Energy Barrier Research Articles

Strain-induced enhancement of surface self-diffusion on strontium titanate (001) surfaces.

We present a numerical investigation of self-diffusion on strontium titanate TiO2-terminated (001) surfaces via density functional theory. Our calculations first indicate that Ti has the highest diffusion barrier with approximately 2.20 eV, thus representing the rate-limiting step for surface self-diffusion. Furthermore, the higher energy barriers of O and Ti in comparison to O2and TiO2indicate electronic activity with the surface atoms. Under the consideration of equi-biaxial strain as it would be encountered in e.g. heteroepitaxial thin films, the diffusion barriers for surface self-diffusion decrease for both compressive and tensile strains between -6% and 2%. For larger strains, we observe plastic deformations. This possibility to lower the energy barrier paves the way for accelerated and possible new mechanisms of surface diffusion and reconstruction of strontium titanate structures in a wide range of applications.

M/BiOCl-(M=Pt, Pd, and Au) Boosted Selective Photocatalytic CO2 Reduction to C2 Hydrocarbons via *CHO Intermediate Manipulation.

Selective CO2 photoreduction to C2 hydrocarbons is significant but limited by the inadequate adsorption strength of the reaction intermediates and low efficiency of proton transfer. Herein, an ameliorative *CO adsorption and H2O activation strategy is realized via decorating bismuth oxychloride (BiOCl) nanostructures with different metal (Pt, Pd, and Au) species. Experimental and theoretical calculation results reveal that distinct *CO binding energies and *H acquisition abilities of the metal cocatalysts mediate the CO2 reduction activity and hydrocarbon selectivity. The relatively moderate *CO adsorption and *H supply over Pd/BiOCl endows it with the lowest free energy to generate *CHO, leading to its highest activity of hydrocarbon production. Specifically, the Pt cocatalyst can efficiently participate in H2O dissociation to deliver more *H for facilitating the protonation of the *CHO and *CHOH, thereby favoring CH4 production with 76.51% selectivity. A lower *H supply over Pd/BiOCl and Au/BiOCl results in a large energy barrier for *CHO or *CHOH protonation and thus a more thermodynamically favored OC─CHO coupling pathway, which endows them with vastly increased C2 hydrocarbon selectivity of 81.21% and 92.81%, respectively. The understanding of efficient C2 hydrocarbon production in this study sheds light on how materials can be engineered for photocatalytic CO2 reduction.

Jointly Improving Anionic-Cationic Redox Reversibility of Lithium-Rich Manganese-Based Cathode Materials by N Surface Doping.

The lithium-rich manganese-based layer oxide (LRMO) with high specific capacity (∼300 mAh g-1) and economic feasibility is accepted as the cathode material for high energy density rechargeable batteries. Accompanied by the additional anionic redox reactions during the initial charging process, LRMO presents oxygen release, sluggish Li+ diffusion, and irreversible transition metal ion (TM) migration, which is responsible for its severe structural deterioration and rapid capacity/voltage decay. Here, the N doping strategy is proposed via feasible treatment of oxygen-vacancy-containing Li1.16Ni0.21Mn0.63O2-δ (LNMO) particles. The as obtained LNMO-N samples demonstrate doping N, partially reduced Mn/Ni cations, and oxygen vacancies on the surface. The DFT calculations and experimental results demonstrate that N replacing the crystal oxygen sites on the surface reduces the energy barrier for diffusion, thereby enhancing the kinetics of Li+ diffusion and improving the reversibility of transition metal migration. Furthermore, N doping induces stacking faults and a more flexible structure. Therefore, LNMO-N exhibits a significantly improved anionic-cationic redox reaction reversibility with a high discharge specific capacity of 296.6 mAh g-1 at 20 mA g-1 within the range of 2.0 to 4.8 V and an impressive initial Coulombic efficiency of 85.9%. Moreover, the rate capability is obviously improved with a remarkable capacity of 215.1 mAh g-1 at 200 mA g-1 in 200 cycles with a capacity retention of 72.52% and exceptional performance of 141.4 mAh g-1 even at a higher current density of 1000 mA g-1.

