High-temperature Electrolyte Research Articles

Improvement of Anode of Prebaked Cell in Aluminum Electrolysis

Compared with the previous self-cultivation anode electrolyzer, the current prebaked anode electrolyzer has advanced technical and economic indexes, high degree of mechanization and automation, and relatively little environmental pollution, which has achieved great development. However, the continuity of aluminum electrolysis production and the limited economic height of anode constitute two contradictory opposites. In order to solve this contradiction, the processes of replacing anode periodically, cleaning the residual electrode and electrolyte, pressing off the residual electrode and phosphorus-iron ring, crushing and grinding the residual electrode have been produced, which has increased the investment and labor cost per ton of aluminum. Moreover, when the anode is replaced, the operator can say that the working environment is harsh and dangerous directly in front of the high-temperature electrolyte, and a large amount of fluorine-containing flue gas is discharged out of order and pollutes the environment due to the opening of the slot cover plate and the placement of the high-temperature residual electrode during the anode replacement. At the same time, pole change has great interference on electrolytic production. At present, inert anodes can't be put into industrial production, and the continuous preparation anodes in Germany have high power consumption, so it is of great practical significance to perfect or improve the existing anode structure. This paper discusses how to solve this problem.

Molten Salt Electrolytes: Computational Analysis of Transport, Electrochemical Properties and Designing New Mixtures

Electric aircraft propulsion has gained traction over the last decade due to possible high-energy density electrochemistries with reasonable cycle life and identification of non-flammable chemistries that can guarantee much better safety. Commercial Li-ion batteries cannot reach such high capacities because of weight limitations that arise from the widely used intercalation electrodes. Also, use of organic electrolytes make them highly susceptible to fire on exposure to air and humidity. Currently, use of Lithium metal anode along with conversion electrochemistries such as Li-O2 and Li-S are being pursued to achieve such high energy densities. Safer inorganic solid-state electrolytes, recently discovered Water-in-Salt electrolytes, molten salt electrolytes are some of the alternatives being pursued for a safer/non-flammable battery.Of these safer alternatives, molten-salt electrolytes offer some attractive properties: liquid at operating temperatures resulting in better electrode-wetting, stable interface with Li-metal anodes and good ionic conductivity; their only drawback being high operating temperatures. In this talk, we will discuss some of the computational studies, driven via atomistic simulations, of the properties of molten-salt electrolytes including transport mechanism and interface stability. We will also discuss predicting electrochemical properties of these high-temperature electrolytes. Further, we will discuss a thermodynamic approach to predicting new molten-salt eutectics with lower melting points.

Fiber-supported alumina separator for achieving high rate of high-temperature lithium-ion batteries

More and more application scenarios of rechargeable batteries like lithium-ion batteries are set up in high-temperature environments, such as large-scale energy storage, aerospace, oil extraction industry, etc. Besides of electrolyte, the separator is also a vital part of the battery's sustainable operation at high temperature working condition, however traditional polyolefin separators and even ceramic-coated polyolefin separators have poor thermal stability. This article provides a fiber-supported aluminum oxide separator with improved flexibility and thermal stability because of the introduced flexible SiC fiber network skeleton. The ceramic separator exhibits electrochemical performance equivalent to commercial separators at room temperature. What's more, with high-temperature electrolyte system, its conductivity at 120 °C reaches 5.12 mS cm−1, which is 3 times higher than that at room temperature, so that the LiFePO4 half-cell has excellent rate performance that still maintains a specific capacity of 140 mAh g−1 for 200 cycles under a rate of 20C at 120 °C. Specially, the half-cell containing the high temperature stable fiber-supported aluminum oxide separator realizes cycles of charging at a high temperature with high rate as 20C and discharging at a room temperature with normal rate of 1C, which is of great guiding significance to practical application.

