Rational design of novel cathode materials in solid oxide fuel cells using first-principles simulations

The search for clean and renewable sources of energy represents one of the most vital challenges facing us today. Solid oxide fuel cells (SOFCs) are among the most promising technologies for a clean and secure energy future due to their high energy efficiency and excellent fuel flexibility (e.g., direct utilization of hydrocarbons or renewable fuels). To make SOFCs economically competitive, however, development of new materials for low-temperature operation is essential. Here we report our results on a computational study to achieve rational design of SOFC cathodes with fast oxygen reduction kinetics and rapid ionic transport. Results suggest that surface catalytic properties are strongly correlated with the bulk transport properties in several material systems with the formula of La_0.5Sr_0.5BO_2.75 (where B = Cr, Mn, Fe, or Co). The predictions seem to agree qualitatively with available experimental results on these materials. This computational screening technique may guide us to search for high-efficiency cathode materials for a new generation of SOFCs.     

Computational screening of anode materials for potassium‐ion batteries

Potassium ion batteries (PIBs) are promising alternatives to Li‐ion batteries due to the abundance of potassium. However, the development of PIBs is in its early stages, and only a few anode materials have been reported. Herein, we explored anode materials for PIBs using high‐throughput computational screening. The alloying and conversion reactions of prospective anode materials were investigated using the Materials Project database. Grand potential diagrams were obtained to examine the reaction potential and theoretical capacity of the anode materials. Calculation results indicated that P, As, Si, and Sb anodes exhibited high theoretical capacities. In addition, the screening results revealed that phosphides generally exhibit a lower reaction potential compared with those of sulfides and oxides. A total of 18 binary compounds that exhibited a high theoretical capacity and a low reaction potential (greater than 450 mAh/g and 0.7 V) were identified as promising anode materials for PIBs. In particular, ZnP₂, CuP₂, SiP, NiP₃, CoP₃, V₃S₄, Nb₃S₅, Bi₂O₃, and Ga₂O₃ exhibited high theoretical capacities.     

Glass-containing composite cathode contact materials for solid oxide fuel cells

The feasibility of adding glass to conventional SOFC cathode contact materials in order to improve bonding to adjacent materials in the cell stack is assessed. A variety of candidate glass compositions are added to LSM and SSC. The important properties of the resulting composites, including conductivity, sintering behavior, coefficient of thermal expansion, and adhesion to LSCF and Mn_1.5Co_1.5O₄-coated 441 stainless steel are used as screening parameters. Adhesion of LSM to LSCF improved from 3.9 to 5.3 MPa upon addition of SCZ-8 glass. Adhesion of LSM to coated stainless steel improved from 1.8 to 3.9 MPa upon addition of Schott GM31107 glass. The most promising cathode contact material/glass composites are coated onto Mn_1.5Co_1.5O₄-coated 441 stainless steel substrates and subjected to area-specific resistance testing at 800 °C. In all cases, area-specific resistance is found to be in the range 2.5-7.5 mOhm cm² and therefore acceptable. Indeed, addition of glass is found to improve bonding of the cathode contact material layer without sacrificing acceptable conductivity.     

Optical properties for and intermediate band materials

First-principles calculations of the energy dependent absorption coefficients are presented in this work in order to understand the optical properties of some materials characterized for an intermediate band (IB) with metallic behavior: Ga₃₂P₃₁Cr and Ga₃₁P₃₂Cr. The calculations are based on local spin density approximation and the pseudopotential method using a localized basis set. The resulting optical spectra is analyzed and broken down into the contributions of the different bands and spin components. The results of the electronic properties show that one of the spin components presents an IB, and the absorption coefficients indicate an increase in the absorption sub-gap as a consequence of the optical transitions between the valence and the IB.     

