bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited, Digital Presentation) High-Efficiency and Stable Perovskite LEDs and Displays with Nanophotonic Methods
Authors: Zhang Qianpeng , Zhang Daquan , Sun Xiaofei , Ren Beitao , Fan Zhiyong
Published: November 2022

Perovskite light-emitting diodes (PeLEDs) have experienced rapid development in the past 8 years. The external quantum efficiencies (EQEs) of red, green, and near-infrared (NIR) PeLEDs have all surpassed the 20% milestone. Meanwhile, the blue PeLEDs also achieved EQEs higher than 10% and are catching up quickly with PeLEDs of other colors.

However, there are still two key problems remaining within the PeLEDs for their further development, namely the light extraction problem and the short lifetime problem. Therefore, in this report, we will discuss our recent work targeting addressing the above two critical problems.

First, our work on improving the light extraction efficiency by deploying the nanophotonic substrates will be introduced. Second, the improvement of the device’s operational lifetime at high luminance conditions with perovskite nanowires embedded in a porous alumina template will be discussed. Third, a full evaporation method that is compatible with industrialization will be shown. Last but not least, our endeavors on the displays based on perovskite materials will be covered.

References

[1] Q. Zhang, M. M. Tavakoli, L. Gu, D. Zhang, L. Tang, Y. Gao, J. Guo, Y. Lin, S. -F. Leung, S. Poddar, Y. Fu, Z. Fan, "Efficient metal halide perovskite light-emitting diodes with significantly improved light extraction on nanophotonic substrates," Nature Communications, 10 (1), 727 (2019).

[2] Q. Zhang, D. Zhang, L. Gu, S. Poddar, Y. Fu, L. Shu, and Z. Fan, “Three-dimensional perovskite nanophotonic wire array-based light-emitting diodes with significantly improved efficiency and stability,” ACS Nano, 14 (2), 1577-1585 (2020).

[3] Y. Fu, Q. Zhang, D. Zhang, Y. Tang, L. Shu, Y. Zhu, and Z. Fan, “Scalable All-evaporation Fabrication of Efficient Light-Emitting Diodes with Hybrid 2D-3D Perovskite Nanostructures,” Advanced Functional Materials, 30, 2002913 (2020).

[4] D. Zhang, Q. Zhang, B. Ren, Y. Zhu, M. Abdellah, Y. Fu, B. Cao, C. Wang, L. Gu, Y. Ding, K.-H. Tsui, S. Fan, S. Poddar, L. Shu, Y. Zhang, D.-B. Kuang, J.-F. Liao, Y. Lu, K. Zheng, Z. He, Z. Fan, “Large-scale Planar and Spherical Light-emitting Diodes Based on Arrays of Perovskite Quantum Wires”, Nature Photonics, 19, 284-290 (2022).
Strongly Quantum-Confined Perovskite Nanowire Arrays for Color Tunable Blue Light-Emitting Diodes
Authors: Fu Yu , Fan Zhiyong
Published: November 2022

Color tunability of perovskite light emitting diodes (PeLEDs) by mixed halide compositional engineering is one of the primary intriguing characteristics of PeLEDs. However, mixed halide PeLEDs are often susceptible to color red-shifting caused by halide ion segregation. In this work, strongly quantum-confined perovskite nanowires (QPNWs) made of CsPbBr3 are grown in nanoporous anodic alumina templates using a closed space sublimation (CSS) process. By tuning the pore size with atomic layer deposition (ALD), QPNWs with diameter of 6.6 nm to 2.8 nm have been successfully obtained, with continuous tunable photoluminescence emission color from green (512 nm) to pure blue (467 nm). To better understand the photo-physics of QPNWs, carrier dynamics and the benefit of alumina passivation are studied and discussed in detail. Eventually, PeLEDs using various diameters of CsPbBr3 QPNWs are successfully fabricated with cyan color (492 nm) PeLEDs achieving a record high 7.1% EQE for all CsPbBr3 based cyan color PeLEDs. And sky-blue (481 nm) and pure blue (467 nm) PeLEDs have also been successfully demonstrated, respectively. The work here demonstrates a unique approach to achieve quantum confined one-dimensional perovskite structures and color tunable PeLEDs, particularly blue PeLEDs.
(Invited) Sustainable Generator and in-Situ Monitor for Reactive Oxygen Species Using Photodynamic Effect of Single-Walled Carbon Nanotubes in Ionic Liquids
Authors: Huang Xiaozhou , Witherspoon Erin , Li Yaonian , Ward Sam , Yu Jingjiang , Wu H Felix , Ding Hanping , Li Qiliang , Wang Zhe , Dong Pei
Published: November 2022

Due to the demand of public health maintenance, disinfectant generator technologies that utilize green processes are becoming attractive. It has been confirmed that single-walled carbon nanotubes (SWCNTs) could generate reactive oxygen species (ROS) in water when illuminated with solar irradiation. However, low efficiency due to the competitive reactions between ROS and water in aqueous media and unclear kinetics hinder their potential practical applications. To overcome these limitations, here, the SWCNTs were studied in a nonaqueous ionic liquid (IL) to form a suspension system to generate superoxide (O2
-) under UV light. The as-obtained O2
- from SWCNTs was qualitatively confirmed by electron paramagnetic resonance and UV-visible spectroscopy. The sustainability of the new SWCNTs/IL system was confirmed by UV-visible spectroscopy and Fourier-transform infrared spectroscopy. The IL proved to be an ideal media that could extend the duration of O2
- from a few microseconds (commonly generated in the water) to at least 65 hours in the IL. The kinetics of photodynamic effect was investigated by electrochemical characterizations. A new method was established to in-situ monitor the O2
- level in the IL system. The O2
- level in the IL was quantitatively determined by combining cyclic voltammetry and chronoamperometry techniques. The SWCNTs/IL system generated 4.11 mM of O2
- in a mini-scale generator, which was excessive to germicidal levels for ROS. The sustainable, long duration and high-yield of the generator exhibited an excellent potential as a generator as well as an in-situ monitor for O2
-. This work could pave the way for O2
- generation using SWCNTs and promote its applications in air and water disinfection for public health, as well as O2
- sensitive chemical sensors for monitoring environmental quality.
(Invited) Ultrawide Bandgap Transistors for High Temperature and Radiation Hard Applications
Authors: Shur Michael
Published: November 2022

