Application In Fuel Cell Systems Research Articles

Experimental Design of High-Performing Open-Cathode Polymer Electrolyte Membrane Fuel Cells

Open-cathode polymer electrolyte membrane fuel cells (PEMFCs) utilize a unique air-cooled system design to eliminate the humidifiers, air compressor, and liquid cooling loop of conventional, liquid-cooled PEMFC systems, thereby greatly reducing system cost. However, the open-cathode PEMFC performance is restricted by poor humidification, high membrane and charge transfer resistances, and overheating due to inefficient thermal and water management. This work aims to strategically modify the membrane electrode assembly (MEA) design to overcome these issues and achieve high open-cathode PEMFC performance that approaches that of liquid-cooled systems. The use of thinner membrane along with short side chain ionomer is found to elevate the cell performance due to increased water retention at the cathode catalyst layer (CCL) and decreased ohmic losses. Thinner gas diffusion layers with high porosity enable additional cell performance increment by improving oxygen availability at the CCL. An overall current density rise of 88% at 0.6 V and 53% at 0.4 V is achieved by the strategically designed MEA for open-cathode cells. The enhanced power density enabled by the custom MEA can both reduce the stack cost and expand the power range of open-cathode PEMFCs, thus expanding their potential use for low-cost fuel cell system applications.

A non-catalytic diesel autothermal reformer for on-board hydrogen generation

The energy density and wide availability of logistic fuels such as JP8 and diesel continue to hold importance as energy carriers for strategic applications. In some fuel cell system applications, such logistic fuels must be reformed on-board to a hydrogen-rich syngas. The relatively well-studied catalytic reforming presents numerous challenges including soot formation and catalyst deactivation when used for commercial or military grade diesel. To address these challenges, we have designed and built a non-catalytic autothermal reformer for liquid hydrocarbons. In this paper, we present experimental data on the performance of this reformer and draw important insights from this data. Results indicate that reactant mixing upstream of the reformer, turbulent Reynolds number and Damkohler number along with operating parameters such as the oxygen-to-carbon ratio and the steam-to-carbon ratio play important roles that affect reactor performance. Currently, we have achieved a carbon-conversion of 88% with an overall reformer efficiency of 82%. We expect further conversion and efficiency improvements once a more efficient reacting mixer is introduced upstream of this reformer, leading to improved technology readiness levels.

Experimental investigations on a non-catalytic diesel autothermal reformer with reacting and non-reacting pre-mixer

Logistic fuels such as JP-8 diesel continue to hold importance as energy carriers for strategic applications due to their energy density and wide availability. For fuel cell system applications, such logistic fuels must be reformed on board to syngas; whereas, the catalytic reforming of commercial or military grade liquid fuels presents numerous challenges. In this study, we examine the possibility of increasing the conversion and energy efficiency of a non-catalytic diesel autothermal reformer by introducing a relatively homogenous mixture into the reactor. We achieve the mixing through two methods: one involving a reacting pre-mixer and the other with a non-reacting pre-mixer. Results demonstrate that a non-reacting pre-mixer enhances energy efficiency by up to 12% points, while increasing the conversion efficiency to nearly 88%. We expect further improvement in both conversion and energy efficiencies once design modifications are carried out to the pre-mixer such that lower residence times and higher ignition delays can be achieved.

High efficiency power electronic converter for fuel cell system application

This paper discusses the efficiency of two power electronic converters connected in cascade in aim to generate the maximum power from the fuel cell and regulate the load voltage under different working conditions and load variations. The first converter is an interleaved boost proposed to minimize the fuel cell voltage ripples and determine the optimum duty cycle to generate the maximum of power. Thereafter, the control of this converter is performed through a Maximum Power Point Tracking approach. To meet the load requirements in terms of voltage regulation, a buck boost converter controlled with a Proportional Integral controller is proposed. This configuration allows generating the optimal power and regulating the load voltage at the same time. The both converters are simulated under Matlab-Simulink to validate the robustness and the efficiency of this new design. Obtained results show the robustness of the new design approach and efficiency improvement of the system.

