M. M. Mench

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

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Publications (66)101.36 Total impact

  • [Show abstract] [Hide abstract]
    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 01/2014; 256:212–219. · 4.68 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 01/2014; 39(7):3387–3396. · 3.55 Impact Factor
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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-. · 1.44 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; · 6.38 Impact Factor
  • ECS Electrochemistry Letters. 01/2013; 2(5).
  • S. Chakraborty, M. Manahan, M.M. Mench
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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 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; 01/2013
  • Subhadeep Chakraborty, Matthew M. Mench
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    ABSTRACT: This paper introduces a modeling paradigm based on a language theoretic framework for stochastic simulation of decision-making in a social setting, where choices and decisions by individuals are increasingly being influenced by a person's online social interactions. In this paper, the dynamics of opinion formation in a networked society have been studied with a joint model that bridges micro-level decisions based on reward maximization and the corresponding social influences which alter the estimate of these reward values. The effect of long term government policies on the stability and dynamics of the population opinion and the effect of including an influencing agent group has been studied. Simulated results on a sample society demonstrate the major impact of a relatively small but sharply opinionated influencing group toward pushing the society toward a desired outcome.
    Proceedings of the 5th international conference on Social Computing, Behavioral-Cultural Modeling and Prediction; 04/2012
  • Kyu Taek Cho, Matthew M Mench
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    ABSTRACT: In this study, the high resolution hydrogen-deuterium contrast radiography method was applied to elucidate the impact of the micro-porous layer (MPL) on water distribution in the porous fuel cell media. At the steady state, deuterium replaced hydrogen in the anode stream, and the large difference in neutron attenuation of the D(2)O produced at the cathode was used to track the produced water. It was found that the water content peaked in the cathode-side diffusion media (DM) for the cell without MPL, but with an MPL on the anode and cathode DM, the peak water amount was pushed toward the anode, resulting in a relatively flattened water profile through components and demonstrating a liquid barrier effect. Additionally, the dynamic water behavior in diffusion media was analyzed to understand the effect of a MPL and operating conditions. The water content in the DM changed with applied current, although there is a significant amount of residual liquid content that does not appear to be part of capillary channels. The effect of the MPL on irreducible saturation in DM and cell performance was also investigated.
    Physical Chemistry Chemical Physics 02/2012; 14(12):4296-302. · 3.83 Impact Factor
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    Sokhee Jung, Matthew M Mench, John M Regan
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    ABSTRACT: pH oppositely influences anode and cathode performance in microbial fuel cells. The differential electrochemical effects at each electrode and the resultant full-cell performance were analyzed in medium pH from 6.0 to 8.0. Potentials changed -60 mV/pH for the anode and -68 mV/pH for the cathode, coincident with thermodynamic estimations. Open circuit voltage reached a maximum (741 mV) at pH 7, and maximum power density was highest (712 mW/m²) at pH 6.5 as the cathode performance improved at lower pH. Maximum current density increased and apparent half-saturation potential (E(KA)) decreased with increasing medium pH due to improved anode performance. An equivalent circuit model composed of two time constant processes accurately fit bioanode impedance data. One of these processes was consistently the rate-limiting step for acetate-oxidizing exoelectrogenesis, with its pH-varying charge transfer resistance R₂ ranging from 2- to 321-fold higher than the pH-independent charge transfer resistance R₁. The associated capacitance C₂ was 2-3 orders of magnitude larger than C₁. R₂ was lowest near E(KA) and increased by several orders of magnitude at anode potentials above E(KA), while R₁ was nearly stable. However, fits deviated slightly at potentials above E(KA) due to emerging impedance possibly associated with diffusion and excessive potential.
    Environmental Science & Technology 09/2011; 45(20):9069-74. · 5.26 Impact Factor
