Membrane Water Content Research Articles

Water Transport in PEFC Cold Startup with Temperature Rise Simulating Adiabatic Condition

In a polymer electrolyte fuel cell (PEFC) startup below freezing point, it is known that shutdown occurs due to the produced water freezing in the cell. The authors’ research group has been conducting experimental studies on the freezing behaviors and mechanism. At −20°C, the generated water freezes at the moment when the water comes out into the catalyst layer (CL) pores, and at −10°C, the generated water moves inside the fuel cell in the supercooled state and freezes (1)-(2). It was also reported that the ice frozen at the micro porous layer (MPL) and CL interface absorbs generated water through the ionomer in the CL (3). This study conducted both model analyses to evaluate the water content in membrane and experimental investigations to confirm the cold start characteristics with temperature rise. A single cell with an active area of 25 cm2 (5 cm × 5 cm) was used in this study. As shown in Figure 1, heaters and heat insulating plates were inserted between the current collectors and the end plates to simulate the adiabatic condition by controlling the cell temperature. Heat release from the sides of in-plane direction was suppressed by winding a heat insulating material (not shown in Figure 1). After a preconditioning process to enhance the performance of a MEA, the initial conditions of water in the cell were carefully controlled by the procedure described in Ref. 1. Then the cell and the chamber were cooled to a target temperature, and cell operation was started. Dry hydrogen and dry air were supplied to anode and cathode. In the model analysis, we considered three phenomena related to water generation and water transport: water generation in cathode CL by the reaction, back diffusion from the CL to membrane, and electro-osmosis from membrane to the CL. Two types of loading current method, ramp loading and 2 step loading, were applied. Figure 2 shows changes in the resistance overvoltage calculated from the evaluated water content in membrane during cold startup at −30°C. In the ramp loading, the applied current density was increased linearly for initial 30 sec to 0.07A/cm2; in the 2 step loading the current densities were set constant, 0.04A/cm2, for initial 30 sec followed by 0.07A/cm2. Here, this model was developed based on the experimental results of isothermal cold startup at −30°C. In the experiments, shutdown due to dry-out occurred in the ramp loading while the startup succeeded in the 2 step loading. In Figure 2, the maximum resistance overvoltage in the 2 step loading is lower, showing advantage in early startup without dry-out. Next, we conducted the cold startup with adiabatic temperature rise at −30°C, as shown in Figure 3. The 2 step loading was applied, and the heaters were used to simulate adiabatic temperature rise due to the heat of reaction during cold startup in the cell at central part in a stack loaded on automobile. In early cold startup, shutdown does not occur, and the cell resistance can be decreased by produced water due to the reaction. Then, cell temperature reaches 0°C at 273 sec before ice formation in the cell perfectly hinder the supply of oxygen. The more appropriate startup method and water transport phenomena in the cell are further investigated in this study. Reference (1) Y. Tabe, et al. , J. Power Sources 208 (2012), 366. (2) Y. Tabe, et al. , J. Electrochem. Soc. 163 (10) (2016), F1139. (3) N. Wakatake, et al. , ECS Trans. 75 (14) (2016), 623. Figure 1

Tailored Catalyst Layer and Micro-Porous Layer Porosity and the Effect on the Performance and Water Content in PEMFC