Social cost-benefit assessment as a post-optimal analysis for hydrogen supply chain design and deployment: Application to Occitania (France)

A lot of recent studies have concluded that hydrogen could gradually become a much more significant component of the European energy mix for mobility and stationary fuel cell system applications. Yet, the challenge of developing a future commercial hydrogen economy still remains through the deployment of a viable hydrogen supply chain and an increasing fuel cell vehicle market share, which allows to narrow the existing cost difference regarding the conventional fossil fuel vehicle market. In this paper, the market penetration of hydrogen fuel cell vehicles, as substitutes for internal combustion engine vehicles has been evaluated from a social and a subsidy-policy perspective from 2020 to 2050. For this purpose, the best compromise hydrogen supply chain network configuration after the sequential application of an optimization strategy and a multi-criteria decision-making tool has been assessed through a Social Cost-Benefit Analysis (SCBA) to determine whether the hydrogen mobility deployment increases enough the social welfare. The scientific objective of this work is essentially based on the development of a methodological framework to quantify potential societal benefits of hydrogen fuel cell vehicles. The case study of the Occitania Region in France supports the analysis. The externality costs involve the abatement cost of CO2, noise and local pollution as well as platinum depletion. A subsidy policy scenario has also been implemented. For the case study considered, the results obtained that are not intended to be general, show that CO2 abatement dominates the externalities, platinum is the second largest externality, yet reducing the benefits obtained by the CO2 abatement. The positive externalities from air pollution and noise abatement almost reach to compensate for the negative costs caused by platinum depletion. The externalities have a positive effect from 2025. Using a societal cost accounting framework with externalities and subsidies, hydrogen transition timing is reduced by four years for the example considered.

A Neural Network-Based Four Phases Interleaved Boost Converter for Fuel Cell System Applications

This paper presents a simple strategy for controlling an interleaved boost converter that is used to reduce the current fluctuations in proton exchange membrane fuel cells, with high impact on the fuel cell lifetime. To keep the output voltage at the desired reference value under the strong fluctuations of the fuel flow rate, fuel supply pressure, and temperature, a neural network controller is developed and implemented using Matlab-Simulink (R2012b, MathWorks limited, London, UK). The advantage of this controller resides in its simplicity, where limited number of tests are carried out using Matlab-Simulink to construct it. To investigate the robustness of the proposed converter and the neural network controller, strong variations of the fuel flow rate, fuel supply pressure, temperature and air supply pressure are applied to both the fuel cell and the neural network controller of the converter. The simulation results show the effectiveness and the robustness of the both the proposed controller and converter to control the load voltage and minimize the current and voltage ripples. As a result of that, fuel cell current oscillations are considerably reduced on the one hand, while on the other hand, the load voltage is stabilized during transient variations of the fuel cell inputs.

Parallel Inductor Multilevel Current Source Inverter for Input Ripple Current Reduction in PEM Fuel Cell Applications

ABSTRACT In a power conditioning fuel cell system, the application of a single phase voltage source inverter (VSI) generates a second harmonic (100/120 Hz) ripple current. The harmonic current reduces life, efficiency and performance of the fuel cells due to hysteresis loss effects. This paper proposes current source inverter (CSI) with multilevel features to reduce the second harmonic (100/120 Hz) current ripple drawn from the Proton Exchange Membrane (PEM) fuel cell. The employment of energy recovery scheme in the proposed five-level multilevel current source inverter (MCSI) introduces a single switching state for each output current level. The proposed energy recovery scheme is able to balance the sharing inductor currents effectively. In addition, the proposed MCSI is also integrated with a boost DC current source in order to reduce the size of input DC link inductor and minimize the circuit structure for a reliable power conditioning PEM fuel cell system application.