Enhancing hydrogen production from steam electrolysis in molten hydroxides via selection of non-precious metal electrodes

There are still gaps in the field of reference electrode that is needed to assist electrolysis in high temperature electrolytes (e.g. molten hydroxides) for H2 gas production. This research aims to fill the gaps by preparing Ni/Ni(OH)2 reference electrode and more importantly testing its effectiveness against important performance factors including; ion conducting membrane (e.g. mullite tubes), internal electrolyte composition, working temperature and electrochemical control (e.g. potential scan rate). Then, this reference electrode was used to study the electrocatalytic activity various cheaper working electrode materials including; stainless steel (St.st), Ni, Mo and Ag in comparison with Pt by the means of chronoamperometry and voltammetry. The effect of introducing steam into electrolyte (eutectic mixture of NaOH and KOH) on the electrocatalytic activity of these working electrodes was also studied. It was observed that the potential of hydrogen evolution with different working electrodes followed an order as; Pt > Ni > St. st > Ag > Mo (positive to negative). The performance of each working electrode was confirmed through chronoamperometry for hydrogen evolution at a constant potential of −0.7 V. It was also found in cyclic voltammetry and confirmed by chronoamperometry that the introduction of steam was apparent as increasing the current density at cathodic limit for hydrogen evolution. This study could help to develop non-precious metal electrodes for the production of hydrogen fuel. In future, there will be a potential in the threshold concentration of steam for H2 gas production.

Electrolyte jet machining of Ti1023 titanium alloy using NaCl ethylene glycol-based electrolyte

Abstract Titanium alloy is increasingly used in industries due to its outstanding properties but machining of such difficult-to-cut metal faces lots of challenges. As an advanced electrochemical machining (ECM) method, electrolyte jet machining (EJM) is a potential alternative for machining of titanium alloy. However, oxide layer usually forms in traditional water-based electrolyte, which prevents uniform dissolution and consequently deteriorates the machining accuracy. To overcome the oxide layer, a novel electrolyte with organic solvent, NaCl ethylene glycol (EG)-based solution, was introduced in EJM of a typical titanium alloy (Ti1023) in this work. The current efficiency curves in NaCl water-based and EG-based electrolytes were experimentally measured, which show opposite behavior. Besides, machining experiments were conducted using different electrolytes. The results show that NaCl EG-based electrolyte helps to avoid formation of oxide layer throughout the EJM process, leading to better comprehensive performance than water-based electrolyte, especially in superimposed translating EJM. In addition, parametric effects on machining performance using NaCl EG-based electrolyte were investigated as the hint for selecting optimum machining conditions. Furthermore, high electrolyte temperature was proposed in this work to enable usage of small nozzle in EJM with EG-based electrolyte for miniaturization of machined geometry.

Character of Selective Anodic Dissolution. Influence of the Alloy Composition

The corrosion electrochemical behavior of copper-based alloys (L63, cupronickel, Monel, Cu–Al) in high-temperature salt electrolytes of various compositions in the galvanostatic mode is studied. Brass L63 is the most promising copper-based alloy for the production of nanoporous and mesoporous materials in salt melts. L63 brass samples have the smallest average pore diameter in experiments with a chloride melt. The pore size was 1.1 μm in the galvanostatic mode under the specified conditions (200 A/m2, 500°C). The results of cyclic voltammetry can be applied to predict the character of electrochemical destruction and to analyze the stages of conjugated anodic processes. The influence of the nature of the second alloy component on the character of electrochemical destruction and the formation of the developed surface layer of the alloys is found.

Development of stacked porous tantalum oxide layers by anodization

Interest in nanoporous tantalum oxide (Ta2O5) has been increasing due to its high variety of applications, from protective coatings, photocatalysts to biomedical devices. Anodization is a surface modification technique, which is inexpensive, versatile, easily scalable and widely used to produce these nanostructures. In this study, Ta2O5 nanoporous surfaces were produced by anodization in HF-free electrolyte composed of ethylene glycol, water and ammonium fluoride (NH4F) with different anodization parameters (electrolyte concentration, applied potential and time). The surface morphology of each sample was investigated by scanning electron microscopy (SEM) and the sample with the more uniform porous nanostructure was characterized in terms of cross-section morphology, chemical composition and crystalline structure. The concentration of NH4F and applied potential demonstrated a significant impact on current-density-time curve, and thereafter in surface morphology. Multiple thin porous nanolayers were formed under strong electrochemical conditions (very high current density and electrolyte temperature). Through chemical analysis, it was possible to detect the presence of fluoride, which is consistent with an amorphous Ta2O5 layer with fluoride ions incorporation. Thereby, managing the electrochemical conditions is crucial to control the morphology of an anodic Ta2O5 layer.

