CO2 Gas Evolution Research Articles

Chemical and Structural Transformations of M-Al-CO3 Layered Double Hydroxides (M = Mg, Zn, or Co, M/Al = 2) at Elevated Temperatures: Quantitative Descriptions and Effect of Divalent Cations.

Layered double hydroxides (LDHs) exhibit diverse chemical compositions and are being designed for promising applications such as CO2 adsorbents. Although many researchers have analyzed CO2 gas evolution and structural transformation behavior at elevated temperatures, there are still inconsistencies in results on the effect of different metal ions in LDHs. In this study, on the basis of atomic/molecular-level findings from our previous study on multistep structural/chemical transformation of Mg-Al LDHs, we analyzed the quantitative gas evolution behavior and structural transformations of M-Al-CO3 LDHs with different divalent metal ions (M = Mg, Zn, or Co, M/Al = 2) at elevated temperatures. Our quantitative analysis revealed that all three LDH samples undergo the three-step chemical transformations: release of interlayer water, partial dehydroxylation of the hydroxyl layers, and complete dehydroxylation of layers and decomposition of interlayer CO32-. However, the temperature range for each step differs, as do the structural transformations for each sample: the layered structure collapses in the first step for Zn-Al LDH and Co-Al LDH, and the third step for Mg-Al LDH. Our results provide for quantitative and concrete understanding of the effect of divalent metal ions in LDHs on thermal decomposition.

Low CI/CO abundance ratio revealed by HST UV spectroscopy of CO-rich debris discs

ABSTRACT The origin and evolution of CO gas in debris discs has been debated since its initial detection. The gas could have a primordial origin, as a remnant of the protoplanetary disc or a secondary exocometary origin. This paper investigates the origin of gas in two debris discs, HD110058 and HD131488, using Hubble Space Telescope (HST) observations of CI and CO, which play critical roles in the gas evolution. We fitted several electronic transitions of CI and CO rovibronic bands to derive column densities and temperatures for each system, revealing high CO column densities (∼3–4 orders of magnitude higher than β Pictoris), and low CI/CO ratios in both. Using the exogas model, we simulated the radial evolution of the gas in the debris disc assuming a secondary gas origin. We explored a wide range of CO exocometary release rates and α viscosities, which are the key parameters of the model. Additionally, we incorporated photodissociation due to stellar ultraviolet (UV) to the exogas model and found that it is negligible for typical CO-rich discs and host stars, even at a few au due to the high radial optical depths in the Extreme ultraviolet radiation (EUV). We find that the current steady-state secondary release model cannot simultaneously reproduce the CO and CI HST-derived column densities, as it predicts larger CI/CO ratios than observed. Our direct UV measurement of low CI/CO ratios agrees with results derived from recent Atacama Large Millimetre/submillimetre Array findings and may point to vertical layering of CI, additional CI removal, CO shielding processes, or different gas origin scenarios.

Residual alkali-evoked cross-linked polymer layer for anti-air-sensitivity LiNi0.89Co0.06Mn0.05O2 cathode

High-energy density lithium-ion batteries (LIBs) with layered high-nickel oxide cathodes (LiNixCoyMn1−x−yO2, x ≥ 0.8) show great promise in consumer electronics and vehicular applications. However, LiNixCoyMn1−x−yO2 faces challenges related to capacity decay caused by residual alkalis owing to high sensitivity to air. To address this issue, we propose a hazardous substances upcycling method that fundamentally mitigates alkali content and concurrently induces the emergence of an anti-air-sensitive layer on the cathode surface. Through the neutralization of polyacrylic acid (PAA) with residual alkalis and then coupling it with 3-aminopropyl triethoxysilane (KH550), a stable and ion-conductive cross-linked polymer layer is in situ integrated into the LiNi0.89Co0.06Mn0.05O2 (NCM) cathode. Our characterization and measurements demonstrate its effectiveness. The NCM material exhibits impressive cycling performance, retaining 88.4% of its capacity after 200 cycles at 5 C and achieving an extraordinary specific capacity of 170.0 mA h g−1 at 10 C. Importantly, this layer on the NCM efficiently suppresses unfavorable phase transitions, severe electrolyte degradation, and CO2 gas evolution, while maintaining commendable resistance to air exposure. This surface modification strategy shows widespread potential for creating air-stable LiNixCoyMn1−x−yO2 cathodes, thereby advancing high-performance LIBs.

