Ion Transport Barriers Research Articles

On the stability and stationarity of the Super H-mode combined with an ion transport barrier in the core

The Super H-mode, a regime with high pedestal pressure and stored energy, is explored on DIII-D and combined with an ion transport barrier in the plasma core to increase performance. A significant improvement of ion temperatures and confinement is facilitated by favorable conditions such as high rotational shear and high ion pedestal temperatures. As a result of a rise in density and simultaneous decrease in rotation, the ion transport barrier disappears during the discharge evolution, leading to a transition from a very high confinement state at early times, to a reduced but still high confinement phase. Additionally, in many discharges, a global magnetohydrodynamic (MHD) event consistent with the coupling of a destabilized internal mode to an edge localized mode causes a large energy loss and leads to a reorganization of the plasma into a lower temperature, higher density state. Depending on the magnitude of the global MHD event, the plasma edge collisionality can increase significantly and shift the operational boundary from the peeling to the ballooning side, which can be understood as a drop out of the Super H-mode channel into standard H-mode. Hence, in Super H-mode discharges with ion transport barriers, both the improved pedestal height and rotational shear contribute to the high stored energy. At very low levels of rotation, the confinement factor for SH modes is still expected to exceed standard H-mode by 20%–30%. With their overall stationarity and high-performance levels, Super H-mode discharges provide an attractive regime for ITER and may enable a more compact design of future fusion power plants.

The role of entrance functionalization in carbon nanotube-based nanofluidic systems: An intrinsic challenge

In this work, experiments, molecular dynamics (MD) simulations, and theoretical analysis are conducted to study ion transport in thin carbon nanotubes (CNTs). Diverse nonlinear relationships between the ionic conductance (G) and the ion concentration (C) are observed. MD simulations show that the distinct G–C dependences are caused by the functionalization of the CNT entrance, which affects the energy barrier for ion transport and changes the ionic conductance. The various G–C relationships are also predicted using the electrokinetic theory by considering the potential generated by the functional groups at the CNT entrance. Practically, the number of functional groups at the CNT entrance is influenced by several factors, including both intrinsic and external effects, which make it difficult to regulate the ionic conductance and pose a challenge to CNT-based nanofluidic systems in practical applications.

Highly Nonuniform Ionic Transport on Ceramic-Polymer Hybrid Solid Electrolyte By Nanometer-Scale Operando Imaging

The ion conductivity of solid-state electrolytes (SSEs) has been greatly enhanced to a level comparable to that of liquid electrolytes, which is critical for fast charging/discharging. However, ion transport has primarily been characterized by macroscopic measurements such as electrochemical impedance spectroscopy (EIS) and galvanostatic profiles of charging/discharging. These measurements essentially reflect an average of microscopic ion-transport phenomena. Ion transport in SSEs can be far more complicated, but detailed microscopic transport characterization studies are currently lacking. Theoretical studies have proposed that ion transport can be governed by highly crystalline-orientation-dependent ionic hopping through the ceramic lattice, and some SSEs can even act as one-dimensional or two-dimensional ion conductors.[1] [2] Characterization methods are needed that measure in-situ ion transport with nm-scale spatial resolution to improve our understanding and tune the ion conduction in solid-state batteries (SSBs).Here, we report on nanometer-resolution in-situ ionic and electronic transport imaging of two advanced polymer-ceramic hybrid electrolytes: a polyimin/LixPySz (Li2S/P2S5:30/70) bulk hybrid SSE[3] and a Li-containing polyacrylonitrile (PAN)-coated Li-ion conductive glass ceramic (LICGC) with components of Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2.[4] Hybrid SSE is a promising approach that combines high ion conductivity of ceramic SSE and high stability of polymer SSE. We achieved the nm-resolution in-situ transport imaging by an atomic force microscopy (AFM)-based half-cell setup consisting of an AFM-probe/SSE/Li-metal structure (see Fig. 1). The AFM probe size ensures the nm-scale spatial resolutions, and we detected the small current in the pA‒fA (10-12‒10-15 A) range flowing through the AFM probe by using a logarithmic-scale current amplifier that detects both the ionic conduction and electronic leaking currents through the SSE.Concerning the bulk hybrid SSE, we found large ionic current fluctuations—five times to one order of magnitude on the LPS region of the SSE. The electronic leaking current is about 5 orders of magnitude smaller than the ionic current. Both the ionic and electronic transport at the LPS/polymer boundary show sharp transitions with no detectable current flowing through the polymer particles. The average ionic current through the LPS region decreases significantly with decreasing polyimine particle size and with extensive cycling, elucidating the Li-dendrite prevention mechanisms of this bulk hybrid SSE by polymer extension into ceramic interparticles.[3] The large ionic current fluctuation is understood in terms of highly anisotropic transport kinetic barriers along the different crystalline axes due to different grain orientations in the polycrystalline ceramic materials;[1] [2] this is a new factor to be mitigated to eliminate Li dendrite formation and growth in the SSBs.Regarding the polymer-coated LICGC SSE, we found significant ionic current fluctuation of 2‒3× the ion current but that is significantly less than in the LPS SSE. This mitigated current fluctuation is likely due to the more homogeneous ion-transport barriers of the glassy material with smaller grains in its amorphous matrix. The electronic leaking current is slightly larger than LPS, four orders of magnitude smaller than the ionic current. The polymer coating reduced the ionic current by several times compared with the bare LICGC SSE without the PAN coating. The PAN coating clearly prevented SSE degradation due to cycling.[4] Without the coating, the SSE after extensive cycling degraded extensively and nonuniformly, with domain sizes of μm to hundreds of μm. The degradation can be ionic blocking with slight electronic leaking as well as highly electronic shunting, depending on different domains or areas. The polymer coating effectively prevented both ionic and electronic degradation. In fact, ionic conduction improved by about 5 times, but electronic leaking was degraded slightly.Our AFM-based imaging opens up novel characterization of ionic and electronic transport in SSEs. The nm-scale inhomogeneous transport mechanisms as revealed by this operando imaging are far beyond the averaged results provided by macroscopic characterizations.

