Proton Exchange Membranes For Applications Research Articles

A scale-bridging model for proton exchange membrane fuel cells: Understanding interactions among multi-physics transports, electrochemical reactions and heterogeneous aging

The lifetime issues caused by catalyst degradation is one of the most critical challenges for the commercial application of proton exchange membrane fuel cells. However, the understanding concerning the interactions among transport, reaction, and catalyst degradation is inadequate for further durability enhancement. Herein, a scale-bridging model that couples a cell-scaled model to reveal the reactive transport process and a catalyst-scaled model to unveil Pt degradation is proposed to capture the degradation characteristics. It is found that the heterogeneous aging is observed in both the through-plane and channel-rib directions due to the enhanced mass loss near the membrane and the water accumulation under the rib, resulting in the mitigation of the core reaction region away from the membrane, thereby causing an increase in ohmic loss after cycles. More importantly, the local oxygen transport resistance increases with degradation, leading to a remarkable cell performance loss under high current density. Additionally, the influences of cell voltage load and inlet humidity on Pt degradation are also investigated. And the proposed gradient catalyst layer shows a significant mitigating effect on Pt degradation. This work reveals the degradation-performance interactions, which is conducive to design the high-performance fuel cell to prolong lifetime.

Applicability of Single-Layer Graphene as a Hydrogen-Blocking Interlayer in Low-Temperature PEMFCs.

Gas crossover is critical in proton exchange membrane (PEM)-based electrochemical systems. Recently, single-layer graphene (SLG) has gained great research interest due to its outstanding properties as a barrier layer for small molecules like hydrogen. However, the applicability of SLG as a gas-blocking interlayer in PEMs has yet to be fully understood. In this work, two different approaches for transferring SLG from a copper or a polymeric substrate onto PEMs are compared regarding their application in low-temperature PEM fuel cells. The SLG is sandwiched between two Nafion XL membranes to form a stable composite membrane. The successful transfer is confirmed by Raman spectroscopy and in ex situ hydrogen permeation experiments in the dry state, where a reduction of 50% upon SLG incorporation is achieved. The SLG composite membranes are characterized by their performance and hydrogen-blocking ability in a fuel cell setup at typical operating conditions of 80 °C and with fully humidified gases. The performance of the fuel cell incorporating an SLG composite membrane is equal to that of the reference cell when avoiding the direct etching process from a copper substrate, as remnants from copper etching deteriorate the performance of the fuel cell. For both transfer processes, the hydrogen crossover reduction of SLG composite membranes is only 15-19% (1.5 barabs) in the operating fuel cell. Further, hydrogen pumping experiments suggest that the barrier function of SLG impairs the water transport through the membrane, which may affect water management in electrochemical applications. In summary, this work shows the successful transfer of SLG into a PEM and confirms the effective hydrogen-blocking capability of the SLG interlayer. However, the hydrogen-blocking ability is significantly reduced when running the cell at the typical humidified operating conditions of PEM fuel cells, which follows from a combination of reversible interlayer alteration upon humidification and irreversible defect formation upon PEM fuel cell operation.

Study of Resistance Extraction Methods for Proton Exchange Membrane Fuel Cells Based on Static Resistance Correction

Accurate extraction of polarization resistance is crucial in the application of proton exchange membrane fuel cells. It is generally assumed that the steady-state resistance obtained from the polarization curve model is equivalent to the AC impedance obtained from the electrochemical impedance spectroscopy (EIS) when the frequency approaches zero. However, due to the low-frequency stability and nonlinearity issues of the EIS method, this dynamic process leads to an additional rise in polarization resistance compared to the steady-state method. In this paper, a semi-empirical model and equivalent circuit models are developed to extract the steady-state and dynamic polarization resistances, respectively, while a static internal resistance correction method is proposed to represent the systematic error between the two. With the correction, the root mean square error of the steady-state resistance relative to the dynamic polarization resistance decreases from 26.12% to 7.42%, indicating that the weighted sum of the static internal resistance and the steady-state resistance can better correspond to the dynamic polarization resistance. The correction method can also simplify the EIS procedure by directly generating an estimate of the dynamic polarization resistance in the full current interval.

