Ternary Carbonate Research Articles

Thermal and electrochemical impact of kaolin on a direct carbon fuel cell

This paper investigates the impact of kaolin, a dominant coal mineral, on the thermal and electrochemical behaviour of the molten ternary carbonate eutectic ((Li,Na,K)2CO3) in the direct carbon fuel cell (DCFC) as a means to simulate long-term operation with a continuous coal feed. Thermogravimetric and differential thermal analysis, coupled with kinetic modelling using the Friedman method, shows a substantial decrease in activation energy for eutectic melting with the addition of kaolin. Electro-oxidation of carbon (graphite) is also enhanced with kaolin in the electrolyte, increasing from 17.68 mA/cm2 at 0 wt% kaolin to the highest value of 162 mA/cm2 with 15 wt% kaolin added. It is shown that the improvement is due to increasing oxide concentration resulting from kaolin dissolution in the electrolyte.

Heat capacity and viscosity of ternary carbonate nanofluids

SummaryRecent studies have shown that eutectic salt mixtures show remarkable enhancement in heat capacity after nanoparticles are dispersed at small concentrations. The exact mechanism behind these heat capacity enhancements is still inconclusive. However, recent studies proposed that the enhancement could be associated with nucleation and grain growth of salt dendritic structures. To investigate the hypothesis, we synthesized several samples of ternary carbonate salt mixture doped with 1% alumina nanoparticles and thermally cycled them at various heating rates and cooled them back to the solid‐state during the synthesis procedure. It can affect the nucleation/grain growth of salt dendritic nanostructures and, as a result, there can be different heat capacity enhancements. A differential scanning calorimetry was employed to characterize the heat capacity values of the systems. It was observed that the heat capacity enhancements decreased with increases in the heating rates. The highest heat capacity enhancement was observed at the lowest heating rate (ie, 2°C/min). A transmission electron microscope was employed to confirm the effect of heating cycling rates on the formation of dendritic structures. Moreover, pH variation method was used to study the effect of the dendritic structures on the heat capacity of the mixture. Furthermore, a rheometer was employed to characterize the rheological behavior. It was observed that nanofluid samples showed shear‐thinning behavior, whereas shear thinning was not observed in pure and nanofluid prepared with the pH variation method.

INFLUENCE of ELECTRIC FIELD on STRUCTURE and PROPERTIES of TERNARY CARBONATE MOLTEN SALT

Molten salt is one of the important heat storage materials in the field of solar thermal utilization, and nanoparticles can improve partial thermal properties of molten salt. To investigate whether nanoparticles with charge can affect the structure of molten salt ions, the micro electric field of nanoparticles was replaced by applied electric field and the liquid Li2CO3- Na2CO3-K2CO3 was solidified in the electric field. DSC was used to determine the phase change temperatures and latent heat, and thermal stability was analyzed by TG curve. At last, the microstructures of molten salt were analyzed by SEM. Results show that the applied electric field can reduce the starting and ending temperatures of the carbonate by about 10°C as well as the latent heat. The mass loss rates of molten salt samples at the positive and negative plates are 1.44% and 0.81% respectively at 700°, and these samples have higher thermal stability than normal molten salt. The applied electric field can produce new microstructure of molten salt near positive and negative plates.

Nickel cobalt manganese ternary carbonate hydroxide nanoflakes branched on cobalt carbonate hydroxide nanowire arrays as novel electrode material for supercapacitors with outstanding performance

