bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Mechanism of Interlayer Transport on a Growing Metal Surface: 2D vs. 3D Growth
Authors: Jonsson Hannes
Published: July 2022

The atomic scale transitions corresponding to diffusion and interlayer transport of metal adatoms on the low energy, close packed surfaces of several transition metals are studied using density functional theory calculations within the generalized gradient approximation. Minimum energy paths and estimates of activation energy are calculated for processes that influence whether the crystal grows layer-by-layer, i.e. 2D growth, or whether new islands nucleate on top of existing islands resulting in 3D growth. In some cases, the path of lowest activation energy for the descent of an adatom, i.e. interlayer transport, turns out to take place near, but not at, a kink site on a step. The energy barrier for the adatom to subsequently round the corner and enter the kink site is significantly higher. This near-kink-descent mechanism promotes the formation of a new row of step atoms and leads to the introduction of additional kink sites, thereby opening up new low activation energy paths for descent and promoting 2D growth. The sites adjacent and above the step edge can provide large binding energy for the adatom, and form a trough along which the adatom can migrate before descending, thereby increasing the probability that an adatom finds a kink site. These features of the energy landscape for an adatom point to the possibility of re-entrant layer-by-layer growth mode and have, for example, been found for Pt(111) and Au(111) surfaces.
(Invited) Electrochemical Liquid-Liquid-Solid Growth of Pd and Pt Intermetallic Crystals
Authors: Wu Henry , Hazelnis Josh , Maldonado Stephen
Published: July 2022

This presentation details the development of electrochemical liquid-liquid-solid (ec-LLS) strategies for the deposition and crystal growth of Pt-group intermetallic compounds. That is, methods where the liquid metal electrode/solvent in ec-LLS is used also as a reactant to form binary and ternary intermetallic compounds will be described. This strategy enables the synthesis and collection of metastable intermetallic and alloy phases that are otherwise unattainable by conventional electrodeposition or metallurgical reactions between constituent metals at room temperature. This presentation will detail how the identity of the liquid metal through its solvation properties and its tendency for electrocapillarity affect the products obtained by ec-LLS.
(Invited) Coordination Controlled Electrodeposition of Metal Nanostructures
Authors: Buck Manfred
Published: July 2022

It is the combination of features related to surface chemistry, charge transfer, and interfacial energies which makes self-assembled monolayers (SAMs) attractive templates for electrodeposition. However, as in other additive processes such as atomic layer or electroless deposition where SAMs are harnessed for area selective deposition, one is faced with substantial challenges when advancing to the ultrasmall scale. Based on defects in a chemically inert SAM, the established scheme of SAM controlled electrodeposition offers a very convenient way to generate patterns but is only applicable down to the length scale of a few tens of nanometers. The statistical nature of defects does not provide the level of control over the deposition process required to move further towards the bottom range of the nanoscale.

For this reason we have been exploring a deposition scheme which builts on features intrinsic to the SAM molecules and, therefore, promises a more precise control over decisive steps in the deposition process.1 The essential point is the paradigm shift from a mushroom like deposition at defects to a deposition via coordinated metal ions using a suitably functionalized SAM. As illustrated in the cartoon, nuclei generated by discharging a two-dimensional layer of ions act as seeds for the deposition from the bulk electrolyte. Yielding layers on top of the SAM, this coordination controlled deposition not only enables a further reduction in lateral dimensions of patterns to below 20 nm but also shifts the percolation threshold, yielding continuous layers at a thickness of about 2 nm. In relation to this the average roughness of below 0.4 nm is substantial and further improvement is needed. Key to this and a further reduction in dimensions is the understanding of the processes determining the seed formation and how these can be controlled by the design of the SAM. Informed by calculations which show a strong interaction between metal atoms and the terminating aromatic unit of the SAM,2 studies of binary layers consisting of coordinating and non-coordinating molecules have been performed. The average size and size distribution of the particles depend on the composition and mixing ratio, and a significant reduction in size to about 2 nm can be achieved, suggested that the diffusion length is reduced and nucleation is promoted in mixed SAMs. The results show that SAMs provide a range of design opportunities through which coordination controlled electrodeposition can be further developed towards ultrasmall structures.

