A Universal Strategy to Enhance Polarization Performance and Anode Reversal Tolerance by Polyaniline-Coated Carbon Support for Proton Exchange Membrane Fuel Cells.

Anode cell reversal typically leads to severe carbon corrosion and catalyst layer collapse, which significantly compromises the durability of proton exchange membrane fuel cells. Herein, three types of commercial carbon supports with various structures are facilely coated by polyaniline (PANI) and subsequently fabricated into reversal-tolerant anodes (RTAs). Consequently, the optimized PANI-coated catalyst RTAs demonstrate enhanced polarization performance and improved reversal tolerance compared to their uncoated counterparts, thus confirming the universality of this coating strategy. Essentially, the surface engineering introduced by PANI coating incorporates abundant N-groups and enhances coulombic interactions with ionomer side chains, which in turn reduces lower carbon exposure, promotes more uniform Pt deposition, and ensures better ionomer distribution. Accordingly, the membrane-electrode-assembly containing the Pt/PANI/XC-72R-1+IrO2 RTA presents a 100 mV (at 2500 mA cm-2) polarization performance improvement and 26-fold reduction in the degradation rate compared to the uncoated counterpart. This work provides a universal strategy for developing durable anodes and lays the groundwork for the practical fabrication of high-performance, low-degradation RTA.

Fundamental and Practical Aspects of Break-In/Conditioning of Proton Exchange Membrane Fuel Cells.

Proton exchange membrane fuel cells (PEMFCs) have proven to be a promising power source for various applications ranging from portable devices to automotive and stationary power systems. The production of PEMFC involves numerous stages in the value chain, with each stage presenting unique challenges and opportunities to improve the overall performance and durability of the PEMFC stack. These include steps such as manufacturing the key components such as the platinum-based catalyst, processing these components into the membrane electrode assemblies (MEAs), and stacking the MEAs to ultimately produce a PEMFC stack. However, it is also known that the break-in or conditioning phase of the stack plays a crucial role in the final performance as well as durability. It involves several key phenomena such as hydration of the membrane, swelling of the ionomer, redistribution of the catalyst and the creation of suitable electrochemical interfaces - establishment of the triple phase boundary. These improve the proton conductivity, the mass transport of reactants and products, the catalytic activity of the electrode and thus the overall efficiency of the FC. The cruciality of break-in is demonstrated by the improvement in performance, which can even be over 50 % compared to the initial state. The state-of-the-art approach for the break-in of MEAs involves an electrochemical protocol, such as voltage cycling, using a PEMFC testing station. This method is time-consuming, equipment-intensive, and costly. Therefore, new, elegant, and cost-effective solutions are needed. Nevertheless, the primary aim is to achieve maximum/optimal performance so that it is fully operational and ready for the market. It is therefore essential to better understand and deconvolute these complex mechanisms taking place during break-in/conditioning. Strategies include controlled humidity and temperature cycling, novel electrode materials and other advanced break-in methods such as air braking, vacuum activation or steaming. In addition, it is critical to address the challenges associated with standardisation and quantification of protocols to enable interlaboratory comparisons to further advance the field.

Performance of the multi-U-style structure based flow field for polymer electrolyte membrane fuel cell.

The design of the reactant gas flow field structure in bipolar plates significantly influences the performance of proton exchange membrane fuel cells (PEMFCs). In this study, we introduced four innovative U-shaped flow field designs, namely: In-Out Multi-U, Out-In Multi-U, Distro In-Out Multi-U, and Distro Out-In Multi-U. To investigate the impact of these various flow fields on PEMFC performance, we conducted computational fluid dynamics (CFD) numerical simulations, validated through model experiments. Our results indicate that the Distro Out-In Multi-U flow field offers notable advantages compared to the conventional parallel flow field (CPFF) and conventional serpentine flow field (CSFF). These benefits include reduced inlet and outlet pressures, lower liquid water content, more uniform liquid water distribution, and a more even current density distribution. Furthermore, the Distro Out-In Multi-U design demonstrates improved efficiency, consuming less H2 (91.9%) than the CSFF while achieving a higher net power density output (10.1%). As a result, for the same power output, the Distro Out-In Multi-U utilizes only 83.5% of the H2 consumed by the CSFF. In summary, the U-shaped structured flow field exhibits superior output performance, enhanced energy efficiency, and improved resistance to flooding. These findings suggest that the U-shaped flow field design holds significant potential as a reactive flow field for PEMFCs.