Electrochromic materials and devices for energy efficient windows

Numerous inorganic and organic electrochromic materials are discussed in the context of developing a film-based optical shutter for a window application. It is possible electronically to alter a window's transmission and reflection properties by use of electrochromic thin films. This allows regulation of conductive and radiative heat transfer rates, with variable optical attenuation. As a result, an aperture can be optically and thermally managed, reducing space heating and cooling loads. The properties of transition metal oxides, such as WO₃, MoO₃, Ir₂O₃ and V₂O₅ are detailed. Organic systems such as heptyl viologen and polytungsten anion are reviewed. Also, intercalated structures are discussed. Various designs of working devices are outlined with emphasis on solid-state configurations. From this quantification, materials and devices with appropriate deposition techniques for window applications are detailed.     

Novel materials for solid oxide fuel cell technologies: A literature review

This study aims to review novel materials for solid oxide fuel cell (SOFC) applications covered in literature. Thence, it was found that current SOFC operating conditions lead to issues, such as carbon surface deposition, sulfur poisoning and quick component degradation at high temperatures, which make it unsuitable for a few applications. Therefore, many researches are focused on cell performance enhancement through replacing the materials being used in order to improve properties and/or reduce operating temperatures. Most modifications in the anode aim to avoid some issues concerning conventionally used Ni-based materials, such as carbon deposition and sulfur poisoning, besides enhancing catalytic activity, once this component is directly exposed to the fuel. It was also found literature about the cathode with the aim of developing a material with enhanced properties in a wider temperature range, which has been compared to the currently used one: LSM perovskite (La_1-xSr_xMnO₃). Novel electrolyte materials can have ionic or protonic conductivity, thus performance degradation must be avoided at several operating conditions. In order to enhance its electrochemical performance, different materials for electrodes (cathode and anode) and electrolytes have been assessed herein.     

Carbon materials for H2 storage

In this work a series of carbons with different structural and textural properties were characterised and evaluated for their application in hydrogen storage. The materials used were different types of commercial carbons: carbon fibers, carbon cloths, nanotubes, superactivated carbons, and synthetic carbons (carbon nanospheres and carbon xerogels). Their textural properties (i.e., surface area, pore size distribution, etc.) were related to their hydrogen adsorption capacities. These H₂ storage capacities were evaluated by various methods (i.e., volumetric and gravimetric) at different temperatures and pressures. The differences between both methods at various operating conditions were evaluated and related to the textural properties of the carbon-based adsorbents. The results showed that temperature has a greater influence on the storage capacity of carbons than pressure. Furthermore, hydrogen storage capacity seems to be proportional to surface area, especially at 77 K. The micropore size distribution and the presence of narrow micropores also notably influence the H₂ storage capacity of carbons. In contrast, morphological or structural characteristics have no influence on gravimetric storage capacity. If synthetic materials are used, the textural properties of carbon materials can be tailored for hydrogen storage. However, a larger pore volume would be needed in order to increase storage capacity. It seems very difficult approach to attain the DOE and EU targets only by physical adsorption on carbon materials. Chemical modification of carbons would seem to be a promising alternative approach in order to increase the capacities.     

An effective method to screen carbon (boron,nitrogen) based two-dimensional hydrogen storage materials

The current critical environmental pollution caused by the huge fossil fuel burning together with the increasingly scarce energy source has inspired much attention on the renewable clean hydrogen energy. Thus, the hydrogen storage materials are very vital for the hydrogen application and will be screened by the high-throughput computational screening procedure in this paper. Generally, metal-modified carbon (boron, nitrogen) nanomaterials can exhibit excellent hydrogen storage capacities. An effective procedure is designed to screen the potential metal decorated carbon (boron, nitrogen) hydrogen storage materials from the Materials Project database, which can be proved to be easily realized and reliable. Totally six ideal structures are obtained for hydrogen storage by considering the thermodynamic stability, the metal decorating, the theoretical hydrogen gravimetric density larger than 5.5 wt%, the PBE band gap smaller than 1.0 eV, and the two-dimensional structure restriction. Furthermore, the binding energy of the metal atom to the screened 2D materials, the average adsorption energy per H₂ adsorbed by the metal, the density of states, the difference charge densities are calculated by the density functional method. We believe that our screening procedure can effectively and accurately search for hydrogen storage materials, which should be the theoretical basis for experimental researches.     

