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The goal of the review series on the H2 economy is to highlight the current status, major issues, and opportunities associated with H2 production, storage, transportation, distribution and usage in various energy sectors. In particular, Part I discussed the various H2 (grey and green) production methods including the futuristic ones such as photoelectrochemical for small, medium, and large-scale applications. Part II of the H2 economy review identifies the developments and challenges in the areas of H2 storage, transportation and distribution with national and international initiatives in the field, all of which suggest a pathway for establishing greener H2 society in the near future. Currently, various methods, comprising physical and chemical routes are being explored with a focus on improving the H2 storage density, capacity, and reducing the cost. H2 transportation methods by road, through pipelines, and via ocean are pursued actively in expanding the market for large scale applications around the world. As of now, compressed H2 and its transportation by road is the most realistic option for the transportation sector.

This work presents the development of liquid-cooled industry-scale bipolar plates for improved water management in PEM Fuel Cells. The methods used for the design development are based on Computational Fluid Dynamics (CFD) modelling and simulation, and Neutron Radiography experiments to analyse liquid water distributions within the cell for different operating conditions. A novel 140 cm2 bipolar plate was designed and manufactured on 0.1 mm thick stainless steel using pre-coated strip steel. CFD modelling carried out for the novel design predicted a significant improvement in terms of cell performance, as well as a more uniform temperature distribution within the membrane. Liquid water distributions were later analysed by neutron radiography experiments, defining a set of different operating conditions (current density, stoichiometry, inlet gases dew point, and cell temperature). Electrochemical and neutron radiography results are presented for all cases and the influence of the operating conditions is discussed. Liquid water distributions within the cell are also analysed and compared against the CFD model results obtained. The influence of the gas flow configuration (reactant gases and cooling water) is clearly observable in the results.

A CFD mesh corresponding to a Proton Exchange Membrane Fuel Cell (PEMFC) with an active area of 50 cm

This work presents the application of CFD (Computational Fluid Dynamics) to the unsteady gas transport modelling in the cathode side of a Polymer Electrolyte Membrane (PEM) fuel cell during an AC impedance test. The CFD model development and results during AC impedance experiments for 1D and 2D cases are presented and discussed. The effect of liquid water was considered by modelling scenarios with saturated (according to water profiles obtained experimentally) and dry Gas Diffusion Layers (GDL). It was observed that the magnitude of the transient variations of the oxygen concentration within the GDL is dependent on the frequency of the AC signal during the test, given the differences between the diffusion characteristic time and the oxygen consumption characteristic time. For the 2D model where the differences under-the-rib to under-the-channel can be analysed, it was verified that oxygen concentration is much higher under the channel, however the amplitude of the oscillations during AC testing are significantly higher under the rib. When comparing saturated and dry GDLs for both models, it was verified that oxygen concentrations are higher for dry GDLs, but the amplitude of the oscillations is however higher for saturated GDLs.

An appropriate degree of mixing in molten salt tanks for Thermal Energy Storage (TES) in Concentrated Solar Power Plants (CSPPs) is required in order to ensure the safe operation of the tank. Otherwise, cooling due to thermal heat losses is prone to result in a high thermal stratification of the salts and eventually local solidification. In this work, the mixing performance of different configurations of ejectors is investigated by means of Computational Fluid Dynamics (CFD). A set of different ejector configurations has been resolved, modifying the number of ejectors, flow direction, and ejector angle. The best configurations are identified, where the highest fluid circulation capacity is achieved by 10 ejectors directing the jet flow in the tangential direction with an inclination angle of 0° with respect to the tank bottom surface. This is increasing the fluid circulation capacity of the tank by more than 100% with respect to the usual configuration implemented in such tanks (ejectors directed to the tank central vertical axis, at 30° angle). In addition, such configuration ensures an enhanced flow circulation in the bottom part of the tank (with an increase of more than 6 times in the flow velocity in the lower section of the tank), reducing the risk of local salt solidification due to heat loss through the bottom surface. However, the shortest mixing times (95% and 99%) are achieved by the configuration with 10 ejectors pumping flow towards the central tank axis with an inclination angle of 0°.

