Intermediate temperature fuel cells based on doped ceria–LiCl–SrCl2 composite electrolyte

A new type of oxide-salt composite electrolyte, gadolinium-doped ceria (GDC)–LiCl–SrCl₂, was developed and demonstrated its promising use for intermediate temperature (400–700 °C) fuel cells (ITFCs). The dc electrical conductivity of this composite electrolyte (0.09–0.13 S cm⁻¹ at 500–650 °C) was 3–10 times higher than that of the pure GDC electrolyte, indicating remarkable proton or oxygen ion conduction existing in the LiCl–SrCl₂ chloride salts or at the interface between GDC and the chloride salts. Using this composite electrolyte, peak power densities of 260 and 510 mW cm⁻², with current densities of 650 and 1250 mA cm⁻² were achieved at 550 and 625 °C, respectively. This makes the new material a good candidate electrolyte for future low-cost ITFCs.     

Oxide ion and proton conduction in doped ceria–carbonate composite materials

The direct current four-probe method has been employed to investigate the conduction of oxide ion and proton in a doped ceria–carbonate composite electrolyte for fuel cells. The measurements are conducted in oxygen and in hydrogen atmospheres in the temperature range of 425–650 °C. The conductivities of both of O²⁻ and H⁺ increase with the increase of carbonate content above the melting point of the carbonate. The ionic conductivities of the composite electrolytes have also been simulated using the effective medium percolation theory. The deviations between experimental results and simulated values of O²⁻ conductivity are caused by the associating effect of ceramic and carbonate phases, which leads to a higher O²⁻ migration energy through the phase interface. According to the comparison of experimental data and simulated values, the conduction mechanisms of O²⁻ and H⁺ have been proposed.     

The effect of ceria content in nickel–ceria composite anode catalysts on the discharge performance for solid oxide fuel cells

Optimum ceria content in nickel–ceria composite anode catalyst from the point of discharge performance is discussed. The ohmic loss increased when the ceria content was higher than 30 mol%. Even though the electrical conductivity of the anode decreased with increasing ceria content in the anode catalyst in association with decreasing nickel content, the ohmic loss was kept low until the ceria content was ≤30 mol% because the semiconducting ceria compensated for the decreased current path owing to the decreasing nickel content. The lowest activation loss was observed when the ceria content in the nickel anode catalyst was 30 mol% and the maximum activation loss was obtained for ceria content of 2 mol%. Ceria content in nickel anode influenced microstructure of the anode matrix. When the CeO₂ content was 2 mol%, sintering of anode catalyst was evident and the porosity of anode matrix was almost 57% - highest in this study. Whereas sintering of anode catalyst was not evident and the porosity of anode matrix was 46% when the ceria content in the nickel anode catalyst was 30 mol%. Activation loss was strongly influenced by microstructure of anode matrix, and highest activation loss when the CeO₂ content was 2 mol% was owing to the inappropriate microstructure for electrochemical reaction: sintering of the anode catalyst and excessive porosity of the anode.     

Validation of H/O conduction in doped ceria–carbonate composite material using an electrochemical pumping method

A hydrogen and oxygen electrochemical pump technique has been employed to elucidate the conduction of proton and oxygen ion in a doped ceria–carbonate composite electrolyte for intermediate temperature solid oxide fuel cells. The composite material shows efficient conductivities of both of the two ions at 650 °C. The molten carbonate phase is important for the migration of both of the two ions. The mechanism of the conduction of proton and oxygen ion is also discussed.     

Stability considerations of semiconductor ionic fuel cells from a LNCA (LiNi0.8Co0.15Al0.05O2-δ) and Sm-doped ceria (SDC; Ce0.8Sm0.2O2-δ) composite electrolyte

Recent advances in composite materials, especially semiconductor materials incorporating ionic conductor materials, have led to significant improvements in the performance of low-temperature fuel cells. In this paper, we present a semiconductor LNCA (LiNi_0.8Co_0.15Al_0.05O_2-δ) which is often used as electrode material and ionic Sm-doped ceria (SDC; Ce_0.8Sm_0.2O_2-δ) composite electrolyte, sandwiched between LNCA thin-layer electrodes in a configuration of Ni-LNCA/SDC-LNCA/LNCA-Ni. The incorporation of the semiconductor LNCA into the SDC electrolyte with optimized weight ratios resulted in a significant power improvement, from 345 mW cm^?2 with a pure SDC electrolyte to 995 mW cm^?2 with the ionic-semiconductor SDC-LNCA one where the corresponding ionic conductivity reaches 0.255 S cm^?1 at 550 °C. Interestingly, the coexistence of ionic and electron conduction in the SDC-LNCA membrane displayed not any electronic short-circuiting but enhanced the device power outputs. This study demonstrates a new fuel cell working principle and simplifies technologies of applying functional ionic-semiconductor membranes and symmetrical electrodes to replace conventional electrolyte and electrochemical technologies for a new generation of fuel cells, different from the conventional complex anode, electrolyte, and cathode configuration.     