Overcoming the Interfacial Limitations Imposed by the Solid-Solid Interface in Solid-State Batteries Using Ionic Liquid-Based Interlayers.

Li-garnets are promising inorganic ceramic solid electrolytes for lithium metal batteries, showing good electrochemical stability with Li anode. However, their brittle and stiff nature restricts their intimate contact with both the electrodes, hence presenting high interfacial resistance to the ionic mobility. To address this issue, a strategy employing ionic liquid electrolyte (ILE) thin interlayers at the electrodes/electrolyte interfaces is adopted, which helps overcome the barrier for ion transport. The chemically stable ILE improves the electrodes-solid electrolyte contact, significantly reducing the interfacial resistance at both the positive and negative electrodes interfaces. This results in the more homogeneous deposition of metallic lithium at the negative electrode, suppressing the dendrite growth across the solid electrolyte even at high current densities of 0.3 mA cm-2 . Further, the improved interface Li/electrolyte interface results in decreasing the overpotential of symmetric Li/Li cells from 1.35 to 0.35 V. The ILE modified Li/LLZO/LFP cells stacked either in monopolar or bipolar configurations show excellent electrochemical performance. In particular, the bipolar cell operates at a high voltage (≈8 V) and delivers specific capacity as high as 145 mAh g-1 with a coulombic efficiency greater than 99%.

Impurity charge state transport in tokamak and stellarator plasmas

The standard one-dimensional formulation of impurity transport has proved to be highly questionable for impurities with medium/high Z, and is unsuitable for tungsten. This allows to reveal an inconsistent interpretation of the coupling between particle transport and ionization/recombination processes. A discrete two-dimensional (2D) Fokker–Planck–Kolmogorov equation with charge and radius variables is proposed to study impurity equilibrium and transport in tokamak and stellarator plasmas. The impurity behaviour is consistently considered in terms of a 2D Markovian stochastic process, which has a complex structure according to probabilistic laws that include particle transport as part of a more general impurity charge state transport. It is found that a self-consistent 2D Markovian impurity equilibrium has the consequence that particle transport corresponding to the stationary state is governed by ionization and recombination processes, which are statistically independent of the particle motion. These generalised 2D coronal equilibrium conditions, usually observed for heavy impurities in experiments, turn out to be the stationary solution of the discrete 2D equation introduced and are justified in a discrete 2D grid model of impurity equilibrium. A complete analysis of the simplest discrete 2D equilibrium cell provides the basis for a general solution, while the grid model is reduced to a set of such local equilibrium cells using a pseudo-state technique.Modelling of the density profiles of carbon, argon and tungsten impurities is carried out by TICS (transport of impurity charge states) code developed using available experimental data. It is found that the introduced equilibrium function, which is a discrete profile of the ratios of reduced ionization and recombination rates, systematically predicts the central accumulation, equilibrium and radial transport of impurities in H- and L-mode and ion transport barrier plasmas, in agreement with the experimental data.

