bluuebunny/crossref_metadata_2025 huggingface dataset:
Graphene-Supported ' Core-Shell ' Carbon Nitride Fe- and Sn-Based Electrocatalysts for the Oxygen Reduction Reaction (ORR)
Authors: Bach Delpeuch Antoine , Negro Enrico , Vezzù Keti , Nawn Graeme , Bertasi Federico , Pagot Gioele , Di Noto Vito
Published: February 2020

One of the major obstacles for the development of feasible low-temperature fuel cells (e.g., proton-exchange membrane fuel cells, PEMFCs, and anion-exchange membrane fuel cells, AEMFCs) is the sluggishness of the oxygen reduction reaction (ORR) kinetics. As of today, carbon-supported Pt-based nanocrystals are the most efficient electrocatalysts (ECs) for the ORR. However, the low abundance of platinum and the insufficient durability of these ECs, which results from the degradation of the carbon support, constitute some of the major obstacles for large-scale commercialization of PEMFC and AEMFC technology [1, 2].

In this study, new "Pt-free" electrocatalysts are prepared and studied for the ORR process. These ECs consist of alloyed Fe-Sn nanoparticles embedded in a carbon nitride “shell” a few nanometers thick, supported on conducting micrometric graphene sheets that act as the “core”. The electrocatalytic precursors are prepared by a sol-gel/gel-plastic process following a protocol previously developed in our laboratory [3]; afterwards, they undergo suitable pyrolysis and activation processes. The proposed electrocatalysts, both pristine (e.g., FeSn0.5-CNl 900/Gr) and activated (e.g., FeSn0.5-CNl 900/Gra) are extensively characterized in order to gain a full understanding of their structural features, proprieties and electrocatalytic performance [4]. The chemical composition is determined by inductively-coupled plasma atomic emission spectroscopy (ICP-AES). The structure is elucidated by powder X-Ray diffraction (XRD); the morphology is inspected by high-resolution scanning electron microscopy (HR-SEM) and high-resolution transmission electron microscopy (HR-TEM) (Fig. 1). Finally, “ex situ” cyclic voltammetry with the rotating ring-disk electrode (CV-TF-RRDE) and “in situ” single fuel cell measurements are carried out to evaluate the electrocatalytic performance as well as to study the ORR mechanism. The preliminary CV-TF-RRDE investigations in an alkaline medium exhibit promising results. Indeed, the catalysts exhibit an overpotential ca. 70 mV higher with respect to a 20 wt.% Pt/C reference (Fig. 2).

Acknowledgements

The authors would like to thank the European Union for the financial support provided by the GRAPHENE Flagship, project “GRAFUS - Graphene and related materials as supports for innovative metal carbon nitride electrocatalysts for anion-exchange membrane fuel cells”.

REFERENCES

[1] R. Othman, A. L. Dicks, Z. Zhu, Int. J. Hydrogen Energy
37, 357 (2012).

[2] S. Zhang, X.-Z. Yuan, J. N. C. Hin, H. Wang, K.A. Friedrich, M. Schultze, J. Power Sources
194, 588 (2009).

[3] V. Di Noto, E. Negro, R. Gliubizzi, S. Lavina, G. Pace, S. Gross, C. Maccato, Adv. Funct. Mater.
17, 3626 (2007).

[4] V. Di Noto, E. Negro, S. Polizzi, F. Agresti, G.A. Giffin, ChemSusChem
5, 2451 (2012).

Figure 1
Corrosion Protection of Silicon Micro Systems with Ultra-Thin Barrier Films for Miniaturized Medical Devices
Authors: Herrera Morales Jorge Mario , Souriau Jean-Charles , Simon Gilles
Published: February 2020

Miniaturized medical devices are becoming increasingly adopted by doctors and patients because they enable new treatment and monitoring capabilities, minimally invasive surgery, improved portability and ease of use. Recent examples include micro pacemakers, micro cochlear implants and ex-situ micro glucose sensors. However, implantable micro devices employing packaging technologies other than metallic enclosures are yet to be seen. Such metallic containers are expensive and can make up to 80% of the volume of the final medical micro device. Physiological monitors such as in-situ pressure sensors and BioMEMS could profit significantly from advances in thin barrier films for corrosion protection of silicon micro devices. Coating films that stop the diffusion and permeation of harmful substances are necessary to protect both the patient and the micro device. Ceramic films deposited by chemical vapor deposition techniques are good candidates for this task due to their low permeability to gases, low chemical reactivity and high conformality. However, few studies are available about the corrosion protection offered by biocompatible coatings to microelectronic devices in representative biological environments. Nine materials previously found non-cytotoxic in-vitro were studied: Al2O3, BN, DLC, HfO2, SiC, SiN, SiO2, SiOC, and TiO2. Ultra-thin films of these materials (5-100 nm) were deposited by plasma enhanced chemical vapor deposition (PECVD) or atomic layer deposition (ALD) on substrates commonly found in electronic micro devices: crystalline silicon, copper, tungsten nitride and polyimide. Characterization of films was performed by x-ray photo electron spectroscopic (XPS), x-ray diffraction (XRD), x-ray reflectometry (XRR), atomic force microscopy (AFM), variable angle spectroscopic ellipsometry (VASE) and helium gas permeability measurements. Aging tests of silicon, copper and tungsten nitride substrates coated with these films were performed for several weeks at different temperatures in phosphate buffer saline (PBS), a saline solution that simulates the chemical environment of human blood plasma. Changes in thickness and chemical composition were monitored by VASE, XPS and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). It was found that SiO2 and SiN films (generally used for protection in the microelectronics industry) are not stable in PBS at 37°C, even though they act as good hermetic barriers against gases. In contrast, films of Al2O3, DLC, SiOC and TiO2 showed very low chemical reactivity in PBS, and one of them was effective as hermetic and diffusion barrier for the corrosion protection of metallic substrates of interest for silicon micro systems. A discussion on the advantages and disadvantages of deposited films and recommendations for corrosion protection of miniaturized medical devices are also included.
Towards Realizing Wearable Batteries: Dual Ion Prussian Blue Analog/Zinc Battery Architecture with Long Cycle Life and High Energy Efficiency
Authors: Gupta Tanya , Kim Andrew , Biswas Shaurjo , Steingart Daniel A
Published: February 2020

