Proton Transfer in Molten Lithium Carbonate: Mechanism and Kinetics by Density Functional Theory Calculations

Using static and dynamic density functional theory (DFT) methods with a cluster model of [(Li2CO3)8H]+, the mechanism and kinetics of proton transfer in lithium molten carbonate (MC) were investigated. The migration of proton prefers an inter-carbonate pathway with an energy barrier of 8.0 kcal/mol at the B3LYP/6-31 G(d,p) level, which is in good agreement with the value of 7.6 kcal/mol and 7.5 kcal/mol from experiment and FPMD simulation, respectively. At transition state (TS), a linkage of O–H–O involving O 2p and H 1 s orbitals is formed between two carbonate ions. The calculated trajectory of H indicates that proton has a good mobility in MC, oxygen can rotate around carbon to facilitate the proton migration, while the movement of carbon is very limited. Small variations on geometry and atomic charge were detected on the carbonate ions, implying that the proton migration is a synergetic process and the whole carbonate structure is actively involved. Overall, the calculated results indicate that MC exhibits a low energy barrier for proton conduction in IT-SOFCs

Can Silver Be a Reliable Current Collector for Electrochemical Tests?

The true functionality of a current collector employed in electrochemical cells is to ensure a low- resistance steady electrons flow between the cell and instrumentation without involving in any local electrochemical reactions of the electrode. In this study, we investigated the effect of curing temperature of a common current collector, silver, on the polarization area specific resistance (ASR) of a cathode. The results explicitly showed that at least one order of magnitude lower ASR for a cathode with Ag cured at 800°C than that cured at 650°C of the same cathode configuration. Microscopic analysis of the 800°C-cured cells revealed a deep penetration and abundant distribution of Ag into the cathode/electrolyte interfacial region. These finely dispersed and highly conductive Ag particles/agglomerates are ORR (oxygen reduction reaction)-active, thus engaging in the local electrochemical reaction and overshadowing the true properties of the cathode under investigation. Based on these results, we call for caution when using Ag as a current collector for electrochemical measurements, particularly at a temperature ≥650°C

First Spectroscopic Identification of Pyrocarbonate for High CO\u3csub\u3e2\u3c/sub\u3e Flux Membranes Containing Highly Interconnected Three Dimensional Ionic Channels

Identification of the existence of pyrocarbonate ion C2O52− in molten carbonates exposed to a CO2 atmosphere provides key support for a newly established bi-ionic transport model that explains the mechanisms of high CO2 permeation flux observed in mixed oxide-ion andcarbonate-ion conducting (MOCC) membranes containing highly interconnected three dimensional ionic channels. Here we report the first Raman spectroscopic evidence of C2O52− as an active species involved in the CO2-transport process of MOCC membranes exposed to a CO2atmosphere. The two new broad peaks centered at 1317 cm−1 and 1582 cm−1 are identified as the characteristic frequencies of the C2O52− species. The measured characteristic Raman frequencies of C2O52− are in excellent agreement with the DFT-model consisting of six overlapping individual theoretical bands calculated from Li2C2O5 and Na2C2O5

Molten Carbonates as an Effective Oxygen Reduction Catalyst for 550–650°C Solid Oxide Fuel Cells

We report the first study that investigates the use of molten carbonates as an effective catalyst to promote electrochemical oxygen reduction reaction (ORR) at the cathode of intermediate temperature solid oxide fuel cells (IT-SOFCs). A series of binary Li-K carbonate compositions were incorporated into the porous backbones of a commercial cathode assembled in symmetrical impedance cells for electrochemical characterization. Within the temperature range of 550–650◦C, we observed that the polarization and ohmic area-specific resistances of the original sample can be significantly reduced by the introduction of molten carbonates. A new ORR charge-transfer model involving two intermediate species CO5 2− and CO4 2− as the fast oxygen absorber and transporter, respectively, was presented as the mechanism for the facile ORR kinetics promoted by molten carbonates

Promoting Electrocatalytic Activity of a Composite SOFC Cathode La\u3csub\u3e0.8\u3c/sub\u3eSr\u3csub\u3e0.2\u3c/sub\u3eMnO\u3csub\u3e3+δ\u3c/sub\u3e/Ce\u3csub\u3e0.8\u3c/sub\u3eGd\u3csub\u3e0.2\u3c/sub\u3eO\u3csub\u3e2-δ\u3c/sub\u3e with Molten Carbonates

