Interfacial Transport Research Articles

Understanding Photovoltage Enhancement in Metal-Insulator Semiconductor Photoelectrodes with Metal Nanoparticles.

A metal-insulator-semiconductor (MIS) structure holds great potential to promote photoelectrochemical (PEC) reactions, such as water splitting and CO2 reduction, for the storage of solar energy in chemical bonds. The semiconductor absorbs photons, creating electron-hole pairs; the insulator facilitates charge separation; and the metal collects the desired charge and facilitates its use in the electrochemical reaction. Despite these attractive features, MIS photoelectrodes are significantly limited by their photovoltage, a combination of the voltage generated from photon absorption minus the potential drop across the insulator. Herein, we use multiscale continuum modeling of the carrier, electrolyte, and interfacial transport to identify strategies for mitigating the deleterious potential drop across the insulator and enabling high MIS photovoltages. To this end, we model Ni/SiO2/n-Si photoanodes that employ a planar Ni film or Ni nanoparticles (np-MIS) and validate both models using experimental polarization curves and photovoltage measurements from the literature. The simulations reveal that the insulator potential drop is lower and hence achieves higher photovoltages for np-MIS structures than MIS structures because the electrolyte screens charge trapped at defect states between the semiconductor and the insulator. This electrolyte charge screening phenomenon can be further leveraged by using low loadings or small nanoparticles, which not only minimize the interfacial potential drop but also improve the photocurrent by enabling more light absorption. These insights contribute to the optimization of the np-MIS structures for sustainable energy conversion.

Interfacial energy-mediated bulk transport across artificial cell membranes

Interfacial energy-mediated bulk transport across artificial cell membranes

Enhanced structural stability and durability in lithium-rich manganese-based oxide via surface double-coupling engineering

Lithium-rich manganese-based oxides (LRMOs) exhibit high theoretical energy densities, making them a prominent class of cathode materials for lithium-ion batteries. However, the performance of these layered cathodes often declines because of capacity fading during cycling. This decline is primarily attributed to anisotropic lattice strain and oxygen release from cathode surfaces. Given notable structural transformations, complex redox reactions, and detrimental interface side reactions in LRMOs, the development of a single modification approach that addresses bulk and surface issues is challenging. Therefore, this study introduces a surface double-coupling engineering strategy that mitigates bulk strain and reduces surface side reactions. The internal spinel-like phase coating layer, featuring three-dimensional (3D) lithium-ion diffusion channels, effectively blocks oxygen release from the cathode surface and mitigates lattice strain. In addition, the external Li3PO4 coating layer, noted for its superior corrosion resistance, enhances the interfacial lithium transport and inhibits the dissolution of surface transition metals. Notably, the spinel phase, as excellent interlayer, securely anchors Li3PO4 to the bulk lattice and suppresses oxygen release from lattices. Consequently, these modifications considerably boost structural stability and durability, achieving an impressive capacity retention of 83.4% and a minimal voltage decay of 1.49 mV per cycle after 150 cycles at 1 C. These findings provide crucial mechanistic insights into the role of surface modifications and guide the development of high-capacity cathodes with enhanced cyclability.

Flash joining of (La0.2Nd0.2Sm0.2Gd0.2Yb0.2)2Zr2O7 high-entropy ceramic to 3YSZ

(La0.2Nd0.2Sm0.2Gd0.2Yb0.2)2Zr2O7 high-entropy ceramic (HEC) and 3 mol% yttria-stabilized zirconia were directly joined in seconds using an innovative pressure-assisted flash joining technique. An optimized shear strength of 26 ± 3 MPa was obtained at 1200 °C under uniaxial pressure of 9 MPa in 30 s. The contact resistance at the interface was found to induce intense local Joule heating, which accelerated interfacial mass transport and the joining process. However, this local heating effect also led to segregation and precipitation of the HEC near the interface, forming large La/Yb-rich rare-earth zirconate grains and intergranular pores. Increasing the pressure inhibited these issues by lowering the contact resistance, suppressing grain growth, and promoting grain sliding, rearrangement, and coalescence of grain boundaries. The proposed mechanism, based on the local heating effect, provides new insights into flash joining, highlighting the critical role of this phenomenon in triggering thermal runaway and mass transport.