Some of the best high-temperature commercial devices are now GaN field-effect transistors (FETs) on silicon substrates. However, these devices cannot meet requirements for space applications requiring high radiation hardness and for operations at temperatures as high as 600 oC. High temperature and radiation hard applications stimulated interest in developing transistors using ultrawideband gap materials including AlN, AlGaN with a high molecular fraction of aluminum, gallium oxide, diamond, boron nitride, and their heterojunctions. A wider bandgap and, therefore, larger energy required to produce an electron-hole pair and larger energy gap discontinuities in heterostructures formed by these materials make them both more tolerant to radiation and more capable of operating at higher temperatures. Insulated gate (Metal Insulator Heterostructure FET (MISHFET) structures with high K-materials implemented in the AlGaN materials system, the power FINFET configurations implemented in GaN and diamond, and gate edge and channel engineering approaches are key technologies for ultra-wide bandgap semiconductor applications. Using all AlGaN materials is now a proven approach to compete with GaN. Measured and predicted materials properties of BN and diamond promise an even better performance but the power device applications of these materials and their heterojunctions have not yet been sufficiently explored. I will review the material parameters of ultra-wideband gap semiconductors and specific device designs linking them to the expected radiation hardness and high-temperature performance and to improving the reliability and lifetime of ultra-wideband gap transistors.
Unsteady Three-Dimensional Simulation of Water Condensation in Gas Diffusion Layer
Authors: Naito Hiroshi , Hirai Shuichiro
Published: November 2022

In polymer electrolyte fuel cells (PEFCs), some of the water produced by the electrochemical reaction accumulates inside gas diffusion layer (GDLs), and degrades the cell performance by preventing the gas transport. In order to further improve the cell performances, it is necessary to accumulate the detailed knowledge about the mechanism of liquid water accumulation. In this study, we investigate the detailed mechanism of liquid water condensation and accumulation by performing three-dimensional unsteady numerical simulation using the volume of fluid method (VOF). The simulation, which consists of a catalyst layer (CL), GDL (substrate only), flow field was performed at 40 ℃ cell temperature and 80% relative humidity. The region where water condenses were identified by solving the temperature field and the H2O concentration field, and it was also observed that water droplets moved between pores due to surface tension force.

Figure 1
Porosity, Porosity Heterogeneity and Morphology Characterization of Microporous Layers of Commercial Gdls
Authors: Chen Yen-Chun , Buechi Felix N. , Karageorgiou Chrysoula , Eller Jens , Schmidt Thomas J.
Published: November 2022

Porosity and morphology of MPLs have a remarkable influence on the performance of PEFCs. However, until now, MPL porosity is largely undetermined for all commercial gas diffusion layers and the MPLs are commonly thought of as a homogeneous layer in thickness and porosity. Many model studies are based on this picture. However, these assumptions are not evidence-based, and can lead to erroneous interpretations of MPL functions. The challenge of having realistic models of MPLs lies in the lack of descriptions of MPL properties on the representative millimeter scale, while its pore structure is on the nanometer scale.

Here, we use laboratory-based, X-ray tomographic microscopy (XTM) to determine the porosity, thickness and their spatial heterogeneity of microporous layers from 15 commercial GDL materials on the operation-relevant, millimeter scale. These properties are relevant to the diffusive transport through diffusion media (cf. Fick’s law).

The porosity distribution is measured by quantifying the volume fraction of a saturating liquid, n-decane, in the fully saturated MPL with a large field of view (FoV) of >10 mm2 and a voxel edge length (determining the image resolution) of 3.6 μm. With optimized X-ray quantum noise control, regional average porosity differences >4.7% can be determined with a 95% confidence level (for every 50 μm 50 μm regions). This resolution in porosity determination allows to define and quantify the degree of spatial porosity heterogeneity for every MPL—a property of MPL that was previously unclear.

Together with the MPL thickness heterogeneity (related to intrusion depth), the MPLs of the 15 commercially available gas diffusion layers from the three international manufactures Freudenberg, Sigracet® and CeTech, are characterized and classified into 5 groups. Contrary to the common homogeneous assumption, the majority of characterized MPLs (especially from Sigracet® and CeTech) actually come with various degrees of porosity and thickness heterogeneity. These differences among MPLs could result in very different water management properties of the respective GDL materials. The representative descriptions of MPL porosity, porosity heterogeneity and thickness heterogeneity also provides realistic input to modeling.

