bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficient and Flexible Perovskite Solar Cell Based on Inverted-Nanocone Structure with Enhanced Mechanical Properties
Authors: Chen Xizi , Tavakoli Mohammad Mahdi , Lin Qingfeng , Leung Siu-Fung , Fan Zhiyong
Published: February 2020

Organohalide lead perovskite materials have attracted tremendous attention because of their high mobility, excellent absorption, long diffusion length, and low-cost fabrication process. These features make them ideal candidates for solar cell devices with power conversion efficiency (PCE) up to 21%. Nowadays, the integration of solar cell devices with nanostructures becomes a new strategy to improve the device performance by enhancement of the light absorption and carriers collection. In fact, the nanostructured substrates can improve not only the performance of device but also the device mechanical robustness and reliability, which are beneficial for flexible devices. Herein, we report an efficient, flexible and mechanically robust-perovskite solar cell using inverted-nanocone (i-cone) plastic. Firstly, a facile and novel solution process is introduced to fabricate UV-cured epoxy substrate with i-cone pattern. Then, in order to deposit a uniform and conformal layer of perovskite on i-cone substrate, a two-step evaporation process is employed. The results of photovoltaic measurement show that the device based on i-cone has a PCE of 11.29%, which is 37% higher than the device on flat substrate. Furthermore, the device on i-cone with aspect-ratio-0.5 demonstrates the highest current density and PCE that is supported by UV-visible and external quantum efficiency tests. More interestingly, the results of bending test illustrate that the efficiency of textured device remains more than 90% of the initial value after 200 mechanical bending cycles, which is remarkably higher than flat device, which degrades down to only 60% in the same condition. To further study the effect of nanostructures on the device performance and mechanical robustness, the finite element mechanical modeling was carried out. The simulation results combined with SEM images demonstrate that the i-cone device relaxes the stress and strain upon device bending more efficient than its counterpart, which suppresses crack nucleation and propagation in different layers of a perovskite solar cell. Also, the top-view SEM images of devices after bending cycles have supported the simulation results. This essentially leads to much improved device reliability and robustness and will have significant impact on practical applications.
(Invited) Understanding the Energy Band Alignment in Inverted Organic Thin-Film Photovoltaic Devices
Authors: Chen Liwei
Published: February 2020

The energy band alignment in thin-film and low-dimensional devices is extremely important. However, experimental determination or theoretical prediction of the energy level alignment has been difficult to realize, especially under typical operating conditions.

Following a recent breakthrough in our group, where SKPM technique was employed to image the vacuum level profile across the depth direction of an operando organic PV device with a conventional stacking structure, here we present the vacuum level alignment measurement on an inverted structure OPV device. Previously, there had been conflicting reports on the built-in field and the device operation polarity. In this talk, we will present a comprehensive understanding of the energy level alignment in inverted structure OPVs, and how the measured parameters can be adopted in numerical modeling of the device physics.
(Invited) Insight into the Electrochemical Activation of Carbon-Based Cathodes for Hydrogen Evolution Reaction
Authors: Ho Johnny C
Published: February 2020

Recently, carbon nanomaterials have been reported with the outstanding electrocatalytic performance for hydrogen evolution reaction (HER) after electrochemical activation; however, the exact activation mechanism is still under extensive debate. In this work, for better understanding the activation, graphite rod and carbon nanohorns, two typical carbon materials in different scales, were electrochemically activated and their catalytic performance on HER was also systematically studied, which showed that the HER performance was greatly affected by the counter electrode employed for the activation. An efficient activation was achieved when a platinum wire was used as the counter electrode and, simultaneously, the Pt transfer from the anode to the cathode was also observed. All these suggest that the improved HER performance was mainly caused by the Pt transfer, rather than the activation of carbon materials themselves. More importantly, our study implied that the Pt dissolution, although being widely ignored, should be taken into reconsiderations during electrochemical tests when Pt metal is utilized as the counter electrode.
Vertically Stackable One-Dimensional p-n ZnO Homojunction Architectures for UV Sensing/Energy Harvesting Applications
Authors: Ko WonBae , Yang SeungMo , Yang JungYup , Yoon KapSoo , Park Jea-Gun , Hong Jin-Pyo
Published: February 2020

For wide-ranging applications in nanoscale optoelectronic and piezoelectric energy harvesting devices, one-dimensional ZnO nano-architecture and single crystalline doped ZnO having n-/p-type conduction are essential. Herein, catalyst-free ZnO sheet-like nanorods (SLNR) p-n homojunction in which the Lithium (Li) served as p-dopants and intrinsically n-type ZnO, respectively, have been synthesized by a controlled in-situ doping process via hydrothermal synthesis for fabricating efficient ultraviolet UV detectable photonic devices. In addition, a comprehensive investigation was carried out on Li-doped ZnO SLNRs to control the amphoteric electrical behavior of Li in ZnO host lattice. In such cases, Li occupies octahedral sites (Lii
O) in the empty cages of the ZnO wurtzite structure and subsequently acts a donor because of the low formation energy, thereby, maintaining or improving the initial n-type behavior of the material. In contrast, the p-type doping by Li atoms occupying Zn site (LiZn) along the growth direction has been achieved by proper thermal activation energy. Further, to obtain n-/p- ZnO nanorods architecture and their vertically stacked p-n homojunctions, the nanorod diameters and morphologies of the ZnO SLNRs were adjusted dramatically by manipulating precursor concentration and growth kinetics. The well-aligned and clean interface between n-/p-ZnO SLNRs could enhance the electron-hole pair generation, transport, separation, thus improved the performance of the homojunction devices. The ZnO p-n homojunction structures have been successfully attained by continuous multi-step solution growth, representing the well-faceted hexagonal SLNR end planes of ZnO segments. The Li-doping effects which are occupied in interstitial site (Lii) or substitutional site (LiZn) in single crystalline ZnO SLNRs were carefully examined through the lattice spacing differences of lattice fringes in high-resolution transmission electron microscopy. An extensive analysis of the luminescence features was carried out in order to identify conduction type conversion from n-type to p-type in the Li-doped ZnO SLNRs. The appearance of acceptor-bound exciton emission, extremely enhancement of near-band-edge emission and the longer carrier life-time indicate that the Li dopants act as desirable shallow acceptor in the ZnO SLNRs. In addition, the SLNR-based p–n homojunctions exhibited distinct electrical features for their potential use as light emitting diodes and UV photovoltaics, thereby spurring progress in the development of practical optoelectronics.

