bluuebunny/crossref_metadata_2025 huggingface dataset:
Doped Transition Metal Nitrides As Efficient Electrocatalysts for Electrochemical Reduction of CO2
Authors: Karamad Mohammadreza , Siahrostami Samira , Gates Ian Donald
Published: February 2020

Electrochemical reduction of CO2 to hydrocarbons and alcohols using intermittent renewable energy sources is a promising approach to store energy into chemical bonds for automotive and industrial applications.1 Among many known catalysts, very few, such as copper, are capable of reducing CO2 to significant amount of hydrocarbons and oxygenates, albeit at high overpotentials.2

In the past, numerous experimental and theoretical efforts have been dedicated to understand CO2 reduction reaction mechanism as well as identify efficient catalysts.3–6Transition metal nitrides have attracted a lot of attention for electrochemical reactions such as oxygen reduction reaction, ammonia synthesis and hydrogen evolution in recent years.7–9 In the present study, we employ Density Functional Theory (DFT) calculations to study a wide range of transition metal nitrides with and without heteroatom dopants for CO2 reduction reaction. We identify several stable and active catalysts. This study suggests that transition metal nitrides are promising catalysts for electrochemical reduction of CO2.

References:

Verma, S., Kim, B., Jhong, H.-R. “Molly”, Ma, S. & Kenis, P. J. A. A Gross-Margin Model for Defining Technoeconomic Benchmarks in the Electroreduction of CO 2. ChemSusChem
9, 1972–1979 (2016).

Hori, Y. Electrochemical CO 2 Reduction on Metal Electrodes. in CO2 Reduction on Metal Electrodes. Modern Aspects of Electrochemistry (eds. Vayenas, C. G., White, R. E. & Gamboa-Aldeco, M. E.) 89–189 (Springer New York, 2008).

Kuhl, K. P. et al. Electrocatalytic conversion of carbon dioxide to methane and methanol on transition metal surfaces. J. Am. Chem. Soc.
136, 14107–14113 (2014).

Peterson, A. A., Abild-Pedersen, F., Studt, F., Rossmeisl, J. & Nørskov, J. K. How copper catalyzes the electroreduction of carbon dioxide into hydrocarbon fuels. Energy Environ. Sci.
3, 1311 (2010).

Karamad, M., Hansen, H. A., Rossmeisl, J. & Nørskov, J. K. Mechanistic Pathway in the Electrochemical Reduction of CO 2 on RuO 2. ACS Catal.
5, 4075–4081 (2015).

Li, Y. & Sun, Q. Recent Advances in Breaking Scaling Relations for Effective Electrochemical Conversion of CO 2. Adv. Energy Mater.
6, 1600463 (2016).

Abroshan, H. et al. Ultrathin Cobalt Oxide Overlayer Promotes Catalytic Activity of Cobalt Nitride for the Oxygen Reduction Reaction. J. Phys. Chem. C
122, 4783–4791 (2018).

Abghoui, Y. et al. Enabling electrochemical reduction of nitrogen to ammonia at ambient conditions through rational catalyst design. Phys. Chem. Chem. Phys.
17, 4909–4918 (2015).

Abghoui, Y. & Skúlason, E. Hydrogen Evolution Reaction Catalyzed by Transition-Metal Nitrides. J. Phys. Chem. C
121, 24036–24045 (2017).
(Invited) Selective Etches for Gate-All-Around (GAA) Device Integration: Opportunities and Challenges
Authors: Oniki Yusuke , Altamirano-Sánchez Efraín , Holsteyns Frank
Published: February 2020

This paper addresses the opportunities and challenges of wet and dry etches in the integration of gate-all-around (GAA) device, which is emerging as a promising solution to replace FinFET [1-3]. For the GAA device fabrication, a quintessential challenge is an isotropic etching of dielectrics, semiconductors, and metals with high selectivity to the exposed materials. In this paper, we will demonstrate the significance of (1) Si/SiGe multi stacked fin reveal, (2) cavity etch and inner spacer formation, (3) nanowire and nanosheet release, and (4) replacement metal gate patterning.

[1] H. Mertens et al., VLSI Tech. Dig., 158 (2016).

[2] H. Mertens et al., IEDM Tech. Dig., 828 (2017).

[3] S. Kal et al., Proc.
SPIE, 10963 (2019).
Effect of Crystal Orientation of InGaAs on the Surface Reactions in Acidic Solutions
Authors: Na Jihoon , Lim Sangwoo
Published: February 2020

Indium gallium arsenide (InGaAs) is one of the candidate materials to replace silicon as a channel of NMOS for its excellent electrical properties [1, 2]. In particular, because InGaAs has a high electron mobility as high as 11000 cm2/V·s, it is suitable as a channel material for high-speed devices [3]. However, InGaAs is easily oxidized in aqueous solution and its oxides can also be dissolved in H2O. In addition, since the InGaAs surface has a ternary crystal structure, the reactivity of each crystal plane may be different. Therefore, in order to introduce InGaAs into the channel material of the future transistor, it is necessary to understand the effect of the various crystal orientations of the InGaAs surface and their constituent elements on the InGaAs surface reactions.

In order to investigate the effect of crystal orientation on the surface reaction of InGaAs, InGaAs (100) surface patterned with square shapes. InGaAs samples were dipped in the solutions of HCl/H2O2, H3PO4/H2O2 and HNO3/H2O2 mixtures. The etched amount and etching profile of InGaAs were measured by scanning electron microscope (SEM).

