Exergoeconomic analysis of a PEM fuel cell at various operating conditions

In this paper, a comprehensive exergoeconomic analysis of a 10 kW PEM fuel cell at various operating temperatures, pressures, cell voltages and air stoichiometries is performed. The analysis is performed at fuel cell operating temperatures (T/T_o) and pressures (P/P_o) ranging from 1 to 1.25 and 1 to 3, respectively. In addition, the calculations are performed on typical fuel cell operating voltages of 0.5 V and 0.6 V and at air stoichiometries of 2, 3 and 4 in order to determine their effects on the exergy cost of the fuel cell. The calculated results demonstrated the significance of the operating pressure, cell voltage and air stoichiometry on the exergy cost of the fuel cell. Furthermore, lower capital cost of the fuel cell, annual O & M cost and hydrogen cost could contribute to a drastic reduction in the exergy cost. Thus, a substantial improvement in the overall results could be achieved.     

Exergy analysis of a PEM fuel cell at variable operating conditions

This paper presents a comprehensive exergy analysis of a 10 kW PEM fuel cell at variable operating temperatures, pressures, cell voltages and air stoichiometrics. The calculations of the physical and chemical exergies, mass flow rates and exergetic efficiency are performed at temperature ratios (T/T₀) and pressure ratios (P/P₀) ranging from 1 to 1.25 and 1 to 3, respectively. In addition, the analysis is conducted on fuel cell operating voltages of 0.5 and 0.6 V and at air stoichiometrics of 2, 3 and 4 in order to determine their effects on the efficiency of the fuel cell. The calculated results illustrate the significance of the operating temperature, pressure, cell voltage and air stoichiometry on the exergetic efficiency of the fuel cell. However, it is recommended that the fuel cell should operate at stoichiometric ratios less than 4 in order to maintain the relative humidity level in the product air and to avoid the membrane drying out at high operating temperatures.     

Thermodynamic analysis of a Proton Exchange Membrane fuel cell

In this study, energy and exergy analyses of a 1 kW Horizon H-1000 XP Proton Exchange Membrane (PEM) Fuel Cell has been investigated. A testing apparatus has been established to analyze the system efficiencies based on the first and second laws of thermodynamics. In this mechanism pure hydrogen has been directly used as a fuel in compressed gas formation. Purity of hydrogen was above 99.99%. The system performance was investigated through experimental studies on energy and parametric studies on exergy by changing the operating pressure and operation temperature. The results showed that the energy efficiency of PEM fuel cell is 45.58% for experimental study and 41.27% for parametric study at full load. Also, 2.25% and 4.2% performance improvements were obtained by changing the operating temperature ratio (T/T₀) from 1 to 1.2 and operating pressure ratio (P/P₀) from 1 to 2, respectively.     

Exergoeconomic assessment of a geothermal assisted high temperature steam electrolysis system

Exergoeconomic formulations and procedure including exergy flows and cost formation and allocation within a high temperature steam electrolysis (HTSE) system are developed, and applied at three environmental temperatures. The cost accounting procedure is based on the specific exergy costing (SPECO) methodology. Exergy based cost-balance equations are obtained by fuel and product approach. Cost allocations in the system are obtained and effect of the second-law efficiency on exergetic cost parameters is investigated. The capital investment cost, the operating and maintenance costs and the total cost of the system are determined to be 422.2, 2.04, and 424.3 €/kWh, respectively. The specific unit exergetic costs of the power input to the system are 0.0895, 0.0702, and 0.0645 €/kWh at the environmental temperatures of 25 °C, 11 °C, and −1 °C, respectively. The exergetic costs of steam are 0.000509, 0.000544, and 0.000574 €/kWh at the same environmental temperatures, respectively. The amount of energy consumption for the production of one kg hydrogen is obtained as 133 kWh (112.5 kWh power + 20.5 kWh steam), and this corresponds to a hydrogen cost of 1.6 €/kg H₂.     

Exergetic performance analysis of a PEM fuel cell

In this paper we investigate the effects of thermodynamic irreversibilities on the exergetic performance of proton exchange membrane (PEM) fuel cells as a function of cell operating temperature, pressures of anode and cathode, current density, and membrane thickness. The practical operating conditions are selected to be 3–5 atm for anode and cathode pressures, and 323–353 K for the cell temperatures, respectively. In addition, the membrane thicknesses are chosen as 0.016, 0.018 and 0.02 cm, respectively. Moreover, the current density range of the PEM fuel cell is selected to be 0.01–2.0 A cm^?2. It is concluded that exergy efficiency of PEM fuel cell decreases with a rise in membrane thickness and current density, and increases with a rise of cell operating pressure and with a decrease of current density for the same membrane thickness. Thus, it can be said that, in order to increase the exergetic performance of PEM fuel cell, the lower membrane thickness, the lower current density and the higher cell operating pressure should be selected in case PEM fuel cell is operated at constant cell temperature. Copyright © 2005 John Wiley & Sons, Ltd.     