Figure 1
Characterization and Comparison of Planar and Trench Silicon Carbide (SiC) Power MOSFETs
Authors: Wang Zhiqiang , Chinthavali Madhu , Campbell Steven
Published: February 2020

This paper presents a comprehensive evaluation and experimental comparison of silicon carbide power MOSFETs through double pulse test. First, a universal hardware platform is designed and developed to test power semiconductor devices with various device packages and measuring requirements. Using the developed platform, the static characteristics and switching performance of the two types of SiC MOSFETs (one planar and one trench type) are evaluated under different case temperatures from 25 oC to 175 oC. Based on the evaluation data, a comparison of both SiC MOSFETs is conducted in terms of their on-state resistance, switching loss, and temperature dependent behavior. It is found that the latest trench SiC MOSFETs present similar switching loss while much lower conduction loss compared to existing commercial planar SiC MOSFETs. Moreover, the trench devices show a nearly temperature independent switching loss, which is beneficial to suppress the potential thermal runaway issue under high temperature continuous operation.
(Invited) Threshold Voltage Modulation By Interface Charge Engineering for High Performance Enhancement-Mode Al2O3/GaN Power Mosfets
Authors: Zhou Qi , Zhang Anbang , Shi Yuanyuan , Wang Zeheng , Liu Li , Chen Wanjun , Zhang Bo
Published: February 2020

III-Nitride metal-oxide-semiconductor field effect transistors (MOSFETs) have great potential for next generation energy-efficient power switching. Due to the fail-safe consideration, the enhancement-mode (E-mode) operation is highly desirable for GaN MOSFETs in power electronics. Furthermore, in high frequency switching applications, devices with high V
TH (e.g. V
TH>6 V) and large gate swing (e.g. >10 V) are required to prevent them from faulty turn-on due to the gate driver failure or electromagnetic interference. Many approaches have been demonstrated in pushing the V
TH more positive [1], [2]. However, achieving high V
TH and good performance simultaneously remains a major challenge due to positive interface fixed charges [3], [4]. In this paper, the presence of positive interface fixed charges (Q
it~1.44×1013 cm-2) at the ALD-Al2O3/GaN interface was found in the fully recessed Al2O3/GaN MOSFETs. The origin of the interface charges is proposed to be the Ga-O bond and metal Ga dangling bond (DB) at the Al2O3/GaN interface generated in the gate recessing process and Al2O3 deposition, respectively. An efficient approach to engineer the interface positive fixed charges was demonstrated by post-dielectric annealing (PDA) in N2, resulting in a reduction of Q
it from 1.44×1013 to 3×1012 cm-2. The reduction of Q
it leads to a significant positive shift in V
TH and an increase of electron mobility that enabling the E-mode operation of Al2O3/GaN MOSFETs with a uniquely high V
TH of +7.6 V and drive current as high as 355 mA/mm. The interface charge engineering method demonstrated in this work is promising to fabricate E-mode GaN devices with uniquely higher V
TH and low on-resistance.

References 1. Y.-H. Wang, et al., IEEE Electron Device Lett., 36, (2015). 2. Z. Tang, et al., IEEE Electron Device Lett., 34, (2013). 3. M. Esposto, et al., Appl. Phys. Lett., 99, (2011). 4. S. Ganguly, et al., Appl. Phys. Lett., 99, (2011).

Figure 1
Temperature Sensitive of Ionic Conductance in Alumina Nanochannels
Authors: Su Yen-Shao , Yeh Li-Hsien
Published: February 2020

Inspired by biological ion channels, nanochannels embedded in a thin alumina membrane have captured much attention of scientists due to their promising applications in energy conversion, ionic diodes, and biosensors. The working principle of these emerging applications is highly related to their ionic current (or conductance) behaviors, which depend on the surface charge property of nanochannels. It is known that the surface charge property of alumina nanochannels is exquisitely dependent on the surface chemistry reaction of dissociable functional groups (e.g., Al-OH) on the channel wall and, therefore, the variation in solution temperature might play a role. Although the relevant studies on the ion transport in alumina nanochannels are ample, the influence of solution temperature has not been discussed so far. Herein, we experimentally investigate the temperature effect on the ionic conductance in alumina nanochannels, which were fabricated by the electrochemical anodic oxidation process. SEM images reveal that the diameter of cylindrical alumina nanochannels we fabricated is about 20-30 nm. Results obtained show that temperature sensitive of nanochannel conductance depends apparently on the levels of pH and salt concentration, which provides useful information for the design of ionic devices used in temperature sensitive applications such as ionic diodes and gates.