Origin of the catalytic activity of face-centered-cubic ruthenium nanoparticles determined from an atomic-scale structure.

The 3-dimensional (3D) atomic-scale structure of newly discovered face-centered cubic (fcc) and conventional hexagonal close packed (hcp) type ruthenium (Ru) nanoparticles (NPs) of 2.2 to 5.4 nm diameter were studied using X-ray pair distribution function (PDF) analysis and reverse Monte Carlo (RMC) modeling. Atomic PDF based high-energy X-ray diffraction measurements show highly diffuse X-ray diffraction patterns for fcc- and hcp-type Ru NPs. We here report the atomic-scale structure of Ru NPs in terms of the total structure factor and Fourier-transformed PDF. It is found that the respective NPs have substantial structural disorder over short- to medium-range order atomic distances from the PDF analysis. The first-nearest-neighbor peak analyses show a significant size dependence for the fcc-type Ru NPs demonstrating the increase in the peak height due to an increase in the number density as a function of particle size. The bond angle and coordination number (CN) distribution for the RMC-simulated fcc- and hcp-type Ru NP models indicated inherited structural features from their bulk counterparts. The CN analysis of the whole NP and surface of each RMC model of Ru NPs show the low activation energy packing sites on the fcc-type Ru NP surface atoms. Finally, our newly defined order parameters for RMC simulated Ru NP models suggested that the enhancement of the CO oxidation activity of fcc-type NPs was due to a decrease in the close packing ordering that resulted from the increased NP size. These structural findings could be positively supported for synthesized low-cost and high performance nano-sized catalysts and have potential application in fuel-cell systems and organic synthesis.

Biogas reforming process investigation for SOFC application

In recent years, research efforts on fuel cells have been addressed on the development of multifuel reformers with particular emphasis toward the potential use of non-traditional fuels. Among these, biogas is considered very promising to be used as syngas source for fuel cell system applications. The interest on this hydrogen source is focused mainly to supply high temperature fuel cells (HTFC). This paper reports a wide experimental research investigation on SOFC device supplied by syngas produced with different biogas reforming processes (steam reforming, autothermal reforming and partial oxidation). Thermodynamic simulations have been performed to determine the reformed gas composition varying process, reaction temperature and steam to carbon – oxygen to carbon ratios. Syngas mixtures obtained were experimentally tested in order to evaluate the performance of a SOFC mono-cell. Furthermore, an analysis of the combination: fuel processor with a SOFC stack has been determined in order to assess the total energy efficiency.