The top etching profiles of InGaAs structure after treatments in HCl/H2O2, H3PO4/H2O2 and HNO3/H2O2 mixtures were shown in Fig. 1. It was first found that the etched amounts of the InGaAs structure were the largest after the treatment of HNO3/H2O2 mixture and the smallest after the treatment of HCl/H2O2 mixture. It is considered that the overall etching rate of InGaAs is increased because the surface oxidation reaction of InGaAs is accelerated by HNO3 having strong oxidizing power. On the other hand, the etched amounts of InGaAs along the [100], [010], and [110] directions were similar each other, but that along the [-110] direction was relatively small. In addition, it was observed that the slope of inclined plane formed after the InGaAs surface etching along the [-110] direction was more gentle than that of the other crystal directions. It is believed that the InGaAs surface is etched in the [-110] direction, revealing the {-1-12}A or {-111}A surface with low surface reactivity [4, 5]. In order to better understand the effect of the various crystal orientations of the InGaAs surface, the cross-sectional etching profiles of photoresist-masked InGaAs after treatment of HCl/H2O2, H3PO4/H2O2 and HNO3/H2O2 mixtures were observed as shown in Fig. 2. It was observed that {-1-12} plane was formed after treatment of HCl/H2O2 mixture and {-111} plane was formed after treatment of H3PO4/H2O2 or HNO3/H2O2 mixture. The results show that the surface reaction of InGaAs is strongly influenced by crystal orientation.

References

[1] J. A. del Alamo, Nature, 479, 317 (2011).

[2] D. H. van Dorp, S. Arnauts, D. Cuypers, J. Rip, F. Holsteyns, S. De Gendt, Solid State Phenom., 219, 56 (2015).

[3] T. P. Pearsall, J. P. Hirtz, J. Cryst. Growth, 54 (1981).

[4] S. Adachi, H. Kawaguchi, J. Electrochem. Soc., 128, 1342 (1981).

[5] D. W. Shaw, J. Electrochem. Soc., 128, 874 (1981).

Figure 1
Surface Reorganization and Rate Enhancement of Spinel LiMn2O4 (LMO) on First Trimethylaluminum/Water Exposure
Authors: Young Matthias J , Letourneau Steven , Warburton Robert , Dose Wesley , Greeley Jeffrey , Johnson Christopher S. , Elam Jeffrey W.
Published: February 2020

Recent work has identified enhanced charge storage capacity in the spinel lithium manganese oxide (LiMn2O4;LMO) lithium ion battery cathode upon a single atomic layer deposition (ALD) cycle comprised of one chemical exposure of trimethylaluminum (TMA) and one exposure of water (H2O). Here, we report further study of the rate capability following one TMA/H2O exposure and identify enhanced rate capability versus pristine LMO. To understand this effect, we experimentally probe the surface composition of LMO with TMA/H2O treatment using X-ray photoelectron spectroscopy (XPS) measurements with inert-transfer. This includes a study of the LMO surface properties following TMA exposure before exposure to H2O. We identify the removal of a surface carbonate layer from LMO upon TMA exposure, and the formation of a Li-rich aluminum oxide surface layer upon subsequent H2O exposure. We also observe a previously undescribed phenomenon of Li ions depleting from the LMO surface upon TMA exposure and returning upon H2O exposure. Ab initio materials modeling is used to complement our measurements and provides fundamental understanding for the effects we observe. The chemical effects we observe are connected with the enhanced rate capability of ALD-coated LMO and are related to a range of emerging studies on carbonate surface layers in battery cathodes, as well as the use of ALD to stabilize battery interfaces.

Figure 1
(Invited) Atomic Layer Processing for Advanced Electronics
Authors: Leusink Gerrit J
Published: February 2020

With devices and interconnects now being scaled to below the limits of even the most advanced lithographic patterning, dimensional control requires new thin-film processes with atomic-scale control of thickness, uniformity, morphology, and material and electrical properties at all levels, from the atomic scale to the equipment scale. With ever increasing complexity in process technologies, chemically selective and/or area-selective processes can be an efficient way to meet future manufacturing requirements. Novel process technologies are needed for deposition, etch and cleans with atomic level precision to enable area-selective-processing at the structure and material level [1].

In this tutorial we will review and discuss trends in Atomic Layer Processing technologies for advanced semiconductor device manufacturing. The topics and technologies explored in this presentation include atomic layer deposition (ALD), atomic layer etching (ALE), selective deposition and etching, advanced surface preparation, EUV lithography, and self-aligned and multiple patterning schemes among others. Applications include critical material and manufacturing challenges for advanced Logic and Memory devices, including high-k oxides and metals, interconnects, capacitors, as well as Patterning, including Multi Patterning, Fully-Self-Aligned patterning and EUV [2].

A key point of this presentation will be to educate attendees how these advanced process technologies can be leveraged synergistically to deliver power, performance, area and cost scaling for future devices. Examples will be given so that attendees can understand how advanced process technologies will be used in future device manufacturing as well as the benefits and tradeoffs in their use.

References:

[1] Rethinking surface reactions in nanoscale dry processes toward atomic precision and beyond: A physics and chemistry perspective, To be published in Japanese Journal of Applied Physics Kenji Ishikawa, Tatsuo Ishijima, Tatsuru Shirafuji, Silvia Armini, Emilie Despiau-Pujo, Richard A. Gottscho, Keren J. Kanarik, Gert J. Leusink, Nathan Marchack, Takahide Murayama, Yasuhiro Morikawa, Gottlieb S. Oehrlein, Sangwuk Park, Hisataka Hayashi, and Keizo Kinoshita.

