Low Activation Energy Barrier Research Articles

Vacancy Pair-Induced Charge Rebalancing with Surface and Interfacial Dual Polarization for CO2 Photoreduction

Poor charge kinetics greatly reduce the efficiency of photocatalytic CO2 reduction. Herein, a synchronous surface and interfacial dual polarization strategy was developed to promote charge separation. Bi–O vacancy pairs in Bi24O31Br10 atomic layers can trigger strong coupling between black phosphorus (BP) and Bi24O31Br10, forming a restructured closely contacted BP–Bi24O31Br10 configuration with a charge-redistributed interface via electronegativity-induced charge rebalancing. The Bi–O vacancy pairs on the surface of Bi24O31Br10 and restructured BP/Bi24O31Br10 interface enable synchronous surface and interfacial dual polarization, creating an electronic bridge from the interior of Bi24O31Br10 to the BP surface, as proven by ultrafast transient absorption spectroscopy. This configuration favors a low CO2 activation energy barrier, effectively stabilizes COOH* intermediates, and decreases the rate-determining step energy barrier. Benefiting from these features, the stable CO generation rate of optimized BP–Bi24O31Br10 reaches up to 39.8 μmol g–1 h–1 via CO2 photoreduction in water, which is 2.4 and 46.8 times higher than those of defective Bi24O31Br10 atomic layers and defect-poor Bi24O31Br10, respectively. This study provides insights into the synchronous design of surface defects and restructured interfaces for dual polarization.

Immobilization of Magnetic Nanoparticles on Cellulosic Wooden Sawdust for Competitive Nudrin Elimination from Environmental Waters as a Green Strategy: Box-Behnken Design Optimization.

The role of engineering in our society is not to just to continue creating chemicals, but sharing the responsibility for environmentally sound appropriate design of substances for a circular economy. Concerning this contemporary strategy, waste wooden sawdust (WSD) as a biobased by-product is augmented with magnetite (Mag) nanoparticles to meet the concept of cyclic application of resources in environmentally relevant photocatalytic reactions. The physical properties of the prepared WSD:Mag material were characterized to emphasis their structure and morphology by using X-ray diffraction (XRD) and transmission electron microscopy (TEM), then the prepared catalyst was applied in augmentation with hydrogen peroxide as a type of photocatalyst in the form of Fenton's reaction system to oxidize Nudrin pesticide in queues media. Twinned WSD:Mag has been verified to exhibit higher performance than pristine single-phase catalysts. System parameters, i.e., pH, hydrogen peroxide, catalyst dozing, and temperature, were studied to check their effect on the reaction activity. In the present study, further promotion of photocatalytic activity of twinned WSD:Mag was obtained by optimizing the process parameters at the optimal reaction time of 30 min. The optimal results investigated via Box-Behnken design regression model based on response surface mythology (RSM) showed that the photocatalytic activity of the twinned catalyst could reach 94% at pH 2.5 and 386 and 38 m/L of H2O2 and WSD:Mag, respectively. The regression coefficient and probability obtained from analysis of variance (ANOVA) were used to check the adequacy of the applied model, and were 92% and 0.02, respectively. Additional confirmatory tests were carried out under optimum conditions for verification and agreed with the predicted values. Experimental data analysis revealed that the reaction is well fitted with the second-order reaction model. Thermodynamic parameters highlighted the oxidation reaction is non-spontaneous at high temperature and exothermic in nature and proceeds at a low activation energy barrier (31.46 kJ/mol). Catalyst recyclability was also checked, which confirmed catalyst sustainability and high removal rates (78%) after six cycles of use. This work introduces a new concept to design a promising environmentally benign photocatalyst with high potential for applicability to environmental remediation of agricultural effluents with a view to a circular economy.