Bubble Behavior and Anode Effect on Different Carbon Anode Designs in Cryolite Melt Applying a See-through Furnace

Anodic CO2 gas evolution is one of the main processes in the Hall-Héroult electrolysis cell for primary aluminium production. This work is a laboratory scale study of the effect of anode geometry, anode orientation and carbon anode material on bubble behavior and bubble properties in cryolite melt. Increased knowledge of the bubble behavior is important for improved design of industrial cells, but also for laboratory‐scale experiments. The anodes studied in this work are frequently applied for investigation of reaction kinetics and mass transport, anode effect, current efficiency, anode quality properties, etc. It is therefore of interest to study the bubble dynamics of these anodes in more detail because bubble evolution is relevant for all the above-mentioned phenomena.The anode potential has been shown to be highly dependent on anode geometry and orientation. For this study four different anode designs were made: horizontal (downward-facing), inverted horizontal (upward-facing), vertical, rod (with both vertical and horizontal surface). For most of the designs, characteristics such as bubble noise, bubble size, and wetting were obtained as a function of current density or anode potential/cell voltage. The bubble noise normally went through a maximum, while the bubble size decreased in the whole current density range. The wetting contact angle showed little variation with current density. It was assumed that the current density had a stronger effect on the contact angle through its effect on the bubble size than the polarization and associated surface roughening.Also, phenomena like nucleation, growth, coalescence, bubble detachment and anode effect were studied for both graphite and industrial carbon as anode material. The nucleation was more pronounced at the industrial carbon due to more active sites confirmed by CT analysis. The coalescence process was found to be independent of current density/potential and carbon anode material and was in the range 16-24 msec. On increased currents anode effect occurred on both anodes, the current being lower for the graphite anode at onset. Video recordings and electrochemical measurements showed more abrupt initiation of the anode effect on the graphite and a strong de-wetting of the anode. With the existence of a (C – F) surface compound on the anode, as long as the anode effect gas could escape the electrode surface, the anode seems to be electrochemically active towards both CO/CO2 and PFC formation during anode effect.In addition to the bubble characteristics and phenomena described, the impact of the results for better anode design for laboratory scale studies is discussed.

Highly Oxidative-Resistant Cyano-Functionalized Lithium Borate Salt for Enhanced Cycling Performance of Practical Lithium-Ion Batteries.

Lithium difluoro(oxalato) borate (LiDFOB) has been widely investigated in lithium-ion batteries (LIBs) owing to its advantageous thermal stability and excellent aluminum passivation property. However, LiDFOB tends to suffer from severe decomposition and generate a lot of gas species (e.g., CO2 ). Herein, a novel cyano-functionalized lithium borate salt, namely lithium difluoro(1,2-dihydroxyethane-1,1,2,2-tetracarbonitrile) borate (LiDFTCB), is innovatively synthesized as a highly oxidative-resistant salt to alleviate above dilemma. It is revealed that the LiDFTCB-based electrolyte enables LiCoO2 /graphite cells with superior capacity retention at both room and elevated temperatures (e.g., 80 % after 600 cycles) with barely any CO2 gas evolution. Systematic studies reveal that LiDFTCB tends to form thin and robust interfacial layers at both electrodes. This work emphasizes the crucial role of cyano-functionalized anions in improving cycle lifespan and safety of practical LIBs.

Highly Oxidative‐Resistant Cyano‐Functionalized Lithium Borate Salt for Enhanced Cycling Performance of Practical Lithium‐Ion Batteries

AbstractLithium difluoro(oxalato) borate (LiDFOB) has been widely investigated in lithium‐ion batteries (LIBs) owing to its advantageous thermal stability and excellent aluminum passivation property. However, LiDFOB tends to suffer from severe decomposition and generate a lot of gas species (e.g., CO2). Herein, a novel cyano‐functionalized lithium borate salt, namely lithium difluoro(1,2‐dihydroxyethane‐1,1,2,2‐tetracarbonitrile) borate (LiDFTCB), is innovatively synthesized as a highly oxidative‐resistant salt to alleviate above dilemma. It is revealed that the LiDFTCB‐based electrolyte enables LiCoO2/graphite cells with superior capacity retention at both room and elevated temperatures (e.g., 80 % after 600 cycles) with barely any CO2 gas evolution. Systematic studies reveal that LiDFTCB tends to form thin and robust interfacial layers at both electrodes. This work emphasizes the crucial role of cyano‐functionalized anions in improving cycle lifespan and safety of practical LIBs.