Figure 1
Advanced Voltage Break Down Analysis By Statistical Open-Source Tool Case Study Based on Polymer Electrolyte Water Electrolysis
Authors: Dizon Arthur , Schuler Tobias , Weber Adam Z. , Danilovic Nemanja , Bender Guido
Published: November 2022

The development of economical hydrogen-production methods is essential to establishing hydrogen as a viable fuel. One promising method of hydrogen production is proton-exchange-membrane water electrolysis (PEMWE), where water is converted electrochemically to hydrogen and oxygen gas. The PEMWE research efforts are multi-faceted and aim to improve material costs, operations costs, and safety, which require robust methods to accurately gauge PEMWE cell performance. Electrochemical cells can be fundamentally characterized in terms of a Tafel equation, which describes the relationship between the faradaic current density and applied potential as a log—linear relationship, respectively. Due to the complex and highly coupled chemistry and physics within the membrane—electrode assembly, the operational ranges of experimental PEMWE data used to extract Tafel parameters are often nebulous, which results in addition of a human element in estimating the appropriate data where a Tafel-kinetic model is assumed to be applicable.

In this work, an algorithm for extracting the Tafel slope was developed to assess the adherence of polarization data to a Tafel-kinetic model. The method was developed using experimental PEMWE data and is a systematic and statistical assessment that uses error propagation and Monte-Carlo simulations of fitted parameters to yield 95% confidence intervals (CIs). As shown in Figure 1a, the CIs are used to identify operational ranges where polarization data is consistent with a Tafel-kinetic model. The method was used to perform a voltage-breakdown analysis, which is shown in Figure 1b. A voltage-breakdown analysis is an analytical tool where voltage losses are quantified and associated with a specific mechanism, such as mass transfer, ohmic resistance, kinetics, and thermodynamics. The algorithm was implemented in a portable and open-source format, which was shown to reduce variability of analyses performed by members of the H2NEW consortia. Applicability of the algorithm should be transferrable to other electrochemical systems and may serve as a standardized method of extracting electrochemical kinetic parameters and performing voltage breakdown analyses.

Acknowledgements

This research is supported by DOE Hydrogen and Fuel Cell Technologies Office, through the H2NEW Consortia.

Figure 1
Graded Catalyst Layers As a Strategy to Increase Power Density and Reduce Catalyst Loading
Authors: Fortin Patrick
Published: November 2022

Proton exchange membrane fuel cells (PEMFCs) offer an attractive solution to reduce the carbon emissions of the transport sector. Despite the continuous efforts of researchers over the past decades, the current landscape of fuel cell technologies shows limitations at the component level in terms of performance, durability, and production cost. The main objective of the work presented here is to improve the power density of fuel cells by understanding the performance limitations of the membrane electrode assemblies (MEAs). To accomplish this objective, a series of in‐situ performance tests and ex‐situ characterisation methods have been used to create correlations between the observed performance, voltage loss breakdowns at the cell level, and the fundamental material property characteristics of state-of-the-art (SoA) MEA components. Specifically, we have explored the development of graded catalyst layers in the x-, y-, and z-direction to improve catalyst utilization, leading to increased power density while simultaneously decreasing catalyst loadings. The optimized catalyst layer structures, in combination with ultrathin proton exchange membranes, have led to high performance MEAs with reduced catalyst loadings compared to commercially available SoA MEAs.
Study of Mechanical Properties of Membrane-Electrode Assemblies for Proton Exchange Membrane Fuel Cells By the Small-Punch Technique
Authors: Hernández Rebeca , Merino Susana , Plaza Daniel , Duque Luis , Folgado M. Antonia , Chaparro Antonio M , Serrano Marta , de Diego Gonzalo
Published: November 2022

Mechanical properties of membrane-electrode assemblies (MEAs) are most relevant for the durability of proton-exchange membrane fuel cells (PEMFCs) [1]. During operation, the MEA must endure eventual changes in the static pressure of anodes and cathodes caused by changes in power demand, gases flow rate, and/or water generation, accompanied by hygrothermal cycles, that cause mechanical stresses in the membrane, leading to cracks and possible fatal failure [2]. In parallel, the mechanical properties of MEAs change irreversibly during power production as a consequence of membrane and electrodes corrosion [3]. Therefore, it is of interest to characterize the mechanical properties of MEAs before assembly, and after operation.

The small-punch is a new technique for testing mechanical properties of solids. It consists of measuring the deformation of a disc of the testing material with a ‘small puncher’, while recording the load (force) exerted by the puncher and the deflection produced on the specimen (Fig. 1a) [4]. The plot load vs deflection allows estimating mechanical strength, fracture toughness, impact, and tensile properties. Most interesting is that the disk specimen can be as small as a few millimeters, which makes the small-punch technique very appropriate when the amount of sample is limited, and for localized studies of mechanical properties.

In this communication, results of the small-punch technique are shown for the study of MEAs operated in single PEMFCs (Fig. 1b). The analysis is carried out of the local mechanical properties on new and degraded MEAs. First results show that local mechanical properties of the aged MEA correlate well with gas feeding conditions and reflect laterally inhomogeneous degradation (Fig. 1b).

Acknowledgement: The work is partially financed by the ELHYPORT project (PID2019−110896RB-I00), Spanish Ministry of Science and Innovation.

[1] X. Huang, R, Solasi, Y. Zou, M. Feshler, K. Reifsnider, D. Condit, S. Burtlatsky, T. Madden, J. Polymer Science: Part B: Polymer Physics, Vol. 44, 2346–2357 (2006).

[2] Z. Lu, M. Lugo, M.H. Santare, A.M. Karlsson, F.C. Busby, P. Walsh, J. Power Sources 214 (2012) 130-136.

[3] M. Pestrak, Y. Li, S.W. Case, D.A. Dillard, M.W. Ellis, Y-H. Lai, C. S. Gittleman, J. Fuel Cell Sci. Technol. (2010), 7(4): 041009.