In recent years Prussian Blue Analogues (PBA) have attracted a lot of interest as a battery material due to their relative safety to skin contact and exceptionally high cyclability. Their open cage structure allow a variety of ions to shuttle in and out and thus store energy. This can be done very rapidly as there is no phase change associated with this process, which makes them stable for over thousands of cycles.(Pasta et al. 2012) Recent developments in this field show the use of zinc to act as the anode, which can exhibit a PBA vs. Zn cell potential as high as 1.7 V. But the performance of such a system reported thus far show less than 10% cycle life as that of  highly reversible PBA half cells. (Zhang et al. 2014)

In this work we demonstrate a high potential aqueous Sodium ion battery with high cycle life, to achieve as much as 500 cycles with over 80% cell capacity retention, which is five times of the maximum reported in literature. (Trócoli and La Mantia 2015)The high potential of Zn and high reversibility of Na+ ion cycling in Copper Hexacyanoferrate lattice is exploited in making a considerable improvement over previous Zn/ Zinc Hexacyanoferrate system. We validate the hypothesis that the slow kinetics of zinc intercalation compared to sodium in Hexacyanoferrates enables preferential intercalation of sodium ions and hence reduce zinc poisoning. We further show the use of Hyper Dendritic Zinc (HD Zn) to improve capacity retention and overall kinetics of the system. Prussian Blue has been used as a fabric dye for over 80 years. The relative safety of the dual ion PBA/HD Zn system that we demonstrate helps us step closer to realizing batteries on fibers woven integrated with wearable electronics.
Metal Oxides Nanoparticles Encapsulated in 3D Porous Carbon Microspheres for High Performance Lithium Storage
Authors: Li Ying , Liu Lianjun
Published: February 2020

Nanostructured metal oxides (e.g., ZnO, CoO, SnO2) have been considered as alternative anode materials for next-generation of lithium-ion battery (LIB) because of their higher reversible capacities (500–1500 mAh g−1) than conventional graphite of 372 mAh g−1. However, the metal oxide particles suffers from fast capacity decay due to its poor electrical conductivity, limited ions transport kinetics, serious aggregation, and large volume expansion (> 200%) and contraction during the charge/discharge process. To address these issues, we synthesized novel 3D porous carbon microspheres (PCM) from low cost raw materials (i.e., sucrose) via a spray pyrolysis method, and developed a new architecture of metal oxides nanoparticles decorated into the PCM by a simple one-pot hydrothermal method. The developed metal oxide/PCM hybrids (e.g., SnO2@PCM, ZnO-CoO@PCM) demonstrated a high reversible capacity, good rate performance, and excellent cycling stability. The superior electrochemical performance is because (1) the continuous and large surface area carbon framework greatly enhanced the electrical conductivity and dispersion of metal oxides nanoparticles, (2) the porous structure with multi-modal pores could warrant good electrolyte diffusion and fast li-ion transport and provide sufficient space to buffer the large volume expansion of the metal oxides,and (3) the nano-sized metal oxide particles (less than 10 nm) are uniformly confined in the pores that avoid the strong aggregation. Our low-cost, eco-friendly and multifunctional materials may hold a significant promise for the construction of advanced electrodes for high performance energy storage devices.Furthermore, the 3D porous nanocomposite architecture could shed light on the design and synthesis of other advanced electrodes for energy conversion and storage.
A Hybrid Dual-Type Sulfur Cathode and a Lithiated Si/SiOx Nanosphere Anode for Li-Sulfur Full Cells
Authors: Lee Sang-Kyu , Park Eunjun , Scrosati Bruno , Hassoun Jusef , Park Min-Sik , Kim Young-Jun , Kim Hansu , Belharouak Ilias , Sun Yang-Kook
Published: February 2020

Lithium−sulfur batteries could become an excellent alternative to replace the currently used lithium-ion batteries. 1 The natural abundance and low cost of sulfur, coupled with the high theoretical energy density of sulfur-based cathodes, namely, 1675 mAh g-1 and 2600 Wh kg-1, are the major advantages of this sulfur battery.2 However, commercialization of lithium−sulfur batteries has so far been limited due to the cyclability problems associated with both the sulfur cathode and the lithium−metal anode.3 Herein, we demonstrate a highly reliable lithium−sulfur battery showing cycle performance comparable to that of lithium-ion batteries; our design uses a highly reversible hybrid dual-type sulfur cathode (solid sulfur electrode and polysulfide catholyte) and a lithiated Si/SiOx nanosphere anode. Our result shows superior battery performance in terms of high specific capacity, excellent charge−discharge efficiency, and notable cycle life, delivering a specific capacity of ∼750 mAh g−1 over 500 cycles (85% of the initial capacity). These promising behaviors may arise from a synergistic effect of the enhanced electrochemical performance of the newly designed anode and the optimized layout of the cathode.