Ionomeric Binders for High Temperature Proton Exchange Membrane Fuel Cells.

High-temperature proton exchange membrane fuel cell (HT-PEMFC) based on phosphoric acid doped polybenzimidazole membrane (PBI/PA) operating at 120-200 °C can provide insensitivity to carbon monoxide (CO) and simplified managements of water and heat and thus attract significant global attention. However, one significant drawback is its low utilization of precious metal catalysts resulted from the PA poisoning and inefficient three-phase boundary. Studies of binder materials in catalyst layers for HT-PEMFC are gradually emerging and there are few literature reviews on this important topic. The purpose of this review is to describe the various types of binders based on their molecular structure and electrochemical properties, with particular emphasis on catalyst layer for fuel cells. Importantly, this review provides a better understanding of relationship between fuel cell performance and the gas permeability and conductivity of different binders. Then, future directions of research and development in binder materials of HT-PEMFC are pointed out.

Parameter extraction of proton exchange membrane fuel cell based on artificial rabbits' optimization algorithm and conducting laboratory tests.

Proton exchange membrane fuel cell (PEMFC) parameter extraction is an important issue in modeling and control of renewable energies. The PEMFC problem's main objective is to estimate the optimal value of unknown parameters of the electrochemical model. The main objective function of the optimization problem is the sum of the square errors between the measured voltages and output voltages of the proposed electrochemical optimized model at various loading conditions. Natural rabbit survival strategies such as detour foraging and random hiding are influenced by Artificial rabbit optimization (ARO). Meanwhile, rabbit energy shrink is mimicked to control the smooth switching from detour foraging to random hiding. In this work, the ARO algorithm is proposed to find the parameters of PEMFC. The ARO performance is verified using experimental results obtained from conducting laboratory tests on the fuel cell test system (SCRIBNER 850e, LLC). The simulation results are assessed with four competitive algorithms: Grey Wolf Optimization Algorithm, Particle Swarm Optimizer, Salp Swarm Algorithm, and Sine Cosine Algorithm. The comparison aims to prove the superior performance of the proposed ARO compared with the other well-known competitive algorithms.

An improved nutcracker optimization algorithm for discrete and continuous optimization problems: Design, comprehensive analysis, and engineering applications.

This study is presented to examine the performance of a newly proposed metaheuristic algorithm within discrete and continuous search spaces. Therefore, the multithresholding image segmentation problem and parameter estimation problem of both the proton exchange membrane fuel cell (PEMFC) and photovoltaic (PV) models, which have different search spaces, are used to test and verify this algorithm. The traditional techniques could not find approximate solutions for those problems in a reasonable amount of time, so researchers have used metaheuristic algorithms to overcome those shortcomings. However, the majority of metaheuristic algorithms still suffer from slow convergence speed and stagnation into local minima problems, which makes them unsuitable for tackling these optimization problems. Therefore, this study proposes an improved nutcracker optimization algorithm (INOA) for better solving those problems in an acceptable amount of time. INOA is based on improving the performance of the standard algorithm using a newly proposed convergence improvement strategy that aims to improve the convergence speed and prevent stagnation in local minima. This algorithm is first applied to estimating the unknown parameters of the single-diode, double-diode, and triple-diode models for a PV module and a solar cell. Second, four PEMFC modules are used to further observe INOA's performance for the continuous optimization challenge. Finally, the performance of INOA is investigated for solving the multi-thresholding image segmentation problem to test its effectiveness in a discrete search space. Several test images with different threshold levels were used to validate its effectiveness, stability, and scalability. Comparison to several rival optimizers using various performance indicators, such as convergence curve, standard deviation, average fitness value, and Wilcoxon rank-sum test, demonstrates that INOA is an effective alternative for solving both discrete and continuous optimization problems. Quantitively, INOA could solve those problems better than the other rival optimizers, with improvement rates for final results ranging between 0.8355 % and 3.34 % for discrete problems and 4.97 % and 99.9 % for continuous problems.