An advanced energy conversion catalyst comprising pristine carbon-nanotubes and conductive polyaniline polymer successfully synthesized and characterized for high temperature and non-humidified polymer electrolyte membrane fuel cells. The fabricated polyaniline-based catalyst shown a good distribution of platinum nanoparticles (Pt-NPs), and displayed an electrochemical surface area of 645 cm2/mgPt. The catalyst indicated remarkable catalytic activity towards the oxygen reduction reaction (ORR). The overpotential of ORR, the open-circuit voltage, and the power density of the polyaniline-based catalyst declined by a 30 mV, increased by a 50 mV, and enhanced by 26.5%, respectively, when compared to the polybenzimidazole-based catalyst. The impedance measurements have emphasized the improved catalytic activity and the enhanced fuel cell performance of the polyaniline-based catalyst, showing a remarkable reduction of 45% in the charge transfer resistance. This study revealed the advantages of using polyaniline as an anchor to improve the Pt-catalytic activity, opening the door for the wide applications of hydrogen energy.

Promising proton exchange membranes comprising a nitrogen-rich and a high molecular weight poly[2,2′-(bipyridyl)-bibenzimidazole] (BipyPBI) polymer as a substrate and graphene oxide (GO) as a filler were successfully fabricated. The synergism of GO on the membrane physicochemical properties, including the acid doping level, acid retention capability, water uptake, swelling degree, mechanical properties, proton conductivity, oxidative stability, and the hydrogen permeability was studied. The results of the study confirmed the fabrication of mechanically robust and highly conductive proton exchange membranes. Regarding the phosphoric acid (PA) doping level, the BipyPBI/GO membrane reached 17 mol of PA per monomeric unit of BipyPBI (an increase of around 69% in PA-doping level compared to the bare BipyPBI membrane). The proton conductivity at 60 °C under anhydrous conditions increased from 0.002 S cm−1 to 0.019 S cm−1 (around 10-folds increase) when 4 wt% of GO was incorporated into the BipyPBI matrix. In addition, the conductivity reached 0.045 S cm−1 at 140 °C. The activation energy of the proton conduction decreased from 45.6 kJ mol−1 for the bare BiPyPBI to 12 kJ mol−1 for the composite membranes, indicating an improved proton mobility where the GO worked as a carrier-bridge for a smooth proton transfer into the polymer matrix. Furthermore, the H2 permeability reached 1.3 Barrer at 140 °C, indicating the fabrication of tightly-packed membranes. These results provide a very promising membrane for fuel cell applications.

A commercial 50 cm2 PEM fuel cell with serpentine flow fields was operated at 2.0 bar (a) and 60 °C with different relative humidity (RH) values for the inlet reactants (a matrix of 3 RH for anode and 3 RH for cathode). Between each test the cell was decompressed and liquid water was thus flushed out. The liquid water build-up and the time evolution during each experiment were recorded by means of Neutron Imaging. A qualitative and quantitative analysis of the results is presented in this work. It was observed that the dynamics of water build-up comprises three main stages, where the major difference is the liquid water accumulation rate. The onset location for the water appearance in the flow field channels was found to be determined by the flow field design, gravity and gas flow direction along the serpentine path. The time evolution of the water progressive accumulation along the flow field channels and cell active area is discussed.

This work presents a method for the analysis of sand-loaded air flow erosion in heritage sites by means of Computational Fluid Dynamics (CFD). This is intended for cases where particle loaded air flow represents a significant contribution to the erosion process. An investigation of the wind erosion over the heritage site of Baelo Claudia, near Tarifa in Spain, is developed in order to present the method. The site is located directly on the beach by the Mediterranean Sea, on one of the windiest locations in South Europe. The presence of large amounts of sand from the beach in such a windy area is making the site extremely prone to suffer from erosion, as evidenced by the present state of one of the most well-known items in the site, the “Cardo of the Columns”. In this study, a CFD model of the “Cardo of the Columns” area, including the terrain features has been developed. The wind has been modelled according to the statistics available of wind velocity and direction for the site, and sand particles have been included in the simulation by means of the Lagrangian Particle Tracking model. The effect of the sand particles over the columns has been modelled with the erosion model from Finnie. Based on simple in situ measurements and assumptions, an erosion rate of 3.55 kg/year has been calculated, which represents a 30% of the total initial mass of the columns. The constants of the CFD erosion model have been calibrated so that results match the theoretical predictions of the erosion rate. In addition, the erosion-caused damage prediction is predicted for evaluating the state of the columns in the next 50 and 100 years, and potential remedial measures such as the installation of wind baffle are evaluated with the aid of the CFD model.

