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This paper presents the fabrication and characterization of a 'T'-shaped methanol-based fuel cell supported on paper. Methanol is used as the fuel and potassium permanganate is used as the oxidant. A polyacrylamide based gel, impregnated with H2SO4 limits the fuel and oxidant cross over and serves as the membrane/electrolyte to facilitate the ion transport between anode and cathode. Composite of nitrogen doped graphene oxide and NiCo2O4 micro-spheres, having flower-like structure, is used as the catalyst on both the electrodes to improve the cell performance. The use of catalyst has led to 5 times increase in the peak power density. The catalysts are characterized using XRD, SEM, EDX and TEM. A stack of two paper cells could illuminate an LED for 30 minutes. A simple mathematical model based on Butler-Volmer kinetics is used to predict the cell performance and predictions are compared with experimental measurements. [ABSTRACT FROM AUTHOR]

The article reports on the impact of the 1957 paper of Carl Wagner and Kalevi Kiukkola on the development of electrochemical probes and tools for fundamental research and practical applications. It reveals that their study lead to the development of technique in measuring surface energies and improved the measurement of chemical diffusion. It further discusses its impact on enhancement of catalytic rates, on the stability chemical sensors, and the development of high temperature fuel cells.

A carbon-cloth gas diffusion layer (GDL) displays better performance than a carbon-paper GDL under humidified conditions. A straight flow field displays better performance than a serpentine flow field. To investigate these phenomena, neutron radiography was used to compare the amount of liquid water that accumulated in test fuel cells. It was found that a larger amount of water accumulated in a carbon-cloth GDL than in a carbon-paper GDL. From the viewpoint of cell performance, the carbon-cloth GDL was less influenced by the accumulated water than the carbon-paper GDL. It is assumed that the broader pore distribution of a carbon-cloth GDL creates oxygen-diffusion paths even if water accumulates in the GDL. With a serpentine flow field, water accumulated in the corner and the gas bypassed the flow field. These phenomena are the main causes of performance deterioration with a serpentine flow field. [ABSTRACT FROM AUTHOR]

This article focuses on the Electrochemical Society meeting held in Los Angeles, California. The first symposium of the Physical and Analytical Electrochemistry Division focused on Durability and Reliability of Low-Temperature Fuel Cells and Fuel Cell Systems. This symposium presented Outstanding Student Paper Awards to students of various universities of the United States. For example, Vishal Mittal of the University of Connecticut got the award for his paper entitled, "Factors Accelerating Membrane Degradation Rate and the Underlying Degradation Mechanism in PEMFC." In this paper, experiments were performed to elucidate the factors and conditions important for photoelectromagnetic degradation.

Information on several topics discussed at the Proton Exchange Membrane Fuel Cells (PEMFC) symposium is presented. The event was attended by over 370 people who have contributed talks and posters. The symposium of five days includes activities like parallel sessions focused on fuel cell systems, cell stack and component hardware, durability, and direct fuel cells. Moreover, $500 were awarded to outstanding students on the field of electrochemical including Kevin Gallagher and Shirlaine Koh.

This paper initially fits a comprehensive set of thermodynamic and transport properties charged mobile defects (protons, oxygen vacancies, and small polarons) in proton-conducting BaZr0.8Y0.2O3−δ (BZY20). The fits are based on recently published measurements, including conductivity, proton concentrations via Karl–Fischer titration, and non-stoichiometry via thermogravimetric analysis, all with wide ranges of temperatures and pressures. These properties are needed for inclusion in physicsbased models. The paper goes on to fit charge-transfer kinetics in Butler–Volmer form, based primarily in protonic-ceramic fuel cell data in button-cell format. These fits use the previously fitted thermodynamic and transport properties without alteration. The next step is to consider the kinetics of H2O-incorporation kinetics (i.e. Stotz-Wagner hydration). Unfortunately, to date, there are no direct measurements of these thermal (i.e. not charge-transfer) kinetics. However, the present analysis shows great sensitivities to the defect-incorporation kinetics, ranging from near equilibration to strong rate limitations. The paper concludes with modeling and interpreting the performance of an electrochemical hydrogen-compression cell, using the newly established properties. [ABSTRACT FROM AUTHOR]

Direct formic acid fuel cells (DFAFCs) have received considerable attention because they can generate a higher power density compared to other direct liquid fuel cells. However, when generated CO2 bubbles are retained in the anode’s porous transport layer (PTL), the performance of the DFAFCs deteriorates. The gas–liquid two-phase flow behavior within a PTL is not clear; therefore, in this work the power-generation characteristics of DFAFCs using two types of PTL, carbon paper and carbon cloth, were investigated. It was found that the maximum current density was approximately 60 mA cm−2 higher with the carbon cloth than with the carbon paper. The CO2 bubble distribution in the anode’s PTLs was visualized by X-ray computed tomography and discuss the effects of the bubbles on the power-generation performance of DFAFCs. We found that interstices in a carbon-cloth PTL provided pathways for bubble migration and release to the channel, so that the bubbles did not deteriorate the power output. Bubble accumulation in a carbon-paper PTL led to a drop in power output, confirming that the structure of the PTL and the CO2 bubbles affect the power-generation characteristics. [ABSTRACT FROM AUTHOR]

