bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Effect of Electrochemical Treatment and pH on VIV/VV Electrode Kinetics
Authors: Sasikumar S P Varsha , Lynch Robert P. , Al Hajji Safi Maria , Buckley D. Noel , Bourke Andrea
Published: September 2022

Cyclic voltammetry and electrochemical impedance spectroscopy were used to investigate the effect of electrochemical treatment of glassy carbon electrodes in electrolytes of various pH on VIV/VV redox kinetics. In all pH treatment electrolytes (pH 0 – pH 6.3), the VIV/VV kinetics are enhanced by cathodic treatment of the electrode and inhibited by anodic treatment. For all pHs, pronounced activation typically occurs at cathodic treatment potentials more negative than ~+0.4 V and the effect is most significant at ~–0.8 V. It is also found that the activating effect of cathodization is enhanced significantly with increasing pH. For all pHs, pronounced deactivation typically occurs at anodic treatment potentials more positive than ~+0.2 V and the effect begins to saturate at ~+1.0 V. Within this deactivation region of potentials, the rate constants decrease linearly with increasing treatment potential and reach similar final deactivation rate constants. The observed effects cannot be fully explained by surface roughening effects during anodization, rather they are attributed to changes to electrode surface functional groups by electrochemical polarization. It is suggested that competing cathodic processes, the rates of which appear to be pH dependent, control the surface functional groups formed and the resulting kinetics of the electrode surface for VIV/VV.
(Invited) The Long Reach of Impedance Measurements: From Flow Cells and Dielectrics to Experimental Artifacts
Authors: Vanysek Petr
Published: September 2022

Several ideas gained over the research involving energy conversion and storage and also teaching about these subjects is presented. In particular, dealing with data reporting and impedance interpretation of experimental artifacts is presented. Some aspects of energy conversion and storage that may bring up skepticism are also discussed.
(Invited) Radiation Damage in the Ultra Wide Bandgap Semiconductor Ga2O3
Authors: Xia Xinyi , Li Jian-Sian , Sharma Ribhu , Ren Fan , Rasel Md Abu Jafar , Stepanoff Sergei , Al-Mamun Nahid , Haque Amanul , Wolfe Douglas , Modak Sushrut , Chernyak Leonid , Law Mark , Khachatrian Ani , Pearton Stephen J
Published: September 2022

Ga2O3 is expected to show similar radiation resistance as GaN and SiC, considering their average bond strengths. However, this is not enough to explain the orders of magnitude difference of the relative resistance to radiation damage of these materials compared to GaAs and dynamic annealing of defects is much more effective in Ga2O3. Octahedral gallium monovacancies are the main defects produced under most radiation conditions because of the larger cross-section for interaction compared to oxygen vacancies. Proton irradiation introduces two main paramagnetic defects in Ga2O3, which are stable at room temperature. Charge carrier removal can be explained by Fermi-level pinning far from the conduction band minimum due to gallium interstitials (Ga
i
), vacancies (VGa), and antisites (GaO). With few experimental or simulation studies on single event effects (SEE) in Ga2O3 , it is apparent that while other wide bandgap semiconductors like SiC and GaN are robust against displacement damage and total ionizing dose, they display significant vulnerability to single event effects at high Linear Energy Transfer (LET) and at much lower biases than expected. We have analyzed the transient response of β-Ga2O3 rectifiers to heavy-ion strikes via TCAD simulations. Using field metal rings improves the breakdown voltage and biasing those rings can help control the breakdown voltage. Such biased rings help in the removal of the charge deposited by the ion strike.
Integration Aspects of Plasmonic TiN-based Nano-Hole-Arrays on Ge Photodetectorsin a 200mm Wafer CMOS Compatible Silicon Technology
Authors: Mai Christian , Marschmeyer Steffen , Peczek Anna , Kroh Aleksandra , Jose Josmy , Reiter Sebastian , Fischer Inga , Wenger Christian , Mai Andreas
Published: September 2022

In this work we present the progress in regard to the integration of a surface plasmon resonance refractive index sensor into a CMOS compatible 200 mm wafer silicon-based technology. Our approach pursues the combination of germanium photodetectors with metallic nanohole arrays. The paper is focused on the technology development to fabricate large area photodetectors based on a modern design concept. In a first iteration we achieved a leakage current density of 82 mA/cm2 at reverse bias of 0.5 V and a maximum optical responsivity of 0.103 A/W measured with TE polarized light at λ = 1310 nm and a reversed bias of 1 V. For the realization of nanohole arrays we used thin Titanium nitride (TiN) layers deposited by a sputtering process. We were able to produce very homogenous TiN layers with a thickness deviation of around 10 % and RMS of 1.413 nm for 150 nm thick TiN layers.
(Invited) Extremely-Thin Body Goi Channel Technology in Nano-Sheet FET Era
Authors: Takagi Shinichi , Chen Chia-Tsong , Han Xueyang , Sumita Kei , Toprasertpong Kasidit , Takenaka Mitsuru
Published: September 2022

Extremely-thin body (ETB) nano-sheet CMOS is expected as a device structure to realize future continuous scaling. Thus, channel materials to maintain high mobility in such an ETB channel are strongly needed. It is revealed through analyses based on a new physical model of thickness fluctuation scattering that ETB GOI channels, particularly (111) GOI channels, are promising for this purpose. High-quality ETB GOI channels are formed by the Ge condensation and smart-cut technology. The operations of Ge p- and n-MOSFETs with the body thickness down to 2 nm are experimentally demonstrated and the body thickness dependencies of the effective mobility are examined. The importance of strain and surface orientation engineering on mobility in an ETB region is addressed.
(Invited) Impact of Polarization Variation on Ferroelectric Field-Effect Transistor and Compute-in-Memory
Authors: Choe Gihun , Yu Shimeng
Published: September 2022

