Single-Walled Carbon Nanotube–Metalloporphyrin Chemiresistive Gas Sensor Arrays for Volatile Organic Compounds

National Science Foundation (U.S.) (DMR-1410718)National Science Foundation (U.S.) (1122374)Massachusetts Institute of Technology. Institute for Soldier NanotechnologiesUnited States. Defense Advanced Research Projects Agency (W911NF-14-1-0087

Health diagnosis and recuperation of aged Li-ion batteries with data analytics and equivalent circuit modeling

Battery health assessment and recuperation play a crucial role in the utilization of second-life Li-ion batteries. However, due to ambiguous aging mechanisms and lack of correlations between the recovery effects and operational states, it is challenging to accurately estimate battery health and devise a clear strategy for cell rejuvenation. This paper presents aging and reconditioning experiments of 62 commercial high-energy type lithium iron phosphate (LFP) cells, which supplement existing datasets of high-power LFP cells. The relatively large-scale data allow us to use machine learning models to predict cycle life and identify important indicators of recoverable capacity. Considering cell-to-cell inconsistencies, an average test error of $16.84\% \pm 1.87\%$ (mean absolute percentage error) for cycle life prediction is achieved by gradient boosting regressor given information from the first 80 cycles. In addition, it is found that some of the recoverable lost capacity is attributed to the lateral lithium non-uniformity within the electrodes. An equivalent circuit model is built and experimentally validated to demonstrate how such non-uniformity can be accumulated, and how it can give rise to recoverable capacity loss. SHapley Additive exPlanations (SHAP) analysis also reveals that battery operation history significantly affects the capacity recovery.Comment: 20 pages, 5 figures, 1 tabl

Enhancing materials for fuel cells and organic solar cells through molecular design

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references.In an effort to make alternative energy competitive to fossil fuels, research in improving efficiencies of solar cells and fuel cells have grown rapidly over the last few decades. One prominent strategy to improving the efficiencies in these devices focuses on engineering materials with customized molecular structure for enhancements in specific properties. Herein, new organic materials are designed and synthesized to enhance selected properties for applications in fuel cells and solar cells. In chapter 1, triptycene poly(aryl ethers) are synthesized and characterized for enhancing ion conductivity of ion exchange membranes in fuel cells. Triptycene motif is incorporated to increase charge density and fractional free volume in the membranes. In Chapter 1.2, sulfonated triptycene poly(ether ether ketone) (S-tripPEEK) is synthesized and studied for proton exchange membranes (PEM). Increasing fractional free volume in the membrane results in high water uptake at relative humidity (RH) from 10 %RH to 90 %RH and higher proton mobility in the membranes. S-tripPEEK membranes show proton conductivities of 334 mS/cm at 85 °C at 90 %RH and 0.37 mS/cm at 85 °C at 20 %RH as compared to 18.9 mS/cm and 0.0014 mS/cm observed in commercially available Nafion117[superscript TM] membranes. In Chapter 1.3, methylimidazolium triptycene poly(ether sulfone)s (MeIm-tripPES) are made for alkaline anion exchange membranes (AAEM) and are found to have ion conductivities of 104 mS/cm at 80 °C in water. Controlled nanophase separation with increased domain size contributed by the triptycene moiety lead to the high observed conductivities. However, the methylimidazolium functional groups on the membranes are not stable to alkaline conditions in the operation of a fuel cell. In Chapter 2, dithiolodithiole (C₄S₄) heterocycle was synthesized and studied as a new building block for organic photovoltaic materials. As an electron-rich fused-ring motif, C₄S₄ is expected to be a more effective electron donor. Comparison with analogous thiophene derivatives shows that C4S4 moiety raises the highest occupied molecular orbital (HOMO) by 0.7 - 1.0 eV, suggesting a stronger electron donating character than thiophene. Furthermore, crystal structures of C4S4 molecules show planarity in the molecule which further reduces the bandgap.by Lionel C. H. Moh.Ph. D

Free volume enhanced proton exchange membranes from sulfonated triptycene poly(ether ketone)

A triptycene based poly(ether ketone) (tripPEEK) was synthesized and sulfonated to form proton exchange membranes. The increase in intrinsic free volume resulting from the incorporation of sterically bulky triptycene moiety, imparts high affinity to water at all levels of relative humidity (RH) from 10% RH to 90% RH. S-tripPEEK membranes showed proton conductivities of 334 mS/cm at 85 °C at 90% RH and 0.37 mS/cm at 85 °C at 20% RH. Membranes of similar ion exchange capacity (IEC) are compared to deconvolute the effect of free volume from IEC in enhancing proton conductivity. Increasing the free volume of the membranes increases the proton conductivity and decreases the activation energy for proton conduction between 10% RH to 90% RH. Keyword: PEMFC; Proton exchange membrane; Sulfonated PEEK; Free volume; Triptycen