In this work, for the first time we are reporting the development of a kind of high rate and long cycle life electrode composed of nickel cobalt manganese ternary carbonate hydroxide (NiCoMn-CH) ultrathin nanoflakes coated on Co-CH nanowire arrays (NWAs), which are directly generated on a nickel foam (NF) support. The hierarchical heterostructures are synthesized via a scalable two step solvothermal strategy without any adscititious surfactant and binder. The smart combination of Co-CH and NiCoMn-CH nanostructures in the nanowire arrays shows significant synergistic effect on the enhancement of the electrochemical performance of the as-fabricated supercapacitors. The as-obtained electrode exhibits excellent conductivity and high specific surface area, resulting in an unprecedented high specific capacitance (up to 3224F g−1 at 1 A g−1 in a three-electrode system) and an ultralong cycling stability (92.4% retention after 6000 successive charge–discharge cycles 5 A g−1). Meanwhile, an asymmetric supercapacitor device assembled of the Co-CH@NiCoMn-CH hierarchical nanostructures as positive electrode and activated carbon (AC) as negative electrode delivers good energy density of 20.31 W h kg−1 at the power density of 748.46 W kg−1 in the operation window 0–1.5 V. This methodology could be generalized to the design of other novel structured nanomaterials for energy storage devices and other applications.

A Novel Li+‐Conducting Polymer Membrane Gelled by Fluorine‐Free Electrolyte Solutions for Li‐Ion Batteries

AbstractGel polymer electrolytes (GPEs), composed of poly(vinylidene fluoride) (PVdF), a ternary solvent of ethylene carbonate : propylene carbonate : dimethyl carbonate, and LiBOB, which are characterized by a novel composition with a fluorine‐free lithium salt, are here proposed. GPEs were firstly prepared through a solution casting procedure using the ternary carbonate solution as a solvent (named ex situ prepared membranes), and then activated by being immersed in a 0.7 M LiBOB‐carbonate solution. Fundamental characterizations, including thermal, spectroscopical, mechanical, and electrochemical analyses, were carried out and compared before and after the activation. GPEs, having the same composition, were also prepared by using a novel procedure (named in situ prepared membranes), involving the formation of PVdF membrane and its activation by the LiBOB electrolyte, as well as subsequent electrochemical characterizations, in the same T‐shape cell. Thus prepared lithium‐ion batteries, employing Sn−C and LiFePO4 electrodes, were demonstrated to exhibit a high capacity of 150 mAh g−1 through the course of cycling.

Carbonate dual-phase improves the performance of single-layer fuel cell made from mixed ionic and semiconductor composite

A mixed ionic and semiconducting composite in a single-layer configuration has been shown to work as a fuel cell at a lower temperature (500–600 °C) than a traditional solid-oxide fuel cell. The performance of a single-layer fuel cell (SLFC) is often limited by high resistive losses. Here, a eutectic mixture of alkali-carbonates was added to SLFC to improve the ionic conductivity. The dual-phase composite ionic conductor consisted of a ternary carbonate (sodium lithium potassium carbonate, NLKC) mixed with gadolinium-doped cerium oxide (GDC). Lithium nickel zinc oxide (LNZ) was used as the semiconducting material. The LNZ-GDC-NLKC SLFC reached a high power density, 582 mW/cm2 (conductivity 0.22 S/cm) at 600 °C, which is 30 times better than without the carbonate. The best results were obtained with the ternary carbonate which decreased the ohmic losses of the cell by more than 95%, whereas the SLFC with a binary carbonate (sodium lithium carbonate, NLC) showed a lower conductivity and performance (243 mW/cm2, 0.17 S/cm at 600 °C). It is concluded that adding carbonates to LNZ-GDC will improve the ionic conductivity and positively contribute to the cell performance. These results suggest a potential path for further development of SLFCs, but also imply the need for efforts on up-scaling and stability to produce practical applications with SLFC.