Gold single-atoms confined at the CeO x -TiO2 interfaces with enhanced low-temperature activity toward CO oxidation

We use CeO x -TiO2 hetero-interfaces generated on the surface of CeO x -TiO2 hybrid oxide supporting powders to stabilize Au single-atoms (SAs) with excellent low-temperature activity toward CO oxidation. Based on intriguing density functional theory calculation results on the preferential formation of Au-SAs at the CeO x -TiO2 interfaces and the high activity of Au-SAs toward the Mars–van Krevelen type CO oxidation, we synthesized a Au/CeO x -TiO2 (ACT) catalyst with 0.05 wt.% of Au content. The Au-SAs stabilized at the CeO x -TiO2 interfaces by electronic coupling between Au and Ce showed improved low-temperature CO oxidation activity than the conventional Au/TiO2 control group catalyst. However, the light-off profile of ACT showed that the early activated Au-SAs are not vigorously participating in CO oxidation. The large portion of the positive effect on the overall catalytic activity from the low activation energy barrier of ACT was retarded by the negative impact from the decreasing active site density at high temperatures. We anticipate that the low-temperature activity and high-temperature stability of Au-SAs that stand against each other can be optimized by controlling the electronic coupling strength between Au-SAs and oxide clusters at the Au-oxide-TiO2 interfaces. Our results show that atomic-precision interface modulation could fine-tune the catalytic activity and stability of Au-SAs.

Theoretical design of Na-rich anti-perovskite as solid electrolyte: The effect of cluster anion in stability and ionic conductivity

The next-generation solid-state batteries need safe and efficient solid-state electrolytes. However, the conventional solid-state electrolytes materials often suffer from low ionic conductivity. The emerging anti-perovskites are potential solid electrolytes materials for their rich cations and tunable crystal structure. Here, the first-principles density functional theory (DFT) calculations are employed to investigate the stability, electronic properties, elastic constants and the ions migration of sodium-rich anti-perovskite Na3SA (A ​= ​AlF4¯, ClO4¯, ICl4¯, IO4¯). Calculations show that the clusters substitution at anion position A of Na3SA displays larger band gap and faster Na ion transport than that of halogen anions (e.g., Cl, Br, I). Among them, the band gaps of Na3SAlF4 and Na3SClO4 exceed 3.5 ​eV, which indicates their excellent electrochemical stability. The AlF4¯ cluster exhibits high sodium ion conductivity (6.55 ​× ​10-2 ​S ​cm-1), low activation energy (0.19 ​eV) and small migration barrier (0.46 ​eV) according to the ab initio molecular dynamics (AIMD) simulations and transition states study. Molecular dynamics simulations suggest that the enhanced ionic conductivity is due to the rotation of cluster ions which promotes the migration of sodium ions; moreover, the large volume created by anion clusters leads to larger lattices which is also benefit for fast ion transport. Therefore, this work designs Na-rich anti-perovskite with high ionic conductivity by substitution of anion clusters and also provides the Na ion transport mechanism for reference in solid-state electrolytes.

Defect-stabilized platinum single atoms and clusters in bilayer nitrogen-doped porous carbon nanocages for synergistic catalysis of basic hydrogen evolution

Alkaline water electrolysis is a safe and efficient method for producing hydrogen that is favored by the industry. At present, single-atom catalysts have attracted extensive attention due to their extremely high atom utilization. However, studies on the single-atom site catalytic mechanism of the Volmer step, the rate-determining step of the cathodic HER reaction, are lacking. Here, we used ZIF-8 to obtain double-layer N-doped porous carbon nanocages, and successfully achieved the co-loading of Pt single atoms and their clusters (NPCN–Pt). The turnover frequency (TOF) and mass activity of NPCN–Pt are 5 and 7.2 times higher than those of commercial Pt/C, respectively, and the former exhibits significantly better stability than Pt/C. Theoretical calculations show that Pt clusters have a lower activation energy barrier for water molecules compared to Pt single atoms, which favors the Volmer step. The ΔGH* of Pt single-atom sites is smaller than that of Pt clusters, which is more conducive to the release of H2. The study shows that Pt clusters and single atoms can synergistically catalyze the HER reaction, providing new ideas for the development of efficient HER catalysts.