Keywords: Nanofluidics; Temperature dependence; Ion transport; Anodic aluminum oxide
(Invited) Automatic Particle and Cell Detection and Manipulation in a Microfluidic Chip
Authors: Song Yongxin
Published: February 2020

This presentation reports our researches on the automatic detection and manipulation of particles and cells in a microfluidic chip. A differential resistive pulse sensor is developed and employed to continually detect and sizing particles. Due to the noise cancelling effect, the S/N is greatly improved. As a result, detection of 220nm particles was achieved with a relative larger sensing gate.

Automatic particle and cell sorting based on their size differences was also reported in this presentation. The RPS sensor was used to sizing the particles or cells. The detected RPS signals were used to automatically trigger the sorting process. Due to the high sensitivity of the RPS sensor, 1um sorting resolution was achieved. This technology can also be used to manipulating cells at a single cell level.

Keywords: Resistive Pulse Sensor, Detection and sorting, single cell levelAbstract

This presentation reports our researches on the automatic detection and manipulation of particles and cells in a microfluidic chip. A differential resistive pulse sensor is developed and employed to continually detect and sizing particles. Due to the noise cancelling effect, the S/N is greatly improved. As a result, detection of 220nm particles was achieved with a relative larger sensing gate.

Automatic particle and cell sorting based on their size differences was also reported in this presentation. The RPS sensor was used to sizing the particles or cells. The detected RPS signals were used to automatically trigger the sorting process. Due to the high sensitivity of the RPS sensor, 1um sorting resolution was achieved. This technology can also be used to manipulating cells at a single cell level.

Keywords: Resistive Pulse Sensor, Detection and sorting, single cell level
Heat Transfer Enhancement By Elastic Turbulence in a Micro Curvilinear Channel
Authors: Zhang Hong Na , Li Dong Yang , Li Xiao Bin , Li Feng Chen
Published: February 2020

With the increasing level of microelectronic techniques, such as MEMS, the effective heat transfer become crucial to their performance. Genernally, the flow in microscale behaves laminar because of the extremely low Reynolds number (Re), which results in very low heat transfer effeciceny. So far, an increasingly efforts have been paid to develop techiniques to improve the heat transfer therein. As is well known in the conventional scale, flow instabilities and turbulence could significantly promote the mixing and heat transfer. Therefore, a great deal of efforts have been paid to to perturb the low Reynolds number flows in order to increase the contact interfaces between fluids with different temperature in microchannel. For example, some efforts are paid to design and utilize specially designed microchannel to excite the unstable flow motion. Another alternative way is to adopt different kinds of working fluid such as nano-fluid, non-Newtonian fluid and so forth. The viscoelastic fluid, a kind of Non-Newtonian fluid, shows nontrivial flow phenomena such as die swell effect (Barus effect), rod climbing effect (Weissenberg effect), Kaye effect, tubeless siphon effect, etc. Moreover, it has been proven that purely elastic flow instabilities or elastic turbulence is possible to be induced under inertialess or creeping flow conditions. This provides another efficient way to realize heat transfer enhancement, which is also the focus of present paper.

In this paper, we carried out experimental and numerical investigations on the heat transfer characteristics of viscoelastic fluid and Newtonian fluid in three dimensional (3D) curvilinear microchannel. For the experiments, microelectronics manufacturing technology was taken to fabricate microchips. Platinum films were embedded in a Polydimethyl-siloxane (PDMS) microchannel in order to measure micro heater and channel wall temperature. The polymer solutions (PAAM) were the chosen viscoelastic fluid and sucrose solutions (Newtonian fluid) were used for comparison. For the numerical simulation, the log-conformation algorithm were implemented into the open source software OpenFOAM in order to simulate the viscoelastic flow at high Weissenberg number. Before simulating the viscoelastic fluid flow passing through the target channel, the numerical solver was firstly validated by two benchmark problems i.e., flow around a cylinder and passing a cross-slot by comparing the obtained dimensionless drag coefficient and flow patterns with those in the existing literatures. Combing the experimental and numerical results, the present identified the heat transfer enhancement by the occurrence of elastic instability and turbulence in a curved microchannel.
Viscoelastic Slip Velocity for Microscale Electrokinetic Flows
Authors: Joo Sang W. , Saadat Amir , Khomami Bamin
Published: February 2020

Microscale electrokinetic flows are often analysed neglecting the full details of the dynamics within the electric double layer (EDL) ajacent to solid boundaries. The high-shear velocity profile within the EDL is simplified by the Helmholtz-Smolukowski velocity, imposed in leu of the noslip boundary condition. For Newtonian fluid this slip boundary condition can be a convenient tool for economical simulation of more complex phenomena. Viscoelastic fluids are ubiquitous in micro devices, and so the slip velocity generalised for non-Newtonian fluids is needed.