Comments on Enhanced ionic conductivity of yttria-stabilized ZrO2 with natural CuFe-oxide mineral heterogeneous composite for low temperature solid oxide fuel cells,Int. J. Hydrogen Energy 42 (2017) 17495–17503

Recently, in this journal the phenomenon of ionic conductivity enhancement has again been claimed to boost the electrical characteristics of a solid electrolyte, this time of the classical oxygen ion conductor yttria-stabilized zirconia. It is demonstrated that the arguments to support the claim are flawed and that the criticized article is another example of a fallacy with regard to ionic conductivity enhancement.     

Exergy recovery in regasification facilities – Cold utilization: A modular unit

The paper deals with the problem of cold recovery for direct utilization both in the site of regasification facility and far from it.A modular LNG regasification unit is proposed having the regasification capacity of 2 billion standard cubic meters/year of gas. The modular plant is based on use of a power cycle working with ethane or ethylene which allows operation of cold energy transfer, contained in LNG to be regasified, in a range of temperatures suitable for multipurpose use of cold, reducing regasification process irreversibility. Some electric energy is produced by the power cycle, but the own mission of modular unit proposed is addressed to deliver cold suitable for industrial and commercial use in the proper temperature range. The option considers, also, the use of carbon dioxide as a secondary fluid for transfer of cold from regasification site to far end users. This option seems very attractive due to expected wide future exploitation of LNG regasification in the world.Results of a detailed thermodynamic and economic analysis demonstrate the suitability of the proposal.     

Semiconductor ionic Ce0.8Sm0.2O2-δ-Na2CO3 – LiCo0.225Cu0.075Ni0.7O 3-δ composite material as electrolyte for low temperature solid oxide fuel cells

Semiconductor ionic electrolytes have obtained much attention because of good ionic conductivity and electrochemical performance. Novel semiconductor ionic NSDC (Ce_0.8Sm_0.2O_2-δ-Na₂CO₃)-LCCN (LiCo_0·225Cu_0·075Ni_0·7O_3-δ) composite materials have been adopted as electrolyte membrane for the first time, in which symmetrical cell composed of NSDC-LCCN membrane is constructed with Ni_0·8Co_0·15Al_0·05LiO₂ (NCAl)-pasted Ni foam electrodes. An open circuit voltage (OCV) above 1 V and improved power density are obtained in the NSDC-LCCN cells, which confirms the functionality of the proposed semiconductor ionic materials. Meanwhile, X-ray diffractometer (XRD) and Scanning electron microscope (SEM) analyses identify the phase purity and homogenous nanocomposite morphology of all the NSDC-LCCN materials samples with various mass ratios. The performance illustrated by much more steady instead of transient state evaluation reveals that 3NSDC-LCCN composite electrolyte is most optimum, and the corresponding cell exhibits a considerable maximum power density of 598 mW cm⁻² at 550 °C, over five times of that of pure NSDC electrolyte cells. Short-term duration test of 3NSDC-LCCN cell at 550 °C shows that the cell could steadily operate up to ~9 h without obvious degradation at a remarkable current density of 469 mA cm⁻², which indicates that NSDC-LCCN composite electrolyte is a promising material for low temperature solid oxide fuel cells.     