Two-dimensional conductive π-conjugated metal-organic frameworks as promising electrocatalysts for highly efficient hydrogen evolution reaction

Two-dimensional conductive π-conjugated metal-organic frameworks (2D c-MOFs), as a new promising electrocatalytic materials, have spurred great research interests, but the systematic research on the structure-property relationship of c-MOF-based electrocatalysts is scarcely reported. Herein we conduct a first-principles study on the screening of a family of 2D c-MOFs (TM3(HITN)2) as HER electrocatalysts, which are constructed by TM atoms and 2,3,8,9,14,15-hexaiminotrinaphthylene (HITN) functional groups. The data suggests that all these 2D TM3(HITN)2 possess metallic with good conductivity for electrochemical reactions due to their intrinsic π-electron conjugation and sufficient interaction between the TM atoms and the organic linkers. Through the complete computational screening, the Zr3(HITN)2 stands out because of its near-zero ΔG*H value and low activation energy barrier. Moreover, the distinguished HER performance of Zr3(HITN)2 can be attributed to the extremely enhanced electron density derived from the C-2p orbitals near the Fermi level accompanied by the size increase of the tri-dentated aromatic linkers. Hence, this study not only highlights a family of promising 2D c-MOF electrocatalysts toward HER, but also supplies a valuable insight on the design of novel and high-performance c-MOF-based materials for better electrocatalysis.

Embedding amorphous SnS in electrospun porous carbon nanofibers for efficient potassium storage with ultralong cycle life

Potassium-ion batteries (PIBs) have gained substantial research interest for scalable and affordable stationary applications owing to their low cost, natural abundance, and high energy density. However, the large size of potassium (K) ion hampers its diffusion and causes significant strain in conventional electrode materials, resulting in low capacity, poor rate capability, and short lifespan. Herein, we develop a new strategy by confining amorphous tin sulfide (a-SnS) in electrospun porous carbon nanofibers (denoted as a-SnS@pCNFs) to realize the highly reversible potassiation/depotassiation of SnS. The amorphous nature of a-SnS enables a lower activation energy barrier towards structural rearrangement during any possible conversion reaction, which facilitates an increased electrochemical stability. Moreover, the pCNF skeleton not only improves the overall electrical conductivity of a-SnS@pCNFs, but also accommodates the volume variation of the SnS during the repeated cycles of charge/discharge. Combining these benefits of a-SnS and the tailored pore structures in pCNFs, the a-SnS@pCNFs composite delivers a high reversible capacity (∼300 mAh g−1 at 1 A g−1), a remarkable rate capability (∼85.4 mAh g−1 at 10 A g−1) and an ultralong lifespan (2000 cycles at 3 A g−1). This work provides a viable strategy to stabilize the conversion and alloying materials with fast and reversible K-ion storage towards practical applications.

Density functional theory study of P-embedded SiC monolayer as a robust metal free catalyst for N2O reduction and CO oxidation

In this work, spin-polarized density functional theory calculations are conducted to evaluate the possible applicability of a single P atom doped silicon carbide (P-SiC) monolayer for reduction of nitrous oxide (N2O). The calculations show that P-doping in SiC monolayer is energetically favorable, and the resulting P-SiC is both dynamically and thermodynamically stable. According to our findings, N2O spontaneously dissociates when it interacts with the P-SiC from its O site without the need for an energy barrier, releasing -2.59 eV of energy. The adsorption energy of CO molecule on the P-SiC is less negative than that of N2O, implying that N2O will predominately occupy the catalyst surface. The CO + Oad reaction is used to remove the remaining oxygen atom (Oad) from the P-SiC surface. The calculations show that the reaction proceeds through a low activation energy barrier of 0.33 eV, which is much lower than the previously reported catalysts. This demonstrates the high catalytic activity of P-SiC surface. Furthermore, the adsorption of H2O and O2 species on the P-SiC nanosheet is investigated. The results show that the presence of these species has no effect on the catalytic activity of the P-SiC surface for N2O reduction. These results show that the proposed novel P-SiC catalyst can be regarded as an efficient material in the development of promising active catalysts for N2O elimination from the environment.

Ni-Al mixed metal oxide with rich oxygen vacancies: CO methanation performance and density functional theory study

Ni-Al mixed metal oxides have been successfully prepared by high shear mixer (HSM) and coprecipitation (CP) methods for low temperature CO methanation. In this work, Ni-Al (HSM-CP) catalyst presented small Ni crystallite size and high surface area, which all contribute to the methanation reaction at low temperature conditions. The obtained Ni-Al (HSM-CP) sample exhibited a mass of defective oxygen, thereby accelerating the dissociation of CO and ultimately increasing the activity of the catalyst. Ni-Al (HSM-CP) catalyst offered the best activity with CO conversion = 100% and CH 4 selectivity = 93% at 300 °C, and the CH 4 selectivity can reach 81.8% at 200 °C. In situ Fourier transform infrared spectroscopy and density functional theory show that CHO and COH intermediates with lower activation energy barriers are produced during the reaction, and hydrogen-assisted carbon–oxygen bond scission is more favorable.

