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Preview: Fuel Cells

Fuel Cells

Wiley Online Library : Fuel Cells

Published: 2017-12-01T00:00:00-05:00


Characterization of an H2/O2 PEMFC Short-Stack Performance Aimed to Health-State Monitoring and Diagnosis


Proton exchange membrane fuel cell (PEMFC) is one of the most promising technologies in energy conversion. Nevertheless, improper operating conditions can severely affect the fuel cell (FC) lifespan. It is a matter of fact, that several degradation mechanisms could take place inside the cell in case of abnormal operating conditions. Among these, improper water managements, fuel quality and starvation conditions can show critical effects on PEMFC performance. Furthermore, if the exposure time to these faulty conditions resulted quite long, irreversible degradations and system ageing would occur. This work aims to investigate the impact of both improper water managements and reactants starvation conditions on H2/O2 PEMFC short-stacks performance. To this purpose, the experimental activity performed to characterize the stack health-state both in normal and abnormal conditions is presented. Particular attention is dedicated to the effects caused by improper conditions on stack electrochemical impedance spectroscopy (EIS) measurements' variations. Depending on the faulty conditions, the experimental results are then analyzed for health-state monitoring and diagnosis purposes.

Impact of Platinum Loading on Performance and Degradation of Polymer Electrolyte Fuel Cell Electrodes Studied in a Rainbow Stack


The paper focuses on the investigation of durability and performance of a low temperature polymer electrolyte membrane fuel cell (PEMFC) stack as a function of Pt loading in automotive test conditions. Major motivations are problems related to the need to reduce the amount of Pt in membrane electrode assemblies (MEAs) in order to make PEMFC more competitive. The particular challenge is to maintain sufficiently high performance and long-term durability. The study shows that for cathode Pt loadings below 0.2 mg cm−2 and for current densities exceeding 1 A cm−2 a sudden drop of performance is observed. The same threshold value is found for the increase of irreversible voltage losses which lead to an intense reduction of PEMFC durability for cathodic loadings below 0.2 mg cm−2. Another durability issue at cathodic Pt loadings < 0.4 mg cm−2 is the acceleration of reversible degradation, which leads to a strong voltage drop during continues fuel cell operation (i.e., without a recovery interruption).

Cover Fuel Cells 6/2017


The cover picture illustrates the concept of using biogas, which evolves from waste dumps, directly as fuel in a solid oxide fuel cell (SOFC) for a highly efficient electricity production. It makes use of the ability of internal reforming – both steam and dry (with CO2) – inside the SOFC anode. As prominent impurity, sulfur compounds can have negative effects of the SOFC performance and durability. More details can be found in the article by Anke Hagen et al., DOI: 10.1002/fuce.201700031.

Unitized Regenerative Fuel Cells: A Review on Developed Catalyst Systems and Bipolar Plates


Severe crisis of energy that our planet is going to face in the near future demands rapid development of alternative energy harnessing and storing devices. Various alternative energy devices have been developed so far, including solar cells, batteries and fuel cells, in order to compete and replace the traditionally used fossil fuel based energy technologies. A very recent addition to the list of such devices is the unitized regenerative fuel cell (URFC), which can function as a dual, i.e., electrolyzer-cum-fuel cell, device. In remote areas, where utilization of conventionally used energy sources results in high expense, URFC can serve as the best energy option, due to its relatively low cost, high efficiency and light weight. URFC utilizes bifunctional electrodes, which function in a dual mode of water electrolysis and fuel cell. The prime focus of URFC research has been to develop various low cost and highly efficient catalysts and catalyst supports towards the fabrication of alternative bifunctional electrodes and to fabricate strong and efficient bipolar plates. The aim of this review is to highlight the main outcomes of these aspects of research on URFCs.

Development of a Bi-cell Proton Exchange Membrane Fuel Cell with Optimized Groove-designed Piezoelectric Actuator


Previous studies demonstrated a piezoelectric proton exchange membrane fuel cell (PZT-PEMFC) stack design composed of three bi-cells in series and a single bi-cell, with a maximum net power density of 0.1608 W cm−2. The present study developed a modified bi-cell design with lower volume and weight by using gold-plated aluminum 6061. A groove-designed PZT actuator enclosed with poly-di-methyl-siloxane (PDMS) curing for 30 min can reduce uneven air feeding. Such an actuator can also improve the performance of both sides of a bi-cell, with only a 0.7% difference in the open circuit voltage (OCV). The experimental results showed that the net power density of the new version of the single bi-cell PZT-PEMFC module was 0.1658 W cm−2.