This work presents an experimental analysis of the time constants associated to diffusion and electrochemical processes in a 50 cm2 Polymer Electrolyte Membrane (PEM) fuel cell. The experimental techniques and results include polarization curves and Electrochemical Impedance Spectroscopy (EIS) analysis of the fuel cell, where the time constants are determined from the analysis of the Distribution of Relaxation Times (DRT). EIS results are also used to determine the cell ohmic resistance, where High Frequency Resistance (HFR) values are calculated from the Nyquist plots. A wide range of operating conditions of the fuel cell are analysed, including back pressure (0.5 bar–1 bar), cell temperature (55 °C, 65 °C, 75 °C), reactant gases relative humidity (30%, 60%, 90%), cathode stoichiometry (λc 2.5–3.5), and oxygen concentration (air and pure oxygen). The effect of the operating conditions on the time constants are discussed, and Damkohler number is introduced and discussed.

This work presents the operating conditions optimization of a 50 cm 2 PEM fuel cell using a one dimensional analytical model previously validated against experimental data for a comprehensive set of different operating conditions of cell temperature, pressure, reactants relative humidity and cathode stoichiometry. The analytical model is used to predict the operating conditions that provide the maximum (and the minimum) power output of the given PEM fuel cell for every value of current intensity. Thus, a maximum performance polarization curve is developed where the operating conditions are not fixed for every current intensity, but modified in order to provide the maximum possible power output for every value of current intensity. The obtained operating conditions have been tested in the real cell showing a good agreement between experimental and modeling results where the maximum error is below 2% for the case of maximum power and 3% for the case of minimum power. The comparison shows that the power output using the operating conditions for the curve of maximum power is about 100% higher than using the curve of minimum power.

This work presents the main steps for the development of a Computational Fluid Dynamics (CFD) model to evaluate the performance of a solar tubular reactor design from the thermal point of view. In this paper a detailed description of the methodology is presented step by step. A simplified reactor design, which consists of a cubical cavity with a single tube, has been selected as base case to illustrate the different models and parameters which take part in the CFD simulations. This base case represents a solar tubular reactor for hydrogen production by means of ferrite thermochemical cycle. The accurate modeling of heat transfer to the packed bed in the interior of the tube is presented, including the effect of the radial distribution of porosity within the porous media. According to the type of reactor and the operating conditions, models and model parameters are analyzed and selected in order to solve the simulation balancing accuracy and required computational time, and the main results are presented. To conclude, the methodology is presented as a powerful tool to identify weaknesses in the design of solar tubular reactor. In addition, the reactor performance at different operating conditions can be evaluated.

This work presents a one dimensional analytical model developed for a 50 cm2 PEM (polymer electrolyte membrane) fuel cell with five-channel serpentine flow field. The different coupled physical phenomena such as electrochemistry, mass transfer of hydrogen, oxygen and water (two phases) together with heat transfer have been solved simultaneously. The innovation of this work is that the model has been validated with two different variables simultaneously and quantitatively in order to ensure the accuracy of the results. The selected variables are the cell voltage and the water content within the membrane MEA (Membrane Electrode Assembly) and GDL (gas diffusion layers) experimentally measured by means of neutron radiography. The results show a good agreement for a comprehensive set of different operating conditions of cell temperature, pressure, reactants relative humidity and cathode stoichiometry. The analytical model has a relative error less than 3.5% for the value of the cell voltage and the water content within the GDL + MEA for all experiments performed. This result presents a new standard of validation in the state of art of PEM fuel cell modeling where two variables are simultaneously and quantitatively validated with experimental results. The developed analytical model has been used in order to analyze the behavior of the PEM fuel cell under different values of relative humidity.

