Reaction Behavior Research Articles

Behavior of sonochemical reaction in small pipe

Abstract The behavior of sonochemical reactions in a small pipe was investigated by indirect ultrasonic irradiation while circulating potassium iodide solution. At a high electric power, the quenching of sonochemical reactions was observed. The reaction rate increased with the liquid flow velocity in the pipe. The reaction rate changed periodically with the distance between the pipe and the liquid surface, and exhibited minimum and maximum values at every quarter of the wavelength of ultrasound. By placing a reflector on the liquid surface, the reaction was accelerated. Formation of standing wave in the pipe significantly enhanced the reaction rate.

Unraveling the Meaning of Effective Uptake Coefficients in Multiphase and Aerosol Chemistry.

ConspectusReactions of gas phase molecules with surfaces play key roles in atmospheric and environmental chemistry. Reactive uptake coefficients (γ), the fraction of gas-surface collisions that yield a reaction, are used to quantify the kinetics in these heterogeneous and multiphase systems. Unlike rate coefficients for homogeneous gas- or liquid-phase reactions, uptake coefficients are system- and observation-dependent quantities that depend upon a multitude of underlying elementary steps. As such, uptake coefficients adopt complex scaling behavior with reactant concentrations and other physicochemical properties of the interface, making predictions of γ particularly challenging.Typically, γgas is obtained by measuring the loss rate of a gas-phase molecule above a liquid or solid surface, relative to its collision frequency. By definition, γgas ≤ 1. Highly efficient reactions proceed at or near the gas-surface collision frequency and exhibit values of γgas near unity. Alternatively, heterogeneous kinetics are often measured using the consumption rate of a condensed phase reactant normalized to the gas-surface collision frequency, yielding instead an effective uptake coefficient (γeff). In many cases, γeff and γgas are not equal, yielding additional insights into the nature of the reaction. For example, substantial diffusive limitations in the condensed phase may inhibit reactivity, yielding γeff ≪ γgas. In contrast, γeff > γgas in the presence of condensed phase secondary reactions, with values of γeff often exceeding 1 for the case of radical chain reactions.In this Account, we will discuss how measurements of γeff in aerosol can uniquely reveal the origins of complex physical and chemical behavior in multiphase reactions under laboratory conditions. For example, measurements of the scaling of γeff with shell thickness during the ozonolysis of core-shell aerosol yields insight into the relative transport and reaction time scales of gaseous oxidants, while measurements of γeff, as a function of relative humidity (RH) during OH radical oxidation of hygroscopic citric acid aerosol, highlight the role that mixing times of particle-phase reactants play in determining aerosol reaction kinetics. Additionally, the scaling of γeff with oxidant and trace gas concentrations during the oxidation of long-chain hydrocarbons in aerosols by OH radicals and chlorine atoms provides distinctive signatures of the underlying competition between free radical propagation and termination mechanisms. Finally, it is shown how changes in γeff that are induced by careful selection of the molecular structure of the particle-phase reactant help to identify new reaction pathways, such as alternative mechanisms for lipid peroxidation, and to report on the reaction kinetics of short-lived reactive species, including Criegee Intermediates. Together, these examples will demonstrate how proper experimental design and accurate measurements of an effective uptake coefficient can be used to interrogate the fundamental steps governing complex multiphase reaction mechanisms.

CosIn: A statistical-based algorithm for computation of space-speed time delay in pedestrian motion

Precise assessment of Space-speed time delay (TD) is critical for distinguishing between anticipation and reaction behaviors within pedestrian motion. Besides, the TD scale is instrumental in the evaluation of potential collision tendency of the crowd, thereby providing essential quantitative metrics for assessing risk. In this consideration, this paper introduced the CosIn algorithm for evaluating TD during pedestrian motion, which includes both the CosIn-1 and CosIn-2 algorithms. CosIn-1 algorithm analytically calculates TD, replacing the numerical method of discrete cross-correlation, whereas the CosIn-2 algorithm estimates the TD from a statistical perspective. Specifically, the CosIn-1 algorithm addresses the precise computation of TD for individual pedestrians, while the CosIn-2 algorithm is employed for assessing TD at the crowd scale, concurrently addressing the imperative of real-time evaluation. Efficacy analyses of the CosIn-1 and CosIn-2 algorithms are conducted with data from single-file pedestrian experiments and crowd-crossing experiments, respectively. During this process, the discrete cross-correlation method was employed as a baseline to evaluate the performance of both algorithms, which demonstrated notable accuracy. This algorithm facilitate the precise evaluation of behavior patterns and collision tendency within crowds, thereby enabling us to understand the crowds dynamics from a new perspective.

