Electrochemical impedance spectroscopy analysis of V–I characteristics and a fast prediction model for PEM-based electrolytic air dehumidification

PEM-based electrolytic air dehumidification is innovative due to its high efficiency, compact size and cleanness. However, high polarization loss and severe performance degradation have been observed, especially at high applied voltages (>2.5 V). Understanding the V–I characteristics is critical to performance optimization. This study experimentally investigated the V–I characteristics and internal response of materials under various operating conditions, with in-situ Electrochemical Impedance Spectroscopy (EIS) methods. Real-time mass transfer, electrochemical polarization and reaction dynamics of PEM components during dehumidification were derived by EIS. Then, a fast prediction model was built to directly predict the dehumidification rate and attenuation without any iteration, suitable for online monitoring and adjustment. Compared to other models, this model can take a quick understanding of the impact of operating conditions on the material characteristics inside the PEM element. The deviations of current density, PEM proton conductivity and moisture removal were 3%, 11.2% and 15.3%, respectively, compared to experiment data. Results showed that when the applied voltage changed from 1.5 to 3.5 V, the high-frequency resistance of the PEM element increased from 1.69 to 2.69 Ω, and the PEM proton conductivity decreased by about 38 times. The sharp drop in PEM proton conductivity resulted in a current attenuation. With this model, requirements for key components of PEM dehumidification were also obtained. Analysis of the overpotential distribution showed that increasing the water retention and reducing the dependence of proton conductivity on water molecules of the PEM can effectively improve the performance. This research provides guidance for the performance optimization and material selection of PEM-based dehumidification.     

Optimization and comparison of two improved very high temperature gas-cooled reactor-based hydrogen and electricity cogeneration systems using iodine-sulfur cycle

To enrich the existing research methods and content, two improved very high temperature gas-cooled reactor and iodine-sulfur (I–S) cycle-based nuclear hydrogen and steam and helium gas turbines electricity cogeneration systems, including the series connection system (SCS) and the parallel connection system (PCS), are proposed and studied. The energy and exergy analysis methods are used to model these two systems, and Aspen Plus is adopted to build the I–S hydrogen production system. The energy consumption and thermal efficiency of the I–S system are analyzed in detail, and the parametric optimization of two improved systems is performed using particle-swarm optimization (PSO) algorithm. Lastly, the performance comparison of the two systems under different operating conditions is conducted. The simulation results show that more than 99% of the energy consumption of the I–S system is occupied by H₂SO₄ section and HIx section, and the system's thermal efficiency is estimated to be in the range of 17.7%–43.3%. After using an internal heat exchange network, a conservative thermal efficiency of 23.7% is achieved. The optimization results show that under zero hydrogen production load, the proposed PCS and SCS can respectively achieve the net electrical power outputs of 172.8 MW and 125.7 MW, the global thermal efficiencies of 49.36% and 35.91%, and the global exergy efficiencies of 51.94% and 37.79%. With the increase of hydrogen production load, the global efficiencies of both systems decrease significantly, but the decreasing rate of PCS is faster than that of SCS. In addition, the performance comparison results indicate that when the hydrogen production load is small or the intermediate heat exchanger's primary side helium outlet temperature is close to the reactor inlet temperature, the PCS would be a better option than the SCS.     

Techno-economic analysis of alternative processes for alcohol-assisted methanol synthesis from carbon dioxide and hydrogen

The novel methanol production from carbon dioxide (CO₂) and hydrogen (H₂) called alcohol-assisted process is simulated. Although the alcohol-assisted process allows the reduction in operating temperature and pressure, the subsequent product purification is complicated. Comparative studies between the conventional CO₂ hydrogenation and the alcohol-assisted processes are carried out (case I–V). The alcohol-assisted processes present the opportunity of increasing the CO₂ conversion per-pass and reducing 25% of the hydrogen consumption, the barriers in the conventional process. However, the product purifications remain challenging due to the azeotrope of methanol and by-products. Energy consumptions decrease in the feed and reaction sections of the alcohol-assisted processes but significant increase in the product purifications. The formation of by-products and the sequence of purification units affect process performance and economics. The obtained results indicate that the product purification and the catalyst development to increase methanol selectivity and produce an easy-separated by-product play key roles in the enhancement of the process feasibility.     

