Low Temperature Proton Exchange Membrane Research Articles

Two-phase flow characteristics on porous layer in PEM electrolyzer under different flow channel layouts

As a promising green energy technology, low-temperature proton exchange membrane (PEM) electrolysis exhibits different reaction efficiencies and flow performances under various flow channel structures, but the specific impacts of these different layouts on performance are not well understood. To reveal the influence of the channel layouts, a two-phase PEM electrolysis model is established based on the experiment in this paper. Combing with flow characteristics, current density, and product distribution in the porous transport layers (PTLs) and catalyst layers (CLs), the results indicate that the flows from different directions have a significant impact on the electrolyzer. The vertical flow, perpendicular to the CLs, can greatly alleviate the product accumulation; meanwhile the transverse flow, parallel to the CLs, has a weaker but noticeable effect in gas ventilation. Partial gas will continue to accumulate in the region of weak vertical flow, especially at the end of the transverse flow. Except for the pin-type layout, other structures have a neat and orderly transverse flow within the porous medium, in the direction perpendicular to the flow channel's orientation. This flow pattern leads to product accumulation increasing along the exit direction, as well as product stagnation in the region of weak flow intensity. To facilitate the product discharge, a new flow channel layout, the pyramidal flow layout is proposed, which navigates the flow trend and enhances the convection near the exit. This new layout greatly evens out the current density and product concentration distribution.

Experimental and numerical investigations on synergistic coupling of metal hydride hydrogen storage systems with low-temperature proton exchange membrane fuel-cell

Hydrogen has emerged as a promising alternative for various energy needs, and metal hydride hydrogen systems offer significant potential due to their near-ambient working conditions and safe storage. This study presents experimental and numerical investigations on a lab-scale metal hydride fuel cell system to showcase its viability in addressing future energy demands. The experimental setup includes a 41-tube Metal Hydride (MH) reactor with an outer cooling jacket, containing 3.75 kg of La0.7Ce0.1Ca0.3Ni5. The output of the reactor is coupled to a 1 kW fuel cell, with controlled hydrogen discharge at temperatures ranging from 30 to 50 °C through numerical modelling. The study found that maintaining the reactor at 40 °C was sufficient to sustain the required bed pressure for a 1 kW fuel cell. Numerical simulations revealed that a 1 kW fuel cell operating at a current density of 0.8 A/cm2 and 50 °C rejected approximately 1.3 kW of waste heat. Moreover, 3.75 kg MH reactor could discharge hydrogen at a constant rate of 13 l/min for 36.3 min with just 125–225 W of heat input, highlighting the thermal coupling potential between these systems. The energy efficiency of the coupled MH-PEMFC system increased by 1.8 times to reach 49% at 50 °C. Additionally, the waste heat generated proved sufficient to provide the required endothermic heat to multiple MH reactors, with a single reactor utilizing only 16.3% of the total waste heat. This integrated system demonstrates promising efficiency and sustainability for future energy applications.

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.

Impact of flow configuration and temperature on water flooding and membrane water content of low-temperature proton exchange membrane fuel cell

Low-temperature proton exchange membrane fuel cells (LT-PEMFCs) have emerged as promising candidates in transportation due to zero-emission, high power density and efficiency. Issues such as liquid water flooding and membrane drying significantly reduce their performance and durability during higher current density operations. Although many simplified 1-D and 2-D models have been proposed, they do not aid in understanding water dynamics and membrane water content for different flow configurations and operating temperatures. This work focuses on the development of a 3-D, multiphase, non-isothermal, physics-based model of the LT-PEMFC to address the above-mentioned issues. The model is validated with experiments performed on a 32 cm2 LT-PEMFC at 40 °C with a hybrid flow configuration. The results suggest that the hybrid configuration provides a power density enhancement of 12 % compared to the parallel configuration at 70 °C. Due to this performance improvement, ΔT of the hybrid configuration has reached 7 °C, which is slightly higher than the parallel configuration's ΔT of 5.7 °C. With an increase in operating temperature from 40 °C to 70 °C, the hybrid configuration experiences a 50% enhancement in the power density. For both temperatures, the hybrid configuration shows a consistent increment in the saturation from inlet to outlet, which creates a favorable pathway for water removal from the cell. The findings from this work suggest that the hybrid configuration is superior to the parallel configuration in terms of power density output, water removal capacity and membrane water content. This work provides valuable insight into overcoming key issues of liquid water flooding and membrane durability.

