Desorption Energy Research Articles

Amorphization Stabilizes Te-Based Aqueous Batteries via Confining Free Water.

Tellurium (Te), with its rich valence states (-2 to +6), could endow aqueous batteries with potentially high specific capacity. However, achieving complete and stable hypervalent Te0/Te4+ electrochemistry in an aqueous environment poses significant challenges, owing to the sluggish reduction kinetics, easy dissolution of Te4+ species, and a controversial energy storage mechanism. Herein, we demonstrate a crystallographic regulation strategy for robust aqueous Te redox electrochemistry. With strong hydrogen bonding, NH4Ac confines free water, prompting the amorphization of TeO2 (a-TeO2). In situ synchrotron characterization, spectroscopy analysis, electrochemical evaluation, and theoretical calculations reveal a specific 4 e- solid-solid transition pathway (Te to a-TeO2) with accelerated diffusion and charge transfer kinetics, attributed to a closer unoccupied electron orbital to the Fermi level and a reduced water desorption energy barrier in a-TeO2. Impressively, the a-TeO2/Te redox exhibits a high reversible capacity of 834 mAh g-1 (99% of Te redox utilization), superior rate performance (644 mAh g-1 at 10 A g-1), and an ultralong lifespan (over 3000 cycles). These findings prove a new tactic to advance aqueous Te redox electrochemistry toward high-energy aqueous batteries.

Impact of partial regeneration method on the reduction of CO2 desorption energy

Amine-functionalized solid materials have shown efficacy for low-concentration CO2 environments; however, their regeneration is often hindered by slow desorption kinetics at low temperatures. To address this, an innovative approach termed “The Partial Regeneration Method” is introduced as a driving method to enable low-temperature regeneration of CO2 adsorbents at low concentration levels. Analysis of desorption kinetics mechanisms reveal that at low temperatures, CO2 molecules exhibit reduced kinetic energy and intraparticle diffusion coefficients. Furthermore, as it approaches chemical equilibrium temperature, the re-adsorption reaction rate increases. The partial regeneration method which selectively targets CO2 molecules with low re-adsorption rates could be more effective in a such low temperature conditions. This method involves intentionally halting regeneration midway and proceeding to the next adsorption process. Experimental application of specific energy requirements and scenario analysis demonstrated a 50.7% decrease in energy consumption compared to the conventional methods. By optimizing amine loading to reduce excessive re-adsorption, the shortened cycle period compensates for the decreased adsorption per cycle. Increasing the number of cycles led to a 97.5% improvement in CO2 adsorption capacity over a one-month period. Thus, when faced with unavoidable inefficient low-temperature regeneration conditions, the proposed partial regeneration method emerges as a promising solution for minimizing energy consumption.

Covalent Organic Frameworks with Regulated Water Adsorption Sites for Efficient Cooling of Electronics.

The excessive heat accumulation has been the greatest danger for chips to maintain the computing power. In this paper, a passive thermal management strategy for electronics cooling was developed based on the water vapor desorption process of the covalent organic frameworks (COFs). The precise regulation for the number of carbonyl group and the ratio of hydrophilicity and hydrophobicity within pore channels was achieved by water adsorption sites engineering. In particular, COF-THTA with abundant water adsorption sites exhibited highest water uptake and desorption energy, which facilitate efficient cooling of electronics. In proof-of-concept testing, COF-THTA coating (40×40 mm) provided a temperature drop of 7.5 °C in 25 minutes at a heating power of 937.5 W/m2, and remained stable after 10 intermittent heat cycles. Furthermore, the equivalent enthalpy of COF-THTA coating can reach up to 1136 J/gcoating. In real application scenarios, COF-THTA coating improved the performance of two real computing devices by 26.73 % and 22.61 %, respectively. This strategy based on COFs provides a new thinking for passive thermal management, exhibiting great potential in efficient cooling of electronics.