1. Z. She, Z. Yao, H. Ménard, S. Tobish, D. Lahaye, N. R. Champness, M. Buck,
Coordination controlled electrodeposition and patterning of layers of palladium/copper nanoparticles on top of a self-assembled monolayer,
Nanoscale 11, 13773-13782 (2019).

2. Z. Yao, M. Buck, M. Bühl,
A Density Functional Theory Study of Pd Aggregation on a Pyridine-Terminated Self-Assembled Monolayer,
Chem. Eur. J. 26, 10555-10563 (2020).

Figure 1
Formation of Titanium Oxide on Nonmetal Substrates and the Coordination Structure of Titanium Ions in Molten Lif-KF
Authors: Okada Kaai , Suzuki Yuta , Goto Takuya
Published: July 2022

Electrodeposition of titanium materials on substrates is an important technique to improve and functionalize the surface properties. Especially electrodeposition of titanium and titanium oxide on a material that is an insulator. However, electrodeposition of an insulator on another insulator is considered to be difficult. If such deposition can be accomplished, it would have a variety of practical applications in both mechanical and electronic industries. We are thus proposing a new method for electrodeposition of titanium oxide on alumina substrates in LiF-KF with the addition of TiO2 and metal titanium. We have carried out the electrodeposition to test hypotheses on deposition of titanium oxide on the alumina surface by employing the three electrodes method in the molten salt. The nickel-wire in contact with alumina substrate was employed as a working electrode to grow titanium oxide on the substrate by the proposed electrochemical process. Titanium oxide deposition grew from the three-phase interface of nickel wire, molten salt and alumina substrate in a radial pattern. The growth rate of the deposition was controlled by adjusting the electrochemical parameters. We have also investigated the melt structure of LiF-KF with the addition of TiO2 and the addition of bulk titanium by combining high temperature Raman spectroscopic technique and density functional theory calculations. These results provide new insight into the growth process of titanium oxide crystals and possibly a new comprehensive plating procedure for titanium oxide on insulator substrates.
(Invited) Operando Scanning Electron and Photoelectron Spectromicroscopy to Study the Nucleation and Growth Phenomena in Liquid and Reactive Solid Electrolytes: The Technique Development
Authors: Kolmakov Andrei A
Published: July 2022

Nucleation and growth (NG) phenomena play a central role in a variety of applications spanning from the back end of line (BEOL) microfabrication to environmental remediation and energy devices performance. Therefore, the development of analytical metrologies, capable to access these phenomena with the high chemical, spatial and temporal resolution is amongst the key tasks of the research community. Probing nucleation and growth phenomena in situ, using traditional high analytical power tools such as SEM, XPS, AES, SPEM, and PEEM, under realistic sample environments, is a great aim but also an experimental challenge due to the apparent sample-to-detector “pressure gap”. Implementation of the electron transparent membranes that separate the reactive, liquid, or dense gaseous sample environments from the high vacuum instrumentation, in principle, resolves this impediment thus the standard analytical surface science equipment can be used. The sample and or device, therefore, need to be covered or encapsulated with a mechanically robust electron transparent impermeable membrane. The thickness of such a membrane defines the energy range and broadening of the transmitted electrons and, therefore, the thinnest membranes such as those made of 2D materials are desirable. Here, using variable pressure SEM, we exemplify the sensitivity of electrochemically driven NG processes to the composition of the ambient environment. Using model liquid electrolytes, we review the capabilities, advantages, and limitations of the graphene membrane-based liquid cells to probe NG processes with electron spectromicroscopy. In particular, we discuss graphene-cupped single orifice and microchannel arrays (MCA), and their applications for electrochemical polarization, nucleation, and growth studies using SEM, AES, SPEM, and PEEM. In addition to local spectromicroscopy, MCA-like designs enable application of high throughput combinatorial data mining algorithms to collect multi-dimensional/ hyperspectral datasets. The experimental artifacts and major limitation of the technique related to radiation damage of the sample will be discussed.
(Invited) In-Situ Observation of Electrodeposition Processes By High Speed Scanning Probe Microscope
Authors: Matsushima Hisayoshi
Published: July 2022

Electrodeposition is important technology for developing the novel functional materials such as MEMS. In nanotechnology term, the metal deposition is one of the hot topics since it can control the surface structure precisely and easily.

