Performance investigation of a transportation PEM fuel cell system

In this study, a comprehensive performance analysis of a transportation system powered by a PEM fuel cell engine system is conducted thermodynamically both through energy and exergy approaches. This system includes system components such as a compressor, humidifiers, pressure regulator, cooling system and the fuel cell stack. The polarization curves are studied in the modeling and compared with the actual data taken from the literature works before proceeding to the performance modeling. The system performance is investigated through parametric studies on energy, exergy and work output values by changing operating temperature, operating pressure, membrane thickness, anode stoichiometry, cathode stoichiometry, humidity, reference temperature and reference pressure. The results show that the exergy efficiency increases with increase of temperature from 323 to 353 K by about 8%, pressure from 2.5 to 4 atm by about 5%, humidity from 97% to 80% by about 10%, and reference state temperature from 253 to 323 K by about 3%, respectively. In addition, the exergy efficiency increases with decrease of membrane thickness from 0.02 to 0.005 mm by about 9%, anode stoichiometry from 3 to 1.1 by about 1%, and cathode stoichiometry from 3 to 1.1 by about 35% respectively.     

Exergoeconomic analysis of a vehicular PEM fuel cell system

In this study, we deal with the exergoeconomic analysis of a proton exchange membrane (PEM) fuel cell power system for transportation applications. The PEM fuel cell performance model, that is the polarization curve, is previously developed by one of the authors by using the some derived and developed equations in literature. The exergoeconomic analysis includes the PEM fuel cell stack and system components as compressor, humidifiers, pressure regulator and the cooling system. A parametric study is also conducted to investigate the system performance and cost behaviour of the components, depending on the operating temperature, operating pressure, membrane thickness, anode stoichiometry and cathode stoichiometry. For the system performance, energy and exergy efficiencies and power output are investigated in detail. It is found that with an increase of temperature and pressure and a decrease of membrane thickness the system efficiency increases which leads to a decrease in the overall production cost. The minimization of the production costs is very crucial in commercialization of the fuel cells in transportation sector.     

Steam electrolysis performance of intermediate-temperature solid oxide electrolysis cell and efficiency of hydrogen production system at 300 Nm h

The steam electrolysis performance of an intermediate-temperature solid oxide electrolysis cell (SOEC) was measured at 650 °C at various steam concentrations. The cell voltage decreased with increasing steam concentration, which was attributed to a decrease in the steam electrode polarization. The highest performance of the SOEC was 1.32 V at 0.57 A cm⁻². On the basis of the electrolytic characteristics of this cell, the efficiency of a hydrogen production system operating at a capacity of 300 N m³ h⁻¹ was estimated. The system efficiency reached a higher heating value (HHV standard) of 98% due to the effective recovery of thermal energy from exhaust gas.     

Thermodynamic and electrochemical analyses of a solid oxide electrolyzer for hydrogen production

In this paper, a modeling of the Solid Oxide Electrolysis Cell (SOEC), through energetic, exergetic and electrochemical modeling approaches, is conducted, and its performance, particularly through exergy efficiency, is analyzed under various operating conditions and state properties for optimum hydrogen production. In a comprehensively performed parametric study, at a single electrolysis cell scale, the effects of varying some operating conditions, such as temperature, pressure, steam molar fraction and the current density on the cell potential and hence the performance are investigated. In addition, at the electrolyzer system scale, the overall electrolyzer performance is investigated through energy and exergy efficiencies, in addition to the system's power density consumption, hydrogen production rate, heat exchange rates and exergy destruction parameters. The present results show that the overall solid oxide electrolyzer energy efficiency is 53%, while the exergy efficiency is 60%. The exergy destruction at a reduced operating temperature increases significantly. This may be overcome by the integration of this system with a source of steam production.     