Optimizing adhesive rheology for stencil printing of fuel cell sealings using supervised machine learning

In a single low-temperature proton exchange membrane fuel cell (LT-PEMFC) stack, the sealings are responsible for preventing leakages, providing electrical insulation and compensating assembly tolerances. This study investigates stencil printing to produce fuel cell sealings and aims to identify reliable conditions to print layer thicknesses of at least 500 μm, typically used for this application and substantially exceeding the current state-of-the-art. First, rheological and print experiments were conducted with 25 distinct adhesives, including ultraviolet (UV) curable acrylics and epoxies, to determine their printability. An adhesive was considered printable when it detached from the stencil without forming bubbles, a print defect that significantly diminishes the process stability. This had to be accomplished at two different squeegee speeds (40 and 160 mm/s), confirming the robustness of the adhesive for the print process. In addition, the impact of the aperture orientation, aperture aspect ratio (AR) and separation speed of the substrate from the stencil were evaluated. Here, it was detected that a multivariable criterion was necessary to reliably predict printability. Thus, classification models based on binary logistic regression, a simple supervised machine learning technique, were proposed using the thixotropy index TI (indicator for viscosity recovery ability), steady-state viscosity at 100 s−1, adhesive surface tension and aperture AR as predictors. The derived models achieved a prediction accuracy ≥88.2%, demonstrating adequate generalisation. Moreover, it was identified that increasing TI is the most effective approach to achieve printability. Finally, the driving physical mechanisms influencing the obtained print results were assessed, and it was shown that a TI value of about 50 Pa s/s is required to reach the minimum layer thickness.

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

Two-phase flow dynamics study in the trapezoidal gas channel of PEM fuel cell based on lattice Boltzmann model

ABSTRACT Water management is a critical challenge in ensuring the performance and durability of low-temperature proton exchange membrane fuel cells (PEMFCs). This study utilizes the phase-field lattice Boltzmann method to conduct three-dimensional numerical simulations, investigating the dynamics of two-phase flow in the cathode gas channel (GC) of PEMFC with a trapezoidal cross-section. The effects of the water inlet location, the surface wettability of GC, the open angle of GC, and the air velocity on liquid water distribution and discharge are analyzed. The results indicate that positioning the water inlet in the middle of the GC significantly enhances PEMFC performance while having minimal impact on average pressure drop. A wall contact angle of 70° or 110°Can optimize fuel cell performance from different directions. Setting a wall contact angle at 70° optimizes gas flow stability and maintains a low-pressure drop value for the GC. A wall contact angle of 110° focuses on optimizing gas reactant diffusion ability into porous electrodes and GC drainage rate. An opening angle of 55° for the trapezoidal gas channel improves overall fuel cell performance. Increasing air velocity facilitates the film flow formation of liquid water on top wall surfaces within the GC.

LT-PEM Fuel Cells diagnosis based on EIS, clustering, and automatic parameter selection

In the field of fuel cells, early detection of faulty conditions can significantly improve the lifetime. Then, signal analysis techniques such as electrochemical impedance spectroscopy combined with machine learning algorithms can generate a representation of the system state of health space using data in known conditions. Although the onboard measurement of EIS can be done by controlling the harmonic content of the power converter at the output of the fuel cell, the implementation of in-vehicle diagnostic algorithms is still limited by the absence of a large database listing the evolution of performance throughout the life cycle. This paper presents a fast-diagnostic method able to consider the occurrence of new data to adapt the dimensional space representing the health state and compensate for the lack of data. Available measurements come from two low-temperature proton exchange membrane fuel cell technologies characterized by two laboratories. The results presented in the paper show that the automatic parameter selection provides performances as good as the ones obtained by an expert. The feasibility of the approach has also been demonstrated on a low-cost embedded platform.