Study of dispersion characteristics and flame propagation, deflagration reaction behaviours of vapor liquid two-phase anhydrous hydrazine and DT-3/air mixtures

Study of dispersion characteristics and flame propagation, deflagration reaction behaviours of vapor liquid two-phase anhydrous hydrazine and DT-3/air mixtures

PtRu Intra‐Cluster Electron Modulation Accelerates Multi‐Scenario Hydrogen Evolution Reaction

AbstractThe development of advanced nanomaterial manufacturing technology and the in‐depth analysis of the structure‐activity relationship are conducive to the sustainable development of platinum‐based catalysts in terms of low cost and high performance. The in situ conversion of Pt4+ and Ru3+ is creatively achieved into highly dispersed, small‐sized heterojunction clusters in the confined space by reductant preset framework materials, and these clusters benefited from the hollow carbon spheres gap supramolecular self‐assembly strategy to achieve high exposure. The intra‐cluster Ru→Pt electron transfer and induced electronic structure modulation enhance the adsorption and activation of H2O molecules at the interface, accelerating the desorption coupling of [H] at the Pt or Ru site. As a catalyst, PtRu/BNHCSs have achieved significant hydrogen production from electrolyzed water in multiple scenarios, exceeding the performance of the commercial Pt/C catalyst. These scenarios include high‐current water splitting to hydrogen in both pH‐neutral and simulated seawater, direct seawater hydrogen production, and anion‐exchange membrane integrated continuous and efficient electrolytic hydrogen production. In situ Fourier transform infrared and in situ Raman interface monitoring techniques reveal the interfacial adsorption behavior of H2O, providing important experimental and theoretical insights for understanding and revealing the synergistic effect and the interfacial reaction behavior of intra‐cluster atoms of PtRu heterojunction.

Mechanism-Inspired Synthesis of Poly(alkyl malonates) via Alternating Copolymerization of Epoxides and Meldrum's Acid Derivatives.

Direct incorporation of malonate units into polymer backbones is a synthetic challenge. Herein, we report the alternating and controlled anionic copolymerization of epoxides and Meldrum's acid (MA) derivatives to access poly(alkyl malonates) using (N,N'-bis(salicylidene)phenylenediamine)AlCl and a tris(dialkylamino)cyclopropenium chloride cocatalyst. This unique copolymerization yields a malonate-containing repeat unit while releasing a small molecule upon MA-derivative ring-opening. Mechanistic and computational studies reveal that the nature of the small molecule released influences overall polymerization kinetics, side reaction behavior, and molecular weight control. Controlled copolymerization of MA derivatives with a range of epoxides ultimately yields a library of new poly(alkyl malonates) with diverse and tunable thermal properties.

Study on the Curing Behaviors of Benzoxazine Nitrile-Based Resin Featuring Fluorene Structures and the Excellent Properties of Their Glass Fiber-Reinforced Laminates.

Benzoxazine and o-phthalonitrile resin are two of the most eminent polymer matrices within high-performance fiber-reinforced resin-based composite materials. Studying the influence modalities of their structures and forming processes on performance can furnish a theoretical basis for the design and manufacturing of superior performance composite materials. In this study, we initially incorporated a fluorene structure into the molecular main chain through molecular design to prepare a fluorene-containing benzoxazine nitrile-based resin. The polymerization reaction behavior and process of this resin were monitored meticulously using differential scanning calorimetry and infrared spectroscopy. Meanwhile, by manipulating the pre-polymerization reaction conditions, the impact of the pre-polymerization reaction on the polymerization behavior of the resin monomer was investigated, respectively. Subsequently, diverse glass fiber-reinforced resin-based composite materials were fabricated via hot-pressing in combination with a programmed temperature rise process. Through the characterization of structural strength and thermomechanical properties, it was found that the composite laminates all manifested outstanding bending strength (~600 MPa) and modulus (>30 GPa). Nevertheless, with the elevation of the post-curing temperature, the structural strength and modulus of the composite materials displayed distinct variation laws. This study also discussed the variation laws of the thermal properties of the composite materials by analyzing the glass transition temperature and crosslinking density. Additionally, the interface bonding effect between the glass fiber and the resin matrix was deliberated through the analysis of the cross-sectional morphology of the composite laminates. The results demonstrated that this work proposes an improved matrix resin system with outstanding thermal stability and mechanical properties that broadens the foundation and ideas for subsequent research.