Hydrogen production with an auto-thermal MSW steam gasification and direct melting system: A process modeling

Municipal solid waste steam gasification and direct melting system is proposed in this study for H₂ production and ash melting simultaneously. Part of the H₂ generated in gasification is extracted for combustion with pure oxygen in the melting zone to provide the energy necessary for auto-thermal operation. A simulation model is developed with Aspen Plus to investigate the performance and optimum conditions of the system. For the feedstock with a lower heating value of 18.91 MJ/kg used in this study, 39.8% of the generated H₂ needs to be extracted to maintain the heat balance of the system at the gasification temperature of 900 °C, melting temperature of 1400 °C, and S/M of 1. The net H₂ yield is ～77.3 kg/t-MSW with a net cold gas efficiency of 49.1% under the same operating condition. An optimum operation condition for T (850–1000 °C) and S/M (0.6–1.0) is determined considering the balance between H₂ production ability and the auto-thermal energy balance.     

Alternative fuelled hybrid electric vehicle (AF-HEV) with hydrogen enriched internal combustion engine

In this paper, hybrid electric vehicle (HEV) that powered by hydrogen (H₂) enriched internal combustion (ICE) engine was studied both simulation and experimental. As an alternative fuel, the usage of H₂ as additional fuel on an ICE that used for HEV, investigated in this partially simulational study for the first time. The study was consisted two parts. In the first part, the effects of 10% H₂ enrichment on performance and emissions were experimented in a 1.8 L Ford Spark Ignition (SI) engine. Then, AVL Boost tool was used for simulation and validation under this ICE's properties and has compared with experimental results. After the simulations and experiments results were found consistent each other, AVL Cruise was used for hybridization of H₂ enriched ICE, for the second part. Combustion, performance and emission values are given comparatively with selected driving cycle of model vehicle were realized with simulation tools. Hybrid mode's ICE becomes more environmentally friendly due to H₂ enrichment with increasing performance. The model HEV has delivered promising results on performance and emission values and this improvement added to literature with this study. Results showed that, enrichment of H₂ is presented 3.56% improvement in ICE torque and 2.37% for ICE power. Cumulative fuel consumption and emission pollution decreased by 12.6% and 14–33% respectively, for hybrid mode.     

A flower pollination optimization algorithm for an off-grid PV-Fuel cell hybrid renewable system

This research work crucially deals with a techno-economic feasibility study for off-grid solar photovoltaic fuel cell (PV/FC) hybrid systems. The hybrid renewable energy system is investigated for feeding electric to remote areas and isolated urban regions in Egypt. To achieve this goal, all the system equipment are modeled, simulated and the area under study data is gathered. The objective function is formulated depending on the total annual cost (TAC). The Flower Pollination Algorithm (FPA), as an efficient recent metaheuristic optimization method, proposed to estimate the optimum number of both PV panels and the FC/electrolyzer/H₂ storage tanks set mandatory where the least total net present value (TNPV) is reached.The loss of power supply probability (LPSP) is considered to enhance the performance of the proposed design. The effect of the variation of FC, electrolyzer, H₂ storage tanks and the PV power system initial cost on the levelized cost of energy (LCOE) is presented through a comprehensive sensitivity analysis.Through Matlab™ program, the numerical simulation results obtained by the FPA algorithm have been compared to the corresponding outcomes while using the artificial bee colony (ABC) and the Particle Swarm Optimization (PSO) techniques. According to the simulation outcomes analysis, the FPA Algorithm has the less fulfillment time and good rendering between the other algorithms. In addition, the optimum system configuration is acquired using FPA with the optimal hybridization of 27 solar PV, 28 FCs, 58 electrolyzers and 37 H₂ storage tanks for an LPSP and PEE of 1.52% and 4.68% respectively. The system TNPV is $3,244,897 with the LCOE of 0.334 $/kWh.     

