bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Two-Dimensional Wide Bandgap Materials for Electronic Applications
Authors: Lee Gwan-Hyoung
Published: February 2020

The emerging two-dimensional (2D) materials, such as graphene, MoS2, and hexagonal boron nitride (hBN), are promising candidates for next-generation electronics. Gapless graphene has intriguing properties of ultrahigh mobility, transparency, tunable charge neutral point, etc. Differently from conventional semiconductors, 2D semiconductors, representatively transition metal dichalcogenides (TMDs), have shown unprecedented characteristics, such as indirect-to-direct band transition, trions, and valleys, which can be utilized to realize new-function devices. Despite rigorous researches on these 2D materials, wide bandgap 2D materials have not been studied widely and actively due to limited material sources. However, it should be noted that these wide bandgap 2D materials are essential for practical applications of 2D-material-based electronics because these insulating blocks are required to form multi-stacked 2D devices. Here I present electrical/optical characteristics of wide bandgap 2D materials, such as hBN and MoO3, and electronic devices consisting of van der Waals heterostructures of the 2D materials. 2D insulators with large bandgap were used as atomically thin insulator or tunnel barrier for ultrathin devices. It was also confirmed that 2D oxide layers can be epitaxially grown on 2D substrates of graphene and hBN. Growth of highly crystalline 2D oxide layers on other 2D layers shows great potential for large scale production of 2D oxides, which are highly useful for future electronics. Our approaches would allow us to come closer to practical applications of 2D materials in industry.
(Invited) Thick, Low-Doped Homoepitaxial Ga2O3 for Power Electronics Applications
Authors: Tadjer Marko J , Koehler Andrew D , Mahadik Nadeemullah A , Glaser Evan , Freitas Jaime A. , Feigelson Boris , Wheeler Virginia D. , Hobart Karl D. , Kub Francis J , Kuramata Akito
Published: February 2020

Monoclinic β-Ga2O3 has attracted significant attention as a high power electronics material based on its ultra-wide energy gap (4.9 eV), high theoretical critical field (8 MV/cm), as well as the commercially availability of inexpensive substrates grown from the melt. In order to achieve breakdown field consistent with the theoretical expectations, however, very high quality epitaxial films with very low doping and defect density will be required. Wong et al. have reported a β-Ga2O3 MOSFET with carrier concentration below 4x1014 cm-3, which is the lowest reported value for epitaxial β-Ga2O3 to date [1]. This talk will discuss the structural and electronic properties for thick homoepitaxial β-Ga2O3 with doping as low as 8x1012 cm-3, corresponding to breakdown voltage in excess of 2.38 kV (3.18 MV/cm), measured without field termination for vertical measurements or edge effects correction in the case of lateral devices. Our results show that current β-Ga2O3 halide vapor phase epitaxial technology can produce epilayers with breakdown field approaching the theoretical value of GaN. In addition, we will discuss the annealing of bulk and epitaxial β-Ga2O3 films in O2 atmosphere as a potential pathway to reduce carrier concentration and possibly improve the breakdown voltage of Ga2O3 Schottky diodes. We show that annealing Ga2O3 in O2 will reduce ND-NA by about an order of magnitude, similar to earlier observations by Kuramata et al. [2]. Furthermore, we will present our approach for overcoming the polaron-induced suppression of room-temperature p-type conductivity in Ga2O3, causing holes to preferentially self-trap instead of being available as free carriers [3]. We show that natural p-type semiconducting oxides such as NiO can be integrated with β-Ga2O3 to form a rectifying heterojunction as a fundamental building block for any viable Ga2O3 power device. Finally, we will discuss the low thermal conductivity of Ga2O3 and present our preliminary thermal management simulations and experimental results.

[1] A. Kuramata, et al., Jpn. Jour. Appl. Phys. 55, 1202A2 (2016).

[2] M.H. Wong, et al., Appl. Phys. Express 10, 041101 (2017).

[3] J.B. Varley, et al., Phys. Rev. B 85, 081109(R) (2012).
Electrical and Material Properties Analysis of 5kV 4H-SiC Schottky Barrier Diodes
Authors: Keum Juyeon , Na Moonkyong , Kang In Ho , Bahng Wook , Koo Bonheun
Published: February 2020

Silicon carbide is an attractive material for next-generation power devices, it has wide band gap and high thermal conductivity. SiC power devices can operate at higher temperatures and voltages compared to silicon devices. But, electrical characteristics of the SiC power devices can be deteriorated by SiC defects. The killer defects such as micropipes and stacking faults have been reduced through the development of SiC growth technique. But still the threading dislocations (TDs) and basal plane dislocations (BPDs) lowered the breakdown voltage and increased the leakage current during device operation [1].