Photocoloring Reaction Behavior in Spironaphthooxazine Nanoparticles under Nanosecond Pulse Laser Irradiation

Photocoloring Reaction Behavior in Spironaphthooxazine Nanoparticles under Nanosecond Pulse Laser Irradiation

A case study for Improving the performance of CaO-activated slag by the reaction behavior of CaO and NaHCO3

In Alkali-Activated Slag, a contradiction exists among pH, setting speed, and strength development. In this study, the reaction behavior between CaO and NaHCO3 is harnessed to regulate the setting speed while optimizing the material properties. The results demonstrated that the pore solution pH of Alkali-Activated Slag rose to over 12.4. At C5S100, the workability and setting time of the material were comparable to or even surpassed those of ordinary Portland cement. It exhibited a compressive strength of 53.9 MPa at 28 days, which was an 85.2 % increase compared to C5S0, and over 70Mpa at 90 days. Additionally, in the microscopic characterization tests, the composite activator facilitates the dissolution hydration of slag, generating more hydration products. This leads to a more compact structure and lower porosity, thereby enhancing the overall performance. This composite activator strategy effectively reconciled the conflict between the practicality of Alkali-Activated Slag and the setting speed and strength development.

Development of a filtered reaction rate model for the non-equimolar reaction

In many applications, the chemical reaction changes the number of moles of the gas phase and hence affects the gas–solid flow structures and the reaction behavior. This study analyzes the effect of such non-equimolar reaction on the meso-scale reaction rate model. Based on the filter technique and the fine-grid simulation data, a meso-scale reaction rate model is proposed by correcting the model established by Huang et al. (AIChE, 2021, 67 (5)) in which only equimolar reaction is involved. The Reynolds number calculated by the filtered gas–solid slip velocity is found to be an important marker in the correction factor. The effectiveness of the new model is demonstrated by prior tests and also posteriori tests in fluidized beds.

Staged evolutionary features of the aromatic structure in high volatile A bituminous coal (hvAb) during gold tube pyrolysis experiments

Low-temperature pyrolysis of coal is a crucial step in the coal thermal conversion process and involves very complex physical and chemical reactions that can have different effects on the coal's structure. The thermal evolution behavior and transformation mechanism of the coal microstructure are not yet fully understood, which also limits the efficient utilization of coal to a certain extent. The aromatic structural features (including size, molecular ordering, nematic symmetry, stacking, and curvature) of the char produced from low-temperature pyrolysis of high volatile A bituminous coal (hvAb) from the Xutuan coal mine, China, were quantitatively assessed via high-resolution transmission electron microscopy (HRTEM) image processing and analytical techniques. The thermal transformation process and the mechanisms controlling it were explored. The results show that, except for the unexpected slight growth of aromatic sheets at 440 °C, the lower pyrolysis temperature (< 521 °C) contributed weakly to their size growth, whereas at higher temperatures (561–600 °C), it significantly increased their size. The aromatic molecular ordering tended to gradually change in three stages: increasing between 340 and 440 °C, decreasing between 440 and 521 °C and increasing again between 521 and 600 °C. The nematic symmetry strength of aromatic fringes also followed a similar pattern with temperature at different scales. Additionally, in addition to a very minor development trend at 440 °C, the stacking did not significantly change at temperatures below 521 °C but developed appreciably further with increasing temperatures at 561–600 °C; however, the average spacing of the stacks did not appear to be significantly reduced at all temperatures. The curvature of the aromatic sheets also varied in different temperature stages, i.e., initially slightly increasing (340–380 °C), then gradually decreasing (380–480 °C), later increasing again (480–521 °C), and eventually decreasing (521–600 °C). The properties of the chemical composition and structure of the initial coal play important roles in the thermal reaction behavior, and the physical and chemical reactions that dominate at the different temperature stages may be responsible for such wiggly trends in the evolution of the aromatic structure. Notably, the properties of the mesophase (approximately 440 °C) strongly influence the subsequent structural transformation. These findings could provide useful information for the microstructure–property relationships and preparation of coal-based carbon materials.

DABCO-Intercalated α-Zirconium Phosphate as a Latent Thermal Catalyst in the Reaction of Urethane Synthesis.

The mixture of hexamethylene diisocyanate (HDI) and butanol (BuOH) with the intercalation compound of 1,4-diazabicyclo[2.2.2]octane (DABCO) with α-zirconium phosphate (α-ZrP) has been evaluated as a latent thermal catalyst at varying temperatures. α-ZrP·DABCO did not show activity at 25 °C, but showed a high level of activity at a higher temperature of 80 °C. To clarify the reaction behavior of HDI-BuOH with α-ZrP·DABCO, a viscosity value of 1200 mPa·s·g/cm2 was reached at 80 °C for 30 min. To investigate the deintercalation behavior of DABCO from the α-ZrP interlayer, it was investigated in BuOH and in HDI, respectively, under heated conditions. Interestingly, XRD patterns showed a reduction in α-ZrP·DABCO for the interlayer distance due to the deintercalation of DABCO in BuOH, while no changes associated with the deintercalation of DABCO were observed in HDI. Butanol was found to be important for the deintercalation of DABCO. To examine the reactivity of bifunctional monomers, the reaction of 1,4-butanediol (1,4-BDO) and HDI with α-ZrP·DABCO were investigated to show good reactivity at 80 °C and stability at 40 °C.

