Efficiency Of Fuel Cell Stack Research Articles

Study on the effects of nano-copper addition on the properties of epoxy resin/graphite composite bipolar plates

Bipolar plates (BPs) are vital components in Proton Exchange Membrane Fuel Cells (PEMFCs), and their performance and cost significantly impact fuel cell stack efficiency and affordability. BPs require excellent conductivity, strength, and corrosion resistance depending on usage conditions. Common graphite and metal-based BPs offer good conductivity, but they have their drawbacks. Graphite lacks strength and is costly to process, while metal-based BPs need additional surface treatments to prevent corrosion. In recent years, composite bipolar plates have gained widespread attention due to their excellent conductivity, mechanical properties, and outstanding corrosion resistance. In this study, we used natural graphite flakes as the main conductive filler and nano-copper as the secondary conductive filler, with epoxy resin as the binder. The composite bipolar plate was prepared using a hot-pressing method. The study found that adding 1 wt% of nmCu can increase the conductivity of the composite BP by 75.2%, but it decreases the flexural strength by 26.84%. The prepared nmCu/G/EP composite BP exhibits an ASR of only 4.00 mΩ cm2 and a corrosion current density of 2.615 × 10−7 A/cm2, meeting the DOE 2025 expectations. After conducting Cu2+ leaching experiments on the prepared composite BP, single-cell performance testing showed a maximum power density of 0.556 W/cm2. This study expands the range of conductive fillers for composite BPs, no longer limited to carbon-based conductive fillers.

Initial Assessment of a Fuel Cell—Gas Turbine Hybrid Propulsion Concept

A fuel cell—gas turbine hybrid propulsion concept is introduced and initially assessed. The concept uses the water mass flow produced by a hydrogen fuel cell in order to improve the efficiency and power output of the gas turbine engine through burner steam injection. Therefore, the fuel cell product water is conditioned through a process of condensation, pressurization and re-vaporization. The vaporization uses the waste heat of the gas turbine exhaust. The functional principles of the system concept are introduced and discussed, and appropriate methodology for an initial concept evaluation is formulated. Essential technology fields are surveyed in brief. The impact of burner steam injection on gas turbine efficiency and sizing is parametrically modelled. Simplified parametric models of the fuel cell system and key components of the water treatment process are presented. Fuel cell stack efficiency and specific power levels are methodically derived from latest experimental studies at the laboratory scale. The overall concept is assessed for a liquid hydrogen fueled short-/medium range aircraft application. Block fuel savings of up to 7.1% are found for an optimum design case based on solid oxide fuel cell technology. The optimum design features a gas turbine water-to-air ratio of 6.1% in cruise and 62% reduced high-level NOx emissions.

Examining the influence of battery sizing on hydrogen fuel cell – battery hybrid rail powertrains (hydrail) for regional passenger railway transport using dynamic component models

To address the transportation sector’s contribution to climate change problems across North America (NA), passenger rail is an attractive solution. However, NA passenger rail traditionally relies on diesel motive power, which has been associated with causing health problems of noise, vibrations, and emissions. High costs of overhead and (or) third rail infrastructure have mostly precluded electrification. This paper examines the impact of battery size on fuel cell stack efficiency for hydrogen fuel cell – battery hybrid (hydrail) railway propulsion systems using dynamic simulations as opposed to existing simulations in the literature that rely on static efficiency values. The journey of the British Rail Class 156 diesel multiple unit is simulated over the round trip from Trehafod to Treherbert (UK) using a series hybrid architecture powertrain. Dynamic simulations at incremental battery masses were used to assess fuel cell efficiency, maximum power, and overall hydrogen consumption. Battery mass is employed as a proxy for power and energy capability of the battery. Results suggest that hydrail passenger railway systems work well, with hydrogen fuel cells handling most load dynamics. Hybridization with batteries works best and reduces fuel cell stack size and hydrogen consumption, with overall 64% stack efficiency.