The discovery of Hafnia-based ferroelectric materials made ferroelectric field-effect transistor (FeFET) a promising nonvolatile memory device and enables aggressive scaling down. However, the ferroelectric layer possesses polarization variation (PV) induced by its crystallinity, whereby FeFET suffers from performance variation. Hence, it is critical to assess its influence quantitatively to utilize the FeFET for storage or compute-in-memory applications. In this review, recent trends and progress of the performance variation on the FeFETs are surveyed. We present the impact of PV on three-dimensional (3D) FeFETs. In addition, to show its capability for compute-in-memory application, the inference accuracy is discussed under the structures. Next, the Voronoi diagram is introduced to model the different sizes and shapes of ferroelectric grains. A comparative study of the device variability with other sources is investigated under different technology nodes. Finally, a machine learning-aided methodology to analyze the variability of FeFET based on the metrology data is proposed.
Properties of Selectively Grown Si:P Layers below 500°C for Use in Stacked Nanosheet Devices
Authors: Rosseel Erik , Porret Clement , Hikavyy Andriy Yakovitch , Loo Roger , Richard Olivier , Martinez Gerardo Tadeo , Batuk Dmitry , Mertens Hans , Dentoni Litta Eugenio , Horiguchi Naoto
Published: September 2022

We report on selectively grown Si:P layers below 500°C targeting application in stacked nanosheet-based devices. In contrast to conventional approaches where selectivity is obtained at low temperatures using Cyclic-Deposition and Etch (CDE) with HCl/GeH4 as an etchant, we rely for this work on Cl2-based etching and the use of a higher order Si precursor which allows to maintain a high wafer throughput at low temperatures. We demonstrate that selective Si:P layers can be obtained with a resistivity below 0.3 mOhm.cm which can be grown selectively on fins and stacks with Si nanosheets.
(Digital Presentation) Selective SiGe Vapor Etching Using Br2 in View of Nanosheet Device Isolation
Authors: Loo Roger , Gosset Nicolas , Isaji Megumi , Kawamura Yumi , Hikavyy Andriy Yakovitch , Rosseel Erik , Porret Clement , Nalin Mehta Ankit , Girard Jean-Marc
Published: September 2022

Both forksheet and CFET device layouts contain local dielectric isolation layers to circumvent junction isolation trade-offs which are specific for these designs. Typical fabrication schemes start with the epitaxial growth of complicated SiGe/Si multi stacks with at least two different Ge concentrations where a Ge-rich SiGe layer is later replaced by an isolating dielectric. This work proposes a low temperature Br2-based vapor etching process as an option for the selective SiGe removal in the isolation fabrication. After initial process screening on blanket epi layers to compare etching behavior for different process gases as function of material composition and crystallinity, it is demonstrated on patterned test structures that Br2 etching enables high etching selectivity of Si0.5Ge0.5 towards Si and Si1-xGex (x = 0.2 - 0.3).
Viewing SiGe Heterostructure for Qubits with Dislocation Theory
Authors: Liu Yujia , Gradwohl Kevin-Peter , Lu Chenhsun , Yamamoto Yuji , Remmele Thilo , Corley-Wiciak Cedric , Teubner Thomas , Richter Carsten , Albrecht Martin , Boeck Torsten
Published: September 2022

Strained isotopically enriched 28Si strained layers in SiGe/Si/SiGe heterostrustructures is an excellent material platform for electron spin qubits. In this work, we report the fabrication of 28SiGe/28Si/28SiGe heterostructures for qubit devices by a hybrid MBE/CVD growth, where the thick relaxed SiGe buffer is realized by a reduced-pressure CVD and the 28SiGe/28Si/28SiGe stack is grown by an MBE. Here, we achieve a fully strained 28Si layer in such heterostructure with a 29Si concentration as low as 200 ppm within the MBE grown layers. It was possible to conclude that 29Si primarily originates from the residual natural Si vapour in the MBE chamber. Furthermore, we also present our studies about the growth temperature effect on the misfit dislocation formation in this heterostructure. It was possible to show that at a low MBE growth temperature, such as 350°C, the misfit dislocation formation is significantly suppressed.
(Digital Presentation) Fabrication of Thick SiGe／Ge Multiple Quantum Wells on Ge-on-Si and Their Optical Properties
Authors: Kanesawa Rena , Wagatsuma Youya , Kikuoka Shuya , Sugiura Yuwa , Sawano Kentarou
Published: September 2022

We fabricate thick strained Si0.1Ge0.9/Ge multiple quantum wells (MQWs) structures on Ge-on-Si, and evaluate their crystallinities and optical properties. As a result, it is found that highly crystalline Si0.1Ge0.9/Ge MQWs are grown both on Ge-on-Si(100) or Ge-on- Si(111), where surface roughness slightly differs between the two. From both MWQs we obtain strong room-temperature photoluminescence (PL) via quantum confinements of carriers in the MQWs. It is also found that the PL peak positions and intensities are different between (100) and (111). Surface roughening is considered to cause reduction in the PL intensity and the peak shift for the (111) case whereas the MQWs on Ge-on-Si(100) shows very smooth surface and resultantly strong PL intensity, indicating that Si0.1Ge0.9/Ge MQWs are promising for applications to light-emitting devices that can be integrated on the Si platform.
Nanosecond Laser Annealing of In-Situ Boron-Doped Ge Layers for Dopant Activation
Authors: Frauenrath Marvin , Acosta Alba Pablo , Papon Anne-Marie , Hartmann Jean-Michel
Published: September 2022