A study of combined biomass gasification and electrolysis for hydrogen production

An integrated system for the production of hydrogen by gasification of biomass and electrolysis of water has been designed and cost estimated. The electrolyser provides part of the hydrogen product as well as the oxygen required for the oxygen blown gasifier. The production cost was estimated to 39 SEK/kg H₂ at an annual production rate of 15?000 ton, assuming 10% interest rate and an economic lifetime of 15 years. Employing gasification only to produce the same amount of hydrogen, leads to a cost figure of 37 SEK/kg H₂, and for an electrolyser only a production cost of 41 SEK/kg H₂. The distribution of capital and operating cost is quite different for the three options and a sensitivity analyses was performed for all of these. However, the lowest cost hydrogen produced with either method is at least twice as expensive as hydrogen from natural gas steam reforming.     

Performance assessment of a direct steam solar power plant with hydrogen energy storage: An exergoeconomic study

Power generation and its storage using solar energy and hydrogen energy systems is a promising approach to overcome serious challenges associated with fossil fuel-based power plants. In this study, an exergoeconomic model is developed to analyze a direct steam solar tower-hydrogen gas turbine power plant under different operating conditions. An on-grid solar power plant integrated with a hydrogen storage system composed of an electrolyser, hydrogen gas turbine and fuel cell is considered. When solar energy is not available, electrical power is generated by the gas turbine and the fuel cell utilizing the hydrogen produced by the electrolyser. The effects of different working parameters on the cycle performance during charging and discharging processes are investigated using thermodynamic analysis. The results indicate that increasing the solar irradiation by 36%, leads to 13% increase in the exergy efficiency of the cycle. Moreover, the mass flow rate of the heat transfer fluid in solar system has a considerable effect on the exergy cost of output power. Solar tower has the highest exergy destruction and capital investment cost. The highest exergoeconomic factor for the integrated cycle is 60.94%. The steam turbine and PEM electrolyser have the highest share of exergoeconomic factor i.e., 80.4% and 50%, respectively.     

Multi‐objective optimization of a combined heat and power (CHP) system for heating purpose in a paper mill using evolutionary algorithm

The present study deals with a comprehensive thermodynamic modeling of a combined heat and power (CHP) system in a paper mill, which provides 50 MW of electric power and 100 ton h^?1 saturated steam at 13 bars. This CHP plant is composed of air compressor, combustion chamber (CC), Air Preheater, Gas Turbine (GT) and a Heat Recovery Heat Exchanger. The design parameters of this cycle are compressor pressure ratio (r_AC), compressor isentropic efficiency (η_AC), GT isentropic efficiency (η_GT), CC inlet temperature (T₃), and turbine inlet temperature (T₄). In the multi‐objective optimization three objective functions, including CHP exergy efficiency, total cost rate of the system products, and CO₂ emission of the whole plant, are considered. The exergoenvironmental objective function is minimized whereas power plant exergy efficiency is maximized using a Genetic algorithm. To have a good insight into this study, a sensitivity analysis of the results to the interest rate as well as fuel cost is performed. The results show that at the lower exergetic efficiency, in which the weight of exergoenvironmental objective is higher, the sensitivity of the optimal solutions to the fuel cost is much higher than the location of the Pareto Frontier with the lower weight of exergoenvironmental objective. In addition, with increasing exergy efficiency, the purchase cost of equipment in the plant is increased as the cost rate of the plant increases. Copyright © 2010 John Wiley & Sons, Ltd.     

Model development and analysis of a novel high-temperature electrolyser for gas phase electrolysis of hydrogen chloride for hydrogen production

In this study, a high temperature electrolyser for the gas phase electrolysis of hydrogen chloride for hydrogen production is proposed and assessed. A detailed electrochemical model is developed to study the J-E characteristics for the proposed electrolyser (a solid oxide electrolyser based on a proton conducting electrolyte). The developed model accounts for all major losses, namely activation, concentration and ohmic. Energy and exergy analyses are carried out, and the energy and exergy efficiencies of the proposed electrolyser are determined to be 41.1% and 39.0%, respectively. The simulation results show that at T = 1073 K, P = 100.325 kPa and J = 1000 A/m², 1.6 V is required to produce 1 mol of hydrogen. This is approximately 0.3 V less than the voltage required by a high temperature steam electrolyser (based on a proton conducting electrolyte) operating at same condition (T = 1073 K, P = 101.325 kPa and J = 1000 A/m²), suggesting that the proposed electrolyser offers a new option for high temperature electrolysis for hydrogen production, potentially with a low electrical energy requirement. The proposed electrolyser may be incorporated into thermochemical cycles for hydrogen production, like CuCl or chlorine cycles.     