A novel high-speed homogenizer assisted process intensification technique for biodiesel production using soya acid oil: Process optimization, kinetic and thermodynamic modelling

Acid oils, which are readily available and cost-effective, show promise as a feedstock for biodiesel synthesis. This study focuses on biodiesel production using soya acid oil having high free fatty acids (FFAs) content of 80.65 %. Biodiesel is produced from high-FFA soya acid oil by employing a novel high speed homogenizer technique through esterification process followed by neutralization step. The process variables affecting esterification reaction have been optimized through response surface methodology (RSM) based Box-Behnken Design (BBD) technique. A maximum FFA conversion of 98.06 % was found at a M:O molar proportion of 18.41:1, a process time of 84.62 min, a catalyst amount of 2.18 wt%, and a rotational speed of 14,100 RPM. The determined activation energy for esterification reaction using high speed homogenizer was 36.82 kJ/mol, which is 1.5 to 2 times lower compared to conventional techniques. Thermodynamic behaviour of esterification reaction was studied and analysed. The resulting biodiesel after the neutralization step meets the EN 14214 standard for conversion rate (minimum 96.5 %) and physicochemical properties, ensuring commercial viability.

Challenges on Developing Room-Temperature Rechargeable Magnesium Batteries with Oxide Cathodes

Constructing sustainable energy systems requires rechargeable batteries with high safety, long cycle life and low production costs. Rechargeable magnesium batteries (RMBs) have been expected to be a promising candidate owing to low resource constraints compared to the commercial Li-based batteries. However, the development of RMBs have been stagnated after the first report of a prototype system, which consists of a Chevrel phase cathode, Mo6S8, and a Cl-based electrolyte.[1] The development of high potential oxide cathodes and non-corrosion Cl-free electrolyte encounters significant difficulties. Specifically, for oxide cathodes, the strong Coulomb interaction between Mg2+ and host structures usually inhibits the solid-state diffusion, causing a significant low discharge capacity compared to the theoretical value and rapid capacity loss during cycling.[2] Besides, non-corrosion electrolytes usually passivate Mg metal anodes and/or induce side reactions on oxide cathodes,[3] where remarkably decreases the cell voltage and accelerates the decomposition of electrolytes and active materials.In this presentation, we introduce our efforts to construct room-temperature RMBs with oxide cathodes and Cl-free electrolytes combining both the experimental and computational approaches. To explore suitable host structures for the topotactic Mg2+ intercalation, we revealed the phase transformation pathways and evaluated cathode properties of various transition oxide cathodes (e.g. MnO2 polymorphs) at both elevated temperature (150℃) and room temperature.[3-6] Moreover, to assess the electrolyte compatibility, we discovered the connection between the solvation environment and the reaction behavior on both the oxide cathodes and Mg metal anodes.[3,7] These findings pave the way for room-temperature RMBs using oxide cathodes.[1] D. Aurbach et al, Nature 407, 724 (2000)[2] T. Ichitsubo et al, J. Mater. Chem. A 21, 11764 (2011)[3] X. Ye, H. Li, T. Ichitsubo et al, ACS Mater. Interfaces 14, 56685 (2022)[4] S. Okamoto, T. Ichitsubo et al, Adv. Sci. 2, 1500072 (2015)[5] K. Shimokawa, T. Ichitsubo et al, Adv. Mater. 33, 2007539 (2021)[6] T. Hayakeyama, H. Li, T. Ichitsubo et al, Chem. Mater. 33, 6983 (2021)[7] X. Ye, H. Li, T. Ichitsubo et al, submitted.

Modulating Confined Interlayer Environment By Hard Lewis Acid Cation for Enhancing Oxygen Evolution Reaction