MOF-derived S, N co-doped porous carbon matrix with single Fe atoms and CoSx nanoparticles dual-sites for enhanced oxygen reduction

Metal-air batteries, as a clean energy technology, are of great significance in alleviating the increasingly serious energy and environmental problems, but the sluggish oxygen reduction reaction (ORR) kinetics of air–cathode severely restrict their development. In this work, a zeolitic imidazole frameworks (ZIFs)-derived dual-site electrocatalyst (Fe/CoSx-SNC) composed of Fe single atom and ultrafine cobalt sulfide nanoparticle sites supported on S, N co-doped porous carbon was successfully prepared. Benefited from the advantages of large specific surface area, high porosity, high-density metal centers, and synergistic effects between the dual sites, Fe/CoSx-SNC electrocatalyst presents excellent electrocatalytic ORR activity with a half-wave potential of 0.885 V, a kinetic current density of 27.00 mA cm−2 (at 0.80 V), and good stability, which are superior to the commercial 20 % Pt/C catalyst. The density functional theory (DFT) calculations reveals that the presence of cobalt sulfide nanoparticles could effectively modulate the electron density around Fe single atom, which reduces the desorption energy barrier (rate-determining step) of *OH on Fe sites. In addition, the rechargeable zinc-air battery assembled with Fe/CoSx-SNC as air cathode oxygen catalyst exhibits a high peak power density of 156.63 mW cm−2 and over 100 h of cycling stability. This study provides a straightforward and feasible approach to precisely adjusting the coordination environment and constructing high-performance metal single-atom-based oxygen electrocatalysts, which will be beneficial to promoting the development of metal-air batteries.

Design of alkali metal oxide adsorbent for direct air capture: Identification of physicochemical adsorption and analysis of regeneration mechanism

Direct air capture (DAC) represents an advanced negative carbon emission technology, with the key being high-performance CO2 adsorbents. First, this work carefully identifies CO2 physisorption and chemisorption by CaO/HcATP (CaO loaded on acid-modified attapulgite) as DAC adsorbent. The chemisorption of amorphous "CaO" plays a crucial role in both the adsorption capacity and rate, with contributions of 66.8 % and 50.85 %, respectively. The adsorption capacity of CaO/HcATP is only 212.4 ± 25.7 µmol/g via the simple CO2 physisorption and improved by 426.7 µmol/g owning to the chemisorption of amorphous CaO. Second, the concentration of silanol groups on CaO/HcATP plays a pivotal role in the adsorption process. The concentration of silanol groups decreases to 3.85 OH/nm2 after undergoing 30 cycles of adsorption-desorption. Then it increases to 9.54 OH/nm2 by adsorbing the moisture in the air, resulting in a recovered adsorption capacity of 90.7 %. Furthermore, the pseudo-first-order adsorption kinetics model effectively predicted the experimental results. Finally, the dual loop of CO2 capture and regeneration is summarized using the CaO/HcATP as DAC adsorbent. The amorphous "CaO" interacts with the surface silanol of HcATP, synergistically capturing CO2 in the form of "CaO···CO2", which reduces desorption energy consumption. The wetting property of HcATP contributes to the regeneration of CaO/HcATP. This work contributes to establishing fundamental principles for designing cost-effective DAC adsorbents.

In-situ engineering of 3D amorphous/crystalline NiFeP/NiMoP/NF composite for improved hydrogen evolution

Developing High-performance, low-cost, and non-noble-metal hydrogen evolution reaction (HER) electrocatalysts are one of the particularly significant elements to triumph over the slow kinetics of water dissociation. However, utilizing non-noble metal electrocatalysts at large-scale applications remains a significant challenge. This work informs the fabrication of porous amorphous NiFeP nanostructures on crystalline NiMoP/NF nanoflakes morphology via straightforward two-step electrodeposition and hydrothermal processes as a binder-free 3D hetero-structured composite catalyst for reliable HER. Based on experimental characterizations and density functional theory (DFT) calculations, the optimized NiFeP@NiMoP@NF electrocatalyst exhibits a favorable amorphous/crystalline morphology and an intrinsic metallic phase. This structure facilitates efficient charge transport and exposes abundant active sites with strong electronic interactions between NiFeP and NiMoP, significantly optimizing the adsorption and desorption energy of H2O and thus leading to easy adsorption of H and OH− on NiFeP@NiMoP and promoting the bubble release, finally improving electrocatalytic HER performance in alkaline media (only need an overpotential of 40 mV to conduct a current density of 10 mA cm−2). The rational and affordable developing technique in this study not only implies the importance of interface engineering in catalyst construction but also opens a new route for synthesizing high-efficiency Ni-based electrocatalysts for a variety of water electrolysis applications.

