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In this work, a poly (vinylidene fluoride) (PVDF) and cellulose acetate (CA) blend membrane is developed using the solution casting method for a direct methanol fuel cell (DMFC). The CA addition in PVDF polymer reduces the dense structure of the polymer and creates a porous surface by increasing the amorphous region that is confirmed by surface morphology and crystallinity examination tests. The high glass transition temperature of CA boosts the protection from the melting of PVDF membrane and increases the thermal shrinkage that reduces the probability of a short circuit. PVDF and CA with abundant hydroxyl groups and carboxylic groups enhance the water uptake, also the hydrogen bonding in between them promotes the mechanical strength and develops a tortuous structure that allows protons to pass through them and block the methanol crossover. The 60% PVDF and 40% CA blend membrane shows an ion exchange capacity value of 0.91 and a methanol permeability value of 4.21 × 10–7 cm2 s−1, which is lower than that of the conventional Nafion 117 membrane (19.5 × 10–7 cm2 s−1). A direct methanol fuel cell with this membrane represents a power density value of 16.5 mW cm−2 with a voltage and current density values of 0.178 V and 165 mA cm−2 at 1 M methanol concentration and room temperature. Moreover, it shows a 70% voltage retention after 20 h of testing of the cell at room temperature that is superior to that of the commercial Nafion 117 membrane (48% voltage retention). [ABSTRACT FROM AUTHOR]

Polymer electrolyte membrane fuel cells (PEMFCs) represent a promising clean energy solution. However, their widespread adoption faces hurdles related to component optimization. This review explores the pivotal role of ionic liquids (ILs) in enhancing PEMFC performance, focusing on their role in polymer electrolyte membranes, catalyst modification, and other components. By addressing key obstacles, including proton conductivity, catalyst stability, and fuel crossover, ILs provide a pathway towards the widespread commercialization of PEMFCs. In the realm of PEMFC membranes, ILs have shown great potential in improving proton conductivity, mechanical strength, and thermal stability. Additionally, the utilization of ILs as catalyst modifiers has shown promise in enhancing the electrocatalytic activity of electrodes by serving as an effective stabilizer to promote the dispersion of metal nanoparticles, and reduce their agglomeration, thereby augmenting catalytic performance. Furthermore, ILs can be tailored to optimize the catalyst‐support interaction, ultimately enhancing the overall fuel cell efficiency. Their unique properties, such as high oxygen solubility and low volatility, offer advantages in terms of reducing mass transport and water management issues. This review not only underscores the promising advancements achieved thus far but also outlines the challenges that must be addressed to unlock the full potential of ILs in PEMFC technology, offering a valuable resource for researchers and engineers working toward the realization of efficient and durable PEMFCs. [ABSTRACT FROM AUTHOR]

The structure of a catalyst layer (CL) significantly impacts the performance, durability, and cost of proton exchange membrane (PEM) fuel cells and is influenced by the catalyst ink and the CL formation process. However, the relationship between the composition, formulation, and preparation of catalyst ink and the CL formation process and the CL structure is still not completely understood. This review, therefore, focuses on the effect of the composition, formulation, and preparation of catalyst ink and the CL formation process on the CL structure. The CL structure depends on the microstructure and macroscopic properties of catalyst ink, which are decided by catalyst, ionomer, or solvent(s) and their ratios, addition order, and dispersion. To form a well-defined CL, the catalyst ink, substrate, coating process, and drying process need to be well understood and optimized and match each other. To understand this relationship, promote the continuous and scalable production of membrane electrode assemblies, and guarantee the consistency of the CLs produced, further efforts need to be devoted to investigating the microstructure of catalyst ink (especially the catalyst ink with high solid content), the reversibility of the aged ink, and the drying process. Furthermore, except for the certain variables studied, the other manufacturing processes and conditions also require attention to avoid inconsistent conclusions. [ABSTRACT FROM AUTHOR]