Low contact resistances are required to continue the miniaturization of CMOS devices and improve the performances of group IV semiconductors’ photodiodes and light emitting devices. In this study, we tried to enhance the electrical activation in in-situ boron-doped germanium by nanosecond laser annealing (NLA), an ultrafast, non-equilibrium process. Similar annealing regimes than that evidenced on SiGe thin layers were seen. Surface structures with shapes and orientations comparable to that after SiGe NLA were found in the surface melt regime. When the entire Ge:B layer was melted, we obtained a flat surface with a root mean square roughness of 1.51 nm. Laser annealing resulted in a redistribution of B, with the formation of electrically inactive clusters that did not contribute to strain. Accordingly, the sheet resistance increased by 70%, from 39.82 Ω/□ up to 68.62 Ω/□, when the layer was melted. This corresponded to an electrically active carrier loss of around 50%, from 8.1x1020 cm-3 down to 3.8x1020cm-3. Even multiple pulses with various energy densities at the same position were not able to improve electrical activation. However, there was some slight improvements of the sheet resistance in the sub melt regime, which needs to be confirmed in future experiments.
Investigation of Band Structure in Strained Single Crystalline Si1-X
Sn
X
Authors: Sahara Keita , Yokogawa Ryo , Shibayama Yuki , Hibino Yusuke , Kurosawa Masashi , Ogura Atsushi
Published: September 2022

We evaluated the optical properties and the band structure of strained single crystalline Si1-x
Sn
x
using spectroscopic ellipsometry. The results suggest a reduction of the band gap at the Γ point and the formation of an optical transition by Van-Hove singularity with higher Sn fraction. In addition, since the reduction of the band gap with increasing Sn fraction at the Γ point is larger than at other points, it is expected the indirect transition type Si1-x
Sn
x
used in this study may eventually change to the direct transition type. Although higher Sn fraction are required to achieve direct transition type Si1-x
Sn
x
, the band structure of strained single crystal Si1-x
Sn
x
was experimentally clarified.
Distribution Evaluation of Optical Properties in Silicon Germanium Films Grown on Silicon Substrates with Graded Silicon Germanium Buffer Layers
Authors: Shibayama Yuki , Yokogawa Ryo , Ogura Atsushi
Published: September 2022

We report on the distribution of the optical properties in strain-relaxed SiGe films. We confirmed that the SiGe film (Ge fraction: 50%) has a larger variation of the extinction coefficient than the SiGe film (Ge fraction: 20%) in the near-infrared region. This result suggests that the distribution of the optical properties of the SiGe film (Ge fraction: 50%) may have a significant effect on process yields while the SiGe film (Ge fraction: 20%) should have a smaller effect on process yields. In addition, we investigate the distribution of Ge fraction, strain and cross-hatch pattern, and consider their relationship to optical properties.
Ga+ Focused Ion Beam Damage in n-type Ga2O3 and Its Recovery after Annealing Treatment
Authors: Xia Xinyi , Al-Mamun Nahid , Daudi Warywoba , Ren Fan , Haque Aman , Pearton Stephen J
Published: September 2022

Focused Ga+ ion milling of lightly Si-doped, n-type Ga2O3 was performed with 2–30 kV ions at normal incidence and beam currents that were a function of beam voltage. The electrical effects of the ion damage were characterized by Schottky barrier height and diode ideality factor on vertical rectifier structures comprising 10 µm epitaxial n- Ga2O3 on n+ Ga2O3 substrates, while the structural damage was imaged by Transmission Electron Microscopy. The forward current-voltage characteristics showed significant deterioration at 5kV. The I-V characteristics no longer showed rectification for the 30kV condition. Subsequent annealing up to 400°C produced substantial recovery of the I-V characteristics for all beam energies and was sufficient to restore the initial ideality factor completely for beam energies up to 5kV. A remarkable reduction of dislocations can be observed in 30 kV ion exposed sample after annealing at 400°C.
Characterization of ALD Ta2O5, Al2O3, and Ta2O5/Al2O3 Nanolaminate as Metal-Insulator-Metal Capacitor Dielectric for GaAs HBT Technology
Authors: Yota Jiro
Published: September 2022

Tantalum pentoxide (Ta2O5), aluminum oxide (Al2O3), and Ta2O5/Al2O3 nanolaminate deposited using atomic layer deposition (ALD) have been characterized and evaluated as metal-insulator-metal (MIM) capacitor dielectric in GaAs hetero-junction bipolar transistor (HBT) technology. The results show that the capacitor with 60 nm of ALD Ta2O5 and Al2O3 capacitor dielectric films resulted in a capacitance density of 3.84x10-15 F/μm2 and 1.37x10-15 F/μm2 and a dielectric constant of 26.1 and 9.3, respectively, while the capacitor with 60 nm of ALD Ta2O5/Al2O3 nanolaminate capacitor dielectric film resulted in capacitance density of 2.40x10-15 F/μm2 and a dielectric constant of 16.3. The capacitance density of capacitor using these three films increased marginally by 2.2% to 4.3%, when the temperature was increased from 25oC to 125oC. No significant change in capacitance density of these ALD films was observed, when the applied voltage was varied from -5 V to +5 V. The leakage current density of the ALD Al2O3, Ta2O5, and Ta2O5/Al2O3 nanolaminate films at an electric field of 3 MV/cm is 2.0x10-16 A/μm2, 6.8x10-8 A/μm2, and 9.2x10-13 A/μm2, respectively. The 60 nm ALD Al2O3 film has higher breakdown voltage of 46 V, compared to the 60 nm ALD Ta2O5 film and the 60 nm Ta2O5/Al2O3 nanolaminate film, which has a breakdown voltage of 22.5 V and 32.7 V, respectively. As the temperature was increased from 25oC to 125oC, the leakage current increased and breakdown voltage decreased for all three ALD films.
(Invited, Digital Presentation) Oxide TFTs Based on Semiconductors and Semimetals
Authors: Zhang Jiawei , Wilson Josh , Song Aimin
Published: September 2022