Fabrication of novel binderless anode via electrophoretic deposition for HT-PEMFC

ABSTRACTWe report a simple strategy to fabricate electrodes for high temperature electrolyte membrane fuel cell (HT-PEMFC) by eliminating binder. The Electrophoretic Deposition (EPD) method was used to fabricate the Gas Diffusion Electrode (GDE) in the absence of the binder. For comparison, the same catalyst ink was used to make hand-spray binderless electrode, and both electrodes used as anodes for Membrane Electrode Assemblies (MEAs) in a HT-PEMFC operating at 140°C. XRD and SEM were used to investigate the microstructure and morphology of GDEs. The ECSA was studied, and CO oxidation and desorption were evaluated. Results indicated proper attachment of electrocatalyst on GDL and better results for CO oxidation and desorption, when binderless EPD method was used. The maximum power density 180 mW cm−2 was obtained for MEA prepared by binderless EPD method. Comparing these results by other works indicate that the binderless EPD electrode could be utilised as the anode for HT-PEMFC.

Cleaner production of ammonium poly-vanadate by membrane electrolysis of sodium vanadate solution: The effect of membrane materials and electrode arrangements

In this study, we put forward a clean and complete process of V2O5 production from vanadium-containing solutions. It features membrane electrolysis for V/Na separation and AMV precipitation. With the aid of membrane electrolysis, the vanadium and sodium in the leaching solution can be directly separated using membrane-electrolysis. Meanwhile, the NaOH in the cathode chamber can also be recycled for vanadium slag decomposition. The electrolysis systems and membrane types have been investigated. It was found that 3-chamber electrolysis was much more energy efficient than the traditional 2-chamber electrolysis, while F8080 membrane showed a better separation efficiency than N117, CMI7000, LF0014 membrane. The main electrolysis parameters were also investigated, and it appeared that high current density and electrolyte temperature, as well as low initial cathodic NaOH concentration were beneficial for the separation efficiency. Under the optimum electrolysis conditions the electricity consumption of producing 750 kg V2O5 and 1000 kg NaOH and was 2151 kW h, with a current efficiency of 92.9%. During the vanadium precipitation process, NH4VO3 was used as precipitant for the first time, avoiding the introduction of impurity ions, such as Cl−, SO42− or Ca2+, realizing zero waste generation by source. A low-sodium medium product of (NH4)2V6O16 was precipitated at pH between 2 and 4. The commercial quality V2O5 product could be obtained by calcination and the ammonium slat was recycled for precipitation. This method can achieve the clean production of V2O5 with no wastewater or solid waste generated through the whole process.

Complex influence of temperature on oxalic acid anodizing of aluminium

Two-step aluminium anodizing is widely used to prepare oxide films with a highly-ordered porous structure through the whole thickness. It can be realized solely at relatively low values of current density in the kinetic anodizing regime that makes this process extremely time-consuming. Temperature is an important thermodynamic parameter which is able to accelerate chemical reactions and mass-transport and, thus, could be suggested as an effective tool to control the growth rate of anodic alumina. Here we report a systematic study of the porous anodic alumina films formation in 0.3 M oxalic acid electrolyte in a wide temperature range. The influence of electrolyte temperature on the kinetics of aluminium anodizing and on the morphology of the obtained anodic alumina films is addressed quantitatively. Current transients registered at various temperatures are used for the calculation of the apparent activation energy of the anodization process in both mild and hard anodizing regimes. In the case of thick oxide films and high electrolyte temperature, the increase in diffusion current contribution leads to switching the kinetically controlled anodizing to the mixed regime which results in destroying the hexagonal pore ordering. Based on the experimental findings, rational electrolyte temperatures and porous layer thicknesses for the first and second anodizing steps are proposed as a guide for express preparation of alumina films with well-ordered porous structure.