Ultra-low Mass Sputtered and Conventional Catalyst Layers on Plasma-etched Nafion for PEMFC Applications


This paper presents performance results for the use of plasma-etched Nafion membranes to suppress polarization losses in proton exchange membrane fuel cells (PEMFCs) configured from 0.1 mg cm−2 conventional Pt/C dispersion and 0.02 mg cm−2 ultra-thin sputter-deposited Pt catalyst layers. Four MEA configurations, namely, etched membrane-conventional electrode, pristine membrane-conventional electrode, etched membrane-sputter electrode, and pristine membrane-sputter electrode cells were explored, and their respective maximum power densities were ∼514.6, 417.9, 170.1 and 138.3 mW cm−2. The results demonstrated that independent of MEA fabrication approach, cells with O2 plasma treated membranes had reduced ohmic resistances and delivered superior performance over their pristine counterparts, validating the utility of membrane etching for achieving improved PEMFC performance.

Zincating Effect on Corrosion Resistance of Electroless Ni-P Coating on Aluminum Alloy 6061


Aluminum and its alloys represent a promising alternative as bipolar plates in proton exchange membrane fuel cell (PEMFC) systems. However, to improve the corrosion resistance they are commonly coated, and electroless Ni-P offers great advantages. The effect of multiple zincating process on the corrosion behavior of electroless Ni-P coatings on AA6061 was investigated. Results of morphological characterization and compositional analysis of the electroless Ni-P coatings showed that as the number of zincating steps increased, the surface became smoother (with decreasing roughness) and the phosphorous content increased. The results of electrochemical impedance measurements and potentiodynamic polarization curves in 0.5M H2SO4 solution showed that the pretreatment used before coating of aluminum with Ni-P has a direct effect on corrosion resistance. The corrosion current density decreased with increasing the number of zincating steps. A significant improvement in corrosion resistance was observed on performing the triple zincating.

An Investigation of PEFC Sub-Zero Startup: Influence of Initial Conditions and Residual Water


Isothermal cold starts of polymer electrolyte fuel cells were performed at sub-zero temperatures and analyzed by means of neutron radiography in order to unravel the relation between the preconditioning of the cell and the cold start capability. It was found out that the initial humidification state of the membrane (determined by its resistance) has a clear correlation with the duration of the initial phase of the cold start, but not with the total duration of startup until cell failure. In the experimental setup the impact of realistic and commercial sealing solutions was taken into account by adding an edge channel. The impact of water accumulations in this region on the cold start capability was assessed. Liquid water located in the outer perimeter of a cell could be directly verified to freeze during cell cool down by a novel dual spectrum neutron radiography method. The amount of water accumulated in the outer cell perimeter showed some correlation with the total duration of the cold start. It was found out that residual water located in the edge channel can initiate freezing of a substantial part of the active area nearby.

Investigation of Spiral Flow-Field Design on the Performance of a PEM Fuel Cell


Polymer exchange membrane fuel cells (PEMFCs) are promising energy converters due to their unique features with an application potential for many sectors. The performance of PEM fuel cells depends on a number of factors, one of which is suitable flow-field design. In this study, the effect of spiral flow-field design is investigated with computational fluid dynamics (CFD) method. The model consists of the transport phenomena in a fuel cell. Electrochemical reactions, mass, heat, energy, species transport, and potential fields equations are solved by ANSYS-FLUENT. The polarization and power density curve, temperature, pressure, and distributions of the gases inside the flow-fields were obtained. The results were compared with the reference geometry. Although the spiral flow-field has considerable ohmic losses, the velocity and pressure distributions of the gases are found to be uniform. Furthermore, it is shown that the spiral flow-field reduces the pressure drop per unit length of the flow-field. When compared to other flow-field designs, the spiral flow-field is found to be quite efficient by means of auxiliary power consumption.