In this study, we fabricated the 5 kV 4H-SiC Schottky barrier diode (SBD) to study the effect of SiC defect on electrical properties of SiC SBDs. The thickness of epitaxial layer was 50 um and the doping concentration is 1E15 cm-3. The device was fabricated with various length of junction termination extension (JTE). Ion implantation was performed to form p surge (Al, 500 °C, 5E19 cm-3) and JTE (B, 500 °C, 2E18 cm-3) regions. Activation annealing was performed at 1700 °C for 60 m. 100 and 30-nm-thick Ni were deposited as the cathode and front-side ohmic metal respectively, and then annealed at 950 °C for 90 s in RTA system. Finally, 100-nm-thick Ni was sputtered on front-side as a Schottky contact metal. We investigated the forward, reverse characteristics, and reverse breakdown voltage of the fabricated 4H-SiC SBDs. The diode characteristics, ideality factor (IF) and Schottky barrier height (SBH) were obtained from the forward electrical characteristics, about the 1.23 and 1.3 eV, respectively. The relative highly ideality factor may be due to rough surface of thick epitaxial layer. The breakdown voltage was obtained above 5 kV with JTE length longer than 60 um. During reverse characteristics the electrically weak points were observed using electroluminescence (EL). The EL spot was mainly aroused from electrically leaky points, it mostly observed at the edge of JTE. Some EL spots were observed inside the JTE or active region. The defects of the fabricated 4H-SiC 5 kV SBDs were analyzed using non-destructive analysis method, X-ray topography (XRT) and electron beam induced current (EBIC). We tried to determine the correlation between the electrical characteristics of the device and the crystal defects in the device.

[1] H. Fujiwara, H. Naruoka, M. Konishi, K. Hamada, T. Katsuno, T. Ishikawa, Y. Watanabe, and T. Endo, Appl. Phys. Lett. 100, 242102 (2012).

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(Invited) Electrochemistry of Transition Metal Oxide Based Mountable Electrochromic Devices
Authors: Deb Biswapriya , Ganesh Gayathri PT , Surendran Sajitha
Published: February 2020

Although electrochromic (EC) “smart” windows are recently making inroads into consumer applications, any large-scale usage needs further maturity in balancing their cost, processability and usability. A flexible and mountable EC device that can be refitted with a normal glass pane has potential to expand the market for existing buildings, by eliminating the requirement of replacing the entire window. Any EC based tunable windows have several functional components such as active/counter electrodes, conducting back panel and electrolyte. One must adopt a viable low temperature based fabrication process for the transition metal oxide (TMO) films with sufficient cycling stability for the intended application. At the same time, a mechanically robust semi-solid/solid polymer electrolyte (SPE) with adequate thermochemical range must be developed for operational safety. In this work, we demonstrate the use of ultraviolet (UV, 365 nm) photoannealing process for TMOs specially optimized to support flexible ECD operations [Figure-1]. This inexpensive and facile process step enabled us to manipulate nanoscale transport properties to extract preferred functionalities. A significant network densification is observed as photo-decomposition of bridging ligands facilitated direct interactions of surface dipoles in those films that produced ~57% improvement in the optical density (OD) [1]. The free-standing SPEs was designed by dispersing Li-salts into polymer matrix followed by thermochemical crosslinking of the host [2,3]. The assembled ECDs were investigated using electrochemical and spectroelectrochemical techniques to identify the sources of device degradations. A typical device fabricated with optimized components showed remarkably high OD (~0.65) and coloration efficiency (CE) ~122 cm2/C at 600 nm.

Keywords: Electrochromic devices, photo-annealing, polymer electrolyte, mountable foils

[1] Gayathri P.T.G., Sajitha S., Vijitha I., Shaiju S.S., and Biswapriya Deb “Tuning of Physical and Electrochemical Properties of Nanocrystalline Tungsten Oxide through Ultraviolet Photoactivation”, Under Revision (2017)

[2] Gayathri P.T.G., Remya R., Biswapriya Deb, “A pragmatic approach to methyl methacrylate based solid polymer electrolyte processing: A case study for electrochromism”, Sol. Energ. Mat. Sol. Cells 140 17–24 2015

[3] Gayathri P.T.G. and Biswapriya Deb “Designing an All-Solid-State Tungsten Oxide Based Electrochromic Switch with a Superior Cycling Efficiency” Adv. Mater. Interfaces 2017, 1700124

Figure-1: TMO based flexible ECD fabrication; optimization of components through electrochemistry and spectroelectrochemistry studies.

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(Invited) Surface Transfer Doping: A Novel Alternative to Classical Doping in Semiconductor Electronics
Authors: Chakrapani Vidhya
Published: February 2020

Electronic properties of semiconductors can be controlled by introduction of appropriate dopants into the bulk lattice. In a recently discovered phenomenon, known as “surface transfer doping,” free electrons or holes can be generated in undoped semiconductor surfaces, without the introduction of foreign atoms, by controlled deposition of thin layer of chemical moieties having appropriate electronic structure. In this type of doping, the nature of electrical conductivity and the direction of electron transfer depend crucially on the relative positions of the Fermi level of semiconductor and the chemical potential of electrons in the surface chemical moieties. This doping phenomenon was first observed in undoped hydrogenated diamond, which showed a p-type surface conductivity when exposed to ambient air.1 In this case, surface conductivity develops spontaneously as a result of electron transfer from diamond to an adsorbed water film on the surface.2
,
3
,
4 Since then, this effect has been exploited for other systems, such as diamond/C60,5 graphene/C60. In addition, the process has been shown to affect electrical, optical and electrochemical properties of several technologically important materials such as single-walled carbon nanotubes,6 graphene,7 gallium nitride and zinc oxide.8 This presentation will give an overview of the recent progress in this field and its impact on the emerging technologies.