In this study, analytical solution extending the Helmholtz-Smolukowski velocity to viscoelastic electroosmotic flow is presented for the first time based on conservation laws. By using the Phan–Thien Tannar (PTT) constitutive model, explicit dependence of viscoelastic rheological parameters, including the relaxation time, the slip parameter and the extensibility parameter, on the slip velocity on the edge of electrical double layer (EDL) is revealed. This report will be instrumental in providing a deep insight into the dynamics of the viscoelastic fluids subject to electrokinetic forces and in making the long-sought micro-scale approximation of complex viscoelastic flow possible.
Electroosmotic Flow through a Tubular Channel
Authors: Liu Bo-Tau , Li Ci-Da
Published: February 2020

In this study, the electroosmotic flow in a charge-regulated tubular channel is considered at low potential and arbitrary double layer thickness. Analytical expressions for the flow velocity and the corresponding asymptotic results for thick double layers that are readily applicable to experimentalists are recovered. For the range of salt concentration usually encountered in practice, the mean flow velocity for the case of constant surface potential differs both quantitatively and qualitatively from that for the case of constant surface charge density. Since this difference is both quantitative and qualitative, the true charged conditions on a channel wall can be inferred by appropriately designed experiments. Using an equivalent circular channel to simulate an elliptic one is inappropriate; in general, neither is assuming electroneutrality on the channel axis even when double layer is ca. 1/3 of the equivalent channel radius.
Electrical Measurement of the Band Gap of Molybdenum Ditelluride and Black Phosphorus in Ambipolar Transistors with Graphene Source/Drain Contact
Authors: Lim June Yeong , Kim Jin Sung , Ahn Jongtae , Yu Sanghyuck , Im Seongil
Published: February 2020

Transition metal dichalcogenides and monoatomic buckled crystals are two-dimensional (2D) semiconductors promising for active material toward nano-electronics and nano-optoelectronics [1]. As some of recent 2D semiconductors, α-MoTe2 and black phosphorus(BP) have been extensively studied due to their optical and electrial propeties. Many groups have theoretically predictd band gap of α-MoTe2 and black phosphorus in a wide range [2], depending on their film thickness. However, only a few experimental measurements have been done. Here, we demonstrate ambipolar α-MoTe2 and black phosphorus transistors with graphene source and drain contacts to determine the band gap of channel. Temperature-dependent transfer characteristics have been used to quantitatively analyze schottky barriers height(ФB) formed at the graphene-to-channel interface as a function of applied gate voltage. Because Fermi level of graphene is modulated to that of channel, we can determine band gap of 11 nm-thin α-MoTe2 and 6 nm-thin black phosphorus are 0.826 eV and 0.416 eV, respectively. Our estimated band gap values appear quite reasonable, proving that our analysis is very useful to estimate the band gap of 2D material.

Figure 1
High Performance Organic Photovoltaics with Transparent Oxide Interlayer
Authors: Kim Hyeok
Published: February 2020

Organic photovoltaics (OPVs) have remarkable attention due to their cost-effective, simple process and large area manufacturing as energy sources for printed and flexible electronics. In this talk, we demonstrate that inorganic interlayer can prominently improve the performance of inverted polymer solar cells with the mixture of [6,6]-phenyl C71-butyric acid methyl ester (PC70BM) and diverse donors, such as poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl(PTB7) and many more.

One of the common technique to enhance the electrical and optical properties of inorganic thin film layer has been suggested with doping of various metals for oxide inorganic films, such as ZnO, TiO2 and other metal oxides. It was recently reported that metal doping of ZnO thin film such as Li, Al, or Ga is an effective way to modify the grain size and orientation of ZnO crystallites. It may predominantly be effective as the structural, optical and electrical properties enhancer. Here, we adopted various metal dopants to inverted OPVs in ZnO and TiO2 interlayers. The doped ZnO film with a number of dopants, thus, such as Al, Ga, In, Li and Cd, was prepared by sol-gel spin coating and the optimized doping concentration appeared for each dopant. As suggested as one of the most highly improved efficiency, In-doped ZnO (IZO) film with 6 at. % of In concentration was intercalated between the ITO electrode and the active layer. As a result, the power conversion efficiency approaches 9 % exceedingly. Moreover, the underlying mechanism was revealed as the suppressed absorption and facilitated electron extraction of inorganic interlayer with metal doping through the first principles calculations and finite difference time domain (FDTD) optical simulation.
Oxidation of CuSn Alloy Nano-Tree and Application for Gas Sensors
Authors: Kaneko Naoto , Shimizu Tomohiro , Ito Takeshi , Tada Yoshihiro , Shingubara Shoso
Published: February 2020

We have found nano-tree of CuSn alloy by DC electroplating with a constant potential mode [1,2]. Nano-tree is a true 3-D structure having many branches which separate from trunk perpendicularly, and sub-branches grow perpendicular from them also. It is well known that SnOx as well as CuOx are good materials for gas sensors. It is of great interest to evaluate gas sensor properties of the Cu-Sn Nano-tree oxide, because it has a very high ratio of surface to volume, and is expected to exhibit excellent properties as sensors. In this study, we carried out oxidation of CuSn nanotrees in air, and also measured resistance change properties by intoducing various reactive gases.

The Cu-Sn nanotrees were grown on Pt thin film electrode with the plating bath containing SnCl2, Cu(NO3)2, ((NH4)2C2O4) and Poly-ethylene glycol (PEG1000).

The oxidation of CuSn nanotrees was carried out in the atmosphere at temperature between 200 to 350 oC. Change in electrical resistance of CuSn nanotrees oxide was measured concomitant with introducing various gases in the chamber.