Monograin materials for solar cells

This paper reviews results of studies on different materials and technologies for monograin layer (MGL) solar cells conducted at Tallinn University of Technology. The MGL consists of monograin powder crystals embedded into an organic resin. The MGL combines the superior photoelectrical parameters of single crystals with the advantages of polycrystalline materials, such as the low cost and simple technology of materials and layers preparation and the possibility of making devices of practically unlimited area. A main technological advantage is the separation between absorber and cell formations. The developments in the field of monograin materials of CuInSe₂, Cu₂ZnSnS₄ and Cu₂ZnSnSe₄ and technical parameters of MGL solar cells are summarized.     

Survey of intermediate band materials based on ZnS and ZnTe semiconductors

A first-principles study, using the local spin density approximation, to design materials with an isolated partially filled intermediate band, based on a II–VI semiconductor is presented. These materials, with an intermediate band of a metallic character, are of great interest as new high-efficiency materials in solar cells. The study presented in this work is based on X₁₀₈Zn₁₀₇M materials, where X=S, Te and M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni and Cu. The results show that the intermediate band is only present in some compounds. The electronic properties and the population analysis have been calculated and analyzed.     

Combustion of multiphase reactants for the synthesis of nanocomposite materials

Controlling nanocomposite composition and morphology is a vital step toward designing new and advanced materials. The current work presents the results of an experimental investigation of the use of mixed-phase reactants for the synthesis of nanocomposite materials. Gas-phase tetramethyltin was used as a precursor for tin dioxide (SnO₂). Metal additives were introduced to the SnO₂ synthesis system using solid-phase metal acetates as the precursors. The physical and chemical properties of the metal acetate reactants, the combustion environment and the nanocomposite materials were characterized in order to clarify the reaction processes important during synthesis of nanocomposite materials from these categories of mixed-phase reactants. X-ray diffractometry was used to determine composition and the crystalline structure of reactant and product materials. Scanning and transmission electron microscopy were used to examine particle morphology of reactant and product materials, and X-ray energy dispersive spectroscopy was used for elemental speciation. The results indicate the metal acetates are an excellent source of metal and metal oxide additives in a flame reactor. The metal acetates rapidly decompose and experience considerable restructuring, leading to metal additives with a range of microstructures in the SnO₂ nanocomposites: from metal encapsulation in SnO₂ to mixed aggregates.     

Carbon-neutral economy with fossil fuel-based hydrogen energy and carbon materials

Hydrocarbon fossil fuels can be considered as hydrogen ores for CO₂-free energy, and carbon ores for carbonaceous construction materials. Hydrogen fuel can be extracted from fossil fuels by decarbonization, and used as an energy resource. The carbon byproduct can be used as a versatile construction material. Carbon materials would sequester carbon, and replace CO₂-generating steel and concrete. Approximate comparison of the global consumption of energy and construction materials suggests a rough mass balance of energy and materials markets. The cost of foregoing the carbon energy content as a fuel can be easily offset by the value of the carbon-based construction material. The nature and properties of carbon materials and conventional infrastructural materials are compared.     

Influence of the bolt torque on PEFC performance with different gasket materials

In this work, different gasket materials (NBR, expanded PTFE and PTFE) with different thicknesses were investigated by evaluating the electrochemical performance as function of a torque moment applies to fasten the cell. Because the materials composing the gasket are subjected to a different deformation, depending on their mechanical properties, a different compression was obtained on the GDL as a function of the clamping force. These effects influence the cell performance, above all the diffusive region of the polarisation curves, where the problems related to the mass transport are more important. These problems are minimised when the cell is fed with gas pressurized at 3 bar_abs, in fact at higher pressure the gas concentration is higher and the diffusion is favoured despite the lowering of GDL porosity due to the compression.When the gas pressure is 1 bar_abs, the cell performance is more evidently affected by the GDL compression and contact resistance increase.In any case, an optimal clamping force was found to be as a function of the mechanical properties of materials composing the gasket. The NBR and Expanded PTFE reached the best performance with a torque moment of 11Nm while the PTFE reached similar performance at 9Nm. It was found that thinner PTFE is more stable than others during the time, with an average power density of 250 mWcm⁻² and the lowest standard deviation. The expected over-compression of the GDL is prevented by distortion of the clamping plates. This distortion results in unexpectedly good cell performance.     