High concentration of carbon monoxide (CO) in the gas mixture entering the fuel cell can cause fuel cell poisoning, which can significantly reduce the life expectancy of the cell. To overcome this problem, we propose a new methodology based on the use of micro-cantilevers to detect minute concentrations of CO in a gas mixture. For this purpose, micro-cantilevers are coated with Copper Y (CuY) zeolite and utilized to selectively adsorb CO on their surface. It is shown that the adsorption of CO yields a measurable shift in the natural frequency of the micro-cantilevers, which can be directly correlated with the concentration of CO in the gas mixture. It is determined that the maximum adsorption capacity of the sensor occurs at 40 °C using CuY zeolite with 10 wt% Cu content. Furthermore, the shift in the natural frequency of the sensor is observed to increase as the thickness of the zeolite layer is increased up to a threshold value corresponding to about a quarter of the thickness of the micro-cantilever. At this point, a clearly measurable shift of about 275 Hz in the natural frequency of the micro-cantilevers is observed. While the maximum frequency shift occurs using a relatively thick zeolite layer, it is observed that, for the range of thicknesses considered, the maximum frequency shift per unit weight of CO adsorbed (sensitivity) decreases as the thickness of the zeolite layer is increased. The methodology proposed in this paper could pave the way towards the development of a portable and self-contained unit to monitor the concentration of CO in a mixture of gases. [ABSTRACT FROM AUTHOR]

In this paper, a long-term durability test for 3910 h is carried out on a low Pt-loading fuel cell stack by simulating the dynamic driving cycles. The performance of a specific membrane electrode assembly (MEA) in the stack before and after the test is analyzed, revealing the high voltage decay rate of the appliance. Various electrochemical and physical characterization techniques are used to analyze the degradation mechanism of the MEA via region-based segmentation technique. The results show that the degradation of MEA performance is mainly due to the agglomeration and loss of Pt nanoparticles in the cathode catalyst. In particular, the growth of catalyst particles occurs at the inlet and outlet of the cathode. A high loss rate of Pt particles at the cathode inlet causes their aggregation at the boundary between the catalyst layer and the membrane where the loss of Pt is initiated. Finally, the migration of the unsupported Pt particles occurs due to the gravity toward the underlying cathode micro porous layer. This study had important implications for promoting the development and commercial application of cost-efficient and long-life MEAs. [ABSTRACT FROM AUTHOR]

We describe the application of several surface profile filters as an enabling tool in the dimensional measurements of an engineering artifact, namely, a fuel cell plate. We recently reported work on the development of a non-contact system for dimensional metrology of bipolar fuel cell plates. That system comprises two laser spot triangulation probes that acquire profile data across a plate. While the non-contact system provides rapid measurements (measurement speed of 100 mm s-1 to 500 mm s-1), the data are noisy and cannot be used directly to obtain features of interest such as channel depth and width. In this paper, we show how different surface profile filters such as the spline, morphological, and robust filters, can be employed to identify and suppress outliers and to produce a mean line that serves as a substitute geometry from which we can determine features of interest. Further, we compare the non-contact probe data against contact probe measurements made using a coordinate measuring machine. Surface profile filters are again useful in correcting the reference data for tip size and also in removing any free form deformation in both data sets prior to parameter evaluation and comparison. [ABSTRACT FROM AUTHOR]

The output characteristics of the Proton-Exchange Membrane Fuel Cells (PEMFCs) are affected by multiple factors, but quantitatively describing the relationships is challenging. In this paper, a semi-empirical dynamic model of PEMFC is established firstly. The influence of a single factor on the output characteristics of PEMFC is analyzed longitudinally. Then, a derivative significance weight analysis based on support vector regression (SVR-DSWA) algorithm is proposed to analyze the influence weights of multi-factors on the output characteristics, and the optimal parameters combinations in different current density regions are obtained by maximizing the output voltage values based on formulated SVR model. The Root-Mean-Square Error (RMSE) of output voltage prediction results based on the SVR algorithm is less than 0.0458, and the accuracy of weight analysis results by using the SVR-DSWA algorithm and the optimal parameters combinations analysis method are verified by 4-factor 3-level orthogonal experiments in low, medium, and high current density regions. The SVR-DSWA algorithm and optimal parameters combinations analysis method can replace the orthogonal experiment to analyze the influence weights and optimal combinations of input factors on the output characteristics within the full current density range rapidly, and has much higher efficiency than the orthogonal experiment. The analysis results can provide theoretical support for improving fuel cell performance and formulating a control strategy. [ABSTRACT FROM AUTHOR]

The surface area of carbon electrodes in redox flowbatteries and fuel cells governs the rates of electrochemical reactions. Carbon cloth electrodes offer greater durability and serve as a potential substitute for conventional carbon paper electrodes. Growing multi-walled carbon nanotubes (MWCNTs) on carbon cloth electrodes is an effective way to increase the surface area and overall performance of these devices. In this study, electrodeposited cobalt nanoparticles were used as seed catalysts to synthesize MWCNTs onto carbon cloth through chemical vapor deposition. Scanning electron microscopy and energy dispersive X-ray analysis confirmed cobalt deposition and uniform MWCNT growth throughout the carbon cloth electrode. The MWCNT cloth, MWCNT paper, and plain carbon cloth were tested in a 3-electrode electrochemical arrangement and a hydrogen-vanadium reversible fuel cell to determine surface enhancement factors and fuel cell performances, respectively. The MWCNT cloth and MWCNT paper have 2-3 times the surface area of their respective conventional substrates. The hydrogen-vanadium reversible fuel cell with MWCNT carbon cloth electrode has a peak power performance of 0.61 W mg-1 cm-2, compared to 0.54 W mg-1 cm-2 for MWCNT carbon paper and 0.29 W mg-1 cm-2 for plain carbon cloth. [ABSTRACT FROM AUTHOR]

Efficient and robust oxygen reduction reaction (ORR) catalysts are essential for the development of high-performance anion-exchange membrane fuel cells (AEMFC). To enhance the electrochemical performance of metal–organic frameworks of cobalt-based zeolite imidazolium skeleton (ZIF-67), this study reported a novel ZIF-67-4@CNT by in situ growing carbon nanotubes (CNTs) on the surface of ZIF-67 via a mild two-step pyrolysis/oxidation treatment. The electrochemical results showed that the as-prepared ZIF-67-4@CNT after CTAB modification exhibited excellent catalytic activity with good stability, with Eonset, E1/2, and Ilimit, respectively were 0.98 V (versus RHE), 0.87 V (versus RHE) and 6.04 mA cm−2@1600 rpm, and a current retention rate of about 94.21% after polarized at 0.80 V for 10 000 s, which were all superior to that of the commercial 20 wt% Pt/C. The excellent ORR catalytic performance was mainly attributed to the large amount of the in situ growing CNTs on the surface, encapsulated with a wide range of valence states of metallic cobalt. [ABSTRACT FROM AUTHOR]