A bottleneck issue of oxide TFTs is the instability under bias stresses and illuminations. Furthermore, the carrier mobility needs improvement for high pixel density and high brightness displays. Here, we use a high work-function Schottky source contact to enable depletion around the TFT source region. This results in a high intrinsic immunity to negative bias illumination stress, no obvious short channel effect, and extremely flat current saturation at low drain voltages. A voltage gain reaching 23,000 V/V is obtained due to the flat saturation current, which is the highest ever achieved with a solid-state transistor. Furthermore, the Schottky barrier depletion allows to utilize ITO to replace IGZO as the channel layer, which significantly enhances carrier mobility. Because ITO is used for both channel and drain electrode, the TFT appears to have no channel, enabling aggressive scaling for a significant increase in flat-panel display pixel aperture ratio, brightness and pixel density.
Intrinsic Channel Mobility Associated with Extended State Transport in IGZO TFTs
Authors: Kabir Muhammad Salahuddin , Powell Eli , Manley Robert G. , Hirschman Karl D.
Published: September 2022

There is wide variation in the interpretation of the interaction and/or independence of channel mobility and charge trapping in IGZO TFTs. Electrical measurements reveal temperature-dependent behavior that is not explained by existing TCAD models employed for defect states and carrier mobility. An IGZO TFT device model has been recently developed using Silvaco Atlas, which accounts for the role of donor-like oxygen vacancy defects, acceptor-like BTS, and acceptor-like interface traps, thus properly regulating the amount of free channel charge. The channel mobility is defined as only a function of temperature, and reflects a thermally-activated diffusive mobility with a distinct activation energy Ea = 40 meV. This thermally activated process is clearly intrinsic, as it is constant over all bias conditions and is not dependent on the steady-state trapped charge level. The model demonstrates a remarkable match to transfer characteristics measured at T = 150 K to room temperature.
(Digital Presentation) Degradation and Recovery of Low Temperature Poly-Si Thin Film Transistors Under DC and AC Bias Stresses
Authors: Liu Han-Wen , Syu Shu-Wei , Huang Bo-Xiang
Published: September 2022

The degradation and recovery phenomena of n-type LTPS TFTs stressed at hot carrier effect region under various bias conditions are investigated. The devices with longer LDD’s length demonstrate less degradation ratio but more recovery ratio, because of the lower transverse electric field. As the AC signals are applied to the gate terminal, the degradation of devices shows no significant dependence of AC signal frequency, but the recovery ratio displays the similar trends as AC signal frequency changing. However, as the AC signals are applied to the drain terminal, the degradation of devices shows very significant dependence of AC signal frequency. The higher the AC signal frequency is, the less degradation the devices show, but the recovery ratio displays the similar trends as AC signal frequency changing. From the results of all stressing conditions, the LTPS TFTs stressed with DC voltages exhibit the largest degradation ratio but almost the least recovery one.
(Invited) High Performance Fully Solution Processed Transistors Towards Flexible Sustainable Electronics
Authors: Bermundo Juan Paolo , Corsino Dianne , Hanifah Umu , Uraoka Yukiharu
Published: September 2022

High performance fully solution-processed amorphous InZnO (a-IZO) thin-film transistors (TFT) were fabricated using low temperature processes such as ultraviolet (UV) treatment, excimer laser annealing (ELA), continuous wave (CW) laser irradiation, and Ar plasma treatment. By employing a self-aligned top-gate structure, these processes can selectively functionalize the IZO semiconductor into conductive electrodes. Thus, a single IZO layer can simultaneously act as both the channel and source/drain electrode. Depending on the low temperature process employed, mobilities of up to 40 cm2 V-1 s-1 can be achieved with low turn on-voltage of -0.4 V and subthreshold swing of 0.2 V dec-1 which is comparable to TFTs fabricated by vacuum process. The low temperature approach also enabled the fabrication of fully solution processed a-IZO TFTs on flexible substrates. Comprehensive analysis of several characterization results suggests that both fluorine and oxygen vacancies play a major role in the high performance fully solution processed a-IZO TFTs.
Performance Enhancement of Solution-Processed SixSnyO TFTs using Solution Combustion Synthesis
Authors: Quino Candell Grace Paredes , Bermundo Juan Paolo , Uenuma Mutsunori , Uraoka Yukiharu
Published: September 2022

In this work, we improved the performance of SixSnyO TFTs using solution combustion synthesis. The mobility of SixSnyO TFTs was significantly improved using SCS which confirms that SCS is beneficial in improving the quality of SixSnyO films. The carbon impurities in the SCS film was also reduced as confirmed by SIMS. The linear mobility for SCS TFT is 3.14 cm2/V s while the sol-gel TFT is 0.08 cm2/V s. We also successfully lowered down the processing temperature to 300 °C using a simple combustion process.
(Digital Presentation) Influence of Fin Width Modulation on Nanoscale FinFET
Authors: Rathore Rituraj S. , Srivastava Viranjay M.
Published: September 2022

In the present research work, the influence of Fin width thickness variation on the electrical performance parameters have been performed for the 14-nm FinFET device. Various Fin angle (i.e., θ) have been considered to analyze the effect of Fin thickness. All the analyzed results have been compared with the ideal FinFET (i.e., θ = 00) device to observe the effect of angle variation on threshold voltage (VTH
), transconductance (gm
), Gate current (IG
) and Drain Induced Barrier Lowering (DIBL). In addition, the impact of Fin width thickness variations has been used to realize the inverter Voltage Transfer Characteristics (VTC). The characteristics comparison reveals that including the effect of Fin width improves the device performance of FinFET devices.
(Invited) Recent Progress in Wide-Bandgap Semiconductor Devices for a More Electric Future
Authors: Kizilyalli Isik C , Blum Spahn Olga , Carlson Eric P
Published: September 2022