Elucidating the Structural Basis of the Intracellular pH Sensing Mechanism of TASK-2 K2P Channels.

Two-pore domain potassium (K2P) channels maintain the cell’s background conductance by stabilizing the resting membrane potential. They assemble as dimers possessing four transmembrane helices in each subunit. K2P channels were crystallized in “up” and “down” states. The movements of the pore-lining transmembrane TM4 helix produce the aperture or closure of side fenestrations that connect the lipid membrane with the central cavity. When the TM4 helix is in the up-state, the fenestrations are closed, while they are open in the down-state. It is thought that the fenestration states are related to the activity of K2P channels and the opening of the channels preferentially occurs from the up-state. TASK-2, a member of the TALK subfamily of K2P channels, is opened by intracellular alkalization leading the deprotonation of the K245 residue at the end of the TM4 helix. This charge neutralization of K245 could be sensitive or coupled to the fenestration state. Here, we describe the relationship between the states of the intramembrane fenestrations and K245 residue in TASK-2 channel. By using molecular modeling and simulations, we show that the protonated state of K245 (K245+) favors the open fenestration state and, symmetrically, that the open fenestration state favors the protonated state of the lysine residue. We show that the channel can be completely blocked by Prozac, which is known to induce fenestration opening in TREK-2. K245 protonation and fenestration aperture have an additive effect on the conductance of the channel. The opening of the fenestrations with K245+ increases the entrance of lipids into the selectivity filter, blocking the channel. At the same time, the protonation of K245 introduces electrostatic potential energy barriers to ion entrance. We computed the free energy profiles of ion penetration into the channel in different fenestration and K245 protonation states, to show that the effects of the two transformations are summed up, leading to maximum channel blocking. Estimated rates of ion transport are in qualitative agreement with experimental results and support the hypothesis that the most important barrier for ion transport under K245+ and open fenestration conditions is the entrance of the ions into the channel.

(Invited) Understanding the Solid-Electrolyte and Electrode Interface via First-Principles Prediction of Potentials and Space-Charge Layers in All-Solid-State Batteries

Solid-state electronic heterojunctions at the solid-electrolyte and electrode interfaces play a critical role in determining ionic transport, and therefore the performance of solid-state batteries and fuel cells. The formation of a “space-charge layer” at the solid electrolyte and electrode interface is often cited as a barrier for ion transport, but a comprehensive first-principles modeling approach is still missing. For solid-state-batteries (SSB), predicting the space-charge-layer formation at the solid-electrolyte-and-electrode interface is even more challenging, as ion insertion and/or reaction with the electrode alters the material and thus band alignments at the interfaces. In this talk, we established a theoretical framework to predict the interface potential profiles from thermodynamic driving forces [1]. We first assumed the electrochemical potential for Li+ ions reached a constant at the open circuit equilibrium condition, then derived the relationship among the electrostatic potential, the lithium chemical potential, Fermi level, ionization potential, and the work function. This relationship yielded quantitative profiles of the electrostatic potential and electronic energy level alignments across the entire battery. This model complemented direct microscopic and macroscopic simulations by rigorously and simultaneously determining the potential drop, electrostatic dipole, and space-charge layer at the interface. The application of this model to the Li/LiPON/LixCoO2 system led to the important discovery that the space-charge layer varies with the state of charge (SOC, i.e. Li concentration in LixCoO2). More specifically we predicted that Li+ transferred from LIPON to Li0.5CoO2, but transferred from Li1.0CoO2 to LiPON, this result unified the seemingly contradictory experimental observations. We also predicted that electron transfer caused the interface dipole that can accelerate or impede Li+ flow during the discharge process at the in LixCoO2/LiPON interface, depending on the SOC. This will have a profound impact on the overpotentials and the overall cycling efficiency. An important design rule was suggested that increasing solid electrolytes’ valence band or engineering the interlayer at the interface can overcome the additional barrier caused by the interface dipole. This modeling framework is general for other solid-state energy storage devices with ionic and mixed conductor interfaces. [1] Michael W. Swift and Yue Qi, Phys. Rev. Lett. 122, 167701 (2019)