References

1. B. Scrosati, J. Hassoun, Y-K. Sun, Energy Environ. Sci., 4, 3287 (2011).

2. E. Peled, A. Gorenshtein, M. Segal, Y. Sternberg, J. Power Sources, 26, 269 (1989).

3. Y-V. Mikhaylik, J. R. Akridge, J. Electrochem. Soc., 151, A1969 (2004).
(Invited) Wide Bandgap (WBG) Power Switching Devices for Distributed Clean Energy Systems
Authors: Shenai Krishna
Published: February 2020

The increased availability of clean and renewable distributed energy at low cost is dramatically changing the way in which 21st century human endeavors are carried out. The impending global warming and climate change are accelerating the development and deployment of environmentally friendly energy technologies in all walks of human life. Solid-state power electronics is a key enabler of emerging global energy economy. This paper will identity the opportunities and challenges in wide bandgap semiconductor materials manufacturing, product design and system integration when developing next generation of energy and power systems for terrestrial and space applications.
(Invited) Characteristics of a Wire-Bonding-Less SiC Power Module Operating in a Wide Temperature Range
Authors: Sato Shinji , Tanisawa Hidekazu , Anzai Takeshi , Takahashi Hiroki , Murakami Yoshinori , Kato Fumiki , Watanabe Kinuyo , Sato Hiroshi
Published: February 2020

Introduction

Using high-speed switching, wide bandgap semiconductor devices can reduce on-resistance in the on-state to realize low power converter losses. In addition, SiC power devices can be operated in high temperatures; thus, their cooling systems can be reduced in size or removed all together, thereby increasing the power density of the power converter. In this study, we designed and fabricated a SiC power module with a built-in snubber circuit. This power module is operable in high temperatures over 200 degrees C.

Design of Power Module for High-Temperature Operation

The manufactured power module, its components, and its circuit diagram are shown in Fig. 1. The module size is 30 × 44 × 29 mm3. Active metal brazing copper (AMC) substrates sandwich the four SiC-metal–oxide–semiconductor field-effect transistors (MOSFETs) in this structure. Two AMC substrates connect via the metal block. The C–R  snubber circuit is built-in on the surface of AMC1 (Fig. 1(b)). The SiC-MOSFET and AMC1 are joined by a flip-chip-bonding technique using an Al bump. The others are joined by Au–Ge solder. Fig. 2 shows the 50-kHz switching waveforms. Fig. 3 shows the circuit configuration for the Fig. 2 waveforms. This power module can realize high-speed switching in a fall time tf @ 25 ns. Surge voltage and ringing are suppressed by the built-in snubber circuit.

Acknowledgment

This work was supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), "Next-generation power electronics/Consistent R&D of next-generation SiC power electronics", and "the Novel Semiconductor Power Electronics Project Realizing Low Carbon Emission Society" (funding agency: NEDO).

Figure 1
(Invited) High Performance Deep Ultraviolet Nanowire Light Emitting Diodes and Lasers
Authors: Mi Zetian , Zhao Songrui , Liu Xianhe
Published: February 2020

Deep ultraviolet light sources are important for a broad range of applications including water purification, disinfection, and medical diagnostics. The currently reported AlGaN planar light emitting diodes (LEDs) and lasers generally exhibit poor performance, due to the presence of large densities of defects and dislocations and the inefficient p-type doping. In this context, we have investigated the molecular beam epitaxial growth and characterization of nearly defect-free AlGaN nanowire heterostructures grown directly on Si substrate. We have demonstrated AlGaN nanowire LEDs that can operate in the UV-B (280-320nm) and UV-C (<280 nm) bands, which exhibit excellent current current-voltage characteristics. We have further demonstrated electrically injected AlGaN nanowire lasers on Si that can exhibit relatively low threshold current densities (~ 100 A/cm2).

In this work, catalyst-free AlGaN nanowires were grown directly on Si substrate by radio-frequency plasma-assisted molecular beam epitaxy. Due to the diffusion controlled growth process, such self-organized AlGaN nanowires exhibit unique core-shell structures, with the presence of Al-rich AlGaN shell. As a consequence, the nonradiative surface recombination can be greatly suppressed. By varying the Al/Ga flux ratio during the growth process, the emission wavelengths can be controllably varied from ~ 210 nm to >340 nm. The nanowire heterostructures exhibit relatively high internal quantum efficiency (~ 80%) at room-temperature in the UV-C band. We have further identified that Mg-dopant incorporation can be significantly enhanced in AlGaN nanowires, compared to their planar counterparts, due to the reduced formation energy for Al(Ga)-substitutional Mg-doping. The resulting AlN nanowire LEDs can exhibit excellent current-voltage characteristics, with a turn-on voltage of 6 V.

