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Understanding the structure evolution, kinetics, and mass transfer for the oxygen reduction reaction (ORR) at the ionomer-catalyst interface is fundamental for the development of anion exchange membrane fuel cells (AEMFCs). Herein, we investigate the structural evolution of ionomer-Pt interfaces during the activation process of polycrystalline Pt (poly-Pt) electrodes and their ORR kinetics and mass transfer characteristics at steady state. The results suggest the ionomer thickness as a critical factor in determining the Pt surface structure and the flux of the O2 diffusion, which in turn affect the subsequent kinetic and mass transfer of the ORR on ionomer-Pt electrode interfaces. Thicker ionomer film leads to a more severe evolution of electrochemical features during the activation process, likely caused by forming more less-active Pt clusters at the ionomer-Pt interface. Thus, the ORR kinetic activity at the steady state decreases with the increase in ionomer thickness. Concurrently, the thicker ionomer leads to a reduced diffusion flux of O2, culminating in a lower limiting current density for the ORR. Additionally, we calculated the diffusion coefficient and solubility of O2 within the FAA-3 alkaline ionomer film, with a comparative assessment against those in the proton exchange membrane (PEM). These findings offer valuable insights into the ionomer-Pt interface in AEMFCs and their effects on performance.
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Using the on-the-fly machine learning force field, simulations were performed to study the atomic structure evolution of the liquid-Al/solid-TiB2 interface with two different terminations, aiming to deepen the understanding of the mechanism of TiB2 as nucleating particles in an aluminum alloy. We conducted simulations using MLFF for up to 100 ps, enabling us to observe the interfacial properties from a deeper and more comprehensive perspective. The nucleation potential of TiB2 particles is determined by the formation of various ordered structures at the interface, which is significantly influenced by the termination of the TiB2 (0001) surface. The evolution of the interface during heterogeneous nucleation processes with different terminations is described using structural information and dynamic characteristics. The Ti-terminated surface is more prone to forming quasi-solid regions compared to the B-termination. Analysis of mean square displacement and vibrational density of states indicates that the liquid layer at the Ti-terminated interface is closer in characteristics to a solid compared to the B-terminated interface. We also found that on the TiB2 (0001) surface different terminations give rise to distinct ordered structures at the interfaces, which is ascribed to their different diffusion abilities.
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The targeted stimulation of micropores based on the transformation of coal's molecular structure is proposed due to the chemical properties and difficult-to-transform properties of micropores. Carbon disulfide (CS2) extraction is used as a targeted stimulation to reveal the internal evolution mechanism of micropore transformation. The variations of microcrystalline structures and micropores of bituminous coal and anthracite extracted by CS2 were analyzed with X-ray diffraction (XRD), low-temperature carbon dioxide (CO2) adsorption, and molecular simulation. The results show that CS2 extraction, with the broken chain effect, swelling effect, and aromatic ring rearrangement effect, can promote micropore generation of bituminous coal by transforming the microcrystalline structure. Furthermore, CS2 extraction on bituminous coal can decrease the average micropore size and increase the micropore volume and area. The aromatic layer fragmentation effect of CS2 extraction on anthracite, compared to the micropore generation effect of the broken chain effect and swelling effect, can enlarge micropores more remarkably, as it induces an enhancement in the average micropore size and a decline in the micropore volume and area. The research is expected to provide a theoretical basis for establishing reservoir stimulation technology based on CS2 extraction.