[4] EN 10371:2021 Metallic materials - Small punch test method. CEN, Brussels (2021)

Figure 1
Catalyst Layer Resistance, Utilization, and Degradation in PEM Electrolysis
Authors: Padgett Elliot , Bender Guido , Haug Andrew , Lewinski Krzysztof A. , Sun Fuxia , Yu Haoran , Cullen David A. , Steinbach Andrew , Alia Shaun M
Published: November 2022

Proton exchange membrane (PEM) electrolysis is a promising route for renewable hydrogen production. However, to enable widespread, low-cost hydrogen generation, PEM electrolyzers must make advances in performance and durability with greatly decreased loadings of iridium as the anode oxygen evolution catalyst. The ionic and electronic resistance of the anode catalyst layer is an important consideration, as high internal resistance lowers catalyst utilization and cell performance while accelerating degradation. Catalyst layer resistance (CLR) is relatively well-understood in fuel cells and other porous electrode systems. However, characterization of CLR is not routinely used in the PEM electrolysis community, and the impacts of CLR for PEM electrolysis are not widely understood.

Here we will present in-situ methods for measuring CLR in electrolysis cells using a non-faradaic H2/H2O condition as well as methods for calculating the associated voltage losses. These methods are applied to anode catalyst layers based on IrO2 nanoparticles as well as dispersed nano-structured thin film (NSTF) Ir catalysts. Trends of CLR, performance, and durability with electrode properties such as loading and interactions between the porous transport layer and catalyst layer will be discussed. We will also present investigation of characteristic uneven degradation of the catalyst layer caused by CLR and strategies for mitigating this degradation mechanism.
(Digital Presentation) Development of Composite Graphite Plate with Multiple Functional Layers for Pemfc
Authors: Fan Runlin , Zheng Junsheng , Chen Jing , Peng Yuhang
Published: November 2022

Composite graphite plates (CGPs) have attracted interest due to competitive benefits such as cheaper cost, lower density, and excellent corrosion resistance. Their mechanical and electrical qualities, on the other hand, are insufficient to meet the PEMFC's standards. In this study, a structural design of CGPs with different functional layers is proposed. In order to attain higher electrical conductivity and air tightness, the surface layer was molded graphite plate with resin infiltration treatment, and the middle layer was a carbon fiber fabric (CFF) as a reinforcing functional layer. The results show that the surface layer prepared from flake graphite (FGL) have a density of 2.1 g/cm3, while the surface layer made by expanded graphite (EGL) have a density of about 1.7 g/cm3 with higher porosity. As a result, the CGPs prepared by using FGL as the surface layer has higher airtightness and structural strength. The CFFs must be oxidized to promote the effective bonding with resin, and the addition of carbon nanotubes (CNTs) can effectively improve the interfacial bonding and reduce the area specific resistance (ASR). At a resin content of 20 wt.% with 2 wt.% CNTs in resin, a CGPs with multilayer construction possess a thickness of 0.4 mm, an in-plane conductivity of 446 S/cm, an ASR of 6.4 mΩ·cm2, a flexural strength of 72 MPa, and a Helium permeability of around 4.4*10-6 std cm3/cm2·s. In addition, the graphite particle size has a significant effect on the electrical conductivity, and the analysis on the cross-sectional morphology of the surface layer indicated that this is primarily due to the anisotropic properties of graphite, with larger particle tends to be more orderly distributed after compression resulting in higher in-plane conductivity.
Study on Long-Term Decomposition Conditions of Hydrogen Peroxide for Oxygen Supply to Pemfcs
Authors: Han Chaehyeok , Cheon Hyungjun , Bae Joongmyeon , Lee Junghun , Yoon Hyunki , Roh Heesook
Published: November 2022

Hydrogen that has high energy density is one of the main energy sources for the next generation. Polymer electrolyte membrane fuel cells (PEMFCs), which can utilize hydrogen's high energy storage density, are a very useful power source. The development of oxygen supply and storage technologies is essential for PEMFCs. Hydrogen peroxide, which has a high oxygen storage density, is present in an aqueous state at room temperature, making it easier to transport and storage in sparse oxygen environments. However, decomposition of hydrogen peroxide by catalyst has some problems. In order to reserve hydrogen peroxide, it is necessary to add stabilizers, but this causes degradation of the catalyst. We identified the effect of hydrogen peroxide stabilizers on the catalyst in the long-time decomposition reaction. The activation time of the catalyst depends not only on the materials of catalyst but also on the reactor design, and on the decomposition conditions. The effect of these variables on activation time were analyzed. As a result, the possibility of using hydrogen peroxide for long-term oxygen supply to PEMFCs was verified. We observed an improved activation time of 23 hours while maintaining an 1.6L/min oxygen flow rate.

Figure 1
Optimization of the Cathode Gas Diffusion Layer Also Matters for Water Electrolyzers
Authors: Yilmaz Abdurrahman , Komini Babu Siddharth , Pasaogullari Ugur , Spendelow Jacob S. , Mukundan Rangachary
Published: November 2022

Polymer electrolyte water electrolyzers (PEMWEs) are a promising technology for the storage of energy from intermittent renewable sources such as wind and solar. PEMWEs split water into hydrogen and oxygen electrochemically. Under typical operating conditions, the hydrogen evolution reaction (HER) in the cathode is not limited by reactant transport, since it is supplied by the rapid transport of protons from the polymer electrolyte and electrons from the external circuit. There are very limited studies on the role of the cathode gas diffusion layer (GDL), typically a carbon-paper based layer. In this study, we investigated the effect of thickness, presence of a microporous layer, and wettability of the cathode GDL. Results show that cathode GDL properties have a significant effect on the performance of the PEMWE cells. Figure 1a shows the importance of the GDL thickness with the optimized GDL compression. The thickest GDL, MGL370 (i.e. 370µm thick ) has the best performance compared to MGL280 (280µm thick) and MGL190 (190µm thick). Compression of the GDL also affects the performance: when the compression is increased from 12% to 25% of the thickness, a performance loss is observed possibly due to damaged carbon fiber network and collapse the pores of the GDL (Figure 1b).