Zirconia: A Unique Multifunctional Ceramic Material

Zirconia ceramics possess the unique combination of multi-functionality. There have been a number of landmark discoveries in the areas of its mechanical, electrical and thermal properties. The material is known to have a number of polymorphs like monoclinic at room temperature, tetragonal normally above around 1170 °C and cubic above around 2300 °C. The high-temperature cubic phase can be stabilized at room temperature by forming a solid solution with di-, tri- or tetravalent metal oxides. Its fracture toughness can be enhanced significantly by taking advantage of the stress-induced polymorphic transformation. Partially stabilized zirconia is known to have the highest toughness among all the monolithic ceramic materials. The addition of zirconia to other ceramics like alumina also toughens the ceramic composite. Stabilization of zirconia to its cubic form generates very large amount of oxygen ion vacancy, thereby enhancing the oxygen diffusivity and oxygen ion conductivity, which makes this material one of the most important solid-state high-temperature electrolytes suitable for electrochemical devices like solid oxide fuel cell, oxygen sensor and oxygen pump. Low thermal conductivity of the material makes it useful as thermal barrier coating for gas turbine blades in order to increase the operating temperature and therefore the efficiency of the turbines. High mechanical strength and high toughness together with excellent resistant to toxicity have made it emerge as a new material for biomedical prosthesis, particularly dental implants. Reinforcing with carbon nano-tube or graphene oxide enhances the mechanical properties and changes the nature of electrical conduction significantly.

PHASE RELATION STUDIES IN THE ZrO2-CeO2-Dy2O3 SYSTEM AT 1500 °С

The systems containing ceria, dysprosium and zirconia are perspective for the development of energy saving technological solutions and solid oxide fuel cells (SOFC). Ceramics based on ZrO 2 is used as a high temperature electrolyte for SOFC. The solid solutions based on CeО 2 are the most perspective electrolytes, operating at moderate temperatures, because of their ionic conductivity and high sensitivity to changes of oxygen partial pressure is much higher than ones of ZrO 2 stabilized with Y 2 O 3 (YSZ). In the present work, first the phase equilibria and physicochemical properties for solid solutions in the ternary ZrО 2 -CeО 2 -Dy 2 O 3 system at temperature 1500 °С (150 h) in air were studied by X-ray diffraction in the overall concentration range of compositions. Cerium oxide nitrate Ce(NO 3 ) 3 ∙6H 2 O and zirconium oxide nitrate ZrO(NO 3 ) 2 ×2Н 2 О of grade «ch» (above 98%, dysprosium oxide (99.99 % produced by Merck Corp.) and analytical-grade nitric acid were used as the starting materials. Samples were prepared with a concentration step of 1-5 mol % from nitrate solutions with subsequent evaporation and decomposіtion of nitrates into oxides through annealing at 1200 °С for 2 h. Powders were pressed in pellets (diameter 5 mm, height 4 mm) under a pressure of 10-30 MPа. XRD analysis of samples was performed by powder procedure on a DRON-3 apparatus at ambient temperature under CuКa radiation. Scanning step was 0.05-0.1 degrees in the range 2θ = 15–90°. Lattice parameters were calculated by the least square method using the LATTIC computer code with an error of not lower than 0.0001 nm for the cubic phase. Any new phase in the ternary system was revealed at 1500 °С. The structure of the boundary binary systems defines the phase equilibria in the ZrО 2 -CeО 2 -Dy 2 O 3 system. Solid solutions based on tetragonal (Т) modification ZrО 2 , cubic (С) modification Dy 2 O 3 and cubic with fluorite-type structure (F) modifications СеО 2 (ZrО 2 ) were determined.