Design and synthesis of highly active and durable electrocatalysts toward oxygen reduction reaction (ORR) is of particular importance for proton exchange membrane fuel cells (PEMFCs), yet remains a grand challenge. Herein, we report the deposition of iron (III) porphyrin (FeP) on house-made Pt/C by rotary evaporation of the mixture of FeP and house-made Pt/C dispersed in chloroform, followed by pyrolysis at 650 °C in argon atmosphere. This approach led to the synthesis of new non-precious metal electrocatalyst (NPME)-Pt/C composites (Pt/C–FeP) with an average nanoparticle diameter of 3.1 ± 1.5 nm without aggregation. According to X-ray photoelectron spectroscopy (XPS), the binding energy of Pt 4f 7/2 became larger due to the presence of pyrolyzed FeP. In addition, the electrochemically active surface area (ECSA) of Pt/C–FeP-650 is 65 m2/g less than that of house-made Pt/C (80.2 m2/g). This implies that the pyrolyzed FeP may have partially covered the surface of Pt nanoparticles and thus lowering the ECSA. Interestingly, the mass activity (MA) of Pt/C–FeP turns out to be 349.0 mA/mg Pt @0.9 V vs. RHE, which is 2.6 times and 1.5 times of house-made Pt/C and commercial Pt/C, respectively. It is speculated that the electronic interaction and possible synergy between Pt and pyrolyzed FeP as NPME might have contributed to the ORR activity improvement despite of partial loss of ECSA. During accelerated durability tests (ADTs), the MA of Pt/C–FeP-650 degrades 64.3% inferior to commercial Pt/C (52.2%). The main reason likely arises from the degradation of pyrolyzed FeP, which is a bottleneck problem confronting NPMEs. Image 1 • A new non-precious metal electrocatalyst (NPME)-Pt/C composite with improved activity was synthesized. • NPME-Pt/C composite has been successfully synthesized by pyrolyzing FeP coated Pt/C. • The improved ORR activity may arise from the electronic interaction and possible synergy between Pt and NPME. [ABSTRACT FROM AUTHOR]

The stability of support materials is crucial for the application of high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), and the corrosion of conventional carbon support poses a significant challenge. In this study, a new type of composite support material, carbon composite niobium nitride (Nb4N5/C) was developed and investigated. Physical characterization demonstrated that Nb4N5 has a unique micro-flower morphology with a large specific surface area, making it an ideal support for Pt nanoparticles. X-ray photoelectron spectroscopy (XPS) analysis revealed that the addition of Nb4N5 reduced the displacement of d-band center of Pt and weakened the bonding between adsorbed oxygen and Pt. The Pt/Nb4N5/C-based catalyst demonstrated better stability than Pt/C after undergoing an accelerated durability test (ADT) of 5000 cycles, indicating the effectiveness of introducing this transition metal nitrides (TMNs) to enhance catalyst stability. Moreover, in the single-cell test at high temperature, the HT-PEMFC based on the Pt/Nb4N5/C catalyst exhibited an impressive peak power density of 520.48 mW cm−2 at 150 °C. After the durability test, it only suffered a decrease of 5.2%, which is more stable than the commercial Pt/C (11.7%), suggesting it is promising candidate for practical HT-PEMFC applications. • Nb 4 N 5 /C composite support enhances stability of HT-PEMFC. • Micro-flower morphology of Nb 4 N 5 offers large specific surface area to support Pt. • Pt/Nb 4 N 5 /C catalyst outperforms Pt/C in performance and durability for HT-PEMFC. • Strong interaction between Pt and Nb4N5 support ensures catalyst activity and durability. [ABSTRACT FROM AUTHOR]

