Reaction Kinetics Research Articles

Tuning Reaction Kinetics of Fluorinated Molecules to Construct Robust Solid Electrolyte Interphases on SiOx Anode

Tuning Reaction Kinetics of Fluorinated Molecules to Construct Robust Solid Electrolyte Interphases on SiOx Anode

Tuning Reaction Kinetics of Fluorinated Molecules to Construct Robust Solid Electrolyte Interphases on SiOx Anode

Tuning Reaction Kinetics of Fluorinated Molecules to Construct Robust Solid Electrolyte Interphases on SiOx Anode

A new Co‐based cathode with high performance for intermediate‐temperature solid oxide fuel cells

AbstractSolid oxide fuel cells (SOFCs) as highly effective energy conversation devices have gained substantial recognition and research interest. The electrochemical properties of the traditional SOFCs are restricted by the sluggish reaction kinetics for the cathode material when lowering the operation temperature to below 600°C. In addition, the stability of the cathode at reduced temperatures is also a big challenge for the widely popularization of SOFC technology. Achieving high activities and stable ORR in the cathode is crucial for the development of SOFCs. The doping active metal method has been demonstrated as an effective approach to optimize the phase structure and improve the ORR activity of the cathode. Herein, we successfully develop an Ir‐doped SrCoO3 − δ (SrCo0.98Ir0.02O3 − δ, SCI) cathode for SOFCs. SCI exhibits a low area‐specific resistance (ASR) of 0.057 Ω cm2 at 650°C, ~ 44% lower than 0.102 Ω cm2 of Ir‐free SrCoO3 − δ. The Ni–Sm0.2Ce0.8O1.90 (SDC) anode‐supported fuel cell with SDC electrolyte and SCI cathode obtains an excellent output performance (e.g., 1,128 mW cm−2 at 650°C). The desired results underscore the feasibility of the Ir‐doping strategy as an optimized method for the exploitation of advancing cathode in SOFCs.

Quantitative x-ray scattering of free molecules

Abstract Advances in X-ray free electron lasers have made ultrafast scattering a powerful method for investigating molecular reaction kinetics and dynamics. Accurate measurement of the ground-state, static scattering signals of the reacting molecules is pivotal for these pump-probe X-ray scattering experiments as they are the cornerstone for interpreting the observed structural dynamics. This article presents a data calibration procedure, designed for gas-phase X-ray scattering experiments conducted at the Linac Coherent Light Source X-ray Free-Electron Laser at SLAC National Accelerator Laboratory, that makes it possible to derive a quantitative dependence of the scattering signal on the scattering vector. A self-calibration algorithm that optimizes the detector position without reference to a computed pattern is introduced. Angle-of-scattering corrections that account for several small experimental non-idealities are reported. Their implementation leads to near quantitative agreement with theoretical scattering patterns calculated with ab-initio methods as illustrated for two X-ray photon energies and several molecular test systems.

Sonochemically Prepared Nanodot Magnesium Fluoride‐Based Anodeless Carbon Substrate for Simultaneously Reinforcing Interphasial and Reaction Kinetics for Sulfide‐Based All‐Solid‐State Batteries

Sonochemically Prepared Nanodot Magnesium Fluoride‐Based Anodeless Carbon Substrate for Simultaneously Reinforcing Interphasial and Reaction Kinetics for Sulfide‐Based All‐Solid‐State Batteries