The effect of molten carbonates (MCs) on polarization resistance (RP), a direct measure of oxygen reduction reaction (ORR) activity, of a composite La0.8Sr0.2MnO3+δ/Ce0.8Gd0.2O2-δ (LSM/GDC) solid oxide fuel cell (SOFC) cathode has been systematically investigated in this study over a temperature range of 550–650°C and partial pressure of oxygen (pO2) span of 10−3 ∼ 1 atm. It is shown that the LSM/GDC cathode, either in the pristine or MC-modified states, can be generally modeled by two consecutive parallel circuits consisting of a resistance and a constant phase element (CPE). The high-frequency RP(HF)//CPE(HF) component is related to a charge-transfer process, while the low-frequency RP(LF)//CPE(LF) counterpart is associated with a surface oxygen dissociative adsorption process. Incorporation of an adequate amount of MC significantly reduces RP(LF) by as much as a factor of 10. Studies on the dependence of RP on temperature and pO2 further reveal that the rate-limiting step of a LSM/GDC cathode has shifted from the original surface oxygen dissociative adsorption to the formation of an intermediate CO2 −4 species in the presence of MC

Limited versus extended cocaine intravenous self‐administration: Behavioral effects and electrophysiological changes in insular cortex

Aims: Limited vs extended drug exposure has been proposed as one of the key factors in determining the risk of relapse, which is the primary characteristic of addiction behaviors. The current studies were designed to explore the related behavioral effects and neuronal alterations in the insular cortex (IC), an important brain region involved in addiction. Methods: Experiments started with rats at the age of 35 days, a typical adolescent stage when initial drug exposure occurs often in humans. The drug-seeking/taking behaviors, and membrane properties and intrinsic excitability of IC pyramidal neurons were measured on withdrawal day (WD) 1 and WD 45-48 after limited vs extended cocaine intravenous self-administration (IVSA). Results: We found higher cocaine-taking behaviors at the late withdrawal period after limited vs extended cocaine IVSA. We also found minor but significant effects of limited but not extended cocaine exposure on the kinetics and amplitude of action potentials on WD 45, in IC pyramidal neurons. Conclusion: Our results indicate potential high risks of relapse in young rats with limited but not extended drug exposure, although the adaptations detected in the IC may not be sufficient to explain the neural changes of higher drug-taking behaviors induced by limited cocaine IVSA

Contrasting Effects of Adolescent and Early-Adult Ethanol Exposure on Prelimbic Cortical Pyramidal Neurons

Background: Adolescence and early-adulthood are vulnerable developmental periods during which binge drinking can have long-lasting effects on brain function. However, little is known about the effects of binge drinking on the pyramidal cells of the prelimbic cortex (PrL) during early and protracted withdrawal periods. Methods: In the present study, we performed whole-cell patch clamp recordings and dendritic spine staining to examine the intrinsic excitability, spontaneous excitatory post-synaptic currents (sEPSCs), and spine morphology of pyramidal cells in the PrL from rats exposed to chronic intermittent ethanol (CIE) during adolescence or early-adulthood. Results: Compared to chronic intermittent water (CIW)-treated controls, the excitability of PrL-L5 pyramidal neurons was significantly increased 21 days after adolescent CIE but decreased 21 days after early-adult CIE. No changes of excitability in PrL Layer (L) 5 were detected 2 days after either adolescent or early-adulthood CIE. Interestingly, decreases in sEPSC amplitude and increases in thin spines ratio were detected 2 days after adolescent CIE. Furthermore, decreased frequency and amplitude of sEPSCs, accompanied by a decrease in the density of total spines and non-thin spines were observed 21 days after adolescent CIE. In contrast, increased frequency and amplitude of sEPSCs, accompanied by increased densities of total spines and non-thin spines were found 21 days after early adult CIE. Conclusion: CIE produced prolonged neuronal and synaptic alterations in PrL-L5, and the developmental stage, i.e., adolescence vs. early-adulthood when subjects receive CIE, is a key factor in determining the direction of these changes

Establishment of the Luoping Biota National Geopark in Yunnan, China

Geoparks in China have been a great success story, with 284 national geoparks and 41 of them accorded UNESCO international status, the highest number for any country in the world. We track the progress of one of the geoparks, Luoping Biota National Geopark in Yunnan Province, from initial plans after its discovery as a key site for the exceptional preservation of Middle Triassic marine fossils in 2007, to acceptance as a National Geopark in 2011. Geoparks combine great scientific importance with accessibility and attraction for tourists. The scientific importance of Luoping is in the fossils, thousands of specimens of marine invertebrates, fishes and reptiles, together with rare elements from land (e.g. insects, plants), representing an important phase in the Mesozoic Marine Revolution, when life was recovering from devastation at the end of the Permian, and 8 million years later, had developed stable ecosystems with a new structure, dominated by predatory fishes and reptiles. The touristic importance of the Luoping Biota Geopark has already been demonstrated by rapid development of facilities and high visitor numbers