The effect of concentration gradients on deflagration-to-detonation transition in a rectangular channel with and without obstructions – A numerical study

Explosions in homogeneous reactive mixtures have been widely studied both experimentally and numerically. However, in accident scenarios, mixtures are usually inhomogeneous due to the localized nature of most fuel releases, buoyancy effects and the finite time between release and ignition. It is imperative to determine whether mixture inhomogeneity can increase the explosion hazard beyond what is known for homogeneous mixtures. The present numerical investigation aims to study flame acceleration and transition to detonation in homogeneous and inhomogeneous hydrogen-air mixtures with two different average hydrogen concentrations in a horizontal rectangular channel. A density-based solver was implemented within the OpenFOAM CFD toolbox. The Harten–Lax–van Leer–Contact (HLLC) scheme was used for accurate shock capturing. A high-resolution grid is provided by using adaptive mesh refinement, which leads to 30 grid points per half reaction length (HRL). In agreement with previous experimental results, it is found that transverse concentration gradients can either strengthen or weaken flame acceleration, depending on average hydrogen concentration and channel obstruction. Comparing experiments and simulations, the paper analyses flame speed and pressure histories, identifies locations of detonation onset, and interprets the effects of concentration gradients.     

The effect of a perforated plate on the propagation of laminar hydrogen flames in a channel – A numerical study

Laminar hydrogen flame propagation in a channel with a perforated plate is investigated using 2D reactive Navies-Stokes simulations. The effect of the perforated plate on flame propagation is treated with a porous media model. A one step chemistry model is used for the combustion of the stoichiometric H₂–air mixture. Numerical simulations show that the perforated plate has considerable effect on the flame propagation in the region downstream from the perforated plate and marginal effect on the upstream region. It is found to squeeze the flame front and result in a ring of unburned gas pocket around the flame neck. The resulting abrupt change in flow directions leads to the formation of some vortices. Downstream of the perforated plate, a wrinkled “M”-shape flame is observed with “W” shape flame speed evolution, which lastly turns back to a convex curved flame front. Parametric studies have also been carried out on the inertial resistance factor, porosity, perforated plate length and its location to investigate their effects on flame evolution. Overall, for parameter range studied, the perforated plate has an effect of reducing the flame speed downstream of it.     

Novel proton-conducting layered perovskite based on BaLaInO4 with two different cations in B-sublattice: Synthesis,hydration, ionic (O2−, H+) conductivity

The present study focused on the novel material with significantly improved properties for the application in the area of clean energy. The new complex oxide BaLaIn_0·5Y_0·5O₄ with layered perovskite structure was obtained for the first time. It was proved that the introduction of Y³⁺ ions in the perovskite layer of BaLaInO₄ leads i) to the rise of the oxygen-ionic conductivity due to the increase in mobility of oxygen ions as a result of the expand of the cell volume and ii) to the enhancement of protonic conductivity due to the increase in the proton concentration and mobility. The sample BaLaIn_0·5Y_0·5O₄ is nearly pure proton conductor below 400 °C and has the protonic conductivity value 1.6?10^?5 S/cm at this temperature.     

Energy loss in electrochemical diaphragm process of chlorine and alkali industry – A collateral effect of the undesirable generation of chlorate

Contamination of NaOH with chlorate constitutes a major problem for the chlorine–alkali industry, particularly when electrolytic cells based on the diaphragm process are employed. In this paper, pilot and laboratory cell experiments revealed that chlorate contamination in diaphragm cells also inhibits hydrogen evolution and gives rise to a significant increase in electrical energy consumption. Electrolysis carried out under conditions that simulated the industrial process (current density 240 mA cm⁻²; temperature 90 °C; brine flux 23 L cm⁻² h⁻¹) revealed that chlorate formation depends on brine flux and NaOH production. The inhibitory effect of chlorate on the main cathodic reaction was demonstrated in bench cell experiments, with cathodic displacement of the hydrogen evolution reaction by more than 100 mV in the presence of 0.4% chlorate compared with ideal conditions in which chlorate formation was absent. This hydrogen generation overpotential can charge the total electric energy balance in more than 5% of the total value, consisting of a critical loss for this process.     

Performance evaluation of an air breathing polymer electrolyte membrane (PEM) fuel cell in harsh environments – A case study under Saudi Arabia's ambient condition

A key parameter that determines the efficiency of proton exchange membrane fuel cells is their operating conditions. Optimization of various components in these fuel cells is pivotal in improving cell performance, as their performance is directly related to the operational conditions the cells are subjected to.This investigation examined the viability of an air breathing fuel cell subjected to ambient conditions in Riyadh in Saudi Arabia. A validated three-dimensional air breathing 5-cell stack, modelled in ANSYS was utilised to generate the results. Furthermore, the work also considered the feasibility of deploying a humidifier unit for the hydrogen inlet, so as to ascertain the physical behaviour of the PEMFC stack. It was observed that the performance of the stack reaches its peak during the summer time (June–August), and hydrogen humidification improves output performance by 40%.     