Positively Charged Hollow Co Nanoshells by Kirkendall Effect Stabilized by Electron Sink for Alkaline Water Dissociation.

While cobalt (Co) exhibits a comparable energy barrier for H* adsorption/desorption to platinum in theory, it is generally not suitable for alkaline hydrogen evolution reaction (HER) because of unfavorable water dissociation. Here, the Kirkendall effect is adopted to fabricate positive-charged hollow metal Co (PHCo) nanoshells that are stabilized by MoO2 and chainmail carbon as the electron sink. Compared to the zero-valent Co, the PHCo accelerates the water dissociation and changes the rate-determining step from Volmer to Heyrovsky process. Alkaline HER occurs with a low overpotential of 59.0mV at 10mAcm-2. Operando Raman and first principles calculations reveal that the interfacial water to the PHCo sites and the accelerated proton transfer are conducive to the adsorption and dissociation of H2O molecules. Meanwhile, the upshifted d-band center of PHCo optimizes the adsorption/desorption of H*. This work provides a unique synthesis of hollow Co nanoshells via the Kirkendall effect and insights to water dissociation on catalyst surfaces with tailored charge states.

Green Solvent γ-Valerolactone (GVL) Facilitates Photocatalytic C-H Bond Activation.

Solvents can significantly influence chemical reactions in condensed phases. Their critical properties are increasingly recognized in various research domains such as organic synthesis and biomass valorization. However, in semiconductor photocatalysis, solvents are primarily viewed as mediums for dissolving and diffusing substances, with their potential beneficial effects on photocatalytic conversions often overlooked. Additionally, common photocatalysis solvents like acetonitrile (ACN) pose serious safety and environmental concerns. In this study, we demonstrate that novel and safe green solvents, such as γ-valerolactone (GVL), can significantly enhance the performance of semiconductor photocatalysis for C-H bond activation. Non-specific solvent-solute interactions are the primary contributors to increased photocatalytic activity in the self-coupling of benzylic compounds. Specifically, GVL's large dielectric constant and high refractive index lower the energy barrier for the rate-determining C-H bond activation step, facilitating a faster coupling reaction. The versatility of GVL is further demonstrated in reactions with multiple reagents and in various oxidation and reduction photocatalytic systems beyond classic C-H bond activation. This work not only pioneers the use of green solvents but also provides comprehensive insights for proper solvent selection in semiconductor photocatalysis.

Machine learning aided design of single-atom alloy catalysts for methane cracking

The process of CH4 cracking into H2 and carbon has gained wide attention for hydrogen production. However, traditional catalysis methods suffer rapid deactivation due to severe carbon deposition. In this study, we discover that effective CH4 cracking can be achieved at 450 °C over a Re/Ni single-atom alloy via ball milling. To explore single-atom alloy catalysis, we construct a library of 10,950 transition metal single-atom alloy surfaces and screen candidates based on C–H dissociation energy barriers predicted by a machine learning model. Experimental validation identifies Ir/Ni and Re/Ni as top performers. Notably, the non-noble metal Re/Ni achieves a hydrogen yield of 10.7 gH2 gcat–1 h–1 with 99.9% selectivity and 7.75% CH4 conversion at 450 °C, 1 atm. Here, we show the mechanical energy boosts CH4 conversion clearly and sustained CH4 cracking over 240 h is achieved, significantly surpassing other approaches in the literature.

Vacancy-Induced Anionic Electrons in Single-Metal Oxides and Their Possible Applications in Ammonia Synthesis.