Nickel Oxide-Aerogel Electrocatalysts for Oxygen Evolution Reaction in Alkaline Media: Experimental Approaches and Modeling-Assisted Strategies for Improving Performance and Durability

Anion exchange membrane water electrolyzers (AEMWEs) represent an attractive technology for producing “green” hydrogen that enables operation on pure water using platinum group metal (PGM)-free electrocatalysts at both anode and cathode. Also, AEMWEs do not require the use of highly concentrated and corrosive alkaline electrolytes and PGM-based catalysts, which are the major drawbacks of the incumbent low-temperature liquid-alkaline and proton exchange membrane electrolyzers, respectively.1,2 In this context, the development of PGM-free electrocatalysts for oxygen evolution reaction (OER) in alkaline media has attracted considerable research interest. Among different types of transition metal-based oxides, Ni oxides doped with Fe have shown the highest OER activity in alkaline media.3,4 Recently, we have developed at Los Alamos National Laboratory (LANL) a series of Ni oxide-based aerogel materials that, primarily in combination with Fe in different proportions, have shown respectable OER performance in the electrochemical cell and at the AEMWE anode operating on either neat deionized water or with a supporting electrolyte, 0.1 M KOH or K2CO3.5 For application at the AEMWE anode, the catalyst integration into the electrode catalyst layer, i.e., combining the catalyst with anion exchange ionomer (AEI) and binding agents, is crucial to prevent catalyst layer delamination and to create a good catalyst/electrolyte interface, which in turn enables high OH- conductivity within the catalyst layer.6 This latter aspect is especially important for achieving high AEMWE performance in pure water operation. In this work, we investigate the impact of combining our Ni-Fe oxide aerogel catalysts with different AEIs (various backbone chemistries, OH- functional groups) and different binding agents (e.g., Nafion ionomer) on the AEMWE performance. We will show that full activation of the catalyst by phase transformation from the original Ni oxide-like structure to the active layered (oxy)hydroxide is essential for achieving high OER activity, and it can be influenced by the catalyst layer composition. By advanced characterization techniques such as high-resolution scanning transmission electron microscopy, X-ray absorption spectroscopy, and Mössbauer spectroscopy, we will shed light onto the phase transformation process that results in superior OER activity of these materials in alkaline media.Following our prior machine learning studies aimed at optimizing for the synthesis of oxygen reduction electrocatalysts,7,8 we will also show how to improve the synthesis of Ni oxide aerogel-based OER catalysts to maximize activity and stability. This work is further supported by density functional theory (DFT) modeling studies to better understand reaction mechanisms, active sites, and ultimately what role transition metal dopants (Fe and Co) play in modifying OER activity. Studies of in situ dissolution of these dopants using DFT-generated, phase-constrained Pourbaix diagrams9 will guide synthesis through understanding this likely materials degradation pathway. References H. A. Miller et al., Sustain. Energy Fuels, 4, 2114–2133 (2020).C. Santoro et al., ChemSusChem, 202200027 (2022).S. Fu et al., Nano Energy, 44, 319–326 (2018)D. Xu et al., ACS Catal., 9, 7–15 (2019).P. Zelenay and D. Myers, "ElectroCat (Electrocatalysis Consortium);” U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Program, 2022 Annual Merit Review and Peer Evaluation Meeting, June 6-8, 2022. https://www.hydrogen.energy.gov/pdfs/review22/fc160_myers_zelenay_2022_o.pdfL. Osmieri et al., J. Power Sources, 556, 232484 (2023).M. R. Karim et al., ACS Appl. Energy Mater., 3, 9083–9088 (2020).W. J. M. Kort-Kamp et al., J. Power Sources, 559 (2023).E. F. Holby, G. Wang, and P. Zelenay, ACS Catal., 10, 14527–14539 (2020).

Transient Characteristics of the Low-Temperature PEMFC: A Comparative Analysis Using a Physics-Based Model

