High Temperature Proton Exchange Membrane Fuel Cell Research Articles

Effective strategy for enhancing the activity and durability of gas diffusion electrode in high-temperature polymer electrolyte membrane fuel cells: In-situ growth of Pt nanowires on dual microporous layers

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.

Understanding Phosphoric Acid Dynamics in High-Temperature Pemfcs: Mechanisms and Durability of PA-PBI and Ion-Pair-Based Systems.

High-Temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) can operate at > 100 oC under anhydrous conditions, providing benefits such as system simplification and superior contaminant tolerance. Most researches on HT-PEMFC have focused on PA-PBI-based system since 1995, however the durability of this system is still on controversial. Some insisted the stable operation of PA-PBI HT-PEMFC, which showed the stability under mild conditions such as low current density about 0.2 A cm-2, while others pointed out the instability specifically under accelerated stress conditions with higher current densities above 0.6 A cm-2, lower ( < 140 oC) or higher ( > 180 oC) operating temperatures, or dynamic protocols like start-up/shut-down cycles, etc.This limited durability of PA-PBI HT-PEMFC is known to be related to acid loss from the membrane-electrode-assemblies (MEAs). Several mechanisms were proposed to explain the linear and nonlinear acid loss behaviors. PA evaporation and steam-distillation are known to explain the constant PA loss. Despite the extensive efforts on mechanisms and acid loss mitigation strategies, current PA-PBI systems still struggle against the limited durability due to PA loss. To improve the durability of HT-PEMFC, a novel system was introduced based on the quaternary ammonium-biphosphate ion-pair coordinated PEM [1]. Due to a stronger interaction in the ion-pair PEMs, the durability was also improved by alleviating the PA loss during PEMFC operation. Nonetheless, the acid retention mechanism of this novel system is not explored yet.Here, we investigate the mechanisms of PA loss and PA retention within electrodes of both PA-PBI-based and ion-pair-based HT-PEMFC systems. Through PA energetics studies and experimental investigations under controlled stress conditions, we elucidate distinct PA loss/retention mechanisms in these systems, leading to different durability behaviors. Our findings offer insights for enhancing the durability of both HT-PEMFC systems [2].[1] Lim, K. H.; Lee, A. S.; Atanasov, V.; Kerres, J.; Park, E. J.; Adhikari, S.; Maurya, S.; Manriquez, L. D.; Jung, J.; Fujimoto, C.; Matanovic, I.; Jankovic, J.; Hu, Z.; Jia, H.; Kim, Y. S. Protonated phosphonic acid electrodes for high power heavy-duty vehicle fuel cells, Nature Energy, 7, 248 (2022).[2] Lim, K. H.; Matanovic, I.; Maurya, S.; Kim, Y.; Castro, E. S.; Jang, J-H.; Park, H.; Kim, Y. S. High temperature polymer electrolyte membrane fuel cells with high phosphoric acid retention, ACS Energy Letters, 8, 529 (2023).

Enhancing PA-PBI Composite Membrane with Metal Oxides Incorporation for HT-PEMFC Operating Above 200 oc

High-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are renowned for their excellent CO tolerance and rapid reaction kinetics [1]. Among the various membrane types, phosphoric acid doped polybenzimidazole (PA-PBI) membranes, phosphoric acd (PA) acts as a proton conductor, facilitating proton transfer through hydrogen bond rearrangement between PA molecules and the PBI backbone [2]. However, the operating temperature of PA-PBI membrane-based HT-PEMFC is constrained by the condensation of PA, limiting their use to below 180 oC and posing a significant challenge for achieving efficient operation above 200 oC.Recent research endeavors have focused on enhancing PA-PBI membranes by incorporating metal oxides to extend their operational temperature range beyond 180 oC. The addition of metal oxides into PA solution leads to the formation of metal hydrogen phosphate, effectively preventing PA evaporation at elevated temperatures ( > 180 oC) and maintaining membrane performance without degradation. Furthermore, the presence of metal oxides facilitates proton transfer to the metal hydrogen phosphate surface, thereby improving ionic conductivity even at temperatures exceeding 200 oC.In this study, we present the synthesis of poly(2,2’-(1,4-phenylene)-5,5’ bibenzimidaozle) (pPBI) composite membranes through an in-situ method, where various metal oxides (SnO2, TiO2, ZrO2) are introduced into the synthesis solution. Through systematic investigation, we evaluate the impact of these metal compounds on fuel cell performance and durability at high temperatures exceeding 200 oC. Our findings shed light on the potential of metal oxide-modified PA-PBI composite membranes for advancing the performance and reliability of HT-PEMFCs in demanding operating conditions.