Experimental investigation and analysis of a new photoelectrochemical reactor for hydrogen production

In this research paper, an experimental investigation of photoactive material titanium dioxide (TiO₂) coated on 180 cm² 316 stainless steel anode is undertaken to study the photoresponse on photoelectrochemical (PEC) hydrogen production. The TiO₂ nanoparticles are first prepared via sol-gel method. A large surface 316 stainless steel anode is coated with TiO₂ nanoparticles by a dip coating apparatus at a withdraw rate of 2.5 mm/s. The nanoparticles are carried on the stainless steel substrate by two-step annealing procedure. The potentiostatic studies confirm the photoactivity of TiO₂ nanoparticles in a photoelectrochemical reactor when exposed to solar ultraviolet (UV) light. The photon to current efficiency measurements carried out on the PEC reactor with TiO₂ coated large surface stainless steel as photoanode demonstrate a significant increase of photoresponse in UV light compared to the uncoated stainless steel prepared under similar conditions. Upon illumination at a power density of 600 W/m², the hydrogen production is observed in TiO₂ coated stainless steel substrate at a measured rate of 51 ml/h while no illumination conditions show a production rate of 42 ml/h. In comparative assessments, the TiO₂ coated substrate shows an increase in photocurrent of 10 mA with an energy efficiency of 1.32% and exergy efficiency of 3.42% at an applied potential of 1.6 V. The present results show a great potential for titanium nanoparticles semiconductor metal oxide in photoelectrochemical hydrogen production application.     

Energetic and exergetic performance evaluations of a geothermal power plant based integrated system for hydrogen production

In this paper, we propose an integrated system aiming for hydrogen production with by-products using geothermal power as a renewable energy source. In analyzing the system, an extensive thermodynamic model of the proposed system is developed and presented accordingly. In addition, the energetic and exergetic efficiencies and exergy destruction rates for the whole system and its parts are defined. Due to the significance of some parameters, the impacts of varying working conditions are also investigated. The results of the energetic and exergetic analyses of the integrated system show that the energy and exergy efficiencies are 39.46% and 44.27%, respectively. Furthermore, the system performance increases with the increasing geothermal source temperature and reference temperature while it decreases with the increasing pinch point temperature and turbine inlet pressure.     

A review: Exergy analysis of PEM and PEM fuel cell based CHP systems

In recent years, growing attention has been given to new alternative energy sources and exergy analysis since fossil fuels cause emissions that have some negative impacts on earth such as global warming, greenhouse effect etc. New power generation systems have been developed in order to reduce or eliminate these impacts as possible. So that, new alternative energy systems have been taken place instead of fossil fuel based systems with nearly zero emission levels. One of them is solid polymer electrolyte or proton exchange membrane (PEM) fuel cell. Although it has significant advantages, there are some disadvantages such as cost, and hydrogen is not a fuel that can be easily obtained. For these reasons, efficiency of a PEM fuel cell has a great significance. Energy efficiency of a system is the most important parameter for utilization. But, energy analysis does not always show the capacity to do work potential of energy of a system. Exergy analysis must be investigated for a system in order to see available work of the system. Because of disadvantages of the PEM fuel cell, exergy analysis has quite importance. In this paper PEM fuel cell and exergy analysis of PEM fuel cell are combined and investigated. A detailed review of the past and recent research activities has been documented. The review focuses on exergy analysis of both PEM fuel cells and PEM based combined heat and power (CHP) systems at different operating parameters. It is concluded that there are a lot of parameters which effects the exergy efficiencies of systems.     

Analysis and performance assessment of a combined geothermal power-based hydrogen production and liquefaction system

In this paper, the thermodynamic study of a combined geothermal power-based hydrogen generation and liquefaction system is investigated for performance assessment. Because hydrogen is the energy of future, the purpose of this study is to produce hydrogen in a clear way. The results of study can be helpful for decision makers in terms of the integrated system efficiency. The presented integrated hydrogen production and liquefaction system consists of a combined geothermal power system, a PEM electrolyzer, and a hydrogen liquefaction and storage system. The exergy destruction rates, exergy destruction ratios and exergetic performance values of presented integrated system and its subsystems are determined by using the balance equations for mass, energy, entropy, energy and exergy and evaluated their performances by means of energetic and exergetic efficiencies. In this regard, the impact of some design parameters and operating conditions on the hydrogen production and liquefaction and its exergy destruction rates and exergetic performances are investigated parametrically. According to these parametric analysis results, the most influential parameter affecting system exergy efficiency is found to be geothermal source temperature in such a way that as geothermal fluid temperature increases from 130 °C to 200 °C which results in an increase of exergy efficiency from 38% to 64%. Results also show that, PEM electrolyzer temperature is more effective than reference temperature. As PEM electrolyzer temperature increases from 60 °C to 85 °C, the hydrogen production efficiency increases from nearly 39% to 44%.     