[2] Perspective: New process technologies required for future devices and scaling, APL Materials 6, (2018), R. Clark, K. Tapily, K.H. Yu, T. Hakamata, S. Consiglio, D. O'Meara, C. Wajda, J. Smith and G. Leusink.
(Invited) Expanding the Toolbox of Atomic Scale Processing: From Materials Control to Selective Processing By Plasma ALD
Authors: Faraz Tahsin
Published: February 2020

As we enter an era of atomic scale devices,1 there is a strict need for precise control over the thickness and properties of materials employed in device fabrication.2,3 Furthermore, next-generation device architectures consist of various material layers with dielectric or conductive properties on planar and three-dimensional (3D) features. This has led to an additional need for expanding the toolbox of atomic scale processing techniques – such as atomic layer deposition (ALD) and atomic layer etching (ALE) – with new approaches in selective processing.2,3,4 As early as 1990, different categories of selectivity during film growth on a patterned planar substrate (composed of different surface materials) have been defined in the literature in terms of area-, phase-, microstructure or chemical composition-selective deposition.5 The last three categories have been defined based on the inherent differences in material properties ensuing from simultaneous growth on a patterned substrate. As a result, these cases are simply different examples of one common selective growth process, namely material property-selective deposition.

Plasma-enhanced atomic layer deposition (ALD) is a technique that uses the reactive species generated in a plasma (i.e. radicals, ions) for growing materials with atomic scale precision. In this work, we will demonstrate how plasma ALD can open new avenues for controlling material properties and carrying out selective processing on both planar and 3D substrates. We will show how plasma ALD can yield simultaneous growth of the same material with different properties (e.g. phase-selective deposition) on a patterned substrate. We will then demonstrate how implementing ion energy control during plasma ALD can enhance the versatility of this processing technique by enabling accurate control over a wide range of material properties during deposition.6,7 And finally, we will show how controlling ion energies during plasma ALD on 3D trench-shaped nanostructures can provide an alternate route for topographically selective materials processing,6 relevant for next-generation device fabrication.3,4

1 Salahuddin et al., Nat. Electron.
1, 442-450 (2018)

2 Knoops et al., J. Vac. Sci.
Technol. A
37, 030902 (2019)

3 Faraz et al., ECS J. Solid State Sci. Technol.
4, N5023-N5032 (2015)

4 Clark et al., APL Mater.
6, 058203 (2018)

5 Carlsson, Crit. Rev. Solid State Mater. Sci.
16, 161-212 (1990)

6 Faraz et al., ACS Appl.
Mater. Interfaces
10, 13158-13180 (2018)

7 Faraz et al., Plasma Sources Sci. Technol.
28, 024002 (2019)

Figure 1
Area-Selective Deposition by a Combination of Organic Film Passivation and Atomic Layer Deposition
Authors: Pasquali Mattia , De Gendt Stefan , Armini Silvia
Published: February 2020

To enable the downscaling of Integrated Circuit (IC) components accordingly to Moore’s law, novel nano-patterning techniques and materials are essential. Self-Aligned patterning schemes, such as Area Selective Deposition (ASD), are receiving increasing attention due to challenges created by the continuous shrinking of critical dimensions (e.g. self-aligned vias to lines in multi-level interconnect architectures). In ASD, a given film is deposited exclusively on the desired growth area with respect to the non-growth area. Typically, this can be achieved by exploiting material properties, such as surface chemical composition variations, in combination with surface-sensitive deposition techniques, such as Atomic Layer Deposition (ALD). In addition, the ALD self-limiting half-cycle surface reactions provide a layer-by-layer growth mechanism, which is strongly dependent upon the chemical reactivity to the underlying layer. Intrinsic growth nucleation variations on different surfaces can be exploited in an ASD scheme, but this effect is typically limited to very few ALD cycles. In this talk, Self-Assembled Monolayers (SAMs) are evaluated as a passivation coating to extend the ASD process window. Potential applications that will be discussed are Copper passivation in a self-aligned via patterning process flow and area-selective bottom-up VIA fill in an interconnect metallization scheme.
Application of Atomic Layer Deposition of Cellulosic Materials Prepared Using 3D Printing Concepts
Authors: Lee Hyunbae , Hwang Heesu , Oh Jiwon , Kim Jaehwan , Lee Myeong-jin , Hwang Jin-Ha
Published: February 2020

Atomic layer deposition offers a 3-diemensional conformal deposition of materials along with the atomic scale control on thickness control at the low-temperature regimes. Metal oxide materials can be exploited to the nanoscale coating onto the underlying materials. The cellulose materials offer ecofriendly applications which can be designed to the versatile fabric products or equivalents. The integration of ALD onto the cellulose materials can be tailored towards stretchable electronics which allows the flexible deformation unlike the previous rigid applications based glass or silicon technologies. Zinc oxide (ZnO) is chosen to be a coating material characteristic of semiconducting conduction. The zinc oxide thin films are deposited through the atomic layer deposition of diethyl zinc (DEZ) water. The ALD-based zinc oxide thin films are characterized by a multitude of physical/chemical probing tools: X-ray photoelectron microscopy for bonding and composition information, X-ray diffraction for crystallinity, atomic force microscopy and scanning electron microscopy for morphological characterization, and dc/ac-based electrical characterizations. Cellulose and its derivatives are ecofriendly materials due to superior features tensile strength and toughness contrary to the pollution-inducing thermoplastic materials. The beneficial features are applied to building materials, pharmaceuticals, cosmetics, and foods. The cellulose-based materials are chemically versatile and artificially controlled. The current work exploits two specific features, i.e. i) the dissolution feature of cellulose acetate in acetone and the OH terminated features of cellulose materials. The flexible cellulose materials are prepared using a 3-dimensional printing concept: the cellulose acetate materials are dissolved intro acetone and the subsequent removal of acetone allows the flexible solid formation of cellulose materials after extrusion through high-resolution 3D-printing. The mesh-typed specimens are subjected to simultaneous measurements on mechanical deformation and electrical resistance. The electrical/dielectric monitoring is performed in the two-point electrode configuration involving ac and dc characterizations. In particular, the frequency-dependent impedance spectroscopy provides a wealth of information on bulk- and/or electrode-responses as a function of mechanical deformation. The applicability of ALD to cellulose materials is discussed in terms of mechanical robustness and electrical reliability required in high-performance stretchable electronics.
(Invited) ALD and ALEt of Transition Metal Dichalcogenide Materials
Authors: Mane Anil U. , Letourneau Steven , Choudhury Devika , Elam J. W.
Published: February 2020