Bipolar Plate design is one of the most active research fields in Polymer Electrolyte Membrane Fuel Cells (PEMFCs) development. Bipolar Plates are key components for ensuring an appropriate water management within the cell, preventing flooding and enhancing the cell operation at high current densities. This work presents a literature review covering bipolar plate designs based on nature or biological structures such as fractals, leaves or lungs. Biological inspiration comes from the fact that fluid distribution systems found in plants and animals such as leaves, blood vessels, or lungs perform their functions (mostly the same functions that are required for bipolar plates) with a remarkable efficiency, after millions of years of natural evolution. Such biomimetic designs have been explored to date with success, but it is generally acknowledged that biomimetic designs have not yet achieved their full potential. Many biomimetic designs have been derived using computer simulation tools, in particular Computational Fluid Dynamics (CFD) so that the use of CFD is included in the review. A detailed review including performance benchmarking, time line evolution, challenges and proposals, as well as manufacturing issues is discussed.

An experimental investigation of the performance and contamination of low and high temperature PEMFCs (polymer electrolyte membrane fuel cells) operating with different concentrations of CO2 at the anode inlet is presented. 50 cm2 MEAs are used in the investigation: Nafion membranes with catalyst Pt loading 0.5 mg cm−2 for both anode and cathode for the low temperature cell, and Celtec P1000 PBI MEAs with catalyst loading 0.75 mg cm−2 in anode and 1 mg cm−2 in cathode for the high temperature cell. An analysis of the relative humidity influence in the contamination process for low temperature polymer electrolyte membrane fuel cells and the temperature effect for both low and high temperature operation range are also investigated in this work. The results show that the performance loss is larger than expected if only a dilution effect were considered, so that a real contamination process occurs in the cell when CO2 is fed to the anode, due to the RWGS (reverse water gas shift) reaction. This contamination effect is analysed and quantified by comparing the polarization curves of the contaminated cell with the ones corresponding to the cell operating with pure hydrogen, following the method described in section 2. The overpotentials for different current densities, CO2 concentrations, relative humidity, and cell temperatures are presented and discussed for both types of fuel cells. Two different regeneration processes (anode feeding with pure H2 and with air) are also presented and discussed. The analysis of the effectiveness of each regeneration strategy also supports that CO produced via the RWGS reaction is adsorbed onto the catalyst.

A 50 cm 2 commercial PEM fuel cell has been used to investigate the effects of a set of different operating conditions on the resulting liquid water distributions in the cell. A comprehensive matrix of operating conditions was analyzed, varying the reactants relative humidity (anode and cathode), cathode stoichiometry, and cell current density. Neutron imaging was used to determine the liquid water distributions within the cell for each operating condition. The obtained neutron radiographs were post-processed and analyzed in order to assess the effects of the different operating conditions. Cell voltage and cell resistance (High Frequency Resistance) were also monitored during the experiments and included in the analysis. Overall, the well-known water distributions corresponding to serpentine flow fields were observed, featuring a progressive water accumulation along the gas flow and towards the outlet port. Cathode channels were showing water accumulation. It was found that the cathode relative humidity had a much larger effect on the cell water content and overall performance than the anode relative humidity for this particular cell.

Molten salts consisting of 60% sodium nitrate and 40% potassium nitrate have been used successfully as a thermal energy collection and storage fluid in different solar thermal plants. However, the relatively high melting point of this mixture (221 °C) represents an important risk of local solidification in the operation of the solar power plants during standby periods. In this work, a computational fluid dynamics (CFD) model is developed to analyze the cooling process of representative state-of-the-art molten salt thermal storage tanks during these standby periods. A comprehensive set of operating conditions is analyzed, covering both hot and cold storage tanks, charging levels, and heat losses. Results show that the onset of local crystallization is highly influenced by the tank charging level. While the risk is relatively high in the case of the minimum charging level, in the case of maximum charging level the risk is minimal as it would require a very long standby period. To summarize the results, this work presents a safe charging level calculation, as a function of the operation temperature and the expected standby duration, which could be used as part of an appropriate operational strategy to avoid the risk of freezing for long standby periods. The model assumptions, the different configurations studied and their results are presented and discussed in detail.