Study on the influence of small molecular gases on toluene reforming in molten salt

The upgrading of tar is a key issue for the sufficient application of biowaste pyrolysis technology. Molten salt, with high migration and diffusion of ions to prevent the deactivation of coke deposition of tar reforming functional metals, is considered as a feasible catalytic reaction medium and heat carrier for the upgrading of tar. The present study investigated the interactions between small molecular pyrolysis gases (including H2, CO, CH4) and main tar model compound in ternary carbonate eutectics (Li2CO3–Na2CO3–K2CO3). The results demonstrated that H2 could be decomposed to produce H radicals, promoting the conversion of toluene into gaseous products. CO32− could consume H radicals required by toluene cracking, making the process toluene polymerized to polycyclic aromatic hydrocarbons be strengthened. On the other hand, CO would react with OH radicals to produce H radicals and could enhance gas-generating process. In addition, toluene could react with CO to form benzaldehyde and phenylacetaldehyde. With the addition of CH4, more H radicals were supposed to be consumed, and toluene cracking process was further inhibited. Finally, the effect sequence of small molecular gases (H2 > CH4 > CO) on toluene reforming reaction was authenticated by investigating the impacts of introducing any two gases in toluene reforming.

Experimental and theoretical research on the thermal properties of carbonate mixtures

In this paper, Na2CO3, Li2CO3 and K2CO3 were selected to prepare carbonate mixtures according to different proportions. The thermal property and stability of the samples were tested by differential scanning calorimeter (DSC). The phase change temperature and latent heat of carbonate mixtures were calculated by theoretical formula, and compared with the experimental data to verify whether the theoretical formula are applicable in the field of high temperature molten salt. The results show that the melting point of carbonates which melted together is about 400°C. And the melting point of ternary carbonates is lower than the single component. The initial crystallization points of some samples are higher than the melting points. The differences between the melting point and the primary crystallization temperature are 5∼20°C. The phase change latent heat of the carbonate mixtures is lower than the single component’s. The latent heat of melting is more than the latent heat of solidifying. The DSC testing curves of the carbonate mixtures are almost coincident. The stability of mixed carbonate is very good. This experiment will provide reference and basis for its application in solar thermal power generation.

Enhanced specific heat and thermal conductivity of ternary carbonate nanofluids with carbon nanotubes for solar power applications

Enhanced specific heat and thermal conductivity of ternary carbonate nanofluids with carbon nanotubes for solar power applications

SiO2-ternary carbonate nanofluids prepared by mechanical mixing at high temperature: Enhanced specific heat capacity and thermal conductivity

Ternary carbonate (K2CO3–Li2CO3–Na2CO3, 4:4:2 mass ratio) can be used as a high-temperature heat transfer and thermal storage medium in concentrated solar power systems. Ternary carbonate nanofluids with 1.0 wt% SiO2 nanoparticles were prepared by mechanical mixing at high temperatures in order to enhance the specific heat capacity and the thermal conductivity. The effects of stirring rate (500 rpm, 750 rpm, and 1000 rpm) and stirring time (15 min, 30 min, and 60 min) on the thermal properties of the as-prepared nanofluids were analyzed. The results showed that the dispersion homogeneity of the nanoparticles in the nanofluids varied with the stirring rate and the mixing time, thereby affecting the formation of special nanostructures. The maximum enhancements in specific heat capacity and thermal conductivity at a temperature of 540 °C, stirring rate of 750 rpm and stirring time of 30 min were 38.5% and 50%, respectively. The specific heat capacity of the optimal nanofluids had no significant deterioration after the thermostatic (at 600 °C for 150 h) and thermal shock (50 cycles) experiments were conducted.

Experimental study on combustion behavior of mixed carbonate solvents and separator used in lithium-ion batteries

In this article, the combustion characteristics of different carbonate mixed solvents are considered by means of cone calorimeter. The coexistence system is composed of ternary carbonate mixed solvent and 1-g 2325 separator. Then, the comparison between coexistence systems and corresponding solvent mixtures is conducted. Experimental findings reveal that the combustion hazard of solvent mixtures is dominated by the component which is more volatile. The 2325 separator is not completely combusted when added to the ternary mixed solvent. The effects of 2325 separator on combustion of four ternary carbonate mixed solvents are different. It can be sure that the hazard posed by the addition of 2325 separator is all increased. More details about these variations have been analyzed.

