Faculty Publications
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Item Compressive cyclic response of PEM fuel cell gas diffusion media(Elsevier Ltd, 2021) Koorata, P.K.; Bhat, S.D.The fuel cell gas diffusion media (GDM) is a highly porous carbon-fiber-reinforced thin composite layer. The experimental response of these materials is observed to be highly nonlinear at low-stress levels. The cyclic mechanical response of GDM is investigated in terms of stiffness and damage parameters. The prediction of the state of deformation in GDM is vital in relating GDM's properties to ohmic and transport losses. To this end, a compressible form of the phenomenological model is proposed to capture the experimental cyclic response accurately. The model is constituent dependent; that is, the cumulative cyclic stress-strain response of GDM is a function of individual constituent phases present in the material. These individual constituents are porous matrix and reinforced fibers. The model hence derived for a typical GDM material, can predict residual strain, hysteresis, and damage quotient associated with the stress softening. This advanced model is implemented in the numerical domain to evaluate the response of the polymer electrolyte fuel cell (PEFC) unit cell. The stress-strain distribution fields are analyzed and compared with those of conventional GDM models. The results point to a remarkable deviation from the conventional notion of structural analysis. © 2020 Hydrogen Energy Publications LLCItem Numerical investigation on the sensitivity of endplate design and gas diffusion material models in quantifying localized interface and bulk electrical resistance(Elsevier Ltd, 2021) Shinde, U.; Koorata, P.K.A localized non-intuitive relationship between electrical interface contact resistance and bulk properties such as bulk electrical resistance and permeability in the fuel cell gas diffusion layer (GDL) is reported. A numerical method is adopted to investigate contact pressure and hence the interface contact resistance at the interfaces of bipolar plate (BPP)|GDL and GDL|Polymer electrolyte membrane (PEM). The results are observed to be sensitive to GDL material models as well as endplate designs. This means, endplates designed to improve the electrical contact resistance or contact pressure at the BPP|GDL interface may not necessarily assure an improvement in bulk properties, in fact, it is observed in this study that these properties are inversely related. Further, a differential deformation in GDL along with consolidation effect is predicted with compressible version of hyperelastic material model. More importantly, it is revealed that the selection of material models plays a significant role in the deformation behaviour of the GDLs irrespective of the clamping design adopted. © 2021 Hydrogen Energy Publications LLCItem Numerical investigation on the improved reactant mass transport with depth-dependent flow fields in polymer electrolyte fuel cell under inhomogeneous gas diffusion layer compression(Elsevier Ltd, 2021) Padavu, P.; Koorata, P.K.; Bhat, S.D.In this work, a numerical model is developed to analyse the effects of depth-dependent reactant flow field geometry under inhomogeneous gas diffusion layer (GDL) compression on the mass transport process and performance of polymer electrolyte fuel cell (PEFC). The types of depth-dependent flow channels considered in this study are: converging channel (depth continuously decreasing) and diverging channel (depth continuously increasing), and the conventional flow field designs. The model is investigated for local and global inhomogeneity due to GDL compression. The localized inhomogeneity is introduced in the flow-field rib as well as channel regions. The results are compared for reactant concentration, water concentration, local current density, and the polarization curve for different flow channel combinations. It is observed that the availability of reactants is higher in case of converging channel design, which leads to an increase in cell performance at higher currents. However, this is subjected to GDL inhomogeneity in compression. We observe in this study that such inhomogeneity, instead of having a significant impact on cell performance, lead to minimal influence in terms of reduction in cell performance. This we observe is due to improved H2 availability at anode and reduced O2 distribution at cathode that ultimately impacts respective hydrogen oxidation reaction (HOR) and reduction in oxygen reduction reaction (ORR). This study aims to investigate the cases for altered variation in cell performance due to change in depth-dependent flow fields. © 2021Item Thermomechanical stability and inelastic energy dissipation as durability criteria for fuel cell gas diffusion media with pre-assembly effects(Elsevier Ltd, 2022) Koorata, P.K.; Bhat, S.D.In this article, pre-assembly hot-press pressure and thermal expansion effects in gas-diffusion layers (GDLs) are addressed to explore the practicalities of the constitutive model reported in the companion article. A facile technique is proposed to include deformation history dependent residual strain effects. The model is implemented in the numerical environment and compared with widely followed conventional models such as isotropic and orthotropic material models. With the normal and accelerated thermal expansion effects no significant variation in stresses or strains is reported with the compressible GDL model in contrast to the conventional incompressible form of the GDL model. The present work identifies the critical differences with advanced and extended variants of the model along with conventional GDL material models in terms of planar stress/strain distribution and the membrane response. Finally, the model is simulated for micro-cyclic stress loads of varying amplitudes that imitate the real working conditions of fuel cell. The inelastic energy dissipation in GDLs is predicted using the proposed model, which is utilized further to distinguish the safe (elastic) and unsafe (inelastic shakedown) operating limits. The inelastic collapse of GDLs is shown to be a active function of high amplitude micro-cyclic load with high initial clamping load. © 2021 Hydrogen Energy Publications LLCItem A phase-dependent constitutive model to predict cyclic electrical