Low-temperature proton exchange membrane fuel cells (LT-PEMFCs) have experienced a considerable technological leap in the last few decades for transportation and stationary applications. Specifically, the precious metal loading in the catalyst layers (CLs) is notably decreased while enhancing the overall cell performance.1 However, the durability and cost remain major factors that affect the widespread commercialization of the LT-PEMFC. Though this can be achieved with further material development, some existing issues may be resolved by implementing effective design and control strategies. A good understanding of fuel cell water dynamics is required to improve durability and performance. Although some dynamic characteristics can be observed from the experiments, a physics-based model of the LT-PEMFC is necessary to study in-depth transient responses under various conditions like current profiles, operating temperatures, pressure, and humidification levels. Lately, the transient analysis of the fuel cell has gained more attention to elucidate the complex transport phenomena.2 Several transient models of the LT-PEMFC are reported to capture the two-phase behavior inside the cell. Usually, these models are 1D, 2D, or single channel 3D with assumptions like isothermal operation, vapor-equilibrated membrane, simplified reaction kinetics, and more.3–5 Hence, they do not provide spatio-temporal insights into the cell performance containing water dynamics with various flow configurations.The current study focuses on a transient physics-based model of the LT-PEMFC for dynamic analysis across its thickness and flow channels. The membrane used in LT-PEMFC requires humidification to enhance the ionic conductivity and function properly.6 This study considers Schroeder’s paradox for the membrane, which exhibits a different water uptake behavior in the presence of saturated water vapor and liquid water.7 The water uptake property is strongly dependent on the temperature. Therefore, we have developed a single polynomial expression for the membrane water uptake, including temperature and water activity dependency. Using the governing equations & empirical correlations from the numerical and experimental studies, we develop a comprehensive 3D, multiphase, non-isothermal, transient physics-based model of the LT-PEMFC that can closely approximate the liquid water transport under various operating conditions. It is a Multiphysics model that couples electrochemical reactions, porous media flow, transport of reactant species, liquid water transport, heat generation, charge transfer, and ionomer water transport. COMSOL Multiphysics is used to solve the model. It provides a spatio-temporal water distribution inside the membrane, CL, microporous layer, gas diffusion layer, and flow channels. Experiments are performed on 32 cm2 LT-PEMFC with the hybrid flow configuration at 75 °C and 80% RH to validate the physics-based model in the steady state condition. The validation study suggests that the present multiphase model estimates the LT-PEMFC performance with an acceptable RMS current density error of 15 mA/cm2. The simulations are operated in the Galvano-dynamic mode, and the corresponding LT-PEMFC response for the hybrid configuration is shown in Figure 1(a) at various operating pressures. Also, the preliminary results of the liquid water saturation under the channel and rib are incorporated in Figure 1(b). It shows that the water accumulation under the rib is more than the channel due to lower local temperature and weaker convection under the rib, promoting water vapor condensation. Further, the comparison between hybrid and parallel configurations is performed and illustrated in this presentation. Another objective is to study how quickly the liquid water saturation and membrane water content react upon changing the load cycle, RH, operating temperature, and flow configuration. This work is an important step toward understanding the impact of various flow configurations and operating conditions on the water dynamics and membrane water content inside the LT-PEMFC. The developed physics-based model would be extended further by considering the membrane deformation due to the shrinking-swelling under the humidification and thermal cycling, which is critical for the performance and degradation.

(Invited) Electron Microscopy Investigation of Electrolyzer Degradation

Low-temperature proton exchange membrane water electrolyzers (PEMWEs) are a key technology for green hydrogen production from renewable energy sources. Developing efficient and durable components for the membrane electrode assembly (MEA) at the heart of the electrolyzer is critical for meeting DOE’s Hydrogen Shot target of $1 per kg of hydrogen by 2031. Of key interest to the efficiency and longevity of the electrolyzer is the anode-side of the MEA, where the costly iridium (Ir) catalyst is prone to dissolution at the high potentials and acidic conditions experienced in the cell. Further, the interfacial contact resistance between the catalyst and porous transport layer (PTL) plays a key role in electrolyzer performance and can degrade over time. Understanding and mitigating these degradation modes is critical for reducing the cost the PEMWEs and enabling commercialization.Here we will present the results of electron microscopy characterization performed on degraded anode catalyst layers and coated PTLs. Cross sections of MEAs submitted to different cycling protocols (square wave, triangle wave, steady-state, etc.) were prepared by diamond-knife ultramicrotomy and studied with in the scanning transmission electron microscope (STEM). Using energy dispersive X-ray spectroscopy (EDS), the dissolution and migration of Ir into the membrane was tracked and correlated with performance losses. The impact of PTL contact area on inhomogeneous degradation in anodes with low catalyst loadings will also be presented. In addition, PTL coating thickness and uniformity will be correlated with interfacial contact resistance measurements using a combination of focused ion beam (FIB), scanning electron microscopy (SEM) and STEM-EDS.Funding for this work was provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office through the H2NEW Consortium. Electron microscopy research conducted as part of a user project at the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory.