A Comparative Study of Energy Control Strategies for a Standalone PV/WT/FC Hybrid Renewable System

This paper aims to design and control a standalone hybrid renewable system, comprising PV panels and wind turbines as the main energy sources along with a fuel-cell stack as a support system. In an attempt to improve the stability and security of the hybrid renewable system, a battery bank, a supercapacitor pack, and an electrolyzer are integrated as storage units, due to the intermittent and fluctuant primary energy sources contribution. In this paper several energy management strategies is designed and simulated and their performance is compared. The energy management strategies taken into account for comparative investigation in the addressed hybrid renewable system are the most commonly used ones, as follows: the state machine control, the rule-based fuzzy logic control, the ANFIS-based control strategy, the equivalent consumption minimization strategy (ECMS) and the external energy maximization strategy (EEMS). The Mandeni’s fuzzy interface system is taken into consideration, in the case of the fuzzy logic control. The ANFIS-based control strategy data requirements (training, checking and testing data set) are prepared via the state machine control, which determines the operation of the backup system and the storage units based on the battery state of charge and the energy demand shortage. The main contribution of the state machine control and the rule based fuzzy logic design approach, in addition to the demanded energy provision, is protecting the battery bank against deep discharge and overcharge. Moreover, the ECMS introduces a cost function based energy management strategy that minimizes the hydrogen consumption of the fuel-cell and the equivalent fuel consumption of the battery bank. In the following, the EEMS maximizes the energy of the storage banks, which results in the total fuel consumption minimization. Three scenarios are taken into account: Pulsed and Constant loads, for short term analysis, and Random loads, for long term analysis. The simulation study demonstrates successful operation of the energy management strategies for different initial battery SOCs, which are selected in a way to cover the operation of the controller in three battery SOC rangers. In addition, design requirements such as the hydrogen consumption, the fuel efficiency, and the fuel-cell stack efficiency are evaluated in the case of all the energy control strategies.

Optimization of a Fuzzy Based Energy Management Strategy for a PV/WT/FC Hybrid

Decline of natural resources reserves , global warming, energy cost increase, and rising electricity demand make clean and sustainable energy provision using hybrid renewable resources inevitable. Solar and wind energy as free and eco-friendly sources of energy have been considered a promising choice for remote (or rural) area electrification. Dependence of PV/WT production on weather condition necessitates integrating a backup system and storage banks. While a fuel-cell system makes a clean backup available, incorporating both energy type and power type storage technologies, such as batteries, hydrogen-based storage systems, and supercapacitors, extends the energy sources/storage units useful lifespan and decreases the operation cost of the system. An energy control system is required to provide the load with reliable, continuous, high quality and economical energy. Considering PV/WT production uncertainty, load power variations and measurement imprecision, energy management system based on fuzzy logic technique serves an effective method to meet the design objectives, such as energy efficiency maximization, reliable and continuous energy supply, DC bus voltage stabilization etc. The fuzzy logic controller is designed based on the prior knowledge and experience of an expert. Thus, it is not an optimal strategy. Aiming to optimize preferred aspects of the fuzzy controller, it should be combined with evolutionary algorithms, such as genetic. Therefore, this paper deals with the rule-based fuzzy logic energy control of an off-grid PV/WT/FC/UC hybrid renewable system. Applying the genetic algorithm, the ECMS and the EEMS) are utilized to tune off-line the fuzzy logic control, in order to the fuel consumption optimization. To reduce computation time during the optimization process, the fuzzy rule set remains fixed. Employing a simulation model of the hybrid renewable system, multiple criteria such as the fuel efficiency, the fuel-cell stack efficiency, and the fuel consumption are taken into account to evaluate the energy management strategy's performance. Simulation results show that The fuzzy-ECMS and the fuzzy-EEMS keeps the battery SOC around the “0.5 ( + ” and the , respectively. As a result, better fuel economy and higher battery lifetime can be achieved via the fuzzy-EEMS and the fuzzy-ECMS, respectively.

Maximizing performance of fuel cell using artificial neural network approach for smart grid applications

This paper presents an artificial neural network (ANN) approach of a smart grid integrated proton exchange membrane (PEM) fuel cell and proposes a neural network model of a 6 kW PEM fuel cell. The data required to train the neural network model are generated by a model of 6 kW PEM fuel cell. After the model is trained and validated, it is used to analyze the dynamic behavior of the PEM fuel cell. The study results demonstrate that the model based on neural network approach is appropriate for predicting the outlet parameters. Various types of training methods, sample numbers and sample distribution methods are utilized to compare the results. The fuel cell stack efficiency considerably varies between 20% and 60%, according to input variables and models. The rapid changes in the input variables can be recovered within a short time period, such as 10 s. The obtained response graphs point out the load tracking features of ANN model and the projected changes in the input variables are controlled quickly in the study.