conductivity in fuel cell gas diffusion media(Elsevier B.V., 2022) Shinde, U.; Koorata, P.K.Structure-property relation in fuel cell gas diffusion layer (GDL) is a dependent function of its constituents. The bulk electrical conductivity of these layers is known to be relative density function varying due to external force or cell operating conditions. To locally predict the changes due to complex working conditions, an accurate model that predicts the nonlinearity of GDLs is highly desirable. To this end, this article proposes a material model that is phenomenologically derived to address the cyclic electrical conductivity of GDLs. Functional variables are taken to operate on porosity variation, fiber contact density, and fiber dislocation parameters. In the presence of these parameters, the results illustrate nonlinear conductivity variation with the magnitude of applied cyclic compressive load. Through successive loading-unloading, the porous structure is modeled to reach a steady-state reflecting stable conductivity-stress behavior for the constant stress limit. An interesting behavior of GDL can be captured where conductivity reduces as compressive load exceeds a threshold limit called break stress due to fiber breakages or dislocations. A greater applicability of this model may lie in mapping localized in-situ response of GDLs under cyclic operations. © 2022 Elsevier B.V.Item Deformation Mechanics of Fuel Cell Gas Diffusion Layer: Cyclic Response and Constitutive Model(Institute of Physics, 2022) Koorata, P.K.The deformation mechanics of a typical gas diffusion layer using experimental and advanced modelling technique is reported. The experimental cyclic response is observed similar to pseudo-elastic materials with highly nonlinear loading/unloading. The cyclic compressive mechanical response of gas diffusion layer (GDL) is modelled to be the outcome of cumulative changes in deformation kinematics of matrix and fiber fractions. The individual mechanisms necessitating the energy dissipation, residual strain, and stress softening during cyclic mechanical response are related to nonlinear hyperelastic matrix with the damage function and inelastic activation function at the interface of constituents. The model predicts highly nonlinear elastic loading, residual strain, hysteresis, and damage quotient associated with stress softening as a function of several cycles. The significant takeaway from this study is in terms of quantifying strength, inelastic nature of individual constituents. The proposed model is simulated for low-level altering stresses of up to twenty cycles. The results show the build-up of residual strains and hysteresis as a function of fuel cell clamping pressure. © 2022 The Electrochemical Society (“ECS”). Published on behalf of ECS by IOP Publishing Limited.Item Electrical/flow heterogeneity of gas diffusion layer and inlet humidity induced performance variation in polymer electrolyte fuel cells(Elsevier Ltd, 2023) Shinde, U.; Koorata, P.K.; Padavu, P.A three-dimensional single-flow channel computational model is used to investigate the performance characteristics of polymer electrolyte fuel cells (PEFC). The combined influence of non-uniform interfacial contact resistance (ICR) and inlet relative humidity (RH), along with the heterogeneous flow properties of the gas diffusion layer (GDL) on the PEFC performance is evaluated. The study considers combinations of full and partial humidification of anode and cathode reactants. Results reveal heterogeneous GDL with non-uniform ICR distribution results in a slight ∼4.4% reduction in current density at 0.3V compared to the homogeneous case. However, under same electrical/flow heterogeneities, the current density is observed to increase by ∼19% to ∼1.3A/cm2 under fully humidified anode and partially humidified cathode (i.e., RHa|RHc = 100%|60%) as compared to ∼1.1A/cm2 under symmetric RHa|RHc = 100%|100%. Interesting observations are made on the temperature distribution and cathodic water fractions. The variation in anodic inlet humidity is observed to have no impact on temperature distribution in the membrane, whereas variation in cathodic inlet humidity is effective in reducing the temperature in the channel regime with a 4K (kelvin) difference among all the cases. It is noted here that the overpotential map is not an indicator for performance loss, at least at full inlet humidity. This parameter is observed to depend on water concentration in the cathode. The study provides a detailed analysis of the distribution of reactant mass fraction, water concentration, current density, temperature, cathodic overpotential, and cell performance for all the simulated cases. © 2022 Hydrogen Energy Publications LLCItem Numerical investigation on the effects of inhomogeneous gas diffusion layer and impact of interfacial contact resistance on the performance of polymer electrolyte fuel cells(Elsevier Ltd, 2024) Shinde, U.; Koorata, P.K.; Padavu, P.In this study, a three-dimensional single channel is numerically modeled to simulate the polymer electrolyte fuel cell (PEFC) with a homogeneous and inhomogeneous gas diffusion layer (GDL). The influence of interfacial contact resistance (ICR) between GDL and current collector ribs (GDL|CC) is also studied. In the present study, GDL is considered as a single component (homogeneous) in one case and inhomogeneous with varying electrical and flow properties to illustrate the inhomogeneity in another case. The inhomogeneity in GDL is primarily caused by localized deformation due to non-uniform contact pressure during fuel cell assemblies. The consideration of ICR is observed to have a significant effect on both the ohmic and mass transport regions of the polarization curve. Inhomogeneous GDL with ICR, considered close to a practical scenario, shows a ∼7% drop in performance evaluation at 0.3V. The study reveals increased consumption of reactants at higher current loads when ICR is assumed negligible. This study examines the effects of homogeneous GDL, inhomogeneous GDL, and the impact of ICR on the distributions of reactant concentration, water concentration, temperature, current density, and polarization curve in PEFC. This study presents the practical aspects of PEFC considering inhomogeneous GDL electrical and flow properties. © 2023 Hydrogen Energy Publications LLC