Topological Hall effect in a non-magnetic metal interfaced to a canted antiferromagnetic insulator in perovskite oxide heterostructures

We report interfacial transport properties in in situ grown orthorhombic perovskite oxide heterostructures consisting of an antiferromagnetic insulator DyFeO3 and a paramagnetic conductor CaRuO3. We observe Hall effect with a step-like increase amounting to an effective magnetic field of 30 T at 20 K. We provide a plausible explanation in the context of topological Hall effect originating from a non-coplanar spin texture and resultant emergent field in DyFeO3 associated with the scalar spin chirality. Our results demonstrate that the proximity effect of the emergent field at heterointerfaces is a universal physical phenomenon, while it has been reported originally in a heterointerface composed of pyrochlore oxides. This will greatly expand the choice of materials to the heterointerfaces for the research in emergent transport phenomena, which has been limited to single compounds with both metallic properties and special spin textures. Additionally, this will pave the way for possible device application of the emergent field by designing and combining perovskite oxides with versatile functionalities such as multiferroicity.

Enhancing interfacial compatibility and ionic transportation kinetics in lithium-rich manganese oxide via magnetron sputtering conformal coating with amorphous LiPON

This study presents the application of magnetron sputtering for the conformal coating of lithium phosphorus oxynitride (LiPON) onto lithium-rich manganese oxide (LRM) materials, aiming to enhance their electrochemical performance through a cost-effective and time-efficient strategy. The LRM with approximately 0.058 % mass loading of LiPON coating (LRM-2) exhibited remarkable reversible capacities of 173.9 mAh/g and 192.5 mAh/g over 200 cycles at 25 °C and 60 °C, respectively, under 1 C charge/discharge current density. Comprehensive characterization studies revealed that LiPON modification significantly improved lithium ionic conductivity, interfacial ion transport kinetics, and interface compatibility with the electrolyte. The stable cathode-electrolyte interface effectively mitigated structural damage to LRM particles, suppressed interfacial oxygen release-induced phase transformation, and stabilized the material’s microstructures. Our sputtering-based conformal coating strategy is easily accessible and low-cost, with significant commercial application potential, offering a promising universal approach for enhancing the electrochemical performance of LRM cathode powder materials.

Nanochannel electrodes facilitating interfacial transport for PEM water electrolysis

Nanochannel electrodes facilitating interfacial transport for PEM water electrolysis

Fluoride Ions Post-Treatment Regulates Interfacial Charge Separation and Transport to Promote Solar Water Splitting of Bismuth Vanadate.

Herein, we propose a simple and effective fluoride (F-) ions post-treatment method to improve the solar water splitting performance of monoclinic BiVO4 (abbreviated as BVO). The surface modification of BVO with functional F- ions not only facilitates the transfer and separation efficiency of carriers at the electrode/electrolyte interface but also promotes the adsorption and activation of water, resulting in a photocurrent of 3.2 mA/cm2 at a bias voltage of 1.2 VRHE. Furthermore, the transfer and separation of carriers in the bulk and on the surface are further regulated by the oxygen vacancies induced by F- ions, thereby enhancing the PEC water splitting performance of BVO. Notably, the experimental findings demonstrate that the introduce of F- ions into the KBi electrolyte enhances the photo-charging process of BVO. Specifically, at a bias voltage of 0.6 VRHE, the BVO-0.12F sample exhibits a stable photocurrent of 1.2 mA/cm2, which is twice as high as that of the initial BVO sample. Remarkably, our study unveils that the addition of F- ions into the KBi electrolyte solution plays a pivotal role in facilitating the separation of charge carriers and promoting interfacial charge transport. Consequently, this further leads to a substantial enhancement in the solar water splitting performance for BVO-0.12F photoanode.

A mesoscopic approach for nanoscale evaporation heat transfer characteristics

We propose a mesoscopic approach for investigating steady/transient nanoscale evaporation heat transfer characteristics, whose kinetic nature makes it an ideal tool to model the evaporation kinetics at the liquid-vapor interface and the microscopic wall-fluid interactions. Simulation of the evaporation of a flat nanoscale thin liquid film demonstrates its capability of resolving kinetically limited evaporation and liquid film adsorption. For the simulation of an evaporating meniscus in a nanochannel, our proposed mesoscopic approach considers the conservation of mass, momentum and energy of both liquid and vapor phases, thereby naturally incorporating both the multi-dimensional heat transfer effect and vapor transport resistance in nano-confined space. We demonstrate that solid-fluid interaction plays dominant roles on the interfacial transport during nanoscale evaporation, and vapor transport resistance has nonnegligible influences on the evaporation heat/mass transport in nano-confined spaces. By handling statistical behavior of molecule ensembles, this mesoscopic approach not only preserves microscopic physics but also has high computational efficiencies, enabling the simulation of space and time domains on the practical application level. This work paves the way for quantitative investigations of steady/transient nanoscale evaporation heat transfer characteristics using mesoscopic approach.