With the increasing demand for hydrogen energy, the non-noble metal catalysts in water splitting for hydrogen production are significant for addressing global environmental issues.[1] Among them, layered transition metal oxide/hydroxide (LTMO/LTMH) materials have drawn more attention for their high tunability of surface or bulk structural transformations after introducing different cations inside the interlayer, which could manifest OER activity.[2] Therefore, birnessite-layered manganese dioxide (MnO2) is considered a potential material for its ability to create a container for cation intercalation, which could significantly enhance its behavior in the oxygen evolution reaction (OER).[3] However, most of the investigations of its application in OER considered MnO2 layers as active sites, which may underestimate the function of intercalated cations and hence blur its real reaction active sites. Using the hard and soft acids and bases (HSAB) theory recently sheds new light and provides a new road for improving OER performance; hard Lewis acid captures hydroxyl and thus speeds up the cleavage of water molecules, generating a demanding local alkaline environment.[4-6] Herein, we grounded the perspective of the intercalated cations based on the HSAB theory, using layered MnO2 as the “container” for accommodating hard Lewis acid cations, achieving using Lewis acid cations for active sites, to enhance OER activity. We use the electrodeposition method to synthesize the precursor layered catalyst, TBA+/MnO2. With the ion exchange process, cations with different Lewis acidities (K+, Fe3+, Co2+, Ni2+, Cu2+, and Zn2+) were intercalated inside this “nano-cell” (interlayer of layered MnO2) to discuss how they influenced the confined surrounding electrolyte environment and electron/mass transport. X-ray diffraction, Raman, and inductively coupled plasma verified the successful synthesis of layered MnO2 with different cations intercalated. The OER results of cation-intercalated MnO2 catalysts exhibited that intercalating the harder Lewis acid significantly influences the interlayer electrolyte environment, markedly accelerating and enhancing the reaction kinetics and OER activity. Furthermore, comparing the OER behavior of intercalated cations, free cations, and bulk metal foils, the intercalated hard Lewis acid cations showed superior reaction kinetics. This work thus provides a clear picture of the role of cations when intercalated into the MnO2 layers during OER and highlights a novel utilization of Lewis acid cations as active sites for enhancing OER activity. Reference [1] Wang, S.; Lu, A.; Zhong, C.-J. Hydrogen Production from Water Electrolysis: Role of Catalysts. Nano Converg. 2021, 8 (1), 4.[2] Kim, Y.; Choi, E.; Kim, S.; Byon, H. R. Layered Transition Metal Oxides (LTMO) for Oxygen Evolution Reactions and Aqueous Li-Ion Batteries. Chem. Sci. 2023, 14 (39), 10644–10663.[3] Ju, M.; Chen, Z.; Zhu, H.; Cai, R.; Lin, Z.; Chen, Y.; Wang, Y.; Gao, J.; Long, X.; Yang, S. Fe(III) Docking-Activated Sites in Layered Birnessite for Efficient Water Oxidation. J. Am. Chem. Soc. 2023, 145 (20), 11215–11226.[4] Pearson, R. G. Hard and Soft Acids and Bases. J. Am. Chem. Soc. 1963, 85 (22), 3533–3539.[5] Zhao, S.; Wang, Y.; Hao, Y.; Yin, L.; Kuo, C.-H.; Chen, H.-Y.; Li, L.; Peng, S. Lewis Acid Driving Asymmetric Interfacial Electron Distribution to Stabilize Active Species for Efficient Neutral Water Oxidation. Adv. Mater. 2024, 36 (7), 2308925.[6] Guo, J.; Zheng, Y.; Hu, Z.; Zheng, C.; Mao, J.; Du, K.; Jaroniec, M.; Qiao, S.-Z.; Ling, T. Direct Seawater Electrolysis by Adjusting the Local Reaction Environment of a Catalyst. Nat. Energy 2023, 8 (3), 264–272. Figure 1

Neutron Depolarization Under Electrochemical Polarization: Investigating Phase Change Reactions in All-Iron Redox Flow Batteries