External pumps (e.g. syringe pump) that operate microfluidic fuel cell (MFFC) devices are inefficient because the amount of electricity required to run such pumps easily exceeds that generated by the MFFC. Herein, we propose a suitable small, lightweight, and external power-free osmosis-driven pump embedded with an MFFC system, capable of steady-flow generation. Methanol and vanadium are used as fuel, and the electrodes are made of carbon paper. We do not utilize sputtering equipment, commonly used for electrode fabrication. To incorporate the carbon paper-based electrode into the MFFC, the cross section of the microchannel is uniquely designed into a bridge-shaped channel, and its electrochemical and fluid dynamic influences are analyzed through experiments and simulations. The total weight of our MFFC system is less than 20 g, the size is approximately 5 cm, and the power density generated is approximately 0.3 mW cm−2. The presented methods will contribute to the development of standalone MFFCs operable for prolonged durations (~1 d), thereby enhancing the possibility of MFFC commercialization. [ABSTRACT FROM AUTHOR]

Voltage cycling causes catalyst nanoparticles in polymer-electrolyte fuel cells to grow. The concomitant loss of interfacial area results in larger kinetic, transport, and possibly ohmic overpotentials. This paper uses recently published experimental data and mathematical models to investigate the evolutions of transport and ohmic resistances to platinum nanoparticles located on the surface and inside the micropores of carbon black supports. Resistance to oxygen transport rises as surface area declines primarily because the flux to each remaining larger platinum particle increases. The path lengths governing oxygen diffusion to surface and buried platinum sites also increase as nanoparticles grow. Platinum nanoparticles on the surface become relatively less favorable as voltage cycling proceeds because they grow faster than platinum in micropores. Because voltage cycling causes total interfacial area to decline, and the fraction located inside micropores to increase, nanoscale ohmic losses increase as a catalyst layer decays. The practical importance of this effect is difficult to discern because proton conductivity in carbon micropores is not well characterized. [ABSTRACT FROM AUTHOR]

This paper discusses the results of an experimental and modelling activity devoted to the analysis of start-up/shut-down of PEM fuel cells under operative conditions representative of automotive applications, when mitigation strategies are implemented. The focus is on air start-ups after long stops, when permeated air into the anode could not be avoided. A transient and physical 2D model was developed, incorporating the main electrochemical reactions and pseudo-capacitive contributions, calibrated on specific experiments and validated on local measurements of potential and current. Through the simulations, the impact of each phenomenon was separated in the complex dynamics of the process, elucidating the key role of platinum oxides. The experimental measurements comprise the local potentials, provided by through-plate Reference Hydrogen Electrodes, and the in-plane currents, measured among four regions of a segmented hardware. A systematic study of mitigation strategies based on stressors is presented, like: anode flow rate, oxygen dilution and temperature. Their effectiveness results from the ability in reducing either the process duration or the maximum potential. The model helps in interpreting the observed changes and to obtain trends of corroded carbon as a function of stressors; a controlling role is played by the anode flow velocity and the anodic oxygen concentration. [ABSTRACT FROM AUTHOR]

Oxygen-electrode-supported solid oxide cells (OESCs) have potential advantages over fuel-electrode-supported cells, including reduced fuel-electrode concentration polarization, better oxygen electrode current collection, and flexibility in the fuel electrode choice. However, there are serious drawbacks including the difficulty of co-firing the oxygen electrode and electrolyte, and oxygen electrode concentration polarization. This paper explores the characteristics of OESCs with La0.8Sr0.2MnO3-d-Zr0.92Y0.16O2-d (LSM-YSZ) electrode-support enhanced by SrTi0.3Fe0.6Co0.1O3-d (STFC) infiltration, thin YSZ electrolyte, and SrTi0.3Fe0.7O3-d (STF) fuel electrodes. The STFC infiltration increases fuel cell maximum power density by >1.5 times and electrolysis current density (at 1.3 V) by >2 times. Cell performance in pure oxygen is compared to that in air, exploring a possible reversible solid oxide cell system configuration where oxygen produced during electrolysis is stored and subsequently used during fuel cell operation. The fuel cell maximum power density is increased from 0.88 W cm-2 in air to 1.37 W cm-2 in oxygen, with limiting current increased from 1.7 to >5.6 A cm-2; the electrolysis performance is essentially unchanged, probably because the electrode air becomes enriched with oxygen during electrolysis. [ABSTRACT FROM AUTHOR]

Three protocols of accelerated startup and shutdown (SU/SD) test were investigated: startup and shutdown with air supply and soak to both anode and cathode (air-SU/SD), hydrogen protected startup and shutdown (H2-SU/SD), and hydrogen protected startup and shutdown with a load (H2-SU/SD with a load). The performance losses, electrochemical surface area (ECSA) reduction, and catalyst layer degradation were characterized and compared for these SU/SD protocols. Air-SU/SD protocol showed much more severe performance loss and catalyst layer degradation than hydrogen protected ones, which confirmed the benefits of hydrogen protection. The temperature effect on air-SU/SD was significant in a broad range from 20 °C to 70 °C, with low temperature greatly reducing the degradation. The mechanism of H2 protection and load drawn in alleviating carbon corrosion was explained based on reactions and charge conservation during SU/SD. This paper provides comprehensive test data and failure analysis to quantify the benefits of H2 protection and load drawn and to facilitate future enhancement of system strategies on SU/SD durability. [ABSTRACT FROM AUTHOR]