Gi, R. S., et al., Jpn. J. Appl. Phys. (1995) 34, 5550

Maier, F., et al., Phys. Rev. Lett. (2000) 85 (16), 3472

Chakrapani, V., et al., Science (2007) 318 (5855), 1424

Foord, J. S., et al., Diam. Relat. Mater. (2002) 11 (3-6), 856

Strobel, P., et al., Nature (2004) 430 (6998), 439

Chakrapani, V., et al., ECS Solid State Lett. (2013) 2 (11), M57

Chen, W., et al., J. Am. Chem. Soc. (2007) 129 (34), 10418

Chakrapani, V., et al., J. Am. Chem. Soc. (2008) 130 (39), 12944
Using a Non-Conventional Layout Style to Improve Pass Device Performance in CL-LDO Voltage Regulators
Authors: Martucci Renan Freitas , Gimenez Salvador Pinillos
Published: February 2020

Currently the need for solutions on a single integrated circuit (IC) focusing on mobile applications (using batteries), more compact with less power consumption, such as mobile phones, tablets, notebooks, data collectors, etc., has become almost mandatory. This approach establishes the electronic systems integrated into a single IC, System-On-Chip (SoC). Accordingly, the integration of power management circuits (Power Management Unit – PMU), such as voltage regulators, which are responsible for feeding with fixed voltage different blocks of a SoC with a large electric current load range. This type of IC has been the focus of much research, aiming to increase its electrical performance and reducing its dimensions. Among the different architectures of linear regulators, linear voltage regulator with no external capacitor and low dropout voltage (Capacitor Less Low Dropout – CL-LDO) has been used widely. One of the key elements of CL-LDO is the pass device MOSFET, which is responsible for providing the supply reference voltage of the hole circuits, independent of the maximum load current. Accordingly, the pass device occupies a large silicon area, which finishes limiting the total area of the linear regulator, even using the minimal technology length. In this context, the objective of this paper is present results from a comparison between two identical CL-LDO voltage regulators, one using a conventional geometry pass device MOSFETs and the other one an octagonal layout style geometry, in SiGe IBM 130nm. By occupying the same layout area (0.00994mm2), the regulator using the non-conventional layout style in the pass device improved significant results in a large range of test possibilities by using physical effects due to the octagonal gate geometry. This kind of approach in back-end analog design flow is quite simple, and doesn't occupy any additional area for the IC, bringing a lot of benefits like higher transconductance and lower on resistance. Considering a 3-sigma process variance, military temperature range, maximum load of 20mA and the input voltage between 1.5V and 2.5V, the conventional layout results in a quiescent current of 30.5585 ± 2.08626µA against 30.5577 ± 2.05037µA from octagonal layout, improving static power consumption. Had also improved power-supply rejection ratio (PSRR) at low frequencies, from -55.76 ± 5.701dB (DC) to -55.78 ± 3.833dB (DC) and PSRR at high frequencies, from -48.81 ± 6.242dB (10kHz) to -48.81 ± 4.905dB (10kHz), maintaining line regulation and load regulation in order of 1,83%/V and 0,083%/mA respectively, for both voltage regulators with different pass device layout styles. With all the results, it is possible to conclude that, by using a non-conventional layout style, the MOSFET shows less yield variation, even with a short channel design, improving mismatch and the final results of a LDO voltage regulator.

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Highly Ion-Conducting, Reversibly Stretchable, and Ultra-Durable Double-Networked Ionogels for Flexible Supercapacitor
Authors: Rana Harpalsinh H. , Park Jeong Hee , Park Ho Seok
Published: February 2020

Flexible energy storage devices perform well under normal condition and their performance merits are well understood. However, energy storage under extreme conditions is still a big challenge because of electrolyte degradation and separator instability for the application such as an electrical vehicle, oil, solar energy storage, aerospace and military. Wet gels such as hydro- and organogels are mechanically strong yet brittle. Among functional gels, gel electrolytes are considered to resolve critical challenges of liquid and solid electrolytes, but they also have the property trade-offs between ion transporting and mechanical properties, as well as between strength and toughness. The performance degradation and safety issue of electrolytes prohibit flexible energy storage from operating under mechanically, thermally and electrochemically extreme conditions. Here, we report a new class of solid electrolyte, “Double Crosslinked Ionogel” based on double network concept. The tailor made ionogel electrolyte/separator structure was prepared by synthesizing double network gel from complimentary polymers and by combining it with room temperature ionic liquid. The unique structure of double crosslinked ionogel electrolyte was characterized by solid-state 13C CP-MAS NMR and FT-IR spectroscopies. Dual crosslinked polymer structure provide greater stretchability (strain ~250%) and high mechanical strength (3 MPa) to the electrolyte. At the same time presence of high amount of ionic liquid results (~60 wt%) in enhanced electrochemical performance i.e. Potential window (~2V), Maximum energy density (~40 Wh kg-1) and Ionic conductivity (~1.8 mS cm-1 at Room temp). With rGO electrodes and prepared ionogel electrolyte/separator, the supercapacitor device shows stable performance up to 180°C with good cyclic stability. High temperature promotes faster ion transport and hence results in enhanced performance in terms of rate capability (≈40%) and maximum device capacitance (≈ 32 F g-1). There was very little performance attenuation observed even under extreme mechanical and thermal stress. The device retains around ~90 % of its initial capacitance even after 100000 of cycles at 150 °C and capable of delivering required energy and power at high temperature.
Fabrication of High Power, Low-Pt Catalyst Coated Membranes
Authors: Garsany Yannick , Swider-Lyons Karen
Published: February 2020