Titanium-based materials as anode materials for sodium ion batteries

钛基材料具有环境友好、安全性好、稳定性好等优点而备受关注。但是钛基材料带隙宽,电子导电性差,比容量低限制了其在钠离子电池领域的发展与应用。本文主要综述了TiO2、Na2TinO2n+1、NaTi2(PO4)3三类钛基材料的结构、电化学性能、改性方法和相关储钠机理。评述了钛基材料存在的问题并展望了其发展前景。今后的研究可以从以下几方面开展：① 深入研究钛基负极材料储钠机理;② 研究多种阳、阴离子掺杂对钛基材料的电子结构的影响,从根本上提高钛基材料的电子导电性;③ 与高比容量负极材料复合,获得兼具稳定性与高比容量优点的复合材料;④ 设计合成具有多级、三维结构的钛基复合负极材料,进一步提高材料的循环稳定性、倍率性能;⑤ 开发新型结构的钛基负极材料。     

Silica based hybrid organic-inorganic materials for PEMFC application

It is of key importance to develop membrane assembly electrodes (MEAs) offering high conductivity, thermal stability and suitable performance in the fuel cell. The mesoporous materials functionalized with acid groups are appropriate candidates to improve membrane's properties. The goal of this work was to assess the addition of functionalized porous silica, bearing different acid groups, on the MEA performance in a PEM type single fuel cell. Ni₅₉Nb₄₀Pt_0.6Fe_0.4 -based amorphous alloys were applied as anode electrocatalysts. The synthesis of functionalized mesoporous silica (UGM-fx) with different acid groups, namely [SO₃H], [COOH] and [PO(OH)₂], was carried out following a nonaqueous sol gel method. The results showed that the MEA containing silica with PO(OH)₂ groups leads to an outstanding fuel cell performance compared to that of the other organic groups-based MEAs and that it outperformed a commercial Pt-based sample. This might be due to the higher proton conductivity exhibited by the phosphonic groups.     

Electrochemical binding and wiring in battery materials

Binders in battery electrodes not only provide mechanical cohesiveness during battery operation but can also affect the electrode properties via the surface modification. Using atomic force microscopy (AFM), we study the surface structuring of three binders: polyvinylidene fluoride (PVdF), carboxymethyl cellulose (CMC) and gelatin. We try to find correlation between the observed structures and the measured electrochemical charge–discharge characteristics. We further measure the binding ability of gelatin adsorbed from solutions of different pHs. While the best binding ability of gelatin is obtained at pH about 9, the least polarization is observed at pH 12. Both properties are explained based on the observed gelatin structuring as a function of pH. In the second part of this study, gelatin is used as a surface agent that dictates the organization of nanometre-sized carbon black particles around micrometre-sized cathodic active particles. Using microcontact impedance measurements on polished pellets we show that using gelatin-forced carbon black deposition the average electronic resistance around LiMn₂O₄ particles is decreased by more than two orders of magnitude. We believe that it is this decrease in resistance that improves significantly the rate performance of various cathode materials, such as LiMn₂O₄ and LiCoO₂.     