A Compact Electrical Model for Microscale Fuel Cells Capable of Predicting Runtime and $I$–$V$ Polarization Performance

The growing popularity and success of fuel cells (FCs) in aerospace, stationary power, and transportation applications is driving and challenging researchers to complement and in some cases altogether replace the batteries of portable systems in the hopes of increasing functional density, extending runtime, and decreasing size. Direct-methanol fuel cell (DMFC) batteries have now been built and conformed to low-cost technologies and chip-scale dimensions. Conventional FC models, however, fail to accurately capture the electrical nuances and runtime expectancies of these microscale devices, yet predicting that these electrical characteristics are even more critical when designing portable low-power electronics. A Cadence-compatible model of a DMFC battery is therefore developed to capture all pertinent dynamic and steady-state electrical performance parameters, including capacity and its dependence to current and temperature, open-circuit voltage, methanol-crossover current, polarization curve and its dependence to concentration, internal resistance, and time-dependent response under various loading conditions—the model can also be extended to other micro- and macroscale FC technologies. The simulation results of the proposed electrical model are validated and compared against the experimental performance of several DMFC prototypes, resulting in a runtime error of less than 10.8% and a voltage error under various current loads of less than 80 mV for up to 95% of its operational life. The root cause of the remaining errors and relevant temperature effects in the proposed model are also discussed.      

Influence of nanofluid on heat transfer in a loop heat pipe

Experiments are conducted to investigate heat transfer characteristics of using nanofluid in a Loop Heat Pipe (LHP) as a working medium for heat input range from 20 W to 100 W. The experiments are carried out by manufacturing the LHP, in which the setup consists of a water tank with pump, a flat evaporator, condenser installed with two pieces of fans, two transportation lines (vapor and liquid lines), copper pipe sections for attachment of the thermocouples and power supply. The uniqueness of the current experimental setup is the vapor and liquid lines of LHP which are made of transparent plastic tube to visualize the fluid flow patterns. In this study, the LHP performance using silica (SiO₂–H₂O) nanofluid with particle volume fraction of 3% which was used as a coolant is examined. The experimental results are verified by simulation using Finite Element Method (FEM). The LHP performance is evaluated in terms of transient temperature distribution and total thermal resistance (R_t). R_t is estimated for both LHP using SiO₂–H₂O nanofluid and pure water cases under a steady state condition. The results reveal the average decrease of 28%–44% at heat input ranging from 20 W to 100 W in total thermal resistance of LHP using SiO₂–H₂O nanofluid as compared with pure water. Therefore, the presence of nanoparticles could greatly enhance the cooling of LHP. The experimental and simulation results are found in good agreement.     

Engineering mesoporosity promoting high-performance polymer electrolyte fuel cells

Proton exchange membranes (PEMs) are a vital component in fuel cells (FCs) that attract significant research interest for the present hydrogen energy use. High proton conductivity of PEMs under various operation conditions highly influences the integrated performance of FCs that determines their commercial applications. Hence mesoporous superacidic sulfated zirconia (S-ZrO₂) is fabricated and introduced into Nafion matrix to construct hybrid PEMs. The mesoporosity of S-ZrO₂ is demonstrated highly controllable. High mesoporosity leads to increased amount of sulfonic groups (SO₃H) aggregating on S-ZrO₂ surface. When introduced in PEMs, the highly mesoporous S-ZrO₂ chemically enhances the amount of proton-containing groups, structurally improves the density of ion channels, and reserves water as effective reservoirs, which resultantly maintains high proton conductivity under variable conditions, and thus the performance of assembled FCs. The S-ZrO₂ exhibits the highest surface area of 181 m² g^?1. The hybrid PEMs loaded with 10 wt% such S-ZrO₂ achieve a highest proton conductivity of 0.83 S cm^?1 that is ～7 time of that for pristine Nafion^® membranes. The power density at 0.6 V of FCs with the hybrid PEMs is 786 mW cm^?2, much higher than that for commercial Nafion 211.     

Empirical correlations for the performance of a PEFC considering relative humidity of fuel and oxidant gases