Three-dimensional Modeling of Gas Purge in a Polymer Electrolyte Membrane Fuel Cell with Co-flow and Counter-flow Pattern


Gas purge is commonly utilized to minimize residual water after shutdown of proton exchange membrane fuel cell (PEMFC) in cold weather, aiming to reduce damage of ice formation on cell performance and durability. In this paper, a three-dimensional multiphase gas purge model of proton exchange membrane fuel cell with co-flow and counter-flow pattern is established to investigate water removal characteristics using two-fluid model. The present model mainly includes water transport in membrane, mass transfer between dissolved water and water vapor in catalyst layer (CL), phase change between liquid water and water vapor in porous media. Several cases with co-flow and counter-flow pattern have been investigated numerically. In the last, gas purge time comparison between a fresh cell and degraded cell is conducted. The numerical results show that counter-flow pattern is better in keeping even water content distribution and avoiding over-drying of membrane. Time constant for gas purge is different in terms of different final target value: water vapor, liquid water saturation, membrane water content. Degraded cells have 2 more seconds than fresh cells when cell temperature is 80 °C and velocity of purge gas 1m s−1.

Shape Optimization of PEMFC Flow-channel Cross-Sections


This paper presents the modeling, simulation and optimization of a single channel proton exchange membrane fuel cell (PEMFC) using computational fluid dynamics methods. The shape optimization of the flow-channels was employed to improve the electrical performance of the fuel cell. The maximization of the current density was the objective function of the single-objective optimization problem, the upper and lower widths of the flow channels were the control variables and a cross-section area restriction was imposed. The optimized flow-channel PEMFC presented improved current generation characteristics, showing higher current and power densities and a more uniform current density distribution than the rectangular flow-channel.

Variable Step Size IC MPPT Controller for PEMFC Power System Improving Static and Dynamic Performances


In this paper, a variable step size IC MPPT controller for the proton exchange membrane fuel cell (PEMFC) power system is proposed. The efficiency of the proposed algorithm has been studied successfully using a 7 kW PEMFC fed by DC-DC boost converter derived using the proposed MPPT controller implemented under Matlab/Simulink environment. Comparison results obtained using both implemented fixed and variable step size IC MPPTs on two scenarios test considering temperature and hydrogen pressure variation show that the proposed variable step size IC MPPT outperforms the conventional fixed step size in static and dynamic performances.

A Direct Manufacturing Cost Model for Solid-Oxide Fuel Cell Stacks


This work details efforts to estimate the direct manufacturing cost of solid oxide fuel cell (SOFC) stack components for combined heat and power applications. The main research goals are to identify the major contributors to fuel cell stack manufacturing costs, examine the influence of both production volume and stack size on cost, and compare the results of the cost trajectories with the U.S. Department of Energy SOFC stack manufacturing cost target of $238 kWe−1 (in 2015) and industry reported cost projections and to identify critical areas for manufacturing research and development. Stack component direct manufacturing costs are modeled for net electricity capacity of 1, 10, 50, 100 and 250 kWe across annual production volumes of 10, 1,000, 10,000 and 50,000 systems per year. Overall stack manufacturing costs range from $5,387 kWe−1 to a minimum of about $166 kWe−1 for a 250 kWe system at 50,000 systems per year. To meet the manufacturing cost target of $238 kWe−1, a minimum annual production of 100–250 MWe per year would be required. Reduction opportunities for stack cost are expected to be available, mainly with the adoption of thinner cells and stack components, higher levels of factory automation, and more sensitive in-line defect diagnostics.

A Simplificative Approach-based Modeling of SOFC Power Systems Fed by Natural Gas


The fuel cell system is modeled to investigate output factors including voltage, power, and system efficiency for various input elements including different fuel composition, the air and fuel temperature and their utilization ratios. The purpose of this study is to examine the proficiency of a tubular solid oxide fuel cell (SOFC) by simplification in modeling calculation which results in the minimum required data. An electrochemical model is defined at first, and different current losses types were calculated in the next step. In further papers the amount of air and fuel is known and in some of them operating temperature must be known. But in this study it is enough to know the current density and required generated power of the SOFC. Since the amount of reacted methane is almost equal to input value, after performing this calculation for several fuel cells and validating it, the most optimal value for methane output is evaluated and output parameters of SOFC are calculated, then results are validated. The effect of main factors, including system temperature, pressure, current density, air and fuel flow rates and air to fuel ratio on the SOFC efficiency, were studied. Modeling method of current study provides optimum air and fuel flow rate.

