Uniform Distribution Of Oxygen Research Articles

Flow regime mechanisms in sequencing batch reactor (SBR) configurations on aerobic granular sludge formation using particle image velocimetry (PIV)

Indah Water Konsortium (IWK) consistently encounters challenges in managing over 7000 sewage treatment plants (STPs) due to inadequate infrastructure for centralized treatment. In addressing the challenge of land acquisition during STP upgrades, aerobic granular sludge (AGS) technology is worth exploring. The AGS systems are designed in sequencing batch reactors (SBRs) as a superior alternative to reduce land requirements. Research trends on AGS formation by flow regime mechanism are not yet fully comprehended for different SBR configurations (column and rectangular-type) as sufficient adjusted aeration rates in producing high-quality effluent. In this study, mature AGS of about 2736 μm was achieved at 57 days of formation in rectangular-type SBR by laminar flow with an aeration rate of 4 L/min. Due to transitional flow dynamics, there was a delay of about 54 % of mature AGS (2505 μm) on day 88 in column-type SBR at an aeration rate of 6 L/min. Microbial growth indicated that effective mixing was essential in wastewater treatment to ensure uniform distribution of oxygen, nutrients, and microorganisms, while excessive agitation must be avoided to maintain granular integrity. Thus, this research offers insights into the novelty of AGS for full-scale application.

Challenges and outcomes of cataract surgery after vitrectomy.

This review examines the challenges and outcomes of cataract surgery after pars plana vitrectomy (PPV), focusing on surgical techniques, timing, and complication management. Cataract formation remains the primary complication post-PPV, affecting approximately 80-100% of patients within two years. Nuclear sclerotic cataracts are most common, occurring in 60-100% of patients over 50, followed by posterior subcapsular cataracts (4-34%), which primarily affect younger and diabetic patients. PPV disrupts the normal oxygen gradient in the vitreous, resulting in a more uniform oxygen distribution and accelerating cataract formation.Post-PPV eyes present unique surgical challenges due to anatomical alterations, including zonular instability and capsular changes characterized by increased fragility, the potential for tears, and altered elasticity. Newer intraocular lens power calculations show promise, but unexpected refractive outcomes may occur. The choice between combined phacovitrectomy and sequential surgeries remains debated, with patient-specific factors guiding the approach. Visual outcomes vary depending on preexisting vitreoretinal pathologies and baseline vision before PPV. Further randomized controlled trials are needed to establish treatment guidelines and improve predictive models. Post-PPV cataract surgery presents unique challenges, including anatomical alterations and an increased risk of capsular complications. These necessitate careful consideration of the surgical approach and highlight the need for further research to optimize outcomes and establish treatment guidelines.

Calculation of oxygen distribution coefficients of RF3 (R = La, Gd) fluorides with the tysonite structure during their crystallization from a melt

Using the method of modified cryoscopy, the thermodynamic distribution coefficients of oxygen k0 in LaF3 and α-GdF3 with a tysonite structure (sp. gr. )were calculated from the fusibility diagrams of condensed systems RF3–R2O3 (R = La, Gd). The calculated coefficients k0 are 1.02 and 1.12 for lanthanum and gadolinium trifluorides, respectively. The values of the coefficients k0 satisfy the condition k0 1, which confirms the formation of maxima in the fusibility curves of tysonite solid solutions tys- RF3–2xOx. For LaF3, the proximity of the distribution coefficient to k0 = 1 corresponds to an almost uniform distribution of oxygen in the volume of the crystallized fluoride melt. Knowledge of oxygen distribution coefficients during crystallization from a melt is important for choosing a strategy for crystallophysical purification of trifluorides RF3 from oxygen impurities and obtaining oxofluorides tys-RF3–2xOx with a given impurity distribution.

Airfoil cross flow field to enhance mass transfer capacity and performance for PEMFC

Proper design of the flow field in bipolar plates is important for improving proton exchange membrane fuel cells in water transport, gas distribution and net power density enhancement. Inspired by the fact that the streamlined design of an airplane airfoil makes the flow resistance reduced, a new airfoil cross flow field is proposed. Airfoil cross flow field is composed of a regular pattern of airfoil pins which are categorized in pin-type flow fields. The effects of different airfoil-pin shapes and arrangements on cell performance were explored. The results showed that airfoil cross flow field improved water management by finely modulating the airflow significantly increasing the gas flow rate in the channel. In addition, the airfoil cross flow field design achieves higher and more uniform oxygen distribution at the interface between the gas diffusion layer and the catalyst layer. The proper shape and arrangement of the airfoil-pins can effectively increase the net power density of the cell by 10.65 % and 2.49 % compared to the conventional parallel flow field and the square-pin flow field. Due to the streamlined design of the airfoil cross flow field, the voltage drop is approximately 60 % of that of the conventional parallel flow field and even slightly lower than that of the square-pin flow field, which demonstrates its high practicality. In summary, the airfoil cross flow field well coordinates the high current density and low voltage drop requirements of proton exchange membrane fuel cells, and some new points of view on flow field design are presented.

