bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of Machine-Washable and Wearable Supercapacitors Using Composite Laminates
Authors: Anjum Nasim , Shen Caiwei
Published: February 2020

Flexible and wearable supercapacitors, as a rechargeable energy storage device, are promising power sources for next-generation wearable electronics and electronic textiles in many consumer, medical, and military applications, as they offer safety, mechanical flexibility, stability, and durability that are lacking in current batteries. However, flexible supercapacitor prototypes reported so far have not demonstrated sufficient mechanical properties that could withstand critical situations, such as folding, twisting, and machine washing, which are commonly happening for real-world applications.

Here we present the design of flexible supercapacitors that are foldable, twistable, and machine-washable due to exceptional mechanical properties of the materials. The devices are constructed using thin composite laminates as electrodes and ion-conducting separators. Each layer of the laminates is composed of randomly distributed activated carbon fibers or glass fibers in polymer electrolyte matrix. Calculations and simulations show that such laminates with proper fiber length and volume fraction of fibers can provide both high strength and high flexibility that enable them to survive critical mechanical deformations, while traditional particle-based electrodes cannot.

The electrochemical and mechanical tests demonstrate that the activation of the carbon fiber surface does not affect much of the mechanical properties of the laminates, but greatly improves the surface area of electrodes, which leads to two orders increase in their electrical double-layer capacitance. The prototypes made of electrode/separator/electrode laminates show adjustable areal capacitances of over 10 mF/cm2. The electrochemical performance has remained unchanged after repeated folding and twisting tests. Moreover, we sewed the devices onto fabrics and washed them together with daily garments in a washing machine, after which we observed no mechanical damage or capacitance degradation.

In conclusion, we believe that the excellent electrochemical performance, flexibility and mechanical durability make the composite laminates-based flexible supercapacitors promising to be integrated with daily garments to power various wearable electronics. The design rules and results are also applicable to developing other flexible functional devices that require extraordinary mechanical properties without sacrificing another function.
Investigation of the Fe / W / O System for Aqueous Electrochemical Capacitor Electrode Materials
Authors: Crosnier Olivier , Goubard Nicolas , Espinosa Angeles Julio Cesar , Douard Camille , Favier Frederic , Brousse Thierry
Published: February 2020

Electrochemical capacitors fill the gap between high energy and high power storage devices. Within this matter EDLCs (Electric Double Layer Capacitors, which store charge electrostatically, are the most studied using carbon based materials. They present excellent performance concerning specific capacitance and cyclability, capable to undergo up to one million of cycles [1]. These materials present a low density, due to the activated carbon, making them unsuitable for applications where a high volumetric capacitance is required. For this special scope alluring high-density polycationic oxides exhibit a reliable advantage over the normal carbon based materials [2].

In this work, several materials of the Fe / W / O system have been investigated. Amongst them, two iron tungstate oxides (FeWO4 and Fe2WO6) are of peculiar interest. They were successfully synthesized by several techniques, such as ceramic, hydrothermal and polyol-mediated routes [3]. The materials obtained underwent different heat treatments in order to acquire a crystalline structure. Afterwards, the different samples were characterized by X-ray diffraction, Scanning Electron Microscopy, Energy dispersive X-ray spectroscopy, Mössbauer Spectroscopy and surface area measurements, BET. The materials were assembled in a composite electrode to be studied in a three electrode set up in aqueous LiNO3 5M by cyclic voltammetry.

The results showed a compromise between the specific surface area, the particle size, morphology, and crystallization, as well as the mean Fe oxidation state that have a direct impact in the electrochemical performance.

References

[1] P. Simon and Y. Gogotsi, Nature Mater., 2008, 7, 845–854.

[2] O. Crosnier et. al., Curr. Opin. Electrochem., 2018, 9, 87–94.

[3] N. Goubard-Bretesché et. al., Electrochem. Comm., 2015, 57, 61–64.
(Invited) Lithium-Ion Battery-Capacitor Hybrid Energy Storage Devices
Authors: Zheng Jim P. , Shellikeri Annadanesh , Hagen Mark Andrew , Cao Wanjun
Published: February 2020

As a new generation of supercapacitor, the Li-ion capacitor (LIC) is an advanced energy storage device which consists of an electric double-layer capacitor (EDLC) cathode and a pre-lithiated anode [1,2], between which the ions shuttle during charge and discharge processes. Because of using pre-lithiated and low surface anode materials, the LIC can be charged to a maximum voltage as high as 4.0 V, which is much higher than of EDLCs and comparable to Li-ion batteries (LIBs); therefore, it allows the LIC and LIB to be assembled in one package as a LIB/LIC hybrid energy storage cell.

We have demonstrated a new hybrid energy storage cell that combines the advantages of both the LIB and the LIC [3], thereby avoiding their inherent defects, while bridging the gap between the high energy densities offered by batteries and the high power densities seen in EDLCs. The energy density and power density of the hybrid cell can be designed to meet the requirements by a reasonable distribution of the ratio between LIB and LIC electrode materials in the internal hybrid cell. For example, we show a hybrid LIC consisting of a Li nickel cobalt manganese oxide (NMC)/activated carbon (AC) composite cathode in combination with an ultra-thin Li film (u-Li) pre-loaded hard carbon anode. Additionally, we show that by utilizing three design approaches: dry composite electrode fabrication method, cathode to anode capacity ratio design, and pre-lithiation method using u-Li, we can demonstrate an energy storage device with excellent cycle life, and that can be tailored by composite ratios within the cathode to fit different applications. Shown here is an in-depth look at various composite material ratios, pre-lithiation calculations and hybrid Li-ion battery-capacitor energy storage device creation based on targeting essential energy-power performance characteristics.