Isothermal and cyclic oxidation behavior of in-situ grown MoSi2-SiC coating on Mo substrate at 1300 °C

We prepared the in-situ grown composite coating layer on Mo substrate to improve the resistance of MoSi2 coating against cyclic oxidation by introducing SiC reinforcement to reduce the thermal expansion mismatch with Mo substrate. Composite coating of MoSi2–19.3 vol% SiC was fabricated using a two-step approach of Mo2C coating on Mo substrate followed by siliconizing to achieve uniform dispersion of nanosized SiC particles in a matrix of equiaxed MoSi2 grains. The superior performance of this coating over monolithic MoSi2 coating was clearly demonstrated through evaluations of bot its isothermal and cyclic oxidation behavior at 1300 °C. In both coatings, diffusion-limited growth of oxide film was observed as indicated by parabolic weight gain up to 100 h at 1300 °C. Slightly faster oxidation rate in this isothermal test was observed in the composite coating and mainly attributed to the fast oxygen transport through open pores and blowholes created by CO gas evolution from the internal oxidation of SiC particles. Composite coating gave rise to drastic improvement of cyclic oxidation resistance at 1300 °C while monolithic MoSi2 coating broke into pieces in less than 35 cycles. Both equiaxed grains of MoSi2 and SiC dispersion was effective in suppressing the occurrence of through-thickness cracks in coating layer due to lower thermal stress generated during cooling to room temperature.

Development of Aluminium Metal Foams via Friction Stir Processing by Utilizing MgCO3 Precursor

Aluminium foams possess multi-functional properties and a low specific weight, making them one of the most suitable choices in the application domain of the automobile and aviation sectors, vibrating machining, and structural parts. Compared to traditional fabrication routes, friction stir processing (FSP) is gaining acceptance as it is a cost-effective, highly efficient, and innocuous process to fabricate the foam precursors from the bulk substrate. In the current study, FSP was utilized to develop a precursor with MgCO3 powder acting as the blowing agent. The FSP experiments were performed as per Taguchi’s L8 orthogonal array. The precursor was heat treated in an electric furnace at a holding temperature of 650 °C for 10 min. After the post-heat treatments, this precursor resulted in a porous structure due to the evolution of CO2 gas from the composite. The simultaneous effect of tool rotation speed, traverse speed, and shoulder diameter was investigated on the pore size and porosity of the foam produced. The composite parameter “unit stirring” is found to be closely related to the processed zone (PZ) and volume processing rate of the processed zone, pore size, and the degree of porosity. The highest porosity of 16.67% was obtained with an average pore size of 10.5 µm. The largest pore size, 17.8 µm, was observed to be associated with a porosity of 14.40%. The analysis of the Kiviat plot revealed that the values of the PZ area and volume processing rate possess a polar symmetry with unit stirring. The pore size and pore density were both found to be symmetrically distributed about the unit stirring.

Role of Superoxide and Singlet Oxygen on the Oxygen Reduction Pathways in Li−O2 Cathodes at Different Li+ Ion Concentration**