Realizating of a low work function (WF) and room-temperature stability in electrides is highly desired for various applications, such as electron emitters, catalysts, and ion batteries. Herein, a criterion based on the electron localization function (ELF) and projected density of states (PDOS) in the vacancy of the oxide electride [Ca24Al28O64]4+(4e-) (C12A7) was adopted to screen out 13 electrides in single-metal oxides. By creating oxygen vacancies in nonelectride oxides, we find out 9 of them showed vacancy-induced anionic electrons. Considering the thermodynamic stability, two electrides with ordered vacancies, Nb3O3 and Ce4O3, stand out and show vacancy-induced zero-dimensional anionic electrons. Both exhibit low WFs, namely 3.1 and 2.3 eV for Nb3O3 and Ce4O3, respectively. In the case of Nb3O3, the ELF at oxygen vacancies decreases first and then increases during the decrease in the total number of electrons in self-consistent calculations due to Nb's multivalent state. Meanwhile, Ce4O3 displays promise for ammonia synthesis due to its low hydrogen diffusion barrier and low activation energy. Further calculations revealed that CeO with disordered vacancies at low concentrations also exhibits electride-like properties, suggesting its potential as a substitute for Ce4O3.

Copper as an Electron Hunter for Enhancing Bi2O2CO3 Electrocatalytic CO2 Conversion to Formate.

Cu-doped Bi2O2CO3 catalyst with copper (Cu) acting an electron hunter for conversion of carbon dioxide into formate is developed. The Cu-Bi2O2CO3 catalyst with hollow microsphere structure extends the duration of CO2 retention on the catalyst, providing a greater number of active sites. It exhibits remarkable performance with conversion efficacy of 98.5% and current density of 800mA cm-2 across a wide potential window (-0.8 to -1.3V vs RHE). Density functional theory investigations reveal that the presence of copper (Cu) significantly enhances the charge density at the active sites and influences the local electronic structure of bismuth (Bi), thereby reducing the energy barrier associated with the transformation of *OCHO species into formate.

Regulating Spin Polarization via Axial Nitrogen Traction at Fe-N5Sites Enhanced Electrocatalytic CO2Reduction for Zn-CO2 Batteries.

Single Fe sites have been explored as promising catalysts for the CO2reduction reaction to value-added CO. Herein, we introduce a novel molten salt synthesis strategy for developing axial nitrogen-coordinated Fe-N5sites on ultrathin defect-rich carbon nanosheets, aiming to modulate the reaction pathway precisely. This distinctive architecture weakens the spin polarization at the Fe sites, promoting a dynamic equilibrium of activated intermediates and facilitating the balance between *COOH formation and *CO desorption at the active Fe site. Notably, the synthesized FeN5, supported on defect-richin nitrogen-doped carbon(FeN5@DNC), exhibits superior performance in CO2RR, achieving a Faraday efficiency of 99% for CO production (-0.4 V vs. RHE) in an H-cell, and maintaining a Faraday efficiency of 98% at a current density of 270 mA cm-2(-1.0 V vs. RHE) in the flow cell. Furthermore, the FeN5@DNC catalyst is assembled as a reversible Zn-CO2battery with a cycle durability of 24 hours. In-situ IR spectroscopy and density functional theory (DFT) calculations reveal that the axial N coordination traction induces a transformation in the crystal field and local symmetry, therefore weakening the spin polarization of the central Fe atom and lowering the energy barrier for *CO desorption.

Asymmetric Ru-In atomic pairs promote highly active and stable acetylene hydrochlorination

Ru single-atom catalysts have great potential to replace toxic mercuric chloride in acetylene hydrochlorination. However, long-term catalytic stability remains a grand challenge due to the aggregation of Ru atoms caused by over-chlorination. Herein, we synthesize an asymmetric Ru-In atomic pair with vinyl chloride monomer yield (>99.5%) and stability (>600 h) at a gas hourly space velocity of 180 h−1, far surpassing those of the Ru single-atom counterparts. A combination of experimental and theoretical techniques reveals that there is a strong d-p orbital interaction between Ru and In atoms, which not only enables the selective adsorption of acetylene and hydrogen chloride at different atomic sites but also optimizes the electron configuration of Ru. As a result, the intrinsic energy barrier for vinyl chloride generation is lowered, and the thermodynamics of the chlorination process at the Ru site is switched from exothermal to endothermal due to the change of orbital couplings. This work provides a strategy to prevent the deactivation and depletion of active Ru centers during acetylene hydrochlorination.

Synthesis and Photophysical Properties of Small Helical Carbon Nanohoops Combined with Computational Studies on Racemization Pathway.