Numerical simulation and exergoeconomic analysis of a high temperature polymer exchange membrane electrolyzer

In this paper, a finite volume numerical method is developed to investigate a high temperature polymer exchange membrane (PEM) electrolyzer cell using a three-dimensional and non-isothermal model. The results that are obtained for the single cell are generalized to a full stack of electrolyzer and an exergoeconomic analysis is performed based on the numerical data. The effects of operating temperature, the pressure of cathode, gas diffusion layer (GDL) thickness, and membrane thickness on the energy and exergy efficiencies and exergy cost of the electrolyzer are examined. This study reveals that by increasing the working temperature from 363 K to 393 K, the exergy cost of hydrogen decreases from 23.16 $/GJ to 22.39 $/GJ, and the exergy efficiency of PEM electrolyzer stack at current density of 10,000 A/m² increases from 0.56 to 0.59. The results indicate that increase of pressure deteriorates the system performance at voltages below 1.4 V. It is concluded that operation of the electrolyzer at higher pressures results in decrease of the exergy cost of hydrogen. Increase of membrane thickness from 50 μm to 183 μm leads to increase of the exergy cost of hydrogen from 23.24 $/GJ to 35.99 $/GJ.     

Thermodynamic performance analysis of a molten carbonate fuel cell at very high current densities

This study is basically composed of two sections. In the first section, a CFD analysis is used to provide a better insight to molten carbonate fuel cell operation and performance characteristics at very high current densities. Therefore, a mathematical model is developed by employing mass and momentum conservation, electrochemical reaction mechanisms and electric charges. The model results are then compared with the available data for an MCFC unit, and a good agreement is observed. In addition, the model is applied to predict the unit cell behaviour at various operating pressures, temperatures, and cathode gas stoichiometric ratios. In the second section, a thermodynamic model is utilized to examine energy efficiency, exergy efficiency and entropy generation of the MCFC. At low current densities, no considerable difference in output voltage and power is observed; however, for greater values of current densities, the difference is not negligible. If the molten carbonate fuel cell is to operate at current densities smaller than 2500 A m⁻², there is no point to pressurize the system. If the fuel cell operates at pressures greater than atmospheric pressure, the unit cell cost could be minimized. In addition, various partial pressure ratios at the cathode side demonstrated nearly the same effect on the performance of the fuel cell. With a 60 K change in operating temperature, almost 10% improvement in energy and exergy efficiencies is obtained. Both efficiencies initially increase at lower current densities and then reach their maximum values and ultimately decrease with the increase of current density. By elevating the pressure, both energy and exergy efficiencies of the cell enhance. In addition, higher operating pressure and temperature decrease the unit cell entropy generation.     

Equivalent electrical model for a proton exchange membrane (PEM) electrolyser

In this work, an electrical equivalent model for a proton exchange membrane (PEM) electrolyser has been developed. Through experimental analysis, the input current–voltage (I–V) characteristic for a single PEM electrolyser cell has been modelled under steady-state conditions. It has been developed by using electrical equivalent circuit topology in which the useful power conversion and losses have been taken into account. Electrolytic hydrogen production rates of PEM electrolyser cell have been calculated with respect to the input current and power. The developed model has been tested with experiments results at the nominal operating temperature. The experimental results have been verified with the developed model results and the relative errors between them are around 1–2%. It has been observed that the electrolytic hydrogen production rate increases with the input current in a linear fashion. But the variation of electrolytic hydrogen production rate with the input electrical power is non-linear (i.e. logarithmic). These characteristics are verified by using the developed electrical equivalent model of PEM electrolyser cell. The parameters of the developed model can also be defined by taking into account of temperature and pressure effects. The equivalent electrical model of PEM electrolyser is very useful for analysing the electrical energy system behaviour in which the energy is stored in the form of electrolytic hydrogen.     