Large-scale and low-cost energy storage systems are necessary to integrate renewable energy technologies into the electrical grid. Among the options, all-iron redox flow batteries (AIRFBs) are a promising candidate as they can strike a good balance between flexibility and modularity [1]. Additionally, they employ sustainable and abundant raw materials in both half cells, thus decreasing their capital costs and their need for maintenance, which contribute to lower levelized cost of storage [2]. However, AIRFBs still suffer from certain operational challenges, such as the unoptimized and segregated electrodeposition of the active species and the competitive hydrogen evolution reaction [3]. Conventional characterization techniques cannot accurately determine the spatial distribution of both reactions within the electrochemical cell, and thus the operational losses they generate still remain unclear.In recent years, several groups have explored non-invasive operando characterization of RFBs by use of nuclear magnetic resonance[4] or fluorescence microscopy[5], among others. Recently, our group developed a neutron radiography-based method to visualize concentrations in solution of redox or charge carrier species, enabling visualization of local concentration effects [6]. Nevertheless, this approach relies solely on species in solution providing high attenuation, such as H-, B-, or Li- containing electrolytes. Therefore, this attenuation mechanism severely restricts the types of species or phases that can be probed, and the regions of interest where the metal electroplating occurs would remain difficult to quantify with conventional neutron imaging [7].In this work, we expand the workspace of neutron radiography in electrochemical cells to systems employing substances of lower neutron cross section by combining the use of in-plane transmission and polarized neutron imaging. With this dual characterization approach, we are able to visualize for the first time the distribution of iron plated species and hydrogen evolution during electrochemical operation in an all-iron redox flow battery. First, we validate the proposed methodology by performing ex-situ measurements of the depolarization response caused by the magnetic momentum of the various iron-containing species that could form during the charging process of the AIRFB system. We find that only purely ferromagnetic substances (e.g. microscale alpha-iron particles) produce a strong and depolarizing response, with a linear dependence between the depolarization coefficient and the weight fraction of the magnetic phase, thus enabling the detection of subtle changes in plated iron content. On the contrary, weak ferri- or paramagnetic compounds, such as Fe2O3, Fe3O4 or FeOOH, do not cause interference in the measured signal.Subsequently, we run an all-iron redox flow battery at the BOA neutron beamline and performed simultaneous neutron imaging under two modes. By means of the polarization contrast neutron imaging, we tracked the electrodeposition of iron during charge and its removal during discharge within the negative electrode, correlating operating conditions with the distribution of the plated species in the porous carbon electrodes. Simultaneously, the neutron transmission mode and subtractive imaging enabled visualization of hydrogen gas evolution and its dynamics within the cell. These results provide insights into the break-in behavior of phase change reactions and the distribution of the simultaneous reactive fronts of the multiphase, hybrid type of flow cell. In turn, we were able to obtain fundamental understanding of the effects of operational and design parameters, such as electrolyte composition, flow field design and flow distribution geometry, and their impact on the mass transfer characteristics and efficiency of all-iron flow batteries. Acknowledgements IGG gratefully acknowledges financial support by “la Caixa Foundation” (ID 100010434) under the fellowship number LCF/BQ/EU20/11810076. AFC gratefully acknowledges funding by the European Union (ERC, FAIR-RFB, ERC-2021-STG 101042844). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. The results of this project are based on experiments performed at the Swiss Spallation Neutron Source, SINQ, Paul Scherrer Institute (Switzerland), with proposal number 20222727 References [1] Dunn, B., Kamath, H., & Tarascon, J. M. (2011). Science, 334(6058), 928-935.[2] Li, B. & Liu, J. (2017). National Science Review, 4(1), 91-105.[3] Zhang, H., & Sun, C. (2021). Journal of Power Sources, 493, 229445.[4] Zhao, A. et al. (2020) Nature¸ 579, 224[5] Wong, A.A., Rubinstein, S.M. & Aziz, M.J. (2021) Cell Reports Physical Science 2(4), 100388[6] Jacquemond, R.R. et al. (2023) ChemRXiv , ID 10.26434/chemrxiv-2023-8xjv5[7] Kardjilov, N. et al. (2011) Materials. Today, 14(6) 248-256

Effect of Formic Acid on Fuel Cell Performance for Automobile Applications

Introduction The allowable concentration of formic acid is defined as 0.2 ppm in Grade D of ISO 14687: 2019, which is the hydrogen quality specification for fuel cell vehicles. The effect of formic acid in hydrogen on polymer electrolyte fuel cell (PEFC) performance has been reported by some researchers [1-4], but the reaction mechanism of formic acid in the PEFC is not well understood. In this study, the reaction behavior of formic acid in the PEFC and its impact on voltage decrease were investigated. Experimental The effect of formic acid in hydrogen was evaluated using a single cell. A “JARI Cell 2” with a 25 cm2 electrode area and double serpentine flow channels was used in the experiment. The anode and cathode catalysts were Pt/C (TEC10E50E, Tanaka Kikinzoku Kogyo). The platinum loadings on the anode and cathode were 0.05 mg cm-2 and 0.30 mg cm-2, respectively. The electrolyte membrane was a fluorine-based material with a thickness of 12 μm. The 22BB (SGL Carbon) gas diffusion layers were used on both the anode and cathode.The single-cell tests were performed at a cell temperature of 60°C and without external humidification. This is because formic acid easily dissolves in water and is likely to be exhausted from the cell with water at high humidification, so no humidification is considered the most severe condition. Before formic acid addition, the preconditioning was conducted at 1.0 A cm-2 of current density using high-purity hydrogen as a fuel for more than 10 hours. Then, formic acid (15-300 ppm) was started to supply the anode. After a period of time, the supply of formic acid to the anode was stopped and the voltage recovery was evaluated. Results and discussion Figure 1 shows the voltage drop over time due to formic acid in hydrogen at a current density of 1.0 A cm-2 and cell temperature of 60˚C. The voltage dropped quickly after the start of the formic acid supply, but the amount was small even at high formic acid concentrations. The voltage drop due to formic acid was 14 mV after 25 hours at 60 ppm and 20 mV after 5 hours at 300 ppm. The voltage was recovered after stopping the formic acid addition.To understand the reaction behavior of formic acid during the fuel cell operation, the anode and cathode exhaust gas were analyzed by gas chromatograph-mass spectrometer. The result showed that no formic acid was detected from the anode or cathode while the fuel cell was operated at a current density of 1.0 A cm-2 with 15 ppm formic acid addition to the anode. Meanwhile, the amount of CO2 equivalent to that supplied to the anode as formic acid was detected from the cathode exhaust gas. The results suggest that formic acid supplied to the anode permeated through the electrolyte membrane as shown in Fig. 2 and was oxidized at the cathode. Acknowledgment This work is based on results obtained from a project, JPNP18011, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Multivalent Cation Additives for Building Dendrite-Free and Stable Electrode-Electrolyte Interface on Lithium-Metal Anodes