Comparative assessment of hydrogen production methods from renewable and non-renewable sources

In this study, we present a comparative environmental impact assessment of possible hydrogen production methods from renewable and non-renewable sources with a special emphasis on their application in Turkey. It is aimed to study and compare the performances of hydrogen production methods and assess their economic, social and environmental impacts, The methods considered in this study are natural gas steam reforming, coal gasification, water electrolysis via wind and solar energies, biomass gasification, thermochemical water splitting with a Cu–Cl and S–I cycles, and high temperature electrolysis. Environmental impacts (global warming potential, GWP and acidification potential, AP), production costs, energy and exergy efficiencies of these eight methods are compared. Furthermore, the relationship between plant capacity and hydrogen production capital cost is studied. The social cost of carbon concept is used to present the relations between environmental impacts and economic factors. The results indicate that thermochemical water splitting with the Cu–Cl and S–I cycles become more environmentally benign than the other traditional methods in terms of emissions. The options with wind, solar and high temperature electrolysis also provide environmentally attractive results. Electrolysis methods are found to be least attractive when production costs are considered. Therefore, increasing the efficiencies and hence decreasing the costs of hydrogen production from solar and wind electrolysis bring them forefront as potential options. The energy and exergy efficiency comparison study indicates the advantages of biomass gasification over other methods. Overall rankings show that thermochemical Cu–Cl and S–I cycles are primarily promising candidates to produce hydrogen in an environmentally benign and cost-effective way.     

An electrochemical study of a PEM stack for water electrolysis

The electrochemical properties of a proton exchange membrane (PEM) stack electrolyzer (9 cells of 100 cm² geometrical area) were investigated at different temperatures. An amount of H₂ of ∼270 l h⁻¹ was produced at 60 A (600 mA cm⁻²) and 70 °C under 876 W of applied electrical power. The corresponding specific energy consumed in the process was 3.24 Wh·l⁻¹H₂. The Faradic and electrical efficiencies were determined. Overall stack efficiencies of 73% and 85%, at 60 A and 70 °C, with respect to the low and high heating value of hydrogen, respectively, were obtained. These results confirmed the successful scale-up of a previous lab-scale device.     

Investigation of biogas and hydrogen production from waste water of milk-processing industry in Turkey

This study is conducted to determine the potential for producing both biogas and hydrogen from a milk-processing waste water in Turkey. The results of this study indicate that a maximum of 54.2 million m³ biogas/yr and 12,670 ton H₂/yr can be produced from milk-processing waste water. A total of $15.1 million worth of energy may be supplied every year from the produced biogas. Some Reference calculations for the production of biogas and the economic evaluation are carried out using actual data taken from the plant. Overall hydrogen production energy efficiency for different types of reforming and for different ambient temperatures ranges between 19 and 70% whereas the overall exergy efficiency for 900 °C reforming and different ambient temperatures changes between 8 and 48%, respectively.     