In this study, the effect of the catalyst layer (CL) and the cathode microporous layer (MPL-C) porosity on the performance and water content of the polymer electrolyte membrane (PEMFC) is investigated. Monodispersed polystyrene (PS) particles are used as pore formers to fabricate CL and MPL with different degrees of porosities. Specially developed miniature Single single cells for neutron imaging experiments with an active area of 8 cm² are implemented with the in-house made catalyst coated membranes and cathode MPLs. The cathode MPLs were coated on a 29 BA substrate, and commercial 29 BC SGL were used on the anode side as the gas diffusion layers (GDLs). Neutron tomography is used to investigate the water content and distribution inside the operating fuel cells. The quantitative analysis of the water thickness under the channels of the cells at RH=120% and I=1 A.cm-2 is shown in figure 1.a. It is observed that the water content has decreased for cell 3 ( CL: 10 wt.% PS, MPL: 10 Vol.% PS) compared to cell 2 ( CL: 5wt.% PS, MPL:10 Vol.% PS) and cell 1 (Reference CL and MPL (without PS)). Polarisation curves for these three cells are provided in Figure 1.b. At current densities higher than I=1 A.cm-2 performance has increased for cell 2 and 3 where the components had higher porosity degree compared to the cell 1 which has a reference CL and reference cathode MPL. The results show that addition of macropores could facilitate the transport of gases and the removal of water at the mass transport regions. This method is currently under investigation by the authors. Further results will be provided in the presentation. Figure 1

Modelling and Controlling of ion transport rate efficiency in Proton exchange membrane (PEMFC), alkaline (AFC), direct methanol (DMFC), phosphoric acid (PAFC), direct forming acid(DFAFC) and direct carbon (DCFC) fuel cells

Ion transport rate of DFAFC, PAFC, AFC, PEMFC, DMFC and SOFC fuel cells have been studied. AFC which uses an aqueous alkaline electrolyte is suitable for temperature below 90 degree and is appropriate for higher current applications, while PEMFC is suitable for lower temperature compared to others. Thermodynamic equations have been investigated for those fuel cells in viewpoint of voltage output data. Effects of operating data including temperature (T), pressure (P), proton exchange membrane water content (λ) , and proton exchange membrane thickness ( on the optimal performance of the irreversible fuel cells have been studied. Performance of fuel cells was analyzed by simulating polarization and power curves for a fuel cell operating at various conditions with current densities.

Effects of flow direction on dynamic response and stability of nonhumidification PEM fuel cell

The flow directions of reactants in the anode and cathode channels have considerable impact on the dynamic responses of the nonhumidification polymer electrolyte membrane fuel cells (PEMFCs). In this study, the dynamic responses of nonhumidification PEMFCs using short-side-chain membranes are investigated with the variation in the flow direction of reactants using a three-dimensional transient simulation model. The dynamic responses of the cell voltages and local transfer currents are analyzed with the abrupt increase in the current density. Generally, the counter-flow cell exhibits a higher performance than the co-flow cell. During the load change, the co-flow cell experiences zero-power periods owing to the low cell voltage. Moreover, the counter-flow cell shows more uniform variation in the local transfer current and yields an even distribution in the overshoot compared to the co-flow cell owing to the higher membrane water content and the lower ionic resistance. However, the counter-flow cell results in a longer settling time compared to the co-flow cell owing to the large increase in the membrane water content. Overall, for the nonhumidification PEMFCs, the counter-flow cell is determined to be a preferred flow design owing to the higher performance and stability.

Finite Time Thermodynamic Optimization of an Irreversible Proton Exchange Membrane Fuel Cell for Vehicle Use

A finite time thermodynamic model of an irreversible proton exchange membrane fuel cell (PEMFC) for vehicle use was established considering the effects of polarization losses and leakage current. Effects of operating parameters, including operating temperature, operating pressure, proton exchange membrane water content, and proton exchange membrane thickness, on the optimal performance of the irreversible PEMFC are numerically studied in detail. When the operating temperature of the PEMFC increases, the optimal performances of PEMFC including output power density, output efficiency, ecological objective function, and ecological coefficient of performance, will be improved. Among them, the optimal ecological objective function increased by 81%. The proton film thickness has little effect on the output efficiency and the ecological of coefficient performance. The maximum output power density increased by 58% as the water content of the proton exchange membrane increased from 50% to the saturation point. The maximum output power density increases with the operating pressure.