Fabrication of High Power, Low-Pt Catalyst Coated Membranes

Yannick Garsany1 and Karen Swider-Lyons2

1 EXCET INC, Springfield, VA

2 U.S Naval Research Laboratory, Washington, DC

In the endeavor to create fuel cells capable of generating high power at low platinum loadings, it is crucial that educational and research laboratories have practical, cost-effective ways to make custom membrane electrode assemblies (MEAs). This talk will describe a reliable and reproducible laboratory-scale fabrication protocol based on ultrasonic spray deposition of standard Pt/carbon electrocatalyst directly onto a perfluorosulfonic acid membrane to produce 10 cm2 catalyst coated membranes (CCMs). The CCMs are then transformed into MEAs by compressing them between commercial gas diffusion media (GDM). We present the scientific rationale and electrochemical and microscopy data to reveal how post-deposition processing of the CCM/MEA and assembly conditions affect the performance of single cell fuel cells. Improper post-deposition processing leads to damage of the pore structure of the catalyst layer and/or GDM, diminishing the overall fuel cell performance. Fuel cells that are not assembled properly, either due to under- or over-compression, have high ohmic resistance or damage to the GDM pore structure, both of which negatively affect the PEMFC performance, despite no structural changes in the CCM. Equipped with the understanding of how to reproducibly fabricate standard Pt/Carbon CCMs/MEAs, we have adapted these protocols and tools to produce CCMs/MEAs with a PtCo/C electrocatalyst, short side-chain ionomers, and woven GDM that produce the high power and low Pt loadings desired for advanced fuel cells (Figure 1).
Water Balance in Polymer Electrolyte Fuel Cells with Ultra-Low Pt Loading: From Modeling to Design
Authors: Eikerling Michael Hermann , Muzaffar Tasleem Ahmad
Published: February 2020

The commercial deployment of polymer electrolyte fuel cells (PEFCs) hinges on breakthroughs in design and integration of highly performing and durable catalyst layers with drastically reduced platinum loading. In this context, experimental studies have shown an unexpectedly large increase of voltage losses upon a marked reduction of the Pt content. In an effort to unravel this behavior, physical modeling of porous electrodes is employed to analyze a wide range of experimental literature data. Detailed evaluation of the data reveals correlated trends in essential fuel cell parameters. These findings are interpreted in view of the tipping water balance that affects the interplay of transport and reaction in catalyst layer and gas diffusion media. As will be demonstrated, the performed model-based analysis warrants the definition of a correlation exponent that should be used to assess the merit of different approaches to catalyst layer fabrication.
Design and Optimization of PEMFC Electrode for Direct Roll-to-Roll Coating Process
Authors: Kim Jung Ho
Published: February 2020

The mass production of polymer electrolyte membrane fuel cells (PEMFCs) requires a reduction in the materials cost. The most costly component of a PEMFC is the membrane electrode assembly (MEA), which contains the precious metal catalyst, platinum. Methods to reduce the associated coats include synthesizing new materials and minimizing platinum loading through advanced manufacturing. The MEAs are generally manufactured by decal transfer method. The decal transfer method necessitates coating wider catalyst layer to adress alignment tolerance stack up and membrane shrinkage issue at lamination. More recently, inkjet printing and low production processing lines have been investgated. The costs of existing processes are too high and not scalable and the film quality can be too low for long life. In order to support large scale manufacturing. alternative methode for MEA fabrication are imperative. Available fabrication techniques, such as direct coating by solution, vapor, or spraying are limited by slow production rate, excessive cost and waste, lack of discrete control and the need for solvent of additives to obtain more uniform coating.

The development a roll-to-roll manufacturing technique to fabricate MEAs by direct coating electrode in discrete patches onto polymer electrolyte membrane (PEM), through implementation of an advance slot-die coating approach. Direct coating is an enabling manufacturing technique that allows for several key advantages and cost reduction including, enhanced fabrication speeds; reduced yield loss potential; increased precious metal catalyst utilization and membrane utilization and elimination of release film cost (which may not be a trivial consumable cost), among others. However, the electrode for direct coating quite limitation about PEM, catalysts, ionomer and solvent system.

In this work, we focus on the design and optimization on the interfacial structures between direct coating electrode and PEMs and their impact on the fuel cell performance. Our approach includes preparation and characterization of direct coating electrode using variuos electrode components.

Figure. (a) Procedure of direct roll-to-roll coating process, and (b) catalysts coated membrane.

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Co-Production of Ethylene and Hydrogen Via Non-Oxidative Dehydrogenation of Ethane Below 400oc
Authors: Wu Wei , Zhang Yuanya , He Ting , Ding Dong
Published: February 2020

Ethylene, a major intermediate in manufacture of polymers and petrochemicals, is conventionally produced by energy intensive high temperature (higher than 800oC) steam cracking of ethane. By using a proton-conducting solid oxide cell (SOC), ethylene and pure hydrogen can be co-produced at a much lower temperature via electrochemical dehydrogenation. In this paper, we report high efficient co-production of hydrogen and ethylene on a proton-conducting Ni-BaZr0.1Ce0.7Y0.2–xYbxO3-δ (BZCYYb) hydrogen electrode supported SOC below 400oC. The SOC presents high Faraday efficiency as well as an ethylene selectivity close to 100%. Our approach decreases the processing energy demand dramatically with no CO2 emission when compared with the traditional ethane steam cracking process. The low temperature electrochemical dehydrogenation process in this study provides a promising prospective for next-generation petrochemical manufacturing, shifting the paradigm from thermal chemical practice to energy-saving and eco-friendly regime.
Design of Rutile Oxide Electrocatalysts for Selective Reduction of CO2 into Liquid Fuels
Authors: Bhowmik Arghya , Hansen Heine A. , Vegge Tejs
Published: February 2020