Decoupling Catalyst and Electrolyte Temperatures to Steer Activity and Selectivity of Electrochemical CO2 Reduction

Despite global initiatives to address climate change, the year 2023 was the hottest year ever recorded in history. The need for technologies to lower carbon emissions and to remove already emitted greenhouse gases is immense. There have been massive efforts to electrochemically drive CO2 conversion to value-added chemicals such as ethylene, ethanol, and acetone using renewable energy.(1) Copper (Cu) is notable for its ability to form high-value C-C bond compounds; however, selectivity and activity challenges remain. Efforts to tackle these issues have focused on catalyst, system and micro-environment developments,(2, 3) and among the critical factors, temperature plays an important role. Of reports that study temperature effects on CO2 reduction (CO2R), usually the entire system is controlled at the same temperature, including the working electrode, electrolyte, and reference electrode. Further, the range of accessible temperatures is usually limited to a range of 10 – 70°C due to the aqueous electrolyte freezing or evaporating.(4, 5)This study focuses on the development and demonstration of an electrochemical system for decoupling the temperatures of the CO2R cathode and the electrolyte. This allows independent optimization of thermodynamic, mass transport, and kinetic, to improve both activity and selectivity of CO2 reduction. The temperatures are separately controlled from 0 – 140 °C for the working electrode, and from 0 – 70°C for the electrolyte. These temperature gradients result in clearly different activity/selectivity trends compared to when a single temperature controls the entire system. While maintaining electrolyte temperature and current density, a lower cathode temperature favored methane formation, whereas a higher cathode temperature favored CO formation. The Faradaic efficiency of ethylene was maintained at 20% despite the changes in the temperature of the cathode. Furthermore, reducing the working electrode temperature effectively restricted H2 formation down to 15%. We attributed this selectivity and activity change to the control of adsorption and desorption energies, thermal and chemical processes of CO2 conversion, and changopanoles in the CO2 solubility in the electrolyte through density function theory and computational fluid dynamics simulations.(6, 7) The system and method developed in this study can be translated to understanding the effects of mass transport and kinetics in other emerging electrochemical conversions for accelerating clean energy generation and achieving global sustainability goalsReferences K. P. Kuhl, E. R. Cave, D. N. Abram, T. F. Jaramillo, New insights into the electrochemical reduction of carbon dioxide on metallic copper surfaces. Energy Environ. Sci. 5, 7050–7059 (2012).D. Higgins, C. Hahn, C. Xiang, T. F. Jaramillo, A. Z. Weber, Gas-Diffusion Electrodes for Carbon Dioxide Reduction: A New Paradigm. ACS Energy Lett. 4, 317–324 (2019).Y. Hori, K. Kikuchi, S. Suzuki, Production of CO and CH4 in Electrochemical Reduction of CO2 at Metal Electrodes in Aqueos Hydrogencarbonate Solution. Chemistry Letters 14, 1695–1698 (1985).R. E. Vos, K. E. Kolmeijer, T. S. Jacobs, W. van der Stam, B. M. Weckhuysen, M. T. M. Koper, How Temperature Affects the Selectivity of the Electrochemical CO2 Reduction on Copper. ACS Catal. 13, 8080–8091 (2023).S. T. Ahn, I. Abu-Baker, G. T. R. Palmore, Electroreduction of CO2 on polycrystalline copper: Effect of temperature on product selectivity. Catalysis Today 288, 24–29 (2017).Y. Zong, P. Chakthranont, J. Suntivich, Temperature Effect of CO2 Reduction Electrocatalysis on Copper: Potential Dependency of Activation Energy. Journal of Electrochemical Energy Conversion and Storage 17, 041007 (2020).K. P. Kuhl, T. Hatsukade, E. R. Cave, D. N. Abram, J. Kibsgaard, T. F. Jaramillo, Electrocatalytic Conversion of Carbon Dioxide to Methane and Methanol on Transition Metal Surfaces. J. Am. Chem. Soc. 136, 14107–14113 (2014). Figure 1