AbstractThe oxygen reduction reaction (ORR) on Au electrodes has been studied in DMSO at different Li+ concentrations. In‐operando fluorescence decay of 9,10‐dimethyl anthracene (DMA) has shown that disproportionation of lithium superoxide Li+O2− into Li2O2 and O2 leads to an increasing fraction of very reactive singlet oxygen (1O2) at high lithium concentration. Singlet oxygen has been identified as the major cause of parasitic reactions leading to capacity fading and high charge overpotential of Li−O2 batteries. Rotating ring‐disk electrode shows quantitative formation of soluble superoxide at low Li+ concentration, a decrease in superoxide yield at high Li+ concentrations is consistent with electrochemical quartz crystal microbalance (EQCM) evidence of Li2O2 deposits. Differential electro chemical mass spectrometry (DEMS) confirms oxygen depletion at the electrode surface during ORR, and O2 evolution during oxidation at 3.1 V (vs. Li/Li+ in DMSO). The spurious solvent decomposition due to the very reactive 1O2 from superoxide disproportionation is revealed by gravimetric EQCM of insoluble by‐products. Furthermore, DEMS provides evidence of CO2 gas evolution from decomposition of Li2CO3 by‐product at 3.7 V (vs. Li/Li+ in DMSO). Preliminary in‐operando full discharge‐charge tests of a Li−O2 battery with 1O2 quencher azide resulted in stable cycling, enhanced capacity and full charge recovery in a round trip.

Gas Evolution from Sulfide-Based All-Solid-State Batteries

The demand for high-performance batteries for electrical vehicles (EV) and large-scale energy storage systems have accelerated the development of all-solid-state batteries. Switching from organic liquid electrolyte to solid electrolyte (SE) ensures, not only the high energy density (Wh/L), but also an intrinsic improvement to safety from the removal of flammable solvent in the liquid electrolyte. However, for the development of all-solid-state batteries, still many problems exist toward commercialisation. One challenge is their chemical/electrochemical stability. In case of Li6PS5Cl argyrodite, their electrochemical decomposition was proposed as following reaction. [1]Li6PS5Cl → Li4PS5Cl + 2Li+ + 2e → Li3PS4 + Sx + LiCl → P2Sx + Sx + LiCl + 3Li+ + 3e (1) However, this proposed reaction is bulk electrochemical decomposition of argyrodite. To understand the decomposition in actual cell, layered oxide cathode/argyrodite composite were analysed by in situ Raman microscopy, X-ray photoelectron spectroscopy and Time-of-flight secondary ion mass spectrometry. [2, 3] This research reports actual solid decomposition product formed by active material and solid electrolyte such as POx or (S2)2- compound. Not only for solid decomposition product, but also gaseous decomposition product can be generated from the interface between cathode materials and SE. Previously, much work has demonstrated that O2 and CO2 gases are released from the positive electrode material within the lithium-ion cell. [4] These exothermic surface reactions are important not only for cell swelling in the long-term usage, but also for cell combustion. However, the gas releasing behaviour of positive electrode mixture in all-solid-state batteries are still not well recognised. In this research, we focused on the gas releasing behaviour of all-solid-state batteries. LiNi0.6Mn0.2Co0.2O2 was selected for cathode materials in this research. For the solid electrolyte itself and LiNi0.6Mn0.2Co0.2O2/SE mixture were analysed by Differential Electrochemical Mass Spectroscopy (DEMS). Furthermore, to understand the importance of surface chemistry, air stored LiNi0.6Mn0.2Co0.2O2 and Al2O3 coated LiNi0.6Mn0.2Co0.2O2were prepared. Since air contamination (H2O and CO2) is detrimental for Ni-rich cathode and battery [5], we propose role of surface chemistry in all-solid-state batteries by comparing different LiNi0.6Mn0.2Co0.2O2 composites. As shown in Figure 1, CO2 and O2 gas evolution is observed within an all-solid-state cell as it is charged up to 5 V, with evolution beginning at ca. 4 V highlighting the requirement of stabilising interfaces even when a solid-state electrolyte is used.Figure 1. Comparison of O2 and CO2 gas evolution from (a) Li6PS5Cl and (b) LiNi0.6Mn0.2Co0.2O2/ Li6PS5Cl composite when charged to 5 V vs. Li/Li+.[1] L. Zhou, N. Minafara, W. G. Zeier, L. F. Nazar, Innovative Approaches to Li-Argyrodite Solid Electrolytes for All-Solid-State Lithium Batteries, Acc. Chem. Res., 54, (2021) 2717–2728[2] Y. Zhou, C. Doerrer, J. Kasemchainan, P. G. Bruce, M. Pasta, L. J. Hardwick, Observation of Interfacial Degradation of Li6PS5Cl against Lithium Metal and LiCoO2 via In Situ Electrochemical Raman Microscopy, Batter. & Supercaps, 3, (2020) 647 –652[3] F. Walther, R. Koerver, T. Fuchs, S. Ohno, J. Sann, M. Rohnke, W. G. Zeier, J. Janek, Visualization of the Interfacial Decomposition of Composite Cathodes in Argyrodite-Based All-Solid-State Batteries Using Time-of-Flight Secondary-Ion Mass Spectrometry, Chem. Mater, 31, (2019), 3745-3755[4]S. Sharifi-Asl, J. Lu, K. Amine, R. Shahbazian-Yassar, Oxygen Release Degradation in Li-Ion Battery Cathode Materials: Mechanisms and Mitigating Approaches, Adv. Energy Mater., 9, (2019) 1900551[5] H. Kim, A. Choi, S. W. Doo, J. Lim, Y. Kim, K. T. Lee, Role of Na+ in the cation disorder of [Li1-xNax] NiO2 as a cathode for lithium-ion batteries, J. Electrochem. Soc., 165, (2018), A201 Figure 1