The effect of imidazolium ionic liquid on the morphology of Pt nanoparticles deposited on the surface of SrTiO3 and photoactivity of Pt–SrTiO3 composite in the H2 generation reaction

Photocatalytic water splitting has great potential in solar-hydrogen production as a low-cost and environmentally friendly method. Different unique techniques used to obtain photocatalysts with various modifications to improve H₂ generation have been introduced. In the present work, SrTiO₃ was successfully synthesized via the solvothermal method in the presence of ionic liquid (IL) - 1-butyl-3-methylimidazolium bromide ([BMIM][Br]) followed by surface decoration with Pt particles using the photodeposition method. The effect of the noble metal content and presence of IL on the morphology, optical and surface properties of SrTiO₃, thereby the effectiveness of hydrogen generation, has been thoroughly examined and presented. Unexpectedly, the presence of [BMIM][Br] at the SrTiO₃ surface affected the interaction between the semiconductor surface and platinum particles formed throughout photodeposition. Platinum particles at the surface of SrTiO₃_IL were found to be in the form of 2D clusters with a size of 1 nm. In comparison, Pt deposited on SrTiO₃ photocatalyst without application of IL created larger, three-dimensional structures with a diameter exceeding 5 nm. This is the reason why the total amount of platinum deposited on the SrTiO₃_IL sample is smaller than that on SrTiO₃ and justifies a higher efficiency of hydrogen generation of Pt modified SrTiO₃ photocatalyst in comparison to SrTiO₃ prepared in the presence of IL. The mechanism of H₂ generation in the water-splitting reaction in the presence of SrTiO₃_Pt photocatalyst was discussed.     

SUNRISE – A caesura after nuclear has gone: Energy in Germany(and in other potentially de-nuclearizing countries)

The German Bundestag decided June 30, 2011 to shut down by 2022 stepwise the complete national nuclear power plant capacity which at the time of decision generated some 22% of the nation’s electricity demand. This presentation tries to present a technology forecast of three potential compensations 1) energy and exergy efficiency gains, 2) renewable energies, and 3) hydrogen energy, thereby bearing in mind that fossil fuels such as coal, mineral oil and natural gas will by no means be gone after that short 10 year transition time. Consequently, not only the three compensations, but also fossil fuels – now efficient to the technological utmost – have to meet the obligation of reducing anthropogenic environmental and climate changing influences, and, in Germany’s case with 75% of its energy demand covered by imports of great importance, try to decrease the almost life risking high import rate by distributing suppliers all over the world and start introducing global clean renewable energies and trade in renewable hydrogen energy. Whether SUNRISE will evolve into a paragon for all those nations thinking of, planning for, or already taking the first steps towards saying farewell to nuclear is too early to determine. The four components of energy sustainability compensating for nuclear – energy and exergy efficiency gains, clean fossil, solar and hydrogen – pluck up courage, make headway and leave nuclear behind. And, in particular, hydrogen energy is and will increasingly become humankind’s common cause!     

Stochastic modeling of polymer electrolyte membrane fuel cell gas diffusion layers – Part 2: A comprehensive substrate model with pore size distribution and heterogeneity effects

A stochastic modeling algorithm was developed that accounts for porosity distribution, fiber diameter, fiber co-alignment, fiber pitch, and binder and/or polytetrafluorethylene fractions. Materials representative of a commercially available GDL were digitally generated based on empirical measurements of these various properties. Materials made with varying fiber diameters and binder/fiber volume ratios were compared with a generated reference material through porosity heterogeneity calculations and mercury intrusion porosimetry simulations. Fiber diameters and binder/fiber ratios were found to be key modeling parameters that exhibited non-negligible impacts on the pore space. These key parameters were found to positively correlate with heterogeneity and mean pore diameter and exhibit a complementary relationship in their impact on the pore space. Because both parameters directly impacted the number of fibers added to the domain, modeling techniques and parameters pertaining to fiber count must be considered carefully.     