Optimization of Oxygen Reduction Activity Via Transition Metal-Oxide Based Composite Electrodes in Acidic Medium

Global warming has occurred due to the usage of fossil fuels and greenhouse gas emissions. Therefore, a change in the energy paradigm can overcome the problems of global warming and air pollution and provide new energy to humanity continuously. Fuel cells are an eco-friendly system that utilizes the electricity generated during the process of producing water from hydrogen fuel. In general, 20 wt% Pt/C is used as the commercial catalyst for polymer electrolyte fuel cells (PEFCs), but challenges remain to solve such as cost and durability. In PEFCs, oxygen reduction reaction (ORR) is an important key as a rate-determining step (RDS) to react the overall reaction. Therefore, it is necessary to develop efficient materials (electrode, membrane, cell, etc.) for improving RDS. Recently, transition metal oxide (TMO) composite electrodes have gained interest in the electrochemical fields. Especially, nickel, cobalt, iron-based oxides are promising materials as non-noble metal electrocatalysts due to their high electric conductivity and various oxidation state.The purpose in this research is to improve ORR performance by controlling active sites and electric conductivity using low amount of noble metals on transition metal doped oxides for the use at the electrode. We have developed composite oxide electrodes with noble-transition metal alloy using solid-state methods. Small amount of noble metal can be alloyed with transition metal to form appropriate oxygen binding energy for oxygen adsorption and desorption, which can improve ORR activity. To check the catalytic activity, cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were analyzed using a rotating disk electrode, and it was found that the noble metal-transition metal alloy oxide composite electrode was effective in enhancing the ORR kinetics. Additionally, the strong interaction between the alloy nanoparticles and oxide support surface enhances chemical stability when used in harsh environments such as acidic media. Furthermore, based on the previous ORR data, we fabricated membrane electrode assembly (MEA) using developed catalysts and confirmed their potential for PEFCs applications.

Scalable Synthesis of AgCl-Derived Ag Structures for Electrochemical CO2 Reduction

Electrochemical CO2 reduction reaction (CO2RR) has the potential to serve as a competent technology capable of reducing the CO2 levels in the atmosphere while utilizing renewable energy. The CO generated from the CO2RR forms a component of syngas (CO/H2), which is highly demanded in the market and industry, recognized for its value as a chemical feedstock. However, to achieve an industrial-level current density, improvement in the CO2-to-CO catalyst is necessary. Au, Ag, and Zn exhibit high CO selectivity in the CO2RR due to their low CO desorption energy barrier and poor hydrogen binding energy, showing over 90% FE of CO. Particularly, Ag is considered a promising catalyst due to its high durability, selectivity, and moderate price. However, it fails to suppress HER at high potential and current regions, limiting the incretion in CO current density.In this study, we developed a scalable AgCl nanocube catalyst for the CO2RR using a sonochemistry-based method. The AgCl nanocube achieved a CO current density of over 400 mA cm-2 in a 0.1 M KHCO3 electrolyte using an MEA cell. AgCl releases Cl and forms Ag surface through an electrochemical reduction process, resulting in AgCl-derived Ag catalysts. This AgCl-derived surface possesses high porosity, enhancing CO2 mass transfer, and promote CO2 adsorption through charged surfaces, leading to high CO current density. The uniform AgCl nanocube catalyst, which can be synthesized on a gram scale under mild conditions, offers cost-effective and rapid catalyst supply. During the reduction process, the AgCl nanocubes break into smaller particles, resulting in an AgCl-derived Ag catalyst with an increased surface area. Surface spectroscopic analysis revealed enhanced CO2 adsorption and the presence of Cl remaining on the catalyst surface. As a result, the AgCl nanocube successfully suppressed HER at high potential regions, maintaining a high level of CO selectivity, thereby increasing the productivity of CO2-to-CO electroreduction. A rapid and scalable synthetic method for nanoparticle that simultaneously obtains a reagent (Cl) that enhances the reaction and a CO2RR catalyst (Ag) could provide insights for future catalyst development.