Interfacial ionic transportation in composite electrolyte induced by element segregation for low temperature fuel cells

Interfacial ionic conduction has been considered to play an important role in composite electrolyte of solid oxide fuel cell (SOFC). However, the contribution of interfacial conduction has not been well evaluated. In this study, interfacial conduction is evaluated in a composite electrolyte composed of (Na0.57K0.43)0.94Li0.06NbO3 (KNN) with ignorable electrical conductivity and ZnO with low bulk ionic conductivity. The dependence of power output on the ratio of KNN and ZnO as well as the size of particles is investigated to understand the influence of interfacial areas on cell performance. Additionally, the issues affecting cell performance is analyzed from the view of electric circuit model by focusing on the electrical property. A method is proposed to indirectly evaluate the existence of charge carriers at the interfaces. Moreover, the segregation of K at the interfaces of KNN and ZnO is confirmed, which is believed to play an important role in forming space charge layers at the interfaces and trigger the formation of high concentration of oxygen vacancies for improving interfacial ionic transportation. This study uncovers that element segregation at the interface of two phases maybe an important issue for ionic transportation at the hetero-interface of composite electrolyte for fuel cell application.

Core-shell engineering of graphite nanosheets reinforced PVDF toward synchronously enhanced dielectric properties and thermal conductivity

Polymer composites integrating high dielectric permittivity (ε′) but low loss, large breakdown strength (Eb) and thermal conductivity (TC), have attracted widespread attention in electronic devices and power systems. To simultaneously achieve these properties in graphite nanosheet (GNS)/poly(vinylidene fluoride, PVDF), the GNS were first encapsulated by a layer of aluminum oxide (Al2O3), and then incorporated into PVDF, and the resulting PVDF nanocomposites’ dielectric properties and TC were explored in terms of the Al2O3 shell thickness and filler loading. The insulating Al2O3 shell serves as a barrier layer for the formation of leakage current and long-distance electron migration thus resulting in much lower dielectric loss and conductivity of the GNS@Al2O3/PVDF. It effectively mitigates the dielectric mismatch between the filler and host matrix, further introduces more traps that can capture charge carriers, and increases the barrier height for electron detrapping subsequently preventing the growth of electric trees and elevating the Eb. Moreover, the Al2O3 interlayer alleviates both the phonon density state and phonon impedance mismatches between the filler and matrix and facilitates the interfacial phonon transport thus leading to improved TC. The dielectric parameters and TC of the GNS@Al2O3/PVDF can be simultaneously modulated by optimizing the Al2O3′s thickness. This work offers an effective approach for designing and fabricating the polymeric nanodielectrics concurrently integrating high ε′ but low loss, enhanced Eb, and TC for prospective applications in power equipment and microelectronic devices.

Investigating thermal transport across the AlN/diamond interface via the machine learning potential

Aluminum nitride (AlN) is an ultrawide-bandgap semiconductor with excellent potential for high-power applications. However, the heat dissipation issue remains a huge challenge for the use of AlN in high-power devices. A promising solution for this problem is to integrate AlN with the diamond heat sink. Therefore, interfacial thermal transport has become a significant bottleneck in thermal management. In this work, one neuroevolution potential is developed based on neural networks, which significantly improves the accuracy of predicting thermal properties compared to traditional potentials and address the issue of inaccurate thermal performance prediction of AlN/diamond heterostructures using traditional potentials. Molecular dynamics simulations based on NEP is adopted to investigate the crystal-orientation-dependent and interfacial-atom-dependent thermal boundary resistance of the AlN/diamond heterostructures after the interfacial bonding. Compared to bonding with Al and C atoms, the TBR decreases by approximately 50 % after bonding with N and C atoms at the interface. Especially for the AlN (0001)-N-diamond (100) heterostructure, the TBR is 0.95 m2·K·GW−1, very close to the theoretical limit of 0.8 m2·K·GW−1 through the diffuse mismatch model (DMM) theory. Finally, the insightful optimization strategies are proposed in this work which could pave the way for better thermal design and management of AlN/diamond heterostructures.

