Search Results (118)

The electrocatalytic CO₂ reduction reaction (CO₂RR) offers an energy-saving and environmentally friendly approach to producing hydrocarbon fuels. The use of a gas diffusion electrode (GDE) flow cell has generally improved the rate of CO₂RR, while the gas diffusion layer (GDL) remains a significant challenge. In this study, we successfully engineered a novel metal–organic framework (MOF) heterojunction through the controlled coating of zeolitic imidazolate framework (ZIF-L) on ultrathin nickel—metal–organic framework (Ni-MOF) nanosheets. This innovative architecture simultaneously integrates GDL functionality and exposes abundant solid–liquid–gas triple-phase boundaries. The resulting Ni-MOF@ZIF-L heterostructure demonstrates exceptional performance, achieving a formate Faradaic efficiency of 92.4% while suppressing the hydrogen evolution reaction (HER) to 6.7%. Through computational modeling of the optimized heterojunction configuration, we further elucidated its competitive adsorption behavior and electronic modulation effects. The experimental and theoretical results demonstrate an improvement in electrochemical CO₂ reduction activity with suppressed hydrogen evolution for the heterojunction because of its hydrophobic interface, good electron transfer capability, and high CO₂ adsorption at the catalyst interface. This work provides a new insight into the rational design of porous crystalline materials in electrocatalytic CO₂RR. Full article

This study focuses on addressing the issues of water flooding and mass transfer limitations in proton exchange membrane fuel cells (PEMFCs) under high current density conditions. A multi-scale gradient pore gas diffusion layer (GDL) is designed to enhance fuel cell performance. The pore structure is precisely controlled using a self-assembled mold, resulting in the fabrication of a GDL with a gradient distribution of pore diameters ranging from 80 to 170 μm. Experimental results indicate that, with the optimized gradient pore GDL, the peak power density of the fuel cell reaches 1.18 W·cm−², representing a 20% improvement compared to the traditional structure. A mechanism analysis reveals that this structure establishes a concentrated water transport pathway through channels while enabling gas diffusion and transport driven by concentration gradients, thereby achieving the collaborative optimization of gas–liquid transport. This approach offers a novel solution for managing water in PEMFCs operating under high current density conditions, and holds significant implications for advancing the commercialization of PEMFC technology. Full article

This study investigates the effects of anode and cathode inlet flow rates (ṁ) on the power performance of bipolar plates in a polymer electrolyte membrane fuel cell (PEMFC). The primary objective is to derive optimal flow rate conditions by comparatively analyzing concentration loss in the I−V curve and crossover phenomena at the anode, thereby establishing flow rates that prevent reactant depletion and water flooding. A single-cell computational model was constructed by assembling a commercial bipolar plate with a gas diffusion layer (GDL), catalyst layer (CL), and proton exchange membrane (PEM). The model simulates current density generated by electrochemical oxidation-reduction reactions. Hydrogen and oxygen were supplied at a 1:3 ratio under five proportional flow rate conditions: hydrogen (${\dot{m}}_{H_2}$ = 0.76–3.77 LPM) and oxygen (${\dot{m}}_{O_2}$ = 2.39–11.94 LPM). The Butler–Volmer equation was employed to model voltage drop due to overpotential, while numerical simulations incorporated contact resistivity, surface permeability, and porous media properties. Simulation results demonstrated a 24.40% increase in current density when raising ${\dot{m}}_{H_2}$ from 2.26 to 3.02 LPM and ${\dot{m}}_{O_2}$ from 7.17 to 9.56 LPM. Further increases to ${\dot{m}}_{H_2}$ = 3.77 LPM and ${\dot{m}}_{O_2}$ = 11.94 LPM yielded a 10.20% improvement, indicating that performance enhancements diminish beyond a critical threshold. Conversely, lower flow rates (${\dot{m}}_{H_2}$ = 0.76 and 1.5 LPM, ${\dot{m}}_{O_2}$ = 2.39 and 4.67 LPM) induced hydrogen-depleted regions, triggering crossover phenomena that exacerbated anode contamination and localized flooding. Full article

Anion exchange membrane electrolyzer (AEMEC) is a promising hydrogen production technology device. An electrochemical model is developed using MATLAB/Simulink to analyze the impact of factors such as anion exchange membrane (AEM) thickness, operating temperature, pressure, and gas diffusion layer (GDL) parameters including GDL thickness, porosity, and pore size. The results showed that as the thickness of AEM, operating pressure, and GDL decreased, the electrolysis efficiency significantly improved, and energy consumption decreased. When the thickness of AEM decreases from 70 microns to 65 microns, it will cause a decrease of 24 mV in cell voltage. This study also found that increasing pressure slightly increases voltage due to higher diffusion overpotential. In addition, changes in GDL porosity and pore size have a significant impact on performance. The lower porosity reduces ohmic loss and improves efficiency. This study highlights the importance of optimizing the design of AEMEC components to improve hydrogen production performance. Full article