Enhanced kinetics of CO2 electro-reduction on a hollow gas bubbling electrode in molten ternary carbonates

Electrochemical reduction of CO2 to value-added carbon and oxygen in lithium-containing molten carbonates at 723 K is a promising approach to the efficient utilization of CO2. It was recently reported that the cathodic process in this transformation is controlled by the sluggish diffusion of the generated O2− ions. The formation of Li2O on the cathode results in partial cathodic passivation of the cathode. To accelerate the reaction kinetics and also eliminate the concentration polarization of the resulting Li2O, the effect of bubbling CO2 through a hollow electrode was examined in this work using a home-made hollow gas bubbling (HGB) electrode. The localised CO2 bubbling not only accelerates the transport of O2− ions by agitating the electrolyte nearby, but the CO2 also reacts with Li2O to form the more soluble Li2CO3. Cyclic voltammetry (CV), linear sweep voltammetry (LSV) and constant current electrolysis were conducted in the melt at 723 K to study the depolarization mechanisms involved in the CO2 bubbling reaction. Using the HGB electrode, the steady-state current density increased from 15.3 mA/cm2 to ~200 mA/cm2 at a potential of −2.4 V (vs. Ag/Ag2SO4). The HGB electrode effectively improved the cathodic kinetics, which is beneficial for CO2 capture and electrochemical conversion.

Form-stable ternary carbonates/MgO composite material for high temperature thermal energy storage

With the fast development of concentrating solar power, a form-stable composite material containing ternary carbonates (K2CO3-Li2CO3-Na2CO3) as high temperature thermal energy storage materials and ceramic MgO as supporting material is proposed to prevent molten salts from leakage and the relevant corrosion. Using cold compression and mixed sintering method, ternary carbonates can be embedded and distributed uniformly in intervals and pores between MgO particles. There aren’t chemical reactions between carbonates and MgO during sintering at a high temperature. Among of samples with different mass ratios, the composite material containing 50 wt% ternary carbonates gives the highest mechanical strength. Specific heat capacity and latent heat of the composite material with an optimal ratio of 5:5 can be up to 1.48 J/g K (450–600 °C) and 158.7 kJ/kg, respectively. It has a relative low melting point (386.4 °C), and it hasn’t obvious mass degradation even at 1000 °C due to the strong adsorption of carbonates in intervals and pores between MgO particles. Moreover, the composite material shows a good thermal cycling stability after 100 cycles. The resulting form-stable composite material can provide a wider service temperature range and a higher thermal storage density based on the utilization of latent heat and sensible heat of molten salts.

Insights into the specific heat capacity enhancement of ternary carbonate nanofluids with SiO2 nanoparticles: the effect of change in the composition ratio.

Ternary carbonate nanofluids have proven to be a promising high temperature thermal energy storage and transfer medium for solar thermal power. For the ternary carbonate K2CO3–Li2CO3–Na2CO3 (4 : 4 : 2, mass ratio) with SiO2 nanoparticles prepared using a two-step solution method, the enhancement of the specific heat capacity was up to 113.7% at 540 °C compared to the ternary carbonate prepared by a direct mixing method. The present work aims to give insights into the marked enhancement of specific heat capacity. The effect of evaporation temperature on the nanostructures formed in ternary carbonate nanofluids is discussed for the enhancement of specific heat capacity. More importantly, based on an analysis of inductively coupled plasma atomic emission spectrometry, it is revealed that the composition ratio of the ternary carbonate, which can influence its specific heat capacity, was changed during the evaporation process in an electrothermal drier. Besides a difference in the solubility of the carbonates in water, it is demonstrated that the heating mode can affect the composition ratio of mixed molten salts.

Perovskite oxide and carbonate composite membrane for carbon dioxide transport

A novel La0.6Sr0.4Co0.2Fe0.8O3−δ based ternary carbonate composite membrane was developed via melting impregnation. The enhanced carbon dioxide permeability is due to the existence of La0.6Sr0.4Co0.2Fe0.8O3−δ, a mixed ionic-electronic conductor, and the carbonate phases. The composite membrane greatly promotes the CO2 surface reaction rate to form CO32− and the subsequent ionic transport rate. To further understand the mechanism, the effect of O2 on carbon dioxide permeability was also analyzed under fuel gas conditions.