Ultra-thin layer of two dimensional (2D) materials mainly transition metal dichalcogenide (TMD) semiconductor possess exceptional properties such as electrical, optical, magnetic, mechanical and chemical. This allows the exploration of internal quantum degrees of freedom of electrons and their potential for use in optoelectronic, energy, and sensor applications. At present, research on 2D-layered TMDs mostly rely on (i) flakes produced by exfoliation from bulk, (ii) synthesis by high temperature (800-1000oC) mostly by chemical vapor deposition or (iii) solution based methods. Although exciting results are being obtained, but all these methods have limitations such as poor quality of the material, lack of precise control of thickness, interface or ability to integrate them into complex 3D devices. Nevertheless, the biggest challenge in realizing their full potential has been the lack of doable material synthesis methods of such films with high uniformity, conformality and interfacing with other materials such as oxides and metals.

Among the various thin film growth methods, atomic layer deposition (ALD) offers the best combination of a controlled layer-by-layer growth of the material with high conformality and suitable integration with other oxides such as dielectrics and metals. At the same time, precisely control thermal-based etching method for 2D-TMD materials are needed. Secondly at present, there are tremendous attention and efforts on development of the thermal vapor based well control etching methods especially on atomic layer etching (ALEt). The successful combination of both ALD and ALEt of 2D-TMD can pave the way to control the synthesis of 2D-TMD layers over large areas. This will be important for 2D-TMD material integration for future successful large-scale complex device structures fabrication.

Here we will first discuss the ALD growth of 2D-TMDs (e.g. MoS2, HfS2 and MgS2) on metals (e.g. Mo, W and TiN), dielectric oxides (e.g. Al2O3, MgO, HfO2, and TiO2) and vice versa. Then precise control etching processes based on molybdenum hexafluoride (MoF6) and H2O vapor will be discussed. The MoF6-H2O precursors based etching process offer several advantages including low cost, low processing temperature, rapid and effective etching spanning the range from continuous etching to atomic layer etching (ALEt). We have used in-situ quartz crystal microbalance (QCM) and Fourier-transform infrared spectroscopy (FTIR) measurements to monitor the deposition and etching 2D-TMDs layers. Next, the deposited and etched 2D-TMDs thin films were analyzed by spectroscopic ellipsometry to determine the thickness and refractive index, and the composition was determined by X-ray photoelectron spectroscopy (XPS). These ex-situ measurements confirmed the 2D-TMDs deposition and etching behavior findings from our in-situ studies.
(Invited) Graphene Nano-Electro-Mechanical (NEM) Devices and Extension to Sensor Applications
Authors: Mizuta Hiroshi , Agbonlahor Gabriel , Miyashita Hiroya , Taketomi Kohei , Lee Jaewook , Huynh Ngoc , Muruganathan Manoharan
Published: February 2020

Graphene, as a monolayer of graphite, has an ultra-high Young’s modulus of ~1 TPa, which makes it a promising candidate for Nano-Electromechanical (NEM) devices. Thanks to highly-stable SP2 bonds in a 2D honeycomb lattice, graphene also features an extremely suppressed electrical noise, making it possible to realize extremly-sensitive sensor. This paper presents an overview on our recent study of novel graphene NEM devices for abrupt switching and ultra-sensitive chemical gas sensing applications. The graphene NEM switches are expected to show minimized electrical leakage, sharp switching response, low actuation voltage, and a high on/off ratio. Three-terminal graphene NEM switches with heterogeneously stacked graphene / h-BN layers are developed, which achieve low-voltage and sub-thermal switching (S ～ 10 mV/dec) at room temperature [1]. We then present nanoscale graphene gas sensors, which detect either resistance or mass changes due to a small number of gas molecules physisorbed onto suspended graphene at room temperature. With the resistance detection method, we show quantized increments in the temporal resistance of approximately 60 Ohm, signifying single CO2 molecule adsorption onto a suspended graphene channel [2][3]. As for the mass detection method, we demonstrate the resonance frequency shift of a doubly-clamped graphene resonator with the mass resolution of hundreds zeotpgram (10-21 g) order [4][5]. We also introduce recent experimental work of applying these graphene nanosensors to detect gas emanated from human skin such as NH3 and acetone of very low concentration of down to ppb level.

This research was supported through the Grant-in-Aid for Scientific Research KAKENHI (18H03861, 18K04260, 25220904) from JSPS, COI program of the Japan Science Technology Agency and collaboration grant by TAIYO YUDEN Co. Ltd.