The high cost of platinum (Pt) catalysts impedes the widespread commercialization of proton exchange membrane fuel cells (PEMFCs). Reducing Pt loading will increase local oxygen transport resistance ($R_{\mathrm{Pt}}^{{\mathrm{O}}_2}$) and decrease performance. Due to the oxygen transport resistance, the reactants in the cathode catalyst layer (CCL) are not evenly distributed. The gradient structure can cooperate with the unevenly distributed reactants in CL to enhance the Pt utilization. In this work, a one-dimensional gradient CCL model considering $R_{\mathrm{Pt}}^{{\mathrm{O}}_2}$ is established, and the optimal gradient structure is optimized by combining the artificial neural network (ANN) model and the genetic algorithm (GA). The optimal structure parameters of non-gradient CCL are l_CL equal to 8.86 μm, r_C equal to 36.82 nm, and I/C equal to 0.48, with the objective of maximum current density (I_max); l_CL equal to 4.24 μm, r_C equal to 36.60 nm, and I/C equal to 0.76, with the objective of maximum power density (P_max). For the gradient CCL, the best gradient distribution enables Pt loading to increase from the membrane (MEM) side to the gas diffusion layer (GDL) side and the ionomer volume fraction to decrease from the MEM side to the GDL side. Full article

The performance and durability of proton-exchange membrane fuel cells (PEMFCs) are dependent on fuel flow, humidifying water, and outgoing water management. Unlike conventional flow fields with linear channels, the complex 3D flow field—featuring repeating baffles along the channel, known as the baffle design—induces a micro-scale interface flux between the gas diffusion layer (GDL) and the flow fields. Thus, an intensive oxygen flow is created that removes excess water from the GDL, thereby improving the fuel cell efficiency. Another approach for channel design is the Turing flow field, which resembles the organization of fluid flows in natural objects such as leaves, lungs, and the blood system. This design enhances the distribution of inlet flow significantly compared with traditional designs. The present study aims to combine the advantages of both Turing and baffle flow field designs and to provide model investigations on the influence of the mixed flow field design on the efficiency of PEMFCs. It was established that the mixed design achieves the highest electrode current density of 1.2 A/cm², outperforming the other designs. Specifically, it achieves 20% improvement over the Turing design, reaching 1.0 A/cm² and generating three times more current than the baffle design, which delivers 0.4 A/cm². In contrast, the conventional serpentine designs exhibit the lowest current density. The mixed flow field design provides better oxygen utilization in the electrochemical reaction, offers optimal membrane hydration, and contributes to superior electrode current density performance. These data illustrate how flow field structure directly impacts fuel cell efficiency through enhancement of current density. Full article

Proton exchange membrane fuel cells (PEMFCs), recognized as promising sources of waste heat for space heating, domestic hot water supply, and industrial thermal applications, have garnered substantial interest owing to their environmentally benign operation and high energy conversion efficiency. Since the uniformity of oxygen diffusion toward catalytic layers critically governs electrochemical performance, this study establishes a three-dimensional, non-isothermal computational fluid dynamics (CFD) model to systematically optimize the cathode flow channel width distribution, targeting the maximization of power output through enhanced reactant homogeneity. Numerical results reveal that non-uniform flow channel geometries markedly improve oxygen distribution uniformity, reducing the flow inhomogeneity coefficient by 6.6% while elevating maximum power density and limiting current density by 9.1% and 7.8%, respectively, compared to conventional equal-width designs. There were improvements attributed to the establishment of longitudinal oxygen concentration gradients and we alleviated mass transfer limitations. Synergistic integration with gas diffusion layer (GDL) gradient porosity optimization further amplifies performance, yielding a 12.4% enhancement in maximum power density and a 10.4% increase in limiting current density. These findings validate the algorithm’s efficacy in resolving coupled transport constraints and underscore the necessity of multi-component optimization for advancing PEMFC design. Full article