Flow field optimization for performance enhancement of planar solid oxide fuel cells

The flow field design is very essential to the material distribution uniformity and overall output performance of planar solid oxide fuel cells. In this paper, the structure of the external manifold and cathode side interconnect is optimized to solve the uneven flow field distribution problem. The effects of crucial geometric parameters on the internal mass transfer, component transport, electrochemical reaction, temperature field and overall output performance of the fuel cell are studied by three-dimensional multi-physics numerical simulation. It is found that the combination of the three-inlet-two-outlet external manifold and cylindrical ribbed interconnect significantly reduces the uneven gas distribution between different channels and greatly improves the diffusion of oxygen under the ribs, thus enhancing the overall output performance of SOFC. Increasing the number of cylindrical ribs is beneficial to the transport and uniform distribution of oxygen. However, the excessive number of cylindrical ribs will hinder oxygen diffusion to the end of the flow channel, resulting in increased concentration polarization along the flow channel. Moreover, reducing the total contact area of the ribs enhances oxygen diffusion beneath the ribs but also raises the contact resistance and may deteriorate the cell performance.

Optimal design of locally improved structure for enhancing mass transfer in PEMFC cathode flow field

At high current density, the mass transfer in proton exchange membrane fuel cells (PEMFC) is significantly influenced by the flow field structure. In this paper, a bilateral track flow field (BTFF) is proposed to improve the transverse and longitudinal mass transfer as well as the water removal capacity of PEMFC. The geometry of the BTFF is optimized by orthogonal tests to obtain the optimal combination of geometric parameters and levels. Then using numerical modeling, the impact of the optimized BTFF (BT6) on the efficiency of the PEMFC was examined. The results show that BT6 significantly improves the utilization of the under-rib region by shortening the reactive gas diffusion path length to obtain a more uniform oxygen distribution, and the average oxygen concentration in the midline of the under-rib of the BT6 is increased by 102.60%, furthermore, the current density is increased by 16.32% compared with that of the parallel flow field (case0). In addition, by reducing the cross-sectional area of the gas flow channel, the BT6 has a higher gas flow velocity, which accelerates the removal of cathode liquid water, and the average liquid water saturation in the midline of the under-rib of the BT6 is reduced by 15.26% compared with case0. Finally, by analyzing the net power density of PEMFC, it can be found that the net power density of BT6 is increased by 15.68% compared with case0, which has good practical application value.

Ramped step flow field to enhance mass transfer capacity and performance for PEMFC

Proton exchange membrane fuel cells (PEMFC) hold great promise for various energy-conversion technologies. Flow channel structure inside bipolar plate plays an important role in water transport, gas distribution and heat transfer for PEMFC. Herein, a novel design of ramped step structure has been proposed, in which the ramps are introduced into the front side of step structures to form a continuous and smooth flow field. The cell performance and improvement mechanism have been investigated by COMSOL. The results show that the net power density of PEMFC with ramped step flow field (RSFF) exhibits an increase of up to 17.55 %, 2.82 %, and 2.29 % when compared to conventional parallel flow field (CPFF), ramp flow field (RFF), and step flow field (SFF), respectively. RSFF can achieve higher and more uniform distribution of oxygen cross the entire gas diffusion layer and catalytic layer. Additionally, increasing the slope angle in RSFF will help to enhance the capacity of mass transfer within a certain range. Furthermore, RSFF improves water management by significantly increasing gas flow velocity at the end of the channel. This work paves the way for the design of tapering flow channels in PEMFC, opening up new avenues for research in this field.