Enhancing the electrochemical and antibacterial characteristics of cation exchange membrane by using synthesized (GO-co-Ag) nanoplates

Electrodialysis cation exchange membranes were modified by incorporating [graphene oxide (GO)-co-Ag] composite nanoplates. The [GO-co-Ag] composite nanoplates were prepared by magnetron sputtering technique assisted with plasma treatment. XRD pattern and SEM image confirmed [GO-co-Ag] formation decisively. SEM, EDX, and SOM images showed relatively uniform surface for prepared membranes. Use of [GO-co-Ag] caused to formation of a compact structure for the blended membranes. The cross-sectional SEM images exhibited a specific direction for [GO-co-Ag], which at nanoscale position. The membrane surface wettability was improved by incorporating of [GO-co-Ag]. Membrane water content, transport number, and permselectivity were enhanced initially by utilizing of [GO-co-Ag] up to 0.5 wt% and then decreased by more concentration. Flux and E-conductivity enhanced sharply by using of [GO-co-Ag]. Use of [GO-co-Ag] into membrane matrix also caused to enhancement of mechanical resistance whereas declines the chemical oxidative stability. Results showed good antibacterial ability for blended membranes in E. coli removal.

Effects of operating conditions on water and heat management by a transient multi-dimensional PEMFC system model

Water and heat management remains a major obstacle to the successful commercialization of proton exchange membrane fuel cell (PEMFC), especially at a complicated system level. To investigate the interaction among stack and associated auxiliary subsystems, a comprehensive transient PEMFC system model is developed, including stack, membrane humidifier, electrochemical hydrogen pump, air compressor, and radiator. Each individual sub-model has been rigorously validated against experimental data. The results show that the system performance deteriorates significantly under relatively low operating current densities (0.5 A cm−2). The voltage degradation is inhibited as more product water is generated and subsequently utilized by the humidifier, enhancing the stack inlet gas humidification. Under low operating current densities, increasing the operating temperature of membrane humidifier is unfavorable as it exacerbates the membrane dehydration. The voltage undershoot is observed, which is caused by the mismatch between dynamic changes of membrane water content in fuel cell and that of humidifier. If the temperature of dry air flowing into humidifier is well managed, the membrane dehydration may be avoided and assisted heating methods for humidifier may be unnecessary. Increasing the air stoichiometry is disadvantageous as it leads to more generated water being rapidly purged out of the system.

Pressure Effect on the PEMFC Performance

AbstractA three‐dimensional and two‐phase computational fluid dynamics (CFD) model for a single serpentine channel polymer electrolyte membrane fuel cell (PEMFC) based on ANSYS FLUENT fsimulation software is used to investigate the pressure effects on the PEMFC performance. The model is validated by a series of experiments and the numerical data fit well with the experiment results. The PEMFC performance is improved as the increase in back pressure. The simulation results revealed an important mechanism between pressure and humidity: a high back pressure could lead to a high relative humidity (RH) in cathode channel, which results in a high membrane water content. Based on this mechanism, the voltage increased by pressurization is divided into 2 parts: the voltage increased by reactants' partial pressure (Nernst potential) and the voltage increased by enhanced membrane water content. The comparison showed that the major benefit of pressurization is to keep adequate water in the membrane. The analysis of net power efficiency is also performed and it shows that the back pressure of 50 kPa is enough at low densities (less than 1,000 mA cm−2) and the back pressure of 100 kPa is needed at high densities (more than 1,000 mA cm−2).

Mixed matrix PES-based nanofiltration membrane decorated by (Fe3O4–polyvinylpyrrolidone) composite nanoparticles with intensified antifouling and separation characteristics