A New Lithium‐Ion Conductor LiTaSiO5: Theoretical Prediction, Materials Synthesis, and Ionic Conductivity

AbstractOwing to the nonleakage and incombustibility, solid electrolytes are crucial for solving the safety issues of rechargeable lithium batteries. In this work, a new class of solid electrolyte, acceptor‐doped LiTaSiO5, is designed and synthesized based on the concerted migration mechanism. When Zr4+ is doped to the Ta5+ sites in LiTaSiO5, the high‐energy lattice sites are partly occupied by the introduced lithium ions, and the lithium ions at those sites interact with the lithium ions placed in the low‐energy sites, thereby favoring the concerted motion of lithium ions and lowering the energy barrier for ion transport. Therefore, the concerted migration of lithium ions occurs in Zr‐doped LiTaSiO5, and a 3D lithium‐ion diffusion network is established with quasi‐1D chains connected through interchain channels. The lithium‐ion occupation, as revealed by ab initio calculations, is validated by neutron powder diffraction. Zr‐doped LiTaSiO5 electrolytes are successfully synthesized; Li1.1Ta0.9Zr0.1SiO5 shows a conductivity of 2.97 × 10−5 S cm−1 at 25 °C, about two orders of magnitude higher than that of LiTaSiO5, and it increases to 3.11 × 10−4 S cm−1 at 100 °C. This work demonstrates the power of theory in designing new materials.

Interfacial Ion‐Transport Mechanism of Li7(Al0.1)La3Zr2O12 Solid Electrolyte Modified by using a Spark Plasma Sintering Method

AbstractA novel interfacial in situ modification for Li7(Al0.1)La3Zr2O12 is designed and prepared by using a spark plasma sintering method. The modified interface with most grain boundary area exhibits excellent interfacial electrochemical properties. The X‐ray diffraction (XRD) and scanning electron microscope (SEM) data indicate that the interfacial modified specimen (spark plasma sintering method, 1000 °C, 5 min) with 38.2(6) nm grain diameter and 32,134 cm2/g grain boundary specific surface area has the highest ionic conductivity (8.84×10−4 S/cm−1). The lithium‐ion transmission mechanism in grain‐internal and grain boundaries is revealed by ab initio theory, using Materials Studio software. Furthermore, the first‐principles calculation data indicate that the migration barrier of Li+ at the Li7(Al0.1)La3Zr2O12 solid electrolyte grain boundary is 0.21 eV, which is only 2/3 of that in the grain internal (0.33 eV). As a result, SPS interfacial in situ processing technology can increase the grain boundary area, thereby reducing the ion transport barrier and the interfacial impedance of the material.

Global Gyrokinetic Simulation of Linear Micro-Instability Using Parameters Referring to HL-2A Plasma with Ion Transport Barrier

Global Gyrokinetic Simulation of Linear Micro-Instability Using Parameters Referring to HL-2A Plasma with Ion Transport Barrier

Borophene as Conductive Additive to Boost the Performance of MoS2-Based Anode Materials

Carbon-based materials, including graphene, porous carbon, and nanotubes, have been widely used as conductive additives to reduce the resistance in semiconductive anode materials of lithium-ion batteries (LIBs) toward better performance and the alleviated battery overheat problem. However, these additives are usually denounced for their low lithium-ion capacity. Moreover, emergence of vacant defect and heteroatom incorporation would open a sizable energy gap accompanied by reduced conductance. Here, by selecting MoS2 as a prototype system, we proclaim the utilization of emerging borophene as the conductive additive in terms of its low ion-transport barrier and robust metallic conductivity against defects and external doping in addition to its high Li-storage capacity. We found that substantial electrons transfer from MoS2 to borophene, producing strong electronic coupling that conduces to favorable interface bonding in combination with improved Li affinity. Incorporation of borophene also compensates the ...