La2Ce2O7 based materials for next generation proton conducting solid oxide cells: Progress,opportunity and future prospects

The development of efficient and environmentally-friendly technology is the only possible way to solve the existing energy and environmental crisis. Solid oxide cells (SOCs) technologies have huge potential in different technologies including energy conversion devices (fuel cells), hydrogen production (electrolysis), co-conversion, natural gas upgrading (conversion of C1 molecules), green synthesis of ammonia, hydrogen separation membrane, and sensors. In few years, great effort has been paid for the development of ionic conducting materials for SOCs. Since Iwahara's discovery of proton conducting oxides in the 1980s, there has been a significant advancement in materials research that has been responsible for the creation of high performance SOCs by modifying the material's properties, such as ionic conductivity, mixed ionic electronic conducting (MIEC) materials, and triple conducting oxides. Recently, La₂Ce₂O₇ (LCO) based materials with ionic (protonic and oxide ion) conductivity have been proposed as a new class of electrolyte for intermediate temperature solid oxide fuel cells as they exhibit high chemical stability, sufficient high ionic conductivity and low temperature sinterability compared to state-of-the-art proton conducting electrolytes. In order to engineer the materials properties, the fundamental understanding of materials such as true crystal structures, crystal structure tolerance ratio, hydration behavior, mechanism of ionic (oxide ions and protons) conduction, catalytic behavior, temperature of operation, ease of processing etc. is needed. All the above information is carefully reviewed for LCO based electrolyte materials with respect to SOCs operation which is not only acting as electrolyte but also as multifunctional properties.     

Computational evaluation of superalkali-decorated graphene nanoribbon as advanced hydrogen storage materials

In this study, we proposed that homo superalkali NM₄ clusters with high tetrahedral geometry, can be applied to develop high-performance hydrogen storage materials. Moreover, their special bonding structures and chemical stability make them ideal units for decoration of different kinds of pristine monolayers. We made a trial to decorate the NLi₄ clusters onto the 1D graphene nanoribbon, and employed density functional theory (DFT) computational studies to solve its electronic structure, and further evaluate its applicability in hydrogen storage. We found that the electronic charges on Li atoms were successfully transferred to the pristine monolayer, thus a partial electronic field around each Li atom was formed. This subsequently leads to the polarization of the adsorbed hydrogen molecules, and further enhances the electrostatic interactions between the Li atoms and hydrogen. Each NLi₄ cluster can adsorb at most 16 hydrogen molecules. For this novel material, its total capacity of hydrogen storage can reach to 11.2 wt %, surpassing the target value of 5.5 wt %, set by the U.S department of energy (DOE) [1], making itself an ideal unit for advanced energy materials design.     

Studies of selected synthesis procedures of the conducting LiFePO4-based composite cathode materials for Li-ion batteries

In this paper technological aspects of a synthesis of phospho-olivine LiFePO₄ based composite cathode materials for lithium batteries are presented. An effective synthesis route yielding a highly conductive composite cathode material was developed. The structural, electrical and electrochemical properties of these materials were investigated. It was shown that the enhanced conductivity of the cathode material is due to the presence of a thin layer of the reduced material which has metallic properties, which is formed on the grain surfaces of the phospho-olivine. We propose a synthesis route yielding LiFePO₄/Fe₂P composite material.     

GaN/Surface-modified graphitic carbon nitride heterojunction: Promising photocatalytic hydrogen evolution materials

The coupling of two-dimensional (2D) layered materials is an effective way to realize photocatalytic hydrogen production. Herein, using first-principles calculations, the photocatalytic properties of GaN/CNs heterojunctions formed by two different graphite-like carbon nitride materials and GaN monolayer are discussed in detail. The results show that the GaN/C₂N heterojunction can promote the effective separation of photogenerated electron and hole pairs, which is attributed to its type-II band orientation and high carrier mobility. However, the low overpotential of GaN/C₂N for photocatalytic hydrogen production limits the photocatalytic performance. On this basis, we adjust the CBM position of the GaN/C₂N heterojunction by applying an electric field to enhance its hydrogen evolution capability. In addition, the GaN/g-C₃N₄ is a type-I heterojunction, which is suitable for the field of optoelectronic devices. This work broadens the field of vision for the preparation of highly efficient photocatalysts.