The electrochemical behavior of the electrode material based on composites of polyaniline (PANI), graphite nanoplatelets (GnP), and polystyrene (PS) matrix was evaluated by applying cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS), for its application in electrochemical supercapacitor which is an advanced energy storing device. Composites were prepared by coating polyaniline on graphite nanoplatelets (PANI/GnP) via in situ emulsion polymerization, exhibiting specific surface area of 178.75 m 2 /g as compared with 72.1 m 2 /g of pristine GnP. The PANI/GnP was then embedded in polystyrene matrix (PANI/GnP/PS), which showed improved electrical conductivity due to an interconnected mesh of PANI/GnP as confirmed by scanning electron microscopy (SEM) morphological analysis. The formation of porous conductive network in PANI/GnP/PS with conductivity value of 8.6 × 10 −3 S/cm resulted in high specific capacitance of 411.3 F/g measured at a current density of 0.5 A/g which corresponded to specific energy of 47.94 Wh/kg and specific power of 281.94 W/kg, as well as the decrease in specific capacitance was 32% even after 1600 charge–discharge cycles showing good rate performance which renders it an ideal material for electrodes in supercapacitors.

In a previous numerical study on heat and mass transfer in air-cooled proton exchange membrane fuel cells, it was found that the performance is limited by heat transfer to the cathode side air stream that serves as a coolant, and it was proposed to place a turbulence grid before the cathode inlet in order to induce a mixing effect to the air and thereby improve the heat transfer and ultimately increase the limiting current and maximum power density. The current work summarizes experiments with different turbulence grids which varied in terms of their pore size, grid thickness, rib width, angle of the pores, and the distance between the grid and the cathode inlet. For all grids tested in this study, the limiting current density of a Ballard Mark 1020 ACS stack was increased by 20%. The single most important parameter was the distance between the turbulence grid and the cathode inlet, and it should be within 5 mm. For the best grid tested, the fuel cell stack voltage and thus the efficiency were increased by up to 20%. The power density was increased by more than 30% and further improvements are believed to be possible.

This study investigates the dynamic behavior of a solid oxide steam electrolyzer (SOSE) system without an external heat source that uses transient photovoltaic (PV) generated power as an input to produce compressed (to 3 MPa) renewable hydrogen to be injected directly into the natural gas network. A cathode-supported crossflow planar solid oxide electrolysis (SOE) cell is modeled in a quasi-three-dimensional thermo-electrochemical model that spatially and temporally simulates the performance of a unit cell operating dynamically. The stack is composed of 2500 unit cells that are assumed to be assembled into identically operating stacks, creating a 300 kW electrolyzer stack module. For the designed 300 kW SOSE stack (thermoneutral voltage achieved at design steady-state conditions), powered by the dynamic 0–450 kW output of PV systems, thermal management and balancing of all heat supply and cooling demands is required based upon the operating voltage to enable efficient operation and prevent degradation of the SOSE stacks. Dynamic system simulation results show that the SOSE system is capable of following the dynamic PV generated power for a sunny day (maximum PV generated power) and a cloudy day (highly dynamic PV generated power) while the SOSE stack temperature gradient is always maintained below a maximum set point along the stack for both days. The system efficiency based upon lower heating value of the generated hydrogen is between 0–75% and 0–78% with daily hydrogen production of 94 kg and 55 kg for sunny and cloudy days, respectively.

A computational fluid dynamics model for high-temperature polymer electrolyte fuel cells (PEFC) is developed. This allows for three-dimensional (3D) transport-coupled calculations to be conducted. All major transport phenomena and electrochemical processes are taken into consideration. Verification of the present model is achieved by comparison with current density and oxygen concentration distributions along a one-dimensional (1D) channel. Validation is achieved by comparison with polarization curves from experimental data gathered in-house. Deviations between experimental and numerical results are minor. Internal transport phenomena are also analyzed. Local variations of current density from under channel regions and under rib regions are displayed, as are oxygen mole fractions. The serpentine gas channels contribute positively to gas redistribution in the gas diffusion layers (GDLs) and channels.

A thin and mechanically stable solid electrolyte interphase (SEI) is desirable for a stable cyclic performance in a lithium ion battery. For the electrodes that undergo a large volume expansion, such as Si, Ge, and Sn, the presence of a robust SEI layer can improve the capacity retention. In this work, the role of solvent choice on the electrochemical performance of Ge electrode is presented by a systematic comparison of the SEI layers in ethylene carbonate (EC)-based and fluoroethylene carbonate (FEC)-based electrolytes. The results show that the presence of FEC as a cosolvent in a binary or ternary solvent electrolyte results in an excellent capacity retention of ∼85% after 200 cycles at the current density of 500 mA g−1; while EC-based electrode suffers a rapid capacity degradation with a capacity retention of just 17% at the end of 200 cycles. Post analysis by an extensive use of X-ray photoelectron spectroscopy (XPS) was carried out, which showed that the presence of Li 2 O in FEC-based SEIs was the origin for the improved electrochemical performance.