Efficient electrochemical CO2 reduction (CO2RR) into liquid fuels can potentially meet three goals at once – large-scale energy storage, CO2 capture and a carbon neutral energy cycle through utilization of renewable energy. Metal catalysts have high overpotential and low Faradic Efficiencies for direct conversion of CO2 to methanol and other liquid fuels. Using computational electrocatalysis simulations based on density functional theory, we show that RuO2-based electrocatalysts, which have been observed experimentally to evolve methanol at low overpotential, can catalyze the reaction through an alternative reaction mechanism. These pathways have oxygen-coordinated intermediates and the oxide catalyst can thus potentially bypass the limitations of the CO*-CHO* scaling relations on metal catalysts. Here, we establish adsorbate scaling relations for such reaction mechanisms and propose an activity volcano with OH* binding as descriptor. We also predict the ideal binding free energy for H* and OH* to facilitate selective CO2RR over H2/CO evolution. 1

Our study shows that adsorbate−adsorbate interaction effects are strong on the RuO2(110) surface and can alter the reaction thermodynamics substantially. Steric and electronic effects on reaction intermediates from varying coverage of CO* spectators can lead to different observed product compositions from experiments. 50% CO* coverage is necessary for obtaining methanol as a product from CO2RR.2

IrO2 and RuO2 binds OH* and other intermediates from CO2RR strongly and falls in the strong binding leg of the activity volcano. We observe that the miscible system IrxRu(1
-
x)O2 exhibits anomalous weaker OH* binding energy in the presence of CO* spectators. We attribute this to a Ru-Ir ligand effect, based on electronic structure analysis. Ir atoms at the bridge site with Ru neighbors, have electron depletion and a t2g orbital shift. Synergistic effects from adsorbate interaction and ligand effects in compositions with intermediate Ru/Ir character for active sites places them close to the top of the activity volcano. The predicted onset potential for formic acid / methanol evolution is −0.2 V RHE. 3

References:

A. Bhowmik, T. Vegge, and H. A. Hansen, ChemSusChem, 9, 3230–3243 (2016)

A. Bhowmik, H. A. Hansen, and T. Vegge, J. Phys. Chem. C, 121, 18333–18343 (2017)

A. Bhowmik, H. A. Hansen, and T. Vegge, ACS Catal., 7, 8502–8513 (2017)

Figure: Theoretical activity volcano for methanol evolution from CO2RR on oxide surfaces. Combined effects from adsorbate interaction and ligand interaction provide path to efficient oxide catalyst design.

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(Invited) Mechanistic Insights into Highly Active Metal Phthalocyanine Catalysts for Electrochemical Carbon Dioxide Reduction
Authors: Manthiram Karthish
Published: February 2020

Electrochemical reduction of carbon dioxide to produce fuels and feedstocks may represent one possible strategy for utilizing carbon dioxide that would otherwise contribute towards global warming. The use of electrical potential for making and breaking chemical bonds can allow for reductions in the temperature and pressure needed to drive reactions, enabling modular conversion of point sources of carbon dioxide. We are interested in organometallic macrocycles which can catalyze the conversion of carbon dioxide to syngas, a key chemical intermediate than can be converted into diverse hydrocarbons, alcohols, acids, and esters.

In our work, we have developed metal phthalocyanine catalysts anchored on modified carbon supports, which exhibit high turnover frequencies for reducing carbon dioxide to carbon monoxide. Our supported catalyst alleviates transport limitations that have complicated prior studies, enabling mechanistic studies that provide a molecular-level picture of how metal phthalocyanines drive the desired proton/electron transfers needed to reduce carbon dioxide. Our results indicate how the reaction can be tuned from an electron transfer mechanism to a proton-coupled electron transfer mechanism, with increased rates for the latter. We have also identified regimes in which the catalyst can operate at high ionic strength, minimizing losses due to ionic resistance.

Our results highlight the interplay of kinetics and transport in the widely observed behavior of metal phthalocyanines, as well as potential strategies for mitigating transport limitations. This may inspire concerted molecular level design of metal phthalocyanine catalysts with engineering of transport in reactors. These studies may enable design of catalysts with current densities needed for scalable electrolyzers.
Effective Strategies for Reducing Carbon Monoxide into Liquid Fuels By Copper Catalysts
Authors: Wang Lei , Nitopi Stephanie Anne , Orazov Marat , Morales-Guio Carlos , Hahn Christopher , Jaramillo Thomas F
Published: February 2020

Understanding the surface reactivity of CO, a key intermediate during electrochemical CO2 reduction, is crucial for the development of catalysts that selectively target desired products for this reaction. In this study, a custom-designed electrochemical flow cell is utilized to investigate planar polycrystalline copper as an electrocatalyst for CO reduction under alkaline conditions. We observed a large positive shift in the overpotential for C-C coupled products under CO reduction conditions compared to CO2 reduction by using the same cell. By investigating the effects of CO partial pressure and electrolyte pH, the aforementioned large potential shift was identified as a pH effect, demonstrating that alkaline conditions can be used to increase the energy efficiency of CO and CO2 reduction to C-C coupled products. Common trends in selectivity were uncovered which indicate both the production of oxygenates and the growth of longer carbon chains are favored at lower overpotentials. These selectivity trends are generalized by comparing to current state of the art rough Cu catalysts, that are able to achieve high oxygenate selectivity by operating at the same geometric current density at lower overpotentials. Combined, these findings outline key design principles for CO and CO2 electrolyzers that are able to produce valuable liquid-phase products with high energy efficiency.