Figure 1 shows SEM images of the electrodeposited CuSn alloy. It is remarkable that nanotrees with many perpendicular branches were formed. Each branch has a one-dimensional structure with a diameter of around a few tens of nm, and grows perpendicularly from the branch. The nanotree structure is almost stable at annealing temperature below 350 oC, however, it is thickened due to volume expansion by oxidation.

Figure 2 shows the gas sensing property of the CuSn nanotree oxide. It turned out that the CuSn nanotree oxide reistance is sensitive against the introduction of H2, the resistance change increased with increasing amount of H2 gas. It is strongly suggested that the CuSn nanotree oxide has a high potential as a gas sensor material with a high sensitivity.

[1] T.Shimizu, et al., Surface and Coating technologies

[2] N. Kaneko , et al, Jpn.J.Appl.Phys. (2016) accepted for publication.

Figure 1
Enhanced Photocurrents in the Vertically Aligned Hybrid CdTe-Si One-Dimensional Nanostructures with High Surface Area
Authors: Lim Jinho , Hwang Sung-Hwan , Jung Hyunsung
Published: February 2020

One-dimensional hybrid CdTe nanostructures on Si nanowires in a wafer batch were synthesized by wet chemical processes. Si nanowires were vertically aligned by the employment of Ag nanoparticles as a catalyst of an electroless etching. The etched Si nanowires were utilized as sacrificial materials for the galvanic displacement reaction to Te nanostructures. The hybrid CdTe on Si nanostructures were created by the wet chemical reaction of the Te nanostructures prepared on aligned Si nanowires. The electrical and optical properties of the fabricated hybrid CdTe-Si nanostructures were characterized. Especially, the one-dimensional hybrid CdTe-Si nanostructures with high surface area demonstrated the enhanced optical current densities. The vertically aligned one-dimensional hybrid CdTe-Si nanostructures can propose an efficient route for the synthesis of hybrid hierarchical nanostructures with high electrical and optical properties in a wafer batch.
Identification of Polarization Losses in High-Temperature PEM Fuel Cells by Distribution of Relaxation Times Analysis
Authors: Schindler Stefan , Weiß Alexandra , Galbiati Samuele , Mack Florian , Danzer Michael A. , Zeis Roswitha
Published: February 2020

In recent years phosphoric acid doped PBI-type fuel cells have drawn much attention as a promising candidate for energy storage and conversion applications at relatively high temperatures (100 – 200 °C). The elevated operating temperature of HT-PEMFCs (high-temperature polymer electrolyte membrane fuel cells) simplifies water and thermal management. In addition, it greatly enhances the fuel cell’s tolerance against impurities (e.g. CO) in hydrogen, which is critical for operation with reformate hydrogen. However, durability and stability of high-temperature PEM-MEAs still need to improve for widespread commercialization [1], and better tools for identifying performance-loss related mechanisms are desirable. A very useful in-situ technique for performance analysis of HT-PEMFCs is electrochemical impedance spectroscopy (EIS). As previously reported, EIS can be used to characterize the impact of different parameters (e.g. stoichiometry, temperature, etc.) on cell kinetics [2, 3]. Equivalent circuit models are usually used to analyze the EIS data and identify the performance-loss related mechanisms.

A major drawback of this approach is that the assumptions for the model equivalent circuits are sometimes ambiguous or even misleading due to the lack of priori knowledge about the electrochemical system under study. Furthermore, a clear separation of various physiochemical processes is difficult if the time constants of these processes overlap significantly in the frequency domain. To overcome these drawbacks, advanced mathematical methods such as Distribution of Relaxation Times (DRT) can be applied. DRT relies on the representation of the polarization impedance by its characteristic time constants and is numerically approximated by a discrete distribution function. This method has been successfully demonstrated for process identification and separation in solid oxide fuel cells (SOFC) [4].

In this study, we applied this technique on high temperature PEM-MEAs for the first time. Electrochemical processes were identified and analyzed by varying cell parameters such as temperature and stoichiometry. The results offer a refined understanding of loss mechanisms and provide valuable guidance for fuel cell improvement and optimization.

[1] A. Chandan, M. Hattenberger, A. El-kharouf, S. Du, A. Dhir, V. Self, B.G. Pollet, A. Ingram, W. Bujalski, J. Power Sources 231 (2013) 264

[2] J. L. Jesperesen, E. Schaltz, S.K. Kær, J. of Power Sources 191 (2009) 289-296

[3] F. Mack, R. Laukenmann, S. Galbiati, J. A. Kerres, R. Zeis, ECS Transactions 69 (17), 1075-1087 (2015)

[4] A. Leonide, V. Sonn, A. Weber, and E. Ivers-Tiffée, Journal of the Electrochemical Society 155 (1) B36-B41 (2008)

Figure 1 Typical Nyquist plot of a phosphoric acid doped PBI-type HT-PEMFC at different current densities (a) and the corresponding distribution function (b).

Figure 1
Electrochemical Performance of Thin-Film Pt3y Electrodes in PEMFC
Authors: Eriksson Björn , Lindahl Niklas , Wickman Björn , Lindstrom Rakel Wreland , Lindbergh Göran , Lagergren Carina
Published: February 2020

In current polymer electrolyte fuel cells (PEMFC), high amounts of platinum catalysts is required due to the sluggish kinetics of the oxygen reduction reaction (ORR). As such it is important to find ways to increase the activity of the ORR catalyst. Previous studies have shown that alloying platinum with yttrium results in a catalyst which is more than six times as active as sole Pt in half cell rotating disk electrode measurements [1].