Artificial intelligence based structural optimization of solid oxide fuel cell with three-dimensional reticulated trapezoidal flow field

Three-dimensional Reticulated trapezoidal flow field (RTFF) is promising in improving the performance and durability of the solid oxide fuel cell (SOFC). However, the structural complexity makes it challenging for the geometry configuration of the splitter and mixer. To this end, an intelligent optimization framework is proposed by coupling artificial neural network (ANN) and non-dominated sorting genetic algorithm-II (NSGA-II), in order to maximize the net power density and oxygen uniformity simultaneously. The ANN prediction model is trained to obtain the computationally efficient surrogate model of the computational fluid dynamics (CFD) numerical simulation. NSGA-II is used for the multi-objective optimization of the RTFF structural parameters. The results illustrate that the prediction model is of high prediction precision and generalization capability. In comparison to SOFC with conventional parallel flow fields (CPFF), the degree of the performance improvement of SOFC with optimized RTFF depends on the working condition, i.e., fuel and air flow rates and operating temperatures. The SOFC with the optimal RTFF achieves a higher molar concentration of oxygen and a more uniform distribution of oxygen and current density than the CPFF SOFC. The proposed optimization framework provides an efficient design method for the development of the next-generation SOFC flow field.

Experimental study on coal combustion by using the ilmenite ore as active bed material in a 0.3 MWth circulating fluidized bed

The oxygen-carrier aided combustion (OCAC) technology which improves the uniformity of oxygen distribution in the fluidized bed and subsequently enhances the combustion efficiency has attracted more and more attention. However, the existing studies on OCAC mainly focused on the combustion of methane or biomass. There were few studies on low-volatile fuels (such as coal), especially pilot-scale studies that have not been reported. In this work, the effectiveness of OCAC technology on coal combustion has been comprehensively evaluated in a 0.3 MWth pilot-scale circulating fluidized bed (CFB) combustor. The experimental parameters including oxygen carrier (OC) proportion, primary air ratio (A) and oxygen concentration have been carefully investigated. The CO, NOx, SO2 and particulate matter (PM) were measured in real-time from the outlet of the cyclone separator by a gas analyzer and electrical low pressure impactor (ELPI). The results showed that the CO emission from the exit of the cyclone was reduced when the inert bed materials were replaced with the ilmenite ore, especially under the conditions of low oxygen concentration and A. The OCAC technology exhibited good thermal buffering capacity and oxygen buffering capacity. Compared to sand as bed material, the SO2 and NOx emission in flue gas under OCAC decreased and increased, respectively, which is attributed to the more uniform oxygen distribution with more available oxygen in the combustor. Such properties also promoted the self-desulfurization reaction of coal ash. However, it also reduces the reducibility area in the combustor and thus weakens the reduction of NOx. Compared to the sand case, the PM emission under OCAC case is more diminutive, especially in the size of 0–0.4 μm, the PM concentration under OCAC case is much lower than that under sand case.

Effect of Thickness and Outlet Area Fraction of Macroporous Gas Diffusion Layers on Oxygen Transport Resistance in Water Injection Simulations

Enhanced water removal through the gas diffusion layer (GDL) is important for the design of high-performance proton exchange fuel cells. In this work, the effects of GDL thickness and open area fraction at the GDL/flow field interface are examined under water invasion for a carbon-paper GDL (similar to Toray TGP-H series). Both uncompressed and inhomogeneously compressed samples are considered. Transport in heterogeneous, macroporous GDLs is modeled by means of a hybrid 3D discrete/continuum formulation based on a subdivision of the porous medium into control volumes due to the lack of a well-defined separation between pore and layer scales. Capillary-dominated transport of liquid water is simulated with an invasion percolation algorithm, while oxygen diffusion is simulated with a continuum formulation. Model predictions are validated with previous numerical and experimental data. It is shown that the combination of thin GDLs (mathrm {thickness} sim 100; mu mathrm {m}) and high GDL/flow field open area fractions can facilitate water removal/oxygen supply from/to the catalyst layer and can provide a more uniform oxygen distribution over large cell active areas. In agreement with previous work, porous flow fields with pore sizes comparable to the GDL thickness are good candidates to meet the above requirements, while improving water removal from the flow field (higher gas-phase velocity than conventional millimeter-sized channels) and ensuring a more uniform assembly compression.

Nanoscale Control of Structure and Composition for Nanocrystalline Fe Thin Films Grown by Oblique Angle RF Sputtering.