A parametric study of polymer membrane electrolyser performance,energy and exergy analyses

In this paper, a mathematical model is developed to study the performance of a polymer membrane electrolyser (PEM) and the effect of different parameters including operating temperature, cathode pressure, membrane thickness, the width and height of channel and current density on the performance and energy and exergy efficiency of PEM electrolyser are investigated. In addition to the resistance overvoltage of components, the concentration overvoltage is modeled using an accurate equation. The model is validated against experimental data. The results indicate that by increasing current density, the voltage of the electrolyser increases, and energy and exergy efficiencies reduce. Increase of temperature from 313 K to 353 K, and decrease of cathode pressure from 40 bar to 1 bar lead to decrease of voltage of the PEM electrolyser by 8.3% and 4.8%, respectively. Moreover, energy and exergy efficiencies increase between 2% and 6% in the range of working temperature and pressure. It is concluded that decrease of membrane thickness, height and width of channel, and increase of exchange current density of the anode and cathode electrodes lead to decrease of voltage of the electrolyser and increase of energy and exergy efficiencies. However, the effect of temperature and cathode pressure and the exchange current densities is greater than the effect of geometric parameters.     

Electrolytic production of hydrogen from aqueous acidic methanol solutions

The electrochemical production of hydrogen (H₂) from liquid methanol in acidic aqueous media was investigated in a proton exchange membrane (PEM) electrolyser, comprising a two-compartment glass cell with a membrane electrode assembly (MEA) composed of a Nafion^® 117 membrane and gas diffusion electrodes (GDE). Methanol electrolysis was studied at concentrations ranging from 0 to 16 M, where 0 M corresponds to water electrolysis. The influence of catalysts (Pt and Pt–Ru), catalyst support (C or black), operating temperatures (23, 50 and 75 °C) and operating modes (dry and wet cathode) were evaluated in the static mode. A theoretical thermodynamic analysis of the system was done as a function of temperature. The limiting current densities, kinetic parameters, including the Tafel slopes and current exchange density, and apparent activation energies were determined.     

Life cycle cost analysis: A case study of hydrogen energy application on the Orkney Islands

Hydrogen can compensate for the intermittent nature of some renewable energy sources and encompass the options of supplying renewables to offset the use of fossil fuels. The integrating of hydrogen application into the energy system will change the current energy market. Therefore, this paper deploys the life cycle cost analysis of hydrogen production by polymer electrolyte membrane (PEM) electrolysis and applications for electricity and mobility purposes. The hydrogen production process includes electricity generated from wind turbines, PEM electrolyser, hydrogen compression, storage, and distribution by H₂ truck and tube trailer. The hydrogen application process includes PEM fuel cell stacks generating electricity, a H₂ refuelling station supplying hydrogen, and range extender fuel cell electric vehicles (RE-FCEVs). The cost analysis is conducted from a demonstration project of green hydrogen on a remote archipelago. The methodology of life cycle cost is employed to conduct the cost of hydrogen production and application. Five scenarios are developed to compare the cost of hydrogen applications with the conventional energy sources considering CO₂ emission cost. The comparisons show the cost of using hydrogen for energy purposes is still higher than the cost of using fossil fuels. The largest contributor of the cost is the electricity consumption. In the sensitivity analysis, policy supports such as feed-in tariff (FITs) could bring completive of hydrogen with fossil fuels in current energy market.     

A review on biomass‐based hydrogen production and potential applications

In this paper, a detailed review is presented to discuss biomass‐based hydrogen production systems and their applications. Some optimum hydrogen production and operating conditions are studied through a comprehensive sensitivity analysis on the hydrogen yield from steam biomass gasification. In addition, a hybrid system, which combines a biomass‐based hydrogen production system and a solid oxide fuel cell unit is considered for performance assessment. A comparative thermodynamic study also is undertaken to investigate various operational aspects through energy and exergy efficiencies. The results of this study show that there are various key parameters affecting the hydrogen production process and system performance. They also indicate that it is possible to increase the hydrogen yield from 70 to 107 g H₂ per kg of sawdust wood. By studying the energy and exergy efficiencies, the performance assessment shows the potential to produce hydrogen from steam biomass gasification. The study further reveals a strong potential of this system as it utilizes steam biomass gasification for hydrogen production. To evaluate the system performance, the efficiencies are calculated at particular pressures, temperatures, current densities, and fuel utilization factors. It is found that there is a strong potential in the gasification temperature range 1023–1423 K to increase energy efficiency with a hydrogen yield from 45 to 55% and the exergy efficiency with hydrogen yield from 22 to 32%, respectively, whereas the exergy efficiency of electricity production decreases from 56 to 49.4%. Hydrogen production by steam sawdust gasification appears to be an ultimate option for hydrogen production based on the parametric studies and performance assessments that were carried out through energy and exergy efficiencies. Finally, the system integration is an attractive option for better performance. Copyright © 2012 John Wiley & Sons, Ltd.     