Li-metal anodes are ideal anode materials for Li-based batteries owing to high theoretical capacity and low redox potential. However, the practical application of Li-metal anodes face challenges, such as uneven deposition morphology and progressive electrolyte decomposition during repeated Li deposition and dissolution. To improve the reversibility, high-concentration electrolytes (HCEs), such as 4 M Li[FSI] in DME,[1] have been reported to effectively flatten the deposition morphology and improve the Coulombic efficiency. Nevertheless, HCEs have several limitations, including poor oxidation stability, high viscosity, and high production costs.[2] Therefore, technologies for creating the HCEs’ features in lower concentration ranges are expected to be developed.In this presentation, we introduce an effective approach to utilize multivalent cations (e.g. Ca2+, Ba2+) as electrolyte additives to construct dual-cation electrolytes (DCEs) for Li-metal anodes. Because multivalent cations have much stronger coordination with anions and solvent molecules than Li+, it is usually difficult to reduce multivalent cations to metal state in organic electrolytes. When multivalent cations are mixed with Li+ in electrolytes, the Coulomb interaction among different cations would modify the solvation structure. Anions are promoted to directly coordinate with cations increasing the ratio of the contact-ion pairs (CIPs) to diminish the free energy of the electrolyte system.[3] This phenomenon creates the solvation environment similar to HCEs, which contributes to maintaining a dendritic-free deposition morphology. Furthermore, as a unique feature of DCEs, multivalent cations are prone to be involved in the formation of solid-electrolyte interphase (SEI) in addition to Li+. The chemical bonds between multivalent cations and the other SEI compositions (e.g., F, O, S, C and N) can enhance the structural stability and functionality of SEI, as an effective controlling factor for the reaction behavior of Li-metal anodes.[4][1] J. Qian, J-G. Zhang et al, Nat. Commun. 6, 6362 (2015)[2] Y. Yamada, A. Yamada et al, Nat. Energy 4, 269 (2019)[3] H. Li, T. Ichitsubo et al, Cell Rep. Phys. Sci. 3, 100907 (2022)[4] H. Li, T. Ichitsubo et al, submitted.

Electrochemical Properties of Lif-Coated Graphite Negative Electrode Modelized By Atomic Layer Deposition

Introduction In recent years, carbon dioxide emissions are rapidly increasing, and electric vehicles (EVs) are expected to play a significant role towards achieving a carbon-neutral society with most of them utilizing Lithium-Ion Batteries (LIBs). The negative electrode active material of LIB is typically made of graphite, and during initial charging, the electrolyte undergoes reductive decomposition at the graphite/electrolyte interface, forming a Solid-Electrolyte Interphase (SEI). SEI exhibits lithium-ion conductivity while being electronically insulating, facilitating highly efficient charging and discharging by suppressing further electrolyte decomposition. On the other hand, the formation of SEI consumes lithium ions, resulting in irreversible capacity loss[1]. Therefore, the nature of SEI has a significant impact on LIB performance. Regarding the composition of SEI, it is known to comprise clusters of inorganic compounds such as LiF, Li2CO3, Li2O and organic decomposition products like polyolefins. Each component has different properties such as LiF was reported to have lower lithium-ion diffusion barrier and higher chemical stability than other inorganic components[2]. However, many aspects of the individual electrochemical roles are still unclear, and forming an excellent SEI is an important issue. Objective In this work, we focused on LiF, which is considered to be a crucial component in SEI[3], and modelized the LiF-coated graphite by employing atomic layer deposition (ALD) on highly oriented pyrolytic graphite (HOPG). We investigated the influence of LiF on the lithium-ion transfer reaction behavior at the graphite/electrolyte interface. Experimental Highly oriented pyrolytic graphite (HOPG) served as the graphite negative electrode, and atomic layer deposition (ALD) was used for the LiF coating. Regarding ALD, LiN(Si(CH3)3)2 and WF6 were used as the Li and F sources, respectively. The deposition temperature was set at 300 °C, and HOPG was deposited at various numbers of cycles (10, 30, 60, and 90 times). X-ray photoelectron spectroscopy (XPS) was performed to analyze the electrode after the ALD coating. Regarding electrochemical measurements, the setup utilized a three-electrode cell with HOPG as the working electrode, lithium metal as the counter and the reference electrodes. 1.0 mol dm−3 LiClO4/EC+DEC (1:1 vol.%) was used as the electrolyte. Cyclic voltammetry (CV) was performed at a scanning rate of 0.1 mV s−1 and a scanning range of 0.005 – 3 V (vs Li+/Li). Electrochemical impedance spectroscopy (EIS) was performed at an applied AC voltage of 5 mV and a frequency range of 100 kHz – 10 mHz. EIS measurement was also performed at different temperature with a holding potential of 0.2 V to obtain activation energy. Results and discussion For the HOPG electrode coated with LiF, XPS analysis was performed and it was confirmed that the LiF coating layer was thickening as the number of coating cycle increased. In the CV measurement results, redox peaks were observed in the range of 0 – 0.6 V, confirming that the intercalation-deintercalation reaction of lithium ion was progressing. From the Nyquist plot obtained by EIS measurements, semicircles derived from SEI were observed in the high frequency region, and semicircles derived from charge transfer resistance were observed in the medium and low frequency regions. The activation energy of the charge transfer resistance was calculated by fitting the Nyquist plot (Figure 1) obtained from the temperature-dependent measurement of EIS, and revealed that the values were 54.8 kJ mol−1 for the uncoated HOPG electrode, 55.1 kJ mol−1 for 10 coatings, and 52.8 kJ mol−1 for 30 coatings, respectively, showing no significant change. On the other hand, the activation energy slightly decreased with increasing number of depositions, which was found to be 49.7 kJ mol−1 and 50.0 kJ mol−1 in the case of 60 and 90 coatings, respectively. This suggests that when the LiF coating layer reaches a certain thickness, lithium-ion charge transfer between the electrolyte and the electrode becomes easier. Details will be discussed in the conference.