We have also demonstrated that self-organized AlGaN nanowire arrays can function as a high Q optical cavity, due to the Anderson localization of light. The AlGaN nanowire lasers consist of n-AlGaN cladding layer, i-AlGaN active region, and p-AlGaN cladding layer. The devices were fabricated using standard photolithography and metallization techniques. Under continuous wave biasing conditions, the devices can exhibit very low threshold current density. For devices operating in the UV-AII (~ 320-340 nm) band, the threshold current density is ~ 12 A/cm2 at 6 K. The threshold current density increases slightly to ~ 200 A/cm2 for operation wavelengths in the UV-C band. The measured threshold current densities are nearly two to three orders of magnitude lower, compared to conventional AlGaN quantum well lasers under either optical pumping or electrical injection.
(Invited) Band Gap Tunable Monolayer WSe2(1-x)S2x Synthesis, Characterization and Device Applications
Authors: Xiang Bin , Huang Jian , Yang Lei , Fu Qi
Published: February 2020

“Band gap engineering” in two-dimensional (2D) materials plays an important role in tailoring their physical and chemical properties. The tuning of the band gap is typically achieved by controlling the composition of the semiconductor alloys.1-4 Here, we report the synthesis and electrical properties of monolayer WSe2(1-x)S2x. The photoluminescence (PL) spectroscopy results confirm the tunable band gap in WSe2(1-x)S2x, which is modulated by varying the S content. Atomic-scale analysis was performed and the chemical composition was characterized using high-resolution scanning transmission electron microscopy and X-ray photoemission spectroscopy. The mobility and carrier concentrations were measured in as-grown monolayer-based transistor devices. The emergency of these 2D materials provides grand possibilities for future semiconductor device applications.

References:

1. Q. Feng, Y. Zhu, J. Hong, M. Zhang, W. Duan, N. Mao, J. Wu, H. Xu, F. Dong, F. Lin, C. Jin, C. Wang, J. Zhang and L. Xie, Adv. Mater., 2014, 26, 2648–2653.

2. Y. Gong, Z. Liu, A. R. Lupini, G. Shi, J. Lin, S. Najmaei, Z. Lin, A. L. Elías, A. Berkdemir, G. You, H. Terrones, M. Terrones, R. Vajtai, S. T. Pantelides, S. J. Pennycook, J. Lou, W. Zhou and P. M. Ajayan, Nano Lett., 2014, 14, 442–449.

3. H.-P. Komsa and A. V. Krasheninnikov, J. Phys. Chem. Lett., 2012, 3, 3652–3656.

4. M. Zhang, J. Wu, Y. Zhu, D. O. Dumcenco, J. Hong, N. Mao, S. Deng, Y. Chen, Y. Yang, C. Jin, S. H. Chaki, Y.-S. Huang, J. Zhang and L. Xie, ACS Nano, 2014, 8, 7130–7137.
(Invited) Hybrid Two-Dimensional Nanosheet Materials for Energy Storage Devices
Authors: Peng Lele , Zhu Yue , Yu Guihua
Published: February 2020

Two-dimensional (2-D) materials have emerged as a promising material platform for next-generation energy storage and conversion devices. Owing to their advantageous features such as high mechanical flexibility, large surface area and open ion transport pathway within 2D layers, graphene and other 2-D metal oxides and metal phosphates based nanosheets materials have shown great promise in flexible high-density energy storage devices. In this talk we will discuss recent progress on graphene/inorganic based hybrid 2-D materials for high-performance energy storage devices including high-rate-capable Li-ion batteries and ultraflexible solid-state supercapacitors.
(Invited) Printed High Performance Flexible Device Sheet
Authors: Takei Kuniharu
Published: February 2020

Due to the unique properties of nanomaterials such as quantum effect, high performance, and mechanical flexibility, devices based on the nanomaterials have attracted great attention for a variety of applications. One of the potential application is for flexible electronics utilizing the characteristics of high performance and mechanical flexibility. By printing or transferring inorganic nanomaterials, high performance transistors and sensors can be readily fabricated on an amorphous sheet such as plastic substrate. However, the patterning methods of nanomaterials are still under development, and many approaches are conducted to make large-scale and uniform patterning on user defined substrates. To realize nanomaterial patterning on a flexible substrate, we have also developed some nanomaterial transfer and printing techniques depending on the dimensional structure of the materials. In this talk, flexible complementary metal-oxide-semiconductor (CMOS) circuits and some physical sensors are introduced using our printing methods. The devices are mainly fabricated by using inorganic nanomaterials. However, organic materials are also used for sensors. By combining both advantages of inorganic and organic materials, high performance transistors with high voltage gain and low power consumption and high sensitive sensors are demonstrated.
(Invited) Microscopic Studies of Black Phosphorus and Its Field-Effect Transistors
Authors: Pan Minghu , Yuan Hui , Xu Ya-Qiong , Zhou Zhixian , Meunier Vincent
Published: February 2020