Temperature Effect on Hydrogen Underpotential Deposition for Pt/C

The charge associated with hydrogen underpotential deposition (HUPD) is routinely used to estimate the apparent electrochemically active Pt surface area (ECSA) of Pt-based electrocatalysts. However, the ECSA estimation is not flawless. The HUPD overlaps with the H2 evolution region, leading to poor deconvolution of the Hupd charge, which becomes more serious as the electrolyte temperature is increased, which in turn leads to an apparent decrease in the HUPD charge decrease with increasing electrolyte temperature.1,2 In this study, we have re-investigate the change in Hupd at various temperatures and attribute the decay of HUPD charge with rise in the electrolyte temperature to the disorder arrangement of surface platinum atoms with exposure to high temperature electrolyte. The experimental procedure is shown in Scheme 1. Figure 1 shows the HUPD charge of Pt/C (TEC10E50E) as a function of potential cycle number. The HUPD charge of Pt/C increased by break-in potential cycles between 0.05 and 1.3 V vs. RHE until 30 cycles, owing to surface cleaning. The HUPD charge gradually decreased after 30 cycles due to dissolution of Pt and/or particle growth. By increasing the electrolyte temperature from 25°C to 60°C, the HUPD charge rapidly decreased from 625±16 mC at 109 cycles to 509±5 mC at 112 cycles. The decrease in Hupd charge cannot be attributed to the above degradation mechanism, since the decay rate of HUPD does not decrease with the same number of break-in cycles. After the temperature was turned back from 60°C to 25°C, the HUPD charge did not change (509±22 mC at 115 cycles). Additional potential cycling lead to a gradual increase in the HUPD charge, and the HUPD charge recovered to 589±16 mC at 145 cycles, which is similar to the the initial HUPD charge at 25°C). It has been reported that the hydrogen adsorption energy on platinum decreases when the d-band center is upshifted.3 Since the d-band center upshifts with increasing roughness factor (decreasing the average coordination number) of surface platinum,2 we interpret our findings to the decay of HUPD charge with increasing electrolyte temperature to the disorder arrangement of surface platinum. This leads to the low adsorption energy of hydrogen due to upshift of d-band center with decreasing the average coordination number of surface platinum. Finally, we note that additional potential cycles for room temperature ECSA measurements is necessary to avoid underestimation of HUPD (apparent ECSA) for Pt-based electrocatalysts after high temperature measurements such as accelerated durability test. This research was supported in part by the “Polymer Electrolyte Fuel Cell Program” from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. References A. Zolfaghari, M. Chayer, and G. Jerkiewicz, J. Electrochem. Soc, 144, 3034 (1997).N. M. Marković, T. J. Schmidt, B. N. Grgur, H. A. Gasteiger, R. J. Behm, and P. N. Ross, J. Phys. Chem. B, 103, 8568 (1999).I. A. Pašti, N. M. Gavrilov, and S. V. Mentus, Adv. Phys. Chem., 2011, 1 (2011). Figure 1

Characteristics of electrodeposited bismuth telluride thin films with different crystal growth by adjusting electrolyte temperature and concentration

Bismuth telluride (Bi2Te3) thin films were prepared with various electrolyte temperatures (10°C–70 °C) and concentrations [Bi(NO3)3 and TeO2: 1.25–5.0 mM] in this study. The surface morphologies differed significantly between the experiments in which these two electrodeposition conditions were separately adjusted even though the applied current density was in the same range in both cases. At higher electrolyte temperatures, a dendrite crystal structure appeared on the film surface. However, the surface morphology did not change significantly as the electrolyte concentration increased. The dendrite crystal structure formation in the former case may have been caused by the diffusion lengths of the ions increasing with increasing electrolyte temperature. In such a state, the reactive points primarily occur at the tops of spiked areas, leading to dendrite crystal structure formation. In addition, the in-plane thermoelectric properties of Bi2Te3 thin films were measured at approximately 300 K. The power factor decreased drastically as the electrolyte temperature increased because of the decrease in electrical conductivity due to the dendrite crystal structure. However, the power factor did not strongly depend on the electrolyte concentration. The highest power factor [1.08 μW/(cm·K2)] was obtained at 3.75 mM. Therefore, to produce electrodeposited Bi2Te3 films with improved thermoelectric performances and relatively high deposition rates, the electrolyte temperature should be relatively low (30 °C) and the electrolyte concentration should be set at 3.75 mM.