Analysis and evaluation of fuel cell technologies for sustainable ship power: Energy efficiency and environmental impact

Amid growing emphasis on achieving carbon neutrality, this study conducts a thorough assessment of different fuel cell technologies for their suitability as primary ship power sources. The primary goal is to evaluate the energy efficiency and carbon footprint impacts associated with adopting fuel cells for ship propulsion. The analysis employs simulation modeling and comparative evaluation to establish key indices: energy efficiency design index (EEDI), energy efficiency operational index (EEOI), and carbon footprint design index (CFDI). These indices consider factors like system weight, maintenance cycle, and fuel economy, ensuring a comprehensive comparison under consistent ship design parameters. Results reveal that liquefied natural gas fuel cells, direct methanol fuel cells, and low-temperature proton exchange membrane fuel cells (LT-PEMFC) outperform other fuel cell systems in terms of energy efficiency and carbon emissions reduction. Their respective EEDI values stand at 11.62, 12.72, and 10.05 g CO2/ton·km, accompanied by corresponding EEOI values of 0.10, 0.13, and 0.11 g CO2/ton·km. Additionally, CFDI values are calculated as 39.10 %, 19.45 %, and 11.64 %, respectively. Notably, the comprehensive assessment underscores LT-PEMFC as the most viable option for ship propulsion, offering improved energy utilization, reduced carbon impact, and decreased operational expenses. These findings contribute valuable insights into the appropriateness of diverse fuel cell technologies for ship power applications, considering both their energy efficiency and environmental implications.

Critical performance comparisons between the high temperature and the low temperature proton exchange membrane fuel cells

Currently, there are only some general concepts about the performance difference between an LT-PEMFC (low temperature proton exchange membrane fuel cell) and an HT-PEMFC (high temperature proton exchange membrane fuel cell), i.e., no literature has been found to conduct direct comparisons between them. In this research, for the first time, according to the same level (low level, medium level or high level) under the same operating condition type (operating temperature or cathode air utilization rate), the tested I-V performance, EIS (electrochemical impedance spectroscopy), LSV (linear sweep voltammetry), and calculated ECSA (electrochemical surface area) are compared between LT-PEMFC and HT-PEMFC. Some mechanisms are further disclosed, for instance, the higher Pt loading in the catalyst layer of an HT-PEMFC and its elevated operating temperature do not result in improved performance, compared to that of the LT-PEMFC. This is attributed to the lower apparent exchange current density in the case of HT-PEMFC.

Boosting the power density of the H3PO4/polybenzimidazole high-temperature proton exchange membrane fuel cell to >1.2 W cm−2 via the deposition of acid-based polymer layers on the catalyst layers

The high-temperature proton exchange membrane fuel cells (HT-PEMFCs) based on H3PO4/polybenzimidazole (PBI) membrane have drawn much attention in recent years. However, the power density of the H3PO4/PBI based membrane electrode assembly (MEA) is still much lower than that of the common perfluorosulfonate membranes based low-temperature proton exchange membrane fuel cells (LT-PEMFCs). Regulation and control of redistribution of H3PO4 in the MEA is a most important issue for the power density improvement of H3PO4/PBI based MEA. Herein, a MEA with new structure is proposed, in which a layer of PBI without H3PO4 doping (referred to as the acid-based polymer layers or APL) is deposited on the catalyst layers. With the application of APL, the peak power density of the H3PO4/PBI based MEA is 902 mW cm−2 in H2/air, and 1.289 W cm−2 in H2/O2 at 180 °C, which is the highest performance for H3PO4/PBI based HT-PEMFC reported in the literature. The results shows that the APL could effectively promote the reasonable redistribution of H3PO4 along the cross section in the MEA, construct more three phase boundaries (TPBs), enhance the electrochemical active surface area (ECSA), thus boosting the performance of H3PO4/PBI based HT-PEMFC.

Effect of Ni loading onto Pt (Pt‐Ni/C) electrocatalysts for PEM fuel cell: A study of ORR activity, stability, and temperature effect

AbstractPt is a noble metal when alloyed with transition metals like Ni onto the carbon support, minimizes the cost and increases the oxygen reduction reaction (ORR) activity and stability of Pt‐Ni/C electrocatalyst in a low‐temperature proton exchange membrane (LTPEM) fuel cell. A simple sonochemical‐based synthesis of Pt‐Ni/C bimetallic nanoparticles is carried out through varying amounts of Ni and Pt precursors. The various combinations of Pt and Ni metal (50:50, 75:25, and 83:17) nanoparticles were uniformly distributed on a carbon support. The shifting of 2θ values to higher levels in XRD patterns confirmed the alloy formation between Pt and Ni. The carbon (60 wt. %) supported Pt and Ni (40 wt. %) electrocatalyst ink is coated on a carbon paper which acts as a gas diffusion layer (GDL). The electrocatalytic performance of Pt‐Ni/C was evaluated in the PEM fuel cell using an electrochemical test station. The best performance was observed with the Pt: Ni (83:17) coated electrocatalyst, which delivered 0.162 W/cm2 power at 0.45 V. Also, the PEM fuel cell performance was enhanced by increasing the single cell's operating temperature.