An increasing number of alternative two-dimensional (2D) materials are being explored in the “post-graphene age”, such as transition metal dichalcogenides (TMDs), silicene, and germanene. These materials are studied with the hope of overcoming graphene’s deficiencies such as its zero bandgap. Among these 2D layered materials, layered black phosphorus (phosphorene) is expected to exhibit superior mechanical, electrical, and optical properties due to an intrinsic and tunable bandgap. It is, besides graphene, the only stable elemental 2D material that can be mechanically exfoliated. Its high hole mobility and direct semiconducting bandgap hold the hope for the development of new electronic devices in the postsilicon era. However, before phosphorene can be integrated in everyday electronics, many aspects of the material still remain to be elucidated. Here we report atomic scale studies of electronic variation related to strain-induced anisotropic deformation of the puckered honeycomb structure of freshly cleaved black phosphorus using a high-resolution scanning tunneling spectroscopy (STS) survey along the light (x) and heavy (y) effective mass directions. Through a combination of STS measurements and first-principles calculations, a model for edge reconstruction and the related edge states are also determined. Besides, we also investigate electrical transport and optoelectronic properties of field effect transistors (FETs) made from few-layer black phosphorus (BP) crystals down to a few nanometers. In particular, we explore the anisotropic nature and photocurrent generation mechanisms in BP FETs through spatial-, polarization-, gate-, and bias-dependent photocurrent measurements. Our results reveal that the photocurrent signals at BP-electrode junctions are mainly attributed to the photovoltaic effect in the off-state and photo-thermoelectric effect in the on-state, and their anisotropic feature primarily results from the directional-dependent absorption of BP crystals.

1. Liangbo Liang, Jun Wang, Bobby G. Sumpter, Vincent Meunier, and Minghu Pan, “Electronic Bandgap and Edge Reconstruction in Phosphorene Materials”, Nano Letters, 2014, 14 (11), 6400–6406

2. Tu Hong, Bhim Chamlagain, Wenzhi Lin, Hsun-Jen Chuang, Minghu Pan, Zhixian Zhou, and Ya-Qiong Xu, “Polarized Photocurrent Response in Black Phosphorus Field-Effect Transistors”, Nanoscale, 6, 8978-8983(2014).
(Invited) Ultrashort Channel Length Black Phosphorus Field-Effect Transistors
Authors: Miao Jinshui , Zhang Suoming , Cai Le , Wang Chuan
Published: February 2020

Layered black phosphorus (BP) is an emerging two-dimensional (2D) semiconductor with a decent bandgap and great mobility that bridges the gap between graphene (extremely high mobility, no bandgap) and transition metal dichalcogenides (low mobility, large bandgap). As a result, 2D layered BP has attracted significant amount of research interest recently as a promising candidate for high-performance ultimately-scaled electronic and optoelectronic devices. To the best of our knowledge, the smallest BP field-effect transistor demonstrated so far has a channel length of approximately 100 nm fabricated by electron beam lithography (EBL). It gets significantly more challenging to further scale down the channel length to below 100 nm due to the limitations in ebeam resist and lift-off process used.

In this paper, we report a novel and facile process combining EBL and angle evaporation to fabricate high-performance top-gated BP transistors with channel length down to 20 nm (the smallest 2D material transistor to date). By controlling the evaporation angle, the channel length of the transistors can be effectively and reproducibly controlled to be anywhere between ~20 to ~70 nm. With the high quality few-layer BP obtained from mechanical exfoliation and ultrashort channel length, such devices exhibit respectable on-current and transconductance up to 174 μA/μm and 50 μS/μm, respectively, at a small drain-to-source voltage of 100 mV. Owing to the use of 2D BP as the channel material, the transistors exhibit no obvious short channel effects, preserving a decent on-off current ratio of 102 even at extremely small channel lengths. Additionally, unlike the unencapsulated BP devices, which are known to be chemically unstable in ambient conditions, the top-gated BP transistors passivated by the Al2O3 gate dielectric layer remain stable without noticeable degradation in device performance after being stored in ambient conditions for more than one week. This work demonstrates the great promise of atomically thin BP for applications in ultimately-scaled transistors.
(Invited) Piezotronics in 1D/2D Nanomaterials for Active and Adaptive Nano-Electronics/Optoelectronics
Authors: Wu Wen Zhuo
Published: February 2020

New technologies for developing smart electronics and optoelectronics with tunable/adaptive functionalities are critical to emerging applications in wearable technology, advanced manufacturing, renewable energy, personal healthcare and environmental monitoring, which demand the active and adaptive interactions between devices and stimuli. Non-electrical stimuli are ubiquitous and abundant in the environment, such as mechanical agitation from human body. It is however not facile to directly interface them using the state-of-the-art silicon technology, in which the fundamental components performing intelligent-bearing operations are prevalently the field-effect-transistors (FETs). Piezoelectric effect has been widely used in sensing, actuation and energy harvesting. Conventional piezoelectric materials such as PZT and PVDF are insulating and therefore not feasible for constructing functional electronics or optoelectronics. The fundamental effect of piezoelectric polarization on charge carrier processes by dynamic perturbation, which has immediate relevance to the abovementioned emerging applications, has been long overlooked. Motived by these, my research has focused on exploring the emerging piezotronic effect, which is the modulation of charge carrier process by dynamic-strain-induced polarization, for nanoscale renewable energy and novel smart electronics/optoelectronics by rational design, manufacturing and integration of nanostructured piezoelectric semiconductors, e.g. 1D ZnO nanowires and 2D single-atomic-layer MoS2. I will discuss the fundamental of piezotronics and the updated progress of related applications. These studies provide the novel approach for modulating device characteristics by tuning the junction/contact properties, which has been unavailable in conventional technologies without modifying the interface structure or chemistry, and may open up opportunities in enabling technology advances in energy harvesting, sensing, human-machine interfacing, robotics, healthcare and more.
Development of Fiber-Based Devices as Energy Harvesters and Self-Powered Sensors
Authors: Chang Ting-Wei , Ke Yi-Yun , Lin Zong-Hong
Published: February 2020