Overcoming Challenges in Ion-Pair Membrane Technology: Advancements in Fuel Cells and Electrochemical Hydrogen Pumps

The Membrane Electrode Assembly (MEA) stands as the pivotal element in electrochemical devices such as fuel cells and electrochemical hydrogen pumps (EHP). Notably, ion-pair High-Temperature Proton Exchange Membrane Fuel Cells (HT-PEMFCs) with reduced phosphoric acid concentrations within the MEA have been innovatively designed, allowing for the integration of diverse ion-conducting binders, known as ionomers, into both the cathode and anode electrodes [1]. This study delineates initial distinctions in MEA configurations among different device types (HT-Fuel cell and EHP), conducting a comprehensive analysis of performance disparities between traditional polybenzimidazole-based systems and various ion-pair proton exchange membranes [2].Subsequently, a detailed exploration unfolds, focusing on the utilization of ion-pair membranes and different ionomer types for the three aforementioned devices. This comprehensive examination offers a unified comparative analysis encompassing ionomer type, membrane thickness, catalyst:ionomer ratio, and phosphoric acid doping levels, particularly in the context of performance at intermediate temperatures (160℃). Conclusions are drawn based on results derived from both half-cell and single-cell evaluations. Finally, overarching guidelines are presented to inform the formulation of high-performance MEA configurations tailored for ion-pair HT-PEMFCs and EHPs.

(Digital Presentation) Graphene as Barriers to Prevent Phosphoric Acid Leaching in High-Temperature PEMFCs

High-temperature PEMFCs running at 120-200℃ with the simplified water management has attracted more attention [1]. However, phosphoric acid molecules in polybenzimidazole membrane electrolyte (PA/PBI) are easily leaching to electrodes, which block pores of carbon fiber electrodes and impact gas transfer. Finally, the power density and durability of PEMFCs are extremely reduced [2].Graphene is a kind of two-dimensional (2D) structure of honeycomb lattice material and can block the penetration of almost all molecules and atoms, which is able to prevent PA molecules leaching as [3]. Our group has investigated a nitrogen-modified reduced graphene oxide (NrEGO) prepared by the electrochemical exfoliation, which has shown excellent performance in enhancing the activity and stability of catalysts [4]. Meanwhile, our previous research developed a single layer graphene loaded electrode. The power density of high-temperature PEMFCs is improved compared with commercial cells after accelerated stress test [5].Therefore, this work used NrEGO flakes as barriers to prevent phosphoric acid leaching to gas diffusion layer with lower Pt loading. In the present results, when the ratio of NrEGO and CB is 2 to 3 and the Pt loading is 0.25 mgPt/cm2, the cell improves 20% of the maximum power density and shows more stable with a decay of voltage by only 0.02 mV/h, which is quiet lower compared with that of 1.14 mV/h in commercial Pt/C.

Enhancement of Mass Transport in Catalyst Layers of HT-PEMFC with Tetrafluorophenyl Phosphonic Acid Binder.

The design and development of new and efficient catalyst binder materials are important for improving cell performance in high-temperature proton-exchange membrane fuel cells (HT-PEMFCs). In this study, a series of tetrafluorophenyl phosphonic acid-based binder materials (PF-y-P, y = 1, 0.83, and 0.67) with rigid structures and controllable degrees of phosphonation were prepared and used in HT-PEMFCs using the ultra-strong acid-catalyzed Friedel-Crafts reaction and the combined Michaelis-Arbuzov reaction. The samples exhibited high stability, low water uptake, superior proton conductivity, and cell performance. In addition, the oxygen mass transport properties of the PF-1-P binder were investigated using high-temperature microelectrode electrochemical testing techniques. Compared with the phosphoric acid-doped polybenzimidazole (PBI) binder, the O2 solubility of PF-1-P binder material increased by 30% (5.36 × 10-6 mol cm-3) and the PF-1-P binder material exhibited better cell stability in HT-PEMFCs. After 10.5 h of discharge at a constant current of 0.12 A cm-2, the MEA voltage decreased by 7.1% and 20.8% in case of the PF-1-P and PBI binders, respectively.