Wide-bandgap (WBG) semiconductors, with their excellent electrical properties, offer breakthrough performance in power electronics enabling low losses, high switching frequencies, and high temperature operation. WBG semiconductors, such as silicon carbide and gallium nitride, are likely candidates to replace silicon in the near future for high power applications as silicon is fast approaching its performance limits. Wide-bandgap power semiconductor devices enable breakthrough circuit performance and energy efficiency gains in a wide range of potential applications. The U.S. Department of Energy’s Advanced Research Project Agency - Energy (ARPA-E) has invested in WBG semiconductors over the past ten years targeting the barriers to widespread adoption of WBGs in power electronics including material and device development. Under ARPA-E projects, medium voltage (10-20kV) WBG device development has commenced to push the voltage boundaries of WBGs. This includes super-junction devices and light triggered photoconductive devices for MV applications. The WBG MV devices will enable MVDC grid distribution applicable to markets including electrified transportation, renewable interconnections, and offshore oil, gas, and wind production. Advanced WBG device ideas are additionally being explored including 3D device structures, WBG integrated circuits, and neutron detectors The progress and challenges of the WBG devices being developed under ARPA-E programs will be reviewed along with thoughts on the future trends of WBG device development.
Modeling of Relative Humidity-Dependent Impedance of Polymer Electrolyte Membrane Fuel Cells
Authors: Tanaka Akihisa , Nagato Keisuke , Tomizawa Morio , Inoue Gen , Nakao Masayuki
Published: September 2022

Equivalent circuit modeling is a powerful technique for analyzing the complex impedance of polymer electrolyte membrane fuel cells. The transmission line model, which is based on reactant transport and electrochemical reactions, is frequently applied to porous electrodes. In this study, the distribution of the local charge transfer resistance was considered to accurately evaluate the dependence of the impedance on relative humidity (R.H.). The impedance of the prepared single cell was measured at 0.7 V under various R.H. conditions. The fitting results to the measured impedance spectra confirmed that a strong positive correlation exists between R.H. and proton conductivity. The exchange current density was determined in advance to simulate the impedance with dependence on R.H. The proposed model can simulate the experimental trend in which the total resistances of proton conduction and charge transfer decreased inversely to R.H.
Modeling of the dynamic behavior of an integrated fuel cell system including fuel cell stack, air system, hydrogen system, and cooling system
Authors: Hasegawa Shigeki , Ikogi Yoshihiro , Kim Sanghong , Kageyama Miho , Kawase Motoaki
Published: September 2022

1-dimentional (1-D) physical modeling methods of the dynamic behavior of an integrated fuel cell (FC) system are investigated, which consist of the models of the FC stack and subsystems of the air, hydrogen (H2), and cooling systems. To ensure numerical simulation of the entire FC system in life-long system operation (> 10 years) in acceptable calculation time, a proper model resolution is selected. The subsystem models are integrated with the FC stack model and controllers developed in our previous research to build a closed-loop simulator of an integrated FC system. It demonstrated that the impacts of the FC stack material properties on the overall FC system performance can be investigated by numerical simulation.
Unsteady Three-Dimensional Simulation of Water Condensation in Gas Diffusion Layer
Authors: Naito Hiroshi , Hirai Shuichiro
Published: September 2022

Liquid water accumulates inside polymer electrolyte fuel cells (PEFCs) prevents gas transport and degrades the cell performance. In this study, we performed an unsteady numerical simulation of water condensation and accumulation in the gas diffusion layer (GDL) of PEFCs using the three-dimensional structure of the GDL obtained by X-ray CT measurement. The temperature and gas concentration fields were solved to obtain the amount of condensation, and the volume of fluid (VOF) method was used for the transport of the gas-liquid interface. As a result of the simulation, the region where condensation occurs was identified and the formation mechanisms of the liquid-water structure is observed.
Multiwalled Carbon Nanotube-Filled Polymer Composites for Direct Injection Molding of Bipolar Plates
Authors: Kypta Chadwick J , Young Brian A , Santamaria Anthony , Hollinger Adam S
Published: September 2022

Fuel cell bipolar plates are commonly fabricated from graphite, however the associated machining costs are a major limitation to fuel cell commercialization. A promising alternative approach to bipolar plate manufacturing is injection molding of polymer composites. Injection molding is well-suited for mass production and polymeric materials can significantly reduce the weight of the bipolar plate. In this study, polymer composites based on nylon were injection molded with different weight percentages of conductive filler. Initially, carbon fiber was added to nylon 6,6 at weight percentages ranging from 10 to 50%. Results show that the percolation threshold for carbon fiber in nylon occurs around 25 wt%. Multiwalled carbon nanotubes (MWCNTs) were then added to the direct injection-molded nylon/carbon fiber composites to investigate the synergistic effects of multiple conductive fillers. By introducing carbon nanotubes into the polymer matrix, the nanotubes act as a bridge between the carbon fibers. SEM images show that the MWCNTs fill the void between fibers due to their smaller size and their ease of dispersion. This bridging creates more conductive pathways within the polymer matrix, increasing the electrical conductivity of the composite. Samples with MWCNTs reached conductivities of 64 S/cm, nearing the United States Department of Energy technical target for bipolar plate conductivity (>100 S/cm).
(Digital Presentation) Correlative Evaluation Between Water Concentration and Voltage Fluctuation of PEFC Under Low-Humidity and Load-Change Operations Based on Laser Spectroscopy
Authors: Nishida Kosuke , Yamaya Naoki , Yin Hanwen , Umekawa Toyofumi , Kawasaki Masahiro
Published: September 2022