The model electrodes in this study are prepared by sputtering a well-defined layer of alloy catalyst onto a gas diffusion layer (GDL). In this manner the composition and thickness of the film can be controlled. These electrodes are studied with single cell PEMFC measurements to characterize the materials, similar to previous work done with these types of electrodes [2]. Using these methods the electrochemical surface area (ECSA), ORR activity, and stability are evaluated. The effects of different MEA preparations will also be investigated.

Scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis as well and X-ray photoelectron spectroscopy (XPS) are used to characterize the structure of the alloy catalyst as well as the bulk and surface compositions, i.e. platinum to yttrium ratio. This characterization is performed on both as-prepared samples and electrodes after being used in the PEMFC.

The main focus is to determine the role of yttrium in platinum thin-film platinum electrodes, and if the excellent activity in half cell experiments will also be seen in real PEMFC measurements.

References

[1] J. Greeley, I. E. L. Stephens, A. S. Bondarenko, T. P. Johansson, H. A. Hansen, T. F. Jaramillo, J. Rossmeisl, I. Chorkendorff and J. K. Nørskov , Nature Chemistry, 2009, 1, 552-556

[2] M. Wesselmark, B.Wickman,C.Lagergren,G.Lindbergh, Electrochimica Acta, 2013, 111, 152-159
Exploring the Lanthanide Contraction to Tune the Activity and Stability of Pt
Authors: Escudero-Escribano María , Malacrida Paolo , Hansen Martin Hangaard , Vej-Hansen Ulrik Grønbjerg , Velázquez-Palenzuela Amado Andrés , Tripkovic Vladimir , Schiøtz Jakob , Rossmeisl Jan , Stephens Ifan E. L. , Chorkendorff Ib
Published: February 2020

The high platinum loadings required to compensate for the slow kinetics of the oxygen reduction reaction (ORR) impede the widespread uptake of polymer electrolyte membrane fuel cells. In order to improve the ORR kinetics and reduce the Pt loading, we can tailor the electronic properties of the Pt surface atoms by means of alloying Pt with other metals. Researchers have intensively studied alloys of Pt with late transition metals such as Ni and Co during the last decades. However, these compounds typically degrade under fuel cell reaction conditions, due to dealloying. In contrast, alloys of Pt and lanthanides present very negative enthalpy of formation [1,2], which should increase their resistance to degradation.

Herein we present eight novel Pt-lanthanide and Pt-alkaline earth ORR electrocatalysts: Pt5La, Pt5Ce, Pt5Sm, Pt5Gd, Pt5Tb, Pt5Dy, Pt5Tm and Pt5Ca [3]. All the materials are highly active, presenting a 3 to 6-fold activity enhancement over Pt. Pt5Tb is the most active polycrystalline Pt-based catalyst reported in the literature. A Pt overlayer with a thickness of few Pt layers is formed onto the bulk alloys by acid leaching [1-3]. Notably, the experimental ORR activity as a function of the bulk lattice parameter and the Pt-Pt distance follows a “volcano” relation [3], with Pt5Tb presenting the highest initial activity while Pt5Gd is the most active after 10 000 cycles stability test between 0.6 and 1.0 V versus the reversible hydrogen electrode. We use the lanthanide contraction to control strain effects and tune the electrocatalytic activity, stability and reactivity of Pt [3].

References

[1] M. Escudero-Escribano, A. Verdaguer-Casadevall, P. Malacrida, U. Grønbjerg, B.P. Knudsen, A.K. Jepsen, J. Rossmeisl, I.E.L. Stephens, I. Chorkendorff, J. Am.
Chem. Soc. 2012, 130, 16476.

[2] P. Malacrida, M. Escudero-Escribano, A. Verdaguer-Casadevall, I.E.L. Stephens, I. Chorkendorff, J. Mater. Chem. A
2014, 2, 4234.

[3] M. Escudero-Escribano, P. Malacrida, M.H. Hansen, U.G. Vej-Hansen, A. Velázquez-Palenzuela, V. Tripkovic, J. Schiøtz, J. Rossmeisl, I.E.L. Stephens, I. Chorkendorff, Science
2016, 352, 73.
Impact of Pressure and Temperature on Hydrogen Permeation in PEM Water Electrolyzers Operated at Asymmetric Pressure Conditions
Authors: Trinke Patrick , Bensmann Boris , Reichstein Sven , Hanke-Rauschenbach Richard , Sundmacher Kai
Published: February 2020

Water electrolyzers are predominantly operated at elevated pressures. This is especially favorable in the context of the subsequent utilization of the produced hydrogen e.g. due to the more efficient, electrochemical and isothermal hydrogen compression or less afford for hydrogen drying. However, higher pressures lead to higher cross-permeation of the product gases in electrolysis cells.

In the present contribution, hydrogen permeation across a fumea EF-40 membrane is systematically investigated for pressure differences between 5-35 bar and for four different temperatures between 22 °C and 60 °C. The measured permeation fluxes show a quadratic dependency on the pressure difference. A permeation model combining a diffusive and convective transport can describe the experimental data quantitatively. For the investigated membrane, the diffusive as well as the proposed convective permeability coefficient and their temperature dependencies are obtained.