Ethylenediamine tetramethylenephosphonic acid boosting the electrocatalytic interface construct and proton transfer for high-temperature polymer electrolyte membrane fuel cells

High-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) show excellent application prospects due to its enhanced tolerance of hydrogen impurity. However, the sluggish electrode kinetics caused by its inefficient electrocatalytic interface and proton transfer severely restricts its performance. To overcome the sluggish electrode kinetics, the ethylenediamine tetramethylenephosphonic acid (EDTMPA) was successfully incorporated into the catalysts layer to regulate the phosphoric acid (PA) distribution to boost the electrocatalytic reaction interface and proton transfer, thus increasing the output power and stability of HT-PEMFCs. The hydrophilic H2PO4− and electron donor N atom of EDTMPA could efficiently decrease the absorption of PA on the catalyst surface and facilitate proton transportation in the membrane electrode, as demonstrated by our experiments. The fuel cell assembled with the prepared membrane electrode shows a high reactivity of 1175 mW cm−2 and excellent stability, which is much better than the past reference report. The results of this work provide new insights into the utilization of small molecules with phosphate groups to enhance phosphate tolerance and proton conduction, and there is also a further improvement in the reactivity, durability, and utilization of the electrocatalysts in HT-PEMFCs.

Improving the performance and long-term durability of high-temperature PEMFCs: A polyvinylpyrrolidone grafting modification strategy of polybenzimidazole membrane

This study introduces an innovative approach to graft Polyvinylpyrrolidone (PVP) onto Polybenzimidazole (PBI) to synthesise Proton Exchange Membranes (PEMs) with high performance and durability. As a widely used hydrophilic polymer in industry, PVP can add numerous nitrogen-containing functional groups to the membrane to enhance its phosphoric acid (PA) binding ability. In this work, Polybenzimidazole-graft-polyvinylpyrrolidone (PVP-g-PBI) polymers with varying grafting degrees were synthesized and tested to investigate the impact of the grafting modification on the membrane's proton conductivity, thermal properties, and electrochemical performance. With the introduction of PVP side chains, the fuel cell showed enhanced PA uptake and substantial improvements in peak power density. Notably, PBI-g-PVP membranes with a grafting degree of 22.4 % achieved a peak power density enhancement up to 1312 mW cm⁻2 at 160 °C, a 59.6 % increase over pristine PBI membranes. Due to the increased PA binding sites in the membrane, the PBI-g-PVP PEMs exhibit better PA adsorption ability and long-term durability than pristine membranes. The accelerated stress test (AST) demonstrated that the PBI-g-PVP membranes maintain a peak power density of 1105 mW cm⁻2 after a 70-h test, equivalent to 183.9 % of the pristine PBI membrane. The improved fuel cell performance and durability of PBI-g-PVP PEMs underscore the potential of this grafting strategy.

High-performance polybenzimidazole composite membranes doped with nitrogen-rich porous nanosheets for high-temperature fuel cells

Traditional phosphoric acid (PA) doped polybenzimidazole (PBI) membranes encounter many issues when used in high-temperature proton exchange membrane fuel cell (HT-PEMFC), including the loss of PA within the membrane and limitations on conductivity. The mixed matrix membranes (MMMs) synergistically combine the advantages of pore fillers and polymer matrix, making them promising candidates for HT-PEMs. Interface compatibility is the main factor affecting the further development of MMMs. This research presented OPBI composite membranes filled with porous nanosheets, featuring average pore diameters of 2.83 nm, 3.38 nm, and 2.60 nm, respectively. The high aspect ratio and plentiful nitrogen components of the nanosheets increase the π-π and hydrogen bonding interactions with the polymer matrix, resulting in outstanding interface compatibility and mechanical properties of MMMs. The results of theoretical calculations indicate that there is a stronger interaction energy between the nanosheets and PA molecules, and the abundant pore structure within the nanosheets facilitates the absorption of PA molecules, leading to the formation of a continuous PA network. Consequently, MMMs exhibited enhanced proton conductivity, as well as improved PA absorption and retention. Furthermore, the effect of pore size distribution of nanofillers on the performance of MMMs were investigated. Membranes composed of nanosheets with large pore size showed a higher conductivity of 176.7 mS cm−1 at 200 °C, leading to excellent performance and stability in assembled H2/O2 fuel cells. This work offers valuable insights into the design of MMMs and high-performance HT-PEMs.