Harvesting Energy from human motions to power portable electronic devices and sensors has been recognized as a new approach to solve the energy problem. In this study, we start to realize the concept by using commercial carbon fibers as the substrates to fabricate nanogenerators. Those fiber-based nanogenerators not only strongly show the potential do develop energy clothes in the near future but also provide an effective way to harvest energy from all directions. Nanowire arrays are designed to grow on carbon fibers first in order to enhance the electric outputs from nanogenerators. By further coating biocompatible polymers on the nanowire arrays, the fiber-based nanogenerators have been successfully demonstrated to harvest mechanical energy from walking. The nanogenerators fabricated in this study could contain two types; one is triboelectric nanogenerator and the other is piezoelectric nanogenerator. Those two types of nanogenerators are working based on different mechanisms, and therefore they can function as self-powered sensors for different targets.
Bioelectrocatalysis of Fructose Dehydrogenase at Polyanilline-Modified Electrodes
Authors: Sarauli David , Schulz Burkhard , Fattakhova-Rohlfing Dina , Lisdat Fred
Published: February 2020

Polymers can provide a suitable chemical environment for the immobilization of biomolecules in an active form on surfaces. Furthermore they can be used to wire redox proteins and enzymes with electrodes. For this purpose mainly redox polymers with well-defined redox centres and conductive polymers with intrinsic electron conductivity are applied. Polyanillines are belonging the latter class of polymers. Their properties can be easily tuned by the substitution pattern on the monomeric units. Recently we have shown that sulfonated polyanillines are suitable partners in the interaction with the enzyme PQQ-dependent glucose dehydrogenase [1]. On the basis of efficient electron exchange  different enzyme electrodes can be constructed [2-4].

In this study we have investigated whether it is possible to connect the multi-domain enzyme fructose dehydrogenase FDH with electrodes using the same group of polymers. The interaction of a sulfonated and methoxy-substituted polyanilline with FDH is studied in solution using UV/Vis spectroscopy. It can be demonstrated that electron transfer from the substrate reduced enzyme to the polymer is feasible, but also that this interaction is enhanced by the presence of calcium ions. Subsequently the reaction has been investigated by electrochemical means with all partners in solution verifying the spectroscopic results. In a next step of development the enzyme has been fixed on planar ITO electrodes by means of a polymer layer. Such an enzyme electrode exhibits effective, substrate-induced bioelectrocatalysis starting at rather low potential (~0mV vs Ag/AgCl). The efficiency can be significantly enhanced when macroporous ITO electrodes are used. They have pore size diameters of ~ 300nm and allow incorporation of higher amounts of polymer and enzyme. A current enhancement of ~ 35 is found compared to the flat ITO. The study demonstrates that sulfonated polyanillines can be considered as valuable matrices in connecting redox enzymes with electrodes.

[1] D. Sarauli; C.G. Xu; B. Dietzel; B. Schulz; F. Lisdat,  Acta Biomater.
2013, 9, 8290

[2] I. Schubart; G. Göbel; F. Lisdat,  Electrochimica Acta
2012, 82, 224

[3] D. Sarauli, C.G. Xu, B. Dietzel, B. Schulz, F. Lisdat, Journal of Materials Chemistry B 2 (21) 2014 3151-3404

[4] D. Sarauli, K. Peters, Xu, B. Schulz, D. Fattakhova-Rohlfing, F. Lisdat, ACS Appl. Mater. Interfaces
2014, 6, 17887
Electrochemical Synthesis of Magnetic Core-Shell Nanoparticles
Authors: Huang Yu-Fen
Published: February 2020

Core-shell nanostructures have attracted considerable interest as a new class of nanomaterials due to the fascinating physical and chemical characteristics. Herein, a facial and low-cost approach was reported for the synthesis of gold@iron oxide  core-shell nanoparticles. By using the citrate-stabilized gold nanoparticles as seeds, the gold@iron oxide nanoparticles were prepared via an electroxidation of iron nail at 1.0 V between the electrodes in aqueous solution. Modulating with the parameters such as pH values, buffers and reaction time make the iron shell thickness to be well controlled. Most importantly, gold@iron oxide nanoparticles turn superparamagnetic after annealing at 350℃ for six hours under nitrogen environment. The enhanced magnetic properties of the resulting core-shell nanoparticles show their future potential in magnetic resonance imaging as well as targeted delivery through magnetofection.
Hybrid Perovskites: A New Class of Compound Semiconductors with Unique Properties
Authors: Wu Tao
Published: February 2020

Organometallic hybrid perovskites have recently attracted enormous attention for photovoltaic, light emitting and other applications. Combining the advantages of both organic and inorganic materials, hybrid perovskites possess a wide range of extraordinary properties, such as tunable band gap, long carrier diffusion length, and ambipolar charge transport. Here, we will discuss first the physics of this interesting class of highly processable materials such as phase transitions and dielectric properties. Various solution and vapor based synthesis routes have been introduced to produce perovskite thin films and nanostructures. Regarding device applications, we will discuss the performance of perovskite solar cells using nano oxides such as SrTiO3, Zn2SnO4, and Cu2O as charge transporting materials. These versatile hybrid materials also found application in electronic devices. In the last part, we will discuss the applications of light sensitive perovskites in ambipolar phototransistors and nonvolatile resistive switching memories.
Simulating RF Performance of Proton Irradiated AlGaN/GaN High Electron Mobility Transistors (HEMT)s
Authors: Mukherjee Shrijit , Patrick Erin , Law Mark E
Published: February 2020