In this study, the physico-chemical properties, separation performance and antifouling ability of mixed matrix PES-based nanofiltration membranes decorated by (Fe3O4–polyvinylpyrrolidone) composite nanoparticles were investigated. The morphology of resulted membranes was characterized by scanning electron microscopy)SEM), scanning optical microscopy (SOM) and 3D surface images. The effect of incorporated nanoparticles on membrane properties and performance was determined using water contact angle, water content, membrane pore size and porosity, tensile strength, water flux, salt rejection and BSA solution filtration. The membrane water content was enhanced slightly by embedding Fe3O4/PVP up to 0.1wt.% in membrane body and then reduced again by more NPs ratio. The water contact angle also decreased from 65.18° for neat membrane to 50.5° for the modified ones. All mixed matrix membranes showed higher water flux compared to pristine membrane that measured 3.14(L/m2h) for bare membrane and 9.96 (L/m2h) for the superior ones. Salt rejection measured 82% for the pristine membrane whereas that was between 77%–90% for the nanocomposite membranes. Membrane tensile strength also improved by increase of composite NPs ratio into the polymer matrix. The nanocomposite membranes showed more BSA solution flux and outstanding antifouling properties compared to bare ones. The FRR measured ∼46.2% for bare membrane whereas that was (∼69.9% to ∼89.5%) for the nanocomposite membranes.

ANFIS-MPPT control algorithm for a PEMFC system used in electric vehicle applications

Fuel cell has been considered as one of the optimistic renewable power technologies for the automotive applications. The output power of a fuel cell is immensely dependent on cell temperature and membrane water content. Hence, a maximum power point tracking controller is essentially required to extract the optimum power from the fuel cell stack. In this paper, an adaptive neuro-fuzzy inference system based maximum power point tracking controller is presented for 1.26 kW proton exchange membrane fuel cell system used in electric vehicle applications. In order to extract the optimum power, a high step-up boost converter is connected between the fuel cell and the BLDC motor. The duty cycle of the converter is controlled by using ANFIS reference model, so that the maximum power is delivered to the BLDC motor. The performance of the proposed controller is tested under normal operating conditions and also for sudden variations in the cell temperatures of the fuel cell. In addition to this, to analyze the effectiveness and tracking behaviour of the proposed controller, the results were compared with those obtained using the fuzzy logic controller. Compared to the fuzzy logic controller, the proposed ANFIS controller has increased the average DC link power by 1.95% and the average time taken to reach the maximum power point is reduced by 17.74%.

Nitrate removal from drinking water by PAN ultrafiltration assisted with cationic surfactants: evaluation of effective factors using response surface methodology

Polyacrylonitrile ultrafiltration membrane was used to remove nitrate from aqueous solution, assisted by variations in cationic surfactant type and structure [cetylpyridinium chloride (CPC) and hexadecyl trimethylammonium bromide (HTAB)]. This paper also studied the effects of membrane thickness (150, 200, 250 µm), nitrate concentration (40, 120, 200 ppm), and surfactant concentration (0.4, 5.2, 10 mM) on removal efficiency. To this end, the required experiments were designed through response surface methodology using design-expert 7.0.0 software. The results showed that CPC was generally more efficient than HTAB due to its hydrophilic head structure. Rejection was improved significantly by increasing surfactant concentration over critical micelle concentration (CMC), but a slight fall was observed for CPC at about 10 mM concentration of surfactant in all nitrate concentrations. The optimal condition was obtained at 8.18 mM CPC, 196.2 ppm nitrate and thickness of 160 µm, which resulted in rejection of 80.29% at 30th min of filtration with an average flux of 19.25 L/m2 h. Increasing pressure showed a positive effect on rejection. Also, modified PVP-optimal membranes (160 µm) associated with different polyvinyl pyrrolidone (PVP) percentages by weight showed higher flux compared to an unmodified optimal membrane. Porosity and water content of optimal membrane were 49.9% and 82.56%, respectively, and surfactants rejection was always close to 100% over CMC.