To evaluate these strategies, we carried out electrochemical CO reduction under alkaline conditions on a new high surface area Cu-based catalyst to operate at low overpotentials. With the Cu nanomaterials that were developed in our work, CO is reduced into multi-carbon oxygenates with almost 100% Faraday efficiency at a potential of only –0.23 V versus the reversible hydrogen electrode. Therefore, we conclude that the competing hydrogen evolution reaction can be supressed by successfully engineering the catalyst and electrochemical conditions. A maximum Faraday efficiency of 60% is obtained for ethanol at only –0.33V vs. RHE, demonstrating the high selectivity of this catalyst for liquid fuels at low overpotentials. Thus, this work successfully implements the design principles for pursuing liquid products that were learned from the work on polycrystalline Cu, demonstrating that there are energy-efficient sustainable pathways for the sequential conversion of CO2 to liquid fuels.
(Invited) Hydrogen Is an AWSM Energy Materials Network!
Authors: Dinh Huyen N. , Randolph Katie , Weber Adam Z. , McDaniel Anthony H. , Boardman Richard , Ogitsu Tadashi , Colon-Mercado Hector , Peterson David , Vickers James W , Miller Eric L.
Published: February 2020

The Energy Materials Network (EMN) is a Department of Energy (DOE) network of national lab-led consortium aimed at accelerating the development and commercial deployment of novel materials by enhancing the accessibility of unique material research resources at the national laboratories to external stakeholders, such as academia and industry. The HydroGEN EMN was launched in October 2016 by the DOE Office of Energy Efficiency and Renewable Energy (EERE) Fuel Cell Technologies Office (FCTO).

HydroGEN (https://www.h2awsm.org/) EMN is a six-lab consortium, led by the National Renewable Energy Laboratory (NREL). It currently comprises six core national laboratories: NREL, Sandia National Laboratory (SNL), Lawrence Berkeley National Laboratory (LBNL), Idaho National Laboratory (INL), Lawrence Livermore National Laboratory (LLNL), and Savannah River National Laboratory (SRNL). HydroGEN aims to accelerate the discovery and development advanced water splitting materials (AWSM) for sustainable, large-scale hydrogen production, in order to more effectively enable the widespread commercialization of hydrogen and fuel cell technologies. With the rollouts of fuel cell electric vehicles (FCEVs) by major automotive manufacturers underway, enabling AWS technologies for the widespread production of affordable, sustainable hydrogen becomes increasingly important.

Hydrogen is a unique energy carrier in that it can be produced from a number of diverse pathways, utilizing a variety of domestically available feedstocks, including natural gas, biomass, and water. Advanced water splitting (AWS) technologies, including advanced electrolysis (low and high temperature), photoelectrochecmical (PEC) and solar thermochemical (STCH) routes, are some of the more versatile pathways, and will play a significant role in long-term, high volume sustainable production.

The HydroGEN Consortium offers an extensive collection of materials research capabilities for addressing RD&D challenges in efficiency, durability and cost. Leveraging the HydroGEN Consortium’s staff of leading technical experts and broad collection of resource capabilities is expected to advance the maturity and technology readiness levels in all the advanced water splitting technologies. In June 2017, DOE EERE FCTO announced the award of 18 new HydroGEN seedling projects, and one project focused on benchmarking advanced water splitting technologies. These 19 new projects utilized 44 unique capabilities across the six HydroGEN core labs. Furthermore, it is a nationwide R&D effort that comprises 10 national labs, 6 companies, and 22 universities. This presentation will provide an overview of the HydroGEN EMN consortium and highlight some of the advanced water electrolysis projects that are focused on hydrogen and oxygen evolution catalysis.
Dual-Ligand Synergistic Modulated Nico-Sulfhydroxides with High Activity and Stability As Oxygen Evolution Electrocatalysts
Authors: Peng Lishan , Shen Jingjun , Lin Taicheng , Wei Zidong
Published: February 2020

The most knotty problem of (electro)catalysis that arises ubiquitously is the notion that the more active catalysts for oxygen evolution reaction (OER) will simultaneously suffer from low resistance toward corrosion. In developing cost-effective stable materials for the oxygen evolution reaction with high activity, precisely tuning the structure of transition-metal materials in atomic level to obtain ideal chemical properties is urgent while difficult to achieve1. In this study, we propose a “dual ligand synergistic modulation” tactics to completely solve the painful compromise between the two conflicted indicators: stability and activity. By substituting S ligand into the adjustable and stable structure of layered hydroxides, which was selected as the start noumenon, we obtain a new class of NiCo2(Sx·OH2-x)y with single phase and homogenous composition. The elaborated designed dual-ligand catalyst ideally inherits the excellent activity of the conventional transition metal sulfides and the superior stability of the conventional transition metal hydroxides and even exceeds the predecessors. Impressively, the optimized NiCo2(SOH)x performs a small overpotential of 0.32 V at 10 mA cm-2, and shows no decay after 30h accelerated ageing even at a large current density of 100 mA cm-2, both of which have entered the top of all the transition-metal hydroxides and sulfides reported to date and exceeded the commercial RuO2 and Ir/C benchmarks. Theoretical calculations further disclose that the OH ligands on the surface of NiCo2(SOH)x could attracts electrons from the antibonding orbital of M-S bonds to M-O bonds, resulting in a strengthened binding energy between metal and S and thus enhancing the stability. Meanwhile, the synergy between S ligands and OH groups appropriately tunes the electronic structure of NiCo2(SOH)x and thus renders it with optimal binding energies for OER intermediates (*OH, *O, and *OOH), which is benefit for facilitate the O2 evolution proceeding. Besides, the varied magnetism induced by the modulation of catalysts’ electronic structure significantly influences the desorption action of paramagnetic O2 from the catalyst surface. The special non-magnetic NiCo2(SOH)x suffers the lowest O2 desorption resistance and proceeds the smoothest reaction kinetics pathway among NiCo2(SxOH2-x)y catalysts, thus owning the topmost OER activity.