Impact of Methanol Reformate on Fuel Cell Anode Performance and Durability

Introduction For many fuel cell system applications hydrogen has to be generated from locally available fuels due to the difficulty to store and transport hydrogen gas. Methanol is one of the high hydrogen content liquid fuels that is readily available in many geographic areas and provides a suitable FC fuel. A fuel processing system, including a reformation stage is usually used to convert the methanol to hydrogen gas to feed to the anode channels of the PEMFC stack. The fuel processor is required to meet specific technical and market demands, such as cost, fuel efficiency and purity levels (e.g., CO, methanol concentration) in its output fuel stream. Meeting those constraints requires a number of reformer and fuel cell stack design trade-offs. For this reason, every reformate based fuel cell system is the result of a series of compromises [1]. In order to understand reformer requirements, a study was conducted on the impacts of a small amount of methanol present in the reformate stream. The goal of this communication is to discuss the impacts of methanol in the reformer output stream on the fuel cell anode performance and durability. Experimental An artificial gas mixture of 71%H2, 20% CO2, 8% N2, and 1% methanol vapor was used to mimic the reformer output fuel stream. All the fuel cell tests were conducted on a Ballard standard research testing cell with an active MEA geometry area of 45cm2. The anode was made with a CO tolerant electrode with 0.1 mg/cm2 PtRu/C catalyst, and the cathode contains 0.4 mg/cm2 Pt/C. The cell operation temperature was 75oC, under 5 psig and 100% RH for both MEA sides. The gas flow rates were set to a very high level in order to keep the reactants concentrations approximately uniform across the MEA active area. In order to understand the methanol impact, a dynamic hydrogen electrode (DHE) was mounted onto some of the MEAs to examine the anode and the cathode potentials [2].Methanol impact on MEA CO tolerance and the anode stability in an accelerating stress testing (AST) were investigated. This AST is used to accelerate the anode degradation in start-up/shutdown processes [3]. Results and Discussions Figure 1 gives the MEA performances with and without the presence of 1% methanol vapor. The polarization behaviors of anode and cathode measured against the DHE are also given in the same plot. As we can see the introduction of 1 % methanol significantly decreased the MEA performance, and this performance loss is dominantly due to cathode performance loss, although the methanol was introduced in the anode side. In-situ cathode cyclic voltammograms were conducted and confirmed that a significant amount of methanol crossed over to the cathode side. The oxidation of the crossover methanol in the oxygen rich cathode occupied the oxygen reduction (ORR) sites and resulted in the decreased ORR activity. In addition, the methanol oxidation current also reduced the ORR current output efficiency.A small stream of air is commonly introduced into the anode under reformed fuel operation in order to oxidize any carbon monoxide present, referred to as “air bleed”. An anode air bleed sensitivity test was used to evaluate the anode catalyst layer CO tolerance. We found that in spite of the lower performance in the presence of methanol, methanol did not significantly impact the air bleed sensitivity.It has been found [3,4] that one of the MEA performance loss failure modes is Ru crossover to the cathode side in reformate tolerant anode designs, due to the use of Ru/C catalyst to improve CO tolerance. The impact of methanol on Ru stability in fuel cell start up /shutdown processes was also studied in this research. More detailed discussion will be presented.

Application of acidic accelerator for production of pure hydrogen from NaBH4

Feasibility of using hydrochloric acid (HCl) as an accelerator for onboard production of hydrogen from sodium borohydride (NaBH4) is investigated. The aim was to examine process efficiency, hydrogen purity and process controllability which concurs onboard 2015 hydrogen storage target (5.5 wt%) for vehicular fuel cell system application. Results showed that a highest yield and controllable hydrogen production rate are achievable upon adopting onboard reaction of HCl (3 M) and an aqueous alkaline solution of 30 % NaBH4 via a T-junction and applying a gas–liquid separation of two stages. Cost evaluation and product stream analysis have demonstrated an exceptional performance for the examined scheme and relevancy to be adopted for feeding vehicular electrochemical fuel cell systems.

Reforming of natural gas using coking-resistant catalyst for fuel cell system applications

A coking-resistant catalyst prepared using a novel catalyst support is characterized and its performance on reforming of natural gas for fuel cell system applications is investigated. Two key issues, i.e., the stability of catalyst under the reforming environment and deposition of carbon on the catalyst surfaces leading to deactivation, have to be resolved. The reforming operations are performed using a modified external autothermal reforming (ATR) approach. Desulfurized natural gas is used as a feedstock to avoid catalyst poisoning and air is exploited as an oxidant. It is found that the reforming catalyst is able to remain stable and free from pulverization at the desired operating conditions when α-Al2O3 is employed as a catalyst support in place of the commonly used γ-Al2O3 counterpart. In addition, the ceria (CeO2)-assisted Pt catalyst coated on the α-Al2O3 support, i.e., Pt/CeO2/α-Al2O3, is able to significantly eliminate the coking problem with a CH4 conversion rate >99% and a generated H2 concentration ∼62% at 1073K. A reaction mechanism is proposed to elucidate the coking-resistance of the catalyst, which also accounts for the stability of the catalyst. The reforming catalyst has been tested continuously for 2400h and is still able to maintain a good operating condition.