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P2-Na0.67Mn0.67Ni0.33O2 is a promising cathode material for sodium ion batteries (SIBs) due to its low cost, high theoretical capacity, and non-toxicity. However, it still suffers from unsatisfactory cycling stability mainly incurred by the Jahn-Teller effect of Mn3+ and electrolyte decomposition on the electrode/electrolyte interface. Herein, the P2-Na0.67Ni0.33Mn0.67O2@PPy (NNMO@PPy) composite applied as cathode materials for SIBs is obtained by introducing conductive polypyrrole (PPy) as coating layer on the P2-Na0.67Ni0.33Mn0.67O2 (NNMO) microspheres. Numerous physical characterization methods indicate that the PPy layer was uniformly coated on the surface of NNMO microspheres without change in phase structure and morphology. The PPy coating layer can alleviate Mn dissolution and effectively suppress the side reactions between the electrolyte and electrode during cycling. The optimal NNMO@PPy-9 with 9 wt% PPy delivers a high capacity of 127.4 mAh/g at the current density at 150 mA g-1, an excellent cyclic stability with high capacity retention of 80.5 % after 300 cycles, and enhanced rate performance (169.3 mAh/g at 15 mA g-1 while 89.8 mAh/g at 600 mA g-1). Furthermore, hard carbon (-)//NNMO@PPy-9 (+) full cell delivers a high energy density of 305.1 Wh kg-1 and superior cycling stability with 88.2 % capacity retention after 150 cycles. In-situ X-ray diffraction experiment and electrochemical characterization verify the highly reversible structure evolution and robust P2-type phase structure of NNMO@PPy-9 for fast and stable Na+ diffusion. This effective strategy of using conductive PPy as a coating layer may provide a new insight to modify NNMO surface, improving the cycling stability and rate capability.
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Prussian blue analogues (PBAs) exhibiting hollow morphologies have garnered considerable attention owing to their remarkable electrochemical properties. In this study, a one-pot strategy is proposed for the synthesis of MnFe PBA open cages. The materials are subsequently employed as cathode electrode in sodium-ion batteries (SIBs). The simultaneous evolution of structure, morphology, and performance during the synthesis process is investigated. The findings reveal substantial structural modifications as the reaction time is prolonged. The manganese content in the samples diminishes considerably, while the potassium content experiences an increase. This compositional variation is accompanied by a significant change in the spin state of the transition metal ions. These structural transformations trigger the occurrence of the Kirkendall effect and Oswald ripening, culminating in a profound alteration of the morphology of MnFe PBA. Moreover, the shifts in spin states give rise to distinct changes in their charge-discharge profiles and redox potentials. Furthermore, an exploration of the formation conditions of the samples and their variations before and after cycling is conducted. This study offers valuable insights into the intricate relationship between the structure, morphology, and electrochemical performance of MnFe PBA, paving the way for further optimizations in this promising class of materials for energy storage applications.
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Electrocatalytic carbon dioxide/carbon monoxide reduction reaction (CO(2)RR) has emerged as a prospective and appealing strategy to realize carbon neutrality for manufacturing sustainable chemical products. Developing highly active electrocatalysts and stable devices has been demonstrated as effective approach to enhance the conversion efficiency of CO(2)RR. In order to rationally design electrocatalysts and devices, a comprehensive understanding of the intrinsic structure evolution within catalysts and micro-environment change around electrode interface, particularly under operation conditions, is indispensable. Synchrotron radiation has been recognized as a versatile characterization platform, garnering widespread attention owing to its high brightness, elevated flux, excellent directivity, strong polarization and exceptional stability. This review systematically introduces the applications of synchrotron radiation technologies classified by radiation sources with varying wavelengths in CO(2)RR. By virtue of in situ/operando synchrotron radiationanalytical techniques, we also summarize relevant dynamic evolution processes from electronic structure, atomic configuration, molecular adsorption, crystal lattice and devices, spanning scales from the angstrom to the micrometer. The merits and limitations of diverse synchrotron characterization techniques are summarized, and their applicable scenarios in CO(2)RR are further presented. On the basis of the state-of-the-art fourth-generation synchrotron facilities, a perspective for further deeper understanding of the CO(2)RR process using synchrotron radiation analytical techniques is proposed.
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The AlxCoCrFeNi2.1 (x = 0, 0.3, 0.7, 1.0, 1.3) multi-component high-entropy alloy (HEA) was synthesized by mechanical alloying (MA) and Spark Plasma Sintering (SPS), The impact of the percentage of Al on crystal structure transition, microstructure evolution and mechanical properties were studied. Crystal structure was investigated by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The results show that with the increasing of Al content, the crystal structure of the alloys gradually transformed from a nanocrystalline phase of FCC to a mix of FCC and BCC nanocrystalline. The hardness was found to increase steadily from 433 HV to 565 HV due to the increase in fraction of BCC nanocrystalline phase. Thus, the compressive fracture strength increased from 1702 MPa to 2333 MPa; in contrast, the fracture strain decreased from 39.8% to 15.6%.