Cu quantum dots anchored core-shell submicrosphere catalyst for electro-enhanced degradation of diclofenac sodium

The low mass transfer efficiency, sluggish redox cycles of metal ions, and poor recycling rate of S2O82-→SO42-→S2O82- greatly limit the application of two-dimensional (2D) electrodes and persulfate (PS) techniques. In this study, an interface engineering strategy was developed to anchor Cu quantum dots (CuQDs) onto a novel Cu-CoO@NC (N-doped carbon) core-shell submicrosphere catalyst. The 3D electrochemical system (2D electrodes combined with Cu-CoO@NC particle electrodes) exhibited excellent catalytic behavior with 99.1 % removal of diclofenac sodium in 30 min. The Cu-CoO@NC catalyst presented effectiveness and strong environmental adaptability in a broad pH range, in actual water bodies, and for multiple PPCPs. Based on the results analyses of experiments and density functional theory (DFT) calculations, the excellent performances of Cu-CoO@NC/PS during electrochemical oxidation (EO) result from the effective mass transfer, efficient interfacial charge transport, rapid redox cycling of bimetallic ions promoted by cathode, repetitive cycle of S2O82- → SO42- → S2O82- caused by anode and multiple active sites of PS.

Tuning cross-plane thermal conductivity of multilayer graphene/h-BN vdW heterostructures via composition distribution

Nanomaterials with low thermal conductivity (TC) are ideal candidates as thermoelectric materials. In this direction, we design innovative multilayer graphene/h-BN (GBN) van der Waals (vdW) heterostructures with gradient composition distribution (C, B and N atoms), inspired by the newly synthesized boron carbonitride nanosheets. Three types of 26-layer GBN models are constructed and investigated, i.e. U-shape, X-shape, A-shape, representing uniform, symmetrical, and asymmetrical distributions of carbon atoms along the cross-plane direction, respectively. Based on non-equilibrium molecular dynamics (NEMD) simulation, we confirm that X-shape GBN model possess the lowest cross-plane TC, approximately 7 times smaller than that of the uniform U-shape graphene. The cross-plane TC can be further reduced by applying tensile strains or decreasing interlayer coupling strength. These findings elucidate the significant role the composition distribution plays in the thermal transport of GBN vdW heterostructures. However, the mechanical properties (Young's nodulus and tensile strength) of the new vdW heterostructures are insensitive to the composition distribution. Our work provides a new perspective for manipulating the interfacial thermal transport of multilayer GBN vdW heterostructures by means of material design and offers a useful guide for rationally designing thermoelectric materials with tailored thermal properties based on vdW heterostructures.

Role of elastic phonon couplings in dictating the thermal transport across atomically sharp SiC/Si interfaces

The interfaces between SiC and the corresponding substrate largely affect the performance of SiC-based electronics. Understanding and designing the interfacial thermal transport across the SiC/substrate interfaces is critical for the thermal management design of these SiC-based power electronics. In this work, we systematically investigate the heat transfer across the 3C-SiC/Si, 4H-SiC/Si, and 6H-SiC/Si interfaces using non-equilibrium molecular dynamics simulations and diffuse mismatch model. We find that the room temperature ITC for 3C-SiC/Si, 4H-SiC/Si, and 6H-SiC/Si interfaces is 932 MW/m2K, 759 MW/m2K, and 697 MW/m2K, respectively, which is among the highest values for all interfaces made up of semiconductors (Yue et al., 2011; Cheng et al., 2020; Wilson et al., 2015; Ziade et al., 2015) [1–4]. The ultrahigh ITC of SiC/Si heterointerfaces at room temperature and high temperatures results from the dictating elastic scatterings at interfaces. We further find the ITC contributed by the elastic scattering decreases with the temperature but remains at a high ratio of 67%-78% even at an ultrahigh temperature of 1000 K. The reason for such a high elastic ITC is the large overlap between the vibrational density of states of Si and SiC at low and middle frequencies (<∼18 THz), which is also demonstrated by the diffuse mismatch model.

Weak Solvation Chemistry in Fluorinated Nonflammable Electrolytes Achieves Stable Cycling in High-Voltage Lithium Metal Batteries.

High-voltage (>4.35 V) lithium nickel-cobalt-manganese batteries are star candidates due to their higher energy density for next-generation power batteries. This poses higher demands for electrolyte design, including compatibility with lithium metals, stability on high-voltage cathodes, speedy interfacial ion transport kinetics, and appropriate concentration. However, electrolytes at the current level of research struggle to balance these demands. Here, we took advantage of the reduced affinity with Li+ and enhanced oxidative stability of three fluorinated linear carbonates to design a series of weakly solvating electrolytes (WSEs) at a low salt concentration of 1 M, which contain abundant ionic cluster structures, leading to the optimization of interfacial chemistry. As a result, WSEs can support the stable cycling of 4.6 V high-voltage Li||NCM811 cells for 300 cycles with a capacity retention of nearly 80%. Moreover, benefiting from the lower desolvation energy of Li+, WSEs achieve superior cycling stability and low polarization under -20 °C. Our work extends the application of WSEs for high-voltage LMBs, providing a promising solution in electrolytes for high-specific-energy lithium batteries.