The diffusive permeability coefficient and its temperature dependency agrees very well with published data for Nafion membranes. The slightly lower value for the EF-40 can be explained by the lower water volume fraction. The obtained convective permeability coefficient indicates a high hydraulic permeability, especially in comparison to recently reported values for Nafion membranes. However, the reported values of the hydraulic permeability show high variations of about two orders of magnitude, with strong dependence on investigated materials, that show the importance of this parameter with regard to convective hydrogen permeation.

The present work discusses two potential reasons for the high obtained hydraulic permeability. The first one is related to the membrane properties. In particular, the lower equivalent weight of the fumea EF-40 membrane could cause the higher hydraulic permeability. Second the electrolysis conditions, in particular the applied small current, might increase the hydraulic permeability due to wider membrane water channels and a change to a hydrophilic membrane surface.

Figure: Parameterized equation in comparison to the experimental results.

Figure 1
Overpotential Analysis in High Pressure Water Electrolysis
Authors: Suermann Michel , Schmidt Thomas J. , Büchi Felix N
Published: February 2020

To store or transport hydrogen (and optionally oxygen) in high pressure tanks or pipelines pressures up to 1000 bar are needed. Pressurized polymer electrolyte electrolyzers are typically operated at around 30 bar to reduce downstream mechanical compression and gas drying stages. Interestingly, often the cell voltage does not show the expected thermodynamic voltage increase [1,2]. Consequently beneficial influences are compensating the compression work, at the expense of higher faradaic losses due to increased gas crossover.

In this work we analyze cell voltages at gas pressures up to 100 bar as function of temperature up to 70 °C and current densities up to 4 A/cm2, considering the three main overpotentials (ohmic, kinetic, mass transport) using a zero-order analysis based on the Tafel kinetics model.

As expected, the ohmic overpotential is mainly a function of temperature and almost independent from pressure. Therefore the overpotential gains with increasing pressure, observed for current densities above about 0.8 A/cm2, stem from the kinetics and/or the mass transport. Both overpotentials decrease with increasing pressure, but over a wide current density region kinetics contribute about two thirds to the voltage gain. The improved kinetics can be attributed to an increased apparent exchange current density, whereas the increased mass transport might be related to smaller gas volumes or velocities resulting in an improved two-phase flow in the porous structures.

Literature:

[1] S.A. Grigoriev, V.I. Porembsky, V.N. Fateev, Pure hydrogen production by PEM electrolysis for hydrogen energy, Int J of Hydrogen Energy, 31 (2006) 171-175.

[2] P. Millet, R. Ngameni, S.A. Grigoriev, N. Mbemba, F. Brisset, A. Ranjbari, C. Etiévant, PEM water electrolyzers: From electrocatalysis to stack development, Int J of Hydrogen Energy, 35 (2010) 5043-5052.
(Invited Plenary) Honda Fuelcell Vehicle Development and Toward the Hydrogen Society
Authors: Moriya Takashi
Published: February 2020

Honda launched new fuel cell vehicle "CLARITY FUEL CELL" in March 10, 2016. In this presentation, I explain the fuel cell vehicle (FCV) development status of Honda including the various main technologies of "CLARITY FUEL CELL". Honda does not only develop the FCV but also small hydrogen station and mobile inverter for power output from FCV. Honda has efforts toward the hydrogen society with concept of "Produce" "use" and "Connect". I explain the small hydrogen station named Smart Hydrogen Stration (SHS) and mobile inverter named "Power Exportor 9000". This explanation will be explained technical conceopts and actual demonstration test resylts. In terms of FCV development, I will explain the FCV development history and future technology direction. Of courese, FCV is not expanded without prepareation of hydrogen infrastructure (Hydrogen Refueling Station : HRS). So this presentation will be explained the situration of HRS preparation and recent direction of movement. Especially, I will introduce the most aggressive Japanese situation. And I expain the future strategy of Honda.
Iridium Nanoparticles Supported on Magneli Phase Ti4O7 for PEM Water Electrolyzers
Authors: Ioroi Tsutomu , Yasuda Kazuaki
Published: February 2020

PEM water electrolysis is one of the promising technologies for hydrogen production from renewable energy sources. Iridium and their oxides are recognized as the most suitable catalyst showing high activity and stability for oxygen evolution reaction (OER) in acidic media [1], however, overpotential is still high and its scarcity and price are also drawbacks. To overcome these problems, a number of studies concerning particle size reduction, catalyst compositions, and utilization of catalyst support have been reported [2]. Among them, use of corrosion-resistant and highly electro-conductive oxides, especially Magneli phase Ti4O7 as catalyst support would be beneficial for reducing Ir loading and increasing durability. We have developed Ti4O7-supported Ir catalyst and examined activity and durability as an anode catalyst of PEM electrolyzer. 

Titanium oxide support was prepared by UV laser technique [3]. Ir/Ti4O7 catalysts obtained by using H2IrCl6 precursor showed conductivity comparable with that of commercial Pt/C. MEAs with the Ir/Ti4O7 anode can be operated up to 4 A cm-2 at low cell voltage < 2.0 V (with DuPont NR212 membrane) with very low Ir loadings (0.25 mg-Ir cm-2). Considering fluctuating nature of the renewable energy inputs, catalyst stability against voltage change should be another important issue. To simulate and accelerate such degradation modes, potential sweep between 1.0 V and 2.0 V at a sweep rate of 500 mV s-1 was applied up to 10,000 cycles. The Ir/Ti4O7 MEA shows limited degradation even after 10,000 cycles. Stability of the cell performance and the catalyst structure will be discussed at the Meeting.