Design Guidelines for Cathode/Electrolyte Interface of Room-Temperature Rechargeable Magnesium Batteries with MnO2 Cathodes

Rechargeable magnesium batteries (RMBs) are strong candidates for large-scale energy storage systems due to their high theoretical energy density, high safety, and low production costs. However, the sluggish solid-state diffusion of Mg2+ in cathode materials and surface passivation of Mg metal anode in organic electrolytes are the main reasons for the stagnant development of RMBs. Since 2015, we have first reported the reversible Mg2+ insertion in a series of oxide cathode materials (MgCo2O4, etc.) at 150 ℃.[1] To explore suitable host structures at room temperature (RT), we have been comprehensively investigated the phase transformation pathways of various MnO2 polymorphs (α, β, γ, δ, and λ) and revealed that the hollandite-type α-MnO2 allows topotactic Mg2+ intercalation up to 200 mAh g-1 as a metastable host structure.[2] To construct full cells, we further investigated the reaction behavior of MnO2 cathodes in two representative electrolytes at room temperature.[3] In 2.26 M Mg[TFSA]2/G3 (saturated concentration at RT), the α-MnO2 cathode had a discharge capacity of about 110 mAh g-1 that was confirmed to be mainly derived from the Mg2+ intercalation. However, the Mg metal anodes were easily passivated in this electrolyte, leading to a significant decrease in discharge voltage. On the other hand, in 0.3 M Mg[Al(hfip)4]2/G3,[4] which allows reversible deposition/dissolution on Mg metal anodes, the MnO2 cathode was involved into the cathodic decomposition of the electrolyte species, where the Mg2+ intercalation was difficult to be maintained.To establish design guidelines for a stable and functional cathode/electrolyte interface, we revealed the reaction mechanism of the α-MnO2 cathode in these two electrolytes with various experimental and computational methods. In 2.26 M Mg[TFSA]2/G3, [TFSA]- has close coordination with Mg2+ as contact-ion pairs (CIPs) and a lower energy level of lowest unoccupied molecular orbital (LUMO) compared to the free state.[5] As a result, [TFSA]- is prone to be involved in the cathodic decomposition and significantly increase the F ratio on the α-MnO2 cathode after discharge. As shown in Fig .1, the decomposition products formed an SEI-like layer which would protect the active particles to enable the genuine Mg2+ intercalation. Conversely, in 0.3 M Mg[Al(hfip)4]2/G3, because [Al(hfip)4]- can only exist in free state and is almost not involved the cathodic decomposition, the protective layer was absence on the α-MnO2 cathode. This results in an unstable cathode/electrolyte interface, from where O2- was released from the host structure to the electrolyte instead of the expected Mg2+ intercalation for charge compensation of Mn reduction.[1] S. Okamoto, T. Ichitsubo et al, Adv. Sci. 2015, 2, 1500072. [2] T. Hatakeyama, H. Li, T. Ichitsubo et al, Chem. Mater. 2021, 33, 6983. [3] X. Ye, H. Li, T. Ichitsubo et al, ACS Appl. Mater. Interfaces. 2022, 14, 56685-56696. [4] J. Herb et al, ACS Energy Lett. 2016, 1, 1227–1232. [5] H. Li, T. Ichitsubo et al, Cell Reports Phys. Sci. 2022, 3, 100907. Figure 1