Enhancing renewable energy utilization and energy management strategies for new energy yachts.

Hydrogen energy, due to its clean and efficient nature, has shown great potential during the current transition period in the shipbuilding industry. However, the application of hydrogen energy in ship energy systems is influenced by variations in operational load and the integration of new energy sources during actual navigation. To address these issues, this paper focuses on optimizing and scheduling the operation of ships under various navigation conditions, considering the distributed nature of hydrogen energy. System simulations were conducted to model the photovoltaic (PV), proton exchange membrane fuel cells (PEMFCs), lithium batteries (LIBs), electrolytic cells (ECs), and energy storage modules of yacht energy systems. Component boundaries and objective functions were set, and two cases (excess photovoltaic state and constant power state) were designed to optimize and regulate the energy balance of hydrogen-powered yachts, enhancing their comprehensive utilization of renewable energy. By comparing the changes in ship energy under the two cases, it was concluded that case 1 ensures the maximum utilization of renewable energy. When photovoltaic power generation is insufficient, the PEMFC and LIB in the system provide the required power to achieve a supply-demand balance. Moreover, when PV power generation is sufficient, hydrogen energy is used to store renewable energy. The optimization method designed in this study can, to some extent, maximize the application of renewable energy in new energy yachts, ensuring the efficiency of the comprehensive energy system of new energy yachts, reducing emissions, and improving the sustainability and economic efficiency of the ships.

Sensitivity and Stability Study of Test Conditions for a 1 kW Proton Exchange Membrane Fuel Cell Stack.

This study investigates the impact of compression force on stack performance and the effect of testing conditions on sensitivity of stack performance. It explores the variation of assembly force on the pressure distribution at different positions in a 1 kW proton exchange membrane fuel cell stack. Polarization curves and high-frequency resistance (HFR) changes of the stack were measured under different assembly forces, and the optimal assembly force of the stack was determined using the average single-cell voltage (HFR-free). The sensitivity of testing conditions was optimized, and the optimum test parameters at different current densities were identified within the selected range. Stack stability was tested at different current densities using the optimized test conditions, and the sensitivity of test conditions was verified by the fluctuation amplitude of single cell voltage and internal impedance.

Functionalized Modified Ti4O7 Polyaniline Coating for 316SS Bipolar Plate in Proton-Exchange Membrane Fuel Cells.

In this paper, the PANI/PDA-Ti4O7 composite coating was prepared on 316L by constant current deposition with a current density of 2.8 mA·cm-2, in which the Ti4O7 powders were modified by PDA (polydopamine). The open-circuit potential of the obtained PANI/PDA-Ti4O7 composite coating is about 365 mVAg/AgCl, which is more positive than that of the bare 316L. During immersion in 1 M H2SO4 + 2 ppm HF for 200 h, the high stable corrosion potential and the lower Rf indicate that the composite coating has long-term corrosion resistance.

Oxygen Reduction Reaction Activity and Stability of Shaped Metal-Doped PtNi Electrocatalysts Evaluated in Gas Diffusion Electrode Half-Cells.

The synthesis of bimetallic and trimetallic platinum-based octahedral catalysts for the cathode of proton exchange membrane fuel cells (PEMFCs) is a particularly active area aimed at meeting technological requirements in terms of durability and cost. The electrocatalytic activity and stability of these shaped catalysts were tested at relatively high potentials (@0.9 V vs RHE) and at lower current densities using the rotating disk electrode, which is less suitable for assessing their behavior under the operating conditions of PEMFCs. In this work, we use a gas diffusion electrode (GDE) half-cell setup to test the performance of the catalysts under application-oriented conditions, relatively higher current densities, and a square-wave stability test. After the stability test, we analyzed the GDE catalytic layer to study the agglomeration and dissolution of the transition metal under these conditions by using high-resolution scanning electron microscopy and energy-dispersive X-ray spectroscopy. The present results provide valuable guidance for developing next-generation active and durable catalysts for PEMFCs.