Code stability is a matter of concern for three-dimensional (3D) fuel cell models operating both at high current density and at high cell voltage. An idealized mathematical model of a fuel cell should converge for all potentiostatic or galvanostatic boundary conditions ranging from open circuit to closed circuit. Many fail to do so, due to (i) fuel or oxygen starvation causing divergence as local partial pressures and mass fractions of fuel or oxidant fall to near zero and (ii) nonlinearities in the Nernst and Butler–Volmer equations near open-circuit conditions. This paper describes in detail, specific numerical methods used to improve the stability of a previously existing fuel cell performance calculation procedure, at both low and high current densities. Four specific techniques are identified. A straight channel operating as a (i) solid oxide and (ii) polymer electrolyte membrane fuel cell is used to illustrate the efficacy of the modifications.

A method which allows for the comparison of polymer electrolyte fuel cell (PEFC) bipolar plates (BPs) with various channel dimensions is outlined here. It is applied to data from an experiment with different channel and land width and channel depth combinations for interdigitated and parallel designs. Channel and land width and channel depth varied from 0.25 mm to 1 mm on six different BP designs, and two stoichiometries were tested. Each condition was performed three times for repeatability. The method calculates the performance of each condition after accounting for reversible voltage and overpotential changes due to varying pressure and after eliminating ohmic resistance as a variable. In these data, the interdigitated flow field outperformed the parallel flow field. Designs are compared using the BP permeability as a benchmark metric. The method then calculates the area-specific ohmic resistance (ASR) of the cell. It was difficult to draw hard conclusions about changes in the ASR between flow field designs, but there may be more consistent liquid water removal from the gas diffusion layer (GDL) with smaller channel dimensions. It was found that concentration losses seem to be primarily a result of channel width, rather than channel depth.

Flow field plays an important role in the performances of the fuel cells, especially in large area fuel cells. In the present work, an innovative, versatile flow field, capable of combining in different conventional modes is reported and evaluated in a polymer electrolyte fuel cell (PEFC) with an active area of 150 cm 2 . The proposed design is capable of offering serpentine, interdigitated, counterflow, dead-end, and serpentine-interdigitated hybrid mode. Moreover, it is possible to switch over from one flow mode to another mode of flow during operation at any point of time. The flow design consists of the multichannel parallel serpentine flow (SP) field and a pair of an inlet and outlet manifolds instead of conventional single inlet and outlet manifold. Flow distribution was successfully altered without affecting the performances, and it was observed a combination of serpentine and interdigitated on the cathode side offered steady performance for more than 20 min when it was operated at a current density of 700 mA cm −2 .

The flow field design of current collectors is a significant issue, which greatly affects the mass transport processes of reactants/products inside fuel cells. Especially for proton exchange membrane (PEM) fuel cells, an appropriate flow field design is very important due to the water balance problem. In this paper, a wavy surface is employed at the cathode flow channel to improve the oxygen mass transport process. The effects of wavy surface on transport processes are numerically investigated by using a three-dimensional anisotropic model including a water phase change model and a spherical agglomerate model. It is found that the wavy configurations enhance the oxygen transport and decrease the water saturation level. It is concluded that the predicted results and findings provide the guideline for the design and manufacture of fuel cells.

Detailed physics-based computer models of fuel cells can be computationally prohibitive for applications such as optimization and uncertainty quantification. Such applications can require a very high number of runs in order to extract reliable results. Approximate models based on spatial homogeneity or data-driven techniques can serve as surrogates when scalar quantities such as the cell voltage are of interest. When more detailed information is required, e.g., the potential or temperature field, computationally inexpensive surrogate models are difficult to construct. In this paper, we use dimensionality reduction to develop a surrogate model approach for high-fidelity fuel cell codes in cases where the target is a field. A detailed 3D model of a high-temperature polymer electrolyte membrane (PEM) fuel cell is used to test the approach. We develop a framework for using such surrogate models to quantify the uncertainty in a scalar/functional output, using the field output results. We propose a number of alternative methods including a semi-analytical approach requiring only limited computational resources.