References

[1] W.J. Cao and J.P. Zheng, “Li-ion Capacitors with Carbon Cathode and Hard Carbon/SLMP Anode Electrodes”, J. Power Sources, 213, 180 (2012).

[2] W.J. Cao, J. Shih, J.P. Zheng, and T. Doung, “Development and characterization of Li-ion capacitor pouch cells”, J. Power Sources, 257, 388 (2014).

[3] Zheng, J.-S., Zhang, L., Shellikeri, A., Cao, W., Wu, Q., & Zheng, J. P. (2017). A hybrid electrochemical device based on a synergetic inner combination of Li ion battery and Li ion capacitor for energy storage. Scientific Reports, 7, 41910.
An Ultra-Fast and Ultra-Stable All-Graphene Lithium Ion Capacitor
Authors: Jin Liming , Zheng Jun-Sheng , Zheng Jim P.
Published: February 2020

Lithium ion capacitors (LICs) are considered as next generation of capacitive energy storage systems , due to their 3~5 times higher energy density than traditional electrochemical double-layer capacitors. However, the battery-type anode inevitably leads to scarified power density and cycling life, due to imbalanced electrochemical performance of two electrodes, which means achieving competitive power density and cycling life simultaneously is an extreme challenge involving in the whole system. We rationally design an ultra-fast and ultra-stable all-graphene LICs, for which various graphene electrode constructions are synthesized orienting in the distinct energy storage principles of two electrodes, and a novel match approach for two electrodes is proposed and applied. Mesoporous graphene (MP-G) cathode is capable to deliver much better high-rate properties and cycling stability, edge carboxyl graphene (G-COOH) anode with expanded graphitic layer spaces enable fast pseudocapacitive and insertion capacity, as well as durability, and an optimal reaction profiles range of G-COOH are systematically determined by a novel quasi-in-situ electrochemical impedance spectroscopy (EIS) to match with MP-G. Thereby, an ultra-fast and ultra-stable LIC system (MP-G//G-COOH) is fabricated and operated in the voltage range of 1.0 ~ 4.2V. As expectedly, MP-G//G-COOH is capable to deliver an ultra-high-power density of 53550 W kg-1and an unprecedented cycling stability of 98.9% retention after 50000 cycles. This result is promising in terms of pushing ultra-fast and ultra-stable LIC system by combining ideal electrode constructions and matching approaches.
(Invited) Design of Biomolecular Piezoelectric Materials for Energy Generators
Authors: Lee Ju Hyuck
Published: February 2020

Piezoelectric materials are excellent generators of clean renewable energy because they can convert ubiquitous vibration and mechanical power into electrical energy. Although traditional piezoelectric materials such as lead zirconate titanate (PZT), lithium niobate, gallium nitride, and barium titanate are practical for energy generation, their fabrication frequently requires environmentally harmful components and/or energy processes. Recent studies on environmental friend biomolecular piezoelectric materials such as amino acids, peptides, proteins, and viruses have great attention because they are applicable to bioelectronics and biomedical applications. Compared with inorganic and synthetic counterparts, however, biomolecular piezoelectric materials have not been extensively studied for general piezoelectric applications because the piezoelectric response of the major piezoelectric components (d33, d31, d11) are weak. Furthermore, the difficulty of fabricating unidirectionally polarized biomolecular piezoelectric structures that can efficiently convert mechanical energy into electrical energy has been a major obstacle to the realization of robust piezoelectric energy generators.

In this talk, I will introduce recent research on strategies and methods for synthesizing and controlling large-scale aligned various biomolecule piezoelectric materials. The orientation and polarization directions of these materials were controlled using biomimetic self-assembly process which is low cost and environmentally friend process. Furthermore, the energy generators based on the biomolecular piezoelectric materials were demonstrated.
Hybridization of Luminescent Solar Concentrator and Triboelectric Touch Sensor with Its Enhancement Via Ferroelectric Polarization
Authors: Yoon Hong-Joon , Kim Sang-Woo
Published: February 2020

Display technology has not only presented information traditionally, but also multifunctional capability, flexibility, lightness and slimness design are desired attributes for being adopted by artificial intelligence (AI) to interact with consumers. In this regard, ferroelectric poly(vinylidenefluoride-co-trifluoroethylene) (PVDF-TrFE) is of great interest as potentially applicable for display power saving material with having mechanical stability, transparency, and electrically controllable polarization. Here, we report the experimental study of a luminescent light harvesting property of CdSe QD embedded P(VDF-TrFE) nanocomposite, whereas concentration of QD is not as much high as to interfere presenting information in visual. In agreement with theoretical calculation, the converted power from luminescent light guided to c-Si solar cell is enhanced by 42% based on the quantum-confined Stark effect (QCSE) owing to ferroelectric polarization of P(VDF-TrFE). The resulting nanocomposite shows enhanced mechanical sensitivity (~40%) by aligned dipole moment of P(VDF-TrFE) upon mechanical contact. This nanocomposite material may potentially be applicable as multimodal display element not only enable to power itself but also detect given mechanical touch.
(Invited) Ultralight Triboelectric Nanogenerators for Portable Self-Charging Power Unit and Self-Powered Sensing Platform
Authors: Yeh Min-Hsin
Published: February 2020