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Solid-state lithium batteries are promising next-generation energy storage systems for electric vehicles due to their high energy density and high safety and require achieving and maintaining intimate solid-solid interfaces for lithium-ion and electron transport. However, the solid-solid interfaces may evolve over cycling, disrupting the ion and electron diffusion pathways and leading to rapid performance degradation. The development of solid-state lithium batteries has been hindered by the lack of fundamental understanding of the interfacial microstructure change over cycling and its relation to electrochemical properties. Herein, we prepared a quasi-solid-state lithium battery, 30%LiFePO4-55%Li1.5Al0.5Ge1.5(PO4)3-15%C| Li1.5Al0.5Ge1.5(PO4)3|Li, by spark plasma sintering, and employed it as a model system to reveal the microstructure evolution at the solid-solid interfaces with electrochemical performance of the batteries. The electrochemical assessment showed that the quasi-solid-state lithium battery exhibited a discharge specific capacity of about 150 mAh g-1 in the first 80 cycles and then experienced severe capacity attenuation afterward, accompanied by a gradual internal resistance increase. Scanning electron microscopy observation showed that more cracks were formed inside the solid-state electrolyte and at the solid-solid interfaces as the battery cycled from 10 to 67 and 157 cycles. Detailed microstructure and phase analysis by high-resolution transmission electron microscopy and selected area electron diffraction discovered that the crack formation and performance decay were mainly caused by (1) the volume change of the LiFePO4 composite cathode during cycling, (2) the grain expansion of the Li1.5Al0.5Ge1.5(PO4)3 solid-state electrolyte at its interface with lithium anode, and (3) the formation of a solid electrolyte interphase layer, comprising Li2CO3, LiF, and LiTFSI, at the cathode-solid-state electrolyte interface. These microstructure changes built up over repeated battery cycling, ultimately causing the structure collapse and battery failure. The microstructure evolution information is expected to guide the design of better structures and interfaces for solid-state lithium batteries.
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Poly (triazine imide) (PTI) generally obtained via ionothermal synthesis features extended π-conjugation and enhanced crystallinity. However, in-depth investigation of the polycondensation process for PTI is an onerous task due to multiple influencing factors and limited characterization techniques. Herein, to simplify the polymerization route and exclude non-essential factors, PTI was prepared by calcining only melamine and LiCl. This study aims to identify the pivotal role of LiCl in PTI formation, which can convert heptazine-based intermediates into more stable triazine-based PTI framework. Based on this discovery, we demonstrate the transformation process of the prepared samples from amorphous Bulk g-C3 N4 to regular PTI, and further prove that the reaction with LiCl causes disruption of heptazine covalent organic frameworks. Additionally, the PTI exhibits higher photocatalytic water splitting performance due to efficient charge carrier mobility and separation, as well as faster reaction kinetics. This discovery deepens understanding of the polycondensation process of PTI crystals and provides insights toward the rational design of crystalline carbon nitride-based semiconductors.
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In the development of nanoenabled technologies for large-scale water treatment, immobilizing nanosized functional materials into the confined space of suitable substrates is one of the most effective strategies. However, the intrinsic effects of nanoconfinement on the decontamination performance of nanomaterials, particularly in terms of structural modulation, are rarely unveiled. Herein, we investigate the structure evolution and decontamination performance of iron (hydr)oxide nanoparticles, a widely used material for water treatment, when confined in track-etched (TE) membranes with channel sizes varying from 200 to 20 nm. Nanoconfinement drives phase transformation from ferrihydrite to goethite, rather than to hematite occurring in bulk systems, and the increase in the nanoconfinement degree from 200 to 20 nm leads to a significant drop in the fraction of the goethite phase within the aged products (from 41% to 0%). The nanoconfinement configuration is believed to greatly slow down the phase transformation kinetics, thereby preserving the specific adsorption of ferrihydrite toward As(V) even after 20-day aging at 343 K. This study unravels the structure evolution of confined iron hydroxide nanoparticles and provides new insights into the temporospatial effects of nanoconfinement on improving the water decontamination performance.