Elementary Steps of Catalytic Reactions Occurring on Metallic Alloy Nanoparticles.

Catalytic reactions running in an adsorbed overlayer on metallic alloy nanoparticles are of high interest in the context of applications in the chemical industry. The understanding of the corresponding kinetics is, however, still limited. One of the reasons of this state of the art is the interplay between adsorption and adsorbate-influenced segregation of metal atoms inside alloy nanoparticles. I scrutinize this interplay by using a generic field model of segregation and the mean-field approximation in order to describe adsorption, desorption, and elementary catalytic reactions. Under steady-state conditions, the segregation is demonstrated to be manifested in the change of the dependence of the activation energies of desorption or elementary reactions on coverage, and the sign of this change is positive. The effect of this change on the apparent reaction orders is briefly discussed as well.

Integrated capture and conversion of CO2 to methane using deep eutectic solvents under mild conditions

Addressing the issues of absorbent regeneration, CO2 compression and purification, and energy consumption during transportation in the integrated carbon capture and utilization (ICCU) process, an integrated technology for CO2 capture and hydrogenation conversion has been proposed. In this study, deep eutectic solvents (DESs) composed of tetramethylguanidine (TMG) and ethylene glycol (EG) were employed to capture and hydrogenate CO2. When a heterogeneous Ru-based catalyst and a TMG:EG DES were used as a catalytic system, CO2 methanation was achieved under mild conditions (170 °C and 8 MPa H2 pressure), with a CH4 yield of up to 75 % and a conversion number (TON) of 148. Importantly, the structure of the DES remained unchanged before and after the reaction, and the catalytic system could be reused three times without significantly diminishing the effectiveness of CO2 hydrogenation. This method not only reduces desorption energy consumption but also benefits from the absorbent’s high specific heat capacity, enabling the absorbent to absorb the heat generated during CO2 hydrogenation and addressing issues such as carbon deposition and catalyst deactivation resulting from poor heat transfer.

Surface reactions of ethanol on UO2 thin film. Dehydrogenation and dehydration pathways

The reaction of ethanol has been investigated on a UO2 thin film by temperature programmed desorption. Two channels for ethanol desorption are identified. The first, in the 250–500 K region, is coverage dependent while the second with a maximum peak temperature (Tp) at ca. 630 K is not. The desorption energy, Ed, of the second channel is found to be equal to ca. 150 kJ/mol with a prefactor of 1012 s−1 and a desorption order n = 2. This is attributed to surface ethoxides re-combinative desorption. This second desorption channel is accompanied by the desorption of acetaldehyde (and hydrogen) and ethylene (and water). Acetaldehyde (CH3CHO) desorption, produced by the dehydrogenation of ethoxides, was sensitive to surface coverage. Its Tp changed from 640 K at θ = 0.06 to 610 K at θ = 1, while ethylene (CH2CH2) desorption Tp, produced by the dehydration of ethoxides did not shift. The molar ratio of these two products (CH3CHO/CH2CH2) of 0.8 is similar to that previously found on a UO2(1 1 1) single crystal and fits with the UO bonding nature that contains a non-negligible fraction of covalency.