Due to their relative radiation hardness, High Electron Mobility Transistors (HEMTs) with an AlGaN/GaN heterostructure are of high interest for space applications. Many studies have been performed to quantify the level of degradation due to proton radiation, with the majority being focused on the effects on the DC or steady-state performance. Fewer studies have evaluated degradation of the radio frequency (RF) performance due to proton radiation. Chen et al. caution that degradation due to proton irradiation has a more measurable impact on the RF performance in comparison to the DC performance [1]. In particular, gate lag and increases in both channel resistance and device capacitance due to fast bulk and surface traps contribute more notably to RF degradation than to DC degradation [1]. Understanding the dynamics of these traps is required for modeling and simulation of GaN HEMTs for RF applications.       

In this paper, we aim to identify the necessary input parameters for future RF simulation of radiation effects on AlGaN/GaN HEMTs. In previous work, we have found that donor traps have a larger role than previously thought on the magnitude of DC performance degradation. We use experimental techniques to identify the donor trap lifetimes and energies, both of which are incorporated into a transient simulation of the HEMT and compared to results obtained experimentally. The experiments are long-term transient measurements of drain current after a step in gate voltage for various temperatures, resulting in the establishment of capture and release time constants associated with donor traps.

(1)    J. Chen, E. X. Zhang, C. X. Zhang, M. W. McCurdy, D. M. Fleetwood, R. D. Schrimpf, S. W. Kaun, E. C. H. Kyle, and J. S. Speck, IEEE Trans. Nucl. Sci, 61 (6), 2959, (2014).
Effects of Cobalt Cation on Low Pt-loaded PEM Fuel Cell Performance
Authors: Cai Yun , Kongkanand Anusorn , Gu Wenbin , Moylan Thomas E
Published: February 2020

PtCo and PtNi alloys are attractive as cathode catalysts in PEM fuel cell systems due to their high catalytic activities. However, dissolution of cobalt or nickel in a fuel cell causes not only oxygen reduction kinetic losses, but also ohmic losses, especially at high current densities, due to the migration of the cations into the ionomer. Several groups [1-3] have developed models to understand these effects on PEM fuel cell performance, mainly focusing on their macroscopic transport properties. To meet stringent cost requirements, the Pt loading in the electrode must be reduced significantly from the levels used in these previous studies. We have found that low Pt loaded cathodes showed larger high-current-density performance losses than higher loaded cathodes for a given cation doping concentration. This result is not readily explained using the current models. In this study, we performed controlled experiments where known amounts of Co or Ni cations were exchanged into the membranes in order to investigate the effect of cation concentration on the performance of cathodes with different Pt loadings, as shown in Figure 1.  We used impedance spectroscopy and limiting current method to study the effect of cation contamination on membrane and electrode proton resistances, local oxygen transport resistance, properties not been quantified in previous studies. These newly acquired results will be used to improve our current model and provide direction for future fuel cell development.

This work was partially supported by the U.S. DOE-EERE under grant DE-EE0000458.

References

[1] B. Kienitz, H. Baskaran, T. Zawodzinski and B. Pivovar, ECS Trans.,
11, 777 (2007)

[2] T. A. Greszler, T. E. Moylan and H. A. Gasteiger, Chapter 49, Handbook of Fuel Cells – Fundamentals, Technology and Applications. Edited by Wolf Vielstich, Harumi Yokokawa, Hubert A. Gasteriger. Volume 6: Advances in Electrocatalysis, Materials, diagnostics and Durability. 2009 John Wiley & Sons, Ltd.

[3] T. Okada, H. Satou, M. Okuno and M. Yuasa, J. Phys. Chem. B, 106 1267 (2002)

Figure 1
Current State of the Art in Water Electrolysis Performance Based on Anion Exchange Membranes
Authors: Ayers Katherine E , Parrondo Javier , Capuano Chris , George Morgan , Ramani Vijay K , Fujimoto Cy
Published: February 2020

Hydrogen represents a major chemical feedstock worldwide, and is currently manufactured primarily from fossil fuel-based sources.  Obtaining hydrogen from non-fossil sources is thus an important part of the overall strategy to reduce greenhouse gas emissions, including the potential tie to transportation infrastructure.  Large scale renewable hydrogen production is also a key part of the global energy storage strategy, to capture peak solar and wind and convert energy that would otherwise be stranded to a deployable source.  Water electrolysis is the only technology currently mature enough to meet the scale requirements in the near term for renewable hydrogen.  However, manufacturing and material cost need to be decreased to meet the economic requirements of these applications.

Commercial options for water electrolysis are currently limited to liquid KOH electrolyte based systems, and proton exchange membrane (PEM)-based systems.   Both have advantages and disadvantages.  Anion exchange membrane (AEM) technology represents a potential hybrid approach which leverages the advantages of both legacy systems.  However, the key obstacle in the AEM systems is the robustness of the polymers, both in the ionomer and membrane form.  The ionomer is subject to chemical degradation leading to loss of integrity of the electrocatalyst layer, while the membrane can lose mechanical strength due to both thermal damage during processing and chemical attack of the polymer backbone during operation, leading to pinhole failures.  The membrane can also lose efficiency through loss of active sites, either through carbonation of the hydroxide conducting sites, or chemical degradation.  These membrane and ionomer materials are much less mature than the PEM analogs, and fundamental understanding is still being developed around polymer design and degradation methods. 

