-2) than that of the Fe/N/C (0.36 W cm-2), and an enhanced stability, i.e., improvement of 3.7% of the current density under a potentiostatic testing at 0.6 V after 40 h. On the other hand, biomass-derived carbon materials have aroused researchers’ much attention, due to their low cost and sustainability. In the fourth part of the thesis, by using the biomass reed stalk which is consists of Si and C, we developed an efficient Si-contained Fe/N/C ORR catalyst. Due to the participating of Si in the Fe/N doping process, the Si-Fe/N/C catalyst possesses enhanced graphitic carbon structure with more nitrogen moieties coordinating with Fe, which makes the Si-Fe/N/C catalyst possess good ORR activity. Importantly, Si-Fe/N/C exhibits better stability (with 94.8% retention of the current after 20,000 s under a high voltage of 0.8 V) than the Fe/N/C counterpart (83.3%) and Pt/C (65.5%). In addition, there is only ∼12 mV of change at 3 mA cm−2 for Si-Fe/N/C after 10,000 potential cycles under O2-saturated electrolyte (vs. ∼19 mV for Fe/N/C and ∼40 mV for Pt/C), as well as higher tolerance toward methanol compared with Pt/C. Taking together, using Si-Fe/N/C catalyst as a substitute for commercial Pt/C could provide possibility in fuel cells and other applications with good ORR performance and high stability. We believe that this work will give more insights to design highly stable catalysts for the clean energy related devices and have significant economic and environment effects by making full use of biomass wastes. More interestingly, we find that even without Fe, the metal-free (Si-N-C) materials derived from biomass reed were demonstrated to be very active for ORR in alkaline media (the fifth part of the thesis). The optimized Si-N-C sample shows an Eonset of ~1.00 V and E1/2 of 0.89 V (vs. reversible hydrogen electrode, RHE), which is one of the best among the reported metal-free ORR catalysts. It also displays better stability for ORR than commercial Pt/C in a half-cell test. Moreover, this reed derived Si-N-C metal-free catalyst exhibits excellent performance as an air cathode for a Zn-air battery device. DFT calculation indicates that the Si and N sites (graphitic-N) in the carbon framework could promote the ORR activity. We believe that our work will give more insights to design more efficient catalysts for the clean energy related devices and bring a great significance to the sustainable development of energy. In addition, during our study of SPRMs materials, we found that the interlayer spacing of the MPC could be well tuned by simply adjusting the heat-treatment temperatures. This phenomena could be very useful for sodium-ion batteries. Therefore, in the last part of the thesis, we did systematic study on this aspect. In detail, the carbon spheres treated at 700 °C (MPC-700) possess unique features, such as a large interlayer spacing (∼0.457 nm), high surface area, structural stability and plenty of micropores, which are favorable for Na insertion, and therefore for high-performance SIB electrode materials. Our results show that the MPC-700 electrode exhibits a high reversible capacity, good cycling stability, and an excellent high-rate performance (∼160 mA h g−1 after 500 cycles at 1000 mA g−1), making it a promising candidate for SIB anode.

Type de document: Thèse Thèse
Directeur de mémoire/thèse: Sun, Shuhui
Co-directeurs de mémoire/thèse: Tavares, Ana
Mots-clés libres: énergie et matériaux
Centre: Centre Énergie Matériaux Télécommunications
Date de dépôt: 10 avr. 2019 15:18
Dernière modification: 10 avr. 2019 15:18
URI: http://espace.inrs.ca/id/eprint/8031

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