The use of Fe films as multi-element targets in space radiation experiments with high-intensity ultrashort laser pulses requires a surface structure that can enhance the laser energy absorption on target, as well as a low concentration and uniform distribution of light element contaminants within the films. In this paper, (110) preferred orientation nanocrystalline Fe thin films with controlled morphology and composition were grown on (100)-oriented Si substrates by oblique angle RF magnetron sputtering, at room temperature. The evolution of films key-parameters, crucial for space-like radiation experiments with organic material, such as nanostructure, morphology, topography, and elemental composition with varying RF source power, deposition pressure, and target to substrate distance is thoroughly discussed. A selection of complementary techniques was used in order to better understand this interdependence, namely X-ray Diffraction, Atomic Force Microscopy, Scanning and Transmission Electron Microscopy, Energy Dispersive X-ray Spectroscopy and Non-Rutherford Backscattering Spectroscopy. The films featured a nanocrystalline, tilted nanocolumn structure, with crystallite size in the (110)-growth direction in the 15–25 nm range, average island size in the 20–50 nm range, and the degree of polycrystallinity determined mainly by the shortest target-to-substrate distance (10 cm) and highest deposition pressure (10−2 mbar Ar). Oxygen concentration (as impurity) into the bulk of the films as low as 1 at. %, with uniform depth distribution, was achieved for the lowest deposition pressures of (1–3) × 10−3 mbar Ar, combined with highest used values for the RF source power of 125–150 W. The results show that the growth process of the Fe thin film is strongly dependent mainly on the deposition pressure, with the film morphology influenced by nucleation and growth kinetics. Due to better control of film topography and uniform distribution of oxygen, such films can be successfully used as free-standing targets for high repetition rate experiments with high power lasers to produce Fe ion beams with a broad energy spectrum.

A novel trickle bed electrochemical reactor design for efficient hydrogen peroxide production

A specific and environmentally benign electrochemical reactor that combines the property of gas diffusion electrode (GDE) with trickling flow property in trickle bed electrochemical reactor (TBER) is designed for intensive hydrogen peroxide (H2O2) production. Compared with other reactors a significant feature of this reactor is the capability to uniformly distribute the oxygen gas all over the cathode bed avoiding oxygen gas transport limitations, electrode limited area, and continuous electrolyte leakage. This reactor consists of two plates as anodes and two porous layers composed of carbon black and polytetrafluoroethylene (C-PTFE) mixture that are pasted on two stainless steel meshes(SSM) to form cathode beds (C-PTFE-SSM). The cathodes are placed on both cathode frame sides which were designed to comprise two separated cathodes. The oxygen gas can flow easily through the space between cathodes and diffuses to the solid-liquid interface to be electrochemically reduced to form H2O2. H2O2 was in situ electrosynthesized in an alkaline solution by the oxygen electrochemical reduction on the cathode surface. All operating conditions that affect the process were systematically investigated. The highest concentration of H2O2 of 46.56 mM was achieved in 40 min and 1.0 V at room temperature, whereas at 0 °C the generated peroxide was 57.86 mM. This significant performance is attributed to the uniform oxygen distribution on the electrode bed making an easy access for gas transport to the electrolyte-cathode interface. The low temperature increases oxygen solubility which increases the production rate as well. Power consumption was also estimated and found to be 4 kWh/kg which is economically beneficial. At different applied cell voltages and best-operating conditions, a kinetic study was conducted for H2O2 electrosynthesized.

Pore-Scale Investigation of Coupled Two-Phase and Reactive Transport in the Cathode Electrode of Proton Exchange Membrane Fuel Cells

A three-dimensional multicomponent multiphase lattice Boltzmann model (LBM) is established to model the coupled two-phase and reactive transport phenomena in the cathode electrode of proton exchange membrane fuel cells. The gas diffusion layer (GDL) and microporous layer (MPL) are stochastically reconstructed with the inside dynamic distribution of oxygen and liquid water resolved, and the catalyst layer is simplified as a superthin layer to address the electrochemical reaction, which provides a clear description of the flooding effect on mass transport and performance. Different kinds of electrodes are reconstructed to determine the optimum porosity and structure design of the GDL and MPL by comparing the transport resistance and performance under the flooding condition. The simulation results show that gradient porosity GDL helps to increase the reactive area and average concentration under flooding. The presence of the MPL ensures the oxygen transport space and reaction area because liquid water cannot transport through micropores. Moreover, the MPL helps in the uniform distribution of oxygen for an efficient in-plane transport capacity. Crack and perforation structures can accelerate the water transport in the assembly. The systematic perforation design yields the best performance under flooding by separating the transport of liquid water and oxygen.