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    ABSTRACT: In this study, the effect of a controlled temperature gradient on water transport across a single fuel cell was quantitatively investigated using high-resolution neutron imaging. The direction of liquid water transport under isothermal and non-isothermal conditions was observed in both hydrophilic and hydrophobic diffusion media (DM). The change in distribution of liquid saturation with time revealed two different mechanisms of water transport; capillary driven flow and phase-change induced (PCI) flow, in which a water vapor concentration gradient is created by condensation at a colder location. This concentration gradient drives diffusion flow toward the colder location. A maximum liquid saturation plateau of ca. 30% was shown for all conditions tested, indicating a critical transition between pendular and funicular modes of liquid water storage was captured. Based on this, it is suggested that PCI-flow may be the main mode of liquid transport below this critical transition threshold, above which, capillary flow dominates. As expected, both average cell temperature and the magnitude of temperature gradient were shown to significantly affect the rate of condensation within the DM. Experimental results were compared with water saturation distribution model predictions from literature and show reasonable qualitative agreement. Finally, it was concluded that current available models significantly over predict vapor phase diffusive transport in saturated fuel cell media using a Bruggeman type model.
    Journal of The Electrochemical Society. 05/2011; 158(6):B717-B726.
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    ABSTRACT: The variable biocatalyst density in a microbial fuel cell (MFC) anode biofilm is a unique feature of MFCs relative to other electrochemical systems, yet performance characterizations of MFCs typically involve analyses at electrochemically relevant time scales that are insufficient to account for these variable biocatalyst effects. This study investigated the electrochemical performance and the development of anode biofilm architecture under different external loadings, with duplicate acetate-fed single-chamber MFCs stabilized at each resistance for microbially relevant time scales. Power density curves from these steady-state reactors generally showed comparable profiles despite the fact that anode biofilm architectures and communities varied considerably, showing that steady-state biofilm differences had little influence on electrochemical performance until the steady-state external loading was much larger than the reactor internal resistance. Filamentous bacteria were dominant on the anodes under high external resistances (1000 and 5000 Ω), while more diverse rod-shaped cells formed dense biofilms under lower resistances (10, 50, and 265 Ω). Anode charge transfer resistance decreased with decreasing fixed external resistances, but was consistently 2 orders of magnitude higher than the resistance at the cathode. Cell counting showed an inverse exponential correlation between cell numbers and external resistances. This direct link of MFC anode biofilm evolution with external resistance and electricity production offers several operational strategies for system optimization.
    Environmental Science & Technology 02/2011; 45(6):2435-41. · 5.26 Impact Factor
  • Tushar Swamy, E. C. Kumbur, M. M. Mench
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    ABSTRACT: The imperfect interfacial contact between the bipolar plate (BP) and the diffusion medium (DM) can have a significant impact on the multi-phase flow and current transport in an operating polymer electrolyte fuel cell (PEFC). The objective of this work is to describe the impact of the BP and DM surface morphologies and the resulting interfacial contact on PEFC performance. In this study, the surface morphology of several BP and DM samples was digitally characterized using optical profilometry (OP). The benchmark surface data were then utilized in a microscopic model developed to simulate the BP|DM interfacial contact under compression. The microscopic model is based on the fractal modeling approach, which provides an accurate representation of the BP|DM interfacial contact by suppressing the resolution dependence of the surface profiles in consideration. Results indicate that the uncompressed surface morphology of mating materials, elasticity of these components, and local compression pressure are the key parameters that influence the BP|DM contact. The model results show that the void space along the BP|DM interface can potentially store a significant amount of liquid water (from 0.85 to 3.5mg/cm2), which can result in reduced durability and performance of the PEFC. The model predicts that a 50% drop in the DM surface roughness results in nearly a 40% drop in the BP|DM contact resistance and a 15% drop in the BP|DM interfacial water storage capacity.