Assessing Long-Term Cycling Stability of Single-Crystal Versus Polycrystalline Nickel-Rich NCM in Pouch Cells with 6 mAh cm-2 Electrodes.

Lithium-ion batteries based on single-crystal LiNi1- x - y Cox Mny O2 (NCM, 1-x-y≥ 0.6) cathode materials are gaining increasing attention due to their improved structural stability resulting in superior cycle life compared to batteries based on polycrystalline NCM. However, an in-depth understanding of the less pronounced degradation mechanism of single-crystal NCM is still lacking. Here, a detailed postmortem study is presented, comparing pouch cells with single-crystal versus polycrystalline LiNi0.60 Co0.20 Mn0.20 O2 (NCM622) cathodes after 1375 dis-/charge cycles against graphite anodes. The thickness of the cation-disordered layer forming in the near-surface region of the cathode particles does not differ significantly between single-crystal and polycrystalline particles, while cracking is pronounced for polycrystalline particles, but practically absent for single-crystal particles. Transition metal dissolution as quantified by time-of-flight mass spectrometry on the surface of the cycled graphite anode is much reduced for single-crystal NCM622. Similarly, CO2 gas evolution during the first two cycles as quantified by electrochemical mass spectrometry is much reduced for single-crystal NCM622. Benefitting from these advantages, graphite/single-crystal NMC622 pouch cells are demonstrated with a cathode areal capacity of 6 mAh cm-2 with an excellent capacity retention of 83% after 3000 cycles to 4.2V, emphasizing the potential of single-crystalline NCM622 as cathode material for next-generation lithium-ion batteries.

Oxidative Dissolution of Tungsten Metal in Na2CO3 under Ar–O2–CO2 Atmosphere

A novel process for the recycling of tungsten from hard tool scraps using carbonate molten salts is proposed. As a fundamental study, the oxidative dissolution of tungsten metal into molten Na2CO3 under Ar–O2 and Ar–O2–CO2 atmospheres was investigated at 1173 K. The results of the oxidative dissolution experiments and the detection of CO gas evolution by infrared spectroscopy revealed the existence of multiple oxidation mechanisms by peroxide/superoxide ions and carbonate ions. The feasibility of each oxidant was discussed by calculating potential– diagrams in molten Na2CO3 at 1173 K. The relationship between the potential and the reaction was investigated using cyclic voltammetry and potential– diagrams.

Effect of Direct Reduced Iron (DRI) on Dephosphorization of Molten Steel by Electric Arc Furnace Slag

We investigated the effect of direct reduced iron (DRI) addition on dephosphorization of molten steel by electric arc furnace (EAF) slag at 1823 K (1550 °C). Various phenomena such as CO gas evolution and slagmaking by gangue oxides in DRI were experimentally observed at each reaction step. Thermodynamic behaviors of phosphorus, oxygen, and carbon were strongly dependent on DRI content. Basicity, which is the thermodynamic driving force of dephosphorization, decreased with the increasing DRI content because SiO2 concentration in the slag was proportional to DRI addition. The excess free energy of P2O5 increased with the increasing SiO2 content in slag. A higher DRI content made dephosphorization difficult by decreasing the basicity and stability of P2O5 in the slag. Therefore, when using DRI in EAF process, it is very important to control the basicity of slag.