Hydrogen storage in scandium doped small boron clusters (BnSc2, n=3–10): A density functional study

In this work, we present the hydrogen adsorption capacity of Sc doped small boron clusters (B_nSc₂, n = 3–10) using density functional theory. Almost no structural change was observed in the host clusters after hydrogen adsorption. Stabilities of the studied clusters were confirmed by various reactivity parameters such as hardness (η), electrophilicity (ω), and electronegativity (χ). The average adsorption energies was found in the range of 0.08–0.19 eV/H₂ inferring physisorption process, and the fact is also supported by the average distance from Sc to H₂ molecules which was in the range of 2.13 Å-2.60 Å. All the clusters were found to have gravimetric density satisfying the target set by the U.S. Department of Energy (US-DOE) (5.5 wt% by 2020). From Bader's topological analysis, it was confirmed that the nature of interaction was likely to be somewhat closed shell type. ADMP molecular dynamics simulations study was performed at different temperatures to understand the adsorption and dissociation of H₂ from the complexes.     

Green hydrogen-based pathways and alternatives: Towards the renewable energy transition in South America's regions – Part A

In recent years, there has been an increased concern regarding the impacts of climate change caused by the increase in anthropogenic CO₂ emissions, and the search for clean energy sources has grown. Hydrogen produced from renewable sources is an alternative to the demand for clean energy. Argentina, Paraguay and Uruguay are countries located in South America with a considerable number of rivers and hydroelectric plants. This study shows the potential production of hydrogen in these countries using the excess energy from hydroelectric plants. While Argentina has a potential generation of 3.44E+10 Kg.year^?1 of H₂, Paraguay and Uruguay presented, respectively, 5.32E+10 Kg.year^?1 and 2.19E+10 Kg.year^?1. Taking into account the economic viability analysis, H production and storage had a profit of 0.2253 US$.m^?3 for Paraguay, 0.2249 US$.m^?3 for Uruguay and a cost of 0.2263 US$.m^?3 in Argentina. The results of this research contribute to the renewable, sustainable energy transition and in accordance with the precepts of the circular economy for the search for new sources of energy. This idea needs to be encouraged around the world, including developing countries.     

Wind turbine availability: Should it be time or energy based? – A case study in Ireland

This paper describes a method for quantifying wind farm availability using two different approaches and comparing the results. Wind turbine suppliers regularly guarantee turbine availability in terms of time. A typical value of 97% is generally taken as the industry standard. This paper shows that this guarantee can potentially under-compensate the wind farm operator for losses sustained depending on when the period of non-availability occurs. Here we present an alternative method to quantify wind farm availability based on energy, which relates the energy losses in an Irish wind farm in 2007 to periods of turbine non-availability. It is shown in this analysis completed at this operational wind farm that while the technical non-availability as a percentage of time is 3%, the percentage of energy lost during downtimes is actually 11%. Based on the financial analysis above, the financial losses are significant. To answer the question should wind turbine availability be time or energy based, this paper shows that it can be advantageous for wind turbine owners to have energy-based calculations as long as the developers have sufficient monitoring of not only wind speed but also SCADA data.     

Analysis of chemical,electrochemical reactions and thermo-fluid flow in methane-feed internal reforming SOFCs: Part I – Modeling and effect of gas concentrations

Direct internal reforming solid oxide fuel cells (DIR SOFCs) have complicated distributions of temperature and species concentrations due to various chemical and electrochemical reactions. The details of these properties are studied by a 3-D numerical simulation in this work. The simulation modeling used governing equations (mass, momentum, energy and species balance equations) generally suitable to porous medium with porosity variable of zero (solid), 0.3 (porous medium) and 1.0 (fluid). Chemical kinetics equations for the internal reforming and shift reactions based on the Langmuir–Hinshelwood model were incorporated. Hydrogen and carbon monoxide oxidations were considered both participating in electrochemical reactions. The experimentally measured current density–potential curves were compared with the simulation data to validate the code, which revealed that the simulation model was able to predict the dilution effect of nitrogen and the mass transfer under high current densities. It is found that the temperature dramatically declined near the fuel inlet with strong endothermic reactions, but it increased along the fluid flow with electrochemically exothermic reactions. A low steam-to-carbon ratio (SCR) led to high steam reforming and water gas shift reaction rates, which generated a greater amount of hydrogen. Therefore, current density increased with low SCR. The average current density due to carbon monoxide electrochemical oxidation varies from 205.3 A/m² under an SCR of 2.0 to 47.6 A/m² under an SCR of 4.0. The average current density due to hydrogen electrochemical oxidation was 5535.4 A/m² under an SCR of 2.0, which was 27 times higher than that of carbon monoxide. The total current density ranged from 5740.8 A/m² under an SCR of 2.0 to 2268.9 A/m² under an SCR of 4.0.