The growing energy demand and the impact of polluting gases lead to the necessity of alternative energy sources and conversion energy devices. Fuel cells (FCs) appears as a suitable solution for facing the mentioned issues. Predicting the behavior of a polymer electrolyte fuel cell (PEFC) under different conditions represents a proper initial step to solve the several issues, e.g., aging water balance problems, which occur inside the cell during the energy conversion process. Understanding microstructural impacts of the diffusion media, water management issues of FCs or the impacts of the inlet reactant gases to the cell represent some of the processes that have to be analyzed to improve the efficiency and behavior of FCs.The current study aims, based on experimentally collected data, to propose empirical correlations that describe and predict the performance of a PEFC. The single cell considered in this study corresponds to a single PEFC with a Nafion® 112 membrane as electrolyte and with an effective area of 25 cm². Relative humidity as a function of the reactive inlet gas temperature, as well as the power and the current density as a function of the cell/reactant gas temperature gradient are analyzed. In addition, correlations for power and current density as a function of the relative humidity (RH) have been proposed. Our correlations are obtained for an operating voltage of 0.6 V. It was shown a strong correlation between the power and current densities with the RH since the membrane conductivity depends mainly on the water content. The PEFC behavior was evaluated at different RHs. The results show big losses of operating power and current densities, as well as an increment of the resistance of the membrane when it operates at low RH.     

Multifunctional layer-perovskite oxide La2-xCexCuO4 for solid oxide fuel cell applications

Materials are always among the first considerations to the development of low temperature solid oxide fuel cells (SOFCs). In this study, we investigate the multifunctionality of a layer-perovskite oxide La_2-xCe_xCuO₄ (LCCO) for its applications in SOFC as cathode, anode and electrolyte. The performances of the LCCO cathode and anode fuel cells are characterized by I–V–P and electrochemical impedance spectra (EIS). Results suggest that LCCO is a good cathode material and it can also deliver impressive anode performance. Though LCCO is noticed to be reduced by H₂ in the anode, the cell performance is relatively stable under multiple times of operation. The existing of ceria and reduced Cu in it may be a reason for its anode catalytic activation. For the application in electrolyte, LCCO is mixed with ionic conductor Ce_0.8Sm_0.2O_2-δ (SDC) in different weight ratios. Differences in power output and open circuit voltage for the cells containing various ratios of LCCO under normal and reverse operation conditions are highlighted. The electronic conductivity of LCCO doesn't bring in electronic leakage if it is kept in a certain range. The multifunctionality of LCCO would enable it to be potentially applied in single layer fuel cell to simplify the structure and fabrication process of SOFC.     

Analytical modeling of polarizations in a solid oxide fuel cell using biomass syngas product as fuel

An analytical model is developed to study fuel type effect on polarizations and performance of SOFC. We consider especially two types of fuel: pure hydrogen and syngas (mixture of H₂ and CO) produced by biomass gasification. The proposed model is based on simultaneous direct oxidation of H₂ and CO at the anode side and uses the dusty-gas model with appropriate diffusion coefficient (binary or mixture coefficient in porous material) to evaluate the concentration polarization and the Butler–Volmer equation to calculate the activation polarization when ohmic polarization is expressed by the well known Ohm’s law. Results analysis show that a fraction of CO of about 24% in syngas improves the performance of SOFC by 23% compared to that obtained by pure H₂.     

Impact of bioethanol impurities on steam reforming for hydrogen production: A review

Hydrogen fuel cells (H₂–FCs) are promising devices for pollution-free and efficient power production. Renewable H₂ from biomass is often produced through catalytic ethanol steam reforming (ESR), which requires a steam/ethanol molar ratio of at least three. The bioethanol obtained by biomass fermentation contains large amounts of water and can be directly subjected to ESR without complex purification steps. However, a wide spectrum of impurities is present in such bioethanol samples, thus complicating the ESR process. Acetic acid, fusel alcohols, ethyl acetate, and sulfur components have been reported as important bioethanol impurities, and also as the main precursors of carbon deposits on the ESR catalyst. On the other hand, amines, methanol, and aldehydes, which are minor bioethanol impurities, have been reported to enhance the H₂ production. This review seeks to define alternatives to reduce the above negative impurities and increase the positive ones during biomass pretreatment and fermentation. Additionally, ESR catalysts are reviewed to identify the features that make them more resistant to deactivation. The combination of strategies to control the impurities during biomass pretreatment, fermentation, purification and the development of highly resistant catalysts may allow processes to produce H₂ from biomass with a low carbon footprint, rendering H₂–FCs an environmentally friendly technology for power production.     

