Matthew M. Mench

The University of Tennessee Medical Center at Knoxville, Knoxville, Tennessee, United States

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Publications (114)247.61 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The roundtrip electrochemical energy efficiency is improved from 63% to 76% at a current density of 200 mA cm−2 in an all-vanadium redox flow battery (VRFB) by utilizing modified carbon paper electrodes in the high-performance no-gap design. Heat treatment of the carbon paper electrodes in a 42% oxygen/58% nitrogen atmosphere increases the electrochemically wetted surface area from 0.24 to 51.22 m2 g−1, resulting in a 100–140 mV decrease in activation overpotential at operationally relevant current densities. An enriched oxygen environment decreases the amount of treatment time required to achieve high surface area. The increased efficiency and greater depth of discharge doubles the total usable energy stored in a fixed amount of electrolyte during operation at 200 mA cm−2.
    Journal of Power Sources 10/2015; 294. DOI:10.1016/j.jpowsour.2015.05.118 · 5.21 Impact Factor
  • Ozgur Cekmer, Sukkee Um, Matthew M. Mench
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    ABSTRACT: In this study, path-percolation theory was applied to randomly generate porous media, and effective porosities of these domains were determined. A statistical approach was pursued to determine effective porosity with confidence levels of 95%, 97%, and 99%. Furthermore, the Lattice-Boltzmann method was applied to obtain the velocity distribution throughout the porous channels to evaluate effective tortuosity. Two dimensional lattices with nine velocity components were utilized for fluid flow simulations. A new effective diffusivity model for porous media was developed using the effective porosity and tortuosity determined by path-percolation and Lattice-Boltzmann theories, respectively. Diffusion behavior of gasses in porous media as a function of porosity is typically unpredictable when the porosity is below 0.6, but the developed diffusion model as a function of effective porosity is shown to be useful in all effective porosity ranges.
    International Journal of Heat and Mass Transfer 07/2015; 86. DOI:10.1016/j.ijheatmasstransfer.2015.02.023 · 2.52 Impact Factor
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    ABSTRACT: In this work, semi-empirical Leverett J-Function relationships relating capillary pressure and water saturation are experimentally derived for commercial and experimental polymer electrolyte fuel cell materials developed for automotive applications. Relationships were derived for Mitsubishi Rayon Corp. (MRC) U105 and General Motors (GM) experimental high tortuosity diffusion media (DM), the micro-porous layer (MPL), and the catalyst layer (CL). The standard Leverett J-Function under-predicted drainage curves for the DM at high saturation levels and significantly under-predicted the capillary pressure requirements for the MPL and CL across the entire saturation range. Composite structures were tested to understand interfacial effects for DM|MPL and MPL|CL. Each additional layer was found to superimpose its effects on capillary pressure onto the previous layers. The MPL formulation tested increased in porosity from a 136 nm peak average to a 153 nm peak average with increased surface porosity of the substrate. Additionally, small voids and pockets that accumulate liquid water were found to exist in the MPL|CL interface. The results of this work are useful for computational modelers seeking to enhance the resolution of their macroscopic multi-phase flow models which underestimate capillary pressure using the standard Leverett J-Function.
    Journal of Power Sources 12/2014; 271:180–186. DOI:10.1016/j.jpowsour.2014.07.163 · 5.21 Impact Factor
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    ABSTRACT: Polymer-electrolyte fuel cells are a promising energy-conversion technology. Over the last several decades significant progress has been made in increasing their performance and durability, of which continuum-level modeling of the transport processes has played an integral part. In this review, we examine the state-of-the-art modeling approaches, with a goal of elucidating the knowledge gaps and needs going forward in the field. In particular, the focus is on multiphase flow, especially in terms of understanding interactions at interfaces, and catalyst layers with a focus on the impacts of ionomer thin-films and multiscale phenomena. Overall, we highlight where there is consensus in terms of modeling approaches as well as opportunities for further improvement and clarification, including identification of several critical areas for future research.
    Journal of The Electrochemical Society 08/2014; 161(12):F1254-F1299. DOI:10.1149/2.0751412jes] · 2.86 Impact Factor
  • Journal of The Electrochemical Society 08/2014; 161(12):X17-X17. DOI:10.1149/2.0461412jes · 2.86 Impact Factor
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    ABSTRACT: The present work demonstrates an innovative concept of obtaining enhanced performance via laser treatment of the cathode-side diffusion medium (DM) while mitigating identified degradation modes. A diffusion medium was modified such that hydrophilic heat affected zones (HAZ) were introduced, which led to localized water redistribution. However, no perforation was created, thus mitigating accelerated degradation of the catalyst layer and diffusion medium. This material was compared to a diffusion medium with 100-mu m diameter perforations that contained heat affected zones surrounding the perforations. In-situ net water drag experiments indicate that at low humidity and low-to-moderate current densities, a non-perforated microporous layer (MPL) forces more water to back diffuse from the cathode to the anode. However, when more water is produced at higher currents or the inlet streams are close to saturation, the non-perforated MPL acts as a barrier to prevent liquid water in the cathode DM from moving toward the anode. Furthermore, a computational model showed that the thermal gradients introduced as a result of the perforations can significantly change the water transport, particularly due to phase-change induced flow. This work adds understanding to the role of the MPL and the laser-induced heat affected zones in polymer electrolyte fuel cell performance. (c) 2014 The Electrochemical Society. All rights reserved.