Figure 1. (a) The ultimate unity of OER performance of NiCo2(SxOH2-x)y. (b) The reaction steps and corresponding free energy diagram of the OER process. (c) OER polarization curves of Ni, RuO2, NiCo2S4, NiCo2(OH)x, and NiCo2(SOH)x and (d) Chronoamperometric curves of Ni, NiCo2(SOH)x and NiCo2S4 at a current density of 100mA/cm2.

Key words: Oxygen evolution, electrocatalysis, dual-ligand modulation

Reference:

Lishan Peng, Jun Wang, Yao Nie, Kun Xiong, Yao Wang, Ling Zhang, Ke Chen, Wei Ding, Li Li, and Zidong Wei*.
ACS Catal.
, 2017, 7, 8184-8191.

Figure 1
Activity and Stability Relationship for Anion Doped CoSxSe2-X Dichalcogenides for the Hydrogen Evolution Reaction
Authors: Li Yawei , Chatterjee Swarnendu , Snyder Joshua David
Published: February 2020

As an ideal clean energy carrier, hydrogen can be produced through polymer electrolyte membrane (PEM) electrolysis by generating H2 from H2O. However, noble platinum group metals (PGM) remain the most common electrocatalysts for hydrogen evolution reaction (HER). The expense and scarcity of these catalytic materials obstruct the wide-spread adoption of electrochemical fuel generation technologies 1. Sulfur based transition metal dichalcogenides (TMDs) have emerged as a promising alternative to PGM HER electrocatalysts as they are abundant, inexpensive, and exhibit a low HER overpotential in acidic environment 2,3.

Here we present a systemic assessment of the compositional dependent HER activity and stability for Co-based mixed chalcogen, CoSxSe2-x, pyrite TMDs. We observe a decrease in HER activity from the single chalcogen TMDs, CoS2 and CoSe2, to mixed chalcogen TMDs, as shown in Figure 1. This observed compositional trend in HER activity can be explained by the unique combination of compositional dependent hydrogen adsorption free energy (ΔGHad) and bulk resistivity/conductivity of the pyrite TMD. With near thermoneutral ΔGHad, the highest resistivity among the compositions was observed. The following increase in Se content leads to the decrease in HER activity due to a steady movement away from optimal ΔGHad. As the composition approaches CoSe2, however, it is observed that HER activity again increases at higher Se contents, with CoSe2 exhibiting similar activity to CoS2. This highlights the convolution of ΔGHad and material conductivity in determining the HER activity. Furthermore, through stability tests under constant potential HER electrolysis, as shown in Figure 2, Se-rich Co-based pyrite TMDs are found to be more durable than S-rich samples. Therefore, with an HER activity matching that of CoS2, but with a dramatic improvement in stability, CoSe2 breaks away from the traditional inverse activity/stability relationship and represents a promising material for non-PGM HER electrocatalysis in acidic based PEM electrolyzers.

Wang, J. et al. Mater.
28, (2016) 215-230.

Chhowalla, H. et al. Nature Chemistry
5, (2013) 263-275.

Jaramillo, T. et al. Science
317, (2007) 100-102.

Figure 1
(Invited) How Can We Maintain the Excellent Performance of the PEM Electrolyzer without the Use of Platinum Group Metals?
Authors: Jensen Jens Oluf
Published: February 2020

The PEM electrolyzer is superior to the alkaline as well as the solid oxide electrolyzers when it comes to rate capability and practical footprint. The cell owes its attractive properties to the combination of a good oxygen reduction catalyst and a durable and highly conductive membrane. The story could end here and often it does, but it is important to realize that there is also a severe limitation to the large-scale roll-out of this system. It relies on platinum group metals for catalysts and in most cases also noble metal coatings of cell components to limit the contact resistance in the acidic environment.

The noble metal issue (cost and availability) and the prospects for replacement of iridium oxide as oxygen catalyst are discussed. Platinum replacement is an active field within PEM fuel cell research. Why is that not the case to a similar extent for PEM electrolyzers? Finally, an alternative route to electrolyzers with rate capability like the PEM electrolyzers, but without the use of noble metals is suggested.
A Novel and Economical Rde-Based Approach for Investigating the Oxidation Evolution Reaction Activity of IrO2-Based Catalyst Coated Membranes
Authors: Kwan Jason Tai Hong , Kroschel Matthias , Nouri-Khorasani Amin , Bonakdarpour Arman , Strasser Peter , Wilkinson David P.
Published: February 2020

Polymer electrolyte membrane water electrolyzers (PEMWE) are clean and scalable energy conversion devices that can assist with electricity peak shaving and storage by converting electricity into hydrogen as an energy carrier 1. However, performance, durability and cost of these systems still require further improvements before they can be widely adopted. In particular, it is desired to have more efficient and lower cost oxygen evolution reaction (OER) electrocatalysts for the anode, because of the high cost and potential losses that are associated with this electrode2. Screening of catalyst materials, as well other expensive cell components (e.g., Ti current collectors and Ti endplates), is in general a slow and rather expensive process due to the inherent high costs of test cell equipment, and the difficulties associated with cell assembly3. Alternative methods based on commonly available and small laboratory-scale electrochemical test equipment, such as the rotating disk electrode, can facilitate the screening process.