Numerical and experimental analysis of liquid water distribution in PEM fuel cells

Abstract Liquid water distribution inside PEM fuel cell is investigated via interactive combination of CFD analysis and neutron imaging on a single 100 cm2 PEM fuel cell. The analysis is conducted with novel anode flow field designed for improved liquid water removal from the cell at higher currents. Numerical and experimental results show good agreement due to the incorporated experimental structural parameters for the membrane-electrode assembly and properly defined membrane water content parameters in conjunction with electro-osmotic drag and back-diffusion expressions in the numerical model. Methodology for achieving such accurate results is shown in detail in this work and complete lists of numerical parameters are provided for developing such numerical model. The CFD model also incorporates new multiphase model with enhanced heat and mass transfer capabilities for water phase change treatment as well as absorption and desorption modelling. This new approach is used to thoroughly study liquid water distribution inside the cell for dry and humid cases, as well as for co-flow vs. counter-flow configuration while the emphasis is directed towards liquid water distribution inside the porous media where condensation predominantly occurs. The robustness of the developed CFD model is demonstrated in its ability to accurately predict water pooling at lower currents, a phenomenon which could previously be only experimentally observed.

Desalination and heavy metal ion removal from water by new ion exchange membrane modified by synthesized NiFe2O4/HAMPS nanocomposite

Magnetic nickel ferrite (NiFe2O4) nanoparticles were synthesized and then modified by a novel hydrogel based on 2-acrylamido-2-methyl propane sulfonic acid (HAMPS). Field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR) analyses were conducted to prove the NiFe2O4/HAMPS nanocomposite formation decisively. The effect of NiFe2O4/HAMPS in the matrix of the heterogeneous cation exchange membrane on separation performance was studied. Adding of NiFe2O4/HAMPS into the membrane body up to 1%wt resulted in an increase of sodium flux obviously. The sodium flux showed a decreased trend at higher nanocomposite ratios slightly. Membrane potential, permselectivity, and transport numbers also showed improving trends. Results exhibited more value for Na+ dynamic transport numbers compared to static ones. Membrane water content and porosity increased from 13.07 to 27.7% and 9.6 to 20.2% by utilizing NiFe2O4/HAMPS, respectively. By adding NiFe2O4-HAMPS into the membrane structure a pronounced improvement in membrane mechanical resistance (~ 94%) and chemical stability was observed. Modified membrane containing 1.0%wt NiFe2O4-HAMPS showed effective separation in Pb2+ (~ 98%), Cu2+ (~ 48%), and Ni2+ (~ 34%) removal. This sample also showed highest current efficiency (78.9%) in Pb2+ removal and lowest energy consumption (6.97 W/mol) compared to others.

In Silico Design and Characterization of Graphene Oxide Membranes with Variable Water Content and Flake Oxygen Content.

Graphene oxide (GO) membranes offer exceptional promise for certain aqueous separation challenges, such as desalination. Central to unlocking this promise and optimizing performance for a given separation is the establishment of a detailed molecular-level understanding of how the membrane’s composition affects its structural and transport properties. This understanding is currently lacking, in part due to the fact that, until recently, molecular models with a realistic distribution of oxygen functionalities and interlayer flake structure were unavailable. To understand the effect of composition on the properties of GO membranes, models with water contents and oxygen contents, varying between 0% and 40% by weight, were prepared in this work using classical molecular dynamics simulations. The change in membrane interlayer distance distribution, water connectivity, and water diffusivity with water and oxygen content was quantified. Interlayer distance distribution analysis showed that the swelling of GO membranes could be controlled by separately tuning both the flake oxygen content and the membrane water content. Water-molecule cluster analysis showed that a continuous and fully connected network of water nanopores is not formed until the water content reaches ∼20%. The diffusivity of water in the membrane was also found to strongly depend on both the water and the oxygen content. These insights help understand the structure and transport properties of GO membranes with sub-nanometer interlayer distances and could be exploited to enhance the performance of GO membranes for aqueous separation applications. More broadly, the high-throughput in silico approach adopted could be applied to other nanomaterials with intrinsic non-stoichiometry and structural heterogeneity.