References

1. M. H. Miles and M. A. Thomason, J. Electrochem. Soc.,
123, 1459 (1976).

2. M. Carmo, D. L. Fritz, J. Mergel, D. Stolten, Int. J. Hydrogen Energy, 38, 4901 (2013).

3. T. Ioroi, H. Kageyama, T. Akita, K. Yasuda, Phys. Chem. Chem. Phys., 12, 7529 (2010).
Nanoporous IrO2 catalyst with Ultrahigh Specific Surface Area Synthesized through an Ammoniating Method for Acidic Oxygen Evolution
Authors: Li Guoqiang , Li Songtao , Liu Changpeng , Xing Wei , Ge Junjie
Published: February 2020

The development of highly active and stable electrocatalysts for OER is urgent due to the slow kinetics and high overpotential of oxygen evolution reaction (OER) [1]. To date, the most promising catalysts for OER are IrO2 based catalysts with ordered porous structures, where a templating method was generally used to ensure the high utilization of the catalysts. However, the synthesis route for such catalysts is generally of high technique complexation, where the templates need to be effectively removed after synthesis [2,3]. Hence, a simple template-free method that leads to the formation of highly porous IrO2 catalysts with high surface area is highly attractive.

Herein, a satisfactory template-free ammoniating method was developed in which NH3 ligand was successfully kept until pyrolysis treatment, thus acting as the pore-forming agent to achieve highly porous IrO2. The specific and electrochemical surface areas of as-prepared IrO2 catalysts increased with the increasing quantity of NH3·H2O additive. Specifically, IrO2 (1:100)-450 °C catalyst synthesized with the highest ratio of NH3 ligand exhibited high specific surface area of 363.3 m2 g-1 as metal oxide. Furthermore, IrO2 (1:100)-450 °C showed remarkable electrocatalytic activity for acidic OER in the whole potential window, which can be ascribed to the high catalysts utilization. As shown in Figure 1, the over-potential for the IrO2 (1:100)-450 °C catalysts to attain current at 10 mA cm-2 was only 282 mV, which was shifted negatively by 31 mV and 46 mV in comparison to the home-made IrO2 (without NH3) and commercial IrO2 (CM) catalysts, respectively. Thus, the NH3 mediating method was found a superior method for increasing catalysts utilization, where the IrO2can be conveniently synthesized in large scale.

Figure 1. CV curves (Left, the inset shows the specific surface area) and LSV curves (Right, the inset shows the TEM of IrO2 (1:100)-450°C) of IrO2 (1:100)-450°C, IrO2 (1:10)-450°C, IrO2-450°C, and IrO2(CM) catalysts.

Acknowledgments

This work is supported by National Basic Research Program of China (973 Program, 2012CB932800), National Natural Science Foundation of China (21433003, 21373199), the Science & Technology Research Programs of Jilin Province (20150101066JC, 20160622037JC).

References

[1] S. Park, Y. Shao, J. Liu, and Y. Wang, Energy Environ. Sci., 5, 9331 (2012).

[2] W. Hu, Y. Wang, X. Hu, Y. Zhou, and S. Chen, J. Mater. Chem., 22, 6010 (2012).

[3] E. Ortel, T. Reier, P. Strasser, and R. Kraehnert, Chem. Mater., 23, 3201 (2011).

Figure 1
Bifunctional Platinum-Cobal Oxide Catalysts for the Oxygen Reduction and Evolution Reactions
Authors: Wang Lei , Wang Chao
Published: February 2020

A bifunctional catalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) could be employed in a unitized regenerative fuel cell, an energy storage device that can be coupled to intermittent renewable energy such as wind or solar to peak-shift electricity to the grid. Though significant work has been done over the past few decades, no catalyst for both ORR and OER with high activity for both reactions have been discovered. It is well know that platinum or platinum based alloys exhibit the highest activities for ORR among all other catalyst, however they display poor activity for OER. In contrary, transition metal (hydro)oxides, such as iron, nickel, or cobalt (hydro)oxides, always possess highly activities for OER but poor activity for ORR. Due to “migration-effect” of transition metal in ORR, in which the free transition metal (hydro)oxides will move to the surfaces of platinum during electrochemical process and results in the dramatically decrease of the ORR activity of Pt eventually, it is impossible to achieve high activity for both ORR and OER by simply mix platinum or platinum based alloy with transition metal (hydro)oxides together. Inspired by this, we developed a novel method to prepare 7nm platinum nanoparticles doped with atomic sized cobalt oxides for the applications of ORR and OER. Our primary results showed that these hetero-structured materials exhibited higher activity than state-of-the-art commercial platinum for ORR, but also 10 times higher activity for OER than Co3O4. Most importantly, our catalysts also demonstrated excellent stability. Apparently, the interfaces must play a dominated role in both ORR and OER. Investigation of the interfaces between platinum and Co3O4 of our catalyst in atomic scale is crucial to understand how the interfaces worked and what kinds of interfaces are better for both ORR and OER. Our work will advanced the fundamental understanding of the metal-oxide interface in enhancing the ORR and OER, which is envisioned to shed light on the design of advanced catalysts for catalyzing complex chemical processes.