Acknowledgment: Financial support from the US Department of Energy through the Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cells Technology Office is gratefully acknowledged.

Figure 1
The Possibility of Intermediate–Temperature (120 oC)–Operated Polymer Electrolyte Fuel Cells
Authors: Kakinuma Katsuyoshi , Taniguchi Hitoshi , Asakawa Takayuki , Miyao Toshihiro , Uchida Makoto , Aoki Yasuhito , Akiyama Tsuyoshi , Masuda Akihiro , Sato Nobuyuki , Iiyama Akihiro
Published: November 2022

The technical possibility and possible issues of an intermediate–temperature–operated polymer electrolyte fuel cell (@120 °C, IT–PEFC) was investigated toward the launching of new fuel cell heavy–duty vehicles. Commercial perfluorosulfonic acid membrane (PSFA, NRE212) and a commercial Pt catalyst supported on carbon (Pt/C: TEC10E50E, TKK) were selected to clarify the possible issues in the fuel cells. The higher oxygen back–pressures, over 200 kPa(abs.), allowed us to obtain higher power densities than those for cells operated at 80 °C (Fig. 1), because the water vapor pressure at 120 °C exceeded 100 kPa(abs.) above 50% RH. The mass activity at 0.85 V increased monotonically with increasing back–pressure above the water vapor pressure of 160 kPa(abs.) at 120 °C, 80% RH. The open circuit voltage (OCV) exceeded 1.0 V for back–pressures above 200 kPa(abs) at the Pt loadings on the cathode catalyst layer above 0.20 mgPt cm–2 (Fig. 2), which would relate with the hydrogen crossover in the PFSA membrane. The mass activity (@0.85 V) decreased moderately with decreasing cathodic Pt loading amount at each back–pressures (Fig. 3), indicating that the limitation of Pt mass activity in the lower Pt loading cathode catalyst layers occurred at 120oC, 80 %RH. The load cycle durability test (0.60V-1.0 V, 6 sec.) of the Pt catalyst supported on carbon at 120 °C at low humidity (20% RH) was higher than that at 120 °C at high humidity (80% RH) and 80 °C at 80% RH (Fig. 4), indicating that effect of Ostwald ripening would mitigate. The degradation of PFSA membrane accelerated at open circuit voltage condition by increasing operating temperature despite of the operation under the high humidity condition of 80% RH. We propose that the further improvement of both the gas transport properties in gas diffusion layers and the durability of the PFSA membrane to realize the IT–PEFC operation.

Acknowledgment

This work was partially supported by funds for the project “Electrolytes, Catalysts and Catalyst layers with Extraordinary Efficiency, power and Durability for PEFCs-2040 (ECCEED’40) from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

Reference

K. Kakinuma, H. Taniguchi, T. Asakawa, T. Miyao, M. Uchida, Y. Aoki, T. Akiyama, A. Masuda, N. Sato, A. Iiyama J. Electrochem. Soc.
169, 044522 (2022).

Figure 1
Optimization Strategies for Commercialization of High-Temperature Pemfcs
Authors: Seselj Nedjeljko , Martinez Alfaro Silvia , Azizi Kobra , Bompolaki Eftychia , Gromadskyi Denys , Hromadska Larysa , Hjuler Hans , Cleemann Lars Nilausen
Published: November 2022

The increasing requirement for renewable energy places high-temperature proton exchange membrane fuel cells (HT-PEMFCs) on the forefront of “green” energy-generating power devices. Compared to certain PEMFC technologies, HT-PEMFCs possess faster electrode kinetics, high tolerance to fuel poisons and impurities, no humidification requirements, simplified cooling and system design.1 Herein we present optimization strategies of membrane electrode assemblies (MEAs) for HT-PEMFCs, focusing mainly on the (1) component characterization, (2) MEA fabrication, and (3) testing protocols. A selection of gas diffusion electrodes (GDEs) was tested, as well as the presence/absence of a microporous layer (MPL) on the cell performance. The catalyst layer (CL) has been modified in the terms of fabrication methods, catalyst type, platinum (Pt) content, as well as a variety of binders and additives. The PEM optimizations focused on varying and testing: (1) the molecular weight (Mw) of polybenzimidazole (PBI) for membrane casting, (2) PEM thickness, and its (3) acid doping levels (ADL). The MEAs were then fabricated at altering hot-pressing conditions and their performances were compared. The MEA testing focused on activation, humidity levels, high current operations, elevated temperature and pressure operations, as well as long-term stationary and dynamic durability protocol studies. The material fabrication optimizations resulted in higher onset and peak-of-life voltages, as well as longer cell durability. Together with optimized cell testing, we have achieved power densities of more than 0.8 W/cm2, with stationary durability of more than 13,000 hours at 0.3 A/cm2 current density, with the degradation rate of 4 μV/h. Originally the dynamic durability was demonstrated with more than 290 start-stop cycles showing the performance degradation of up to 100 µV/cycle, however, new tests show degradation rates of less than 46 µV/cycle. The performance and durability that we have demonstrated here position HT-PEMFCs as matured technology that can enter the mass market as a commercial and reliable electrochemical power device, to answer the ever-increasing societal energy demands in the age of climate change.