Thermodynamic and Exergy Analysis of Reversible Solid Oxide Cell Systems

Reversible solid oxide cell (SOC) technology could enable efficient electrical energy storage of renewable energy, enhancing sustainability and efficiency of current energy systems, reducing at the same time equipment requirement. SOCs are devices able of converting electrical energy into chemical fuels, through electrolysis, and chemical fuels into electricity, through electrochemical oxidation. Although a SOC can theoretically work in both modes, the same can not be directly said for a system. Basically, high conversion system efficiencies largely depends on the addition of specific bottoming cycles, usage of specific components or specific operative conditions. For instance, it is expected that a SOEC system requires a large heat transfer equipment to bring liquid water from ambient (15 °C - 25 °C ) to the cell operative temperature (700 °C - 800 °C). Conversely, SOFC major requirements would concern gas and air pre-heating. Looking at pressurized systems, while SOFC systems are mainly based on gas compression, electrolysis includes compression of liquid water to a large extent. Although the same process is performed, gas and liquid compression have a completely different energy demands for different equipment (pump and compressor). In literature, reversible systems have not yet been widely investigated. Consequently, there is the need to address possible configurations and evaluate their conversion performances. The main goal of the present work is to address differences and similarities among simple SOFC and SOEC systems, based on hydrogen oxidation and steam electrolysis. In order to evaluate which are important variables in determining SOFC and SOEC conversion efficiencies, how do variables affect system efficiencies, and which are crucial auxiliary components in a SOFC or SOEC system, the present work proposes a thermodynamic analysis. Both energetic and exergetic point of views are adopted to estimate system and components performances. Systems are modelled with the flowsheet programming tool Aspen Plus. Since this software does not include a built-in model of SOFC and SOEC, these are devised ad hoc. Scope of the analysis is to identify useful operative regimes for a reversible system, comparing SOFC and SOEC system based on the same variables. Temperature, pressure, reactant composition, utilization factor and current density emerge as key variables that determine system efficiency. SOC systems are studied at atmospheric (~ 1 bar) and high pressure conditions (10 bar), as well as at different current densities. For a 90% inlet molar fraction of hydrogen and steam for SOFC and SOEC mode respectively, a fuel cell stack efficiency of ~44% at 800 °C, with a power output of 12 MW is achieved. At atmospheric conditions, overall system energy and exergy efficiencies are ~40% and ~41% in SOFC mode. However, at 10 bar, for the SOFC system, auxiliary compression work is larger than produced. Thus in absence of a bottoming cycle like a Gas Turbine (SOFC-GT systems have been shown to be highly efficient) the pressurisation does not result into a feasible system. Current densities and stack area obtained in the SOFC mode are used as inputs for SOEC simulations. Power requirements of SOEC are 18273 kW (~ 1bar) and 19890 kW (10 bar), with voltages equal to 1.142 V and 1.243 V, at atmospheric and pressurized conditions respectively. The corresponding atmospheric SOEC configuration energy and exergy efficiencies of 75.35% and 85.54% are obtained. A similar energy efficiency (76.50%) but lower exergy efficiency (81.44%) is observed for the pressurized SOEC system. Higher exergy losses in the pressurized case are because of the higher current density leading to higher exergy losses within the SOEC. Another contribution appears to be from the wasted fraction of input exergy linked to a higher system outlet temperature and pressure. Heat recovery especially of the water stream also contributes to the exergy losses. SOEC pressurization can anyway be an advantage from a system point of view. For instance in case of liquid fuel production, syngas pressurization could be replaced by pressurized electrolysis, enhancing overall efficiency. This is due to the lower energy intensity associated with liquid water pressurization, compare to gas. Looking at system operation and obtained efficiencies, it is feasible to design a reversible SOFC / SOEC system. Overall, multiplying SOFC and SOEC efficiencies, total reversible system energy efficiency is around 30%. This value could be increased with system modifications such as varying the SOFC current density, or introducing SOFC anode and cathode recirculation.

Simulation study of a proton exchange membrane (PEM) fuel cell system with autothermal reforming