Structural origin of electrical conductivity of copper lithium metaphosphate glasses

We have sought the structural origin of the recently reported electrical conductivity of lithium copper phosphate glass system (50-x) Li2O-xCu2O-50 P2O5, as lithium oxide is gradually replaced by Cu2O. The structure of these glasses was determined by X-ray photoelectron spectroscopy, Fourier Transform Infrared Spectroscopy and Raman spectroscopy. The results show the presence of both mobile Cu+ and relatively immobile Cu2+ ions. The relative fraction of Cu2+ [Cu2+/Cutot] and non-bridging oxygen increases with x; the latter indicating a tendency towards depolymerization of the network. On the other hand, there is enhanced crosslinking within the network as PO⋯Li bonds are replaced by relatively covalent PO⋯Cu bonds. This leads to a more cross-linked structure and a progressive reduction of the optimum sites for the jumping of both Li+ and Cu+, in agreement with the observed increase of the energy barrier for ion transport as Li2O is replaced by Cu2O.

Paving the way to nanoionics: atomic origin of barriers for ionic transport through interfaces.

The blocking of ion transport at interfaces strongly limits the performance of electrochemical nanodevices for energy applications. The barrier is believed to arise from space-charge regions generated by mobile ions by analogy to semiconductor junctions. Here we show that something different is at play by studying ion transport in a bicrystal of yttria (9% mol) stabilized zirconia (YSZ), an emblematic oxide ion conductor. Aberration-corrected scanning transmission electron microscopy (STEM) provides structure and composition at atomic resolution, with the sensitivity to directly reveal the oxygen ion profile. We find that Y segregates to the grain boundary at Zr sites, together with a depletion of oxygen that is confined to a small length scale of around 0.5 nm. Contrary to the main thesis of the space-charge model, there exists no evidence of a long-range O vacancy depletion layer. Combining ion transport measurements across a single grain boundary by nanoscale electrochemical strain microscopy (ESM), broadband dielectric spectroscopy measurements, and density functional calculations, we show that grain-boundary-induced electronic states act as acceptors, resulting in a negatively charged core. Besides the possible effect of the modified chemical bonding, this negative charge gives rise to an additional barrier for ion transport at the grain boundary.

Ion transport barriers triggered by plasma polarization in gyrokinetic simulations

The creation of ion transport barriers by externally induced sheared E × B flows is investigated with the global, full-f and flux-driven gyrokinetic code GYSELA. A gyrokinetic source of vorticity is designed and proves to be efficient in polarizing the plasma. Induced sheared electric fields develop in the turbulent core and are accompanied by the creation of a transport barrier. The barrier and the sheared flow relax quasi-periodically because of zonal flow activity and a destabilizing temperature anisotropy induced by the vorticity source. A new cyclic mechanism leading to the relaxation of transport barriers in tokamaks is discovered.

Theory and Simulation of Ion Conduction in the Pentameric GLIC Channel

GLIC is a bacterial member of the large family of pentameric ligand-gated ion channels. To study ion conduction through GLIC and other membrane channels, we combine the one-dimensional potential of mean force for ion passage with a Smoluchowski diffusion model, making it possible to calculate single-channel conductance in the regime of low ion concentrations from all-atom molecular dynamics (MD) simulations. We then perform MD simulations to examine sodium ion conduction through the GLIC transmembrane pore in two systems with different bulk ion concentrations. The ion potentials of mean force, calculated from umbrella sampling simulations with Hamiltonian replica exchange, reveal a major barrier at the hydrophobic constriction of the pore. The relevance of this barrier for ion transport is confirmed by a committor function that rises sharply in the barrier region. From the free evolution of Na(+) ions starting at the barrier top, we estimate the effective diffusion coefficient in the barrier region, and subsequently calculate the conductance of the pore. The resulting diffusivity compares well with the position-dependent ion diffusion coefficient obtained from restrained simulations. The ion conductance obtained from the diffusion model agrees with the value determined via a reactive-flux rate calculation. Our results show that the conformation in the GLIC crystal structure, with an estimated conductance of ~1 picosiemens at 140 mM ion concentration, is consistent with a physiologically open state of the channel.

Simulation of Small Size Divertor Tokamak Plasma Edge in the L-regime with ion Transport Barrier

Simulations of L-regimes of small size divertor tokamak plasma edge have been performed with the B2SOLPS5.0 2D fluid transport code for wide range parameters. A conclusion has been made that, radial electric field in the vicinity and inside separatrix is near to neoclassical electric field value. The poloidal E × B drifts and compensating parallel fluxes in the scrape off layer are large in the L-regime with ITB due to steeper gradients while the qualitative pattern of the flows is similar to that of the L-mode.