Effect of anodizing conditions on the cell morphology of anodic films on AA2024‐T3 alloy

The effects of applied current density, anodizing time, and electrolyte temperature on the cell and pore morphology of anodic films and the voltage‐time response obtained during galvanostatic anodizing of AA2024‐T3 alloy in sulphuric acid electrolytes have been studied. Scanning electron microscopy was employed to observe the film morphology. Sponge‐like porous structure was promoted by anodizing at relatively low current density and high electrolyte temperature. In contrast, linear porous structure was favoured under the converse conditions. Intermediate conditions resulted in films containing either sequential layers of the 2 morphologies or a morphology incorporating features of the 2 types; such conditions were associated with anodizing voltages in the range 25 to 35 V. The reasons for the morphological differences are proposed to be due to interactions between film growth stresses and stresses arising from oxygen evolution on the development of the alumina cells.

Electrode kinetics at the Pt, O2|La0.9Sr0.1ScO3-δ interface

Most of the ceramic proton conductors reveal considerable hole conductivity in an oxidizing ambient. This results in a necessity of taking into account the nonfaradaic current when studying the electrode kinetics in electrochemical cells with high-temperature protonic electrolytes. The present paper is an attempt to elucidate the electrode kinetics of oxygen reaction at a Pt, O2|La0.9Sr0.1ScO3-δ (LSS10) interface. The polarization conductivity has been determined as a function of temperature (600–900 °C) and oxygen partial pressure (2.1 × 104 > pO2 > 1 Pa) by means of impedance spectroscopy using the elementary model in terms of an equivalent electrical circuit with the bypass resistance of hole transport in the electrolyte. Possible routes of oxygen reaction at the Pt, O2|La0.9Sr0.1ScO3-δ interface have been discussed, and diffusion of the electron holes in LSS10 was proposed as the rate-determining stage of the electrode process.

Effect of the electrolyte composition on the corrosion of 12Kh17 steel in molten alkali metal carbonates

The corrosion of 12Kh17 steel in the melts of alkali metal carbonates containing additions of various chemical types is studied using anodic potentiostatic polarization. The morphology of the 12Kh17 steel surface is analyzed by electron-probe microanalysis. The introduction of corrosion passivators and activators affects the mechanism of local corrosion damages. The corrosion of the steel proceeds according to an electrochemical mechanism. Carbonate anions serve as oxidizers of the steel along with oxygen dissolved in the melt. Treatment of a corrosive medium can be used to protect metallic constructions against corrosion in high-temperature salt electrolytes. Combined introduction of corrosion activators and passivators in a salt phase makes it possible to form protective layers with a high corrosion resistance.

Synthesis and electrochemical properties of potassium 5-trifluoromethyl-1,3,4-thiadiazole-2-thiolate/disulfide redox couple

A new redox couple, composed of the reduced species potassium 5-trifluoromethyl-1,3,4-thiadiazole-2-thiolate 2 and the oxidized species 5,5′-bis (2-trifluoromethyl-1,3,4-thidiazole) disulfide 3, was synthesized and characterized chemically and electrochemically when dissolved in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (EMITFSI). Platinum (Pt), glassy carbon (GC) and cobalt sulfide-coated indium tin oxide glass (ITO-CoS) electrodes were used. The diffusion-controlled redox processes were shown to be electrochemically irreversible. At higher electrolyte temperature, the current densities are enhanced, and the potential difference between the anodic and cathodic peaks is decreased, in conjunction with a decrease in the viscosity of the electrolytic medium. The best electrocatalytic performance was obtained with the ITO-CoS electrode, followed by GC and Pt electrodes. A greater thiolate/disulfide ratio favors larger anodic current densities, whereas a smaller ratio leads to higher cathodic current densities. Preliminary stability studies of the ITO-CoS electrode confirmed the very good electrochemical and mechanical stability of this electrode considered as a serious candidate to replace platinum as the counter electrode in dye-sensitized solar cells (DSSCs). The electrolytic media studied in this work exhibits a very low absorption of visible light, contrarily to the conventional I3−/I− mediator, offering the possibility of illumination of the device via the counter electrode.