This paper presents the results of a study for a 100 kW net electrical power PEM fuel cell system. The major system components are an autothermal reformer, high and low temperature shift reactors, a preferential oxidation reactor, a PEM fuel cell, a combustor and an expander. Intensive heat integration within the PEM fuel cell system has been necessary to achieve acceptable net electrical efficiency levels. The calculations comprise the auxiliary equipment such as pumps, compressors, heaters, coolers, heat exchangers and pipes. The process simulation package ‘ASPEN-HYSYS 3.1’ has been used along with conventional calculations. The operation conditions of the autothermal reformer have been studied in detail to determine the values, which lead to the production of a hydrogen rich gas mixture with CO concentration at ppm level. The operation parameters of the other reactors have been determined considering the limitations implied by the catalysts involved. A gasoline type hydrocarbon fuel has been studied as the source for hydrogen production. The chemical composition of the hydrocarbon fuel affects the favorable operation conditions of autothermal reforming and the following fuel purification steps. Thermal efficiencies have been calculated for all of the major system components for selected operation conditions. The fuel cell stack efficiency has been calculated as a function of the number of cells (500–1250 cells). Efficiencies of all of the major system components along with auxiliary unit efficiencies determine the net electrical efficiency of the PEM fuel cell system. The obtained net electrical efficiency levels are between 30 (500 cells) and 37% (1250 cells). Hence, they are comparable with or higher than those of the conventional gasoline based internal combustion engine systems, in terms of the mechanical power efficiency.

Critical flow rate of anode fuel exhaust in a PEM fuel cell system

A manual purge line was added into the exterior fuel exhaust stream of a Ballard PEM stack in a Nexa™ power module. With the addition of manual exhaust purge, high levels of inert gases were intentionally added to the anode feed without changing normal operational procedures. A new method of determining the critical minimum flow rate in the anode exhaust stream was given by an anode mass balance. This type of operation makes dual use of membranes in the MEAs as both gas purifiers and as solid electrolytes. The PEM stack was successfully operated with up to ca. 7% nitrogen or carbon dioxide in the absence of a palladium-based hydrogen separator at ca. 200 W power level. Nitrogen in the anode stream was concentrated from 7.5% to 91.6%. The system maintained a fuel efficiency of 99% at a manual purge rate of 2.22 ml s −1 and no auto purge. The fuel cell stack efficiency was 64% and the stack output efficiency was 75%. The overall system efficiency was 39%. After troublesome CO and H 2S poisons were removed, a hydrocarbon reformate containing high levels of CO 2 and H 2O was further used in the Nexa™ stack. The size and complexity of the fuel processing system may be reduced at a specified power level by using this operational method.

Simulation Study of a PEM Fuel Cell System with Steam Reforming#

This article summarizes the results of a study for a 100 kWe DC electrical power PEM fuel cell system. The system consists of a pre-steam reformer, a steam reformer, high and low temperature shift reactors, a preferential oxidation reactor, a PEM fuel cell, a combustor, and an expander. Acceptable net electrical efficiency levels can be achieved via intensive heat integration within the PEM fuel cell system. The calculations take into account the auxiliary equipment such as pumps, com pressors, heaters, coolers, heat exchangers and pipes. The process simulation package “Aspen-HYSYS 3.1’’ has been used. The operation parameters of the reactors have been determined considering all the technical limitations involved. A gasoline type hydrocarbon fuel has been studied as hydrogen rich gas source. Thermal efficiencies have been calculated for all of the major system components for selected operation conditions. The fuel cell stack efficiency has been calculated as a function of cell numbers (500, 750, 1000, and 1250 cells). Efficiencies of all of the major system components along with auxiliary unit efficiencies determine the net electrical efficiency of the PEM fuel cell system. The obtained net electrical efficiency levels are between 34 (500 cells) to 41% (1250 cells). #Contributed by the Organizing Committee for the First International Exergy, Energy and Environment Symposium (IEEES-1). Paper presented at IEEES-1, Izmir, Turkey,13-17 July 2003. Manuscript received by IJGE on 2003-12-23; final revision received on 2004-02-10. Corresponding guest editors: I. Dincer and A. Hepbasli.

Simulation Study of a PEM Fuel Cell System with Steam Reforming#

Abstract This article summarizes the results of a study for a 100 kWe DC electrical power PEM fuel cell system. The system consists of a pre-steam reformer, a steam reformer, high and low temperature shift reactors, a preferential oxidation reactor, a PEM fuel cell, a combustor, and an expander. Acceptable net electrical efficiency levels can be achieved via intensive heat integration within the PEM fuel cell system. The calculations take into account the auxiliary equipment such as pumps, com pressors, heaters, coolers, heat exchangers and pipes. The process simulation package “Aspen-HYSYS 3.1’’ has been used. The operation parameters of the reactors have been determined considering all the technical limitations involved. A gasoline type hydrocarbon fuel has been studied as hydrogen rich gas source. Thermal efficiencies have been calculated for all of the major system components for selected operation conditions. The fuel cell stack efficiency has been calculated as a function of cell numbers (500, 750, ...