Chrome incorporation in high-pressure Fe–Mg oxides

Abstract. The occurrence of Cr-bearing oxide phases as inclusions in diamonds and in extraterrestrial materials has the potential to serve as an indicator of formation conditions. However, such an application requires detailed knowledge of phase stabilities and the influence that Cr may have on its stability. To this end, the incorporation of Cr in high-pressure post-spinel Fe–Mg oxide phases was experimentally investigated at pressures of 14–22 GPa and temperatures between 1100 and 1600 °C using a multi-anvil press. We find that neither the Fe3Cr2O6 nor the Mg3Cr2O6 endmember composition is stable over the expected range of pressure and temperature where Fe5O6 itself is known to be stable. Further experiments along the Fe32+Fe23+O6–Fe32+Cr2O6 binary indicate only small amounts of Cr substitution are possible: ∼ 0.12 cations Cr per formula unit or ∼ 6 mol % Fe32+Cr2O6 component. In contrast, complete solid solution is apparent across both the Fe22+(Cr,Fe3+)2O5 and the Mg2(Cr,Fe3+)2O5 binaries, and there are indications of complete solution in the entire (Mg,Fe2+)2(Cr,Fe3+)2O5 quaternary system. The O5-structured phase usually coexists with (Fe,Mg)O. At 16–20 GPa, a post-spinel phase with O4 stoichiometry was occasionally encountered, having either a modified Ca-ferrite- (mCF-FeCr2O4) or a Ca-titanate-type (CT-MgCr2O4) structure. In one high-temperature experiment at 1600 °C, an unquenchable Mg-rich phase with a reconstructed Mg4Fe23+O7 stoichiometry occurred together with Mg2(Cr,Fe3+)2O5. In one experiment at 1100 °C and 16 GPa with a bulk composition of Mg2(Cr0.6,Fe0.43+)2O5, an assemblage of O5 phase + eskolaite–hematite solid solution + periclase was obtained together with minor amounts of the CT-type phase and a β-(Cr,Fe)OOH phase. The occurrence of these two minor phases in this low-temperature experiment is an indicator of variable reaction kinetics amongst the starting materials, which caused chemical heterogeneities to develop at the onset of the experiment. The structural systematics of Fe22+(Cr,Fe3+)2O5 and (Fe2+,Mg)2(Cr,Fe3+)2O5 solid solutions were investigated. It is notable that the Fe3+ and Cr endmembers have somewhat different crystal structures, belonging to space groups Cmcm (no. 63) and Pbam (no. 55), respectively. The phase transition occurs around the midpoint of the Fe3+–Cr joins. In spite of complexities in the behavior of the unit-cell parameters, the variation in molar volume with composition deviates only slightly from linearity. Wüstite and periclase coexisting in our experiments reveal the incorporation of up to 9 wt % and 25 wt % Cr2O3, respectively. This is consistent with the minor Cr contents reported for some ferropericlase inclusions in natural diamond. The limited solubility of other cations in Fe5O6 limits the likelihood of it being an accessory phase in the Earth's deep upper mantle and transition zone, except in Fe-rich environments. In contrast, the O5 phase appears to be more flexible in accommodating a range of divalent and trivalent cations, suggesting that this phase is more likely to be stabilized, potentially where redox reactions related to diamond formation occur.

The Alkynyl π Bond of sp-C Enhanced Rapid, Reversible Li–C Coupling to Accelerate Reaction Kinetics of Lithium Ions

The Alkynyl π Bond of sp-C Enhanced Rapid, Reversible Li–C Coupling to Accelerate Reaction Kinetics of Lithium Ions

Correlative electron microscopy of discontinuous precipitation

This paper presents a comprehensive study on discontinuous precipitation (DP) in Al-22 at.% Zn alloy, leveraging the correlative and synergic effects of advanced microscopy and modelling techniques. The study is structured into three pivotal steps: in-situ scanning electron microscopy combined with an energy backscattered diffraction analysis for real-time monitoring and an analysis of DP reaction kinetics and grain boundary misorientations; transmission electron microscopy and an energy X-ray dispersive microanalysis for detailed observation of solute-depleted α and solute-rich β lamellae, offering insights into the kinetics of the reaction front (RF) and solute concentration profiles; and a sophisticated modelling approach addressing the limitations of direct observation methods by simulating solute concentration changes within αphase lamellae during RF go-and-stop cycles. This multifaceted approach elucidates the nuances of DP mechanisms, from the nucleation and growth of precipitates to the estimation of instantaneous RF velocity and the impact of grain boundary misorientations. The integration of these methodologies enhances our understanding of DP kinetics and morphology at both meso- and nanoscales, highlighting the significant role of correlative microscopy in metallurgical research. The findings not only deepen our grasp of the fundamental mechanisms driving DP reactions but also provide a valuable comparison framework for experimental data, potentially guiding the development and optimization of metallurgical processes.

