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Title: Intrinsically microporous polymer materials for electrodes and membranes
Author: Rong, Yuanyang
Awarding Body: University of Bath
Current Institution: University of Bath
Date of Award: 2017
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Microporous materials have received much attention and offer new opportunities in electrochemistry because of their interesting properties. Compared with the corresponding nonporous materials, the highly porous structure may facilitate internal mass transport process, provide accessibility to binding sites and provide size selectivity. A new class of microporous materials, polymers of intrinsic microporosity (PIMs) emerged about ten years ago. They combine the microporosity generated from the rigid and contorted backbones and the processibility of linear molecular polymers, which make them particularly attractive for the applications in gas storage, membrane separations and also in electrochemistry. PIM-EA-TB containing ethanoanthracene (EA) and Tröger’s base (TB) is one of the most interesting PIMs and has a high BET surface area around 1000 m2 g-1. Most of the work in this thesis are based on PIM-EA-TB. Results chapters focus on catalysis in PIM films, ion flux in free-standing PIM membranes and carbonization of PIM-EA-TB. Electrochemical oxidation of glucose is important due to the practical applications in glucose sensing and in biological fuel cells. However, the practical application of many catalysts is limited by the poisoning by interferences such as proteins and chloride. Here, PIM-EA-TB was spin-coated onto the surface of supported gold nanoparticles to protect the catalysts from poisoning. It was demonstrated that the PIM-EA-TB film would not negatively affect the catalytic performance of gold nanoparticles for glucose oxidation. Also, it provided effective protection against protein poisoning because of its rigid backbone and rigid molecular structure preventing protein access. Chloride poisoning was reduced but not surpressed. In addition to nanoparticle catalysts, water-insoluble molecular catalysts were investigated. PIM-EA-TB was used as a rigid host for model catalyst, tetraphenylporphyrin (FeTPP). FeTPP was immobilised in the PIM-EA-TB film and then deposited on the electrode to create a high density heterogenised catalysts. Different compositions of PIM and FeTPP and different scanrates were investigated to reveal the catalytic mechanism. The PIM hosted FeTPP catalysts showed facile electron transfer and effective electrocatalytic reduction of oxygen and peroxide. The 4-(3-phenyl-propyl)-pyridine was applied to the PIM-FeTPP film to give an organogel in 12 order to investigate the liquid-liquid interface. The PIM immobilisation method could offer a new opportunity to the immobilisation of a wide range of the molecular catalysts. The understanding of transport processes in PIM-EA-TB membranes is important for the development of further applications in the electrochemistry. Different types of anions were investigated to see the anion uptake and charge transport in PIM-EA-TB films. Three cases were investigated, including the oxidation of ferrocene, the reduction of protons and the transport of anions and protons in the PIM-EA-TB thick films. In all three cases, the diameter and hydrophobicity of anions are important in the competing effects. The pKa of PIM-EA-TB was determined and novel ionic diode effects were observed. Nanofluidic devices are used to regulate the flow of ions to one preferential direction and they have great importance because of the similarity to biological ion channels and the application in biochemical fields. PIMs were explored to the possibility to establish an artificial ion channel with the gate function. A thin film preparative method was introduced to produce thin free-standing polymer films. The 300 nm PIM-EA-TB films supported on a poly-ethylene-terephthalate (PET) film with a 20 m diameter microhole exhibited ionic diode behaviour. Only when the cation and anion had different mobility, the current rectification effects were observed. Different pH values of the electrolyte were also investigated and resulted in a gradual change in rectification effects. Porous carbon materials have wide applications in different fields such as gas separation, water purification, catalyst supports, and fuel cells. One of the common methods to produce the porous carbon is the carbonization of polymers. However, the challenge is that it is difficult to control the pore size and pore distribution. PIM-EA-TB was carbonized at 500 °C in vacuum to produce a novel type of microporous carbon. The microporosity and morphology of the PIM precursor remained after carbonization. The new material exhibited relatively low electrical conductivity and low activity in the electrochemical oxygen reduction. The capacitance of the new carbon material was investigated and found to vary with pH depending on the protonation status of micropores. 13 Finally, the carbonized PIM films were used to control the formation of platinum nanoparticles. Platinum nanoparticles are important catalysts in many areas but may suffer from high costs and lack of reproducibility. Therefore, it is important to reduce the amount of platinum, increase the utilization of platinum as well as control the particle size. The carbonized PIM films still have the microporosity and offer an ideal substrate for platinum nanoparticles. The platinum nanoparticles were formed at the same time with the carbonization of PIM, which helped to control the size of platinum nanoparticles. Compared with bare platinum, the platinum nanoparticles produced by PIM-EA-TB showed a high electrochemically active surface area and good catalytic performances for oxygen reduction, methanol oxidation and glucose oxidation. Much less platinum (1μg per cm2) was needed to achieve the same catalytic performance compared to the bulk platinum.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available