We present a novel and economical method for testing electrolysis CCMs and potential current collectors in a rotating electrode (RDE) setup. This method eliminates the difficulties which are often associated with ink preparation and sample drying which are encountered in thin film RDE (TF-RDE) testing. Very recently, we have successfully demonstrated this approach for evaluation of oxygen reduction reaction (ORR) electrocatalysts used in PEMFC applications4. The modified-RDE (MRDE) presented here allows a user to obtain very high current densities (~ 2 A cm-2) which is similar to those normally obtained with PEMWE hardware and test stations (Figure 1). Polarization measurements, kinetic analysis and accelerated degradation tests (ADT) have been performed with a commercial IrO2-based CCM using the MRDE, and are compared with those of PEMWE hardware results. The approach, methodology and the results will be presented at the meeting.

References:

A. S. Aricò, S. Siracusano, N. Briguglio, V. Baglio, A. Di Blasi, and V. Antonucci, J. Appl. Electrochem., 43, 107–118 (2013).

H. Dau, C. Limberg, T. Reier, M. Risch, S. Roggan, and P. Strasser, ChemCatChem, 2, 724–761 (2010).

A. S. Lohoff, L. Poggemann, M. Carmo, M. Müller, and D. Stolten, J. Electrochem. Soc., 163, F3153–F3157 (2016) http://jes.ecsdl.org/lookup/doi/10.1149/2.0211611jes.

J. T. H. Kwan, A. Bonakdarpour, G. Afonso, and D. P. Wilkinson, Electrochim. Acta, 258, 208–219 (2017) http://linkinghub.elsevier.com/retrieve/pii/S0013468617322090.

Figure 1: The effect of different titanium current collector meshes on OER performance using a commercial IrO2-based CCM obtained by the MRDE tool. Inset shows pictures of the different Ti meshes examined.

Figure 1
Turnip-Inspired BiVO4/CuSCN Heterojunction Photoanode for Highly Efficient Photoelectrochemical Water Splitting
Authors: Vo Truong-Giang , Chiu Jian-Ming , Tai Yian , Chiang Chia-Ying
Published: February 2020

Inspired by the functions and structures of the root and stalk of a turnip, a novel BiVO4/CuSCN heterojunction was constructed for photoelectrochemical water splitting, by initially fabricating bulky BiVO4 film (the root) and subsequently depositing p-type CuSCN nanorods (the stalk) on top. This BiVO4/CuSCN photoanode produced an enhanced photocurrent density of 1.78 mAcm-2 and hole injection efficiency of 82% at the potential 1.23 V vs. RHE. About 45% increase in photocurrent density coupled with a dramatic cathodic shift (~220 mV) in onset potential compared with bare BiVO4. The heterojunction also possesses external quantum efficiency of approximately 33% in the range from 350-450 nm with fairly high solar energy conversion efficiency (0.5%). The unique electrode architecture design favors the facile water splitting process over conventionally fabricated electrode by providing the more active sites and facilitates transportation and consumption of photoinduced holes, open a new route for the high-efficiency photoanodes.

Figure 1
Investigating Redox States and Reaction Dynamics of Ni-Based Nano-Catalysts for Alkaline Water Splitting
Authors: Qiu Zhen , Edvinsson Tomas
Published: February 2020

Design and synthesis of highly active and cost-effective electrocatalysts for hydrogen and oxygen generation by water electrolysis can be of paramount importance, as hydrogen has been considered as one of the most promising energy alternatives to traditional fossil fuel-based energy because of its high specific energy density and potentially clean production. Here, we investigate the interfacial cause-effect-relationships in the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) for Ni-based nano-catalysts by modifying the structure and performing in-situ characterization during the reaction. Based on different pH condition during synthesis of NiO nanoflakes (NFs), we show that the crystal growth direction and morphology of the NiO nanostructure can be altered according to the different surface charges, which control the exposure of the surface active sites, resulting in much improved catalytic performance. Additionally, by incorporating a redox active dopant (Fe), NiO can be tuned into higher catalytic efficiency and becomes bi-functional with respect to the OER and the HER processes under alkaline conditions. Exploring the 3D synergistic NiFe nano-layered double hydroxide, we find improved catalytic performance after prolonged use, where the current density increases from 9.3 mA cm-2 to 12.7 mA cm-2 during 100 h running at 1.7 V without iR compensation in a 2-electrode system. In order to understand the function and precise mechanism of metal doping and the synergistic effect to improve the catalytic property after prolonged use, we utilize in situ Raman spectroscopic and in situ electrochemical impedance spectroscopy (EIS) to monitor the interfacial redox state and reaction dynamics. As we all know, the material structure plays a vital role on improving the electrocatalytic property and stability. The structural and physical characterization on 3D ultrathin NiFe nano-layered double hydroxide were also investigated with XRD, TEM, EELS and XPS before and after 100 h electrolysis in a two electrode configuration in 1 M KOH at room temperature. The structure changes after the oxygen evolution reaction are minor, while, after the hydrogen evolution reaction, the catalyst undergoes recrystallization as observed by selected area electron diffraction (SAED), with markedly improved electrocatalytic activity. The successful identifications of the underlying reasons for the electrocatalytic improvement opens the possibilities for a rational design of Ni-based nano-catalysts, and possibly also for other material systems for use as efficient electrocatalysts for practical alkaline HER and OER processes.