The water bottle flipping experiment: a quantitative comparison between experiments and numerical simulations

Abstract The water bottle flip experiment is a recreational, non-conventional illustration of the conservation of angular momentum. When a bottle partially filled with water is thrown in a rotational motion, water redistributes throughout the bottle, resulting in an increase of moment of inertia and thus a decrease in angular velocity, which increases the probability of it falling upright on a table as compared with a bottle filled with ice. The investigation of this phenomenom is accessible to undergraduate students and should allow them to gain better understanding of combined translational and rotational motions in classical mechanics. We report a series of detailed experiments that are quantitatively compared with numerical calculations based on a simple theoretical framework in which the water volume is decomposed into thin slices of a rigid body that are subjected to fictitious forces in the non-inertial frame of the spinning bottle. This model also allows us to capture and predict other experimental configurations. Finally, we discuss additional counter-intuitive effects that contribute to bottle stabilization on landing.

Low-temperature reactivity, extinction, and heat release rate of non-premixed cool flame at elevated pressures

Understanding the fundamental characteristics of high-pressure cool flames is crucial for the development of advanced and efficient low-temperature combustion engine technologies. The pressure dependency of multi-oxygen addition branching reactions in low-temperature chemistry significantly influences the dynamics, structure, and reactivity of cool flame. This study investigates the non-premixed cool flame of diethyl ether (DEE) at elevated pressures. The results show that pressure rise promotes low-temperature chemistry and significantly extends the extinction limit of cool flame. It is found that the cool flame heat release rate is correlated with the product of pressure and the square root of the pressure-weighted strain rate, Q∼aP·P, which is different from that of hot flames, Q∼aP. The radical index concept for atmospheric cool flames is extended to high-pressure cool flames allowing to decouple the mass and thermal transports from the chemical kinetics term to evaluate the fuel reactivity at elevated pressures. The radical index shows that the low-temperature reactivity of DEE is enhanced with the pressure and is higher than n-dodecane by a factor of 19, 18.3, and 16.4 for 1, 3, and 5 atm, respectively. Kinetic analysis reveals that pressure rise results in QOOH stabilization and promotions of the second O2 addition and the chain-branching reaction pathway for multiple OH radical productions.

Experimental and chemical kinetic study on effects of H2-DME fusion addition on laminar premixed flame speed and flame instability for ammonia composite combustion

Improvement of the laminar flame speed and stability for ammonia combustion by using H2 and DME has received significant attention. In this study, the characteristics of NH3/H2, NH3/DME and NH3/H2/DME were investigated in constant-volume bomb with high-speed schlieren technique and chemical kinetics. The results show that DME or H2 addition mainly acts as “start-up" or “acceleration" for ammonia laminar flame speed increasing, respectively. In NH3/H2/DME laminar flame, the increase of DME addition ratio not only increases the intensity but also advances the onset of self-acceleration. At ammonia substitution ratio of 10 %–70 %, the Markstein length of NH3/H2/DME flame are all significantly improved compared with pure ammonia flame. The H2-DME fusion-addition can mitigate the reduction of flame thickness and keep a relatively minor thermal expansion ratio. In NH3/H2/DME laminar flame, DME addition can increase the Lewis number greater than 1.0 at ammonia substitution ratio of 10 %–40 %, which significantly reduce the thermo-mass diffusion instability in comparison with H2 addition. Based on mixture design method and experimental validation, it was found that the flame speed at 473 K, 5 bar and φ = 1 for NH3/H2/DME blending ratios of 53.94 %/26.61 %/19.45 % are greater than those of NH3/H2 and NH3/DME with the same ammonia substitution ratios.

Carbonyl Compounds Regulate Atmospheric Oxidation Capacity and Particulate Sulfur Chemistry in the Coastal Atmosphere.