Packaging contests between viral RNA molecules and kinetic selectivity.

The paper presents a statistical-mechanics model for the kinetic selection of viral RNA molecules by packaging signals during the nucleation stage of the assembly of small RNA viruses. The effects of the RNA secondary structure and folding geometry of the packaging signals on the assembly activation energy barrier are encoded by a pair of characteristics: the wrapping number and the maximum ladder distance. Kinetic selection is found to be optimal when assembly takes place under conditions of supersaturation and also when the concentration ratio of capsid protein and viral RNA concentrations equals the stoichiometric ratio of assembled viral particles. As a function of the height of the activation energy barrier, there is a form of order-disorder transition such that for sufficiently low activation energy barriers, kinetic selectivity is erased by entropic effects associated with the number of assembly pathways.

Non-energetic Formation of Ethanol via CCH Reaction with Interstellar H2O Ices. A Computational Chemistry Study.

Ethanol (CH3CH2OH) is a relatively common molecule, often found in star-forming regions. Recent studies suggest that it could be a parent molecule of several so-called interstellar complex organic molecules (iCOMs). However, the formation route of this species remains under debate. In the present work, we study the formation of ethanol through the reaction of CCH with one H2O molecule belonging to the ice as a test case to investigate the viability of chemical reactions based on a “radical + ice component” scheme as an alternative mechanism for the synthesis of iCOMs, beyond the usual radical–radical coupling. This has been done by means of DFT calculations adopting two clusters of 18 and 33 water molecules as ice models. Results indicate that CH3CH2OH can potentially be formed by this proposed reaction mechanism. The reaction of CCH with H2O on the water ice clusters can be barrierless (because of the help of boundary icy water molecules acting as proton-transfer assistants), leading to the formation of vinyl alcohol precursors (H2CCOH and CHCHOH). Subsequent hydrogenation of vinyl alcohol yielding ethanol is the only step presenting a low activation energy barrier. We finally discuss the astrophysical implications of these findings.

Designing a durable high-rate K0.45Ni0.1Fe0.1Mn0.8O2 cathode for K-ion batteries: A joint study of theory and experiment

K-ion batteries (KIBs) hold great promise for large-scale energy storage. However, the absence of suitable cathode materials limits their practical application. Meanwhile, rationally designing advanced cathode materials for KIBs remains an open question. In this work, based on density functional theory calculations, we find that the bond stability of Fe−O is higher than that of Co−O in layered transitional metal (TM) oxides. Additionally, the K-ion migration in the Fe-based layered TM oxide has a significantly lower activation energy barrier than that in the Co-based one. Based on this theoretical prediction, we successfully synthesized a low-cost K0.45Ni0.1Fe0.1Mn0.8O2 cathode, which shows excellent structural stability and superior K-storage properties, including durable cycle life and high-rate capability. Moreover, the designed K0.45Ni0.1Fe0.1Mn0.8O2 cathode possesses a great full-cell performance with a discharge capacity of ∼75 mA h g−1 and capacity retention of ∼80% after 100 cycles. The results show that Fe has better structural stability and K-ion diffusion than high-cost Co in layered oxide cathodes, and this finding provides new insights into the design of low-cost and high-performance KIB layered cathodes. This work highlights the feasibility of a theory-guided experiment in screening promising battery materials.