With rapid development of portable electronic devices and systems, mandatory requirements of portable, lightweight, and significantly sustainable power sources have attracted huge attention. Li-ion batteries or other energy storage devices are commonly used as a stable power supply for driving these electronic devices with small-scale energy consumption at the μW to mW level. Nevertheless, in modern personal electronics, batteries are usually the largest or heaviest component in the whole device, and moreover, the crucial problem of batteries is their limited lifetime and thus their need to be charged or replaced frequently. To conquer this problem, self-powered systems as integrated by an energy harvester and an energy storage device has been proposed and developed to simultaneously harvest and store ambient energy in the form of electricity, which opens potentials for sustainable and maintenance-free applications. Here, we report a ultralight cut-paper-based self-charging power unit (PC-SCPU) that is capable of simultaneously harvesting and storing energy from body movement by combining a paper-based triboelectric nanogenerator (TENG) and a supercapacitor (SC), respectively. Utilizing the paper as the substrate with an assembled cut-paper architecture, an ultralight rhombicshaped TENG is achieved with highly specific mass/volume charge output (82 nC g−1/75 nC cm−3) compared with the traditional acrylic-based TENG (5.7 nC g−1/5.8 nC cm−3), which can effectively charge the SC (∼1 mF) to ∼1 V in minutes. PC-SCPU is demonstrated as a sustainable power source for driving wearable and portable electronic devices such as a wireless remote control. To further enhance the output performance of TENG for extending the possible applications in portable electronic devices, we also report an ultrahigh output power of whirligig-inspired TENG (Wi-TENG) designed according to an antiqueue whirligig toy that is capable of converting low-frequency pulling motion into a high-frequency rotation. It shows that the rotor in the Wi-TENG achieves a maximum speed of 11,250 rpm. Ultrahigh charge transfer quantity of ~310 μC and output power of 40.18mW are obtained by per pulling of Wi-TENG. Moreover, a maximum short circuit current of 317 μA and a constant open-circuit voltage peak value of 153 V can be generated by the Wi-TENG, which can rapidly charge a commercial capacitance (100 μF) to ~14 V within 10 s. After power management, this Wi-TENG is successfully demonstrated as a portable sustainable power source for driving a commercial blood glucose meter.
A High-Power Density Triboelectric Nanogenerator for Harvesting Wave Energy
Authors: Zhao Tiancong , Xu Minyi , Chuan Wang , Zhang Steven L. , Li Zhou , Wang Zhong Lin
Published: February 2020

The global power by waves breaking around the coastlines worldwide has been estimated to be 2-3TW, and if wave energy is collected on open oceans, the global wave power is estimated to be one order of magnitude larger[1]. The water wave energy could turn out to be an even more benign source of power than wind, due to its abundance in the ocean [2]. Although it is a promising prospect for harvesting wave energy, most technologies for capturing wave power still remain in the testing phase. Currently, traditional devices usually harvest wave energy with complex hydraulic or mechanical structures and they drive an electromagnetic generator by transforming the energy from the water waves into rotary motion or linear reciprocal motion. However, these current oceans wave energy apparatuses exhibit unsatisfactory energy harvesting efficiency, high cost, and other methods of harvesting energy would have to be implemented [3-4]. In this work, a high-power density triboelectric nanogenerator (HPD-TENG) is designed and systematically investigated.This HPD-TENG is designed to be built by multiple units made of PTFE balls and 3D printed arc surface coated with melt adhesive reticulation nylon film. The integration of power generation model together with the kinetic model for the HPD-TENG is proposed and studied. The HPD-TENG can effectively transform arbitrary directional wave energy into electrical energy by utilizing charged balls rolling on optimized arc surface induced by ocean wave excitation. Furthermore, with the power generation units increases from 1 to 10 in one block, the power density increases linearly from 1.03 W/m3 to 10.6 W/m3. This indicates that the power density of the HPD-TENG increases proportionally with the number of units connected in parallel without rectifiers due to its distinctive mechanism and structure. Hence the design of HPD-TENG can be regarded as an innovative and effective approach for large-scale blue energy harvesting through integrating more units to form HPD-TENG networks.

References:

Wang, Z. L. “Toward the blue energy dream by triboelectric nanogenerator networks,” Nano Energy 2017, 06.035

Tollefson, J. “Power from the Oceans: Blue Energy,” Nature 2014, 508, 302-304.

Schiermeier, Q.; Tollefson, J.; Scully, T. “Electricity without Carbon,” Nature 2008, 454, 816-823.

Zhang, S. L.; Xu, M.; Zhang, C.; Wang, Y.-C.; Zou, H.; He, X.; Wang, Z.; Wang, Z. L. “Rationally Designed Sea Snake Structure Based Triboelectric Nanogenerators for Effectively and Efficiently Harvesting Ocean Wave Energy with Minimized Water Screening Effect,” Nano Energy 2018, 48, 421-429
(Invited) Piezo-Phototronics Effects on the Collective Behavior of Injected Excitons in GaN-Based Multi-Quantum Wells at Threshold
Authors: Li Ding
Published: February 2020

Realizing Bose-Einstein condensation (BEC) has found intense interest. Up to now extreme conditions like very low temperature and high magnetic field were usually necessary to achieve BEC for low density systems consisting of atoms. Recently, many efforts have been devoted to finding a solid-state system in which BEC can take place. Photoexcited excitons as light-mass bose particles, consisting of bound electron–hole pairs in semiconductors, had triggered intense interest for long time. Excitons as bosons, which can be generated at high density in semiconductor quantum wells, are potential candidates to realize exciton condensation. If their binding energy is higher than kT, which is given for excitons in gallium nitride (GaN) with binding energy of 48 meV, additional confinement in a quantum well (QW) should increase the interaction between excitons and thus offer the chance to observe exciton condensation.