    Electrochimica Acta - ELECTROCHIM ACTA. 01/2011; 56(8):3060-3070.
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    ABSTRACT: Redox flow batteries (RFBs) are enjoying a renaissance due to their ability to store large amounts of electrical energy relatively cheaply and efficiently. In this review, we examine the components of RFBs with a focus on understanding the underlying physical processes. The various transport and kinetic phenomena are discussed along with the most common redox couples. KeywordsFlow battery–Redox–Regenerative fuel cell–Flow cell–Vanadium
    Journal of Applied Electrochemistry 01/2011; 41(10):1137-1164. · 1.84 Impact Factor
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    ABSTRACT: Journal of Power Sources j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j p o w s o u r a b s t r a c t In this study, cathode-side, bi-layered diffusion media (DM) samples with micro-porous layer were per-forated with 300 m laser-cut holes (covering 15% of the surface area in a homogenous pattern) using a ytterbium fiber laser to investigate the effect of structural changes on the gas and water transport. Under reduced humidity conditions (50% inlet relative humidity on the anode and cathode), the perforated DM were observed to increase the potential by an average of 6% for current densities ranging from 0.2 to 1.4 A cm −2 . However, the perforated DM showed reduced performance for current densities greater than 1.4 A cm −2 and at all currents under high-humidity conditions. Neutron radiography experiments were also performed to understand the changes in liquid water retention characteristics of DM due to the laser perforations. Significant water accumulation and water redistribution were observed in the perforated DM, which helps explain the observed performance behavior. The results indicate that the perforations act as water pooling and possible channeling locations, which significantly alter the water condensation, storage, and transport scheme within the fuel cell. These observations suggest that proper tailoring of fuel cell DM possesses significant potential to enable fuel cell operations with reduce liquid overhead and high performance.
    Journal of Power Sources 01/2011; 196:5573-5582. · 4.68 Impact Factor
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    ABSTRACT: The relationship between anode microbial characteristics and electrochemical parameters in microbial fuel cells (MFCs) was analyzed by time-course sampling of parallel single-bottle MFCs operated under identical conditions. While voltage stabilized within 4days, anode biofilms continued growing during the six-week operation. Viable cell density increased asymptotically, but membrane-compromised cells accumulated steadily from only 9% of total cells on day 3 to 52% at 6weeks. Electrochemical performance followed the viable cell trend, with a positive correlation for power density and an inverse correlation for anode charge transfer resistance. The biofilm architecture shifted from rod-shaped, dispersed cells to more filamentous structures, with the continuous detection of Geobacter sulfurreducens-like 16S rRNA fragments throughout operation and the emergence of a community member related to a known phenazine-producing Pseudomonas species. A drop in cathode open circuit potential between weeks two and three suggested that uncontrolled biofilm growth on the cathode deleteriously affects system performance.
    Bioresource Technology 01/2011; 102(1):416-21. · 4.75 Impact Factor
  • Matthew M. Mench
    Fuel and Energy Abstracts 01/2011; 36(21):13867-13867.
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    ABSTRACT: The Penn State chapter of the International Association for Hydrogen Energy supplied a team of 12 members to enter the 1st IAHE Hydrogen Design Competition. Our design team decided to build a portable fuel cell. The design objective was to limit the cell size to 6 cm × 6 cm × 2 cm, and the goal was to achieve maximum power over 1 h of operation. The type of fuel cell we chose was a proton exchange membrane (PEM) fuel cell, using hydrogen and oxygen as the fuel and oxidizer, respectively. The final design converged to a cell stack containing 6 bipolar/end plates, i.e. 5 cells, each measuring 6 cm × 6 cm × 1.975 cm, each with an active area of approximately 25 cm2. The total open circuit voltage was approximately 4.75 V, indicating an average 0.95 V per cell. With an active area of 25 cm2, the maximum power observed during operation was approximately 1.7 W cm−2. The maximum sustained power over 1 h averaged 1.15 W cm−2. The total cost of the project totaled $2245.
    Fuel and Energy Abstracts 01/2011; 36(21):13875-13879.
  • Kyu Taek Cho, Matthew M. Mench