Co complex modified on Eupergit C as a highly active catalyst for enhanced hydrogen production

In present paper, the preparation and catalytic activity of Eupergit C polymer (EC) modified Co complex was reported. Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Brunauer-Emmett-Teller Surface Area Analysis (BET), Fourier Transform Infrared Spectroscopy (FT-IR), Transmission Electron Microscopy (TEM) coupled with energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) were used to characterization of catalyst. EC modified-Co complex was the first time examined as a catalyst in NaBH 4 hydrolysis to H 2 evolution. The kinetic calculations were determined by using two different kinetic methods. The low activation energy barriers were achieved as 21.673 kJ mol −1 for nth order model and as 21.061kJmol −1 for Langmuir-Hinshelwood (L-H) model at low temperatures. EC modified-Co complex catalyst exhibited high performance with H 2 evolution rates of 3914 mL H 2 g cat −1 min −1 and 9183 mLH 2 g cat −1 min −1 at 30 °C–50 °C. Additionally, Langmuir–Hinshelwood mechanism was explained for EC modified Co complex catalyzed sodium borohydride hydrolysis reaction. The reusability experiments showed that EC modified-Co complex catalyst maintained excellent stability with 100% conversion and without significant lost after the 6th run. • Preparation of Eupergit C polymer (EC) modified Co complex catalyst. • The first time examination of EC modified Co complex catalyst in NaBH 4 hydrolysis. • Attainment to high H 2 evolution rate of 9183mL H 2 . g cat −1 min −1 at low temperature. • Achievement of low activation energy barriers of 21.673 and 21.061;kJmol −1 . • Excellent stability without significant lost after the 6th run in NaBH 4 hydrolysis.

Design metal-free single-atom catalyst P@BN for CO oxidation: A DFT-D study

Single-atom catalysts (SACs) have arisen significant interest in catalysis and have the superior advantage for CO oxidation. In the current study, beyond the normal single-metal atom catalyst, we designed a new type of metal-free single-atom catalyst based on P doped BN surface. The catalytic mechanism and electronic analysis of CO oxidation on P doped BN metal-free single-atom catalyst is studied by using DFT-D simulation. We found that the phosphorus is preferable to anchor on the boron vacancy of h-BN, and the 3p states of the P dopant would be the key to activate the pre-adsorbed O2. Due to the high catalytic performance and stability of metal-free single-atom, fast charge-transfer kinetics is permissible via catalysis. CO oxidation on the P doped Bv/BN is found to be feasible with the direct formation of CO2 from the cleavage of P–O bonds (ER2 pathway: O2 + CO → CO2 + O) and followed by the reaction process (O + CO → CO2) with low activation energy barriers, indicating that the CO oxidation might be ready at a low temperature. Our work is helpful to reveal the significant role of P dopant for the CO oxidation and shed light on design the new type metal-free single-atom catalyst with low cost, high-performance catalytic activities.

N2O Hydrogenation on Silver Doped Gold Catalysts, a DFT Study

In this study, the full reaction mechanism for N2O hydrogenation on silver doped Au(210) surfaces was investigated in order to clarify the experimental observations. Density functional theory (DFT) calculations were used to state the most favorable reaction paths for individual steps involved in the N2O hydrogenation. From the DFT results, the activation energy barriers, rate constants and reaction energies for the individual steps were determined, which made it possible to elucidate the most favorable reaction mechanism for the global catalytic process. It was found that the N2O dissociation occurs in surface regions where silver atoms are present, while hydrogen dissociation occurs in pure gold regions of the catalyst or in regions with a low silver content. Likewise, N2O dissociation is the rate determining step of the global process, while water formation from O adatoms double hydrogenation and N2 and H2O desorptions are reaction steps limited by low activation energy barriers, and therefore, the latter are easily carried out. Moreover, water formation occurs in the edges between the regions where hydrogen and N2O are dissociated. Interestingly, a good dispersion of the silver atoms in the surface is necessary to avoid catalyst poison by O adatoms accumulation, which are strongly adsorbed on the surface.

A computational study on the potential application of carbon nitride nanosheets in Na-ion batteries.

In the current study, the C3N monolayer, as a two-dimensional material, was considered as a suitable anode material in sodium-ion (Na-ion) batteries (NIBs) by performing first-principles density functional theory (DFT) computations. It was shown that the metallic feature of the Na-ion is retained after its adsorption onto various sites on the surface of the C3N monolayer. The C3N monolayer has negative adsorption energy values for the Na-ion. Afterwards, the C3N monolayer was shown to have a greater maximum theoretical capacity of 543.89 mAh/g for the Na-ion in comparison with other materials based on our computations. Due to the low activation energy barrier of approximately 0.112eV, migration of the Na-ion, which includes diffusion on the surface of the C3N monolayer, is rapid, demonstrating its great capability for fast charge-discharge processes. Ultimately, it was shown that, for the Na, the C3N monolayer possesses a low average open-circuit voltage, i.e., 0.83V. These results show that it is possible to utilize the C3N monolayer in NIBs as an anode material.