Liquid Cooling of Fuel Cell Powered Aircraft: The Effect of Coolants on Thermal Management

Abstract Electric propulsors powered by Proton Exchange Membrane Fuel Cells (PEMFCs) offer a net zero solution to aircraft propulsion. Heat generated by the PEMFCs can be transferred to atmospheric air via a liquid cooling system; however, the cooling system results in parasitic power and adds mass to the propulsion system, thereby affecting system specific power. The design of the cooling system is sensitive to the choice of liquid coolant and so informed coolant selection is required if associated parasitic power and mass are to be minimized. Two approaches to selection of coolants for PEMFC-powered aircraft are presented in this paper for operating temperatures in the range 80-200°C (this covers low, intermediate, and high temperature PEMFCs). The first approach uses a Figure of Merit (FoM) alongside minimum and maximum operating temperature requirements. The FoM supports the selection of coolants that minimize pumping power and mass while maximizing heat transfer rate. The second approach uses a cooling system model to select ȜPareto efficientȝ coolants. A hybrid-electric aircraft using a PEMFC stack is used as a representative case study for the two approaches. Hydrocarbon-based coolants are shown to be favorable for the case study considered here (aromatics for PEMFCs operating at &amp;lt;130°C and aliphatics for PEMFCs operating at &amp;gt;130°C). As the PEMFC operating temperature increases, the parasitic power and mass of the TMS decreases. Operating at elevated temperatures is therefore beneficial for liquid cooled PEMFC-powered aircraft. Nevertheless, there are diminishing performance gains at higher operating temperatures.

Introduction of polymeric ionic liquids containing quaternary ammonium groups to construct high-temperature proton exchange membranes with high proton conductivity and stability

A series of membrane materials suitable for high-temperature proton exchange membranes (HT-PEM) were successfully prepared by introducing polymeric ionic liquids (PILs) containing quaternary ammonium groups into ether-bonded polybenzimidazole (OPBI). The structure of the cross-linked membrane has a strong interaction with phosphoric acid (PA), which enhances proton transport and PA retention. To ensure better overall performance of the cross-linked membrane, the optimal PIL content is 30 wt% (OPBI-PIL-30 %). The PA uptake of OPBI-PIL-30 % membrane was 323.24 %, and the proton conductivity at 180 ℃ was 113.94 mS cm−1, which was much higher than that of OPBI membrane. It is noteworthy that the PA retention of OPBI-PIL-30 % membrane could reach 71.38 % after 240 h of testing under the harsh environment of 80 ℃/40 % RH. The membrane showed better acid retention capacity of 86.89 % at 160 ℃ under anhydrous environment. The OPBI-PIL-20 % membrane achieved the maximum power density of 436.19 mW cm−2, attributed to its favorable mechanical characteristics and proton conductivity. By these excellent properties, it is shown that OPBI-PIL-X membranes containing quaternary ammonium groups have the potential to be applied in high temperature proton exchange membrane fuel cells (HT-PEMFCs).

Theoretical Studies on the Chemical Degradation and Proton Dissociation Property of PBI used in High-Temperature Polymer Electrolyte Membrane Fuel Cells.