Alkaline fuel cells running at elevated temperature for regenerative fuel cell system applications in spacecrafts

The energy supply is one of the most important subsystems of spacecrafts. Its layout depends on factors like size or mission profile and contributes strongly to the spacecraft mass. Nowadays, secondary batteries are the common energy storage for space missions. However for certain applications regenerative fuel cell systems (RFCS) offer mass savings due to their higher energy density. A RFCS is composed of an electrolyser and a fuel cell. In a first step water is electrolysed by electrical energy. Hydrogen and oxygen are stored in tanks. Later they are supplied to the fuel cell. There they recombine to water providing electrical energy. The total efficiency of the process and the mass of the complete RFCS are strongly affected by the fuel cell efficiency. It can be increased by elevating the fuel cell operation temperature. This leads to a higher energy density and enables mass reductions of the radiator which is necessary in space to get rid of the waste heat. In this article the effect of the temperature on the radiator area is calculated. The impact on efficiency and fuel cell mass is outlined. Tests results of the operation of an alkaline fuel cell between 60 °C and 140 °C are presented.

A look at design and application of fuel cell systems

Over the past few years, the direct conversion of chemical into electrical energy via fuel cells has been at the center of attention of electrochemical research and technology development. This is due not only to the complexity of fuel cell reactions and the general awareness of the technological potential of fuel cells but is also a result of society's strive towards developing environmentally-friendly power generation. In the reaction between hydrogen and oxygen for example, the only chemical product is water. The fuel cell, initially developed in the sixties as an on-board power supply unit for spacecraft, has now found new applications in powering submarines, in decentralized power supply systems, in portable charging docks for small electronics and in sensor technology. In the quest for a highly efficient, emission-free drive system, the development of mobile automotive fuel cell units is proving to be quite promising. Fuel cell technology constitutes a highly varied field which extends from available fuels and their processing, through the fundamentals of electrochemical processes, especially electro-catalysis, right to the numerous new concepts in systems technology for complete fuel cell aggregates including the control of gas, water and heat management. Many publications now appear annually in this field. The number of patent applications, especially from the industrial sector, has also risen over the past ten years. However, this paper is related to the design and application of fuel cell systems. Key words: Design, fuel, cell systems, power generation.

Modeling and Experimental Study of PEM Fuel Cell Transient Response for Automotive Applications

This paper presents an analysis of the dynamic response of a low pressure proton exchange membrane (PEM) fuel cell stack to step changes in load, which are characteristic of automotive fuel cell system applications. The goal is a better understanding of the electrical and electrochemical processes when accounting for the characteristic cell voltage response during transients. The analysis and experiment are based on a low pressure 5 kW proton exchange membrane fuel cell (PEMFC) stack, which is similar to those used in several of Tsinghua's fuel cell buses. The experimental results provide an effective improvement reference for the power train control scheme of the fuel cell buses in Olympic demonstration in Beijing 2008.

Materials Performance of Modified 430 Stainless Steel in Simulated SOFC Stack Environments for Integrated Gasification Fuel Cell System Applications

The corrosion behaviors of a low silicon and aluminum 430 stainless steel with and without ceria surface treatment were investigated in a simulated coal syngas at 800 {degree sign}C and in air. Thermodynamic calculations were made to predict carbon activities for the coal syngas as a function of temperature. At 800 {degree sign}C, carbon activity is ~1.1, which indicates that carbon that forms could diffuse into the steel and induce carbon corrosion, e.g. carburization and metal dusting. The surface morphology was investigated with X-ray diffraction and scanning electron microscopy. In coal gas, the scale formed on bare steel consisted of Mn1.5Cr1.5O4 and Cr2O3 and on ceria treated steel (Fe, Mn)O, FeCr2O4, Cr2O3, and CeCrO3. Both materials underwent carburization, but not metal dusting. The results of oxidation in air using a thermogravimetric apparatus confirmed that the 430 sample was less resistant to oxidation than the 430 treated with ceria.

Hydrogen and Sulfur Sensors for Fuel Cell System Applications

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