To bring BEC into daily applications, it is highly desirable to realize BEC in a real-world device at room temperature (RT) and free from extreme conditions. Here, we report a simple way to realize boson condensation in a low energy state in GaN-based multi-quantum-well (MQW) laser diodes (LD) at RT. It is revealed by the analysis of abnormal electrical and optical behaviour of GaN-LDs. At threshold, due to the piezo-phototronics effects and the coherent light field, the involved excitons (bosons) in the QW, as dipoles, behave collectively with identical energy and the same direction, which means that they condense into a coherent low energy state. This is confirmed by a redshift of electroluminescence spectra. This quantum effect corresponds to a phase transition in a far-from-equilibrium system, which is an open system exchanging matter and energy with the outside.
The Thermal Characteristics of AlGaN/GaN Hemts with Different Channel Width
Authors: Lin Wei-Chun , Zhong Yi Nan , Tsai Ming-Yan , Ho Wei-Cheng , Yu Yi-Hsuan , Hsin Yue-Ming
Published: February 2020

In this study, the thermal characteristics of AlGaN/GaN HEMTs with different channel widths were investigated. The thermal characteristics including threshold voltage, maximum transconductance (gm,max), on-state current, and on-resistance were investigated from 30 to 150 °C with the increment of 10°C. All devices have the same source, gate and drain widths, but difference in the channel widths. The channel width (Wchannel) is determined by a current blocking region between the source and drain. Device A is a conventional device with gate width (WG) of 50 mm without the current blocking region. Therefore, the channel width is the same as the gate width. Device B, C, and D have the gate width of 50 mm but different channel widths of 27.5, 25, and 12.5 mm, respectively. The dimension of the channel width was implemented by ion-implantation at the process step of device isolation. All epitaxial layers were grown on Si substrate. All devices were passivated by a 200-nm PECVD SiN without field plates. The devices under test are with a gate-source distance (LGS) of 4-µm, a gate length (LG) of 2-µm, gate width (WG) of 50-µm, and a gate-drain distance (LGD) of 10-µm.

At room temperature, device B, C, and D with smaller channel widths show the improved on-state current density, subthreshold swing, and gm. Device D shows a gm,max of 239 mS/mm compared to the 127 mS/mm of the device A. A significant improvement was observed in gm,max of device D due to the large ratio of WG/Wchannel. A better capability of the gate control is achieved. However, the thermal characteristics show the opposite trend. The measured thermal coefficients of the threshold voltage, gm,max, on-state current, and on-resistance of the device D are 2.1´10-4, -6.7´10-3, -3.4´10-3, and 1.1´10-2 1/°C compared with 1.5´10-5, -1.4´10-3, -2.1´10-3, and 7.2´10-3 1/°C of the device A. The possible reason is due to the current crowding at the corners of the blocking region. A suitable heatsink design or back side via are required to reduce the thermal impact.

Figure 1
(Invited) Defects and Development of High Power Vertical GaN Based Structures
Authors: Goorsky Mark S. , Bai Tingyu , Liao Michael , Wang Yekan Steven , Huynh Kenny , Yu Peter HSUAN MING
Published: February 2020

This presentation highlights the use of x-ray scattering and electron microscopy to characterize selectively doped GaN layers for high power vertical diodes. Examples from these techniques will include assessment of residual impurities and crystalline damage in selectively doped regions resulting from dry etching or ion implantation processes and if such defects are removed by subsequent etching and / or annealing steps. X-ray reflectivity (XRR) combined with high angle reciprocal space mapping and dynamical diffraction simulations are effective means by which to assess the strain and defect distribution in the wafers. Advanced synchrotron techniques, through the use of hard x-ray nanoprobes and diffraction imaging, offer further insight into the development of these technologies. Transmission Electron Microscopy measurements, including electron energy loss spectroscopy, energy dispersive x-ray analysis, and selected area diffraction patterns, determine whether impurities were introduced by the selective doping process and whether the damage removal processes were able to remove growth and implantation-induced defects. A better understanding of the roles of defects on device performance is based on these techniques.
Constrained Optimization of Proton Exchange Membrane Fuel Cells Using a Finite Element Approach
Authors: Lamb James , Andrei Petru
Published: February 2020

Our group has recently proposed a large scale optimization technique for computing the optimum distribution of platinum particles in proton exchange membrane fuel cells (PEMFCs) [1]. The basic idea of the technique was to use the adjoint method to compute the catalyst sensitivity functions and to introduce these functions in a gradient-based algorithm to estimate the optimum catalyst distribution in the catalyst layers [2]. In our previous work, constraints were taken into consideration using the formalism of Lagrange multipliers on the functional space of possible catalyst distributions [3]. Although robust, this approach was restricted to equality constraints and could not be applied to the more general case in which constraints enter as inequalities in this optimization function.