To investigate the voltage undershoot behavior in polymer electrolyte fuel cells (PEFCs) operated under low-humidity and load-change conditions, it is necessary to precisely grasp the transient water transport within the cell. This study has developed a single-ended fiber-optic sensor to quantify the water vapor concentration in flow channels of PEFCs based on laser spectroscopy and investigated the correlation between the water behavior in the anode and the voltage fluctuation during low-humidity and current-cycle operations. The effects of inlet humidification, load current range and compression pressure on the voltage undershoot were also examined. The results revealed that the large undershoot and the temporal drop of anode water concentration occurs due to the strong electro-osmotic effect when the current density increases steeply at the low humidifications of Anode/Cathode=30/0, 0/30, 30/30 %RH. It was also found that the high load current of 1.0 A/cm2 and the strong cell compression of 2.0 MPa reduces the undershoot after several current cycles because of the water accumulation on the anode side.
Flooding Characteristics and Countermeasures in a PEM Fuel Cell System
Authors: Breitinger Jonas , Hellmann Mark , Kemmer Helerson , Kabelac Stephan
Published: September 2022

PEM fuel cell systems in automotive applications must provide a low minimum power compared to their maximum power. Especially systems without external humidification require a rather low stoichiometry and elevated pressure at the cathode to avoid dry-out at low load operation. Targeted experiments show that this may cause flooding, as the gas velocity becomes too low for sufficient liquid water drainage. An increase of the gas velocity would cause a membrane dry-out, negatively impacting the cells performance and lifetime. One solution for this issue is proposed in this work: a dynamic operation of the air system, which is periodically switched between one set point for membrane humidification and another one for liquid water drainage. A sophisticated experimental fuel cell system is used to test the proposed solution on a 100kW stack.
Power Generation Performance of Polymer Electrolyte Fuel Cells with Electrocatalysts Supported on SnO2 in High Current Density Range
Authors: Ogawa Taichi , Inoue Yusuke , Yamamoto Kotaro , Yasutake Masahiro , Noda Zhiyun , Lyth Stephen Matthew , Matsuda Junko , Nishihara Masamichi , Hayashi Akari , Sasaki Kazunari
Published: September 2022

The durability of conventional Pt/C catalysts is still an important technical issue for polymer electrolyte fuel cells (PEFCs). SnO2-supported electrocatalysts with carbon materials as electronic conductive frameworks have the potential to achieve both high catalytic activity and high durability against carbon support corrosion. However, it is still necessary to optimize cell preparation conditions to improve electrochemical cell performance especially in the high current density range. Here, PEFCs with such electrocatalysts are prepared by varying the preparation conditions of the catalyst layer in the membrane electrode assembly (MEA) and a combination of gas diffusion layers (GDLs) and sealant thicknesses. Microstructural optimization is still needed for improving cell performance and minimizing overvoltages.
Multiscale Study of PEMFC in Marine Environment: Impact of a NaCl Spray on Durability
Authors: Lamard Marie , Auvity Bruno , Buttin Paul , Rosini Sébastien , Retière Clément
Published: September 2022

The present work investigates the effects of a salt spray injected into the airflow of Proton Exchange Membrane Fuel Cells (PEMFCs) at various time scales and contamination levels, with the final aim of identifying the appropriate protection for maritime applications. A dedicated experimental setup generates a sodium chloride (NaCl) mist in the cathode airflow to contaminate single cells and stacks. Constant current density tests led to lifetime shortening with partial recovery after cathode rinsing. Then, Membrane Electrode Assemblies (MEAs) post-mortem characterizations revealed that NaCl was present in the cathode gas diffusion layer, and chlorine reached the catalyst layer for high concentrations. Furthermore, chlorides enhanced current collectors and bipolar plates degradation as corrosion products were identified in MEAs and stack effluents. Overall, this study reports that NaCl effects on PEMFCs not only depend on the concentration but also on the MEA type, plate material, and startup/shutdown procedure.
Metallic Gas Diffusion Layers for Polymer Electrolyte Fuel Cells
Authors: Yamamoto Kotaro , Yasutake Masahiro , Noda Zhiyun , Lyth Stephen Matthew , Matsuda Junko , Nishihara Masamichi , Hayashi Akari , Sasaki Kazunari
Published: September 2022

Porous carbon materials are widely used as gas diffusion layers (GDL) in polymer electrolyte fuel cells (PEFCs). Further improvements of these carbon materials are required, including cost reduction and improved mechanical strength. For example, the low mechanical strength of carbon-based GDLs limits the extent to which they can be thinned to reduce PEFC size and cost. Here, the applicability of various metallic GDLs is examined for reducing thickness and cost. Stainless steel GDLs coated with gold (Au) were prepared via physical vapor deposition, as a proof-of-concept. It is revealed that a thin Au coating results in reduced overvoltage and improved cell performance. Whilst Au is expensive and should eventually be replaced with inexpensive materials for practical applications, this work shows that conventional metallic materials could be applied as GDLs if the electrical contact is sufficiently improved.
Investigation of a Correlation Between IV Performance and Cathode Structure for MEAs Using Mesoporous Carbon Supports
Authors: Yasufuku Daichi , Nagayama Mayumi , Sasaki Kazunari , Hayashi Akari
Published: September 2022