SOFC Operation with Real Biogas


Biogas is a valuable energy source and will be available in future in systems relying on renewables. It is an attractive fuel for solid oxide fuel cells (SOFC), which are able to utilize the carbon contained in the biogas and which produce electricity with high efficiency. In the current paper, state-of-the-art SOFCs were studied regarding performance and durability in relation to biogas as fuel and considering important contaminants, specifically sulfur. First, the catalytic behavior in relevant synthetic biogas mixtures was studied and the potential of dry reforming was demonstrated. Successful long term operation of an SOFC under both, conditions of steam and dry reforming, i.e., addition of steam or CO2 to avoid carbon formation was shown. For the steam reforming case a remarkable period of 3,500 h, hereof 3,000 h in the presence of H2S was achieved. Finally, a real biogas from a landfill gas unit was used as fuel. The concept of dry reforming was realized. The SOFC was successfully operated with and in one case even without a specific gas cleaning unit.

Effect of Aluminum Titanate (Al2TiO5) Doping on the Mechanical Performance of Solid Oxide Fuel Cell Ni-YSZ Anode


The mechanical behavior of un-doped and 1–10 wt.% aluminum titanate doped NiO-YSZ anodes was evaluated in the oxidized and reduced state of the material. Sample bars 25 × 5 × 2 mm were fabricated and tested in a three-point bending apparatus and statistical analyzes of the collected data were performed. A remarkable enhancement of the flexural strength was found both for the reduced and oxidized state of the material when compared to the un-doped samples. In both cases, the development of a secondary phase was observed proportional to the doping amount of aluminum titanate. Morphological analysis along with preliminary phase identification and suspected mechanisms for strength enhancement are presented and discussed.

Electrophoretic Deposition of Gadolinium-doped Ceria as a Barrier Layer on Yttrium-stabilized Zirconia Electrolyte for Solid Oxide Fuel Cells


Replacing the electronically conductive (LaSr)MnO3±δ (LSM) cathode in the LSM/yttrium-stabilized zirconia (YSZ) system with the mixed ion-electron conductive (MIEC) (LaSr)(CoFe)O3–δ will promote cathode performance in solid oxide fuel cells (SOFCs) significantly. However, a barrier layer between LSCF and YSZ is necessary for preventing chemical reaction between these two components. In this study, a gadolinium-doped ceria (GDC) barrier layer was deposited on the YSZ electrolyte by scalable and cost-effective electrophoretic deposition (EPD). Polypyrrole (PPy) was coated on the YSZ surface as the conductive agent. A highly compact GDC green layer was obtained by the EPD process in an ethanol-based suspension. GDC barrier layers ranging in thickness from 5 µm to 8 µm were successfully densified at temperatures as low as 1,300 °C. The performance of these cells was evaluated using a symmetrical cell configuration through electrochemical impedance spectroscopy (EIS). Ohmic resistance of the GDC barrier layer made by EPD versus the conventional spin-coating method was reduced by 0.09 Ω cm2 at 750 °C, which generally accounts for 30% of the total ohmic resistance for the electrode-supported fuel cells (0.30 Ω cm2). This result suggests that EPD is a highly desirable method for efficiently manufacturing an electrolyte barrier layer with improved performance.

Internal Partial Oxidation Reforming of Butane and Steam Reforming of Ethanol for Anode-supported Microtubular Solid Oxide Fuel Cells


Internal partial oxidation reforming of butane and steam reforming of ethanol were investigated using microtubular solid oxide fuel cells (SOFCs) supported on nickel-gadolinia doped ceria (Ni-GDC) anodes for portable power sources in emergency situations and for mobilities, such as vehicles, robots and drones. At an oxygen/carbon (O/C) ratio of 1.0, which is a coking condition in the equilibrium, the Ni-GDC anode deteriorated for 28 h by internal partial oxidation of butane at 650 °C. However, power generation was also impossible after 8 h and 79 h at steam/carbon (S/C) = 1.0 and 1.5, respectively, by internal steam reforming of ethanol despite of no carbon deposition condition in the equilibrium at 650 °C. Power can be generated for more than 100 h at O/C = 1.5 in butane and at S/C = 2.0 in ethanol. For internal partial oxidation reforming of methane and steam reforming of ethanol in SOFCs, the O/C and S/C ratios are significantly important to prevent carbon deposition on the Ni-GDC anode.