Synergistically Functionalized Pyridinyl- and Phosphine-Oxide-Based Semifluoro-Sulfonated Copolytriazole Membrane Preparation via “Click” Polymerization for Proton Exchange Membrane Applications

Synergistically Functionalized Pyridinyl- and Phosphine-Oxide-Based Semifluoro-Sulfonated Copolytriazole Membrane Preparation via “Click” Polymerization for Proton Exchange Membrane Applications

Temperature-relevant degradation in amorphous carbon coated SS316L bipolar plates for PEMFC

The corrosion of metallic Bipolar Plates (BPs) has become a key bottleneck in the practical application of proton exchange membrane fuel cells (PEMFCs). Environmental factors inside the PEMFCs significantly accelerate the degradation of electrical conductivity and durability of metallic BPs. In this work, we investigated the corrosion behavior and conductive properties of amorphous carbon coating (a-C) coated SS316L in a simulated PEMFC environment at various operating temperatures. The results showed that the corrosion current density (Icorr) of a-C varied in a range of 2.3–8.7 nA/cm2 when subjected to a temperature range of 40–80 °C. Additionally, the interfacial contact resistance increased from 4.36 to 9.56 mΩ/cm2 with a rise in temperature. The reasons could be ascribed to two aspects. First, the a-C maintained the good chemical stability of sp2/sp3 bonds regardless of temperature changes, favoring remarkable anti-corrosion and good conductivity. Second, the higher temperatures intensified the penetration of corrosive species, accelerating the dissolution process of a-C coated SS316L and leading to substantial corrosion failure.

Hybrid Membrane of Sulfonated Poly(aryl ether ketone sulfone) Modified by Molybdenum Clusters with Enhanced Proton Conductivity.

Developing novel proton exchange membranes (PEMs) with low cost and superior performance to replace Nafion is of great significance. Polyoxometalate-doped sulfonated poly(aryl ether ketone sulfone) (SPAEKS) allows for the amalgamation of the advantages in each constituent, thereby achieving an optimized performance for the hybrid PEMs. Herein, the hybrid membranes by introducing 2MeIm-{Mo132} into SPAEKS are obtained. Excellent hydrophilic properties of 2MeIm-{Mo132} can help more water molecules be retained in the hybrid membrane, providing abundant carriers for proton transport and proton hopping sites to build successive hydrophilic channels, thus lowering the energy barrier, accelerating the proton migration, and significantly fostering the proton conductivity of hybrid membranes. Especially, SP-2MIMo132-5 exhibits an enhanced proton conductivity of 75mScm-1 at 80°C, which is 82.9% higher than pristine SPAEKS membrane. Additionally, this membrane is suitable for application in proton exchange membrane fuel cells, and a maximum power density of 266.2mWcm-2 can be achieved at 80°C, which far exceeds that of pristine SPAEKS membrane (54.6mWcm-2). This work demonstrates that polyoxometalate-based clusters can serve as excellent proton conduction sites, opening up the choice of proton conduction carriers in hybrid membrane design and providing a novel idea to manufacture high-performance PEMs.

Operando synchrotron-based X-ray study and intervention approaches of graphene-related-materials for investigating the performance and durability of HT-PEMFC

The application of high-temperature proton exchange membrane fuel cells (HT-PEMFCs) addresses challenges in water management, fuel purity, and overheating under high current density. However, phosphoric acid (PA) migration hinders their development. This study uses synchrotron-based X-ray fluorescence spectroscopy to investigate PA and catalyst migration. Interventions with single-layer graphene and electrochemically exfoliated graphene oxide improve performance and durability. X-ray absorption spectroscopy provides insights into relevant mechanisms, advancing understanding of membrane electrode assembly preparation and the intricate influences of PA and catalyst migration on performance and durability in HT-PEMFCs.

2,5-Substituted Thiophene Functionalized Semifluorinated Polytriazoles and Evaluation of Low-Temperature Proton Exchange Membrane Application with Elevated Oxidative Stability

2,5-Substituted Thiophene Functionalized Semifluorinated Polytriazoles and Evaluation of Low-Temperature Proton Exchange Membrane Application with Elevated Oxidative Stability

Structural and Transport Properties of Hydrophilic and Hydrophobic Modified Ionomers in Proton Exchange Membrane Fuel Cells.

The sluggish commercial application of proton exchange membrane fuel cells (PEMFCs) with low Pt loading is chiefly hindered by concentration polarization loss, particularly at high current density regions. Addressing this, our study concentrates on the ionomer membranes in the cathode catalyst layer (CCL) and explores the potential of incorporating additional hydrophilic or hydrophobic components to modify these ionomers. Therefore, an all-atom model was constructed and for the ionomer and hydrophilic and hydrophobic modifications were implemented via incorporating SiO2 and PTFE, respectively. The investigation was conducted via molecular dynamics (MD) simulations to predict the morphology and structure of the ionomer and analyze the kinetic properties of oxygen molecules and protons. The simulation results elaborate that the hydrophilic and hydrophobic modifications favor the phase separation and the self-diffusion coefficients of oxygen molecules and protons are enhanced. Considering the hydration level of the ionomer films, hydrophilic modification facilitates mass transfer under low-hydration-level conditions, while hydrophobic modification is more effective in optimizing mass transfer as the hydration level increases. The optimal contents of SiO2 and PTFE for each hydration level in this work are 9.6% and 45%, respectively. This work proposes a reliable model and presents a detailed analysis of hydrophilic and hydrophobic modifications, which provides theoretical guidance for quantitative preparations of various composite membranes.