In this work we will present a new optimization method for PEFMCs that includes inequality constraints. The method is still based on the computation of the catalyst sensitivity functions using the adjoint method but allows the optimizer to search for solutions away from the boundaries imposed by the constraints. By using this method, we are able to compute the global optimum platinum distribution inside the catalyst layer. In addition, we extend the method to the calculation of the optimum porosity and Nafion distribution in the gas diffusion and catalyst layers, respectively. Details about the numerical implementation of the method and sample optimization results will be presented and compared to previous results at the meeting.

References

[1] J. Lamb, G. Mixon and P. Andrei, “Adjoint Method for the Optimization of the Catalyst Distribution in Proton Exchange Membrane Fuel Cells”, Journal of the Electrochemical Society, 164, E3232 (2017).

[2] J. Lamb, G. Mixon, and P. Andrei, “Mathematical Optimization of the Spatial Distribution of Platinum Particles in the Catalyst Layer of PEMFCs”, ECS Transactions 2017 77(11): 1179-1196.

[3] J. Lamb and P. Andrei, “Analysis of Sensitivity of PEMFC Parameters to Non-Uniform Platinum Deposition Diagnostics and Characterization Methods”, ECS Transactions 2017 80(8): 291-300.
Understanding Pyrolysis of PGM-Free Electrocatalysts with X-Ray Computed Tomography
Authors: Huang Ying , Shum Andrew , Rezaei Talarposhti Morteza , Asset Tristan , Parkinson Dilworth Y. , Barnard Harold , Atanassov Plamen , Zenyuk Iryna V.
Published: February 2020

Atomically dispersed Fe-N-C electrocatalyst is the emerging advanced type of PGM-free catalyst. Its activity arises from a multitude of active sites, often viewed as co-catalytic (bifunctional sites), such as atomically-dispersed iron in nitrogen coordination (FeNx) and pyridinic and pyrrolic nitrogen moieties in graphene structures. The synthesis of Fe-N-C electrocatalysts involves a pyrolysis step, for which physical and chemical transformations are not well understood. Various ramps and temperature holds are currently used to evaporate precursors and solvents and to achieve the electrocatalyst’s high electric conductivity. An additional pyrolysis step, termed second pyrolysis, is sometimes used. Recipes exist with the pyrolysis of various precursors to arrive at catalyst that contains a high content of nitrogen. Here, Fe(NO3)3 .9 H2O and an aromatic amine charge-transfer organic salt, nicarbazin, was used. Custom pyrolysis furnace built by the Advanced Light Source’s (ALS) 8.3.2 beamline scientists was used that was capable of having gas circulation, high temperature and, at the same time, a rotating stage for x-ray computed tomography (CT) imaging. After ball-milling, the sample was placed on a ceramic stage of the vertical furnace with a circulating gas mixture of nitrogen and 7 % hydrogen. The catalyst was inserted at 525°C and then furnace temperature was increased; first to 900°C in 12 min (31.25 °C/min) and then to 975°C in 8 min (9.375 °C/min). After a 45 min hold time, the catalyst was removed from the furnace. Seven X-ray CT scans were performed during this pyrolysis process. This is the first study to use micro X-ray CT to observe the morphological changes of a catalyst powder during a pyrolysis process. Figure 1 shows the schematic of the stage, the quartz tube used to seal the gases and the ceramic stage for the catalyst placement. A photograph of our mounted catalyst within the pyrolysis chamber on the rotating stage is shown by Figure 1b and a temperature profile by Figure 1c. We have found that most of the changes in the catalyst morphology happen during the temperature ramp to 975oC and during cool down. The temperature hold at 975°C did not result in significant powder morphological changes. A follow-up study was conducted where the temperature ramp was studied in more detail with X-ray CT scans taken every 100°C. Furthermore, a second pyrolysis study was conducted where morphological changes were not observed.

Figure 1. a) Schematic of pyrolysis stage and gases circulation, b) a photograph of our sample mounted within the pyrolysis chamber at 8.3.2 ALS during imaging, c) the temperature ramp during pyrolysis and d) the evolution of catalyst morphology during temperature ramp.

Figure 1
Effect of Cathode Catalyst Layer Structure on the Performance of PEFC
Authors: Heggo Dalia , Ma Yulei , Balci Beste , Kageyama Miho , Yamaguchi Kazuhiro , Kawase Motoaki
Published: February 2020

One of the routes to promote PEFC commercialization is to reduce its manufacture cost. Platinum represents more than 50% of PEFC cost. Therefore, two targets can be considered; reduction of platinum loading (g/cm2) at cathode, and increase specific catalytic activity towards reaction (mA/cm2
pt).

On the other hand, the effectiveness factor has an inherent relation with current density and mass transfer of reactants (oxygen and proton), which are existing simultaneously. For investigating cathode behavior, two dimensionless moduli, representing diffusion limitations due to oxygen and proton mass transfer resistances, have been proposed 1.