This work presents an experimental investigation on the preferential accumulation of liquid water in the channels of a multiple serpentine PEMFC with 50 cm 2 active area. Neutron imaging was used for visualizing the liquid water distribution during the cell operation for a wide range of operating conditions. Liquid water accumulation in the cathode channels was observed for most of the operating conditions, with a preferential accumulation in certain channels of the flow field. A statistical analysis was performed in order to determine the main characteristics of this accumulation (i.e. channel number and degree of accumulation). As cathode channels were positioned in vertical direction, it was found that gravity effects had an important influence in the accumulation, as well as the relative position of the channel with respect to the inlet and outlet locations. The gas flow direction had also a major impact on the water accumulation within the channels, with significantly more water accumulated in channels with upwards gas flow.

This work presents the validation carried out for a three dimensional CFD 50 cm2 PEM fuel cell model, particularly focus on the prediction of liquid water distributions within the cell. The CFD model was previously validated against a set of experimental polarization curves, where model results adequately matched the experimental curves. An extension of the validation is presented in this work, by performing a comparison of the local liquid water distributions predicted by the model with the liquid water distributions of the real cell. The experimental measurements were obtained by means of Neutron Imaging, where a set of different cell operating conditions was tested. Although the exact quantitative results are not directly comparable due to differences in the cell setup, qualitative results show a very good agreement between the model results and the water distributions observed in the neutron radiographs. A model validation approach using local variable distributions (such as liquid water in this case) in addition to the integral quantities (i.e. polarization curves) is necessary to ensure the validity of models.

A novel modelling framework for the simulation of the diffusive mass transport limitations occurring at GDL local scale of PEFCs is presented, in particular in relation with the distribution of liquid water in the porous media. The distinctive characteristic of this framework is the fact that the distribution of liquid water is not predicted by the model but it is instead mapped into the simulation model from available experimental measurements, obtained with neutron imaging. The presence of liquid water is thus included in the model as a modifier for the gas diffusion transport, and not directly calculated by the model. This allows for a coupling of experimental measurements and model development that is expected to allow a further progress of highly reliable models for the understanding of local fuel cell phenomena. A 1D cell is analyzed, and the effective diffusion coefficient and the n exponent in the diffusion correction factor is calculated from the results of the combination of modelling and experimental data. An extension of the method for a 2D cell is also introduced.

This paper analyzes safety aspects inside a Fuel Cell vehicle using Computational Fluid Dynamics (CFD) tools. The research considers an introduction of a leak of hydrogen inside the vehicle, and its dispersion for a set of typical ventilation conditions is analyzed. The leak of hydrogen has been modelled according to the properties of hydrogen and depending on the pressure difference between the hydrogen storage tank (200 bar) and the atmosphere. The parameters considered for the simulations are the flow rate of cabin ventilation air and hydrogen’s leak. The results obtained for the hydrogen molar concentration are investigated in different sections of the vehicle. Significant differences between front and rear areas are observed, with higher hydrogen concentrations near the rear ventilation vents. The volume of the vehicle within ignition risk (4–75% hydrogen concentration) is also investigated. Finally, different risk mitigation measures are also proposed.

A Computational Fluid Dynamics (CFD) model developed for a 50 cm 2 Fuel Cell with parallel and serpentine flow field bipolar plates was presented in an article published in the International Journal of Hydrogen Energy 35 (2010) 11,533–11,550 [1] . The experimental validation details were presented as well in an article published in the International Journal of Hydrogen Energy 35 (2010) 11,437–11,447 [2] . A good agreement between numerical results and experimental measurements were obtained except for the high current density region where mass-transport limitations dominate the voltage loss. This short communication presents an update on the last simulations performed, where an improved prediction of the polarization curve is obtained. The physical and computational aspects of the reasons underlying the improvement of the results are discussed.