Decarbonizing cement plants via a fully integrated calcium looping-molten carbonate fuel cell process: Assessment of a model for fuel cell performance predictions under different operating conditions

This study is part of a comprehensive research devoted to the integration of a Calcium Looping (CaL) process with a Molten Carbonate Fuel Cell (MCFC) for the decarbonisation of a full-scale cement plant. In the proposed process, where the energy intensive oxy-combustion occurring in the CaL calciner is replaced with a conventional combustion in air. The CO₂-rich gas leaving the calciner is injected into the MCFC cathode while the anode side is fuelled by H₂-rich gases produced by a sorption-enhanced reforming (SER) process. The high CO₂-concentrated gas leaving the anode will be sent to valorisation processes and/or the CO₂ final disposal.Here we focus on modelling, simulation and characterization of the MCFC used as a device for CO₂ separation as well as electricity production, here considered as a process by-product. Polarization curves (I–V curves) and Electrochemical Impedance Spectroscopy (EIS) were measured to support the development and the calibration of a semi-empirical model obtained by theoretical consideration.The experimental campaign demonstrated that the fitted model is able to reproduce the real cell performance when varying the temperature, H₂ concentration, CO₂ concentration at anode and cathode respectively as well as CO₂ CaL capture rate.Indeed, the average difference between numerical and experimental results is always below 2%.Results also demonstrated that the MCFC can be usefully considered as an efficient CO₂ concentrator, with a CO₂ fraction at the anode outlet that is greater than 51% on a dry basis.     

Improved artificial neural network method for predicting photovoltaic output performance

To ensure the safety and stability of power grids with photovoltaic (PV) generation integration, it is necessary to predict the output performance of PV modules under varying operating conditions. In this paper, an improved artificial neural network (ANN) method is proposed to predict the electrical characteristics of a PV module by combining several neural networks under different environmental conditions. To study the dependence of the output performance on the solar irradiance and temperature, the proposed neural network model is composed of four neural networks, it called multi- neural network (MANN). Each neural network consists of three layers, in which the input is solar radiation, and the module temperature and output are five physical parameters of the single diode model. The experimental data were divided into four groups and used for training the neural networks. The electrical properties of PV modules, including I–V curves, P– V curves, and normalized root mean square error, were obtained and discussed. The effectiveness and accuracy of this method is verified by the experimental data for different types of PV modules. Compared with the traditional single-ANN (SANN) method, the proposed method shows better accuracy under different operating conditions.     

Lattice Boltzmann method modeling and experimental study on liquid water characteristics in the gas diffusion layer of proton exchange membrane fuel cells

Water transport through the gas diffusion layer (GDL) is vital to proton exchange membrane fuel cells (PEMFCs), especially under flooding conditions. In this paper, a two-dimensional (2D) lattice Boltzmann method (LBM) is applied to reveal the water dynamic characteristics in GDL, and the computational domain is reconstructed based on the experiment. In-situ experiments, including I–V performance and electrochemical impedance spectroscopy (EIS) tests under flooding conditions, are carried out and analyzed. It is found that the porosity distribution inside the GDL is a crucial factor in water dynamic behavior research. The horizontal liquid water saturation (HS_w) under the channel of real GDL (with porosity distribution) at 0.4 relative thickness are 3.2 times, 2.1 times and 3.4 times higher than the ideal GDL (without porosity distribution) in the case of 0.8 mm, 1.2 mm and 2.0 mm, respectively. The numerical simulation and experimental study show that water dynamic characteristics under the rib influence cell performance directly. In our LBM model, the GDL water distribution inconsistency (Var_w) under 2.0 mm width rib is 43.1% and 28.0% higher than that under the 0.8 mm and 1.2 mm rib, respectively. With the rib wider from 0.8 mm to 2.0 mm, some parts of cell impedance such as R_mt, R_ct, and L_mt increase 64.22%, 98.89%, and 47.46%, respectively. However, GDL under the channel shows no influence on water transport process.     