Enhancing the performance of proton exchange membranes: Incorporating layered double hydroxides into low sulfonated polyether sulfone octyl sulfonamide composite membranes

An interesting approach was employed to fabricate ion exchange membranes tailored for proton exchange membrane applications. This involved blending low sulfonated polyether sulfone octyl sulfonamide (LSPSO) with Layered Double Hydroxides (LDHs) clay at varying weight ratios (1 wt%, 3 wt%, and 6 wt%). Comprehensive characterization of the resulting composite membranes was conducted using diverse techniques, including Fourier-transform infrared spectroscopy, X-Ray diffraction, scanning electron microscopy, and thermogravimetric analysis, to evaluate surface morphology and thermal stability. Notably, the thermal performance of the composite membrane exhibited significant enhancements compared to the pristine LSPSO membrane. The inclusion of 6 wt% LDHs in the composite membrane led to a substantial increase in proton conductivity, rising from 35.04 mS/cm to 143.75 mS/cm at 100 °C. This discovery underscores the potential of the LDHs/LSPSO composite membrane as an electrolyte membrane for high-temperature fuel cell applications.

Dynamic accelerated stress test and coupled on-line analysis program to elucidate aging processes in proton exchange membrane fuel cells

The application of hydrogen proton exchange membrane fuel cells (PEMFC) in greenhouse gas emission free heavy-duty vehicles requires extremely durable PEMFC components with service lives in the range of 30,000 h. Hence suitable test and analysis methods are required that reflect realistic operation scenarios, but significantly accelerate aging. For this purpose, a dynamic accelerated stress test was developed, which is coupled with a comprehensive in-depth in-situ and ex-situ analysis program to determine the aging processes of a PEMFC membrane electrode assembly (MEA). The test comprehends dynamic cycling between low, moderate and high load, different temperature and humidity conditions as well as recovery sequences to distinguish between reversible and irreversible failure modes. All phases of the PEMFC system (i.e. solid, liquid and gaseous) are monitored on-line during aging by sophisticated electrochemical, mass spectrometric and ion chromatographic analytical methods. The structural and elemental composition of the MEA before and after the aging program (post-mortem) are investigated by X-ray fluorescence, scanning and transmission electron microscopy. This program was able to age a commercial PEMFC to end-of-life in 1000 h, while providing an accurate picture of the aging processes involved.

Enhanced performance of high-temperature proton exchange membranes via polyfluorene cross-linked zwitterionic liquid

A satisfactory trade-off between physical/chemical stability and conductivity is crucial for high-temperature proton exchange membrane (HT-PEM) applications. Herein, a series of ether-free polyfluorenes cross-linked with zwitterionic liquids possessing both quaternary ammonium (QA+) and sulfonate ion (–SO3−) were prepared as crosslinked cHFTP–VIPSx via UV irradiation. Compared with non-crosslinked HFTP–TMA, crosslinked cHFTP–VIPSx exhibited enhanced conductivity, dimensional stability, oxidation stability, and phosphoric acid retention, which are attributed to the well-developed crosslinked structure and incorporated –SO3- groups. The as-fabricated H2/air single cell with a cross-linked cHFTP–VIPS30 achieved a higher peak power density (728 mW cm−2) than that of uncross-linked HFTP–TMA (287 mW cm−2) at 120 °C. Considering their enhanced performance, these cHFTP–VIPSx membranes cross-linked with zwitterionic liquid are promising HT-PEM materials for fuel cells.

Transition metals anchored on nitrogen-doped graphdiyne for an efficient oxygen reduction reaction: a DFT study.