High-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are gaining more and more attention due to their higher efficiency than low-temperature ones. Polybenzimidazole (PBI) membranes are the most popular membranes used in HT-PEMFCs. However, their chemical stability and chemical degradation mechanisms, which directly affect the lifetime of fuel cells, have been hardly reported. We applied the density functional theory and used ABPBI as an example membrane to investigate the chemical degradation mechanisms of PBI membranes. The possible degradation mechanisms that occurred on eight sites have been proposed, where sites 2 and 3 located on the phenyl ring are determined as two weak sites toward OH radical and oxygen molecule attack. When the terminal is the H atom at site 7, it is also weak under OH radical attack. Regarding these, the substituent effect on the chemical stability of polymers has been studied. By introducing four -C2F5 or -CN groups, the barrier heights of the corresponding degradation reactions are increased; thus, the chemical stabilities of related membranes are improved. The selection of terminal atoms was also explored for alleviating the chemical degradation of the membrane. The investigated proton transfer properties of nine model compounds revealed that introducing four -C2F5 or -CN groups improves the proton dissociation properties occurring at the cathode. The increase of phosphoric acid concentration is helpful for the proton transfer at both the membrane and the cathode. This work may hopefully help the design and synthesis of HT-PEMFCs with good stability and high efficiency.

Polybenzimidazole nanocomposite membranes containing imidazole-functionalized UiO-66 nanocrystals with optimal interfacial compatibility for high-temperature proton exchange membrane fuel cells

Metal–organic framework (MOF) nanofillers have attracted significant attention recently for high-temperature proton exchange membrane fuel cell (HT-PEMFC) applications because of their excellent effectiveness for enhancing the performance of proton exchange membranes (PEMs) based on phosphoric acid–doped polybenzimidazole (PBI). Universitetet i Oslo-66 (UiO-66) is one of the most used zirconium-based MOFs. In this study, we synthesized amine-functionalized UiO-66, imidazole-functionalized UiO-66, and sulfonated UiO-66 as nanofillers for adjusting the interfacial compatibility of PBI-based nanocomposite membranes. The results demonstrated that incorporating functionalized UiO-66 nanocrystals simultaneously improved tensile strength, oxidative stability, and proton conductivity of the membranes. Moreover, the imidazole-functionalized UiO-66 nanofiller exhibited optimal interfacial compatibility with polybenzimidazole and more significantly improved membrane properties than the other nanofillers. The PEM containing 10 wt% imidazole-functionalized UiO-66 achieved a 113% increase in proton conductivity at 170°C (0.0418 S/cm) and a 249% increase in the maximum power density of the fuel cell (406.1 mW/cm2).

Constructing immobilized H3PO4 network in nanosized ZSM-5 zeolitic framework achieves high proton conductivity after acceleration acid leaching test

In the midst of demand for the high and stable anhydrous proton conducting membrane for the high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), phosphoric acid (PA)-doped polybenzimidazole (PBI) is positioned as one of the most promising candidates. The key to develop the PA-PBI is to address the issue of phosphoric acid leaching, which causes significant performance deterioration. Here we introduced the nanosized ZSM-5 zeolite which plays the role of the rigid cage for confining H3PO4 to the PBI, and then evaluated by utilizing the acceleration acid leaching test (ALT) to put long-term operation in perspective. The ZSM-5 not only retain the high degree of PA after ALT, but also constructs the efficient proton conducting channel derived by the chemically-immobilized H3PO4 in pore channel. After ALT, PBI electrolyte membrane with 5 wt% of ZSM-5 exhibited 2.8 × 10−5 S cm−1 of proton conductivity at 150 °C anhydrous condition, which is three orders higher magnitude than pure PBI (1.1 × 10−8 S cm−1). Furthermore, H2/O2 HT-PEMFC single-cell constructed with PBI/5%ZSM-5 displayed an excellent maximum power density of 387 mW cm−2 at 150 °C anhydrous conditions, even after the ALT. The results indicate the possible improvement of the long-term stability of the fuel cell by utilizing readily available ZSM-5.