A three-dimensional, full-scale, single-phase finite element model has been developed for a liquid-fed direct methanol fuel cell (DMFC) with serpentine flow patterns. Equations for conservation of mass, momentum, and species are coupled with electrochemical kinetics in anode and cathode catalyst layers (CCLs). At the anode and cathode sides, only the liquid and the gas phases are considered, respectively. The significant benefit of a full-scale model is that the effect of physical parameters and distribution of the concentration of species can be realized in different channels for a desired section within the flow patterns. The model is used to study the effects of different operating parameters on fuel cell performance. Comparing numerical and experimental results demonstrate that the single-phase model slightly over-predicts the results for polarization plot. The modeling results also show that the porosity, temperature, and methanol concentration play a key role in affecting the DMFC polarization curve.

Pr 1.9 A 0.1 NiO 4 (A = Ca, Sr, Ba) are synthesized and characterized by X-ray powder diffraction (XRD), infrared spectrum (IR), and X-ray photoelectron spectroscopy (XPS). The effects of alkaline earth doping on the covalence of Pr–O and Ni–O bond, the mean valence of Ni, and the hydroxide absorption ability of material surface are studied. It is found that the covalence of Pr–O and Ni–O bond increases with the decrease of alkaline earth element radius. Meanwhile, the mean valence of Ni and the surface hydroxide absorption ability are enhanced. The electrochemical measurement results indicate that the O 2 − 2 /OH − replacement reaction is facilitated by the increase of mean valence of Ni in the material. The best oxygen reduction reaction (ORR) activity is found in Pr 1.9 Ca 0.1 NiO 4 . The current density of 2.16 mA cm −2 is obtained at a potential of −0.6 V (versus Hg/HgO). The tafel slope is 66.48 mV decade −1 , close to Pt/C material.

Present research deals with multiphysics, pore-scale simulation of Li–O 2 battery using multirelaxation time lattice Boltzmann method. A novel technique is utilized to generate an idealized electrode–electrolyte porous media from the known macroscopic variables. Present investigation focuses on the performance degradation of Li–O 2 cell due to the blockage of the reaction sites via Li 2 O 2 formation. Present simulations indicate that Li–air and Li–O 2 batteries primarily suffer from mass transfer limitations. The study also emphasizes the importance of pore-scale simulations and shows that the morphology of the porous media has a significant impact on the cell performance. While lower porosity provides higher initial current, higher porosity maintains sustainable output.

The Butler–Volmer equation has been widely used to analyze the electron transfer for electrochemical simulation. Although it has been broadly employed with numerous successful applications, the Butler–Volmer equation needs to be solved numerically to find the activation overpotential, which results in the increase of the calculation difficulties. There are also some parameters in Butler–Volmer equation such as exchange current density and symmetry factor that are not always known parameters. In order to avoid the latest mentioned limitation and the numerical calculation which is time consuming and for simplification, there are some approximation equations such as Tafel, linear low polarization, and hyperbolic sine approximation. However, all these equations are only applicable in a specific range of current density or definite condition. The aim of this paper is to present a new form of Butler–Volmer equation using algebraic operation to calculate activation overpotential. The devised equation should be accurate, have a wide application range, able to remove any numerical calculation, and be useful to find exchange current density. In this research, a new form of Butler–Volmer equation and a new approximation equation (called K–J equation) have been successfully derived. The comparison result shows that the new derived form is exactly equal to the Butler–Volmer equation to calculate the activation overpotential, and it removed the necessity of numerical calculation to find the activation overpotential. In addition, the K–J approximation has a good agreement with Butler–Volmer equation over a wide range of current density and is applicable to predict the activation loss.

Dye-sensitized solar cells (DSSCs) have been identified as a viable alternative for conventional solar cells. As liquid electrolyte based DSSCs have several drawbacks, attention has now been diverted toward gel polymer electrolytes (GPEs), which can be placed in between liquid electrolytes and solid electrolytes. In this study, attempts were made to investigate the effect of salt concentration of the GPE on the performance of DSSCs. The GPE used for the study consists of polyvinylidene fluoride (PVdF), ethylene carbonate (EC), propylene carbonate (PC), 1-methyl 3-propyl immidazolium iodide (1M3PII), and iodine (I 2 ). Conductivity variation with salt concentration as well as with temperature was first investigated. DSSCs were then fabricated for all the salt concentrations to observe the relationship between salt concentration, conductivity, and performances of DSSCs. The composition 1.6 PVdF/4 EC/4 PC/1.3 1M3PII/0.1308 I 2 (weight basis) exhibited the highest conductivity, and it was 3.55 × 10 −3 S cm −1 at 28 °C. The sample was an anionic conductor. DSSCs fabricated with the samples having different salt concentrations showed that current density ( J SC ), fill factor (FF), and efficiency ( η ) follow the same variation that exists between conductivity and salt concentration. Open circuit voltage ( V OC ) seemed to be not depending on the conductivity and salt concentration very much.