To estimate mass transport resistances, effectiveness factor and intrinsic reaction rate constant, experiments were carried out by varying cathode catalyst layer (CCL) structure on a membrane electrode assembly (MEA). The MEA, fabricated by decal transfer method, consisted of a Nafion membrane (NR-212, 50 μm) with Pt/C weight ratio of 0.3, 0.4 and 0.5 in 10 μm CCL. The ionomer (I)/C ratio was 1. The CCL was prepared by two methods. The first, Pt particles were supported on carbon (Ketjen black) relevant to the required Pt/C ratio (Standard catalyst preparation). The second, lower Pt/C ratios were manipulated by adding carbon black (CB) to a prepared catalyst mixture contained 50% Pt/C where Pt loading was 0.3 mg/cm2 (CB dilution method). The IR corrected voltage (electromotive force) was calculated by measuring the polarization curves and membrane resistance using an electrochemical measurement system. The impedance spectra were measured in a range of frequency from 10 mHz to 100 kHz.

The analysis of the results using our dimensionless moduli approach may support having deeper insight that could accelerate the development of PEFC.

Reference:

M. Kawase et al., AIChE J., 63, 249–256 (2017) http://doi.wiley.com/10.1002/aic.15545.

Figure 1
New Hydrogen-PEMFC Portable System and Applications
Authors: Ferreira-Aparicio Paloma , Molinero Antonio , Oller Juan Carlos , Barcala José Miguel , Santamaría Santiago , Serrano José Luis , Chaparro Antonio M
Published: February 2020

Hydrogen portable applications may overcome shortcomings of batteries especially concerning autonomy and safety. On the other hand, energy systems based on fuel cells and hydrogen are more complex and voluminous, compared with battery systems where the energy storage and power consumption are integrated in the same device. It is for this reason that fuel cells for portable applications require new architectures and working conditions that allow minimizing system requirements without the loss of efficiency.

This communication will show new developments for hydrogen portable applications, concerning cell configuration, stacks, and systems, in order to improve portability and efficiency and decreasing fuel cell system consumption. The cells are able to work under full passive conditions, without the aid of fans and purging valves. The stack configuration allows easy integration, repairing, and dismantling of single cells without affecting the other cells. Power generation systems have been developed based on boost converter electronic and the integration of supercapacitors to provide short events of high power demands to the applications. Results of system behavior and response in real applications will be shown.

Acknowledgements.

This work was supported by the Ministerio de Economía y Competitividad of Spain, and Fondo Europeo de Desarrollo Regional (FEDER), Project E-LIG-E, ENE2015-70417-P (MINECO/FEDER).

Figure 1
Effect of Side Chain Length in Phosphoric Acid Based Membranes on Nanophase-Segregation and Transport
Authors: Lawler Robin , Caliendo Charles , Jang Seung Soon
Published: February 2020

Due to the high conductivity and stability, perfluorinated sulfonic acid (PFSA) proton exchange membranes such as Nafion are currently the standard for polymer electrolyte membranes (PEMs). While boasting superior conductive properties at standard conditions, Nafion dehydrates at high temperature and low humidity, drastically compromising its performance. While functionalization of PFSA membranes with phosphoric acid has been shown to improve conductivity under low-humidity conditions, these membranes still require optimization as they lack a practical level of conductivity. In this study, we use computational methods to investigate the nanophase-segregation and transport in phosphoric acid membranes in comparison to Nafion membranes, and analyze the effect of side chain length on these two properties. It is found that, as in sulfonic acid membranes, larger water clusters are formed in phosphoric acid membranes with longer side chains. However, unlike in sulfonic acid membranes, the phosphoric acid groups associate closely with one another via hydronium bridging, which suppresses proton hopping. Therefore, it is inferred that the proton transport is decreased with increasing the phosphoric acid side chain length. Based on these results, we recommend opting for shorter side chain lengths when designing phosphoric acid membranes.
Ionic Liquid Interlayer for Enhanced Oxygen Reduction Reaction Electrocatalyst Activity and Durability
Authors: Snyder Joshua David , Li Yawei
Published: February 2020

After a period of dynamic advancement in oxygen reduction reaction (ORR) electrocatalyst activity, through the development of unique material nano-architectures and compositional gradients, we have seen a stagnation in the general performance metrics, especially at the membrane electrode assembly (MEA) level. We argue that in order to push past our current plateau, we must look beyond the catalyst material and develop strategies to manipulate and optimize the interface between the catalyst and the aqueous electrolyte. Here we will present our work in the development of ionic liquid interlayers, on the order of 1 nm in thickness, on nanostructured and single crystal electrocatalysts, which are found to yield significant enhancements in both ORR activity and durability. It is through the manipulation of interfacial water, due to the presence of the hydrophobic/protic ionic liquid interlayer, that a more optimal solvation of adsorbed intermediates is achieved, resulting in enhanced ORR activity, and a relative decrease in the oxophilicity of the surface, enhancing the potential dependent stability of the catalyst. Additionally, the low metal ion solubility within the ionic liquid interlayer increases the barrier for metal dissolution. We will present our analysis of the mechanism of activity and durability enhancement as well as demonstrate the unique advantages of ionic liquid interlayers in proton exchange membrane fuel cell (PEMFC) MEAs.
Highly Stable Polybenzimidazole (PBI) Grafted graphene As Catalyst for Polymer Electrolyte Membrane Fuel Cells
Authors: Li Chenzhao , Liu Yadong , Yu Kang , Xie Jian , Ferreira Paulo Jorge
Published: February 2020