    Journal of The Electrochemical Society 07/2014; 161(10):F1061-F1069. DOI:10.1149/2.0591410jes · 2.86 Impact Factor
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    ABSTRACT: An experimental study to investigate the through-plane thermal conductivity of three different diffusion media (DM) used in polymer electrolyte fuel cells (PEFCs) as a function of compression (from 0.1 MPa to 2 MPa) and saturation (from 0 to 25%) was performed. Additionally, measurements to determine the stress–strain relationship for the materials were made using an optical microscope. Both compression and water content had a significant impact on the through-plane thermal conductivity, which should be accounted for in multiphase modeling efforts. An analytical expression for the theoretical maximum of the through-plane thermal conductivity, as a function of both compression and saturation, was developed to help understand the nature of liquid connectivity in saturated pores. Additionally, a relationship was developed to predict actual thermal conductivity of the tested materials as a function of both compression and saturation based on experimentally measured data.
    Journal of Power Sources 06/2014; 256:212–219. DOI:10.1016/j.jpowsour.2014.01.015 · 5.21 Impact Factor
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    ABSTRACT: We present an in situ electrochemical technique for the quantitative measurement and resolution of the ohmic, charge transfer and diffusion overvoltages at the negative electrode of an all-vanadium redox flow battery (VRFB) using electrochemical impedance spectroscopy (EIS). The mathematics describing the complex impedance of the V+2N+3 redox reaction is derived and matches the experimental data. The voltage losses contributed by each process have been resolved and quantified at various flow rates and electrode thicknesses as a function of current density during anodic and cathodic polarization. The diffusion overvoltage was affected strongly by flow rate while the charge transfer and ohmic losses were invariant. On the other hand, adopting a thicker electrode significantly changed both the charge transfer and diffusion losses due to increased surface area. Furthermore, the Tafel plot obtained from the impedance resolved charge transfer overvoltage yielded the geometric exchange current density, anodic and cathodic Tafel slopes (135 +/- 5 and 121 +/- 5 mV/decade respectively) and corresponding transfer coefficients alpha = 0.45 +/- 0.02 and beta = 0.50 +/- 0.02 in an operating cell. (C) 2014 The Electrochemical Society.
    Journal of The Electrochemical Society 04/2014; 161(6):A981-A988. DOI:10.1149/2.045406jes · 2.86 Impact Factor
  • Jon P. Owejan, Thomas A. Trabold, Matthew M. Mench
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    ABSTRACT: Under typical proton exchange membrane fuel cell (PEMFC) operating conditions, temperature gradients through the porous gas diffusion layer (GDL) can result in product water condensation. As a result, non-uniform partial saturation of the GDL changes the local effective porosity and tortuosity encountered by oxygen diffusing to the catalyst layer. This additional transport resistance reduces the partial pressure of oxygen at the catalyst surface of an air-fed cathode. In the current work, this phenomenon is investigated in two-dimensions using limiting current experiments that define GDL boundary conditions along with simultaneous neutron imaging to measure the local water content relative to the flow field geometry. The subsequent effective diffusion coefficient vs. saturation relationship derived from this method is reported for two common GDL carbon fiber substrates. It is also shown that the land vs. channel distribution of liquid water must be accounted for to accurately predict diffusion resistance. These results represent the first time that the effect of water saturation on effective diffusion coefficient has been directly measured in situ, thus enabling accurate determination of the exponent "n" in the modified Bruggeman relationship for two commercially available gas diffusion layer materials.
    International Journal of Heat and Mass Transfer 04/2014; 71:585-592. DOI:10.1016/j.ijheatmasstransfer.2013.12.059 · 2.52 Impact Factor
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    ABSTRACT: Liquid water saturation profiles were determined using high resolution neutron radiography for commercially available fuel cell materials and hardware. Temperature, pressure, and relative humidity (concentration) gradients were imposed on the cell to determine individual influences on water content for each gradient. The asymmetric anode/cathode channel/land architecture used in this work results in significant water accumulation in the anode diffusion media with saturation values of up to ∼50%. Anode water content was found to change substantially with imposed pressure or concentration gradient, whereas the cathode saturation profile remained relatively consistent, indicating the channel/land ratio and thickness have a determinant role in diffusion media retention. The data generated in this work has been made publicly available through www.pemfcdata.org, and should be useful for computational modelers seeking validation data.
    International Journal of Hydrogen Energy 02/2014; 39(7):3387–3396. DOI:10.1016/j.ijhydene.2013.12.021 · 2.93 Impact Factor
  • 12/2013; 2(3):A29-A31. DOI:10.1149/2.001303eel