Hydrogen desorption kinetics of hafnium hydride powders

The kinetics of hydrogen gas release from hafnium hydride are investigated by combining experiments and density functional theory. The material is a candidate neutron shield for compact nuclear reactors, where hydrogen release will lead to a degradation in moderating function. Experimentally, we have studied the decomposition of epsilon phase (HfH2-x) powders from 25 to 1000 °C using thermogravimetry and X-ray diffraction. Isochronal heating reveals 3 characteristic desorption peaks corresponding to the release of hydrogen from each phase (ε-HfH2-x, δ-HfH1.6-x and α-Hf), at ∼ 350, 415, and 700 °C. This is well supported by the modelling output from density functional theory. A Kissinger analysis allowed for activation energies for desorption to be calculated (∼150 kJ/mol, 170 kJ/mol and 90 kJ/mol respectively). The peak shape and desorption rate data suggests that a second order diffusion limited reaction controls the ε→ε+δ desorption, a first order interface limited reaction controls ε+δ→δ, and a surface limited zeroth order reaction limits the desorption of the δ+α phases. The analysis suggests that, at least for δ→α regime, engineering solutions for improved thermal stability should focus on reductions in surface reactivity.

Enhancement of Water Productivity and Energy Efficiency in Sorption-based Atmospheric Water Harvesting Systems: From Material, Component to System Level.

To address the increasingly serious water scarcity across the world, sorption-based atmospheric water harvesting (SAWH) continues to attract attention among various water production methods, due to it being less dependent on climatic and geographical conditions. Water productivity and energy efficiency are the two most important evaluation indicators. Therefore, this review aims to comprehensively and systematically summarize and discuss the water productivity and energy efficiency enhancement methods for SAWH systems based on three levels, from material to component to system. First, the material level covers the characteristics, categories, and mechanisms of different sorbents. Second, the component level focuses on the sorbent bed, regeneration energy, and condenser. Third, the system level encompasses the system design, operation, and synergetic effect generation with other mechanisms. Specifically, the key and promising improvement methods are: synthesizing composite sorbents with high water uptake, fast sorption kinetics, and low regeneration energy (material level); improving thermal insulation between the sorbent bed and condenser, utilizing renewable energy or electrical heating for desorption and multistage design (component level); achieving continuous system operation with a desired number of sorbent beds or rotational structure, and integrating with Peltier cooling or passive radiative cooling technologies (system level). In addition, applications and challenges of SAWH systems are explored, followed by potential outlooks and future perspectives. Overall, it is expected that this review article can provide promising directions and guidelines for the design and operation of SAWH systems with the aim of achieving high water productivity and energy efficiency.

Infrared spectra of solid-state ethanolamine: Laboratory data in support of JWST observations

Context. Ethanolamine (NH2CH2CH2OH; EA) has been identified in the gas phase of the interstellar medium within molecular clouds. Although EA has not been directly observed in the molecular ice phase, a solid-state formation mechanism has been proposed. However, the current literature lacks an estimation of the infrared band strengths of EA ices, which are crucial data for quantifying potential astronomical observations and laboratory findings related to their formation or destruction via energetic processing. Aims. We conducted an experimental investigation of solid EA ice at low temperatures to ascertain its infrared band strengths, phase transition temperature, and multilayer binding energy. Since the refractive index and the density of EA ice are unknown, the commonly used laser interferometry method was not applied. Infrared band strengths were determined using three distinct methods. In addition to evaluating EA band strengths, we also tested the advantages and disadvantages of different approaches used for this purpose. The obtained lab spectrum of EA was compared with the publicly available MIRI MRS James Webb Space Telescope observations towards a low-mass protostar. Methods. We used a combination of Fourier-transform transmission infrared spectroscopy and quadrupole mass spectrometry. Results. The phase transition temperature for EA ice falls within the range of 175 to 185 K. Among the discussed methods, the simple pressure gauge method provides a reasonable estimate of band strength. We derived a band strength value of about 1 × 10−17 cm molecule−1 for the NH2 bending mode in the EA molecules. Additionally, temperature-programmed desorption analysis yielded a multilayer desorption energy of 0.61±0.01 eV. By comparing the laboratory data documented in this study with the JWST spectrum of the low-mass protostar IRAS 2A, an upper-limit for the EA ice abundances was derived. Conclusions. This study addresses the lack of quantitative infrared measurements of EA at low temperatures, crucial for understanding EA’s astronomical and laboratory presence and formation routes. Our approach presents a simple yet effective method for determining the infrared band strengths of molecules with a reasonable level of accuracy.