The search for highly active and low-cost single-atom catalysts for the oxygen reduction reaction (ORR) is essential for the widespread application of proton exchange membrane fuel cells. Transition metals anchored on nitrogen-doped graphdiyne (GDY) have attracted considerable interest as potentially excellent catalysts for the ORR. However, the relationship between the active site and nitrogen-doped GDY remains unclear. In this work, we conducted a systematic investigation of sp-hybridized N atoms anchoring single transition metal atoms of 3d and 4d on GDY (TMC2N2) as electrocatalysts for the ORR. Firstly, 18 kinds of TMC2N2 were determined to have good thermodynamic stability. Due to the extremely strong adsorption of *OH, TMC2N2 exhibits inferior ORR performance compared to traditional Pt(111). Considering that *OH adsorption hinders the catalytic activity of TMC2N2, we modified the OH ligand of TMC2N2 to develop the high-valent metal complex (TMC2N2-OH) aiming to enhance the electrocatalytic activity. The adsorption of intermediates on most TMC2N2-OH is weakened after the modification of the OH ligand, especially for the adsorption of *OH. Thus, by comparing the ORR overpotential of catalysts before and after ligand modification, we find that the catalytic activity of different TMC2N2-OHs improves to various degrees. MnC2N2-OH, TMC2N2-OH, and TcC2N2-OH exhibit relatively high ORR catalytic activity, with overpotentials of 0.93 V, 1.19 V, and 0.92 V, respectively. Furthermore, we investigated the cause of improved catalytic activity of TMC2N2-OH and found that the modified coordination environment of the catalyst led to adjusted adsorption of ORR intermediates. In summary, our work sheds light on the relationship between nitrogen-doped GDY and transition metal sites, thus contributing to the development of more efficient catalysts.

Design and multilevel regulation of transition metal phosphides for efficient and industrial water electrolysis.

Renewable energy electrolysis of water to produce hydrogen is an effective measure to break the energy dilemma. However, achieving activity and stability at a high current density is still a key problem in water electrolyzers. Transition metal phosphides (TMPs), with high activity and relative inexpensiveness, have become excellent candidates for the production of highly pure green hydrogen for industrial applications. In this mini-review, multilevel regulation strategies including nanoscale control, surface composition and interface structure design of high-performance TMPs for hydrogen evolution are systematically summarized. On this basis, in order to achieve large-scale hydrogen production in industry, the hydrogen evolution performance and stability of TMPs at a high current density are also discussed. Peculiarly, the practical application and requirements in proton exchange membrane (PEM) or anion exchange membrane (AEM) electrolyzers can guide the advanced design of regulatory strategies of TMPs for green hydrogen production from renewable energy. Finally, the challenges and prospects in the future development trend of TMPs for efficient and industrial water electrolysis are given.

One-pot preparation of crosslinked network membranes via knitting strategy for application in high-temperature proton-exchange membrane fuel cells

Balancing phosphoric acid (PA) uptake with the dimensional stability of PA-doped membranes is a major challenge in the field of high-temperature proton-exchange membranes.

Designing of Hexagonal Nanosheets with Edge‐Sharing [IrO6] Octahedral Crystals for Efficient and Stable Acidic Water Splitting

AbstractThe oxygen evolution reaction (OER) is a critical factor for advancing the industrial application of proton exchange membrane (PEM) electrolyzers. However, the low mass activity of iridium‐based catalysts has become a critical obstacle in improving the efficiency of the OER. To address this problem, a hexagonal system nanosheet structure with lattice distortion and edge‐connected [IrO6] octahedron is designed to enhance both mass activity and durability. This material exhibits a high mass activity of 217 mA mgIr−1 at 1.55 V relative to the reversible hydrogen electrode (RHE), which is 13 times greater than that of Rutile IrO2. Furthermore, the voltage of T‐CsIr exhibits no significant increase after 400 h of continuous operation at a current density of 10 mA cm−2. Integrating X‐ray experimental analysis with theoretical calculations reveals that the shortening of the Ir─Ir bond and the reduction of Ir3+ proportion effectively modulate the adsorption energy of the rate‐determining step, thereby significantly promoting the kinetics of the OOH* deprotonation process. These results demonstrate that regulation of lattice distortion is a feasible approach to effectively improve the OER catalytic performance.

Tetra-Coordinated W2 S3 for Efficient Dual-pH Hydrogen Production.