An Air Over-Stoichiometry Dependent Voltage Model for HT-PEMFC MEAs

In this work, three commercially available Membrane Electrode Assemblies (MEAs) from Advent Technology Inc. and Danish Power Systems, developed for a use in High Temperature Proton Exchange Membrane Fuel Cell (HT-PEMFC), were tested under various Operating Conditions (OCs): over-stoichiometry of hydrogen gas (1.05, 1.2, 1.35), over-stoichiometry of air gas (1.5, 2, 2.5), gas oxidant (O2 or air) and temperature (140 °C, 160 °C, 180 °C). For each set of operating conditions, a polarization curve (V–I curve) was performed. A semi-empirical and macroscopic (0D) model of the fuel cell voltage was established in steady state conditions in order to model some of these experimental data. The proposed parameterization approach for this model (called here the “multi-VI” approach) is based on the sensitivity to the operating conditions specific to each involved physicochemical phenomenon. According to this method, only one set of parameters is used in order to model all the experimental curves (optimization is performed simultaneously on all curves). A model depending on air over-stoichiometry was developed. The main objective is to validate a simple (0D) and fast-running model that considers the impact of air over-stoichiometry on cell voltage regarding all commercially available MEAs. The obtained results are satisfying with AdventPBI MEA and Danish Power Systems MEA: an average error less than 1.5% and a maximum error around 15% between modelled and measured voltages with only nine parameters to identify. However, the model was not as adapted to Advent TPS® MEA: average error and maximum error around 4% and 21%, respectively. Most of the obtained parameters appear consistent regardless of the OCs. The predictability of the model was also validated in the explored domain during the sensibility study with an interesting accuracy for 27 OCs after being trained on only nine curves. This is attractive for industrial application, since it reduces the number of experiments, hence the cost of model development, and is potentially applicable to all commercial HT-PEMFC MEAs.

Investigation of phosphoric acid influence on the oxygen reduction reaction on carbon-supported platinum electrocatalyst via rotating disk electrodes

Phosphoric acid (PA), utilized as an electrolyte in high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), has been observed to exert a detrimental effect on oxygen reduction reaction (ORR) electrocatalyst, consequently compromising cell performance. To comprehensively elucidate the impact of phosphoric acid on ORR, this study employs a range of electrochemical techniques, including electrochemical impedance spectroscopy and voltammetry method. The negative influence of PA on commercial Pt/C electrocatalyst manifests differently under various potentials and PA concentrations. Upon the introduction of PA, the decay rate and amplitude of ECSA, as calculated by Hupd adatoms, are notably smaller compared to the kinetic current density generated by the oxygen reduction reaction. Particularly, in the kinetic-controlled potential range, the negative impact of PA becomes more pronounced at higher electrode potentials, accompanied by a significantly steeper Tafel slope. Additionally, the EIS results suggest that phosphoric acid may gradually transform into polyphosphoric acid at a high concentration, accentuating the poisoning effect of PA under steady-state conditions. However, a high PA concentration can substantially alter the electrolyte properties, potentially leading to an inaccurate assessment of PA tolerance in electrocatalysts. Hence, it is imperative to consider the appropriate PA concentration when evaluating PA tolerance and to discern the poisoning mechanism under different electrode potentials.

Analyzing and modeling of CO purging for high-temperature proton exchange membrane fuel cells

Purging offers a straightforward and cost-effective means of eliminating inert gases that accumulate in high-temperature proton exchange membrane fuel cells (HT-PEMFC) operating in dead-end anode (DEA) mode. Nevertheless, earlier studies primarily concentrated on inert gases, overlooking the significant challenge posed by the strong adsorption of CO within HT-PEMFC, complicating the use of inert gas methods for CO purification. This paper presents an analytical model that was validated experimentally. Leveraging this model, the paper analyzes the crucial parameter of CO concentration within the anode and deduces theoretical extreme values. Subsequently, it proposes purging strategies tailored to different operational conditions. The findings indicate that the minimum CO concentration within HT-PEMFC is influenced by current, feed gas flow rate, and feed gas CO concentration. Additionally, the maximum CO concentration is affected by the off-duration of the purge valve in addition to these factors. Specifically, under the operating condition of 473.15 K, adopting a CO concentration threshold purge strategy is recommended, whereas under the operating condition of 448.15 K, voltage drop and CO concentration threshold purge strategies should be respectively implemented above and below the cutoff line based on the current. This research contributes to mitigating the issue of CO accumulation in DEA mode.

Unique Self-Phosphorylating Polybenzimidazole of the 6F Family for HT-PEM Fuel Cell Application.