Carbonyl compounds play a crucial role in the formation of ozone (O3) and secondary aerosols, with recent studies particularly highlighting formaldehyde (HCHO) as a significant contributor to the missing particulate sulfur. However, evaluations based on field observations are limited, especially in clean marine environments. Utilizing observation data from a coastal mountain site in May 2021 in Qingdao, northern China, we reveal the important regulating effect of carbonyls in atmospheric oxidation capacity and particulate sulfur chemistry using detailed chemical box models. Photolysis of gaseous carbonyls accounted for >90% and >60% of the primary sources of HO2 and RO2, respectively, contributing 38% of net O3 production. Notably, HCHO alone constituted 80% of the primary HO2 and 15% of net O3 production. Using a multiphase model with updated HCHO-related chemistry, we determine that HCHO chemistry can account for up to 30% of total particulate sulfur (the sum of hydroxymethanesulfonate and sulfate) and address more than one-third of the simulated sulfate gap. The emission-based multiphase model indicates that the HCHO-related pathway remains significant and can account for 20% of the particulate sulfur under clean marine conditions. These findings underscore the importance of carbonyls, particularly HCHO, in regulating the atmospheric oxidation capacity and particulate sulfur chemistry in the marine atmosphere, urging further laboratory studies on chemical kinetics and field measurements of particle-phase carbonyls.

Water structures and anisotropic dynamics at Pt(211)/water interface revealed by machine learning molecular dynamics

Abstract Water molecules at solid–liquid interfaces play a pivotal role in governing interfacial phenomena that underpin electrochemical and catalytic processes. The organization and behavior of these interfacial water molecules can significantly influence the solvation of ions, the adsorption of reactants, and the kinetics of electrochemical reactions. The stepped structure of Pt surfaces can alter the properties of the interfacial water, thereby modulating the interfacial environment and the resulting surface reactivity. Revealing the in situ details of water structures at these stepped Pt/water interfaces is crucial for understanding the fundamental mechanisms that drive diverse applications in energy conversion and material science. In this work, we have developed a machine learning potential for the Pt(211)/water interface and performed machine learning molecular dynamics simulations. Our findings reveal distinct types of chemisorbed and physisorbed water molecules within the adsorbed layer. Importantly, we identified three unique water pairs that were not observed in the basal plane/water interfaces, which may serve as key precursors for water dissociation. These interfacial water structures contribute to the anisotropic dynamics of the adsorbed water layer. Our study provides molecular-level insights into the anisotropic nature of water behavior at stepped Pt/water interfaces, which can influence the reorientation and distribution of intermediates, molecules, and ions—crucial aspects for understanding electrochemical and catalytic processes.

Molten Salt Modulation of Potassium-Nitrogen-Carbon for the Breaking Kinetics Bottleneck of Photocatalytic Overall Water Splitting and Environmental Impact Reduction.

Sluggish interfacial water dissociation and the O2 evolution reaction (OER) kinetics are the main obstacles that limit the photocatalytic overall water-splitting performance. A molten salt modulation of potassium-nitrogen-carbon is herein demonstrated as the formation of highly crystalline potassium-doped poly(triazine imide) (KPTI). The in situ X-ray diffraction patterns and theoretical calculation show that the KCl melt can significantly reduce the free energy for the polycondensation of triazine building blocks owing to the formation of a kinetically stable KPTI. Benefiting from the presence of potassium-carbon-nitrogen moiety, the catalyst not only weakens the excitonic confinement to improve the separation efficiency of photogenerated charge carriers but also enhances the stability of carbon sites by suppressing the undesired C═O formation. Moreover, KPTI accelerates water dissociation by forming interfacial K·H2O clusters with an ordered structure, which supplies sufficient protons for the H2 evolution reaction and lowers the energy barrier to enhance the kinetics of OER. Therefore, a stable photocatalytic overall water-splitting performance can be achieved over KPTI with a stoichiometric generation of products (H2 and O2). Life cycle assessment shows that a carbon-neutral scenario can be achieved on KPTI production in the near term with an increase in green power in the electricity grid.