Amiloride-Sensitive Sodium Channels on the Parietal Human Peritoneum: Evidence by Ussing-Type Chamber Experiments

The mesothelium is part of the peritoneal water and ion transport barrier essential for peritoneal dialysis (PD) treatment and has a central role in the pathogenesis of peritoneal fibrosis and ultrafiltration failure observed in many PD patients. We investigated the effect of amiloride on the transmesothelial electrical resistance (RTM) of isolated parietal human peritoneum. Intact sheets were obtained from seven patients (three men, four women; mean age, 64 +/- 8 years). Fourteen peritoneal planar sheets were transferred to the laboratory in oxygenated Krebs-Ringer bicarbonate solution at 4 degrees C within 30 minutes after removal and mounted in an Ussing-type chamber. Amiloride (10(-3) mol/L) added apically (n = 8) caused a rapid rise of the RTM to 24.15 +/- 0.76 [OMEGA]H cm2 and a subsequent value persistence (p < 0.05); added basolaterally (n = 6), it increased the RTM to 22.66 +/- 0.59 [OMEGA]H cm2 within 1 minute, which persisted throughout the experiment. RTM was measured before and serially for 30 minutes after addition of amiloride. Control RTM was 20.29 +/- 0.86 [OMEGA]H cm2. These results indicate a rapid inhibitory effect of amiloride on the ionic permeability of parietal human peritoneum. The increase in the RTM observed after addition of amiloride clearly indicates the existence of amiloride-sensitive sodium channels on the human parietal peritoneal membrane, which may play some role in the ultrafiltration process and sodium removal during PD.

Zonal flow and GAM dynamics and associated transport characteristics in reversed shear tokamaks

Zonal flow behaviour and its effect on turbulent transport in reversed magnetic shear tokamaks are investigated by global simulations of electrostatic ion temperature gradient driven turbulence. When the safety factor q is reduced. zonal flows in a minimum q region change from oscillatory to stationary and suppress the turbulent transport effectively This result indicates that the change of zonal flow behaviour in the minimum q region may trigger the formation of ion transport barriers.

Anisotropic Conductivity Over In-Plane and Thickness Directions in Nafion-117

Proton conductivity of Nafion-117 membranes in the direction of thickness was measured in , 30–90% relative humidity, by means of 2- and 4-probe methods in thickness direction developed in this group. Heavy conductivity anisotropy of was found over the in-plane and thickness directions for membranes pretreated by hot-pressing at high temperature of and pressures of 1200 and , respectively. On the other hand, no conductivity fade was found for membrane pretreated at in the thickness direction compared to that in the plane direction. Small angle X-ray scattering measurements revealed ion domains flattened along the in-plane direction and ordered along the thickness direction. The origin of the persistent conductivity anisotropy is believed to come from the maximized potential energy barrier for ion transport in interaggregate along the thinned thickness direction.

New perspective on the mechanism of alleviating salt stress by spermidine in barley seedlings

Salt stress is considered to be a major limiting factor for plant growth and crop productivity. Salt injuries in plants are mostly due to excess Na+ entry. A possible survival strategy of plants under saline environments is the effective compartmentation of excess Na+ by sequestering Na+ in roots and inhibiting transport of Na+ from roots to shoots. Our previous study showed that exogenous application of polyamines (PAs) could attenuate salt injuries in barley plants. In order to further understand such protective roles of PAs against salt stress, the effects of spermidine (Spd) on sodium and potassium distribution in barley (Hordeum vulgare L.) seedlings under saline conditions were investigated. The results showed that exogenous application of Spd induced reductions in Na+ levels in roots and shoots with comparison of NaCl-treated plants, while no significant changes in K+ levels were observed. Correspondingly, the plants treated with Spd exogenously maintained high values of [K+]/[Na+] as compared with salt-stressed plants. Moreover, it was shown by X-ray microanalysis that K+ and Na+ accumulated mainly in the exodermal intercellular space and cortical cells of roots under salinity stress, and low accumulation was observed in endodermal cells and stelar parenchyma, indicating Casparian bands possibly act as ion transport barriers. Most importantly, Spd treatment further strengthened this barrier effects, leading to inhibition of Na+ transport into shoots. These results suggest that, by reinforcing barrier effects of Casparian bands, exogenous Spd inhibits Na+ transport from roots to shoots under conditions of high salinity which are beneficial for attenuating salt injuries in barley seedlings.