Synthesis and characterization of M-doped ceria-ternary carbonate composite electrolytes (M = erbium, lanthanum and strontium) for low-temperature solid oxide fuel cells

Three different series of doped ceria-based composite electrolyte consisting of M-doped ceria (M = Ce0.85Er0.15O2-δ (ErDC), Ce0.85La0.15O2-δ (LaDC) and Ce0.95Sr0.05O2-δ (SrDC)) and ternary carbonate (mixture of Li2CO3, Na2CO3 and K2CO3) were developed as functional solid electrolytes for low-temperature solid oxide fuel cells. X-ray diffraction, transmission electron microscopy and UV–visible spectroscopy were used to analyze the chemical stability, morphology, and bandgap, respectively, of the prepared composite powders. All composite electrolytes exhibited cubic fluorite structure as a primary phase and small peaks corresponding to (Li/Na/K)2CO3 as an amorphous phase. The bulk densities of the sintered composite electrolyte pellets were in the range of 3.34 g/cm3–3.45 g/cm3. The total conductivity of the composite electrolyte materials was evaluated by electrochemical impedance spectroscopy in air and hydrogen (90 vol% N2 + 10 vol% H2) in the temperature range of 350 ºC–650 °C. The SrDC-ternary carbonate composite electrolyte showed the highest conductivity of 0.092 Scm−1 and lowest activation energy at 650 °C in hydrogen. The formation of hydrated phase from chemical interaction between the carbonates and hydrogen gas and the presence of Sr2+ and cerium ions is useful in enhancing the proton conduction in the SrDC-ternary carbonate system.

Corrosion behavior of aluminide diffusion coatings in low temperature molten carbonate electrolysis environments

Interest on low‐temperature molten carbonate electrolysis processes (T < 600 °C) for advanced energy conversion and storage applications appears to be progressively growing in literature. However, the corrosion of metallic materials in molten carbonate salts in equilibrium with the acidic CO2‐rich electrolysis gas atmospheres has been scarcely studied. In this work, the corrosion stability of a low‐activity FeAl aluminide diffusion coated 316 L stainless steel has been tested in a ternary carbonate eutectic mixture Li2CO3‐Na2CO3‐K2CO3 by 48 h‐immersion tests at 500 °C under CO2 atmosphere. Before the corrosion testing, the coated steel samples were pre‐oxidized in air at 750 °C in order to generate a protective thin alumina film on the aluminide coating surface. The salt immersion results indicate that FeAl aluminide coatings are not stable in acid molten carbonate environments due to rapid transformation of the pre‐existing alumina film into a non‐protective mixed Fe‐Al oxide crystalline layer. Corrosion degradation has been found to consist of both general and localized forms of attack. Factors affecting FeAl aluminide coating corrosion have been analyzed and discussed in detail.

Novel findings in conversion mechanism of toluene as model compound of biomass waste tar in molten salt

Molten salt owning large specific heat capacity and thermal conductivity coefficient is a promising reaction medium for catalytic pyrolysis/gasification of biomass waste. The understanding of tar conversion mechanism in molten salts is of great importance and needs to be clarified. The present study investigated the interactions between ternary carbonate eutectics (Li2CO3-Na2CO3-K2CO3) and main tar model compounds during pyrolysis and CO2 gasification process. The results showed that the molten salt could dramatically suppress the gas productivity (H2 and CH4) of toluene. A high molar ratio of CO2 in molten salt gasification would further inhibit the H2 yield, probably through the reverse water gas shift reaction. Meanwhile, a tendency towards polycyclic aromatic hydrocarbons (PAHs) formation was identified by examining liquid product in both molten salt pyrolysis and gasification process. And the formation of PAHs was likely correlated to the consumed H radical pool via its reaction with CO32− and/or CO2. Tar-containing alcohols and carboxylic acids could provide with free radicals and effectively inhibit the PAH generation. Meanwhile, the OH radical could react with CO32− to generate less active carbonate radical and hydroxyl, resulting in more fused liquid product. Introducing OH and H containing substance was recommended to enhance the decomposition of aromatics in molten carbonates.