Hydrogen refueling stations (HRSs) that dispense hydrogen to fuel cell vehicles need to ensure the quality of hydrogen to avoid contamination of the vehicle’s expensive fuel cell stacks. Currently, stations verify their fuel quality only periodically to ensure that they meet the strict fuel quality standards specified by either International Organization for Standards (ISO) or Society for Automotive Engineers (SAE). The development of hydrogen contaminant detectors (HCDs) that can provide low cost continuous monitoring at the HRS can be an invaluable asset in protecting fuel cell vehicles from any fuel contamination in-between infrequent expensive analysis of hydrogen fuel quality. An HCD capable of detecting < 200 ppb of CO in hydrogen is presented in this paper. The HCD is based on an electrochemical hydrogen pumping cell whose ultra-low loaded working electrode is poisoned by the contaminant, thus reducing its hydrogen oxidation reaction rate. The hydrogen pumping cell consists of a Nafion® membrane, a sputtered Pt working electrode, a Pt/Ru counter/pseudo-reference electrode and an internal water wicking system that provides humidification to the membrane and electrodes. When this HCD is operated in a pulsed voltammetry mode, it can provide stable CO response for thousands of hours in a HRS. [ABSTRACT FROM AUTHOR]

An analytical model for resistance to oxygen transport in air electrodes containing carbon black supports with high surface area was developed by combining a Thiele modulus--effectiveness factor approach at the agglomerate scale (~150 nm) with nanoscale diffusional resistance in carbon micropores/pits (~5 nm). This paper extends an earlier model for transport resistance to platinum nanoparticles on low surface area carbon. Differences in transport resistances between catalyst layers with high and low surface area carbon blacks predicted by the model with reasonable geometric dimensions and physical properties are consistent with experimental observations. [ABSTRACT FROM AUTHOR]

A novel microstructural modeling approach was developed to stochastically generate a realistic 3D structure of carbon fiber paper based gas diffusion media used in polymer electrolyte fuel cells (PEFCs). The in-house developed algorithm features a stochastic structure generator that allows creating full-length non-overlapping fibers, carbonized binder, and PTFE as distinct phases according to the carbon paper manufacturing process. The resulting 3D structure consists of a high-aspect ratio paper sheet which is large enough to contain an accurate representation of the variability expected from the manufacturing process, as confirmed by thorough validation with experimental data. Three characteristic subdomains with low, average, and high porosity were selected from the sheet to analyze the distribution of transport properties and determine correlations to structural features such as porosity, fiber alignment, and orientation. The range of simulated transport properties were found to be in good agreement with experimental data and provides a practical data set including bulk average and statistical variation for each property. The stochastic modeling framework reported herein is based entirely on in-house developed algorithms that can be applied as a design tool for development and analysis of new gas diffusion materials for fuel cells. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) exhibits relatively high proton conduction even at low relative humidity (RH) and temperatures. Thus, multi-layered GO film (GO paper) is a promising electrolyte in various cells and batteries. We report the in-plane and through-plane proton conductivities of GO paper at low RH and room temperature. The conductivities were 10−5-10−4 S/cm at RH of 10–20%. We examined the performance of a graphene oxide fuel cell (GOFC) with GO paper as the electrolyte at low RH (<20%) and room temperature. We demonstrated that a simple membrane electrode assembly (MEA) based on Pt/GO/Pt system functioned as a H2/O2 fuel cell. The GOFC with Pt/C electrodes afforded better fuel cell performance than a MEA composed of Pt/C electrodes and Nafion electrolyte. GO paper composed of nano-sized GO (nanoGO) flakes enhanced the performance of the GOFC, particularly the current density. Furthermore, a composite of Fe phthalocyanine (PcFe) /reduced GO (rGO)/TiO2 could act as the Pt-free oxygen electrode in GOFC, although the fuel cell performance should be improved for practical applications. Our study suggests that a low cost GOFC without a Nafion electrolyte and noble metal electrodes could be fabricated in the near future. [ABSTRACT FROM AUTHOR]

This paper presents the fabrication and characterization of a micro alkaline direct ethanol fuel cell. The device has been conceived as a feasibility demonstrator, using microtechnologies for the fabrication of the current collectors and traditional techniques for the membrane electrode assembly production. The fuel cell works in passive mode, as expected for the simplicity required for micro power systems. Non-noble catalysts have been used in order to implement the main advantage of alkaline systems, showing the feasibility of such a device as a potential very-low-cost power device at mini- and micro scales. [ABSTRACT FROM AUTHOR]

Water transport through the cathode and oxygen presence/absence in the anodic solution, are important for operation and performance of single chamber microbial fuel cells (SCMFCs). This study focused on water transport and biofilm formation on carbon papers with different characteristics: hydrophobicity, thickness, and presence of a micro porous layer (MPL). The results showed that higher hydrophobicity, thicker structures and the presence of the MPL decreased the water transport over time. The carbon papers with low hydrophobicity had complete penetration of biofilms and higher water transport, while those with high hydrophobicity and MPL had no biofilm penetration and lower water transport, indicating a clear correlation of biofilm penetration and water transport across carbon papers. Salt precipitation on carbon papers clogged the pores and resulted in lower water transport. Cyclic voltammograms using Au/Hg microelectrode inserted near the cathode indicated the absence of oxygen in the anodic solution due to the oxygen consumption by aerobic/anaerobic biofilms on cathodes. The results of water transport and oxygen presence illustrated that the biofilms can be used as a cost-effective membrane/separator for SCMFCs. [ABSTRACT FROM AUTHOR]

