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Title:Application of ambient mass spectrometry in electrochemical systems
Author(s):Liu, Yao-Min
Director of Research:Gewirth, Andrew A
Doctoral Committee Chair(s):Gewirth, Andrew A
Doctoral Committee Member(s):Nuzzo, Ralph G; Sweedler, Jonathan V; Rodríguez-López, Joaquín
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Mass spectrometry
Desorption electrospray ionization
Solid electrolyte interface
Cathode electrolyte interface
Electrolyte degradation
Electrochemical cell coupled to mass spectrometry
EC coupled to MS
Sonic spray ionization
Online detection
Paper-based analytical devices
Paper-based electrochemical cell
Magnesium electrolyte
Abstract:This thesis focuses on applying ambient mass spectrometry in electrochemical systems. The first section of the thesis introduces the utilization of desorption electrospray ionization mass spectrometry (DESI-MS) to confirm the existence and composition of the cathode electrolyte interface (CEI) in lithium ion batteries. The electrode-electrolyte interface or solid electrolyte interface (SEI) formed via electrolyte decomposition on the anode is largely responsible for the stable cycling of conventional lithium ion batteries. Similarly, there is a lesser-known analogous layer on the cathode side of a lithium ion battery, termed the cathode electrolyte interface (CEI), whose composition and role are debated. DESI-MS is applied to study common lithium ion battery cathodes. CEI formation on the LiMn2O4 cathode material is observed after cycling between 3.5 and 4.5 V vs Li/Li+ in electrolyte solution containing 1 M LiPF6 or LiClO4 in 1:1 (v/v) ethylene carbonate (EC) and dimethyl carbonate (DMC). Intact poly(ethylene glycol) dimethyl ether is identified as the electrolyte degradation product on the cathode surface by the high mass-resolution Orbitrap mass spectrometer. When EC is paired with ethyl methyl carbonate (EMC), poly(ethylene glycol) dimethyl ether, poly(ethylene glycol) ethyl methyl ether and poly(ethylene glycol) are found on the surface simultaneously. The presence of ethoxy and methoxy end groups indicates both methoxide and ethoxide are produced and involved in the process of oligomerization. Au surfaces cycled under different electrochemical windows as model systems for Li-ion battery anodes are also examined. Interestingly, the identical oligomeric species to those found in the CEI are found on Au surfaces after running five cycles between 2.0 and 0.1 V vs. Li/Li+ in half-cells. These results show that DESI-MS provides intact molecular information on battery electrodes, enabling deeper understanding of the SEI or CEI composition. The next section of the thesis focuses on demonstrating a technique that allows online coupling of electrochemistry to mass spectrometry (MS). Coupling of an electrochemical cell to MS is a powerful approach for identifying intermediates and products of electrochemical reactions in situ. In addition, electrochemical transformations have been used to increase ionization efficiency and modify analytes prior to MS, improving sensitivity and chemical specificity. Recently, there has been significant interest in developing paper-based electroanalytical devices as they offer convenience, low cost, versatility, and simplicity. This section describes the development of tubular and planar paper-based electrochemical cells (P-EC) coupled to sonic spray ionization (SSI) mass spectrometry (P-EC/SSI-MS). The EC cells are composed of paper sandwiched between two mesh stainless steel electrodes. Analytes and reagents can be added directly to the paper substrate along with electrolyte, or delivered via the SSI microdroplet spray. The EC cells are decoupled from the SSI source, allowing independent control of electrical and chemical parameters. P-EC/SSI-MS is used to characterize various reactions such as oxidations of cysteine, dopamine, polycyclic aromatic hydrocarbons, and diphenyl sulfide. The results show that P-EC/SSI-MS has the ability to increase ionization efficiency, to perform online EC transformations, and to capture intermediates of EC reactions with a response time on the order of hundreds of milliseconds. The short response time allowed detection of a deprotonated diphenyl sulfide intermediate, which experimentally confirms a previously proposed mechanism for oxidation of diphenyl sulfide to pseudodimer sulfonium ion. This section introduces paper-based EC/SSI-MS via development of two device configurations (tubular and planar electrodes), as well as discusses the capabilities, performance, and limitations of the technique. The last section of the thesis demonstrates the application of the technique introduced in the previous section. The paper substrate of the P-EC is extended into the electrolyte solution and a reference electrode is inserted into the electrolyte solution to form a three-electrode cell. Reagents can be delivered via SSI emitter or placed in the electrolyte solution. The P-EC/SSI-MS system features synchronized behavior demonstrated by cysteine oxidation. The mesh electrode surface can be modified by sputter coating. Reaction intermediates and products of glycerol oxidation at the polarized Pt or Au-coated mesh electrode are monitored by SSI-MS in situ. The short response time allowed detection of glyceraldehyde in glycerol oxidation on Pt surface, which was previously reported non-detectable without sample pretreatment. The results show that sequential two-electron transfer steps (glycerol → glyceraldehyde → glyceric acid → glycolic acid/formic acid) dominate on Pt, while glycolic acid is the major product on Au. The high temporal resolution as well as high modulability of the cell makes P-EC/SSI-MS a powerful tool for identifying reaction intermediates and products of electrochemical processes.
Issue Date:2017-07-10
Rights Information:Copyright 2017 Yao-Min Liu
Date Available in IDEALS:2017-09-29
Date Deposited:2017-08

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