We herein report the facile synthesis of two helical carbon nanorings with small ring sizes, cyclo[6]paraphenylene-1,5-naphthylene ([6]CPPNap1,5), and cyclo[6]paraphenylene-1,5-anthrylene ([6]CPPAn1,5). The structures were determined by NMR and HR-MS. X-ray single-crystal data of [6]CPPNap1,5 was also achieved. The strain energy and racemization processes were investigated by DFT calculations. The reduced ring sizes result in increased ring strain and elevated energy barriers. The photophysical properties were studied by UV-Vis absorption, fluorescence emission, and time-resolved fluorescence decay.

Phase interface engineering enables state-of-the-art half-Heusler thermoelectrics

In thermoelectric, phase interface engineering proves effective in reducing the lattice thermal conductivity via interface scattering and amplifying the density-of-states effective mass by energy filtering. However, the indiscriminate introduction of phase interfaces inevitably leads to diminished carrier mobility. Moreover, relying on a singular energy barrier is insufficient for comprehensive filtration of low-energy carriers throughout the entire temperature range. Addressing these challenges, we advocate the establishment of a composite phase interface using atomic layer deposition (ALD) technology. This design aims to effectively decouple the interrelated thermoelectric parameters in ZrNiSn. The engineered coherent dual-interface energy barriers substantially enhance the density-of-states effective mass across the entire temperature spectrum while preser carrier mobility. Simultaneously, the strong interface scattering on phonons is crucial for curtailing lattice thermal conductivity. Consequently, a 40-cycles TiO2 coating on ZrNi1.03Sn0.99Sb0.01 achieves an unprecedented zT value of 1.3 at 873 K. These findings deepen the understanding of coherent composite-phase interface engineering.

Constructing Favorable Microenvironment on Copper Grain Boundaries for CO2 Electro-conversion to Multicarbon Products.

The electrochemical CO2 reduction reaction (eCO2RR) to multicarbon chemicals provides a promising avenue for storing renewable energy. Herein, we synthesized small Cu nanoparticles featuring enriched tiny grain boundaries (RGBs-Cu) through spatial confinement and in situ electroreduction. In-situ spectroscopy and theoretical calculations demonstrate that small-sized Cu grain boundaries significantly enhance the adsorption of the *CO intermediate, owing to the presence of abundant low-coordinated and disordered atoms. Furthermore, these grain boundaries, generated in situ under high current conditions, exhibit excellent stability during the eCO2RR process, thereby creating a stable *CO-rich microenvironment. This high local *CO concentration around the catalyst surface can reduce the energy barrier for C-C coupling and significantly increase the Faradaic efficiency (FE) for multicarbon products across both neutral and alkaline electrolytes. Specifically, the developed RGBs-Cu electrocatalyst achieved a peak FE of 77.3% for multicarbon products and maintained more than 134 h stability at a constant current density of -500 mA cm-2.

Accelerating Anhydrous Proton Transport in Covalent Organic Frameworks: Pore Chemistry and its Impacts

AbstractProton conduction is important in both fundamental research and technological development. Here we report designed synthesis of crystalline porous covalent organic frameworks as a new platform for high‐rate anhydrous proton conduction. By developing nanochannels with different topologies as proton pathways and loading neat phosphoric acid to construct robust proton carrier networks in the pores, we found that pore topology is crucial for proton conduction. Its effect on increasing proton conductivity is in an exponential mode other than linear fashion, endowing the materials with exceptional proton conductivities exceeding 10−2 S cm−1 over a broad range of temperature and a low activation energy barrier down to 0.24 eV. Remarkably, the pore size controls conduction mechanism, where mesopores promote proton conduction via a fast‐hopping mechanism, while micropores follow a sluggish vehicle process. Notably, decreasing phosphoric acid loading content drastically reduces proton conductivity and greatly increases activation energy barrier, emphasizing the pivotal role of well‐developed proton carrier network in proton transport. These findings and insights unveil a new general and transformative guidance for designing porous framework materials and systems for high‐rate ion conduction, energy storage, and energy conversion.