Graphene is a single atomic-tick graphite layer. The carbon atoms in the graphene plane are saturated due to the bonding structure: each has 3 covalent bonds with three neighboring carbon atoms in the graphene plane, the lone px

e-
form a long range conjugated system, a big π bond. This leads to some unique properties: excellent electric conductivity and chemical stability, which are critically needed for catalyst supports in polymer electrolyte membrane fuel cells (PEMFCs).[1] The catalyst support stability plays a significant role in determining the overall durability of PEMFC systems when PEMFCS are subjected to very high potential cycling , for example, from 1 V to 1.5 V. However, there are three major obstacles for graphene supported Pt based catalysts in PEMFCs: 1) there are limited bonding sites for catalyst landing on the graphene basal plane, which lead to migration/aggregations of Pt nanoparticles when subjected to harsh accelerated durability tests (ADTs); 2) it is very difficult for Nafion ionomer particles and graphene based catalyst mixing together to form a uniform catalyst ink, which results in the poor catalyst/ionomer interface. 3) For MEA preparation using ink spraying method, when ink is dried, the π-π interaction makes 2D graphene sheets easily restacking back to graphite structure, which could severely block the mass transport of gas and water, leading to poor MEA performance at high current.

To overcome these barriers, we propose a novel approach to transfer the 2D graphene sheets into 3D composite with sufficient channels and pores for facile mass transport. This is realized by developing the highly stable hierarchical polybenzimidazole (PBI) -grafted nano-graphene supported Pt catalysts for PEMFCs and applying spacers during ink formulation. Nano- graphene, comparing with normal graphene, has smaller dimensions as the catalyst supports, which makes the pores/channels between graphene sheets much shorter, facilitating the mass transport. It is expected to see some extra voltage gains at the high current density.

In order to construct appropriate pore structures in the catalyst layers, spacers are introduced. However, although the initial performance somehow increases with such modification, yet the support durability remains same and to some extents, decrease little bit. In this case, the hypothesis raised that during durability test, the spacers themselves are corroded and graphene sheets are restacked. To overcome this barrier, we apply more stable spacer that match the durability of graphene. Nano-silicon powder is very stable during voltage scan between 1.0V to 1.5V but is not conductible. To remedy this drawback, we coat highly graphitized carbon over its surface, which gives very promising durability and conductivity for overall MEA electrode.

[1]. Geim, A. K.; Novoselov, K. S. Nat. Mater. 2007, 6, 183
Preparations of Highly Active Pd-Based Order Intermetallic Compounds and Relationship between Surface Structure and Electrocatalytic Activity
Authors: Gunji Takao , Matsumoto Futoshi
Published: February 2020

Pd-based structurally ordered phase nanoparticles (NPs)/carbon black (CB) were successfully prepared by reduction of precursors of Pd and secondary materials using ethylene glycol as a reducing agent and an annealing procedure. In one of our studies, we developed structurally ordered intermetallic PdCu3 which has Cu3Au type structure electrocatalysts with excellent ORR activity in acidic media. High electrocatalytic activity of ordered intermetallic PdCu3 was inspired by electrochemically dealloy process. This electrochemical phenomenon on high catalytic activity was discussed by both density functional theory calculations and X-ray photoelectron spectroscopy. In this poster session, we have summarized our recent results.
One-Step Synthesis of Manganese Doped Single Atom Catalysts for Oxygen Reduction Reaction in Polymer Electrolyte Membrane Fuel Cells
Authors: Stracensky Thomas Stephen , Ding Shuo , Lattimer Judith , Mukerjee Sanjeev , Xu Hui
Published: February 2020

Current commercial catalysts for polymer electrolyte membrane fuel cells (PEMFCs) require platinum group metal (PGM) catalysts that lead to high costs, thus preventing viable commercialization of PEM fuel cells. Many investigations into PGM-free catalysts have led to the identification of single metal atom sites coordinated with 4 nitrogens as being highly active. One of the best performing metal centers in the acidic environment of the PEMFC is Iron (Fe). Highly active iron-based catalysts have been synthesized easily via a one-step method of doping Iron into a ZIF-8 framework; however, there have been membrane degradation concerns due to the Fenton reaction products that are generated by Fe. Manganese (Mn) has recently been proposed as a potential metal center for the highly active metal-N4 catalyst site as theory predicts that it will have good activity and increased stability1 .

The best performing Mn-based catalysts have been synthesized from a Mn doped ZIF-8 structure, but due to the high oxophilicity of Mn and difficulty in incorporating Mn into the ZIF structure, a laborious Mn catalyst synthesis route has been adopted, which requires acid leaching, secondary doping, and multiple pyrolysis steps2. This causes problems in scaling up the synthesis and limits the active site density when compared to the Fe catalyst.

We aim to use highly reactive Mn metal precursors in an air-free environment to incorporate Mn into the metal sites of ZIF. High temperature pyrolysis (1100°C) leads to manganese catalyst synthesis in one step.

We show that using a highly active manganese borohydride precursor allows for the formation of a metal organic framework (MOF) when combined with 2-methylimidazole, which can subsequently be pyrolyzed to form the target catalyst. Using zinc borohydride as a secondary metal source we can also form bimetallic MOF structures with increased thermal stability and varied Mn loading. With this strategy Mn can be incorporated directly into the metal MOF sites with a wide range of Mn loading. The utilization of an air-free environment prevents metal oxide formation thus giving a facile one step synthesis of a manganese-based catalyst.

(1) Liu, K.; Qiao, Z.; Hwang, S.; Liu, Z.; Zhang, H.; Su, D.; Xu, H.; Wu, G.; Wang, G. Mn- and N- Doped Carbon as Promising Catalysts for Oxygen Reduction Reaction_ Theoretical Prediction and Experimental Validation. 2018.