Generally, in metal electrodeposition, an adatom deposited on the electrode diffuses and reaches a step or kink before forming a crystal. In the process, the solvents and additives adsorbed on the surface are often incorporated into the deposits. Since they works as an impurity in the film, they induce the crystal defects and surface defects, which may cause the performance degradation of the produces. Because each processes occur at high speeds and on the atomic scale, the deposition mechanism is difficult to understand.

The methods for observing the nucleation have been developed in various ways. With the invention of the scanning probe microscope (SPM) in the 1980’s, we could directly observe the nanostructure. It has been applied to the electrodeposition in aqueous solution. However, since SPM usually takes some time to observe the surface, it is very difficult to catch the dynamic process such as the nucleation and growth of the deposits. Therefore, I believe that the high-speed SPM is the promising solution of both temporal and special problems.

There are two types of SPM: scanning tunneling microscope (STM) and atomic force microscope (AFM). In the former type, there is a video rate STM (Video STM) that can capture up to 30 frames per second. Furthermore, the spatial resolution can reach the atomic scale. For example, the Bi kink growth along the step is reported and Pb surface diffusion on the Cu surface is clarified [1-3]. However, since the tunneling current flows continuously between the probe and the substrate during the measurement, it is necessary to sufficiently consider the effects on electrochemical reactions.

Although the resolution of the high-speed scanning AFM (HS-AFM) is inferior to that of the STM, the influence of the probe can be less. Therefore, in addition to the nucleation phenomenon during Cu electrodeposition (Fig. 1-A) [4], we have observed the weak adsorption of PEG polymer that is known as the major additives during the electrodeposition (Fig.1-B). By taking the advantage of the low contact pressure of the probe, the transient behavior of nucleation and growth of electrolytic nanobubbles can be observed.

In this presentation, the dynamic variations of the electrolytic nucleation & growth by using a high-speed SPM will be presented.

References

H. Matsushima et al., Faraday Discuss., 193 (2016) 171.

A. Taranovskyy et al., Phys. Chem. Chem. Phys., 14 (2012) 10579.

S. Guezo et al., J. Phys. Chem. C, 115 (2011) 19336.

T. Yoshioka et al., Electrochim. Acta, 302 (2019) 422.

Figure 1
(Invited) The Oxygen Reduction Reaction Kinetics on a Platinum /Graphene Surface
Authors: Diankov Georgi , Hong Soonwook , Park Joonsuk , Xu Shicheng , Sinclair Robert , Pande Vikram , Viswanathan Venkatasubramanian , Goldhaber-Gordon David , Prinz Fritz
Published: July 2022

The oxygen reduction reaction (ORR) is rate-limiting in polymer electrolyte fuel cells over a wide range of overpotentials. To improve our understanding of the underlying physics and chemistry of ORR, we created a model system with atomically-ordered interfaces that allows us to distinguish between bulk and electronic effects on catalytic behavior. Specifically, we developed a facile way of growing thin, epitaxial Pt nanostructures on graphene, which serves as both growth substrate and electrode. Rotating disc electrode measurements showed a high specific activity relative to platinum on glassy carbon. The enhanced ORR activity was observed despite consistent measurements that show a small electrochemically-active surface area arising from the fact that virtually all carbon atoms in monolayer graphene are surface atoms. This talk will address the reasons for the increase of ORR activity in view of the new ground state of atomically thin platinum on graphene.
(Invited) Cooperative Fe Sites on Transition Metal (Oxy)Hydroxides for High Oxygen Evolution Activity
Authors: Boettcher Shannon W.
Published: July 2022