The electrochemical science that makes many energy conversion and storage technologies work rests on our knowledge and understanding of heterogeneous materials and material systems. The function and functionality of those systems share many common features across a wide range of technologies including fuel ceils, batteries, capacitors, and membranes. The science that controls that functionality for these complex material systems is typically summoned in fragments to design a specific device. The present paper discusses an attempt to create a codified multiphysics approach to that general subject, across multiple scales in space and time, for heterogeneous functional materials, or "HeteroFoaM" as we call it. The scope of the paper will be necessarily limited to a general definition of the problem focused on a few specific examples of the progress made for directions that support technologies such as conversion of chemical energy to electricity, membranes for selective transport, and charge storage devices. The principal motivation for this approach is to establish the science that controls emergent properties in heterogeneous functional materials as a foundation for design of functional material systems with performance not bounded by constituent properties. [ABSTRACT FROM AUTHOR]

Spherical-aberration-corrected environmental transmission electron microscopy (AC-ETEM) was applied to study the catalytic activity of platinum/amorphous carbon electrode catalysts in proton-exchange-membrane fuel cells (PEMFCs). These electrode catalysts were characterized in different atmospheres, such as hydrogen and air, and a conventional high vacuum of 10-5 Pa. A high-speed charge coupled device camera was used to capture real-time movies to dynamically study the diffusion and reconstruction of nanoparticles with an information transfer down to 0.1 nm, a time resolution below 0.2 s and an acceleration voltage of 300 kV. With such high spatial and time resolution, AC-ETEM permits the visualization of surface-atom behaviour that dominates the coalescence and surface-reconstruction processes of the nanoparticles. To contribute to the development of robust PEMFC platinum/amorphous carbon electrode catalysts, the change in the specific surface area of platinum particles was evaluated in hydrogen and air atmospheres. The deactivation of such catalysts during cycle operation is a serious problem that must be resolved for the practical use of PEMFCs in real vehicles. In this paper, the mechanism for the deactivation of platinum/amorphous carbon electrode catalysts is discussed using the decay rate of the specific surface area of platinum particles, measured first in a vacuum and then in hydrogen and air atmospheres for comparison. [ABSTRACT FROM AUTHOR]

High temperature solid oxide cells (SOC) are highly efficient and environmentally friendly electrochemical systems for the H2/H2O and/or CO/CO2 redox reactions. The cells can be operated reversely either in electrolysis (SOEC) or fuel cell (SOFC) mode which facilitates this technology for power-to-gas-to-power application in renewable energy storage systems. However, the successful market introduction and public acceptance of the SOEC technology require high quality, reliability and reproducibility of the corresponding cells and stacks. Therefore, in the European funded project “Solid oxide cell and stack testing, safety and quality assurance” (SOCTESQA) pre-normative test modules and programs for high temperature solid oxide cells and stacks have been developed. Different EU project partners have tested identical SOC stacks in several testing campaigns with the same test programs. The paper presents and compares the results of the stacks in SOEC operation which have been obtained by application of the three most important test modules, e.g. current-voltage characteristics, electrochemical impedance spectroscopy and operation at constant current. The results are analyzed and discussed in context to the test input parameters, e.g. gas temperatures and steam supply stability. Quality aspects like repeatability and reproducibility among the different partners and among different test methods are statistically evaluated and discussed. [ABSTRACT FROM AUTHOR]

Significantmass-transport resistances in polymer-electrolyte-fuel-cell catalyst layers (CLs) impose a lower limit on Pt-loading levels, hindering wide-spread fuel-cell commercialization. The origin of this resistance remains unclear. Minimization of CL mass-transport resistance is imperative to achieve better CL design and performance. In this paper, an operando method based on H2 limiting current is used to characterize and quantify CL resistance in traditional porous Pt/carbon-based electrodes. CL sub-resistances are isolated using continuum multiscale modeling and experiments, investigating the effects of reactant molecular weight, pressure, and ionomer to carbon weight ratio. The results expose CL resistance including both interfacial and transport components, although the majority of the CL resistance is ascribed to a local resistance close to the Pt reaction sites, which includes interfacial resistance and local transport resistance. Variations in temperature, humidity, and primary particle loading (Pt:C ratio) highlight the impact of operating conditions and CL design parameters on CL sub-resistances. The observed trends guide optimization of CL design to achieve novel low-loaded fuel-cell electrodes. [ABSTRACT FROM AUTHOR]

To the authors' best knowledge, this is the first parametric investigation of the effect of polytetrafluoroethylene (PTFE) treatments on the heterogeneous through-plane local porosity distributions of PTFE-treated gas diffusion layers (GDLs) for polymer electrolyte membrane fuel cells (PEMFCs). In this work, the through-plane porosity distributions of uncompressed PTFE-treated paper GDLs were measured from high resolution microscale computed tomography visualizations. We analyzed paper GDLs with varying thicknesses and PTFE treatments. When compared to untreated GDL porosity distributions, we observed that the application of PTFE resulted in decreased local porosities near the surface regions and non-uniform distributions of PTFE throughout the material. The rate of porosity decrease with increasing PTFE application is in agreement with the literature. The changes to the overall through-plane porosity distributions are more significant than the changes to the average bulk porosities, which are attributed to batch-specific manufacturing variations. This work provides new insight into the effects of PTFE treatments on GDL through-plane porosity distributions, which are expected to inform future PEMFC models. [ABSTRACT FROM AUTHOR]

The prevailing method for modeling water transport in hydrophobic fuel cell diffusion media employs the same two-phase generalization of Darcy's law widely used for analyzing the movement of oil and water through soil and porous rock. Recent experiments, however, have identified certain problems when the same approach is applied to the nonwoven carbon papers used in fuel cell diffusion media. These problems could be addressed by generalizing the Darcy formulation still more, but significant challenges, such as measuring the relevant material properties, still remain. Instead, this paper proposes a simpler model adapted specifically for fuel cells. Based on analysis of published experiments, the proposed one-dimensional model for heat and two-phase water transport assumes a uniform liquid pore saturation wherever the diffusion medium is wet and neglects the capillary pressure gradients required to transport water in liquid form. In addition to the properties for dry transport, the two-phase water transport model requires just one additional material parameter-the ratio of dry to wet effective gas diffusion coefficients-which can be measured by straightforward limiting current methods. Example half-cell solutions for a Toray diffusion medium show how the proposed model can reproduce changes in oxygen transport resistance observed in limiting current experiments. [ABSTRACT FROM AUTHOR]