Proton OnSite has developed cell designs and manufacturing processes which improve the robustness of the existing AEM materials, and have also collaborated with several membrane partners to develop improved materials.  Most recently, the Illinois Institute of Technology (IIT) performed mechanistic studies to determine potential membrane degradation pathways, while both IIT and Sandia provided materials for cell testing.  In this talk, results of these studies will be discussed, as well as resulting performance in commercial stack hardware.  Proton has currently achieved  stable operation of  the AEM cell for over 1700 hours, with over 1000 hours at 500 mA/cm2, and has scaled the technology to a 1 L/min prototype AEM generator.  Comparison to state of the art in PEM technology and the ultimate outlook for each technology will also be discussed.
Proton and Metal Cage-Based Anion-Conductive Fluoropolymers for AMFCs
Authors: Xu Shaoyi , Jiang Rong , Gao Yong
Published: February 2020

Alkaline membrane fuel cells (AMFCs) have attracted a great deal of attention due to its use of non-precious metal catalysts.  However, the lack of chemically stable and highly ion-conductive anion-exchange polymer membrane has impeded the development and adoption of AMFCs by our society.  Under strong alkaline conditions, hydroxide anions can be both a nucleophile and a strong base that degrade the hydrocarbon polymer backbones as well as the anion-exchange groups attached to the side chains of the polymer.  Typically, positively charged quaternary amine or guanidinium groups are used for hydroxide transportation.  Unfortunately, these functional groups are subjected to nucleophilic and elimination attacks by hydroxide anions.

In this presentation, we will disclose a new class of chemically stable anion-exchange fluoropolymers that can be casted into AMFC membranes.  The structure of a proton trap-based fluoropolymer is shown in the attached figure.  This polymer was chemically synthesized from a perfluorosulfonic acid (PFSA) via a novel C-C coupling reaction.  The highly fluorinated polymer backbone and side chains were known to tolerate chemical degradation while its proton cage group is robust against caustic conditions.  In our polymer, a proton is encapsulated inside a three-dimensional cage and it is protected from hydroxide attacks.  Such a polymer demonstrated remarkable stability in strong alkali media with good ion conductivity.  In our talk, we will also discuss several other types of anion-exchange fluoropolymers including zirconium-based membranes and lithium cage-based electrolytes.

Figure 1
Development and Characterization of a Dithionite / Air Fuel Cell
Authors: Noack Jens , Tübke Jens , Pinkwart Karsten
Published: February 2020

With the increase of renewable energy sources in an electrical network, the need for energy storage increases. Depending on the application, there are different ways to store electrical energy. For electrochemical energy storage options exist in the form of batteries, redox flow batteries and fuel cells coupled with electrolysis. The longer the storage time, the lower the cost of energy storage medium must be in order to be competitive with other technologies. Batteries and redox flow batteries use reversible electrochemical reactions, fuel cells do not normally what makes specially adapted electrolysers required. Wherever possible, simple and rapid electrochemical reactions for the reversal of the reactions are required, as for example are found in the redox couple H2/2H+. The reactions of organic redox couples of DMFC and DEFC can be electrochemically not reversed. Another way could be combinations of anodes of dissolved ions with an oxygen cathode, thereby “burning” the salt solutions which results in direct ion liquid fuel cells. A representative is the vanadium / oxygen fuel cell in which divalent vanadium ions are oxidized to trivalent at the anode by means of oxygen at the cathode [1]. The reactions can be reversed by vanadium / water electrolysis in the same cell as a reversible fuel cell (redox flow battery) [2, 3] or externally with a separate electrolysis cell [4].

Here we would like to report a work in which we have built and studied an alkaline fuel cell with the inexpensive redox couple dithionite / sulfite.

Anode:                S2O4
2- + 4 OH- -> 2 SO3
2- + 2 H2O + 2 e-                    E0= -0.294 V

Cathode:             O2 + 2 H2O + 4 e- -> 4 OH-                                           E0= +1.227 V

Cell:                    2 S2O4
2- + O2 + 4 OH- -> 4 SO3
2- + 2 H2O                   E = 1.530 V

As with the VOFC the reactions in a separate or the same cell may be reversed, and thus serve as an energy storage. For investigating the feasibility of such a cell a carbon-based anode and a platinum catalyst cathode for the ORR was used. The investigations were carried out by means of polarization curves, discharge tests and impedance spectroscopy using the cell voltage and the half-cell potentials and showed a maximum power density of 2 mW/cm² at room temperature. Under these conditions the oxidation of dithionite at carbon was much slower than the ORR. With a 0.85 M Na2S2O4the cell reached 12.4% energy efficiency and an energy density of 8.6 Wh/L.

1 C. Menictas, M. Skyllas-Kazacos, Journal of Applied Electrochemistry 2011, 41, 1223–1232.

2 S. S. Hosseiny, M. Saakes, M. Wessling, Electrochemistry Communications 2011, 13, 751–754.

3 J. grosse Austing, C. Nunes Kirchner, E.-M. Hammer, L. Komsiyska, G. Wittstock, Journal of Power Sources 2015, 273, 1163–1170.

4 J. Noack, T. Roth, M. Hihn, J. Tuebke, The 7th International Green Energy Conference & The DNL 1st Conference on Clean Energy, Dalian, China, 2012

Figure 1