An optimal or near to optimal design and operation of a direct liquid fuel cell (DLFC) stack requires an understanding of the relevant physical phenomena across length scales in the stack. In particular, perturbations between cells can arise due to external manifold design as well as variations in material and design parameters between cells. In this work, we seek to derive closed-form analytical expressions that capture the global stack performance, as well as individual cell behavior such as cell potential, current density, and methanol distribution. This approach allows for the simulation of large stacks with near to negligible computational overhead. Finally, the solutions are demonstrated for a stack subjected to perturbations in the anode inlet velocity of each cell.

A one-dimensional analytical model of a direct methanol fuel cell (DMFC) was presented. This model was developed to describe the electrochemical reactions on the anode and cathode electrodes, and the transport phenomena in fuel cell consisting of methanol transport from anode to cathode through the membrane (methanol crossover), diffusion of reactants in gas diffusion layers (GDLs), and fluid flow in flow channels. One of the main strike features of this work was that the complicated relations were simplified logically and the model was solved analytically by the first-order differential equation. The results of the model indicated that increasing the current density led to lower methanol concentration in anode in spite of higher oxygen concentration in cathode. The presented model supports the experimental data well.

In a proton exchange membrane fuel cell (PEMFC), the hydrogen feed into the anode in a periodical pressure swing, so-called hydrogen pressure pulsation feed (HPPF), significantly affects the transport phenomena of hydrogen and water in the anode flow field. HPPF could adjust the distribution of the back diffusion water and the hydrogen partial pressure along the anode flow channels, improve hydrogen mass transfer in the anode flow field, and enhance the diffusion of hydrogen in the porous medium (anode diffusion layer). On the other hand, HPPF technique could mitigate the anode flooding issue caused by water back diffusion from the cathode, improve the fuel cell performance. In this work, the principle of HPPF technique was introduced and analyzed by a mathematic approach. Some of the important parameters used in HPPF technique, such as amplitude of pulsation pressure, pulsating frequency, etc., were experimentally investigated on dead-end mode PEMFC stack. The experimental results showed that the amplitude of pressure pulsation, pulsating frequency, and position applied for HPPF highly affected the performance of the PEMFC stack. It can be seen that higher the frequency and/or amplitude of pressure pulsation, the better the performance of PEMFC stack.

Due to the tight coupling of physical processes inside solid oxide fuel cells (SOFCs), efficient control of these devices depends largely on the proper pairing of controlled and manipulated variables. The present study investigates the uncontrolled, dynamic behavior of an SOFC stack that is intended for use in a hybrid SOFC-gas turbine (GT) system. A numerical fuel cell model is developed based on charge, species mass, energy, and momentum balances, and an equivalent circuit is used to combine the fuel cell's irreversibilities. The model is then verified on electrochemical, mass, and thermal timescales. The open-loop response of the average positive electrode-electrolyte-negative electrode (PEN) temperature, fuel utilization, and SOFC power to step changes in the inlet fuel flow rate, current density, and inlet air flow rate is simulated on different timescales. Results indicate that manipulating the current density is the quickest and most efficient way to change the SOFC power. Meanwhile, manipulating the fuel flow is found to be the most efficient way to change the fuel utilization. In future work, it is recommended that such control strategies be further analyzed and compared in the context of a complete SOFC-GT system model.

Degradation tests of two phosphoric acid (PA) doped polybenzimidazole (PBI) membrane based high temperature polymer electrolyte membrane (HT-PEM) fuel cells were reported in this paper to investigate the effects of start/stop and the presence of methanol in the fuel to the performance degradation. Continuous tests with H2 and simulated reformate which was composed of H2, water steam and methanol as the fuel were performed on both single cells. 12-h-startup/12-h-shutdown dynamic tests were performed on the first single cell with pure dry H2 as the fuel and on the second single cell with simulated reformate as the fuel. Along with the tests electrochemical techniques such as polarization curves and electrochemical impedance spectroscopy (EIS) were employed to study the degradation mechanisms of the fuel cells. Both single cells showed an increase in the performance in the H2 continuous tests, because of a decrease in the oxygen reduction reaction (ORR) kinetic resistance probably due to the redistribution of PA between the membrane and electrodes. EIS measurement of first fuel cell during the start/stop test showed that the mass transfer resistance and ohmic resistance increased which can be attributed to the corrosion of carbon support in the catalyst layer and degradation of the PBI membrane. During the continuous test with simulated reformate as the fuel the ORR kinetic resistance and mass transfer resistance of both single cells increased. The performance of the second single cell experienced a slight decrease during the start/stop test with simulated reformate as the fuel.