Figure 1. Performance of Blue World Technologies MEAs: (A) from different production batches showing small performance scatter, and (B) i-V and power curves at elevated pressures.

Reference:

1. O. Jensen, D. Aili, H. A. Hjuler, Q. Li, High Temperature Polymer Electrolyte Membrane Fuel Cells - Approaches, Status and Perspective, ISBN 978-3-319-17081-7; DOI 10.1007/978-3-319-17082-4, Springer International Publishing, New York, 2015.

Figure 1
Highly Durable Pt-Based Core-Shell Catalysts with Metallic and Oxidized Cobalt Species for Boosting the Oxygen Reduction Reaction
Authors: Oezaslan Mehtap , Janssen Marek , Weber Philipp , Park Daseung , Klein Jochen
Published: November 2022

A self-supported Pt-CoO alloy catalyst has recently been reported as a new concept for Pt-based catalysts combining high surface area with high ORR activity. [1] Very recently, the presence of cobalt oxide species within Pt-Co catalyst after electrochemical dealloying in acidic media has also been reported by Weber et al. [2] However, the elemental distribution particularly for light elements like oxygen as well as the influence of the Co oxide on the ORR activity are still unclear to date.

We prepared a disordered PtCoOx alloy catalyst using wet-impregnation - freeze-drying - thermal annealing method. [3] After electrochemical activation by dealloying, the less noble metal is dissolved from the nanoparticle surface and the remaining Pt surface atoms are forming a protective particle shell referred to as core-shell catalyst. [2, 3] Using high resolution scanning transmission electron microscopy in combination with electron energy loss spectroscopy (STEM-EELS) we were able to explore the detailed structure of the activated PtCoOx catalyst with a Pt-enriched shell. Based on the EELS elemental maps of Pt, Co and O, we observed that oxygen is mainly located at the interface between the Pt-enriched shell and the PtCoOx alloy core. Thus, the CoOx species are highly stable during the electrochemical dealloying in acidic media. The ORR mass activity (0.56 ± 0.14 A mgPt
-1 at 0.9 VRHE) of the PtCoOx core-shell catalyst is 2.5-times higher, whereas the ORR specific activity (592 ± 171 µA cmPt
-2 at 0.9 VRHE) is 3-times higher than that for commercial Pt/C (0.24 ± 0.05 A mgPt
-1, 187 ± 29 µA cmPt
-2). The stability of the CoOx species and the electrochemical catalyst durability were tested by using an accelerated stress test (AST, 10,000 cycles from 0.5 to 1.0 VRHE) in acidic media. Here, the PtCoOx core-shell catalyst showed an improved electrochemical durability compared to Pt/C and maintains 85% of the initial ECSA, 54% of the initial ORR mass activity and 68% of the initial ORR specific activity, respectively. From the STEM-EELS and XPS measurements, we revealed an increase of the thickness of the Pt-enriched shell of several monolayers after the AST protocol. Very surprisingly, the cobalt oxide in the sub-surface layers still remains, but it is less narrowly distributed than before the AST experiment.

Thus, we suggest that the Co oxide species in PtCoOx alloy catalyst might have a positive effect on the ORR performance and durability and could even be a yet undiscovered alternative to metallic cobalt.

Reference:

[1] G.W. Sievers et al., Nat. Mater., 2021, 20, 208-213;

[2] D.J. Weber et al., J. Mater. Chem. A, 2021, 9, 15415-15431;

[3] M. Oezaslan et al., J. Electrochem. Soc., 2012, 159, B394-B405.
Core-Shell Electrocatalysts with Nanocolumnar Pt Thin Film Shell on Carbon Support Core for Polymer Electrolyte Membrane Fuel Cells
Authors: Basurrah Assem Omar , Ergul Busra , Badradeen Emad , Yang Zhiwei , Bourdo Shawn , Karabacak Tansel
Published: November 2022

Polymer Electrolyte Membrane Fuel Cell (PEMFC) is one of the most promising energy conversion technologies with zero carbon emission, and has received significant attention especially for automotive applications. State-of-the-art PEMFCs use platinum or platinum-alloy nanoparticles distributed on carbon as the electrocatalyst. However, there are still significant challenges for PEMFCs before widespread commercialization including short lifetime and high initial cost mainly originating from the catalyst related issues. Recent research efforts have focused on approaches that would improve catalyst lifetime, reduce its manufacturing cost, and reduce the amount of platinum used without losing activity. In this work, we present a new core-shell electrocatalyst design that can potentially address the challenges of conventional PEMFC catalysts. The design involves a shell of nanocolumnar Pt thin film coated on carbon support core (Pt-TF/C). Pt-TF layers were deposited on carbon powder by high-pressure sputtering (HIPS) and their oxygen reduction reaction (ORR) activity relevant to PEMFCs was investigated. HIPS is a simple physical vapor deposition technique that is scalable and easily applicable to industrial sputter deposition systems, in which atoms come to the substrate surface at different angles to form columnar structures. Pt-TF/C powder samples with various types of carbon were produced and studied to investigate their ORR performance. Electrochemical characterization of the samples was performed by cyclic voltammetry and rotating disk electrode measurements. The Pt-TF-to-carbon mass ratios were measured by quartz crystal microbalance and thermogravimetric analysis. X-ray diffraction analysis showed the presence of Pt on the carbon support. Our preliminary results on specific activity, mass activity, and electrochemically active surface area indicate a promising electrocatalyst durability.
Local Hydrophobicity of Atomically Dispersed Fe-N-C Catalysts and Its Impact on the Oxygen Reduction Reaction in Membrane Electrode Assembly
Authors: Atanassov Plamen , Liu Yuanchao , Murphy Eamonn , Mamania Divija Nitin , Khedekar Kaustubh , Zenyuk Iryna V.
Published: November 2022