Correlating Effects of Catalyst Loading and Porous Transport Layer Morphologies on Operation of Polymer Electrolyte Water Electrolyzers

Polymer electrolyte water electrolyzers (PEWEs) are a promising technology to produce green hydrogen with high efficiencies at low temperature [1]. The widespread deployment of this technology is hindered by the catalyst cost and durability issues [2]. Higher anode catalyst loadings are currently used to enable longer operating time of the PEWEs. Interface between catalyst layer and porous transport layer (PTL) is not well understood, especially for novel PTLs with varied morphological properties, such as sintered vs. fiber. [3] The PTLs’ bulk properties, interface, catalyst loading, and catalyst distribution all impact cell performance and possible correlation between these properties needs further investigation.This study focuses on catalyst layers with different loadings, and the resulting catalyst layer-PTL interfaces with two different types of PTLs (sintered Ti and fiber Ti). For a given loading, two different electrode configurations have been compared namely the catalyst coated membrane (CCM) and gas diffusion electrode (GDE). The current density was applied from 1 to 5 A/cm2 with a constant liquid water flow rate and temperature of 60oC. We categorized the PEWEs into three categories according to catalyst loading, (1) high loadings: 1.75– 2.20 mg/cm2, (2) medium loadings: 1.00– 1.26 mg/cm2, and (3) low loadings: 0.50– 0.65 mg/cm2. Operando x-ray computed tomography (CT) and radiography were used to observe the catalyst distribution and oxygen transport in all the samples. The interfacial analysis using the tomography data and electrochemical testing gives insight into the percentage triple phase contact area (%TPCA) and the cell performance, respectively. Herein, we present a comprehensive comparative analysis of the catalyst loadings as well as the correlate cell performance with the %TPCA and the double layer capacitance.We observed a Tafel slope difference of over 10 mVdec-1 between sintered CCMs and sintered GDEs at low loadings suggesting proton or electron transport limitations at the interface. We then tested the cells at steady state conditions for 90 hours and compared the initial and final performances. Over 600 mV increase in the overpotential for low loaded fiber CCMs was observed, compared to < 200 mV increase for its high loaded counterpart at 1.5 A/cm2 after the steady state holds (Figure 1c-d). Computational fluid dynamics (CFD) with the Lattice Boltzmann Method (LBM) was used to simulate the oxygen transport in the PTLs with varying catalyst loadings, which showed underutilization of transport pathways for lower loaded fiber PTLs and showing that sintered PTLs have more uniform oxygen distribution due to more uniform through-plane morphological properties. Additionally, with the x-ray radiography study, we showed that having large oxygen slugs in the channel is preferred, as long as oxygen content in the channels is below 80 %.

Influence of Heating Modes of Compacted Samples from Nickel Powders with Nanosized Particles on Their Interaction with Air

In this paper, we study compact samples of pyrophoric nickel powders with the average particle size of 85 nm, obtained by the chemical-metallurgical method. For the first time, it is experimentally shown that it is possible to passivate compact samples with a diameter of 3 mm from pyrophoric nickel powders with nanosized particles in air. For a relative density of 0.4 to 0.5, the passivation time is only 3–5 s. According to the X-ray phase analysis data, only the Ni phase is observed in passivated samples. It is found that passivated samples retain their thermal stability in air upon slow (<10 deg/s) heating to ~200°C, which is an important parameter for fire safety when handling nanopowders. The electron microscopic analysis of the passivated samples did not reveal traces of sintering of nickel nanoparticles, including after checking for thermal stability. The uniform distribution of oxygen over the passivated samples according to the data of energy dispersive analysis (the standard deviation is 0.9 at %) indicates the volumetric nature of the interaction of the samples with air during passivation. For the obtained passivated samples, the critical heating conditions were determined, under which self-ignition occurs, which is in agreement with N.N. Semyonov’s classical theory of thermal explosion.

Investigation on the Optimal Angle of a Flow-Field Design Based on the Leaf-Vein Structure for PEMFC

As a critical component, the bipolar plate appreciably affects the performance of proton exchange membrane fuel cell (PEMFC). The flow field structure on the bipolar plate is significant in transporting the internal reaction gas and excess water. In the nature, the leaf veins provide efficient branch networks to the plant, contributing to distribute the nutrients in the whole system. By bionic means, a similar branching structure can be used to design flow channels on the bipolar plates for PEMFC, which helps distribute the reactant gas evenly and manage the water better. In this paper, a three-dimensional isothermal single phase model of the bio-inspired flow channel design based on the leaf vein pattern was presented. The effect of the angle between the main channel and sub-channels on the performance of PEMFC was studied at various cases. A PEMFC of 10.24cm2 activation area was assembled and examined experimentally. The results showed that increasing the angle appropriately was beneficial to improving the uniform oxygen distribution and excess water removal. After comprehensively analyzing the electrochemical performance, species distribution, and power loss of PEMFC, the optimal angle was presented.