The performance of proton exchange membrane fuel cells (PEMFCs) is greatly affected by their operating parameters, especially at high current densities. An advanced concentration loss model is proposed to improve a semi-empirical model describing PEMFC polarization, with the aim of accurate prediction at the whole current density interval from low to high levels. Experiments are designed to verify the improved semi-empirical model. Model comparison shows that the improved semi-empirical model has a better prediction accuracy and generalization ability than others. The effects of operating parameters and structural parameters on PEMFC performance are analyzed. The results indicate that a relatively high operating temperature, pressure, and gas diffusion layer (GDL) porosity can increase PEMFC performance. The influence of relative humidity and PEM thickness on PEMFC performance is different at low and high current densities. A relatively high humidity can improve PEMFC performance at a low current density, but PEMFC performance will be reduced if the relative humidity is too high at a high current density. A thinner PEM thickness can improve PEMFC performance at a low current density, but PEMFC performance does not necessarily improve with a decreasing PEM thickness at a high current density. Overall, the improved semi-empirical model realizes an accurate analysis of PEMFC performance from a low to high current density. Full article

A gas diffusion layer (GDL) is an essential component for the efficient operation of proton exchange membrane fuel cells, requiring stable mechanical strength and uniform stress distribution to achieve higher durability. The various microstructure characteristics of GDLs have coupled and complex effects on mechanical properties, which have not been fully considered in previous studies. In this study, we have combined stochastic reconstruction techniques, explicit dynamics compression simulation, and orthogonal design methods to evaluate and optimize the coupling effects of carbon fiber diameter, porosity, GDL thickness, and fiber orientation coefficient on the mechanical properties of pore-scale GDLs. Finally, mathematical expressions have been developed to predict stress distribution under compression. The results show that the impact of fiber diameter and porosity is greater than that of GDL thickness and fiber orientation coefficient. Average stress and stress uniformity increase with increases in fiber diameter, fiber orientation coefficient, and GDL thickness, but porosity shows an opposite trend. We achieved a remarkable reduction of 292% in optimal average stress and a significant enhancement of 278% in stress uniformity. The mathematical expressions have been validated for accuracy by considering the simultaneous coupled effects of various microstructural characteristics. This work provides valuable engineering tools for enhancing the performance and durability of GDLs and fuel cells. Full article

One of the key challenges in optimizing the transfer characteristics of carbon cloth gas diffusion layers (GDLs) is accurately evaluating their effective transport properties. In this work, a stochastic reconstruction algorithm based on structural parameters was developed to generate virtual carbon cloth GDLs with varying porosities, carbon fiber diameters, and length-to-thickness ratios. A pore-scale random walk model was also developed to predict the permeability, tortuosity, and effective diffusivity of the GDLs with well-validated accuracy. The results show that higher porosity and larger carbon fiber diameters enhance the diffusion and transfer of oxygen through the GDL, and when the length-to-thickness ratio exceeds 2, the permeability stabilizes. The model developed in this study offers the advantages of low computational cost, accurate representation of the material’s microstructure, and broad applicability, making it a powerful and convenient tool for predicting the transport properties of porous media. Full article

Due to its low stiffness, the gas diffusion layer (GDL) exhibits significant deformation under a compression service condition, thereby exerting a nonlinear and strong coupling influence on fuel cells’ performance. Therefore, it is of great practical significance to study the structural characteristics evolution of GDLs. The microstructure of the GDLs was obtained using micro-X-ray computed tomography in this study, and their structural properties were analyzed comprehensively and quantitatively. The morphology of GDLs exhibited significant variations across manufacturers due to disparities in the materials and manufacturing processes. The distribution of the pore equivalent diameter and sphericity in GDLs conformed to a normal distribution, with irregular shapes. The fiber length distribution in the unit followed a Gamma distribution, showing a random and uneven distribution in the XY plane. When compressed, the average fiber length was reduced, and a substantial increase in isolated pores was observed. However, the quantity of long fibers and connected and isolated pores decreased after acidification treatment. Full article