Nanoscale Simulation of Plastic Contaminants Migration in Packaging Materials and Potential Leaching into Model Food Fluids.

Polymers are the most commonly used packaging materials for nutrition and consumer products. The ever-growing concern over pollution and potential environmental contamination generated from single-use packaging materials has raised safety questions. Polymers used in these materials often contain impurities, including unreacted monomers and small oligomers. The characterization of transport properties, including diffusion and leaching of these molecules, is largely hampered by the long timescales involved in shelf life experiments. In this work, we employ atomistic molecular simulation techniques to explore the main mechanisms involved in the bulk and interfacial transport of monomer molecules from three polymers commonly employed as packaging materials: polyamide-6, polycarbonate, and poly(methyl methacrylate). Our simulations showed that both hopping and continuous diffusion play important roles in inbound monomer diffusion and that solvent-polymer compatibility significantly affects monomer leaching. These results provide rationalization for monomer leaching in model food formulations as well as bulky industry-relevant molecules. Through this molecular-scale characterization, we offer insights to aid in the design of polymer/consumer product interfaces with reduced risk of contamination and longer shelf life.

Ultrafast electron transfer at the In2O3/Nb2O5 S-scheme interface for CO2 photoreduction

Constructing S-scheme heterojunctions proves proficient in achieving the spatial separation of potent photogenerated charge carriers for their participation in photoreactions. Nonetheless, the restricted contact areas between two phases within S-scheme heterostructures lead to inefficient interfacial charge transport, resulting in low photocatalytic efficiency from a kinetic perspective. Here, In2O3/Nb2O5 S-scheme heterojunctions are fabricated through a straightforward one-step electrospinning technique, enabling intimate contact between the two phases and thereby fostering ultrafast interfacial electron transfer (<10 ps), as analyzed via femtosecond transient absorption spectroscopy. As a result, powerful photo-electrons and holes accumulate in the Nb2O5 conduction band and In2O3 valence band, respectively, exhibiting extended long lifetimes and facilitating their involvement in subsequent photoreactions. Combined with the efficient chemisorption and activation of stable CO2 on the Nb2O5, the resulting In2O3/Nb2O5 hybrid nanofibers demonstrate improved photocatalytic performance for CO2 conversion.

Tuning interfacial fluidity and colloidal stability of membranized coacervate protocells

The cell membrane not only serves as the boundary between the cell’s interior and the external environment but also plays a crucial role in regulating fundamental cellular behaviours. Interfacial membranization of membraneless coacervates, formed through liquid-liquid phase separation (LLPS), represents a reliable approach to constructing hierarchical cell-like entities known as protocells. In this study, we demonstrate the capability to modulate the interfacial membrane fluidity and thickness of dextran-bound coacervate protocells by adjusting the molecular weight of dextran or utilizing dextranase-catalyzed hydrolysis. This modulation allows for rational control over colloidal stability, interfacial molecular transport and cell-protocell interactions. Our work opens a new avenue for surface engineering of coacervate protocells, enabling the establishment of cell-mimicking structures and behaviours.

Designing the Interface Layer of Solid Electrolytes for All-Solid-State Lithium Batteries.

Li1.3Al0.3Ti1.7(PO4)3 (LATP) is one of the most attractive solid-state electrolytes (SSEs) for application in all-solid-state lithium batteries (ASSLBs) due to its advantages of high ionic conductivity, air stability and low cost. However, the poor interfacial contact and slow Li-ion migration have greatly limited its practical application. Herein, a composite ion-conducting layer is designed at the Li/LATP interface, which a MoS2 film is constructed on LATP via chemical vapor deposition, followed by the introduction of a solid polymer (SP) liquid precursor to form a MoS2@SP protective layer. This protective layer not only achieves a lower Li-ion migration energy barrier, but also adsorbs more Li-ion, which is able to promote interfacial ion transport and improve interfacial contacts. Thanks to the improved migration and adsorption of Li-ion, the Li symmetric cell containing LATP-MoS2@SP exhibits a stable cycle of more than 1200h at 0.1mAcm-2. More remarkably, the capacity retention of the full cell assembled with LiFePO4 cathode is as high as 86.2% after 400 cycles at 1C. This work provides a design strategy for significantly improving unstable interfaces of SSEs and realizing high-performance ASSLBs.