The catalyst layer (CL) is the only electrochemical reaction site in proton exchange membrane fuel cells (PEMFCs), decisive in their performance. Herein, a mild and simplified strategy is implemented into the in-situ growth of Pt–Pd alloy catalysts on the gas diffusion layer (GDL) as the CLs for PEMFCs. Pt/C is used as the nucleation site to assist the in-situ growth of the Pt–Pd CL. The as-prepared Pt–Pd CL behaves as a multi rhombic-pyramidal structure, which are evenly distributed on the GDL surface. The effect of the Pt/Pd atomic ratio on the electrocatalytic activity is investigated through a single-cell performance test, and the optimal atomic ratio is determined to be 1/2, which exhibits excellent cell performance and low activation polarization loss. Meanwhile, the single-cell test results reveal that Pt 1 Pd 2 CL reaches optimal performance at a loading of 0.122 mg cm−2 (∼0.06 mg Pt cm−2), with a peak Pt-specific power density of 14.23 W mg−1 (6.81 W mg−1 in PtPd), approximately 3.96 times that of a commercial Pt/C CL (0.2 mg Pt cm−2). Furthermore, Pt 1 Pd 2 CL shows significantly better stability than the commercial Pt/C CL, indicating that the in-situ preparation of the Pt-based CL has an excellent prospect for the commercial development of PEMFCs. [Display omitted] • In situ grown Pt–Pd CL is developed for PEMFC operation. • The Pt–Pd CL exhibits a multi rhombic-pyramidal structure with high active sites exposure. • The Pt–Pd CL maintained high electrocatalytic activity with reduced Pt loading. • The resultant PEMFC shows excellent performance and stability. • The peak Pt-specific power density was up to 14.23 W mg−1 (6.81 W mg−1 in PtPd). [ABSTRACT FROM AUTHOR]

With emerging demand of potable and wearable electronic devices, reliable and flexible energy suppliers are inevitable. Polymer electrolyte membrane fuel cells (PEMFCs) attract great attention due to high energy density and sustainability. However, non-bendability limits their application in flexible electronic devices. To make PEMFCs adaptable and flexible, considerable efforts have been devoted to developing various bendable components or advanced techniques. This review, therefore, focuses on the advancement of components and relative techniques of flexible PEMFCs, which determine the performance and durability, while achieved little concern in other reviews. The components and techniques include membrane, flexible catalytic layer, flexible gas diffusion layer, flexible bipolar plates, assembly of single cell or stack, store or supply of fuel and oxidant. In each section, the materials or techniques commonly used in conventional PEMFCs are summarized firstly, followed by the reasons why they aren't appliable to flexible PEMFCs and then proceeding to the development of flexible components and relevant techniques of flexible PEMFCs. Subsequently, the flexible PEMFCs' performance and durability are presented, reaching to 100–200 mW cm−2 and dozens of hours, respectively, still far lower than those of conventional PEMFCs. Finally, a brief perspective on remaining challenges and future development of flexible PEMFCs are provided. [Display omitted] • Crucial insights and information on flexible PEMFC are provided. • Materials and components for achieving flexibility are summarized. • Assembly techniques for flexible single cell and stack are presented. • Performance and durability under various bending conditions are analyzed. • Remaining challenges and future development on flexible PEMFC are discussed. [ABSTRACT FROM AUTHOR]