Formation Characteristics of Pt-Ni Alloy Nanoparticles Fabricated by Nanolamination of Atomic Layer Deposition in Hydrogen.

Forced-flow atomic layer deposition nanolamination is employed to fabricate Pt-Ni nanoparticles on XC-72, with the compositions ranging from Pt94Ni6 to Pt67Ni33. Hydrogen is used as a co-reactant for depositing Pt and Ni. The growth rate of Pt is slower than that using oxygen reactant, and the growth exhibits preferred orientation along the (111) plane. Ni shows much slower growth rate than Pt, and it is only selectively deposited on Pt, not on the substrate. Higher ratios of Ni would hinder subsequent stacking of Pt atoms, resulting in lower overall growth rate and smaller particles (1.3-2.1 nm). Alloying of Pt with Ni causes shifted lattice that leads to larger lattice parameter and d-spacing as Ni fraction increases. From the electronic state analysis, Pt 4f peaks are shifted to lower binding energies with increasing the Ni content, suggesting charge transfer from Ni to Pt. Schematic of the growth behavior is proposed. Most of the alloy nanoparticles exhibit higher electrochemical surface area and oxygen reduction reaction activity than those of commercial Pt. Especially, Pt83Ni17 and Pt87Ni13 show excellent mass activities of 0.76 and 0.59 A mgPt -1, respectively, higher than the DOE target of 2025, 0.44 A mgPt -1.

New Morphology Modifier Enables the Preparation of Ultra-Long Platinum Nanowires Excluding Mo Component for Efficient Oxygen Reduction Reaction Performance.

The structural tailoring of Pt-based catalysts into 1D nanowires for oxygen reduction reactions (ORR) has been a focus of research. Mo(CO)6 is commonly used as a morphological modifier to form nanowires, but it is found that it inevitably leads to Mo doping. This doping introduces unique electrochemical signals not seen in other Pt-based catalysts, which can directly reflect the stability of the catalyst. Through experiments, it is demonstrated that Mo doping is detrimental to ORR performance, and theoretical calculations have shown that Mo sites that are inherently inactive also poison the ORR activity of the surrounding Pt. Therefore, a novel gas-assisted technique is proposed to replace Mo(CO)6 with CO, which forms ultrafine nanowires with an order of magnitude increase in length, ruling out the effect of Mo. The catalyst performs at 1.24 A mgPt -1, 7.45 times greater than Pt/C, demonstrating significant ORR mass activity, and a substantial improvement in stability. The proton exchange membrane fuel cell using this catalyst provides a higher power density (0.7 W cm-2). This study presents a new method for the preparation of ultra-long nanowires, which opens up new avenues for future practical applications of low-Pt catalysts in PEMFC.

Chemical Vapor Deposition Toward Efficient Bimetallic Atomically Dispersed Oxygen Reduction Catalysts.

Non-precious metal-based nitrogen-doped carbon (M-Nx/C) shows great potential as a substitute for precious metal Pt-based catalysts. However, the conventional pyrolytic methods for forming M-Nx/C active sites are prone to issues such as the lack of synergistic interactions among bimetallic atoms and the potential encasement of active sites, leading to compromised catalytic efficiency and hindered mass transfer. In this work, a highly active FeCo-N-C@U-AC electrocatalyst is developed with a high density of active sites, adequate exposure of catalytic sites, and robust mass transfer capability using the chemical vapor-phase deposition (CVD) technique. The resulting catalyst demonstrates impressive oxygen reduction reaction (ORR) catalytic performance and stability, with half-wave potentials of 0.820 V (0.1 M HClO4) and 0.911 V (0.1 M KOH), respectively. It also exhibits significantly enhanced stability, retaining 93.25% and 98.38% of current after continuous 50 000 s of durability testing, surpassing the retention rates of Pt/C (80.31% in HClO4 and 84.96% in KOH electrolytes). Notably, when employed as a cathode catalyst in proton exchange membrane fuel cells (PEMFCs) and zinc-air flow batteries (ZAFBs), the FeCo-N-C@U-AC catalyst delivers peak power densities of 859 and 162 mW·cm-2, respectively, showcasing competitive performance comparable to benchmark Pt/C.