Proton Exchange Membrane Fuel Cells (PEMFCs) are widely regarded as promising clean energy technologies due to their high energy conversion efficiency, low environmental impact, and versatile application potential in transportation, stationary power, and portable devices. Central to the operation and performance of PEMFCs are advancements in materials and manufacturing processes that directly influence their efficiency, durability, and scalability. This review provides a comprehensive overview of recent progress in these areas, emphasizing the critical role of membrane electrode assembly (MEA) technology and its constituent components, including catalyst layers, membranes, and gas diffusion layers (GDLs). The MEA, as the heart of PEMFCs, has seen significant innovations in its structure and manufacturing methodologies to ensure optimal performance and durability. At the material level, catalyst layer advancements, including the development of platinum-group metal catalysts and cost-effective non-precious alternatives, have focused on improving catalytic activity, durability, and mass transport. Similarly, the evolution of membranes, particularly advancements in perfluorosulfonic acid membranes and alternative hydrocarbon-based or composite materials, has addressed challenges related to proton conductivity, mechanical stability, and operation under harsh conditions such as low humidity or high temperature. Additionally, innovations in gas diffusion layers have optimized their porosity, hydrophobicity, and structural properties, ensuring efficient reactant and product transport within the cell. By examining these interrelated aspects of PEMFC development, this review aims to provide a holistic understanding of the state of the art in PEMFC materials and manufacturing technologies, offering insights for future research and the practical implementation of high-performance fuel cells. Full article

Proton exchange membrane fuel cells (PEMFCs) are being pursued for applications in the maritime industry to meet stringent ship emissions regulations. Further basic research is needed to improve the performance of PEMFCs in marine environments. Assembly stress compresses the gas diffusion layer (GDL) beneath the ribs, significantly altering its pore structure and internal transport properties. Accurate evaluation of the PEMFC cathode’s electrochemical performance at the pore scale is critical. This study employs a three-dimensional multicomponent gas transport and electrochemical reaction lattice Boltzmann model to explore the complex interplay between GDL compression and factors such as overpotential, pressure differential, porosity, and porosity gradient on PEMFC performance. The findings indicate that compression accentuates the reduction in oxygen concentration along the flow path and diminishes the minimum current density. Furthermore, compression exacerbates the reduction in current density under varying pressure conditions. Increased local porosity near the catalyst layer (CL) enhances oxygen accessibility and water vapor exclusion, thereby elevating the mean current density. Sensitivity analysis reveals a hierarchy of impact on mean current density, ranked from most to least significant: overpotential, porosity, compression, porosity gradient, and pressure difference. These insights into the multicomponent gas transfer dynamics within compressed GDLs inform strategic structural design enhancements for optimized performance. Full article

In polymer electrolyte membrane fuel cells, the gas diffusion layer (GDL) is composed of porous media and serves a critical role as a mass transport layer, facilitating reactant gas diffusion, removal of water generated in the catalyst layer, and electron transport. Artificial spacings known as perforations can be introduced to improve water management within this mass transport system. However, the impact of these perforations on the effective electrical conductivity has not been adequately studied. This study employs numerical methods to investigate water management and effective electrical conductivity in the presence of perforations, aiming to provide indicators for optimal design. The pseudopotential lattice Boltzmann method is utilized, which is particularly advantageous for modeling two-phase flow and electron transport in complex geometries. Using this numerical approach, we analyze water penetration in GDL structures and effective electrical conductivity based on electric potential fields focusing on geometric parameters such as the perforation size. Our results demonstrate a relationship between water management efficiency and effective electrical conductivity, suggesting the existence of an optimal perforation diameter. Moreover, when there is a water-induced penetration pattern due to the perforated structure, both the effective electrical conductivity and water management are enhanced at a lower porosity of the GDL structure. Full article

The proton exchange membrane fuel cell (PEMFC), with a high energy conversion efficiency, has become an important means of hydrogen energy utilization. However, water condensation is unavoidable in the PEMFC because of low operating temperatures. The impact of liquid water on PEMFC performance and stability is significant. The gas diffusion layer (GDL) provides a critical transport path for liquid water in the PEMFC. Liquid water saturation and distribution in the GDL determine water flooding and mass transfer efficiency in the PEMFC. In this study, focusing on the effects of the water introduction method, osmotic pressure, and contact angle, the liquid water transport in the GDL was numerically investigated based on a pore-scale model using the volume of fluid (VOF) method. The results showed that compared with the conventional water introduction method without cracks, the saturation and spatial distribution of water inside the GDL obtained in the simulation were more consistent with the experimental results when the water was introduced through the microporous layer (MPL) crack. It was found that increasing the osmotic pressure resulted in a faster rate of water penetration, faster approaching the steady-state performance, and higher saturation. The ultra-high osmotic pressure contributed to the secondary breakthrough with a significant increase in saturation. Increasing the contact angle caused higher capillary resistance, especially in the region with small pore sizes. At a constant osmotic pressure, as the contact angle increased, the liquid water gradually failed to penetrate into the small pores around the transport path, causing saturation reduction and an ultimate failure to break through the GDL. Increasing the contact angle contributed to a higher breakthrough pressure and secondary breakthrough pressure. Full article