Progress in solid fuel utilization in fuel cells relies on devising effective delivery mechanisms for solid fuel and oxygen to the electrochemical reaction site. This paper provides a mechanistic overview of the different delivery modes and vehicles that have been adopted for engaging solid fuel and oxygen at the electrochemical interface to achieve efficient oxidation of carbon. Also, a "CO shuttle" mechanism is proposed to explain the operation and behavior of several direct carbon fuel cell (DCFC) approaches in CO2 or inert environments. This paper also introduces the operating principle and experimental results of a concept: the fluidized bed (FB) DCFC. It consists of a solid oxide fuel cell arrangement coupled to a Boudouard-type FB dry gasifier. A maximum power density of 175 mW/cm2 (or 4 W) was achieved at 850°C for the conversion of activated carbon in this FB-DCFC arrangement. [ABSTRACT FROM AUTHOR]

Sodium borohydride (NaBH4) presents interesting options for electrochemical power generation acting either as a hydrogen source or an anodic fuel for direct borohydride fuel cells. Though there have been several papers concerning electrochemical determi nation of relevant thermodynamic and kinetic parameters to the borohydride (BH4-) system, there are many basic aspects that have not yet been systematically studied. This paper reports chronopotentiometric studies of the electrooxidation of BH4- at a gold. electrode in 2 M NaOH solutions at temperatures ranging from 25 to 65°C. Gold displays a rather good BH4- oxidation activity, and the overall oxidation process is shown to be irreversible involving a number of exchanged electrons close to the theoretically expected value of 8. For the specific potential and concentration ranges observed, the results suggest that the ratedetermining step is an irreversible, diffusioncontrolled, oneelectron oxidation step for which several key kinetic parameters (a, ks, and Ecl0) are calculated. [ABSTRACT FROM AUTHOR]

This is the first in a series of papers in which we introduce a validated Leverett function appropriate for SGL 24 series carbon paper fuel cell diffusion media (DM) that describes the capillary pressure as a function of liquid saturation and hydrophobic additive content. The presented relationship was derived based on the benchmark data gathered from direct measurements of drainage capillary pressure-saturation of differently engineered DM (coated with a microporous layer) tailored with various poly(tetrafluoroethylene) content (ranging from 5 to 20 wt %) at room temperature under no compression. A key feature of the relationship is that the contact angle is implicitly embedded into the hydrophobicity parameter, thereby eliminating any ambiguity regarding the selection of a representative surface contact angle. A detailed comparative analysis of the present Leverett function and the standard Leverett function with the experimental data was performed. The standard Leverett function is found to exhibit significant deviation from the experimental data, whereas the present empirical function successfully predicts the capillary pressure over the entire saturation domain. Finally, additional spontaneous capillary imbibition experiments were performed to obtain estimates for the water retention capacity of a typical fuel cell DM as a function of the hydrophobicity of bilayered DM. [ABSTRACT FROM AUTHOR]

Transparent polymer electrolyte fuel cells (PEFCs) with parallel- and serpentine-channel flowflelds have been developed to study liquid water formation and transport on the anode side. In situ observations reveal that liquid water in the anode channels results from condensation of water on cooler and more hydrophilic channel walls and that water available for condensation in the anode comes either from the cathode through membrane transport or from hydrogen consumption. No water droplets can be found on the anode gas diffusion layer (GDL) surface, in sharp contrast with the cathode side. Moreover, GDL wettability has much influence on water distribution in the anode for the cell operated at low current density (0.2 A/cm²). Using hydrophobic GDL at low current density, water is prone to condense on the channel surfaces rather than inside hydrophobic carbon paper GDL. The condensed water then accumulates and results in channel clogging in the anode. In contrast, by using untreated carbon paper as the anode GDL, it is found that channel clogging by liquid water is avoided under similar operating conditions. This finding implies that water distributions in the anode with hydrophilic and hydrophobic anode GDLs differ much from each other at low current density. Finally, experiments suggest that water condensation on the channel surfaces is a primary mechanism for liquid water formation and anode flooding and that elevating the anode plate temperature modestly is effective to avoid surface condensation and mitigate anode flooding. - [ABSTRACT FROM AUTHOR]

Physico-chemical models are key for a successful use of lithium-ion batteries, especially under extreme conditions. For correctly simulating of the internal battery states and battery aging a suitable set of material properties is needed. This work presents methods to extract these parameters from commercial cells and demonstrates them analyzing a high-power prismatic cell. In a first step, the electrolyte analysis is described, followed by an examination of the active material. The composition as well as the porous structure are measured using optical emission spectroscopy and Hg-porosimetry. To determine the electrochemical properties of the electrode materials, coin cells with lithium as counter electrode are build. With these test cells, open circuit voltage curves and galvanostatic intermittent titration technique measurements are performed to determine the electrode balancing as well as the diffusion constants of the active material. Electrochemical impedance spectroscopy experiments on the full cell are used to determine the charge transfer. In the second part of this paper, a determination of the thermal parameters as well as a validation for the complete parameterization are described. [ABSTRACT FROM AUTHOR]

Synthesis and characterization of a RhxSy catalyst with high mass specific electrochemical active surface area (ECSA/mass) for the H2-Br2 fuel cell are discussed in this paper. Supporting carbon materials were functionalized to create more suitable nucleation sites for the precipitation of rhodium sulfide nano-particles resulting in a catalyst with a smaller particle size, better particle distribution, and higher hydrogen oxidation and evolution reaction performance. XPS and FT-IR were used to analyze the amounts and the types of surface functional groups on the carbon substrate. The results confirm that the dominant functional group on the carbon is the ketone group. TEM and cyclic voltammetry results confirm that the catalysts with treated carbon have smaller average particle size (7.2 nm vs. 13.2 nm) and higher mass specific ECSA (21.8 m2/g-Rh vs. 9.1 m2/g-Rh) than those with the untreated carbon. The H2-Br2 fuel cell test results show that the catalysts with functionalized carbon have better performance in the kinetic region but poorer performance in the mass transfer dominant region. The issue was identified to be due to the poor affinity of the ketone group on the carbon surface with the Nafion ionomer in the catalyst ink and is currently being addressed. [ABSTRACT FROM AUTHOR]