(2) Li, J.; Chen, M.; Cullen, D. A.; Hwang, S.; Wang, M.; Li, B.; Liu, K.; Karakalos, S.; Lucero, M.; Zhang, H.; et al. Atomically Dispersed Manganese Catalysts for Oxygen Reduction in Proton-Exchange Membrane Fuel Cells. Nat. Catal.
2018, 1 (12), 935–945.
A Synthesis of Efficient Composite Catalyst Based on Fe-N-C Catalyst and Platium for Oxygen Reaction Reduction
Authors: Zhang Xuelin , Hou Chenjun , Zhang Yujun , Zhang Yufeng , Liu Xiaowei
Published: February 2020

Globally, because of the consumption of fossil fuel, the proton exchange membrane fuel cells (PEMFC) have received great attention. Among them, direct methanol fuel cells(DMFC) have been applied into many fields, such as computers, global positioning systems(GPS) and portable devices. Platinum catalysts are considered as one of the most efficient catalysts for the oxygen reduction reaction(ORR),which is one of the most essential processes for the DMFC. However, the low methanol resistance limits the application of Platinum catalyst in DMFC. Fe-N-C catalyst has an excellent methanol selectivity and showes a good ORR activitity with great potential as a non-precious metal catalyst. However, the performance of Fe-N-C catalysts is impossible to exceed that of Pt-based catalysts, leading to the irreplacebility of Pt catalyst in DMFC.As a result, the composite catalyst made by Fe-N-C catalyst and Platnum catalyst was synthesized and expected to take advantage of the high methanol resistance of Fe-N-C catalyst and brilliant ORR activity of Platinum catalyst.

Herein, we reported a synthesis of an efficient composite catalyst based on Fe-N-C catalyst and Pt catalyst. The Fe-N-C catalyst was gained as described by Piotr Zelenay. Furthermore, 50mg Fe-N-C catalyst dissolved into 12ml isopropanol and 48ml ethanediol was fixed with 4.42ml H2PtCl2-ethanediol solution with a density of 20mg/ml and stirred for 3h. After making the pH of the solution 12 by 1M NaOH-ethanediol and N2 injection for 10 min, the solution was put into the microwave to heat until 130-150 degrees. After cooling to the room temperature, the pH was set as 3 by 1M HNO3. The FeNC-Pt catalyst was obtained after filtration and freeze drying.

For RDE tests on the FeNC-Pt catalyst, the ink was prepared by mixing 3mg catalyst dissolved into 2.1ml isopropanol and 29µl Nafion, which was stirred for 40min to achieve a good dispersion. 7µl ink was coated on the surface of RDE, making the loading of Pt 20µg cm-2. The linear sweep voltammetry(LSV) tests were conducted at the speed of 1600rpm in O2 and N2 saturated 0.1M HClO4 solution respectively. The half-wave potential of FeNC-Pt catalysts was about 20mV higher than Pt-C catalyst(0.86V vs 0.84V), which proved a more efficient performance of FeNC-Pt catalyst. The electrochemical areas(ECA) of the catalysts were gained by cyclic voltammetry(CV) tests, and the FeNC-Pt catalyst showed a larger ECA than the Pt-C catalyst. The methanol resistance test was conducted in N2-saturated 0.5M H2SO4-0.5M CH3OH solution, and the FeNC-Pt catalyst showed a better performance.

Figure 1
Fe-N-C with Ultra-Low Pt Content Electrocatalyst for the Oxygen Reduction: Investigation of the Electrocatalytic Activity and Stability
Authors: Vasconcellos Carlos S. , Aggio Ricardo B , Galiote Nelson Alexandre , Lima Fabio H. B.
Published: February 2020

The high platinum loadings in the cathode is a critical obstacle for the commercialization of H2/air PEM fuel cells. Earth-abundant Fe-N-C electrocatalysts are under focus due to their high electrocatalytic, but this material suffers from poor stability due to the carbon corrosion by the undesired H2O2 species that are formed in parallel to H2O1. Herein, Fe-N-C was utilized as support for the deposition of ultra-low amounts of Pt nanoparticles2,3. The obtained results showed an oxygen reduction activity very similar to the state-of-the-art carbon-supported platinum (20 wt.%), and a considerable increase in the stability when compared to pure Fe-N-C. The main features that control the stability of the synthesized electrocatalyst is discussed in this study. The results from this investigation may contribute to further advance in the development of cost-effective and durable ORR electrocatalysts for PEM fuel cells.

References

M. Ferrandon, X. Wang, A. J. Kropf, D. J. Myers, G. Wu, C. M. Johnston, P. Zelenay, Electrochim. Acta 110 (2013) 282 – 291.

A. K. Mechler, N. R. Sahraie, V. Armel, A. Zitolo, M. T. Sougrati, J. N. Schwammlein, D. J. Jones, and F. Jaouen, J. Electrochem. Soc. 165 (13) (2018) F1084 - F1091.

L. Chong, J. Wen, J. Kubal, F. G. Sen, J. Zou, J. Greeley, M. Chan, H. Barkholtz, W. Ding, D-J. Liu, Science 362 (2018) 1276–1281.

Acknowledgements

Authors gratefully acknowledge financial support from FAPESP (2013/16930-7, and 2016/13323-0), CNPq (306469/20162), and Capes.