High-temperature polymer-electrolyte membrane fuel cells (HT-PEMFCs) are a very important type of fuel cells since they operate at 150-200 °C, making it possible to use hydrogen contaminated with CO. However, the need to improve the stability and other properties of gas-diffusion electrodes still impedes their distribution. Self-supporting anodes based on carbon nanofibers (CNF) are prepared using the electrospinning method from a polyacrylonitrile solution containing zirconium salt, followed by pyrolysis. After the deposition of Pt nanoparticles on the CNF surface, the composite anodes are obtained. A new self-phosphorylating polybenzimidazole of the 6F family is applied to the Pt/CNF surface to improve the triple-phase boundary, gas transport, and proton conductivity of the anode. This polymer coating ensures a continuous interface between the anode and proton-conducting membrane. The polymer is investigated using CO2 adsorption, TGA, DTA, FTIR, GPC, and gas permeability measurements. The anodes are studied using SEM, HAADF STEM, and CV. The operation of the membrane-electrode assembly in the H2/air HT-PEMFC shows that the application of the new PBI of the 6F family with good gas permeability as a coating for the CNF anodes results in an enhancement of HT-PEMFC performance, reaching 500 mW/cm2 at 1.3 A/cm2 (at 180 °C), compared with the previously studied PBI-O-PhT-P polymer.

Performance enhancements of power density and exergy efficiency for high-temperature proton exchange membrane fuel cell based on RSM-NSGA III

In this study, a three-dimensional simulation model was developed and a multi-objective optimization of a single-channel high-temperature proton exchange membrane fuel cell (PEMFC) was carried out by the response surface methodology (RSM) and the non-dominated genetic algorithm III (NSGA III). Firstly, five main influencing factors including operating temperature (T), operating pressure (p), gas diffusion layer porosity (εGDL), proton exchange membrane (PEM) thickness (Mmem) and anode stoichiometry ratio (λa) were identified. The optimization objectives include three cell performance evaluation indexes: power density (wpow), system efficiency (ηsystem), and exergy efficiency (ηexergy). Secondly, the prediction accuracies of the RSM and artificial neural network (ANN) for the three performance evaluation indexes of high-temperature PEMFC were compared. Finally, the optimal solution from the Pareto solutions derived through RSM-NSGA III. The results show that the maximum wpow, maximum ηsystem and maximum ηexergy are 0.793 W cm−2, 22.31 % and 54.69 %, respectively. The optimal result obtained by combining EWM and VIKOR is wpow = 0.6726 W cm−2, ηsystem = 19.44 % and ηexergy = 54.01 %, respectively. The corresponding condition is T = 447.18 K, p = 1.15 atm, εGDL = 0.617, Mmem = 0.0412 mm, and λa = 1.26, respectively. Moreover, the suggestions are provided for the design of more efficient high-temperature PEMFC.

A pore scale model study of mass transfer and electrochemical reaction in cathode catalytic layer of high-temperature polymer electrolyte membrane fuel cells

The mass transfer and related electrochemical reactions in the catalytic layer (CL) are crucial for the performance of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), but there is a lack of understanding of the optimal phosphoric acid content and Pt/C catalyst loading in the CL. In this work, we investigate the influences of Pt/C catalyst numbers (NPt/C) and phosphoric acid film thickness (δPA) on mass transfer and electrochemical reactions of the cathode CL using a pore-scale model (300 × 300 × 300 nm3). The results reveal that larger NPt/C and δPA can impede oxygen diffusion, while lower NPt/C and δPA lead to fewer reaction active sites and lower conductivity, both of which result in lower current density. Therefore, the balance of three-phase transport is extremely important for CL. There is a 3D volcanic relationship between current density, Pt/C catalysts, and phosphoric acid film. At NPt/C = 200 (7407 per μm3) and δPA = 4 nm (the volume fractions of 37.22 % and 17.87 %), the highest current density can be achieved at a potential of 0.5 V (vs. RHE), which increased with the decrease of potential. This work is valuable for understanding the optimizing the microstructure and three-phase transport pathway of the CL to improve the performance of HT-PEMFCs.