[1] N. H. Van, M. Muruganathan, J. Kulothungan and H. Mizuta, Nanoscale 10, 12349-12355 (2018)

[2] J. Sun, M. Muruganathan, and H. Mizuta, Sci. Adv., 2, e1501518–e1501518 (2016)

[3] M. Muruganathan, J. Sun, T. Imamura, and H. Mizuta. Nano letters 15, 8176 (2015)

[4] M. Muruganathan, F. Seto, and H. Mizuta, IJAT 12(1) 24-28 (2018)

[5] M. Muruganathan, H. Miyashita, J. Kulothungan, M. Schmidt, H. Mizuta, IEEE Sensors 2018, New Delhi, India, October (2018)
(Invited) 3D Conformal Printing of High-Performance and Flexible Thermoelectric Devices Using Colloidal Nanocrystals
Authors: Zhang Yanliang
Published: February 2020

The flexible thermoelectric generator (f-TEG) is a very promising technology for energy harvesting to enable self-powered wireless sensors and wearable devices, an area of exponential growth. Here, we present a scalable and cost-effective additive manufacturing process to fabricate f-TEGs using colloidal nanocrystals, and an innovative and highly efficient photonic sintering method to sinter large areas of printed films using pulsed light. Flexible TE films and devices were printed using screen printing and aerosol jet printing, followed by pulsed photonic sintering process. The pulsed sintering confines the delivered thermal energy within the printed film region without over heating the substrate, enabling TE film sintering on flexible polymer based substrates with relatively low melting point. In addition, the pulsed sintering limits grain size growth due to an ultrafast heating and cooling process, and lower thermal conductivity can be achieved than films sintered by conventional thermal processing.

The p-type and n-type printed films demonstrate peak ZTs of 1 and 0.43 near room temperature along with superior flexibility, which is among the highest reported ZT values in flexible thermoelectric materials. A flexible thermoelectric device fabricated using the printed films produces a high power density above 19 mW/cm2 with 80 ºC temperature difference between the hot side and cold side. The additive printing and photonic sintering can enable a highly scalable and low-cost roll-to-roll manufacturing process to transform high-efficiency colloidal nanocrystals into high-performance and flexible TEG devices for widespread applications.
(Invited) Innovative Advances in Copper Electroplating for IC Substrate Manufacturing
Authors: Ganesan Kousik , Manepalli Rahul , Wall Marcel , Wentzel Andrew , Castro Helme , Li Wencaho , Heaton Thomas
Published: February 2020

Low cost electroplating of copper to create Fine Line Space (FLS) features and Blind Micro Via’s (BMV) is a key technology element of high density substrates for integrated circuit packaging. In this work, we demonstrate a capable deposition methodology to influence gap fill behavior inside microvia along with a uniform deposit in the fine line patterned regions for substrate packaging applications. Interconnect circuitry in IC substrate packages comprises of stacked microvia that varies in depth from 20µm to 100µm with an aspect ratio of 0.5 to 1.5 and fine line patterns defined by photolithography. Photolithography defined pattern regions incorporate a wide variety of feature sizes including large circular pad structures with diameter of 20µm - 200µm, fine traces with varying widths of 3µm - 30µm and additional planar regions to define a IC substrate package. Electrodeposition of copper is performed to establish the desired circuit. Electrodeposition of copper in IC substrate applications holds certain unique challenges in that they require a low cost manufacturing process that enables a void free gap fill gap fill inside the microvia along with uniform deposition of copper on exposed patterned regions. Deposition time scales to establish the desired metal thickness for such packages could range from several minutes to few hours. In this work, we show case an electrodeposition methodology that achieves void free gap fill inside the microvia and uniform plating in FLS (Fine Lines and Spaces) regions with significantly higher deposition rates than traditional approaches. In order to achieve this capability, systematic experimental and simulation studies were performed to show a strong correlation of the independent parameters that govern the electrodeposition process to the deposition kinetics and deposition uniformity in fine patterned regions and gap fill rate inside the microvia.
Enhancing Capacitance of Electrochemical Capacitors By Multi-Layer Electrodeposition of Manganese Dioxide
Authors: Mujammami Fahad , Cameron Hayden , Beyad Yaser , Donne Scott W
Published: February 2020

Energy usage has increased substantially in recent years with an estimated global energy production predicted to reach 28 TW by 2050. Currently, approximately 85% of energy is generated from the combustion of fossil fuels such as coal, petroleum products and natural gas, which are neither sustainable nor eco-friendly. Renewable sources such as solar, wind and hydrothermal are alternatives to replace the current non-renewable primary energy source. This renewable energy dominated future leads to a world where energy storage systems need to be efficient to sustain the heavy loads because of increasing energy demands.

Currently any renewable energy source must be paired with an energy storage device such as, a capacitor, battery, flywheel, pumped hydro or compressed air, to utilize both the energy produced and to increase the efficiency of the device. As renewable energy devices become more powerful and efficient, so must the energy storage device paired to it. Thin-film MnO2 deposits have exhibited properties that are highly desirable for use as ultracapacitors, due to its exceptional performance, high abundance, cheap production costs and non-toxicity.