The cathode catalyst layer in PEFC plays an important role for further improvement of performance and durability toward heavy–duty vehicles. Since carbon is the main component to define the porous cathode structure, realization of optimal structure of carbon is desired. Therefore, in this study, using lab-made Pt/mesoporous carbon and Pt/mesoporous carbon fiber, and commercially available Pt/Ketjen Black as cathode materials, membrane electrode assemblies were made, and evaluated electrochemically and structurally. Then, a correlation between IV performance and three dimensional structure was investigated. From the three dimensionally reconstructed images, we found that large carbon particles most likely lead to higher ohmic resistance owing to interparticle resistance between the particles. Homogeneous distribution of large pores was found to lower concentration overvoltage.
PEFC Electrocatalysts Using Sn-Based Materials Dispersed on Mesoporous Carbon
Authors: Nishiizumi Ryosuke , Inoue Yusuke , Yasutake Masahiro , Noda Zhiyun , Lyth Stephen Matthew , Nishihara Masamichi , Matsuda Junko , Hayashi Akari , Sasaki Kazunari
Published: September 2022

Significant improvement in the durability of polymer electrolyte fuel cell (PEFC) electrocatalysts is essential for heavy-duty applications. Carbon-based supports suffer from carbon corrosion during start-stop potential cycles, leading to Pt detachment. Load cycles can also cause degradation mainly associated with Pt dissolution/re-deposition. Here, nanocomposite electrocatalysts with Pt and SnO2 decorated on mesoporous carbon (MC) are prepared for improvement of start-stop and load-cycle durability. These nanocomposite electrocatalysts are found to be deposited within the mesopores of the MC support. It is demonstrated by half-cell tests that such electrocatalysts exhibit a high durability for potential changes simulating start-stop and load-cycles.
Investigation of Pt/Fe-N-C Hybrids Towards ORR in Acidic Environment
Authors: Schonvogel Dana , Nagappan Nambi Krishnan , Bengen Nina , Müller-Hülstede Julia , Wagner Peter
Published: September 2022

Metal-nitrogen-carbon (M-N-C) compounds such as Fe-N-Cs are currently the most promising platinum group metal free catalysts for oxygen reduction. Regarding the overriding goal of reducing PEM fuel cell production costs by reducing the amount of platinum, the use of Fe-N-Cs as catalytic active support is investigated in this study. Activity and stability of Pt in different contents on a commercial Fe-N-C is compared to Pt on a typical carbon black. Pt nanoparticles are well-distributed on both support classes. However, electrochemical surface and mass activity of Pt is lower on Fe-N-C compared to carbon black. Although Pt does not profit in any catalytic matter from interaction with Fe-N-C, the Pt/Fe-N-C in total has a boosting effect on ORR activity being important for future strategies to lower the Pt content in PEM fuel cells.
Visualization and Observation of Spatial Temperature Distribution in Reversible Solid Oxide Cells through Simulation and Thermal Imaging
Authors: Fukumoto Takuro , Endo Naoki , Natsukoshi Katsuya , Tachikawa Yuya , Harrington George Frederick , Lyth Stephen Matthew , Matsuda Junko , Sasaki Kazunari
Published: September 2022

Understanding the phenomena which occur inside a solid oxide cell in operation is important in the development of more efficient devices. However, it is difficult to experimentally visualize the distribution of the internal power generation state due to the very high temperature operation. In this study, the performance of a reversible solid oxide cell (r-SOC) was simulated to visualize current-voltage (I-V) characteristics and internal temperature distribution. The validity of the model was verified by comparing with the I-V characteristics and temperature distribution experimentally measured by an actual cell. The establishment of this technique will eventually enable the simulation of cell stacks and systems.
Ni-Alloy Fuel Electrodes for Reversible Solid Oxide Cells
Authors: Yamada Kei , Tachikawa Yuya , Lyth Stephen Matthew , Matsuda Junko , Sasaki Kazunari
Published: September 2022

Reversible solid oxide cells (r-SOCs) are devices that can operate efficiently in both fuel cell and electrolysis operation modes. Nickel is widely used as an anode in conventional solid oxide fuel cells (SOFCs), but this agglomerates due to redox cycling, leading to irreversible performance degradation, making it unsuitable for r-SOCs. Here, we apply alternative electrodes to r-SOCs, in which Ni-Co alloy functions as a catalyst and an electronic conductor, whilst Ce0.9Gd0.1O2 (GDC) functions as a mixed ionic-electronic conductor. The electrochemical performance of these Ni-Co-GDC electrodes and their reverse-operation durability in r-SOCs are evaluated, and the effect of varying the amount of Co is investigated, compared with conventional cermet fuel electrodes. These novel materials exhibit high electrochemical performance and durability against SOFC/SOEC reverse-operation cycling.
Electrochemistry of Neodymium in an Equimolar NaCl-KCl Melt without and with Addition of Fluoride Ions
Authors: Markovich Sergey I , Popova Anna V , Kuznetsov Sergey A
Published: September 2022

The paper presents results of neodymium electrochemical behavior in chloride and chloride-fluoride melts. It was shown that the process of neodymium electroreduction in the NaCl-KCl-NdCl3 melt proceeds in two stages. It was established by diagnostic criteria of voltammetry that the discharge process of Nd(III) to Nd(II) at a sweep rate in the range of 0.6 ≤ n ≤ 1.0 V s-1 is not complicated by reaction disproportionation. In this study diffusion coefficients, activation energy of diffusion for Nd(III) complexes and standard rate constants of charge transfer for the Nd(III)/Nd(II) redox couple in the NaCl-KCl melt were determined. It was shown that the addition of fluorine anions into the NaCl-KCl-NdCl3 melt leads to stabilization of the higher oxidation state of neodymium in chloride-fluoride melts and neodymium in the intermediate oxidation state +2 in these melts does not exist.
(Digital Presentation) Charge Transfer Kinetics of the Ti(IV)/Ti(III) Redox Couple in the Cesium Chloride-Cesium Fluoride Melt with Addition of Alkaline Earth Metal Cations
Authors: Vetrova Daria A. , Kuznetsov Sergey A
Published: September 2022