Optimized Tungsten Disulfide via Pyrolytic Deposition for Improved Zn‐ion Batteries

The selection and optimization of cathode materials are crucial for enhancing the performance of aqueous zinc‐ion batteries. In this work, different active materials were created by combining sulphur powder and polydopamine in four different mass ratios. The novel N‐doped carbon/WS2 is obtained. Thanks to the optimization of the dopamine‐carrying tungsten ion precursor and sulfur powder (1:2, 1:4, 1:6 and 1:8), the four samples exhibited diffenert morphology. The N‐C/WS2‐6‐based zinc ion batteries with the highest specific capacity, 120.0 mAh/g in the first discharge at 2.0 A/g, and 78.0 mAh/g after 2500 cycles, with a capacity retention of 65%, had a relatively good overall performance, according to the results. The reaction kinetics characteristics of the N‐C/WS2‐6 cathode reveal that enhanced pseudocapacitive behavior facilitates the diffusion of Zn2+

High-Density Atomically Dispersed Metals Activate Adjacent Nitrogen/Carbon Sites for Efficient Ammonia Electrosynthesis from Nitrate.

While electrocatalytic reduction of nitrate to ammonia presents a sustainable solution for addressing both the environmental and energy issues within the nitrogen cycle, it remains a great challenge to achieve high selectivity and activity due to undesired side reactions and sluggish reaction kinetics. Here, we fabricate a series of metal-N-C catalysts that feature hierarchically ordered porous structure and high-density atomically dispersed metals (HD M1/PNC). Specifically, the as-prepared HD Fe1/PNC catalyst achieves an ammonia production rate of 21.55 mol gcat-1 h-1 that is at least 1 order of magnitude enhancement compared with that of the reported metal-N-C catalysts, while maintaining a 92.5% Faradaic efficiency when run at 500 mA cm-2 for 300 h. In addition to abundant active sites, such high performance benefits from the fact that the high-density Fe can more significantly activate the adjacent N/C sites through charge redistribution for improved water adsorption/dissociation, providing sufficient active hydrogen to Fe sites for nitrate ammoniation, compared with the low-density counterpart. This finding deepens the understanding of high-density metal-N-C materials at the atomic scale and may further be used for designing other catalysts.

Dual carbon confining SnO2 nanocrystals as high-performance anode for sodium-ion batteries

The increasing global demand for sustainable energy sources has driven research into sodium-ion batteries (SIBs) for large-scale energy storage. However, their electrochemical performance is hindered by poor reaction kinetics and significant volume expansion in electrode materials. In this work, we developed a dual-carbon-confined SnO2 nanocrystal anode (CNTs@SnO2@NC) designed for high-performance SIBs. This innovative structure uses carbon nanotubes (CNTs) and a nitrogen-doped carbon (NC) coating to stabilize SnO2, ensuring structural integrity during charge/discharge cycles. The CNTs network in CNTs@SnO2@NC can alleviate the agglomeration of SnO2 nanocrystals to a certain extent; With its superior electronic conductivity, CNTs can enhance the anode's conductivity and function as an electronic highway; The sodiophilic properties and good electrical conductivity of CNTs enable sodium ions to migrate rapidly on the surface of the nanotubes. Moreover, numerous external defects and active sites generated by nitrogen doping enhance the sodium ion absorption capabilities; The existence of nitrogen-doped carbon coating can effectively accommodate the volume changes of SnO2 and enhance the structural stability of CNTs@SnO2@NC composites during the repeated charge and discharge cycles. As a result, the CNTs@SnO2@NC composite demonstrates excellent electrochemical performance, achieving capacity of 235 mAh g−1 at 0.1 A g−1 over 100 cycles and 102 mAh g−1 at 1.0 A g−1 over 300 cycles. In a full-cell configuration with a Na3V2(PO4)3 cathode, it delivers 38 mAh g−1 at 100th cycle at 0.1 A g−1. This study underscores the substantial improvements achieved by dual-carbon confinement for high-performance SIB anodes, offering a promising direction for future anode material design.