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    ABSTRACT: The possibility of large-scale attacks using chemical warfare agents (CWAs) has exposed the critical need for fundamental research enabling the reliable, unambiguous and early detection of trace CWAs and toxic industrial chemicals. This paper presents a unique approach for the identification and classification of simultaneously present multiple environmental contaminants by perturbing an electrochemical (EC) sensor with an oscillating potential for the extraction of statistically rich information from the current response. The dynamic response, being a function of the degree and mechanism of contamination, is then processed with a symbolic dynamic filter for the extraction of representative patterns, which are then classified using a trained neural network. The approach presented in this paper promises to extend the sensing power and sensitivity of these EC sensors by augmenting and complementing sensor technology with state-of-the-art embedded real-time signal processing capabilities.
    Measurement Science and Technology 11/2013; 24(11):5102-. DOI:10.1088/0957-0233/24/11/115102 · 1.35 Impact Factor
  • Ozgur Cekmer, Jacob M. LaManna, Matthew M. Mench
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    ABSTRACT: To measure gas phase diffusion coefficients across porous media, an apparatus called a Loschmidt diffusion cell is often utilized. In previous studies with such an apparatus, an infinite-length assumption is used to simplify the analytical solution. Experimentally, cell lengths must be quite long and measurement time is very brief to fulfill this assumption. In this study, Fick's second law is applied, and separation of variables with shifted homogeneity technique is performed for data analysis to enable design of a more compact experimental apparatus with extended measurement times and improved precision. The analytical solution is proved by both the inverse-matrix method and finite-volume discretization. Finally, using the new analytical solution obtained, the effective diffusion coefficient is determined for porous media used in fuel cell applications.
    International Journal of Heat and Mass Transfer 10/2013; 65:883-892. DOI:10.1016/j.ijheatmasstransfer.2013.06.062 · 2.52 Impact Factor
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    ABSTRACT: Anode dry-out is the main mechanism identified to limit operation in an open metallic element (OME) PEFC. The fundamental water transport mechanisms in the OME PEFC were examined in order to engineer further improved performance and higher temperature operation required for efficient heat rejection. Specifically, the net water drag (NWD) was measured over a range of conditions and analyzed with respect to electrochemical impedance spectroscopy and performance. As the cell operating temperature was increased, the effect of back diffusion was reduced due to the diminishing liquid water content in the cathode catalyst layer, and at critical liquid water content, anode dry-out was triggered primarily through electro-osmotic drag. Addition of cathode humidity was shown to promote high temperature operation mostly due to improved water back diffusion. The same mechanism can be achieved by creating a pressure differential across the membrane, with higher pressure on the cathode side. Stable operation was demonstrated at 90 °C using a polymer electrolyte membrane. Real time NWD measurements during transient anodic dry-out conditions were consistent with gradual membrane dehydration. The trade-off between liquid water overshadowing cathode catalyst sites and its contribution in promoting back diffusion is a key factor in systems with anode dry-out limited operation.
    Journal of Power Sources 10/2013; 239:433–442. DOI:10.1016/j.jpowsour.2013.03.145 · 5.21 Impact Factor
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    ABSTRACT: An experimental method for measurement of local redox potential within multilayer electrodes was developed and applied to all-vanadium redox flow batteries (VRFBs). Through-plane measurement at the positive side reveals several important phenomena including potential distribution, concentration distribution of active species and the predominant reaction location within the porous carbon electrodes.
    Chemical Communications 06/2013; 49(56). DOI:10.1039/c3cc42092b · 6.72 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The possibility of large-scale attacks using chemical warfare agents (CWAs) has exposed the critical need for fundamental research enabling the reliable, unambiguous, and early detection of trace CWAs and toxic industrial chemicals. This paper presents a unique approach for identification and classification of environmental contaminants by perturbing an electrochemical (EC) sensor with an oscillating potential rather than static voltage levels. The dynamic response, being a function of the degree and mechanism of contamination, is then processed with a symbolic dynamic filter for extraction of representative patterns, which are then classified using a trained neural network. Extraction of statistically rich information from the current response enables identification of characteristics species even when they are mixed with other confounding gases. The approach presented in this paper promises to extend sensing power and sensitivity of these EC sensors by augmenting and complementing the sensor technology with state-of-the-art embedded real time signal processing capabilities.
    American Control Conference (ACC), 2013; 06/2013
  • 223th ECS Meeting; 05/2013
  • 223th ECS Meeting; 05/2013
  • 223th ECS Meeting; 05/2013
  • Guoqing Xu, Jacob LaManna, Matthew M. Mench
    223th ECS Meeting; 05/2013

Publication Stats

2k Citations
247.61 Total Impact Points

Institutions

  • 2011–2014
    • The University of Tennessee Medical Center at Knoxville
      Knoxville, Tennessee, United States
  • 2004–2011
    • Pennsylvania State University
      • Department of Mechanical and Nuclear Engineering
      University Park, Maryland, United States
  • 2007–2010
    • William Penn University
      Worcester, Massachusetts, United States