The electrochemical behavior of the Ti(IV)/Ti(III) redox couple in the CsCl-CsF(10 wt.%)-K2TiF6 melt was studied. The standard rate constants of charge transfer for the Ti(IV)/Ti(III) redox couple in CsCl-CsF(10 wt.%)-K2TiF6-based melts with additions of alkaline earth metal cations (Mg2+, Ca2+, Sr2+ and Ba2+) were determined by cyclic voltammetry method. The activation energies of charge transfer process were calculated. The linear dependence of charge transfer rate constants on the ionic potential of alkaline earth metal cations was found.
Anion Equilibria and Stability of Quaternary Phosphonium Chloroaluminate Ionic Liquids
Authors: Durkin David P. , Stachurski Christopher D. , Cosby James , Trulove Paul C. , Mantz Robert A
Published: September 2022

The anion equilibria and thermal stability in a series of quaternary trialkyloctylphosphonium chloroaluminate ionic liquids are investigated qualitatively by Raman spectroscopy, broadband dielectric spectroscopy, and nuclear magnetic resonance spectroscopy. Results indicate that Lewis acidic chloroaluminate ionic liquids based upon the phosphonium cation are less stable than those based upon other molecular cations. A slow time-dependent drop in room-temperature dc ionic conductivity as well as a step drop at elevated temperatures is tentatively attributed to a reaction involving the Lewis acidic Al2Cl7
- anion and the phosphonium cations. This reaction results in significant changes in the 1H, 13C, and 31P NMR spectra, but only minor changes in the Raman spectra. Furthermore, extended time at elevated temperatures results in a significant quantity of neutral aluminum chloride sublimating from the liquid. These results demonstrate an unusual reactive instability of phosphonium-based Lewis acidic chloroaluminate ILs.
(Digital Presentation) Electrode Potentials of Gallium in Fused Alkali Chlorides
Authors: Tokarev Oleg V. , Volkovich Vladimir A. , Ryzhov Alexander A. , Maltsev Dmitry S.
Published: September 2022

Electrochemical properties of gallium were investigated in 3LiCl–2KCl and 6NaCl–9KCl–5CsCl eutectic based melts at 430–700 and 500–760 oC, respectively. Zero current potentiometry was employed for studying the electrochemical behavior of gallium. Gallium ions in two oxidation states, Ga(III) and Ga(I), were present in the melt in contact with the metal. Formal standard electrode and red-ox potentials of gallium, E*(Ga/Ga(III), E*Ga/Ga(I) and E*Ga(I)/Ga(III), in these molten alkali chloride mixtures were determined.
(Digital Presentation) Reaction of Oxygen with Samarium Chloride Solutions in Molten Alkali Chlorides: An Electrochemistry Study
Authors: Volkovich Vladimir A. , Ryzhov Alexander A. , Doroshenko Darya A.
Published: September 2022

Transient electrochemistry techniques (cyclic and square wave voltammetry) were applied to studying the kinetics of reaction of oxygen with solutions of samarium chloride in molten alkali chlorides. The experiments were performed in LiCl–KCl and NaCl–KCl–CsCl eutectic mixtures at 550–750 oC and in NaCl–KCl equimolar mixture 750 oC. The course of the reactions was followed by recording voltammograms at the certain time intervals during bubbling excess oxygen through the melt. Treating samarium containing melts with oxygen resulted in decreasing concentration of samarium ions in the electrolyte. The reaction had first-order kinetics in respect to samarium chloride. Reaction rate constants and activation energy of the reaction were determined.
Determination of the Formation Potential of Solid-Electrolyte Interphase in Some Amide-Type Ionic Liquids Containing Metal Salts
Authors: Kato Shodai , Serizawa Nobuyuki , Katayama Yasushi
Published: September 2022

The formation potentials of the solid-electrolyte interphase (SEI) on a platinum and glassy carbon electrode in two amide-type ionic liquids, 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (BMPFSA) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA), containing some metal salts were investigated by cyclic voltammetry in the presence of ferrocene (Fc). It is considered that the SEI with the thickness of less than a few nm can be observed by monitoring the shift in the peak potential of Fc+/Fc. The SEIs began to form at ~2.4 V vs. Li|Li(I) in the presence of lithium salts because of a lowering of the lowest unoccupied molecular orbital level of the anion by the interaction with lithium ion. In the case of BMPTFSA containing Ni(TFSA)2, the SEI began to form at –0.7 V vs. Ag|Ag(I), suggesting that the deposition of Ni may be hindered by the SEI formation.
Electrodeposition of Crystalline Si Using a Liquid Zn Electrode in Molten KF–KCl–K2SiF6
Authors: Moteki Wataru , Norikawa Yutaro , Nohira Toshiyuki
Published: September 2022

We propose a novel Si electrodeposition process using a liquid Zn electrode in molten KF–KCl. As the first step of the study, electrochemical measurement and electrolysis were conducted in a KF–KCl–K2SiF6 melt at 923 K. Cyclic voltammograms at a liquid Zn electrode showed the reduction currents due to Si–Zn formation around 0.8 V vs. K+/K. Si deposition was conducted by potentiostatic electrolysis at 0.75 V using liquid Zn in a BN crucible as an electrode. Crystalline Si was deposited not at the boundary between Zn and the molten salt, but at the bottom and side interfaces between Zn and the BN crucible, indicating that Si was electrodeposited via Si–Zn alloy formation. Galvanostatic electrolysis at −20 mA cm−2 with various electrical charges showed that the Si particle size increased with increasing charge, confirming the growth of crystalline Si. Finally, a mechanism of Si electrodeposition via Si–Zn alloying was discussed.