Solar assisted green photocatalysis for deducing carbamate insecticide from agriculture stream into water reclaiming opportunity

ABSTRACT ‘Ultraviolet’ and ‘Solar’ wastewater treatment units are used augmented with nanocrystals of magnetite, Fe2O3, which were previously synthesised via a cost-efficient co-perception route. The nanocrystals produced were used as a Fenton reagent source for the oxidising carbamate pesticide in aqueous solution through a combination of natural abundant solar radiation as well as artificial UV source. System parameters were examined and the optimal operating conditions were investigated to maximise the system yield. The objective optimisation was attained using a Box-Behnken factoring design (BBD) based on Response Surface Methodology, RSM. A mathematical model was developed and the maximal removal efficiency reached to 84.1% within 15 min of reaction time. Furthermore, the chemical oxygen demand was then investigated and it was oxidised and deduced to 57%. Analysis of the experimental data revealed that a second-order reaction model is best described the reaction kinetics. The calculated thermodynamic parameters suggested that the non-spontaneous nature of oxidation at high temperature was corroborated by positive Gibbs free energy change ∆G• and negative entropy, ∆S• values. Also, the negative values of enthalpy, ∆H•, indicated that the reaction was exothermic. The low activation energy barrier (−35.85 kJ/mol) indicated that the reaction proceeds at a low energy level.

DFT study on reaction mechanism of di-tert-butylphenol to di-tert-butylhydroxybenzoic acid

Experimental studies on the Kolbe–Schmitt reaction and its side reactions have made great progresses; however, the relative theoretical studies fall behind. In order to study the mechanism of the Kolbe–Schmitt reaction with 2,6-di-tert-butylphenol and 2,4-di-tert-butylphenol as reactants, we carried out theoretical calculation studies at the M06-2X/Def2-SVP/SMD level of theory using the Gaussian 09 D.01 software package. For the reactant 2,6-di-tert-butylphenol, there is a dynamic equilibrium between the main product and side product, which can rapidly transform into each other at 160 °C by crossing the Gibbs free energy barrier of 14.1 kcal/mol. Moreover, the relative Gibbs free energy of the main product and side product is close; both of them may be observed in the experimental system. However, for 2,4-di-tert-butylphenol, the main product is thermodynamically favorable due to its lower Gibbs free energy, while the side product is kinetically favorable due to the lower activation energy barrier; the main product and the side product compete with each other. We hope the study can shed light on the Kolbe–Schmitt reaction.

Porous Edge Confinement: High Carrier Potential and Low Activation Energy Barrier Synergistically Boosting the Efficiency of Selective Photocatalytic Co2 Conversion

Porous Edge Confinement: High Carrier Potential and Low Activation Energy Barrier Synergistically Boosting the Efficiency of Selective Photocatalytic Co2 Conversion

A novel PdC monolayer with fully dispersed Pd atoms and a rigid carbon backbone: an intrinsic versatile electrocatalyst for overall water splitting and the corresponding reverse reaction.

The electrocatalytic overall water splitting and the corresponding reverse reaction play a vital role in future renewable energy systems and, hence, are frontiers of catalysis research. In this work, we identify a heretofore unknown two-dimensional palladium carbide using the structure swarm intelligence algorithm. The proposed monolayer, named α-PdC, consists of fully dispersed Pd atoms and a rigid carbon backbone, exhibiting high mechanical, dynamical, and thermal stability with desirable electrical conductivity. Further calculations show that the proposed monolayer is an intrinsic multifunctional electrocatalyst. It possesses an excellent catalytic performance toward the hydrogen evolution reaction (HER), the oxygen evolution reaction (OER), and the oxygen reduction reaction (ORR) with low overpotentials. Specifically, the overpotential for the HER is only -0.01 V, and the significantly low activation energy barrier (0.16 eV) on α-PdC elucidates the fast kinetics. Moreover, α-PdC could also be highly active towards the OER and ORR with comparable overpotentials (0.38 and 0.27 V, respectively). This study identifies an intrinsic versatile electrocatalyst with potential applications in the fields of energy conversion and storage.