AC impedance or electrochemical impedance spectroscopy (EIS) is becoming a fundamental technique used by researchers and scientists in proton exchange membrane (PEM) fuel cell analysis and development. In this work, in situ impedance measurements are presented for a series of operating conditions in a 50 cm 2 fuel cell. The electrode charge transfer resistance was determined from the corresponding arcs of the Nyquist diagrams. The analyses were performed for H 2 /O 2 and H 2 /air operation at different stoichiometric factors and reactant gases humidification. Characteristic time scales of charge transfer processes at the different operating conditions were estimated from the corresponding Bode plots. These values were used for a non-dimensional analysis of the different fuel cell electrochemical and transport processes, namely electrochemical reaction versus GDL reactant transport. Fuel cell adapted Damkholer numbers are thus presented, where the results indicate that the GDL diffusion transport is the limiting process for the cases under analysis, especially when air is used as oxidant. Additional analysis of channel convective mass transport versus GDL diffusive mass transport is also presented.

The work and conclusions gained from the analysis of five new underground interchange buildings ongoing in Madrid, Spain, is presented. An additional study was performed for a typical two-level interchange building, and the methodology and results are presented in this paper. First, different ventilation and air conditioning strategies have been analyzed. The main goal is to find the most efficient design in order to maintain pollutants concentration and temperatures below the designed values, at minimum investment and operation costs. Different strategies have been modelled and compared using a Computational Fluid Dynamics (CFD) code, taking into account the buses circulation and the different pollution and heat sources. The final solution developed is based on a physical separation between the island area and the dock area. Conclusions on the efficiency of the different design strategies and possible pitfalls are presented. Secondly, different fire scenarios are analyzed. The main goal is to check whether the fire fighting measures planned, such as mechanical ventilation and a curtains system to define smoke sectors are able to cope with a fire emergency situation. A model for the bus fire has been developed, including heat release and smoke production. The main results presented are temperature fields, visibility and smoke concentration.

This work presents a Computational Fluid Dynamics (CFD) model developed for a 50 cm 2 fuel cell with parallel and serpentine flow field bipolar plates, and its validation against experimental measurements. The numerical CFD model was developed using the commercial ANSYS FLUENT software, and the results obtained were compared with the experimental results in order to perform a model validation. A single parameter, namely the reference exchange current density, was fitted to calibrate the model results. All other model parameters were determined from technical data sheets, literature survey, or experimental measurements. A discussion on different validation issues and model parameters is provided. The results of the numerical model show a good agreement with the experimental measurements for the different bipolar plates and range of operating conditions analysed. However, inaccuracies in the results in the mass-transport polarization region were observed, presumably when liquid water in the channels produces a blockage effect that cannot be modelled with the multiphase flow model currently implemented.

This work presents experimental performance results for a 50 cm 2 Polymer Electrolyte Membrane (PEM) Fuel Cell, including polarization curves and Electrochemical Impedance Spectroscopy (EIS) analysis of the Fuel Cell. EIS results were used for the determination of the cell ohmic resistance as well as charge transfer resistances under different operating conditions. Different combinations of operating conditions and bipolar plate designs were analysed. In particular, the effect of the cathode oxygen concentration, reactant gases humidification, and bipolar plate (BP) design were assessed. Butler–Volmer (BV) kinetic parameters such as the charge transfer coefficient were also determined from Tafel plots. The electronic contact resistances were measured for both Bipolar Plate designs, and the membrane protonic resistances were calculated. Its dependence on the BP flow field design and operating conditions is addressed. The results obtained in this work are aimed both at gaining insight into the fundamental processes determining the fuel cell performance, and at determining parameters needed for Computational Fuel Cell Dynamics (CFCD) numerical simulations.

In the present work, a computational model based on an Eulerian–Eulerian approach was used for the simulation of the transient two-phase flow in a rectangular partially aerated bubble column. Superficial gas velocities (UG) ranging from 0.24 to 2.30 cm/s were used throughout both the experiments and the simulations. The calculated results were verified by comparing them with experimental data including measurements of gas hold-up, plume oscillation period (POP) and Sauter mean bubble diameter. The study shows the effect of mesh refinement, time-step and physical model selection, the latter regarding the role of bubble size distribution and non-drag forces, on the computational results. According to the results presented here, the representation of bubble populations using multiple size groups (MUSIG model) instead of a single group improves the prediction of the experimental parameters under study. Additionally, the results obtained after including the virtual mass force term do not differ considerably from those obtained including only the drag force. On the contrary, as a consequence of introducing the lift force term into the model, the gas hold-up is overestimated and a non-symmetric bubble plume oscillation appears, a fact that is not experimentally observed.