Comparative investigation of composition, microstructure and property influences on electrocatalysis of two representative cathodes: BaCo0.4Fe0.4Zr0.1Y0.1O3-δ versus Ba0.5Sr0.5Co0.8Fe0.2O3-δ

BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) and Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) perovskites are two representative high-performance cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Here, symmetric cell tests demonstrate that polarization resistance values of BCFZY cathode are only 0.21–0.29 times those of BSCF cathode at 740–660 °C, and 0.21–0.26 times those of BSCF cathode at the oxygen partial pressures of 1.00–0.10 atm. Distribution of relaxation times (DRT) is applied to detect individual electrode processes overlapped in impedance spectra, which finds that the dominant processes of oxygen dissociation, subsequent species transfer and reduction on BCFZY cathode are superior to those of BSCF cathode. By temperature-programmed desorption of oxygen (O2-TPD), thermal expansion coefficient (TEC) measurements, scanning electron micrograph (SEM) and energy dispersive spectra measurements, the strong oxygen combination ability with higher activation energy of oxygen desorption (Ed = 84 kJ mol-1), peculiar surface state with evident nano-particle structure, more matchable TEC (19.0 × 10-6 K−1) and excellent interfacial connection with the electrolyte are observed on BCFZY cathode to account for its distinctive catalysis, as compared to BSCF cathode (Ed = 68 kJ mol-1, TEC = 24.2 × 10-6 K−1).

Exploring complete catalytic cycle of methane oxidation to methanol on Cu2O2 stabilized within MIL-53(Al) framework: A combined DFT and microkinetic study

Although inspiration from copper-based natural enzymes has shown promise in improving catalyst design for methane-to-methanol (MTM) oxidation, high productivity, and selectivity under mild conditions remain a significant challenge. This study constructs the dinuclear copper (Cu2) species stabilized within the metal-organic framework (MOF), MIL-53(Al), containing Cu as efficient catalytic sites and explores the ability of different oxidants (O2, N2O, and H2O2) to oxidize Cu2 into the dicopper-oxo (Cu2O2) species using density functional theory (DFT) calculations. Our results indicate the kinetic and thermodynamic favorability of Cu2O2 species formation using O2 as an oxidant within the MIL-53(Al) framework. Furthermore, the thermal stability of Cu2O2/MIL-53(Al) has been verified via ab initio molecular dynamics (AIMD) calculations. The kinetics of the complete MTM oxidation cycle over Cu2O2/MIL-53(Al) have been studied using both DFT and microkinetic simulation methods. The present study predicts that the C-H activation on the Cu2O2/MIL-53(Al) has a low free energy barrier (0.77 eV) and that the high stability of CH3 and its very low free energy barrier in the C-O coupling step favors the methanol formation over the formaldehyde. More importantly, Cu2O2/MIL-53(Al) exhibits high methanol selectivity owing to the inhibition of CH3 dehydrogenation and low methanol desorption energy (0.21 eV). Microkinetic simulations confirm the methanol production under relatively mild reaction conditions (200–280 K and 1 bar). This work provides insights into the feasibility of selective MTM oxidation over this family of MOF under mild conditions.