Model-based degradation prediction on impedance data and artificial neural network for high-temperature polymer electrolyte membrane fuel cells after hydrogen starvation

Degradation caused by H₂ starvation is a typical reason for a limited lifetime in high-temperature polymer electrolyte membrane fuel cells (HT-PEM FC). Here, a long short-term memory (LSTM) artificial neural network (ANN), trained on experimental electrochemical data from a long-term H₂ starvation/regeneration routine, was used to predict the effect of H₂ starvation.In a first application, different voltage decreases were simulated, which FCs typically exhibit during starvation/regeneration routines. The results of three simulation scenarios (3, 5 and 10 mV decrease per regeneration step) showed that critical resistances appeared at output voltages of 0.51, 0.49 and 0.48 V, respectively (compared to the reference voltage of 0.6 V).In a second application, the same FC was virtually set to continue to operate normally (i.e., under regeneration conditions) at certain degrees of starvation, after which voltage was virtually kept constant at 0.48, 0.50 and 0.51 V. For 0.48 and 0.50 V, all simulated resistances fluctuated critically, which corresponded well to experimental data. However, for 0.51 V all simulated resistances never reached critical values. Hence, a safe operational voltage range between 0.6 and 0.51 V is suggested for stable continued FC cycling, which would prevent the occurrence of more severe (irreversible) degradation.     

Titanium dioxide-coated copper electrodes for hydrogen production by water splitting

Pt is the most commonly used electrode and catalyst materials for H₂ production via water splitting as it provides the highest Gibbs free energy of H₂ adsorption (ΔG_H) an d overpotential. However, as Pt catalysts are expensive and difficult to mass-produce, several efforts have been made to identify suitable substitutes. Although Cu provides lower ΔG_H and overpotential than Pt, it exhibits better catalytic performance than other catalysts and is suitable for H₂ production. However, corrosion of Cu may affect its stability of Cu electrode. To overcome this limitation, we have coated a layer of carbon on the copper electrode and then synthesized titanium dioxide-(TiO₂-) on the C/Cu electrode for water splitting application. Carbon black (CB) has excellent electrical conductivity and stable resistance for effective working as an electrochemical catalyst, and TiO₂ has diverse applications because of its low-cost, non-toxic, and corrosion-resistant characteristics. In this study, TiO₂ was synthesized on C/Cu electrodes under UV irradiation for different durations. The optimum irradiation duration was determined to be 15 min via surface and electrochemical analyses. To identify the potential applications of this TiO₂–C/Cu electrode, we used artificial wastewater as the electrolyte. The synthesized TiO₂–C/Cu electrode exhibited better stability than C/Cu electrode. Further, H₂ production with TiO₂–C/Cu electrode was higher than that with C/Cu electrode at the same current density. We also investigated the effect of TiO₂–C/Cu electrode on decomposition of formaldehyde.     

Development of cube-type SOFC stacks using anode-supported tubular cells

Tubular SOFCs have shown many desirable characteristics such as high thermal stability during rapid heat cycling and large electrode area per unit volume, which can accelerate to realize SOFC systems applicable to portable devices and auxiliary power units for automobile. So far, we have developed anode-supported tubular SOFCs with 0.8–2 mm diameter using Gd-doped CeO₂ (GDC) electrolyte, NiO-GDC anode and (La, Sr)(Co, Fe)O₃ (LSCF)-GDC cathode. In this study, a newly developed cube-type SOFC stack which consists of three SOFC bundles was designed and examined. The bundle consists of three 2 mm diameter tubular SOFCs and a rectangular shaped cathode support where these tubular cells are arranged in parallel. The performance of the stack whose volume is less than 1 cm³ was shown to be 2.8 V OCV and over 1 W at 1.6 V under 500 °C. Cathode loss factor due to current collection from cathode matrix was also estimated using a proposed model.     

Modelling of solid oxide fuel cells with internal glycerol steam reforming

The direct application of glycerol in solid oxide fuel cell (SOFC) for power generation has been demonstrated experimentally but the detailed mechanisms are not well understood due to the lack of comprehensive modeling study. In this paper, a numerical model is developed to study the glycerol-fueled SOFC. After model validation, the simulated SOFC demonstrates a performance of 7827 A m^?2 at 0.6 V, with a glycerol conversion rate of 49% at 1073 K. Then, parametric analyses are conducted to understand the effects of operation conditions on cell performance. It is found that the SOFC performance increases with decreasing operating voltage or increasing inlet temperature. However, increasing either the fuel flow rate or steam to glycerol ratio could decrease the cell performance. It is also interesting to find out that the contribution of H₂ and CO to the total current density is significantly different under various operating conditions, even sometimes CO dominates while H₂ plays a negative role. This is different from our conventional understanding that usually H₂ contributes more significantly to current generation. In addition, cooling measures are needed to ensure the long-term stability of the cell when operating at a high current density.