Comparative exergy analysis of sorption enhanced and conventional methane steam reforming

Exergy efficiency analysis tool is used to evaluate sorption enhanced steam reforming in comparison with the industrial hydrogen production route, steam reforming. The study focuses on hydrogen production for use in high pressure processes. Thermodynamic sensitivity analysis (effect of reforming temperature on hydrogen yield and reforming enthalpy) was performed to indicate the optimum temperature (650 °C) for the sorption enhanced reforming. The pressure was selected to be, for both cases, 25 bar, a typical pressure used in the industrial (conventional) process. Atmospheric pressure, 1000 °C and CO₂ as inert gas were specified as the optimum operating parameters for the regeneration of the sorbent after performing exergy efficiency analysis of three realistic case scenarios. Aspen Plus simulation process schemes were built for conventional and sorption enhanced steam reforming processes to attain the mass and energy balances required to assess comparatively exergy analysis. Simulation results showed that sorption enhanced reforming can lead to a hydrogen purity increase by 17.3%, along with the recovery of pure and sequestration-ready carbon dioxide. The exergy benefit of sorption enhanced reforming was calculated equal to 3.2%. Analysis was extended by adding a CO₂ separation stage in conventional reforming to reach the hydrogen purity of sorption enhanced reforming and enable a more effective exergy efficiency comparison. Following that analysis, sorption enhanced reforming gained 10.8% in exergy efficiency.     

Effect of gasification agent on the performance of solid oxide fuel cell and biomass gasification systems

In this paper, an integrated solid oxide fuel cell (SOFC) and biomass gasification system is modeled to study the effect of gasification agent (air, enriched oxygen and steam) on its performance. In the present modeling, a heat transfer model for SOFC and thermodynamic models for the rest of the components are used. In addition, exergy balances are written for the system components. The results show that using steam as the gasification agent yields the highest electrical efficiency (41.8%), power-to-heat ratio (4.649), and exergetic efficiency (39.1%), but the lowest fuel utilization efficiency (50.8%). In addition, the exergy destruction is found to be the highest at the gasifier for the air and enriched oxygen gasification cases and the heat exchanger that supplies heat to the air entering the SOFC for the steam gasification case.     

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.     

Energy and exergy analysis of a PV-T integrated ethanol PEM electrolyzer

A photovoltaic-thermal (PV-T) integrated ethanol proton exchange membrane electrolyzer (PEME) was proposed as a low-energy consuming energy storage option for renewable-sourced electricity as well as a way for simultaneous chemical production in this study. Energy and exergy analyses were applied to each component of the system (e.g., pumps, heat exchanger, PV-T, PEME, and separation unit (SPU)) and the whole system to assess the system performance. The mathematical modelling of the whole system along with its main components except for the SPU was done using the Engineering Equation Solver (EES) software package while the SPU was modelled through the ASPEN Plus. A detailed modelling of the PEME was also included. The effects of the PV-T and PEME parameters on energy and exergy efficiencies of the system were evaluated while the improvement potentials and scale up options were discussed. Energy and exergy efficiencies of the proposed system at the optimum operation of the PEME and under average climatic conditions in the city of Izmir, Turkey were determined to be 27.8% and 3.1%, respectively. Energy and exergy efficiencies of the system were mainly regulated by the PV-T and PEME, whose energy and exergy efficiencies were 40.6%, 56.6% and 13.8%, 14.1%, respectively. Effective PEME parameters for energy and exergy efficiencies of the system were membrane conductivity, membrane thickness, anode catalyst and the operation temperature of the PEME. By changing the PV-T and PEME parameters and by scale-up, energy and exergy efficiencies of the system could be improved.     

Thermodynamic analysis and experimental investigation of a unique photoelectrochemical hydrogen production system

In this study, we thermodynamically analyze and experimentally investigate a continuous type hybrid photoelectrochemical H₂ generation reactor. This system enhances solar spectrum use by employing photocatalysis and PV/T. Additionally, by replacing electron donors with electrodes to drive the photocatalysis, the potential of pollutant emissions are minimized. In this study, the present reactor is tested under electrolysis operation during which the present reactor is investigated under three different inlet mass flow rates (0.25, 0.50, and 0.75 g/s) and four different operating temperatures (20, 40, 60, and 80 °C). Some parametric studies are run by varying the environmental temperature between 0 and 40 °C. In addition, the impact of coating the membrane electrode assembly of the reactor with Cu₂O is investigated. The present results show that the highest energy and exergy efficiencies occur at the environmental temperature of 20 °C which is about 60% and 50%, respectively. The Cu₂O coated membrane gives a lot higher current readings, meaning that the coating makes the membrane more conductive and increases H₂ production by permitting ions at a higher rate.     