Developing high performance catalyst based on Pd/C catalyst is critical in investigating and commercializing direct formic acid fuel cell. The improvement of the electron-transfer rate of novel catalysts could solve the sluggish reaction kinetics of formic acid electro-oxidation reaction in some extent. We have demonstrated that phosphotungstic acid (PWA) modified Pd/C catalyst could improve the electro-oxidation activity toward formic acid. In this paper, the electrochemical oxidation reaction kinetics of PWA modified Pd/C catalyst were studied by cyclic voltammetry (CV), Tafel polarization, electrochemical impedance spectroscopy (EIS) and rotating disc voltammetry (RDV) at different scanning rates and temperatures. The results showed that smaller apparent activation energy, charge transfer resistance and Tafel slope of formic acid electro-oxidation from Pd/PWA-C electrode catalyst was obtained, which indicated better electrocatalytic kinetics by PWA modification. The rate-determining step of formic acid electro-oxidation is diffusion process and reaction paths are different with potential. The larger diffusion coefficients of Pd/PWA-C electrode catalyst was verified by CV, EIS and RDV, respectively. With the help of electrochemical measurements, it is concluded that PWA modified Pd/C catalyst has better electrocatalytic activity and faster kinetic performance for formic acid electro-oxidation. [ABSTRACT FROM AUTHOR]

In this paper, direct-modeling-based Lattice Boltzmann Method (LBM) combined with in-situ flow visualization, is used to explore fundamentally the transport of liquid-water inside the gas-diffusion layers (GDLs) used in polymer electrolyte fuel cells. Studies of the water evolution, water saturation, and breakthrough pressure inside a GDL with single and multiple injection points under land and channel geometries are explored. The model and experiment demonstrate good agreement between geometries of GDLs provided in this study which were obtained by a three-dimensional (3-D), reconstructed micro-structure from micro X-ray computed tomography (CT). The overall predictions of water evolution within the GDL agree well with the data visualized from the X-ray CT experiment for all cases studied. It also reveals that the liquid-water saturation profiles inside the GDL and breakthrough pressure are different when the location of the water injection point is altered, thereby providing analysis as to the impact of microporous layers or catalyst-layer functioning. Moreover, the uncompressed GDL undergoes a significantly different mechanism of water transport than that of the compressed GDL. Furthermore, the predictions show that the wettability variation is one of the key factors of the saturation characteristics. [ABSTRACT FROM AUTHOR]

Numerous technologies, such as batteries and fuel cells, depend on electrochemical kinetics. In some cases, the responsible electrochemistry and charged-species transport is complex. However, to date, there are essentially no general-purpose modeling capabilities that facilitate the incorporation of thermodynamic, kinetic, and transport complexities into the simulation of electrochemical processes. A vast majority of the modeling literature uses only a few (often only one) global charge-transfer reactions, with the rates expressed using Butler-Volmer approximations. The objective of the present paper is to identify common aspects of electrochemistry, seeking a foundational basis for designing and implementing software with general applicability across a wide range of materials sets and applications. The development of new technologies should be accelerated and improved by enabling the incorporation of electrochemical complexity (e.g., multi-step, elementary charge-transfer reactions and as well as supporting ionic and electronic transport) into the analysis and interpretation of scientific results. The spirit of the approach is analogous to the role that Chemkin has played in homogeneous chemistry modeling, especially combustion. The Cantera software, which already has some electrochemistry capabilities, forms the foundation for future capabilities expansion. [ABSTRACT FROM AUTHOR]

Numerous experiments have demonstrated that oxygen transport losses in conventional cathode catalyst layers in polymer-electrolyte fuel cells increase as the amount of platinum is decreased. This paper develops an analytical agglomerate model for kinetics and transport that incorporates localized spherical diffusion and adsorption kinetics at the scale of the catalyst nanoparticles. This hierarchical structure provides an improved description of mass transport inside agglomerates at high fluxes. Predictions using morphological parameters and physical properties from the literature are commensurate with published investigations into the influence of platinum loading on oxygen transport. [ABSTRACT FROM AUTHOR]

Potentiostatic current transient is widely used to analyze the diffusion controlled three-dimensional nucleation process. SH model has a satisfied performance for almost all potentiostatic testing. However, some deviations between experimental results and the SH model's expression at decreasing period were reported. In this paper, we describe the deviation as resulting from diffusion depth is limited in electrolytic cell. Through a stochastic model is proposed, we derive an equation to describe reaction near the electrode surface of solute ions and their migration out of the diffusion zone. The theoretical model describes a limited-diffusion process using hemispherical nucleus revealed in SH model and Brownian motion in MD model. This model give a detail description of multiple nucleation process during electrodeposition. Based on the descriptions, it can be seen that SH model is a limiting case of our model, as diffusion depth R →+∞. And the equations also reveal the relationship between SH model and our new model. In addition, our theoretical equations are powerful enough to reproduce the potentiostatic current transient curves obtained from gold electrodepositing process. This work advances earlier models a step further and gives an explanation for the deviations between experimental data and standard model's description. [ABSTRACT FROM AUTHOR]