Two-dimensional (2D) transition-metal dichalcogenides (TMDs) have emerged as promising catalysts for the hydrogen evolution reaction (HER) that play a crucial role in renewable energy technologies. Breaking the inherent structural paradigm limitations of 2D TMDs is the key to exploring their fascinating physical and chemical properties, which is expected to develop a revolutionary HER catalyst. Herein, we unambiguously present metallic W2 S3 instead of energetically favorable WS2 via a unique stoichiometric growth strategy. Benefiting from the excellent conductivity and hydrophilicity of the tetra-coordinated structure, as well as an appropriate Gibbs free energy value and an enough low energy barrier for water dissociation, the W2 S3 as catalyst achieves Pt-like HER activity and high long-term stability in both acidic and alkaline electrolytes. For application in proton exchange membrane (PEM) and anion exchange membrane (AEM) electrolysers, W2 S3 as the cathode catalyst yields excellent bifunctionality index (ɳ =1.73 V, ɳ =1.77 V) and long-term stability (471 h@PEM with a decay rate of 85.7 μV h-1 , 360 h@AEM with a decay rate of 27.1 μV h-1 ). Our work provides significant insight into the tetra-coordinated W2 S3 and facilitates the development of advanced electrocatalysts for sustainable hydrogen production.

Tetra‐Coordinated W2S3 for Efficient Dual‐pH Hydrogen Production

AbstractTwo‐dimensional (2D) transition‐metal dichalcogenides (TMDs) have emerged as promising catalysts for the hydrogen evolution reaction (HER) that play a crucial role in renewable energy technologies. Breaking the inherent structural paradigm limitations of 2D TMDs is the key to exploring their fascinating physical and chemical properties, which is expected to develop a revolutionary HER catalyst. Herein, we unambiguously present metallic W2S3 instead of energetically favorable WS2 via a unique stoichiometric growth strategy. Benefiting from the excellent conductivity and hydrophilicity of the tetra‐coordinated structure, as well as an appropriate Gibbs free energy value and an enough low energy barrier for water dissociation, the W2S3 as catalyst achieves Pt‐like HER activity and high long‐term stability in both acidic and alkaline electrolytes. For application in proton exchange membrane (PEM) and anion exchange membrane (AEM) electrolysers, W2S3 as the cathode catalyst yields excellent bifunctionality index (ɳ =1.73 V, ɳ =1.77 V) and long‐term stability (471 h@PEM with a decay rate of 85.7 μV h−1, 360 h@AEM with a decay rate of 27.1 μV h−1). Our work provides significant insight into the tetra‐coordinated W2S3 and facilitates the development of advanced electrocatalysts for sustainable hydrogen production.

Selective Etching of Metal-Organic Frameworks for Open Porous Structures: Mass-Efficient Catalysts with Enhanced Oxygen Reduction Reaction for Fuel Cells.

Fe-Nx-C-based single-atom (SA-Fe-N-C) catalysts have shown favorable oxygen reduction reaction (ORR) activity. However, their application in proton exchange membrane fuel cells is hindered by reduced performance owing to the thick catalyst layer, restricting mass transfer and the O2 supply. Metal-organic frameworks (MOFs) are a promising class of crystal materials, but their narrow pores exacerbate the sluggish mass-transport properties within the catalyst layer. This study developed an approach for constructing an open-pore structure in MOFs via chelation-assisted selective etching, resulting in atomically dispersed Fe atoms anchored on an N, S co-doped carbon framework. The open-pore structure reduces oxygen transport resistance in the membrane electrode assembly (MEA) with unprecedented ORR activity and stability, as evidenced by finite element simulations. In an acidic electrolyte, the OP-Fe-NC catalyst shows a half-wave potential of 0.89 V vs RHE, surpassing Pt/C by 20 mV, and a current density of 29 mA cm-2 at 0.9 ViR-free in the MEA. This study provides an effective structural strategy for fabricating electrocatalysts with high mass efficiency and atomic precision for energy storage and conversion devices.

Thermal management of an open-cathode PEMFC based on constraint generalized predictive control and optimized strategy

The application of open-cathode proton exchange membrane fuel cell (PEMFC) has been extended to unmanned aerial vehicles (UAVs), light duty vehicles and other fields, but its performance is highly affected by the temperature fluctuation of stack and ambient temperature. This paper aims to design a thermal management system to achieve higher stack performance and lower fan power consumption by considering ambient temperature and practical application. To do that, a new temperature control strategy is first proposed by studying the relationship between optimal operating temperature and ambient temperature. Then, a model of 1000 W stack including thermal system is built for designing a temperature controller based on constraint generalized predictive control (CGPC). After that, the CGPC controller is enhanced by adding optimized strategy and control rules related to practical application to avoid irreversible damage especially when the current density increases. Finally, the control system with enhanced CGPC is effectively reduce the average error compared with PI control, which is only 0.032 °C. The proposed control strategy with additional control rules is valid by experiments and shows higher performance and lower fan duty cycle of 28.9 % compared with manufacture's default strategy. Thus, the proposed method has significant for widespread application of PEMFC.