Electron Sponge Effect by Dynamic-Regulated Electron Self-Flow toward Coupled Electrochemical Ammonia Synthesis.

A dynamic-regulated Pd-Fe-N electrocatalyst was effectively constructed with electron-donating and back-donating effects, which serves as an efficient engineering strategy to optimize the electrocatalytic activity. The designed PdFe3/FeN features a comprehensive electrocatalytic performance toward the nitrogen reduction reaction (NRR, yield rate of 29.94 μg h-1 mgcat-1 and FE of 38.43% at -0.2 V vs RHE) and oxygen evolution reaction (OER, 308 mV at 100 mA cm-2). Combining in situ ATR-FTIR, XAS, and DFT results, the role of the interstitial-N-dopant-induced electron sponge effect has been significantly elucidated in strengthening the electrocatalytic NRR process. Specifically, the introduction of a N dopant, an electron acceptor, initiates the generation of robust Lewis-acidic Fe sites, facilitating free N2 capture and bonding. Simultaneously, after NH3 adsorption, the N dopant can back-donate electrons to Fe sites, strengthening the NH3 deportation through weakening the Lewis acidity of Fe centers. Besides, the electron-deficient Fe sites contribute to the reconstruction of FeOOH, the real active species during the OER, which accelerates the four-electron reaction kinetics. This research offers a perspective on electrocatalyst design, potentially facilitating the evolution of advanced material engineering for efficient electrocatalytic synthesis and energy storage.

Revealing the Chemical and Structural Complexity of Electrochemical Ion Exchange in Layered Oxide Materials.

Soft chemistry techniques, such as ion exchange, hold great potential for the development of battery electrode materials that cannot be stabilized via conventional equilibrium synthesis methods. Nevertheless, the intricate mechanisms governing ion exchange remain elusive. Herein, we investigate the evolution of the long-range and local structure, as well as the ion (de)intercalation mechanism during electrochemical Li-to-Na ion exchange initiated from an O3-type lithium-layered oxide cathode. The in situ-formed mixed-cation electrolyte leads to competitive intercalation of Li and Na ions. While Li ion intercalation predominates at the beginning of initial discharge, Na ion cointercalation into a different layer results in ion redistribution and phase separation, with the emergence of a P3-Na phase alongside an O3-Li phase. Further, this study spatially resolves the heterogeneous nature of electrochemical ion exchange reactions within individual particles and provides insights into the correlations between local Ni redox processes and phase separation. Overall, electrochemical ion exchange leads to a mixed-phase cathode and alters its reaction kinetics. Those findings have important implications for the development of new metastable materials for renewable energy devices and ion separation applications.

Toward Practical Li–S Batteries: On the Road to a New Electrolyte

AbstractThe lithium–sulfur (Li–S) battery system has attracted considerable attention due to its ultrahigh theoretical energy density and promising applications. However, with the increasing demands on S loading and electrolyte content, practical Li–S batteries still face several serious challenges, such as slow reaction kinetics at the cathode interface, unstable anode interface reactions, and undesirable crosstalk effects between the cathode and anode. Traditional electrolyte systems often struggle to address these challenges under practical conditions, thereby rendering it imperative to establish a new electrolyte system for practical Li–S batteries. This review first discusses the necessity of establishing a new electrolyte and propose specific parameter requirements, such as the electrolyte‐to‐sulfur mass ratio (Em/S). Subsequently, some electrolyte modification strategies proposed by researchers are summarized to address the different challenges associated with practical Li–S batteries. Finally, the combination of different strategies is reviewed, aiming to reveal more effective design approaches that simultaneously address multiple challenges, while providing guidance for establishing a new balanced electrolyte for practical Li–S batteries. This article promotes the development of new electrolytes for practical Li–S batteries and can act as a reference for the development of electrolytes for other secondary batteries.