Carbon corrosion of Pt/C electrocatalyst in the cathode is a critical issue for the practical application of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). Herein, we introduce a nanolayer composed of TiO 2 nanoparticles between Pt and carbon support, which not only protects the carbon from corrosion but also forms a strong metal-support interaction between Pt and TiO 2. The Pt nanoparticles are uniformly dispersed on the prepared C@TiO 2 support (mean size: 2.27 nm). After potential sweeping for 5000 cycles in the acid solution, the electrochemical surface area loss of the homemade Pt/C@TiO 2 is 10.9%, which is approximately half of that of commercial Pt/C (19.1%). In the practical HT-PEMFC single cell, Pt/C@TiO 2 exhibits superior durability than Pt/C as well. After the accelerated durability test, the maximum power density of Pt/C@TiO 2 -MEA decreases by 8.6%, which is significantly lower than that of Pt/C-MEA (23.9%), suggesting a great potential application of Pt/C@TiO 2 in HT-PEMFCs. • The protective TiO 2 layer on carbon black consists of numerous TiO 2 NPs. • Pt NPs with a mean size of 2.27 nm uniformly distribute on C@TiO 2. • Strong metal-support interaction helps in anchoring Pt NPs to the TiO 2 surface. • Pt/C@TiO 2 exhibits comparable ORR activity to commercial Pt/C. • Pt/C@TiO 2 shows superior durability in both RDE and HT-PEMFC single cell systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Order-structured CL was prepared and used in the cathode of HT-PEMFC. • Order-structured CL consists of Pt NWs supported on vertically aligned TiO 2 NRs. • Ordered structure enables fast mass transport and efficient Pt utilization. • Synergistic effects of stable TiO 2 NRs, 1D Pt NWs, and SMSI between TiO 2 and Pt. • The MEA with ordered cathode CL achieved superior performance and durability. For large-scale commercialization of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), the issues of high Pt loading and unsatisfactory durability must be addressed. Disordered cathode catalyst layer (CL) with the random distribution of Pt/C electrocatalysts, binders, and pores is proved as one main reason for the motioned issues due to the limited Pt utilization efficiency, tortuous mass transport, and poor stability of Pt/C. Herein, we construct an ordered cathode CL consisting of in-situ grown Pt nanowires on the vertically aligned TiO 2 nanorods array, coupled with carbon nanotubes as conductors to enhance the mass transfer characteristics and durability. In the single cell tests, the membrane electrode assembly (MEA) with ordered cathode CL achieves 3.53-fold Pt mass-specific peak power density compared to a conventional MEA. The Pt loading is only 20 % of the latter. Meanwhile, much better durability is confirmed. The superior performance and durability are attributed to the synergistic effects of ordered structure, stable TiO 2 nanorods, one-dimensional features of Pt nanowires, and strong metal-support interaction between TiO 2 and Pt. This work provides new insight into CL design and facile fabrication method of the ordered CL, which is of great significance for the large-scale application of HT-PEMFC. [ABSTRACT FROM AUTHOR]

A novel enhanced membrane electrode assembly (MEA) was successfully developed by incorporating a phosphoric acid (PA)-loaded Schiff base network (SNW)-type covalent organic framework (COF) as an additive to the catalyst layer (CL) to improve the performance of proton exchange membrane fuel cells (PEMFCs) under low humidity conditions. The unique network structure and PA-loaded H 3 PO 4 @SNW-1 material have excellent water management and proton transfer abilities. Direct use of this material as a CL additive can significantly enhance the performance of PEMFCs under varying humidification conditions. The optimization of the additive content, the impact of the anode/cathode modification, and the operating temperature of PEMFCs were studied using electrochemical characterization and single cell tests. The maximum power density of MEAs with 15 wt.% H 3 PO 4 @SNW-1 added to the anode CL at a normal operating temperature of 60 °C was 745 mW cm−2 and 690 mW cm−2 under full humidification (100% RH) and low humidification (21% RH), respectively, both of which were higher than that of conventional MEAs. Furthermore, preliminary durability test and 10-day intermittent operation demonstrate the potential of the proposed PEMFCs in actual operation in harsh environments. • H 3 PO 4 @SNW-1 COF possesses water management and proton transfer abilities simultaneously. • The COF additive improves PEMFC performance in various humidity conditions. • Comprehensive optimization on the MEA with H 3 PO 4 @SNW-1 COF were conducted. • Durability testing shows good potential for practical use in low humidity environments. [ABSTRACT FROM AUTHOR]

The challenges related to the proton exchange membrane (PEM) of proton exchange membrane fuel cells and direct methanol fuel cells are high swelling, loss of mechanical structure strength and high fuel crossover at elevated temperatures that cause low efficiency. The single polymer membrane may replace the commercial membrane with its dimensional stability and low swelling but it shows low proton conductivity. Hydrophilic additives such as polymers and nanomaterials increase the strength of the single polymer membrane internal channels through interaction and lockdown the swelling while maintaining proton conduction through the Grotthuss and Vehicular methods. However, these additives still have limited capability of enhancing attributes of PEM such as limited water absorption, proton conductivity and loose interaction with the single polymer membrane due to their limited or weak functional groups. Hydrophilic group functionalization such as sulfonic groups, phosphonic groups, amino acid groups, carboxylic groups, zwitterionic groups, silane groups and acid doping with additives further strengthen the walls of channels, prevent swelling and capture more water molecules that increase proton conduction. This review article describes the different types of functionalized additives, their application in the membrane of fuel cells, further improvements in these modified additives, application methods and future prospects. [Display omitted] • Types of additives for PEM of PEMFC and DMFC are reviewed. • The additive proton conduction mechanisms are discussed in detail. • Deficiencies in existing additives for PEM are reviewed. • The benefits of functionalizing additives with hydrophilic groups are reviewed. • Limitations and future improvisations of functionalized additives for PEM are provided. [ABSTRACT FROM AUTHOR]