Recovery, Regeneration, and Reapplication of PFSA Polymer from End-of-Life PEMFC MEAs.

We have developed a recovery, regeneration, and reapplication process for Nafion, a perfluorinated sulfonic acid (PFSA) ionomer, from end-of-life (EoL) low-temperature proton-exchange membrane (PEM) fuel cells (FCs). Samples of PFSA PEM recovered from EoL membrane-electrode assemblies (MEAs) with a history of close to 19,000 h of operation were recycled by dissolving the polymeric material in ethanol and applying the dissolved PFSA ionomer for producing the ionomer phase of the catalyst layer of new PEMFC cathodes. Structural characterizations show a marginally lower abundance of sulfonic groups for the EoL PEM compared to a fresh sample. Sulfonation of the former was employed to regenerate sulfonic groups to compensate for the lost ones. New gas-diffusion electrodes (GDEs) were prepared with the recycled PFSA ionomer both with and without sulfonation, and MEAs with these GDEs as cathodes were assembled through a state-of-the-art procedure. Electrochemical characterizations of the GDEs and single-cell studies of the MEAs showed that the electrochemical performances of catalyst layers containing recycled PFSA ionomer were at least similar to those containing fresh. Durability studies of the GDEs and MEAs, performed through a three-electrode liquid cell and a single cell, respectively, show the highest durability for the GDE/MEA with PFSA ionomer recycled without applying the sulfonation step. However, the GDE with PFSA ionomer obtained from recycling a re-sulfonated PEM shows a durability comparable to that of the GDE with fresh PFSA ionomer. Hence, PFSA material aged during PEMFC operation may be employed to produce highly functional and durable regenerated PFSA ionomer for PEMFC catalyst layers. The studied process of PFSA ionomer recycling is highly attractive for industrial adoption.

On the Acid Stability of PGM-Free OER Catalyst for H2 Production in PEMWE

Low temperature proton exchange membrane water electrolyzer (PEMWE) represents a critical technology for green hydrogen production. It offers the advantages of significantly higher current density and higher H2 purity, rendering it a preferred technology when high energy efficiency and low footprint are essential.Working in the oxidative and acidic environment under high polarization voltage, however, adds substantial demand to the electrode catalyst and the support. This is particularly the case at anode where the oxygen evolution reaction (OER) takes place. At present, the platinum group metal (PGM) materials such as Ir black or Ir oxide are catalysts of choice. Their high cost and limited reserve, however, adds a significant cost to PEM electrolyzer, which contributes to the overall expense of hydrogen production next only to the cost of electricity. Replacing Ir with earth-abundant transition metal oxides could help to reduce the electrolyzer system cost.Argonne National Laboratory has recently designed and prepared a new family of PGM-free OER catalyst for PEM electrolyzer. The new catalysts have high porosity and unique nanoarchitecture, and have demonstrated very promising activity and durability in both rotating disk electrode (RDE) and in operating PEMWE.The most challenging aspect of PGM-free OER catalyst is its stability in the acidic media. To this end, we conducted extensive structural characterizations as well as computational modeling. Particularly, in situ X-ray absorption spectroscopy combined with high resolution imaging revealed insightful information on the electronic and surface structural changes during the electrochemical reaction. Computational Pourbaix diagram also elucidated the catalyst stability under the acidic OER operating condition. Acknowledgement: This work is supported by U. S. Department of Energy, Hydrogen and Fuel Cell Technologies Office through Office of Energy Efficiency and Renewable Energy and by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357.