Effect of g-C3N4 loading on TiO2/Bentonite nanocomposites for efficient heterogeneous photocatalytic degradation of industrial dye under visible light

TiO2/clay nanocomposites tend to have high photocatalytic efficiency than commercial TiO2 (Degussa P25) due to their high porosity, surface area, the presence of active sites and optical transparency. However, its inactivity in the visible region of the solar spectrum makes it unsuitable for practical use. Hence, the nanocomposite of TiO2 with bentonite clay has been coupled with visible light active graphitic carbon nitride (g-C3N4) by wet impregnation process at room temperature. The as-prepared nanocomposite was then used to photocatalytically degrade (90%) reactive brilliant red dye (RBR- X3BS) in 100 min of time under visible light irradiation. The high activity was attributed due to the suppression of electron-hole recombination as the electron was transferred from g-C3N4 to TiO2 and there was a strong electrostatic interaction between g-C3N4 and bentonite clay. To investigate the reactive species responsible for the photodegradation of dye, different radical scavengers were employed and it was observed that the % degradation was highly affected by the addition of DMSO and ascorbic acid which indicated that electrons (e−) and superoxide radicals (O2-) have played an important role in dye degradation. The reusability efficiency of the as-prepared nanocomposite was examined for 5 consecutive cycles. Complete photo-mineralization of the dye was confirmed by the evolution of CO2 gas (37 ppm) which was monitored by gas chromatography (GC). From the comparative study of literature, it can be proposed that our as-synthesized g-C3N4/TiO2/bentonite nanocomposites could be employed as an efficient photocatalyst for the degradation of RBX-3B dye.

Enhanced Stability of Coated Carbon Electrode for Li–O2 Batteries and Its Limitations

The increasing demands for electric vehicles have spurred a worldwide search for next-generation rechargeable batteries with higher energy density. Among various battery systems, the lithium–oxygen (Li–O2) chemistry offers one of the highest theoretical energy densities, which can reach 3500 Wh kg−1 based on the reaction 2Li+ + O2 + 2e− = Li2O2 (E0 = 2.96 V vs. Li/Li+). The most widely used air electrodes are carbon-based materials because of their large surface areas per weight and high electrical conductivity, which are suitable for promoting the electrochemical formation of Li2O2 on the electrode, providing a high gravimetric energy density. For these reasons, carbon-based air electrodes have been intensely researched in recent years, and various types of carbon materials such as porous carbon, carbon nanotubes (CNTs), and graphene have been reported as air electrodes. Recent studies, however, have shown that parasitic reactions involving carbon-based air electrodes could be one of the factors resulting in the deterioration of the electrochemical cycling of Li–O2 batteries.[1-3] Upon cycling, carbon can react with Li2O2, a discharge product deposited on the carbon electrode, to form insulating Li2CO3, which degrades the efficiency and cycle stability. Moreover, carbon itself can be corroded under high oxidizing potential in Li–O2 batteries and can thus be passivated with carbon-containing byproducts. The damaged carbon surface aggravates the electrolyte decomposition, resulting in the formation of additional byproducts. These byproducts from the electrolyte and carbon electrode can be partially decomposed during charge and typically lead to the evolution of CO2 gas instead of O2. As the cycle continues, insulating byproducts are gradually accumulated, which generally results in a high overpotential, low round-trip efficiency, and short cycle life. Therefore, the design of a strategy to reduce side reactions in the carbon electrode is imperative to achieve high electrochemical stability of Li–O2 batteries. Our previous work demonstrated that defect sites on carbon materials are more susceptible to reaction with discharge products and are prone to decompose more easily, serving as seeds for side reactions.[3] Thus, a carbon air electrode with higher crystallinity could exhibit more stable cycle properties. However, the preparation of highly crystalline carbon generally requires high-temperature treatment above 2000°C and substantially reduces the surface area, leading to a relatively small discharge capacity. Moreover, the complete removal of the defects in the production of large-surface carbon materials is not trivial. Instead, appropriate passivation of defect sites for a given carbon material may be a suitable approach to fabricate stable carbon-based air electrodes. Selective growth of materials specifically on the defect sites with the minimal amount of coating would be ideal to prohibit the side reactions without excessively increasing the weight of the air electrode. It was previously reported that Al2O3 and Pd could be coated on carbon using atomic layer deposition (ALD) to protect the air electrode and reduce the overpotential, resulting in enhanced cycle stability.[4] Nevertheless, the insulating nature of Al2O3 caused a large overpotential during cycling, and the high price of the noble metal remains an issue. Moreover, it is not clearly understood how and to what extent these coating materials can aid in the reduction of the side reactions and whether its effect is maintained with extended cycling. Herein, we demonstrate that the effect of coating is not limited to the protection of the carbon electrode but also remarkably suppresses the decomposition of the electrolyte. These results were analyzed using in situ differential electrochemical mass spectroscopy (DEMS) with labeled isotopic 13C air electrode in the electrolyte composed of 12C for the Li–O2 cell. In contrast to the pristine carbon electrode, the coating provided effective protection, which reduced the evolution of undesirable gases from both the electrolyte (12CO2) and carbon electrode (13CO2), with high efficiency of O2 evolution, resulting in enhanced cycle stability (>100 cycles). Nevertheless, the coating materials were gradually detached from the surface of the carbon materials because of the formation of a discharge product at the interface between the carbon and coating materials during cycling, leading to exposure of the bare carbon electrode and degradation of the Li–O2 cell. This study suggests that a method to prevent the detachment of the coating material as well as further understanding of the growth mechanism of discharge products, which affects the delamination of the coating, should be sought after in the future.