The influence of heating conditions of the samples of nickel nanopowders on the modes of their interactions with the air

In the present work, compact samples of pyrophoric nickel nanopowders with an average particle size of 55 nm obtained by the method of chemical metallurgy were investigated. The possibility of passivation of compact samples 3 mm in diameter made of nickel pyrophoric nanopowders in the air is experimentally shown for the first time. The time of complete passivation is only 3–5 s for a relative sample density 0.4–0.5. According to X-ray phase analysis, only Ni phase was observed in passivated samples. It was found that passivated samples maintain thermal stability in the air at slow (< 10 °C/s) heating to ~ 200 °C; it is an important parameter for fire safety at handling of nanopowders. The analysis of passivated samples by the SEM method showed no traces of sintering of nickel nanoparticles, even after testing for thermal stability. The uniform distribution of oxygen within passivated samples according to energy dispersive X-ray analysis data indicates the volumic nature of the interaction of samples with the air during passivation. For the passivated samples, critical heating conditions were determined, under which self-ignition occurs.

Passivation of Compact Samples of Nickel Nanopowders and Modes of Their Interaction with Air

It was experimentally shown for the first time that compact samples of pyrophoric nickel nanopowders can be passivated in air for 3–5 s. The passivation of the samples was confirmed by the absence of noticeable heat release during slow heating to 200°C, an insignificant oxygen content according to the data of X-ray powder diffraction analysis and scanning electron microscopy, and the retention of the chemical activity of the samples. The uniform distribution of oxygen throughout the sample suggests the volumetric nature of their interaction with air during the passivation. The critical conditions for heating of passivated samples under which ignition occurs were determined.

Development of cathode cooling fins with a multi-hole structure for open-cathode polymer electrolyte membrane fuel cells

The main purpose of this study is to investigate how a newly designed cooling fin affects the performance of open-cathode polymer electrolyte membrane fuel cells (OC-PEMFCs) at high current densities with the aid of experiments and simulation. The novel fin, denoted as the CASE-1 cooling fin, comprises a multi-hole structure (MHS) in the rib region. An OC-PEMFC stack with the CASE-1 cooling fins exhibits a higher performance under higher current densities than that with conventional cooling fins, which are referred to as CASE-2 cooling fins. Owing to several dead zones at the fan duct, sufficient air is not provided to the edges of the OC-PEMFC stack, where the 1st and 20th fuel cells are located; however, the MHS mitigates this decrease in the performance at the edge cells. Results of numerical simulation show that the oxygen mole fraction for CASE-1 cooling fins is higher than that for CASE-2 at the gas diffusion layer/membrane electrode assembly (GDL/MEA) interface indicating uniform oxygen distribution throughout the MEA area. These all results indicate that the CASE-1 cooling fin induces a positive oxygen distribution, resulting in a significant improvement in performance at higher current densities.

Performance enhancement of polymer electrolyte membrane fuel cells with a hybrid wettability gas diffusion layer

A numerical simulation by using a three-dimensional multiphase polymer electrolyte membrane (PEM) fuel cell model and the volume of fluid (VOF) method is performed to investigate a newly designed hybrid wettability gas diffusion layer (GDL) for performance enhancement of PEM fuel cells. The hybrid wettability GDL has interchangeable distributions of relatively low and high hydrophobic regions along the gas flow direction. The low hydrophobic regions are characterized by high porosity and low water removal performance, whereas the high hydrophobic regions have low porosity and strong water removal ability. Simulation results show that the water removal process, mass diffusion and output performance of fuel cells greatly depend on the wettability degree distributionin the hybrid wettability GDL. In comparison with conventional GDL designs, the hybrid wettability GDL with polytetrafluoroethylene (PTFE) content of 10 wt% and 20 wt% for low and high hydrophobic regions at 1.5 mm intervals exhibits advantages in the enhancement of water removal from the gas flow channel and the mass diffusion within porous electrodes. Therefore, it can improve the uniform distribution of oxygen, the liquid water saturation and the reaction rate and ultimately benefit the stable operation and output performance of PEM fuel cells. Result also shows that the limiting current density of the optimal hybrid wettability GDL increases by 4.45% compared with that of the conventional GDL with PTFE content of 20 wt%. Furthermore, the study reveals that hybrid wettability GDL designs exhibit a greater advantage at high RHs than at low RHs.