Characterisation tools development for PEM electrolysers

Electrochemical impedance spectroscopy (EIS), current interrupt (CI) and current mapping (CM) were investigated as in-situ characterisation tools for PEM electrolysers. A 25 cm² cell with titanium anode and carbon cathode plates were utilised in this study. A commercial MEA consisting of 1 mg IrO₂/cm² on the anode and 0.3 mg Pt/cm² on the cathode was used. The electrocatalyst was deposited on Nafion^® membranes. The electrochemical losses in a PEM electrolyser namely: activation, ohmic and mass transfer losses were identified using EIS and CI and both the advantages and disadvantages of the methods were discussed. The current distribution over the membrane electrode assembly (MEA) at different current densities was measured using the current mapping method. It is also shown that under the given experimental conditions the current density decreases along the serpentine flow field.     

Exergoeconomic analysis of hydrogen production from biomass gasification

In this study, we investigate biomass-based hydrogen production through exergy and exergoeconomic analyses and evaluate all components and associated streams using an exergy, cost, energy and mass (EXCEM) method. Then, we define the hydrogen unit cost and examine how key system parameters affect the unit hydrogen cost. Also, we present a case study of the gasification process with a circulating fluidized bed gasifier (CFBG) for hydrogen production using the actual data taken from the literature. We first calculate energy and exergy values of all streams associated with the system, exergy efficiencies of all equipment, and determine the costs of equipment along with their thermodynamic loss rates and ratio of thermodynamic loss rate to capital cost. Furthermore, we evaluate the main system components, consisting of gasifier and PSA, from the exergoeconomic point of view. Moreover, we investigate the effects of various parameters on unit hydrogen cost, such as unit biomass and unit power costs and hydrogen content of the syngas before PSA equipment and PSA hydrogen recovery. The results show that the CFBG system, which has energy and exergy efficiencies of 55.11% and 35.74%, respectively, generates unit hydrogen costs between 5.37 $/kg and 1.59 $/kg, according to the internal and external parameters considered.     

Potential methods for geothermal-based hydrogen production

In this study, four potential methods are identified for geothermal-based hydrogen production, namely, (i) directly from the geothermal steam, (ii) through conventional water electrolysis using the electricity generated from geothermal power plant, (iii) using both geothermal heat and electricity for high temperature steam electrolysis and/or hybrid processes, (iv) using the heat available from geothermal resource in thermochemical processes to disassociate water into hydrogen and oxygen. Here we focus on relatively low-temperature thermochemical and hybrid cycles, due to their greater application possibility, and examine them as a potential option for hydrogen production using geothermal heat. We also present a brief thermodynamic analysis to assess their performance through energy and exergy efficiencies for comparison purposes. The results show that these cycles have good potential and become attractive due to the overall system efficiencies over 50%. The copper–chlorine cycle is identified as a highly promising cycle for geothermal hydrogen production. Furthermore, three types of industrial electrolysis methods, which are generally considered for hydrogen production currently, are also discussed and compared with the above mentioned cycles.     

Energy and exergy analyses of magnesium-chlorine (Mg-Cl) thermochemical cycle

In this paper, we conduct energy and exergy analyses of the magnesium-chlorine (Mg-Cl) thermochemical cycle for hydrogen production and examine the respective cycle energy and exergy efficiencies. We also undertake a parametric study to investigate how the overall cycle performance is affected by changing the reference environment temperature and operating conditions. The results show that Mg-Cl cycle offers a good potential due to its high energy and exergy efficiencies as 63.63% and 34.86%, respectively, based upon the conditions and parameters considered. In this regard, Mg-Cl cycle appears to be a promising low temperature thermochemical cycle. It may, therefore, compete with other low temperature thermochemical and hybrid cycles such as the copper–chlorine cycle.