The Effects of Adding Heteropolyacids to Phosphoric Acid Doped Polybenzimidazole for Enhanced Conductivity in High Temperature Fuel Cell Applications

With the current expansion of the global population, the demand to reduce our dependence on fossil fuels and reduce our emissions of pollutants has led to the development of fuel cells as alternatives for clean power generation. There are several types of fuel cells, but polymer electrolyte membrane fuel cells (PEMFCs) have stood out because they are well suited for transportation and small scale stationary power generation. PEMFCs have outstanding power density, rapid start-up, and high efficiency.1 In addition, PEMFC’s operation is simple and free of pollution. Despite several advantages, current PEMFCs are not widely commercialized because they are still too expensive and need higher durability. At the moment, PEMFCs generally operate below 100ºC due to the need to fully humidify commonly used perfluorosulfonic acid electrolytes such as Nafion®. As a result, current PEMFCs require high purity hydrogen that can only be cost effectively produced from natural gas at this time. At low operating temperatures, the catalysts are poisoned by CO that must be completely removed. The catalysis problem can be solved by increasing the PEMFCs operating temperatures above 120ºC.2 High temperature operation is a promising way to improve PEMFC performance; it has been shown that higher operating temperatures would increase chemical kinetics at the anode electrode, which introduces the use of lower cost hydrogen. In addition, operating at elevated temperatures would also provide easier water and thermal management.2 One approach in designing a high temperature electrolyte membrane for PEMFCs is acid doping into aromatic polymer materials that have high temperature stability. The polymer is typically chosen to contain basic sites that serve as proton acceptors, forming an ion-pair after doping with an inorganic acid.3 One of the most interesting acid-base membranes that have been discovered is based on polybenzimidazole (PBI) doped with phosphoric acid, shown in Figure 2. PBI has long been recognized as an excellent candidate for use in the high temperature fuel cell environment.4 Although the proton conductivity of pure PBI is low, doping with phosphoric acid causes a remarkable increase in its proton conductivity. PBI contains imide groups that can be easily doped with phosphoric acid, and it forms a membrane with excellent thermal and mechanical stability upon casting. More importantly, the resulting electrolyte membrane has very high proton conductivity at temperatures above 120ºC, even in the absence of water. The proton transport in acid-base membranes occurs mainly through a Grotthuss Mechanism, where the proton transfer occurs through the hopping of protons between two molecules via rearrangement of their hydrogen bonds.1 This mechanism allows for proton conductivity even in the absence of water at temperatures above 120ºC. Although the use of phosphoric acid in PBI introduces high proton conductivity, the phosphoric acid still dissolve in the presence of liquid water and does not enhance the oxygen reduction reaction at the cathode4. Long-term operation of phosphoric acid doped PBI membranes often loses proton conductivity due to acid leaching. The free phosphoric acid also degrades and embrittles the polymer. As a result, the membrane is degraded at elevated temperatures, has poor mechanical properties, and has a narrow operational temperature range. Our preliminary results indicate that doping phosphoric acid in PBI in the presence of super-protonic conducting oxides such as heteropolyacids (HPA) successfully generated high temperature electrolyte membranes for PEMFCs (Figure 2). More importantly, HPA not only increases the barrier to prevent water from escaping the membrane at elevated temperatures, but also adds more acid sites, as a consequence, giving additional paths for proton transport.3These membranes at different doping levels and with various percentages of HPA conduct well at temperatures above 100ºC and can potentially be used as PEMs in high temperature applications.

High Temperature Stability of Nitride Ceramic Materials in LiF-NdF3-Nd2O3 Molten Salts System

Nd-Fe-B permanent magnets have been used in a wide variety of applications because of their high magnetic flux density. So, demand for neodymium has been increasing in worldwide. In this study, an electrowinning process was performed in high temperature molten salts. However, a corrosion resistant material for use in the molten salt must be found for stable operation because of the harsh corrosion environment of the electrowinning process. Therefore, for this paper, boron nitride(BN), aluminum nitride(AlN), and silicon nitride() were selected as protective and structural materials in the high temperature electrolyte. To investigate the characteristics of BN, AlN, and , in molten salts, materials were immersed in the molten salts for 24, 72, 120, and 192 hours. Also, surface condition and stability were investigated by SEM and EDS and corrosion products were calculated by HSC chemistry. As a result, among BN, AlN, and , AlN was found to show the best protective material properties.