High-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) suffer from high platinum (Pt) loading and limited lifetime issues due to the low Pt efficiency of the conventional electrode and poor durability of Pt/C catalyst under harsh operating conditions. Thus, dual microporous layer (MPL) structured gas diffusion layers were developed, utilizing formic acid reduction for the in-situ growth of Pt nanowires (NWs). The optimal ratio of the hydrophilic and hydrophobic MPLs was determined to be 1:1. The resulting Pt NWs gas diffusion electrode (GDE) achieved a significantly high Pt mass-specific peak power density, which was 2.48 times higher than the conventional Pt/C GDE. After accelerated degradation tests, the peak power density and the electrochemically active surface area of Pt NWs GDE decreased by 10.84 % and 4.47 %, respectively, significantly lower than those of the conventional Pt/C GDE. The superior activity and durability of Pt NWs GDE are attributed to its binder-free characteristic, the outstanding activity and stability of one-dimensional Pt NWs, and the strong adherent force between the in-situ grown Pt and the carbon substrate. This study provides a straightforward and effective strategy to reduce the Pt loading and enhance electrode durability, thereby facilitating the large-scale application of HT-PEMFCs. • Dual MPL structured GDLs were developed. • The optimal ratio of hydrophilic and hydrophobic MPLs was 1:1. • In-situ growth of Pt NWs on the hydrophilic MPL by formic acid reduction. • Pt NW GDE shows superior Pt efficiency and durability than conventional Pt/C GDE. [ABSTRACT FROM AUTHOR]

In pursuit of enhanced methanol tolerance and thermal stability, a cost-effective solution was developed by integrating varied proportions of zeolitic imidazolate framework-67 (ZIF-67), a metal-organic framework, into a sulfonated polyvinylidene fluoride (SPVDF) matrix-based proton exchange membrane (PEM). Through comprehensive characterization, the uniform dispersion and chemical functionalities of SPVDF and ZIF-67 was confirmed by Scanning electron microscopy(SEM), Fourier transform infrared spectroscopy (FT-IR) respectively. This uniform dispersion is attributed by the electrostatic interaction between the –NH 2 group of Himm unit and -SO 3 H group of SPVDF create a strong hydrogen bonding network (i.e. acid-base pair) resulted in improved membrane surface hydrophilicity, water uptake, proton conductivity. Further the incorporation of ZIF-67 led to a composite membrane with significantly lower methanol permeability (1.5 × 10−7 cm2 s−1) compared to Nafion 117 (20 × 10−7 cm2 s−1). For glass transition and crystallization behavior of SPVDF-1 showed good miscibility enhance the membrane thermal and mechanical stability. This reduction is attributed to the presence of a large active surface area with small pores acting as a barrier against methanol permeation. Furthermore, single-cell tests in a direct methanol fuel cell (DMFC) demonstrated that the SPVDF-1 membrane achieves a maximum power density of 82.4 mW cm−2, surpassing that of Nafion 117 (75.9 mW cm−2). These results underscore the potential of the developed SPVDF-1 membrane as a promising alternative for DMFC applications. [Display omitted] • Sulfonated polyvinylidene fluoride (SPVDF) embedded zeolitic imidazolate framework-67 (ZIF-67) hybrid PEM. • ZIF-67 enhance membrane hydrophilic sites, thermal and chemical stability. • SPVDF-1 showed low methanol permeability 1.5 × 10−7 cm2s−1 than Nafion 117 • SPVDF/ZIF-67 achieved maximum power density of 82.4 mW cm−2. [ABSTRACT FROM AUTHOR]