Non-precious metal electrocatalysts with atomically dispersed transition metal sites have shown promising performance for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. The Fe-N-C catalysts, with single iron atom coordinated by nitrogen atoms (FeNx) on carbonaceous supports, exhibits outstanding ORR activity as compared to its other metal counterparts (M-N-C). [1] The Fe-N-C catalysts synthesized via sacrificial support method (SSM) showed superior ORR performance and this family of Fe-N-C electrocatalysts is so far the only commercially available PGM-free catalysts for fuel cell application. [2] For membrane electrode assembly (MEA) performance, the pore structure [3] and surface hydrophobicity [4] of the carbon matrix are of particular significance, because the high current throughput requires good oxygen transport and well-controlled water management on cathodes. In this talk, we present the local hydrophobicity of SSM-based Fe-N-C electrocatalysts [1] and its impact on the ORR macrokinetics in MEA. Specifically, nitrogen physisorption and water vapor physisorption were used to study the pore morphology and the local surface hydrophobicity, respectively. As shown in Figure 1, the sacrificial templated Fe-N-C catalyst showed a large amount of mesoporosity while its surface was very hydrophobic, as indicated by the little water uptake through whole pressure range. Such porosity and local hydrophobicity features were further correlated to its macrokinetic performance in a study of water partial pressure dependence under MEA configuration.

Reference

[1] T. Asset and P. Atanassov, Joule, 2020, 4, 33.

[2] https://pajaritopowder.com

[3] Y. Huang, Y. Chen, M. Xu, T. Asset, P. Tieu, A. Gili, D. Kulkarni, V. de Andrade, F. de Carlo, H. S. Barnard, A. Doran, D. Y. Parkinson, X. Pan, P. Atanassov, and I. Zenyuk, Materials Today, 2021, 47, 53.

[4] L. Liu, S. J. Tan, T. Horikawa, D. D. Do, D. Nicholson and J. Liu, Adv Colloid Interface Sci, 2017, 250, 64.

Figure 1
Which Properties Should Anion-Exchange Membranes Have to Achieve a Longer Fuel Cell Lifetime?
Authors: Yassin Karam , Rasin Igal G , Brandon Simon , Dekel Dario R
Published: November 2022

The substantial advancements and availability of new cost-effective materials have drawn significant attention to the technology of anion-exchange membrane fuel cells (AEMFCs). The anion exchange membrane (AEM) is a core component in AEMFCs, essential for conducting hydroxide ions and, more importantly, controlling water transport between the fuel cell electrodes. In this contribution, we apply the computational methodology outlined in Refs. [1,2] to explore the effects of various membrane properties on AEMFC performance and its stability. We specifically consider the following parameters: (A) water diffusivity, (B) membrane thickness, (C) ion exchange capacity (IEC), (D) maximum hydration level (λmax) corresponding to ionomer/water contact (maximum number of water molecules per functional group), (E) hydroxide conductivity, and (F) degradation rate constant of the AEM functional group.

First, we describe our modeling approach, which includes a one-dimensional isothermal and time-dependent model of AEMFC operations. The model considers the chemical degradation process of the ionomeric materials in the cell, transport phenomena through the anode and cathode gas diffusion layers, anode and cathode catalyst layers, and the membrane. Finally, the electrochemical reactions, hydrogen oxidation in the anode and oxygen reduction in the cathode, are described by Butler-Volmer kinetics. We present our main findings, demonstrating that membrane water diffusivity and λmax have the most significant impact on AEMFC lifetime, followed by membrane thickness and IEC, attributed to enhanced water distribution across the cell. We also demonstrate the significance of improving functional group stability to performance stability, while AEM hydroxide conductivity shows a negligible effect on AEMFC lifetime. Finally, we perform dimensional analysis and provide an analytical, useful correlation to estimate the AEMFC lifetime of selected membranes from the literature and compare it to the measured operation time. In conclusion, this work highlights important AEM parameters aimed at improving AEM designs in order to enhance the performance stability of AEMFCs.

[1] D.R. Dekel, I.G. Rasin, S. Brandon, Predicting performance stability of anion exchange membrane fuel cells, J. Power Sources. 420 (2019) 118–123. https://doi.org/10.1016/j.jpowsour.2019.02.069.