In this work the layered MnO2 thin-films were produced using a duty cycle method in which a constant potential is pulsed throughout the duration of the electrodeposition, this allowed for both the number and duration of pulses and rests to be varied which has ultimately enabled studying the effect of those factors on the performance of the MnO2 thin-films. The performance of the MnO2 thin-films were then analysed by sweeping the potential between 0.2-0.8 V vs SCE in a solution of 0.5 M K2SO4 for 250 times to observe cycling efficiency and morphological changes after cycles.
Improved Water Management of Electrospun Nanofiber Membrane Electrode Assemblies at High Current Densities Measured in Operando Using Neutron Radiography
Authors: Chintam Kavitha , Waldrop Krysta , Baker Andrew M. , Workman Michael J , Mukundan Rangachary , LaManna Jacob M , Hussey Daniel S , Jacobson David L , Gumeci Cenk , Dale Nilesh , Slack John James , Borup Rod L. , Pintauro Peter N.
Published: February 2020

Electrospun PFSA-Pt/C nanofiber mats have demonstrated promise as electrodes for PEM fuel cells that are highly scalable and show improved performance and durability compared to traditional sprayed electrodes.1,2 As a result, it is of great interest to understand the underlying mechanisms responsible for these gains, so that these electrode structures may be optimized in order to further increase performance and durability.

Neutron radiography was used to measure water formation through the cross-sections of sprayed gas diffusion electrodes (denoted GDE) and electrospun PFSA-Pt nanofiber electrodes (denoted NF) during operation. Both GDE and NF-containing MEAs were assembled in custom hardware specifically designed for use within the neutron beam and operated in a differential cell configuration at 80°C, with variable RH and current density. Initial polarization results (Figure 1a) demonstrated a lower OCV for the NF electrodes, which were attributed to shorting at the through-holes within the active area, specific to the custom-built imaging hardware. Regardless, the performance of NF electrodes is improved at high (2 A/cm2) current densities. Through-thickness water profiles at 0.2 V (Figure 1b) show that the water concentration is around 2x lower within the MEA and GDLs in the NF-containing MEA compared to the baseline GDE. The lower water contents suggests improved performance in the mass transport region, commensurate with the observed polarization curves. Hardware issues are currently being addressed, and further test results exploring effects of RH, current density, and NF composition, will be discussed.

Acknowledgements

This research is supported by the U.S. Department of Energy Fuel Cell Technologies Office, through the Fuel Cell Performance and Durability (FC-PAD) Consortium (Fuel Cells Program Manager: Dimitrios Papageorgopoulos and Technical Development Manager: Greg Kleen).

References

P. N. Pintauro, “Fuel Cell Membrane-Electrode-Assemblies with Ultra-Low Pt Nanofiber Electrodes,” Fuel Cell R&D Annual Merit Review Proceedings, 2018.

Brodt, R. Wycisk, N. Dale, and P. Pintauro, “Power Output and Durability of Nanofiber Fuel Cell Cathodes with PVDF and Nafion/PVDF Binders”, J. Electrochem. Soc.,
163
, F401-F410 (2016).

Figure 1
(Invited) Quantifying the Distribution of Catalyst Support Carbon Corrosion
Authors: Fairweather Joseph D. , Yu Paul Taichiang , Zhang Jingxin , Lakshmanan Balsu
Published: February 2020

Catalysts for proton exchange membrane fuel cell (PEMFC) electrodes are commonly dispersed on granular carbon supports to maximize performance. The carbon material will rapidly oxidize if exposed to high potential excursions, so PEMFC systems need to minimize these conditions such that lifetime damage is kept low. Diagnostic methods are used to evaluate operating conditions and mitigation strategies.

This presentation first reviews several diagnostic approaches to quantify carbon support corrosion (Table). While cross-section electrode thickness is the most reliable indicator of support loss, other methods are desirable for higher sensitivity, greater convenience, or non-destructive sample throughput. However, these alternative methods generally involve greater uncertainty and more convoluting factors. Workarounds for these complications will be discussed, along with the application of a current distribution board for estimating carbon loss across the active area of a cell. The presentation concludes with examples of support corrosion distribution observed in automotive-competitive fuel cells (Figure).

Figure 1
(Invited) High Performance Commercial Nafion(TM) PFSA Materials for Fuel Cells and Water Electrolyzers
Authors: Park Andrew Michael , Daly Christopher , Augustine Evan , Inci Bora
Published: February 2020

Perfluorosulfonic acid (PFSA) materials are perhaps the key enabling component for many polymer electrolyte membrane devices such as fuel cells and water electrolyzers. PFSA materials are by far the most proven class of polymer in this field, and are therefore uniquely capable to support the expected commercial expansion over the next few years. PFSA suppliers will be relied upon to deliver quality products at scale to the marketplace. At the same time, increasing performance demands across the industry require novel materials research and product optimizations to support diverse OEM growth plans.

Chemours™, a recent spinoff from the DuPont® corporation in 2015, assumes all expertise and production capacity associated with the Nafion™ brand of PFSA materials. Chemours™, leveraging this historical PFSA leadership position, is excellently positioned to support electrochemical device proliferation. Significant R&D investments are being made to improve product offerings in membranes and ionomer dispersions to support the hydrogen economy. This presentation will summarize Chemours™’ recent efforts and future product direction for PEM fuel cell and water electrolyzers.
Characterizing Durability of PFSA Membranes of PEM Fuel Cell Based on Numerical Fatigue Crack Propagation
Authors: Hasan Morshed , Santare Michael H
Published: February 2020