Fine-tuning the photophysical properties of Imidazo[1,2-a]pyridine-based dyes by the change in substituent and solvent media: DFT and TD-DFT studies

In the present work, photophysical properties of the nine excited-state intramolecular proton transfer (ESIPT) active 2-(2 -hydroxyphenyl)imidazo[1,2-a]pyridine (HPIP)-based dyes A1-A9 (X= H, Me, F, Cl, OMe, OH, CN, NO2 and CF3) were investigated at PBE0/6-31++G(d,p) and M06-2X/6-31++G(d,p) levels of theory in the gas phase and solvent media. The structural parameters, relative energies, vibrational spectra, photophysical properties, potential energy curves, natural bond orbital (NBO) charges, hole and electron isosurfaces, electron density properties and reduced density gradient (RDG) spikes were computed. The H-bonding is strengthened at the S1 state by comparing infrared vibrational spectra, the relevant bond length and bond angle, electron density properties and RDG analysis. The results revealed that ESIPT in the A1-A7 and A9 in the gas phase is a barrier-less process, while there is an energy barrier for the A8 (X=NO2). In polar solvents, it is predicted that the ESIPT process only in A5 and A6 is a barrier-less process. The A2, A4 and A5 exhibited the greatest redshift in the keto fluorescence emission in tetrahydrofuran solvents. The significant Stokes shift observed in the S1-K emission of certain dyes makes these molecules highly appealing for various applications such as chemosensors, fluorescent probes, laser dyes and optoelectronic devices.

Surface‐Like Diffusion of Fast Ions in Framework Energy Materials for Li‐ and Na‐Ion Batteries

AbstractThe rate performance, power density, and energy efficiency of electrochemical devices are often limited by ionic conductivities in electrolyte and electrode materials. Framework Prussian blue analogs and dense niobium oxides have been identified as high‐rate electrodes for sodium‐ and lithium‐ion batteries, respectively, yet the origin of the extremely high solid‐state Na+/Li+ transport is not fully understood. Of critical importance is the fact that their ultra‐low activation energy and anomalous pre‐exponent factor cannot be satisfactorily rationalized from conventional theory of solid‐state diffusion in the crystal lattice. Here, assisted by density‐functional‐theory calculations, we argued that the true origin is a unique surface‐like diffusion mechanism of the intercalation ions. In a surface‐like migration event, a mobile ion moves along the channel wall via a low coordination number and low migration barrier experiencing minimal steric hindrance. It is similar to surface diffusion in the conventional picture and contrasts with lattice diffusion from one interstitial/vacancy site to another one with high coordination number, crowded saddle‐point geometry and high migration barrier. We found that the shifting from solid‐state lattice diffusion to surface‐like diffusion is determined by the size difference between the mobile ion and the diffusion channel, and a lowest migration energy barrier can be reached by mediating the channel size. The analogy to gas diffusion in molecular sieves shall be discussed. Additionally, the effects of defects and crystal water in Prussian blue analogs were also discussed for better understanding their rate performances in experimental scenarios.

Electrocatalytic nitrogen reduction to ammonia by atomically precise Cu6 nanoclusters supported on graphene oxide.

The electrocatalytic nitrogen reduction reaction (NRR) enables the production of ammonia by the use of renewable energy, providing a direct method for nitrogen fixation. Nevertheless, the NRR process under ambient conditions is often impeded by inertness of N2 and the occurrence of hydrogen evolution as a byproduct in aqueous electrolytes, resulting in a diminished reaction rate and reduced efficiency. In this study, we synthesized Cu6(SMPP)6 nanoclusters (Cu6 NCs for short) and immobilized them on graphene oxide (GO) to investigate their electrocatalytic nitrogen reduction reaction (ENRR) using an H-cell setup. The GO-supported Cu6 NCs exhibit enhanced catalysis with a high NH3 yield rate of 4.8 μg h-1 cm-2 and a high faradaic efficiency up to 30.39% at -1.1 V. Quantum chemistry calculations reveal that the Cu6S6 cluster on GO support facilitates the N2 adsorption and NN bond activation with a surmountable energy barrier for the potential-determining step (N2* → NNH*).