Design of Noble-Metal-Free Membrane Electrode Assemblies Based on Metal Chalcogenides for Electrochemical Hydrogen Production Via Alkaline Seawater Electrolysis

The production of large amounts of green hydrogen (H2) by electrochemical water splitting represents one of the key pillars to reach net-zero by 2050. As one of the major drawbacks, both low-temperature proton-exchange membrane (PEM) as well as anion-exchange membrane (AEM) electrolysis still rely on the utilization of noble metals in the catalyst layers driving the evolution of H2 and oxygen (O2) on the cathode (HER) and on the anode (OER), respectively. Beyond that, the requirement for highly pure water feeds to prevent degradation of the cell performance over time was previously addressed as one of the main concerns. In particular, this holds true for arid regions located close to the ocean. Advantageously, these coastal arid zones provide essentially unlimited access to seawater, coupled with ample solar irradiation and wind throughout the entire year.[1]One of the major challenges for direct seawater electrolysis lies in the development of selective catalysts, especially for the anode due to the inherently faster reaction kinetics of the competing two-electron chlorine evolution reaction (ClER). Nickel-iron layered double hydroxides (NiFe-LDH) were identified as active and selective OER electrocatalysts in a previous study[2] by our group. Dionigi et al.[3] recently reported a general design principle for selective seawater electrolysis, in which alkaline pH values > 7.5 are claimed to favor OER over ClER for overpotentials < 480 mV.At the cathode, state-of-the-art electrolyzers utilize Pt-based catalysts for an efficient HER.[2] For direct seawater electrolysis, however, not only the high cost but also the weak stability due to chloride-induced corrosion restrict the applicability of Pt-based electrodes. In our contribution, we thus present noble-metal free catalyst materials based on metal chalcogenides with high HER activity and improved stability in alkaline seawater electrolyte in a single-cell electrolyzer setup. Membrane-electrode assemblies (MEAs) with superior corrosion-resistance by a modification of the porous transport layers (PTLs) for both cathode and anode will be presented, which outperform reference MEAs containing Pt-based cathodes in alkaline seawater electrolysis. The optimized noble-metal-free electrode design (fig. 1) combined with well-controlled electrolyte feeding enables alkaline seawater electrolysis operating at industrially relevant current densities.

Low stoichiometry operation of the anode side of a low-temperature proton exchange membrane fuel cell – A modeling study

A single-channel proton exchange membrane fuel cell model (anode side) based on computational fluid dynamics is used to investigate the possibility of operating a fuel cell at low stoichiometric flow ratios using completely dry inlet hydrogen. A case study of three different stoichiometric flow ratios (ξ = 1.01, ξ = 1.03, ξ = 1.05), three different operating temperatures (343.15 K, 347.15 K, 353.15 K), and three different operating pressures (1 atm, 1.2 atm and 1.5 atm) are presented. It is found that the predicted hydrogen concentration and relative humidity (RH) in the catalyst layer (CL) have opposite trends: the RH in CL decreases with increasing stoichiometric flow ratios, but it reaches 100% at the outlet. While hydrogen concentration in CL increases with increasing stoichiometric flow ratios and the largest difference is at the inlet, with a maximum of 3.6%. The results also suggest that PEM fuel cells may be operated in a stoichiometric flow ratio as low as ξ = 1.01 at the anode side. This cell operation would allow open-ended anode operation without a recirculation system, thus significantly reducing system complexity and cost. The CFD code is disclosed to provide a starting point for more complex model development.

Experiment and performance evaluation of an integrated low-temperature proton exchange membrane fuel cell system with an absorption chiller

When the typical operation temperature of the Proton Exchange Membrane Fuel Cell (PEMFC) reaches 333.15–363.15 K, the ratio of electrical energy to waste heat generated by the PEMFC is about 1. In this paper, an absorption chiller with LiBr/[BMIM]Cl/CH3OH as the working pair is proposed to convert the waste heat into cooling capacity. The PEMFC and absorption chiller (AC) systems have been studied from the energy and efficiency point of view. The COP of the integrated system can reach a maximum of 0.85, which is remarkably 0.35 higher than that of the individual PEMFCs. The electrochemical process of the PEMFC and the thermodynamic process of the AC systems are calculated using MATLAB. The results show that the PEMFC operation temperature of 353.15–358.15K is sufficient to drive the AC and meet the requirement of 273.15–283.15K evaporation temperature and 308.15–313.15K condensation temperature. Meanwhile, when the electric power output from the PEMFC is 100 kW, the AC can output approximately 60 kW cooling capacity, which is sufficient to meet the cooling demand of the commercial bus.