Fatigue crack growth in the Perfluorosulfonic-acid (PFSA) ionomer membranes with mechanical reinforcement and chemical stabilizer represents a key barrier in improving the durability of the polymer electrolyte membrane (PEM) fuel cell. Both ex-situ and in-situ Paris regime fatigue crack behaviors can be evaluated numerically based on the critical plastically dissipated energy (CPDE) ahead of the crack tip. Some fairly good agreement between the finite element (FE) computational crack predictions and the ex-situ experimental crack propagation rates have been found for different polymers in previous work1. In a similar fashion, the fatigue crack growth criteria (e.g., CPDE) of Nafion®-based ionomer membranes can be determined numerically at various environmental conditions (RH and T). The determined fatigue crack criteria, then, will be implemented in a 2D unit fuel cell FE model following the reference work2 with extensions. Thus, in-situ fatigue crack behaviors of the ionomer membranes can be evaluated in response to different operating circumstances. This numerical scheme can be used to evaluate the mechanical integrity of different ionomer membranes in the screening process by the manufacturer/buyer. Moreover, in further implementations, the results from this modeling can be used in exploring the synergy between chemical (e.g., gas-crossovers) and mechanical failures (e.g., fatigue cracks) in PEM fuel cell membranes.

REFERENCES

G. Ding, A. M. Karlsson, and M. H. Santare, Int. J. Fatigue, 94, 89–96 (2017) http://dx.doi.org/10.1016/j.ijfatigue.2016.09.012.

G. Ding, M. H. Santare, A. M. Karlsson, and A. Kusoglu, J. Power Sources, 316, 114–123 (2016) http://dx.doi.org/10.1016/j.jpowsour.2016.03.031.
Optimization Ionomer Distribution on Porous Carbon Catalyst Support to Commercialize Low Pt Loaded PEMFCS
Authors: Ott Sebastian , Orfanidi Alin , Anke Björn , Lerch Martin
Published: February 2020

One of the major drawbacks towards PEMFC (polymer exchange membrane fuel cell) commercialization is the high amount of platinum needed at the cathodic electrode, due to the inherent slow kinetics of the oxygen reduction reaction. It has been widely known that the reduction of the Pt loading at the cathodic electrode leads to significant voltage losses. The origin of which has been correlated to electrode structure, ionomer distribution, type of catalyst support, and location of the Pt particles on the carbon support. A recent study by Orfanidi et al showed that by introducing positively charged nitrogen groups into the carbon structure lead to a more homogeneous distribution of the ionomer, which results in higher performance even at low Pt loaded electrodes [1].

In the present study, a series of different N-functionalized Ketjenblack are synthesized and fully characterized to investigate their use as support material for Pt based electrodes. Pre-oxidized Ketjenblack was heat treated in ammonia at different temperatures [2] followed by Pt precipitation via an ethylenglycol method. This new type of catalyst significantly reduces the additional mass transport resistance and report an unprecedented high coverage of the ionomer over the high surface area carbon supports, especially under dry operating conditions, in addition to high stability under voltage cycling. Those enhanced transport behaviors are deduced to local transport phenomena in the porous carbon structure and we give a tailoring approach for such a carbon material within this work. Our catalyst presents significant advantages as it facilitates manufacturing processes of the electrodes, due to the columbic interaction between the ionomer and the –NHx groups on carbon support, ensuring homogeneous ionomer distribution.

This work sheds light into the effect of the different N based groups towards better understanding of the interaction of ionomer with the carbon support. Our concept can be transferred to other kinds of partially amorphous carbon and is not limited to Pt as an active material. Introduction of such a modification step in the production line of electrocatalysts paves the way for PEMFC commercialization in automotive applications, due to enhancement in mass transport and stability.

Literature

[1] A. Orfanidi, P. Madkikar, H.A. El-Sayed, G.S. Harzer , T. Kratky, H.A. Gasteiger, Journal of the Electrochemical Society
2017, 164, F418-F26.

[2] K.F. Ortega, R. Arrigo, B. Frank, R. Schlöten, A. Trunschke, Chemistry of Materials
2016, 28, 6826-6839.
Co-Axial Nafion Nanowire Electrode
Authors: Komini Babu Siddharth , Mukundan Rangachary , Cullen David A. , Spendelow Jacob S
Published: February 2020

State-of-the-art polymer electrolyte fuel cells rely on platinum (Pt) or Pt-alloy on carbon supports mixed with ionomer for high power density. The high Pt loading in the cathode is still a barrier for commercialization of PEFCs. Conventional electrodes are fabricated in an uncontrolled ink deposition process that produces random aggregates of catalyst, ionomer, and pore volume (1). The high tortuosity and poor percolation of ionomer in these random aggregates cause low effective conductivity, requiring the use of high ionomer content to minimize Ohmic losses due to proton conduction. This causes severe mass transport limitations during high current density operation and requires a higher loading of Pt to meet the performance targets. The diffusion of reactants through the thick ionomer film adds an additional transport resistance and becomes significant at lower Pt loadings (2). The ionomer also poisons the surface of the catalyst, reducing the activity of the catalyst. Decreasing the negative effects of ionomer films would enable a significant increase in performance.

In our previous work, we have shown that aligned Nafion pillars in the cathode catalyst layer can improve ionic conductivity enabling reduction of ionomer in the catalyst layer (3). In this work, we present a novel electrode architecture where the three functional domains (catalyst, ionomer, and pore) are separated and aligned vertically as shown in Figure 1a. Pt nanofilm is coated surrounding the Nafion nanowire to fabricate a coaxial nanowire electrode. Figure 1b. shows the High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of the coaxial nanowire electrode. The pore domain provides an additional modifiable parameter to control the wettability of the electrode.