Formate/formic acid has been an intriguing fuel for fuel cells and biofuel cells over the last two decades. The common challenge with formate/formic acid biofuel cells has been the use of NAD-dependent formate dehydrogenase, which requires a diffusive cofactor and problematic cofactor regeneration systems. In this paper, we explore the bioelectro-oxidation of formate usingMo-containing formate dehydrogenase from E. coli (Mo-FDH) for development of a new HCOO-/O2 enzymatic fuel cell (EFC). Mo-FDH was coupled with a benzylpropylviologen-based linear polyethylenimine (BPV-LPEI) redox polymer to fabricate a formate bioanode and laccase incorporated with anthracene-modified multi-walled carbon nanotubes (Ac-MWCNTs) to promote direct electron transfer was used for the O2 biocathode. The resulting Mo-FDH/laccase EFC has an open-circuit potential of 1.28 ± 0.05 V, with corresponding maximum current and power densities of 17 ± 7 μA cm-2 and 18 ± 6 μW cm-2, respectively. These results correspond to the highest open circuit potential for a HCOO-/O2 EFC. [ABSTRACT FROM AUTHOR]

This paper presents a two-dimensional (2D) computational model of a polymer electrolyte fuel cell (PEFC) with a platinum group metal-free (PGM-free) catalyst cathode that can significantly reduce PEFC costs by eliminating the need for expensive platinum catalysts. Due to their comparatively low volumetric activity, PGM-free cathodes are an order of magnitude thicker than their Pt-based counterpart. The resulting need for greater electrode thickness to achieve sufficient power density requires careful attention to the transport losses across the thicker cathodes. The presented model is used to correlate the composition and morphology of the cathode to PEFC performance. The model is a complete cell, continuum model that includes an advanced agglomerate model for a microstructurally consistent representation of the cathode. A unique feature of the approach is the integration of morphology and transport parameter statistics extracted from nano-scale resolution X-ray computed tomography (nano-CT) imaging of PGM-free cathodes. The model was validated with experimental results of PGM-free cathodes with varying Nafion loading. Our key findings are a need for increased cathode hydrophobicity and increased ionomer conductivity through either reduced tortuosity or increased bulk conductivity. We further use the model to evaluate targets for the volumetric activity and active site density for future catalysts. [ABSTRACT FROM AUTHOR]

Hydrogen-vanadium reversible fuel cells were tested using a Pt/C hydrogen electrode, carbon vanadium electrode and interdigitated flow fields at both electrodes. Vanadium electrolyte flow rate was varied to study its effect on mass transport performance. Two types of vanadium electrodes were explored, a single layer of high surface area carbon nanotube (CNT) electrode and three layers of nitric acid-treated carbon paper. Finally, four types of Nafion membranes were examined to determine the effect of membrane type and thickness on fuel cell charge and discharge performance. Higher performance was observed with higher vanadium flow rate, thinner membranes and a CNT vanadium electrode. Peak power density of greater than 540 mW/cm² was obtained using a NR212 membrane and CNT vanadium electrode. [ABSTRACT FROM AUTHOR]

In this paper, we present experimental results about the influence of a hydrophobic coating of gas diffusion layers (GDL) and the existence of a micro porous layer (MPL) on the cold start capability of Polymer Electrolyte Fuel Cells (PEFC). The experiments were performed on five different cell configurations with an active area of 1 cm2 including GDLs of 0, 5, 20 wt% PTFE with and without MPL. Two different experiments were realized: First, a statistical analysis of more than 700 isothermal cold starts was performed to analyze the stochastic freezing behavior of supercooled water inside the fuel cells. Second, a certain number of cold starts were investigated with high-resolution neutron radiography in order to understand the implications of the water distribution on the freezing mechanism. Especially at low coating loads, it was found that cell-to-cell variations are more dominant than variations of the materials. In contrast, a significantly reduced variability between the individual cells as well as a general reduction of the probability of cell failure was observed at high coating loads. The observed effects can be mainly explained by changed morphology of the investigated materials. Regarding the existence of an MPL, only minor effects were observed which could be assigned to a different local distribution of water in the porous layers. [ABSTRACT FROM AUTHOR]

In this work, micro-computed tomography (μCT) imaging is presented as a novel and robust tool for characterizing the surface roughness andmorphological properties of polymer electrolytemembrane (PEM) fuel cell gas diffusion layers (GDLs).Commercially available paper and felt GDLs with varying degrees of hydrophobic treatments and microporous layer (MPL) coatings were characterized. GDL surface height data was obtained from high resolution three-dimensional (3D) μCT reconstructions (2.44 μmwide voxels), where large samples (approximately 4.5 mm × 4.5 mm) were used in order to capture the roughness features of the GDL, MPL crack depths, MPL crack widths, and MPL crack lengths. A sensitivity study reveals the significance of sample size and surface height thresholding on roughness parameters in this work. Therefore, the authors warn that caution must be exercised when selecting surface roughness measurements for modelling applications and that scanning size and resolution should correspond to the phenomena that are being investigated. [ABSTRACT FROM AUTHOR]

In this paper, electro-catalytic reduction of oxygen in Sr-doped lanthanum nickelates, La2-xSrxNiO4+δ (0 ≤ x ≤ 0.4) Ruddlesden-Popper (R-P) phase, has been investigated. The oxygen reduction reaction (ORR) kinetics is evaluated via electrochemical impedance spectroscopy (EIS) with the symmetric cell configuration. The maximum performance is achieved with the un-doped La2NiO4+δ, ~0.13 Ωcm² at 800°C. Sr doping decreases the electrode performance progressively. Further detailed analysis indicates that bulk ionic diffusion and surface oxygen exchange co-limit the ORR of those cathodes. Sr substitution leads to both lowered bulk diffusion and surface exchange rates. With high Sr content (x = 0.3, 0.4), oxygen ion transfer resistance between nickelate/electrolyte is observed. As for the surface exchange process, oxygen adsorption is suggested to be the main rate-limiting step (RLS) according to the reaction orders, which is retarded further by the oxidation of Ni2+ to Ni3+ as Sr content increases. The possible role of incorporation process in determining the overall reaction rate is also discussed. [ABSTRACT FROM AUTHOR]