Reduction Behavior of Dolomite-Fluxed Magnetite: Coke Composite Pellets at 1573\xa0K (1300\xa0\xb0C)

High-temperature behavior of magnetite—coke composite pellet fluxed with dolomite was investigated by customized thermogravimetric analyzer (TGA) at 1573 K (1300 °C). The overall reaction was influenced by C/O ratio and dolomite content. The reduction was accelerated by increased amount of dolomite, while the samples with higher C/O ratio showed the improved reduction degree. X-ray diffraction (XRD) pattern of reduced pellet showed the phase changes of the iron oxides. Noticeable iron peaks were observed when the sample reached the final stage of reduction. CO and CO2 gases released from the reaction were measured by Infrared (IR) gas analyzer. Relation between enhanced reducibility of pellets and larger CO gas evolution from the Boudouard reaction was confirmed from the analysis. Compressive strengths were studied for the practical assessment of reduced pellets. Samples with low-reduction degree showed better physical property. Excessive amount of dolomite also deteriorated the integrity of pellets.

Enhanced catalytic behavior of Ni alloys in steam methane reforming

Abstract The dissociation process of methane on Ni and Ni alloys are investigated by density functional theory (DFT) in terms of catalytic efficiency and carbon deposition. Examining the dissociation to CH3, CH2, CH, C, and H is not sufficient to properly predict the catalytic efficiency and carbon deposition, and further investigation of the CO gas-evolving reaction is required to completely understand methane dissociation in steam. The location of alloying element in Ni alloy needed be addressed from the results of ab-inito molecular dynamics (MD). The reaction pathway of methane dissociation associated with CO gas evolution is traced by performing first-principles calculations of the adsorption and activation energies of each dissociation step. During the dissociation process, two alternative reaction steps producing adsorbed C and H or adsorbed CO are critically important in determining coking inhibition as well as H2 gas evolution (i.e., the catalytic efficiency). The theoretical calculations presented here suggest that alloying Ni with Ru is an effective way to reduce carbon deposition and enhance the catalytic efficiency of H2 fueling in solid oxide fuel cells (SOFCs).

N,N-Diethyl-diaminopropane-copper(ii) oxalate self-reducible complex for the solution-based synthesis of copper nanocrystals.