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    ABSTRACT: In this work, the coupled effects of flow field geometry and diffusion media (DM) material structure on evaporative water removal during gas purge are investigated with the ex-situ test methods developed in previous works [31] and [32]. Three different flow field structures with various land to channel width ratios (L/C) were utilized with paper and cloth-type DM to understand the impact of L/C and DM properties on evaporative water removal rate, water distribution in DM, purge efficiency, and irreducible saturation. In the capillary flow dominant regime, it was determined that evaporative water removal is not significantly affected by L/C or DM properties, and can be semi-empirically correlated with critical purge time. The cloth-type DM was found to be superior to paper-type to mitigate the in-plane impedance of the land on water removal. In addition to the ex-situ evaporative tests, neutron radiography was utilized to visualize the in-situ water removal behavior. Results validate a novel purge protocol suggested by the authors in a previous study to achieve a more efficient and durable gas purge that preserves membrane durability.
    International Journal of Hydrogen Energy. 11/2010;
  • Kyu Taek Cho, Matthew M. Mench
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    ABSTRACT: This work is devoted to delineating the fundamentals of evaporative water removal from diffusion media (DM) to achieve highly efficient and durable gas purge. Multiphase water transport from DM during gas purge is characterized by a balance of internal capillary liquid water flow and water vapor diffusion. In this study, DM with polytetrafluoroethylene (PTFE) content ranging from 0 to 20 wt%, and DM with three different geometric pore structures are utilized to understand this material property effect. It is found that overall evaporative water removal rate increases as PTFE content decreases and as the geometric pore structure changes from a two- to a more three-dimensional structure. This is due to the increase of wettability and porous space favorable for the water transport. The effect of phase-change-induced (PCI) flow and capillary flow on water removal is compared, and it is found that PCI flow is dominant at lower saturation of DM, whereas capillary flow is dominant at higher saturation. The results of this study build upon a previous study by the authors (Cho and Mench [17]), and are useful to understand the competing phenomena of water removal in PEFC DM. The ultimate goal of this work is to guide material design to achieve purge that preserves membrane durability with reduced shutdown power requirements.
    Journal of Power Sources. 10/2010;
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    ABSTRACT: A two-dimensional, non-isothermal, anisotropic numerical model is developed to investigate the impact of the interfacial morphology between the micro-porous layer (MPL) and the catalyst layer (CL) on the polymer electrolyte fuel cell (PEFC) performance. The novel feature of the model is the inclusion of directly measured surface morphological information of the MPL and the CL. The interfacial morphology of the MPL and the CL was experimentally characterized and integrated into the computational framework, as a discrete interfacial layer. To estimate the impact of MPL|CL interfacial surface morphology on local ohmic, thermal and mass transport losses, two different model schemes, one with the interface layer and one with the traditionally used perfect contact are compared. The results show a ∼54 mV decrease in the performance of the cell due to the addition of interface layer at 1 A cm−2. Local voids present at the MPL|CL interface are found to increase ohmic losses by ∼37 mV. In-plane conductivity adjacent to the interface layer is determined to be the key controlling parameter which governs this additional interfacial ohmic loss. When the interfacial voids are simulated to be filled with liquid water, the overpotential on the cathode side is observed to increase by ∼25 mV. Local temperature variation of up to 1 °C is also observed at the region of contact between the MPL and the CL, but has little impact on predicted voltage.
    Journal of Power Sources. 07/2010;

Publication Stats

528 Citations
101.36 Total Impact Points

Institutions

  • 2011–2014
    • The University of Tennessee Medical Center at Knoxville
      Knoxville, Tennessee, United States
    • University of Tennessee
      • Department of Mechanical, Aerospace and Biomedical Engineering
      Knoxville, TN, United States
  • 2012
    • Lawrence Berkeley National Laboratory
      • Environmental Energy Technologies Division
      Berkeley, CA, United States
  • 2003–2011
    • Pennsylvania State University
      • • Department of Civil and Environmental Engineering
      • • Department of Mechanical and Nuclear Engineering
      University Park, MD, United States