Ice Nucleation Mechanisms on Platinum Surfaces in PEM Fuel Cells: Effects of Surface Morphology and Wettability.

Understanding the ice nucleation mechanism in the catalyst layers (CLs) of proton exchange membrane (PEM) fuel cells and inhibiting icing by designing the CLs can optimize the cold start strategies, which can enhance the performance of PEM fuel cells. Herein, mitigating the structural matching and templating effects by adjusting the surface morphology and wettability can inhibit icing on the platinum (Pt) catalyst surface effectively. The Pt(211) surface can inhibit icing because the atomic spacing of (211) crystalline surface is much larger than the characteristic distance of ice crystal, thereby mitigating the structural matching effects. A water overlayer on the Pt surface induced by the strong attraction of Pt can act as a template for ice layers and plays an important role in the icing process. Buckling of water overlayer due to the larger atomic spacing of (211) crystalline surface mitigates the templating effect and inhibits icing. Moreover, the water overlayer on the hydrophobic Pt(211) surface with fewer water molecules also mitigates the templating effect, which makes ice nucleation more difficult than homogeneous nucleation. These findings reveal the ice nucleation mechanisms on the Pt catalyst surface from the molecular level and are valuable for catalyst designs to inhibit icing in CL.

Degradation prediction of fuel cell systems based on different operating conditions in dynamic cycling condition.

In this paper, the degradation of PEMFC under different operating conditions in dynamic cycle condition is studied. Firstly, according to the failure mechanism of PEMFC, various operating conditions in dynamic cycle condition are classified, and the health indexes are established. Simultaneously, the rates and degrees of the output voltage decline of the PEMFC under different operating conditions during the dynamic cycling process were compared. Then, a model based on variational mode decomposition and long short-term memory with attention mechanism (VMD-LSTM-ATT) is proposed. Aiming at the performance of PEMFC is affected by the external operation, VMD is used to capture the global information and details, and filter out interference information. To improve the prediction accuracy, ATT is used to assign weight to the features. Finally, in order to verify the effectiveness and superiority of VMD-LSTM-ATT, we respectively apply it to three current conditions under dynamic cycle conditions. The experimental results show that under the same test conditions, RMSE of VMD-LSTM-ATT is increased by 56.11 % and MAE is increased by 28.26 % compared with GRU attention. Compared with SVM, RNN, LSTM and LSTM-ATT, RMSE of VMD-LSTM-ATT is at least 17.26 % higher and MAE is at least 5.65 % higher.

Analyzing Key Factors Influencing Water Transport in Open Air-Cooled PEM Fuel Cells.

The current limitations of air-cooled proton exchange membrane fuel cells (AC-PEMFCs) in water and heat management remain a major obstacle to their commercialization. A 90 cm2 full-size AC-PEMFC multi-physical field-coupled numerical model was constructed; isothermal and non-isothermal calculations were performed to explore the effects of univariate and multivariate variables on cell performance, respectively. The isothermal results indicate that lower temperature is beneficial to increase the humidity of MEA, and distribution uniformity at lower stoichiometric ratios and lower temperatures is better. The correlation between current density distribution and temperature, water content, and concentration distribution shows that the performance of AC-PEMFCs is influenced by multiple factors. Notably, under high current operation, the large heat generation may lead to high local temperature and performance decline, especially in the under-channel region with drier MEA. The higher stoichiometric ratio can enhance heat dissipation, improve the uniformity of current density, and increase power density. Optimal fuel cell performance is achieved with a stoichiometric ratio of 300, balancing the mixed influence of multiple factors.