Experimental and numerical study on the performance of a new high-temperature packed-bed thermal energy storage system with macroencapsulation of molten salt phase change material

In this paper, a new high-temperature packed-bed thermal energy storage system (PBTES) with macro-encapsulation of molten salt phase change material has been established. A new phase change material (PCM) capsule is designed and constructed with the macro-encapsulated molten salt as its PCM. The ternary carbonate Li2CO3-K2CO3-Na2CO3 (32–35–33 wt%) has been selected as the optimal option of PCMs. The melting point is 395.1 °C and the energy storage density is 174.7 kJ·kg−1. Moreover, the thermal performances such as the temperature evolution of heat transfer fluid and that of PCM capsule, average charging/discharging rate and overall heat storage efficiency are investigated in detail. Finally, a mathematical model is presented complementarily to simulate the thermal performance of PBTES. The results are concluded as follows. (1) The temperature variation of the heat transfer fluid and that of the capsule in the PBTES are obtained. There is a certain temperature difference between the capsule and the heat transfer fluid. Moreover, the convection heat transfer resistances of the capsule and the heat transfer fluid are the main influential factors in the heat exchange process. It can be improved by the inlet temperature and mass flow rate of the fluid. (2) The improvement of inlet temperature and mass flow rate in PBTES can increase its charging and discharging efficiencies. The overall efficiency of the system can be increased to 86.1% from 77.4% through increasing inlet temperature from 425 °C to 465 °C. The efficiency will up to 83.6% from the level of 80.6% by the rise of mass flow rate. (3) To compare the shell and tube thermal storage system, the charging and discharging rates of PBTES are 1.8–3.2 times that of the former one. The overall efficiency of PBTES is 1.9–2.4 times that of shell and tube thermal storage system. (4) According to the numerical simulation results, the good agreements of temperature evolution are achieved between the numerical results and experimental data, and the shorter diameter is optimal to the PBTES because a larger diameter will increase the charging time. In summary, the PBTES is an efficient method of heat storage. The study proposes a design of such the PBTES for a first step implementation of the technology and the improvement of thermal performance optimization.

A deep insight into carbon conversion during Zhundong coal molten salt gasification

Molten salt gasification is a promising way for collaborative use of solar energy and Zhundong coal, with in situ capture of Cl/S-pollutants as well as alkali metals. The present study provides a deep insight into carbon conversion during molten salt gasification of a typical Zhundong coal in ternary carbonate eutectics (Li2CO3-Na2CO3-K2CO3). The results demonstrated that the molten salt gasification of Zhundong coal underwent a rapid devolatilization of raw coal and then the gasification of char. The interactions between CO2 and volatiles promoted the cracking of macromolecular compounds, increasing the carbon conversion efficiency during the devolatilization process. The gasification of char was mainly determined by the direct reaction with molten salt, which was slightly affected by the CO2 concentration in the carrier gas. The results of char characterization evidenced that the condensation/graphitization of char was stimulated in the molten eutectics. Meanwhile, a large amount of O-containing groups, especially carbonyl groups, were formed in the molten salt treated char with carbonates as oxygen supplier. Under the influence of molten salts, some carbonyl groups would be formed inside the char. However, the decomposition of those carbonyl groups was suppressed by the mass transfer resistance of the released CO and/or CO2. Applying proper feeding mode, such as feeding coal in pulverized form, could enhance the contact of coal, molten salt and CO2, which remarkably promoted the interactions between molten salts and char containing functional groups.