Optimization of operating parameters of a polymer exchange membrane electrolyzer

In this research, the operating parameters of proton exchange membrane (PEM) electrolyzer are optimized in order to decrease the required input voltage using Taguchi method. The considered parameters include the operating temperature, the pressure of cathode and anode, membrane water content, membrane thickness, and cathode and anode exchange current density. First, a thermodynamic model is developed for the PEM electrolyzer, and then the Taguchi method is applied for optimization of the electrolyzer performance. The signal to noise ratio (SNR) and the analysis of variance (ANOVA) method are also performed to determine the contribution ratio of effective parameters. The results reveal that the optimal condition is achieved at maximum working temperature, membrane water content, and cathode and anode exchange current density and at minimum membrane thickness, cathode pressure, and anode pressure. The anode exchange current density has considerable effect on the electrolyzer voltage with contribution of 67.15% while the membrane water content and the anode pressure have a minor influence with contribution of 1.1% and 0.42%, respectively.

Experimental investigation of the effect of membrane water content on PEM fuel cell cold start

In this study, the effect of membrane water content on proton exchange membrane (PEM) fuel cell cold start is investigated experimentally in detail. The cyclic voltammetry (CV) and high frequency resistance (HFR) are introduced to character electrochemical active surface area (ECSA) of the electrode and water content in the cell. Under normal condition, it is found that ECSA decreases with the decrement of membrane water content and a critical point of water content exists for the ECSA sharp decrement. Under cold start operation, low initial water content aggravates the voltage drop when the load is applied. The high initial water content leads to a rapid membrane water saturation, causing a short shutdown time, while the low initial water content may lead to a bad cold start performance. For the excessive low initial water content, the voltage reversal due to water electrolysis and carbon corrosion is also considered. Besides, the HFR is also recorded during cold start operation to estimate ice formation in the cell. It is indicated that a proper initial membrane water content after purge is significantly vital for PEM fuel cell cold start to achieve the balance of ECSA and ice storage capacity.

Tailoring the Characteristics of Poly (phenylene-ether-ether) sulfone Membrane for Efficient Glycerol/Biodiesel Separation

Poly (phenylene-ether-ether) sulfone membrane was fabricated and characterized by efficient glycerol/biodiesel separation produced from waste cooking oils trans-esterification. The membrane preparation was processed by phase inversion technique. The morphology, Physico-chemical properties and separation behavior of membranes were studied at various PPEES concentration. A uniform surface was observed for the prepared membranes by scanning electron microscopy. AFM images exhibited that surface roughness was decreased from 9.24 to 7.26 nm by the increase of PPEES concentration from 12 to 15 %wt. Similar trend was found for the membrane Flux, water content, and porosity by the increase of PPEES content ratio up to 15 %wt. The efficiency of glycerol removal and mechanical strength was also improved by the increase of polymeric matrix concentration.

Computational Fluid Dynamics Study of Serpentine Flow Field Proton Exchange Membrane Fuel Cell Performance

Fuel cell is an electro-chemical device that directly converts the chemical energy of fuel into usable electrical form without any toxic byproducts. Flow field plates are backbone of the fuel cell. It is the essential component of fuel cell with multifunctional character. In the present work, a complete three-dimensional steady-state isothermal single phase computational fluid dynamics model is proposed for a proton exchange membrane fuel cell with serpentine flow channel to analyze the species transport phenomenon. The numerical model was developed and analyzed using ANSYS FLUENT 15.0 and simulations were carried out to get the key parameters like variation of oxygen, hydrogen, liquid water activity, and water mass fraction in the flow channels, membrane water content, and membrane protonic conductivity. The numerical results show that, when the cell is operated at higher current densities, i.e. lower cell voltage, hydrogen and oxygen consumption is more as well as water generation is also more. The effect of cell operating temperature and reactants inlet humidity on cell performance was also studied. Finally, the polarization curve obtained was compared with the experimental results and it was found that the numerical results are having good agreement with the experimental results.

Preparation of PVA-Based Hollow Fiber Ion-Exchange Membranes and Their Performance for Donnan Dialysis.