Energy, Exergetic, and Thermoeconomic Analyses of Hydrogen-Fueled 1-kW Proton-Exchange Membrane Fuel Cell.

Exergy analysis evaluates the efficiency of system components by quantifying the rate of entropy generation. In general, the exergy destruction rate or irreversibility rate was directly obtained through the exergy balance equation. However, this method cannot determine the origin of the component's entropy generation rate, which is a very important factor in system design and improvement. In this study, a thorough energy, exergy, and thermoeconomic analysis of a proton-exchange membrane fuel cell (PEMFC) was performed, providing the heat transfer rate, entropy generation rate, and cost loss rate of each component. The irreversibility rate of each component was obtained by the Gouy-Stodola theorem. Detailed and extensive exergy and thermoeconomic analyses of the PEMFC system determined that water cooling units experience the greatest heat transfer among the components in the studied PEMFC system, resulting in the greatest irreversibility and, thus, the greatest monetary flow loss.

Effect of Heat Treatment on Structure of Carbon Shell-Encapsulated Pt Nanoparticles for Fuel Cells.

Polymer electrolyte membrane fuel cells (PEMFCs) have attracted much attention as highly efficient, eco-friendly energy conversion devices. However, carbon-supported Pt (Pt/C) catalysts for PEMFCs still have several problems, such as low long-term stability, to be widely commercialized in fuel cell applications. To address the stability issues of Pt/C such as the dissolution, detachment, and agglomeration of Pt nanoparticles under harsh operating conditions, we design an interesting fabrication process to produce a highly active and durable Pt catalyst by introducing a robust carbon shell on the Pt surface. Furthermore, this approach provides insights into how to regulate the carbon shell layer for fuel cell applications. Through the application of an appropriate amount of H2 gas during heat treatment, the carbon shell pores, which are integral to the structure, can be systematically modulated to facilitate oxygen adsorption for the oxygen reduction reaction. Simultaneously, the carbon shell functions as a protective barrier, preventing catalyst degradation. In this regard, we investigate an in-depth analysis of the effects of critical parameters including H2 content and the flow rate of H2/N2 mixed gas during heat treatment to prepare better catalysts.

Magnetic Array-Aided Visualizing PEMFC Degradation Heterogeneity.

Analyzing degradation heterogeneity of proton exchange membrane fuel cell (PEMFC) while maintaining high practicality is consistently challenging, primarily due to the destructive and costly nature of existing techniques relying on material characterization. In this work, a designed magnetic array integrating 16 sensors within 25 cm2 space is used for direct scanning and imaging of PEMFC performance heterogeneity during its degradation. Results are validated through degradation mechanism analysis and material characterization, confirming its potential in guiding the development of durable materials.

Similarities and Differences between Gas Diffusion Layers Used in Proton Exchange Membrane Fuel Cell and Water Electrolysis for Material and Mass Transport.

Proton-exchange membrane fuel cells (PEMFCs) and water electrolysis (PEMWE) are rapidly developing hydrogen energy conversion devices. Catalyst layers and membranes have been studied extensively and reviewed. However, few studies have compared gas diffusion layers (GDLs) in PEMWE and PEMFC. This review compares the differences and similarities between the GDLs of PEMWE and PEMFC in terms of their material and mass transport characteristics. First, the GDL materials are selected based on their working conditions. Carbon materials are prone to rapid corrosion because of the high anode potential of PEMWEs. Consequently, metal materials have emerged as the primary choice for GDLs. Second, the mutual counter-reactions of the two devices result in differences in mass transport limitations. In particular, water flooding and the effects of bubbles are major drawbacks of PEMFCs and PEMWE, respectively; well-designed structures can solve these problems. Imaging techniques and simulations can provide a better understanding of the effects of materials and structures on mass transfer. Finally, it is anticipated that this review will assist research on GDLs of PEMWE and PEMFC.