[2] K. Yassin, I.G. Rasin, S. Brandon, D.R. Dekel, Elucidating the role of anion-exchange ionomer conductivity within the cathode catalytic layer of anion-exchange membrane fuel cells, J. Power Sources. 524 (2022) 231083. https://doi.org/10.1016/j.jpowsour.2022.231083.
The Development of Anion Exchange Ionomer for Electrocatalysts in Application of Anion Exchange Membrane Fuel Cells
Authors: Maumau Thandiwe Rebecca , Maxakato Nobanathi Wendy , Msomi Phumlani Fortune
Published: November 2022

Anion exchange membrane fuel cells (AEMFCs) are known to be able to address the use of expensive platinum catalyst by employing non-PGMs (Platinum Group Metal) metal catalysts, affordable ionomers, and greater fuel flexibility. All that provides AEMFCs with advantages over PEMFCs. However, AEMFCs have not been reported to achieve high current density as desired at fault by the lack of understanding of ionomer-catalyst interaction. For stable operation of AEM-based devices, water sorption and swelling of the thin anion exchange ionomer (AEI) layer are coupled to its catalyst binding ability. Unfortunately for AEM fuel cell field there exists no commercial material as Nafion® exists for the PEM fuel cell field. The development of a high performance and durable anionic catalyst binders also referred to as anion exchange ionomers (AEIs) is the major challenge for AEMFCs. This study aims to develop an improved AEI to be tested in both in-house and commercial electrocatalysts. Electrocatalytic activity using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and chronoamperometry (CA) will be carried out for all the electrocatalysts with the use on the developed AEI instead of the usually used nafion ionomer. Characterization techniques will include transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) for particle size, crystal structure and morphology respectively of the electrocatalysts. For the developed AEI dynamic light scattering (DLS) (with an ELS-Z Zeta-potential and particle size analyzer), nuclear magnetic resonance (NMR), and Fourier-transform infrared spectroscopy (FTIR) for size distribution profile, material molecular structure and composition.
Understanding the Role of Atomic Defects in Nanocarbon Support with Cooperative Fe Host As Single Atoms/Nanoclusters Towards Superior Electrocatalysis
Authors: Khan Kishwar , Nam Gyutae , Sevim Melike , Ahn Yoojin , Liu Meilin
Published: November 2022

High-performance electrocatalysts for oxygen reduction reaction (ORR) are vital to many chemical and energy transformation processes. To date, however, the role of atomic defects in nanocarbon (NC) supports for ORR electro-catalysts is still poorly understood. In this presentation, we report our findings in understanding the contribution of atomic defects in NC supports to a series of transition metals (TM) based electro-catalysts to enhance the ORR activity and stability in an alkaline medium. The defect structures and their local coordination are characterized using Operando X-ray absorption spectroscopy and ex-situ Raman spectroscopy. Moreover, the atomic level structure and morphology of the materials are revealed using high-resolution transmission electron microscopy. Further, density functional theory calculations are used to gain deeper insight into the mechanisms of electro-catalytic processes. Our studies not only result in a highly promising ORR electro-catalyst in an alkaline medium but also open a new avenue for rational design of more efficient catalysts for other chemical and energy transformation processes.
(Invited) Computational Modeling of Void Formation Mechanism at the Lithium/Solid-Electrolyte Interface
Authors: Barai Pallab , Fuchs Till , Janek Jürgen , Srinivasan Venkat
Published: November 2022

Stabilization of the lithium deposition by the introduction of solid electrolytes was attempted in the past with partial success. However, electrochemical dissolution of lithium from the metal electrode to the solid electrolyte introduces unique challenges, such as, formation of micron sized voids at the electrode/electrolyte interface. These interfacial pores form due to stripping of lithium at a rate higher than they can actually be replenished from the bulk. Presence of these porous domains will minimize the electrochemically active surface area, dramatically increase the interfacial resistance, and effectively render the cell unusable. In the present research, a phase field based computational framework is developed that can capture the evolution of these micron sized voids at the lithium/solid-electrolyte interface during the electrochemical dissolution of lithium. Importance of lithium surface diffusion in determining the pore morphology is introduced for the first time. Impact of applied current density, external pressure, and operating temperature on the dynamics of void evolution is investigated in detail.

Figure 1
Bicontinuous-Structured Elastomeric Electrolytes for High-Energy Solid-State Lithium-Metal Batteries
Authors: Lee Michael J , Han Junghun , Kim Bumjoon J , Lee Seung Woo
Published: November 2022

The use of lithium (Li) metal anodes in solid-state batteries is a strong strategy as a next-generation battery technology for surpassing the energy density and safety of conventional Li-ion batteries. However, in practice, current solid-state electrolytes have been limited to realize Li metal batteries due to their insufficient electrochemical and mechanical properties. Here, we design a new class of elastomeric electrolytes having a 3D interconnected plastic-crystal phase within the elastomer matrix—plastic crystal-embedded elastomer electrolytes (PCEEs).1 To elucidate the effects of structural changes in PCEEs on Li-ion transport property, mechanical elasticity, and electrochemical performance, we investigate various phase-separated structures of PCEEs by adjusting each phase’s volume ratio. Among these structures, we reveal that bicontinuous-structured PCEE, consisting of an equal volume ratio of elastomer to plastic-crystal phase, is well-balanced to develop the efficient ion-conducting, plastic-crystal pathways within a mechanically robust, cross-linked elastomer matrix. Hence, this optimal PCEE shows a combination of high ionic conductivity (>10-3 S cm-1) at ambient temperature, high Li-ion transference number (>0.70), and good mechanical resilience (elongation at break ≈ 300%). A full cell configured with the optimized PCEE, a limited Li source, and a high loading LiNi0.83Mn0.6Co1.1O2 cathode delivers a high energy density exceeding 430 Wh kganode+cathode+electrolyte
-1. Understanding the structure-property-electrochemical performance relationship of PCEE through structural control can form the basis of structure-controlled elastomeric electrolytes, holding substantial promise in various electrochemical energy storage systems.

References

1. Lee, M. J.; Han, J.; Lee, K.; Lee, Y. J.; Kim, B. G.; Jung, K.-N; Kim, B. J.; Lee, S. W. Elastomeric electrolytes for high-energy solid-state lithium batteries. Nature
2022, 601, 217-222.