Hollow fiber type cation-exchange (C-HF) membranes and hollow fiber type anion-exchange (A-HF) membranes were prepared from poly (vinyl alcohol) (PVA)-based copolymer with cation-exchange groups and by blending PVA and polycation, respectively, by a gel fiber spinning method. In order to control the water content of the hollow fiber membranes, the membranes were cross-linked physically by annealing, and then cross-linked chemically by using glutaraldehyde (GA) solutions at various GA concentrations. The outer diameter of C-HF and A-HF membranes were ca. 1000 μm and ca. 1500 μm, respectively, and the thickness of the membranes were ca. 170 μm and 290 μm, respectively. Permeation experiments were carried out in two Donnan dialysis systems, which included mixed 0.1 M NaCl and 0.1 M CaCl2/C-HF /3 × 10−4 M CaCl2 and mixed 0.1 M NaCl and 0.1 M NaNO3/A-HF/3 × 10−4 M NaNO3 to examine ionic perm selectivity of the membranes. In the Donnan dialysis experiments using C-HF membranes, uphill transport of the divalent cations occurred, and, in the case of A-HF membranes, uphill transport of NO3− ions occurred. C-HF and A-HF membranes had about half of the flux in the uphill transported ions and also about half of the selectivity between the uphill transport ions and driven ions in comparison with those of the commercial flat sheet cation-exchange membrane (Neosepta® CMX) and anion-exchange membrane (Neosepta® AMX). Yet, IEC of C-HF and A-HF membranes were about one fifth of CMX and less than half of AMX, respectively. Since hollow fiber membrane module will have higher packing density than a flat membrane stack, the hollow fiber type ion-exchange membranes (IEMs) prepared in this study will have a potential application to a Donnan dialysis process.

The Positive Effect of Different 24-epiBL Pretreatments on Salinity Tolerance in Robinia pseudoacacia L. Seedlings

As a brassinosteroid (BR), 24-epibrassinolide (24-epiBL) has been widely used to enhance the resistance of plants to multiple stresses, including salinity. Black locust (Robinia pseudoacacia L.) is a common species in degraded soils. In the current study, plants were pretreated with three levels of 24-epiBL (0.21, 0.62, or 1.04 µM) by either soaking seeds during the germination phase (Sew), foliar spraying (Spw), or root dipping (Diw) at the age of 6 months. The plants were exposed to salt stress (100 and 200 mM NaCl) via automatic drip-feeding (water content ~40%) for 45 days after each treatment. Increased salinity resulted in a decrease in net photosynthesis rate (Pn), stomatal conductance (Gs), intercellular:ambient CO2 concentration ratio (Ci/Ca), water-use efficiency (WUEi), and maximum quantum yield of photosystem II (PSII) (Fv/Fm). Non-photochemical quenching (NPQ) and thermal dissipation (Hd) were elevated under stress, which accompanied the reduction in the membrane steady index (MSI), water content (RWC), and pigment concentration (Chl a, Chl b, and Chl). Indicators of oxidative stress (i.e., malondialdehyde (MDA) and antioxidant enzymes (peroxidase (POD) and superoxide dismutase (SOD)) in leaves and Na+ content in chloroplasts increased accompanied by a reduction in chloroplastid K+ and Ca2+. At 200 mM NaCl, the chloroplast and thylakoid ultrastructures were severely disrupted. Exogenous 24-epiBL improved MSI, RWC, K+, and Ca2+ content, reduced Na+ levels, maintained chloroplast and thylakoid membrane structures, and enhanced the antioxidant ability in leaves. 24-epiBL also substantially alleviated stress-induced limitations of photosynthetic ability, reflected by elevated chlorophyll fluorescence, pigment levels, and Pn. The positive effects of alleviating salt stress in R. pseudoacacia seedlings in terms of treatment application was Diw > Sew > Spw, and the most positive impacts were seen with 1.04 µM 24-epiBL. These results provide diverse choice for 24-epiBL usage to defend against NaCl stress of a plant.