Experimental and modeling studies on char combustion under pressurized O2/H2O conditions

The desorption kinetic parameters for pressurized combustion and gasification reactions were determined based on a C++ program coupled with the Langmuir-Hinshelwood (L-H) kinetic model developed and experimental data from pressurized char combustion, and the established L-H kinetic model for pressurized char-O2/H2O combustion was refined in the current paper. The activation energy for desorption in reactions involving pressurized char-O2 and char-H2O was determined to be 250.8 kJ/mol, accompanied by a pre-exponential factor of 5.42 × 1010 g/(m2 s). Using this foundation, the current research conducted simulations to investigate the impacts of temperature, pressure, and H2O concentration on the oxidation adsorption rate (Rads,oxi), desorption rate (Rdes), gasification adsorption rate (Rads,gas), and the competitive influences of kinetics and diffusion processes within the pressurized char-O2/H2O combustion. The simulation results indicate a gradual increase in Rdes and Rads,gas with char conversion to reach a peak, followed by a gradual decline. Conversely, the Rads,oxi varies smoothly throughout the char conversion process. At 1673 K/1.0 MPa, the char-O2/H2O reaction rate is primarily constrained by Rads,oxi and Rads,gas, with the adsorption reaction serving as the rate-controlling step. Moreover, it was noted that a rise in pressure resulted in a linear increase in Rads,oxi, Rdes, and Rads,gas. At elevated temperatures, the impact of pressure on them becomes more noticeable. However, the introduction of H2O mitigates this effect. Elevated temperature and pressure facilitate the competition on the kinetics of char-O2 combustion for O2 diffusion, resulting in the conversion of char being more susceptible to O2 diffusion rate limitation. With the addition of 20 % H2O, the competition effect was weakened. In the case of pressurized combustion involving char and O2/H2O, the char conversion is primarily constrained by the O2 diffusion rate and is scarcely influenced by the H2O diffusion rate.

Insights into Mechanisms of Reverse Water Gas Shift Activity Enhancement over Reverse Microemulsion‐Synthesized CuCeO2

AbstractCopper‐doped ceria (CuCeO2) catalysts with 0–26.5 Cu/(Cu+Ce) at% were synthesized via the reverse microemulsion method. X‐ray diffraction analysis of freshly synthesized and spent (post‐reaction) catalysts showed no separate phase of copper or copper oxide, indicating that Cu was incorporated into the CeO2 lattice, replacing Ce. Temperature programmed desorption experiments showed that the activation energy of CO2 desorption increased for higher Cu loadings, indicating stronger CO2 adsorption. This phenomenon was attributed to enhanced formation of oxygen vacancies due to Cu doping. X‐ray photoelectron spectroscopy further confirmed the enhanced generation of oxygen vacancies due to Cu incorporation. Catalytic performance evaluation with the H2/CO2 feed in the 300–600 °C range showed that all catalysts were 100 % selective to CO generation, with higher Cu loadings resulting in CO2 conversion close to equilibrium values at 500–600 °C. The activation energy of the reaction, determined through reaction tests, exhibited inverse relationship with the activation energy of CO2 desorption. The relationship between these two energy barriers is explored, providing valuable insights into the mechanism of RWGS activity enhancement.

Effect of nano-aluminum hydroxide on the liquid phase properties and fire-fighting foam performance of the mixed surfactants solution

Short-chain fluorocarbon surfactants show synergistic effects with hydrocarbon surfactants in foaming and foam stability. Nano-aluminum hydroxide (nano-ATH) was added as an additive to the short-chain fluorocarbon surfactant mixture solution, which was found to increase the surface tension and viscosity of the surfactant mixture solution, and decrease the foaming properties of the solution, as measured by Wilhelmy method, Waring Blender method and viscometer. By measuring zeta potential experiments, surfactant molecules were found to be adsorbed on nano-ATH through charge gravity, which increased the desorption energy of nano-ATH. Measuring the visco-elastic modulus of the solution by rheometer, it was found that nano-ATH increased the visco-elastic modulus of the surfactant mixture solution, which improved the foam's resistance to the external disturbances. Observed by the image analysis system on the foam, the uniform distribution of nano-ATH in the liquid film reduced the coarsening and coalescence speed of foam. Through the self-developed oil resistance test, nano-ATH enhanced the oil resistance stability and inhibition of fuel vapor diffusion of the foam by about 12 %; through self-developed foam fire extinguishing and anti-burning tests, nano-ATH shortened the fire extinguishing time of the two-phase foam by 25 %, and showed better fire extinguishing and anti-burning performance than the foam.