An On-Demand Safety Gas Generator for Solid Oxide Fuel Cell and Electrolyzer Systems


With their high electrochemical efficiency, solid oxide fuel cells (SOFCs) and solid oxide electrolyzers (SOEs) offer viable means of reducing energy sector greenhouse gas emissions and storing surplus renewably-generated power. At present, these systems have operating temperatures of over 600 °C. During start-up, following cooling or in an emergency shut-off situation, a premixed safety gas is necessary which prevents damage to the cell's anode substrate. To date, safety gas has been industrially produced and stored in compressed gas cylinders. Given an SOFC system's size, these cylinders must be transported and stored in close proximity and replaced following gas expenditure. The storage space required, as well as the continuous replacement of gas cylinders, increases system size and costs. This paper presents a solution to this problem in the form of a specially developed safety gas generator that generates an on-demand synthetic safety gas via the system's infrastructure. The functionality of this component is experimentally validated in tests conducted with a 4-cell stack.

Two-way Operations of a DMFC with a Vapor Feed and With a Liquid Feed


Using a cell module with a porous carbon plate, two-way operations of a specific direct methanol fuel cell (DMFC) with a vapor feed (VF) of neat methanol and a liquid feed (LF) of a dilute methanol solution were conducted, and the cell performances were compared to each other in order to clarify which condition produced the better performance. The comparison was conducted at different air humidities, i.e., 30, 60, 90 and 100%, and cell temperatures, i.e., 313, 323 and 333 K. As a result, about a 10% higher power density was obtained by the LF-DMFC, whereas about a 2% higher efficiency was obtained by the VF-DMFC at the optimum air humidity and 323 K. These performances were achieved by significantly different mass transports through the membrane.

Cu- and Co-Modified Pd/C Nanoparticles as the High Performance Cathodic Catalysts for Mg-H2O2 Semi-Fuel Cell


We had prepared PdxCoy/C and PdxCuy/C nanocatalysts with different actomic ratio of Pd and Co or Cu via modified sodium borohydride reduction method and investigated their electrocatalytic properties for hydrogen peroxide (H2O2) reduction reaction with emphases on the effects of composition and structure. The activities of PdxCoy/C and PdxCuy/C catalysts increased firstly and then decreased with the amount of Pd adding. Both the Pd8Co/C and Pd8Cu/C showed the better catalytic performance than that of the other Pd and Co or Cu atomic ratio. The Pd8Co and Pd8Cu NPs were 3–4 nm in size and uniformly distributed on the C surface in an alloy way. The Pd8Co/C and Pd8Cu/C catalysts exhibited a superior activity and stability on H2O2 electroreduction reaction than the Pd/C and the commercial Pd/C (JM) catalysts, which due to Co and Cu enter into the Pd lattice and alter the electronic structure of Pd. The Mg-H2O2 semi-fuel cells with the two catalysts supported on the carbon paper as the cathodes expressed a peak power density of 140 mW cm−2 for the Pd8Co/C cathode and 168 mW cm−2 for the Pd8Cu/C cathode.

Surface Modification Allows High Performance for Solid Oxide Fuel Cells Fabricated by a Single-step Co-firing Process


The power output of solid oxide fuel cells using samarium doped ceria electrolyte fabricated by a single-step co-firing process is enhanced by using a surface modification strategy. This strategy leads to the cell performance improving from 401 mW cm−2 to 523 mW cm−2 at 700 °C, with an increase of more than 30% been achieved, which is very encouraging considering the large electrolyte thickness (∼500 µm). The cell resistance, including both polarization resistance and the ohmic resistance, decreases dramatically by employing the surface modification method. Those results reveal that the surface modification improves the cathode/electrolyte interfacial contact, which results in a reduced total cell resistance and leads to a better cell performance.