Insights into Allosteric Inhibition of the AcrB Efflux Pump: Role of Distinct Binding Pockets, Protomer Preferences, and Crosstalk Disruption.

AcrB, a key component in bacterial efflux processes, exhibits distinct binding pockets that influence inhibitor interactions. In addition to the well-known distal binding pocket within the periplasmic domain, a noteworthy pocket amidst the transmembrane (TM) helices serves as an alternate binding site for inhibitors. The bacterial efflux mechanism involves a pivotal functional rotation of the TM protein, inducing conformational changes in each protomer and propelling drugs toward the outer membrane domain. Surprisingly, inhibitors binding to the TM domain display a preference for L protomers over T protomers. Metadynamics simulations elucidate that Lys940 in the TM domain of AcrB can adopt two conformations in L protomers, whereas the energy barrier for such transitions is higher in T protomers. This phenomenon results in stable inhibitor binding in l protomers. Upon a detailed analysis of unbinding pathways using random accelerated molecular dynamics and umbrella sampling, we have identified three distinct routes for ligand exit from the allosteric site, specifically involving regions within the TM domains─TM4, TM5, and TM10. To explore allosteric crosstalk, we focused on the following key residues: Val452 from the TM domain and Ala831 from the porter domain. Surprisingly, our findings reveal that inhibitor binding disrupts this communication. The shortest path connecting Val452 and Ala831 increases upon inhibitor binding, suggesting sabotage of the natural interdomain communication dynamics. This result highlights the intricate interplay between inhibitor binding and allosteric signaling within our studied system.

Energy Barriers for the Spontaneous Magnetization Reversal of the Atomic Co Chains on Pt(664) Surface in the Model with Dzyaloshinskii–Moriya Interaction

The analytical approach has been developed in the framework of the continuous XY-model. This approach allows calculating the spontaneous magnetization reversal time of finite-length atomic chains on the metallic surface. The interaction of the magnetic moments of atoms is described by the classical Hamiltonian, which includes the Heisenberg exchange interaction, the Dzyaloshinskii–Moriya interaction, and the magnetic anisotropy energy. Using the Co/Pt(664) system as an example, it has been shown that the proposed method is in a good agreement with the results of the numerical simulation in the limit of short and long atomic chains. And for atomic chains of intermediate length, it can be used to estimate an upper bound on the spontaneous magnetization reversal time. We obtained the dependences of the spontaneous magnetization reversal time of finite-length Co chains the value of the exchange integral, parameters of the magnetic anisotropy, and also on the value of the projection of the Dzyaloshinskii vector onto the axis perpendicular to the plane containing the magnetic moments of the atoms. It is shown that the proposed method has a wide range of applicability both in terms of temperature and the values of the physical parameters characterizing the magnetic properties of the atomic chains.

Ordering Sulfonic Groups Facilitate a Li3N‐Enriched Interphase via Directing the Decomposition of LiNO3

AbstractThe practical application of high‐energy lithium (Li) metal anodes is plagued by the severe issues of interfacial instability. The Li3N originated from the decomposition of LiNO3 is believed to endow the solid electrolyte interphase (SEI) with high stability and ionic conductivity. However, the precise control on the decomposition of LiNO3 is still challenging due to the sophisticated reaction pathways and high energy barriers. In this study, a self‐assembled monolayers (SAMs) with densely packed and long‐range ordered sulfonic acid groups on an alumina‐coated separator are designed. By providing a strong dipole moment, this SAMs efficiently facilitate the rapid and deep decomposition of LiNO3, leading to the formation of an SEI rich in Li3N nanocrystals. Notably, under the stringent conditions of 5 mA cm−2 and 5 mAh cm−2, the Li/Li symmetric cell is still able to cycle stably for 1000 h under the stable nitrided interface induced by the SAMs. Consequently, the application scenarios of SAMs technology in precisely controlling electrolyte decomposition processes are successfully expanded to stabilize the interphase of metallic Li anode with high energy‐density.