Acknowledgments

This research is supported by DOE Fuel Cell Technologies Office, through the Fuel Cell Performance and Durability (FC-PAD) Consortium; Technology manager: Greg Kleen.

References

S. Litster and G. McLean, Journal of Power Sources, 130, 61 (2004).

N. Nonoyama, S. Okazaki, A. Z. Weber, Y. Ikogi and T. Yoshida, Journal of The Electrochemical Society, 158, B416 (2011).

S. K. Babu, J. S. Spendelow and R. L. Borup, in Meeting Abstracts, p. 1385 (2017).

Figure 1
In-Situ Heating and TEM Characterization of Pt-Cu Nanoframes
Authors: Gong Mingxing , Zhao Tonghui , Wang Deli
Published: February 2020

Increasing the atomic utilization and catalytic activity of Pt is an effective way to promote the commercial application of fuel cells. In this paper, platinum-copper nanoframes (Pt-Cu NFs) were prepared by a simple solvothermal method. For electrocatalytic activity, the Pt-Cu NFs exhibit enhanced oxygen reduction activity due to the unique open structure, electronic effect and geometric effect regulation. However, the dissolution of the transition metal Cu leads to a rapid decay of its stability, which is unable to adapt to long-term operation. Further improvement of its stability is highly desired. Thus, we have attempted to prepare Pt-Cu intermetallic compounds to achieve the phase transition from disordered alloys to ordered intermetallic to enhance their catalytic stability. The results show that the high temperature treatment can achieve its transformation into an ordered phase, and the stability is improved to a large extent, but the activity is reduced because of the aggregation during the high temperature treatment thus the structure was difficult to maintain. In order to explore the structural evolution in the process of ordering, in-situ electron microscopy is used to characterize the structural change trend in the heating process, and it is expected to provide guidance and help for the follow-up works.

Figure 1 is here.

Figure 1. In-situ TEM observation of Pt-Cu NFs during heating treatment.

Keywords: Oxygen Reduction Reaction, Pt-Cu Nanoframes, Intermetallics, In-situ heating

References:

[1] C. Chen, Y. Kang, H. Xin, P. Yang, Highly Crystalline Multimetallic Nanoframes with Three-Dimensional Electrocatalytic Surfaces, Science, 2014, 343, 1339-1343.

[2] D. Wang, H. L. Xin, R. Hovden, D. A. Muller, F. J. DiSalvo, H. D. Abruna, Structurally Ordered Intermetallic Platinum-cobalt Core–shell Nanoparticles with Enhanced Activity and Stability as Oxygen Reduction Electrocatalyst, Nat. Mater. 2013, 12, 81-87.

Figure 1
Effect of Nitrogen Doping on Oxygen Reduction Activity of TiO2 in Acidic Media
Authors: Ishihara Akimitsu , Nagai Takaaki , Murase Noriko , Arao Masazumi , Kuroda Yoshiyuki , Matsuzawa Koichi , Mitsushima Shigenori , Furukawa Kou , Imai Hideto , Lee Kunchan , Ota Ken-ichiro
Published: February 2020

In order to develop low-cost nonprecious metal cathodes that have both high activity of oxygen reduction reaction (ORR) and high durability as alternatives to Pt-based electrocatalysts for practical fuel cell vehicle application, we have focused on group 4 and 5 oxide-based compounds because they are insoluble in acidic media and are much less expensive than platinum. We already demonstrated that titanium and zirconium oxide-based compounds prepared from these oxy-phthalocyanines showed definite ORR activities [1,2]. However, these types of the catalysts used multi-walled carbon nano-tubes as a support and deposited carbon derived from phthalocyanine as a local electron conduction path. Carbons are fundamentally oxidized at high potential and temperature. Therefore, carbon-free nonprecious ORR catalysts are required for fuel cell vehicle application. An arc-plasma deposition method is useful to control the oxidation state of the oxides without heat-treatment. We prepared zirconium oxide-based cathode using tin-oxide based electroconductive support by arc-plasma deposition as a carbon-free nonprecious metal cathode. Fig. 1 shows the potential-ORR current density curves of the ZrOx/SnO2-based support prepared by arc-plasma deposition method, the SnO2-based support, and the TixNbyOz+Ti4O7 [3] in 0.1 M H2SO4 at 30 oC. The ZrOx/SnO2-based support had superior ORR activity. Fig. 2 shows comparison of the onset potential of the ZrOx/SnO2-based support and the TixNbyOz+Ti4O7 in 0.1 M H2SO4 at 30 oC. Both onset potentials are above 1.1 V vs. RHE, indicating that these active sites are superior in quality. Figs. 1 and 2 suggested the great potential of carbon-free nonprecious metal oxide-based cathodes.

Acknowledgment

The authors thank the New Energy and Industrial Technology Development Organization (NEDO) for financial support. This work was conducted under the auspices of the Ministry of Education, Culture, Sports, Science and Technology (MEXT) Program for Promoting the Reform of National Universities.

References

[1] M. Chisaka, A. Ishihara, H. Morioka, T. Nagai, S. Yin, Y. Ohgi, K. Matsuzawa, S. Mistushima, K. Ota, ACS Omega, 2, 678-684, (2017).

[2] S. Tominaka, A. Ishihara, T. Nagai, K. Ota, ACS Omega, 2, 5209-5214, (2017).

[3] A. Ishihara, M. Hamazaki, M. Arao, M. Matsumoto, H. Imai, Y. Kohno, K. Matsuzawa, S. Mitsushima, K. Ota, J. Electrochem. Soc., 163, F603-F609 (2016).

Figure 1