Metal oxalates (C2O42-, ox) have been explored as promising precursors for the direct transformation of their oxalate moieties into metallic or metal oxide crystals via thermal decomposition without the formation of any byproducts due to releasing CO2 gas. The copper(ii) oxalate (Cu(ox)) crystal is a coordination polymer composed of an infinite coordination network with a thermal decomposition temperature around 300 °C; however, their insoluble nature in any solvents and relatively high decomposition temperature do not allow the solution-based syntheses of surface-modified metallic Cu nanocrystals (NCs) in the presence of various surfactants such as long-chain alkylamines and alkylcarboxylates which have been used for increasing the dispersibility of NCs in organic solvents. In this study, the insoluble nature of Cu(ox) is overcome by mixing Cu(ox) crystals and N,N-diethyl-1,3-diaminopropane (dedap) to form a discrete complex, [Cu(ox)(dedap)2], whose structure is determined by X-ray crystallographic analysis. The obtained complex is well soluble in polar solvents and miscible with surfactants. Furthermore, it is decomposed at a moderate temperature of <170 °C with the evolution of CO2 gas; as a result, Cu NCs dispersible in organic solvents have been synthesized in suitable surfactants, such as the mixture of oleic acid, dodecylamine, and octylamine utilized as a reaction solvent. In addition, their potential application of the surface-modified Cu NCs as a conductive-ink has been preliminarily tested. The Cu film sintered at 280 °C exhibits a resistivity of 40 μΩ cm.

Carbonate clumped isotope paleothermometry: a review of recent advances in CO2 gas evolution, purification, measurement and standardization techniques

Carbonate clumped isotope paleothermometry is based upon the principle that the formation temperature of carbonates is proportional to the relative abundance of 13C18O16O in CO2 produced through carbonate acid digestion. Furthermore, the relative abundance of 13C18O16O is independent of the δ 18O value of parent water, providing a viable alternative to the classic oxygen isotope carbonate-water paleothermometer. The temperature resolution of this newly developed paleothermometer primarily relies on the analytical techniques required to determine the clumped isotope composition of a carbonate mineral. These analytical techniques involve: (1) CO2 gas evolution, in which carbonate is reacted with phosphoric acid, yielding CO2 with a clumped isotope composition proportional to the carbonate formation temperature; (2) CO2 purification, in which a rigorous purification of acid-liberated CO2 is achieved by removing contaminants; (3) clumped isotope measurement, in which a customized gas-source isotope ratio mass spectrometer quantifies the raw clumped isotope composition (Δ47) of the purified CO2 gas; and (4) inter-laboratory standardization, in which raw Δ47 values are normalized with respect to a community-accepted reference frame. This review provides an overview and comparison of the analytical techniques currently utilized in stable isotope laboratories for Δ47 measurements, specifically discussing carbonate pre-treatment techniques, phosphoric acid digestion systems, isotope and temperature effects during carbonate phosphoric acid digestion, CO2 purification processes, and the challenges associated with the measurement and standardization of the Δ47 value. Continued refinement of these analytical techniques will aid in reducing sample size, increasing sample throughput, and improving Δ47 external precision and associated paleotemperature resolution. Furthermore, these advances may assist in elucidating the source of discrepancies in slope between two groups of reported carbonate clumped isotope thermometer calibrations.

CO2 leakage in shallow aquifers: A benchmark modeling study of CO2 gas evolution in heterogeneous porous media

The physicochemical processes associated with CO2 leakage into shallow aquifer systems are complex and span multiple spatial and time scales. Continuum-scale numerical models that faithfully represent the underlying pore-scale physics are required to predict the long-term behavior and aid in risk analysis regarding regulatory and management decisions. This study focuses on benchmarking the numerical simulator, FEHM, with intermediate-scale column experiments of CO2 gas evolution in homogeneous and heterogeneous sand configurations. Inverse modeling was conducted to calibrate model parameters and determine model sensitivity to the observed steady-state saturation profiles. It is shown that FEHM is a powerful tool that is capable of capturing the experimentally observed outflow rates and saturation profiles. Moreover, FEHM captures the transition from single- to multi-phase flow and CO2 gas accumulation at interfaces separating sands. We also derive a simple expression, based on Darcy's law, for the pressure at which CO2 free phase gas is observed and show that it reliably predicts the location at which single-phase flow transitions to multi-phase flow.