Solid acids as electrolyte materials for proton exchange membrane (PEM) electrolysis: Review

Proton exchange membrane (PEM) electrolysis provides an effective and clean way to produce high purity hydrogen directly from water. By increasing the working temperature, the efficiency of the device may be greatly enhanced. Solid acids, materials which present a chemistry between an acid and a salt, make potential candidates to use as proton conducting electrolytes. These compounds undergo a structural change which leads to a highly conductive superprotonic phase at temperatures above 140 °C that makes them desirable for use in a PEM electrolyser. However, a stable material with good proton conductivity (>10⁻² S cm⁻¹) in the range of 150–300 °C is desirable. This review focuses on the most promising solid acid materials, analyzing their structure, properties and limitations for water electrolyser applications. In addition the possible use of such materials in fuel cells is reviewed.     

Identification and monitoring of a PEM electrolyser based on dynamical modelling

To improve the efficiency and the safety of hydrogen electrolysis stations, some technological studies are still under investigation both on methods and materials. As methods, control, monitoring and diagnosis algorithms are relevant tools. This work focuses on the dynamical modelling and the monitoring of Proton Exchange Membrane (PEM) electrolyser. Our contribution consists of three parts: to propose a model of an analytical–dynamical PEM electrolyser, dedicated to control and monitoring; to identify the model parameters and to propose adequate monitoring tools. The proposed model is deduced from physical laws and electrochemical equations and consists of a steady-state electric model coupled with a dynamic thermal model. The estimation of the model parameters is achieved using identification and data fitting techniques based on experimental measurements. Taking into account the information given by the proposed analytical model and the experimentation data (temperature T, voltage U and current I) given by a PEM electrolyser, the model parameters are identified. After estimating the dynamical model, model-based diagnosis is used to monitor the PEM electrolyser and to ensure its safety. We illustrate how our algorithm can detect and isolate faults on actuators, on sensors or on electrolyser system.     

Modeling efficiency and water balance in PEM fuel cell systems with liquid fuel processing and hydrogen membranes

Integrating PEM fuel cells effectively with liquid hydrocarbon reforming requires careful system analysis to assess trade-offs associated with H₂ production, purification, and overall water balance. To this end, a model of a PEM fuel cell system integrated with an autothermal reformer for liquid hydrocarbon fuels (modeled as C₁₂H₂₃) and with H₂ purification in a water–gas-shift/membrane reactor is developed to do iterative calculations for mass, species, and energy balances at a component and system level. The model evaluates system efficiency with parasitic loads (from compressors, pumps, and cooling fans), system water balance, and component operating temperatures/pressures. Model results for a 5-kW fuel cell generator show that with state-of-the-art PEM fuel cell polarization curves, thermal efficiencies >30% can be achieved when power densities are low enough for operating voltages >0.72 V per cell. Efficiency can be increased by operating the reformer at steam-to-carbon ratios as high as constraints related to stable reactor temperatures allow. Decreasing ambient temperature improves system water balance and increases efficiency through parasitic load reduction. The baseline configuration studied herein sustained water balance for ambient temperatures ≤35 °C at full power and ≤44 °C at half power with efficiencies approaching ∼27 and ∼30%, respectively.     

Hydrogen crossover in high-temperature PEM fuel cells

In this paper, hydrogen crossover was measured in an environment of high-temperature proton exchange membrane (PEM) fuel cells using a steady-state electrochemical method at various temperatures (T) (80–120 °C), backpressures (P) (1.0–3.0 atm), and relative humidities (RH) (25–100%). An H₂ crossover model based on an MEA consisting of five layers – anode gas diffusion layer, anode catalyst layer, proton exchange membrane (Nafion 112 or Nafion 117), cathode catalyst layer, and cathode gas diffusion layer – was constructed to obtain an expression for H₂ permeability coefficients as a function of measured H₂ crossover rates and controlled H₂ partial pressures. The model analysis suggests that the dominant factor in the overall H₂ crossover is the step of H₂ diffusing through the PEM. The H₂ permeability coefficients as a function of T, P, and RH obtained in this study show that the increases in both T and P could increase the H₂ permeability coefficient at any given RH. However, the effect of RH on the permeability coefficient seems to be more complicated. The T effect is much larger than that of P and RH. Through experimental data simulation an equation was obtained to describe the T dependencies of the H₂ permeability coefficient, based on which other parameters such as maximum permeability coefficients and activation energies for H₂ crossover through both Nafion 112 and 117 membranes were also evaluated. Both Nafion 112 and Nafion 117 showed similar values of such parameters, suggesting that membrane thickness does not play a significant role in the H₂ crossover mechanism.