Heterogeneous electrocatalysts for the oxygen evolution reaction (OER) are complicated materials with dynamic structures. They exhibit potential-induced phase transitions, potential-dependent electronic properties, variable oxidation and protonation states, and disordered local/surface phases. These properties make understanding the OER, and ultimately designing higher-efficiency catalysts, challenging. Measurements of intrinsic activity show that, by far, the most-active phases for OER under alkaline conditions are Fe-containing mixed-metal oxyhydroxides, but exactly how they function remains controversial. I will discuss our work to understand the key properties of these catalysts, including morphology, composition, and molecular/electronic structure, and how they evolve and are dynamic under active catalytic conditions. Specifically, I will highlight new work where we have been able to systematically control the concentration of surface Fe species on NiOOH and CoOOH host structures. We discover that the per-Fe turn-over frequency (TOFFe) for the OER increases nearly linearly with the Fe concentration, providing clear evidence for cooperative effects between Fe atoms and suggestive of a mechanism involving multiple Fe sites that is supported by density functional theory calculations. In sum, these concepts inform design strategies for higher-performance catalyst architectures and for their incorporation into practical electrolyzer devices to make clean hydrogen fuel from inexpensive renewable electricity for green long-distance transportation and long-duration energy storage.
(Invited) Fundamental Study of Electrodeposition of Li Metal By Using an Ultla-Micro-Electrode
Authors: Nishikawa Kei
Published: July 2022

Li metal is a promising candidate for negative electrode of next-generation batteries. However, the dendrite growth during cycles is fatal problem for commercialization. It is indispensable to control the morphological variation of Li metal electrode during cycles. Generally, the evaluation of Li metal electrode is performed by coin cells and pouch cells. These cells utilize electrodes with cm-scale. In that case, the reaction distribution sometimes happens to make the analysis difficult. In this study, an ultra-micro-electrode (UME) is utilized as a model electrode in order to discuss the mechanism of electrodeposition and electrochemical dissolution of Li metal. The electrodeposited Li metal onto UME was analyzed by several technique mentioned below. The morphological variation of electrodeposited Li metal was observed by a SEM. 3D structure of the electrodeposited Li metal was observed by cut and see technique of a cryo-FIB-SEM. The nano-scale surface layer of the electrodeposited Li metal was analyzed by a cryo-TEM and STEM-EELS measurement. This presentation will discuss the mechanism of the electrodeposition of Li metal from mm to nm scale based on those measurement.
Influence of 1,1-Dimethylpropargylamine on Nickel Electroplating
Authors: Moazezi Alireza , Schmidt Udo , Ispas Adriana , Bund Andreas
Published: July 2022

Nickel electroplating is widely used for decorative thin films, for better abrasion resistance and increased corrosion protection. The properties of the nickel deposit, such as its structure and morphology, can be varied by adding different organic additives to the nickel electrolyte. For example, additives such as coumarin and saccharin are used in nickel plating to generate a nickel film with uniform thickness on rough substrates.

Levelling is referred to as a process of progressive reduction of surface roughness during electrodeposition. In this case, scratches or non-uniform structures on the cathode represent the initial roughness, and the result of cathodic deposition is a smooth levelled layer with reduced roughness. In this type of levelling, more metal is deposited in the grooves than on the elevated surface features. This is due to the fact that metal deposition is less inhibited in the recessed features. True levelling requires the presence of appropriate levelling agents and brighteners. A wide variety of organic compounds are used as brighteners e.g. olefinic, acetylenic and sulphur and nitrogen containing compounds.

The singular and synergistic effect of the following additives on Ni electroplating was investigated and discussed in this work, such as the 1,1-dimethylpropargylamine (MPA:5 to 20 mg/L), sulfopropylated butynediol (HBOPS: 7.5 or 75 mg/L), 1-(3-sulfopropyl)-pyridinium betaine (PPS: 1.6, 3.2 or 150 mg/L), saccharin (1.5 g/L) and sodium allyl sulfonate (ALS: 1.5 g/L).

Reflectance and colour measurements showed that the samples coated from nickel electrolyte containing 5mg/L MPA and 7.5 mg/L HBOPS exhibited better uniformity, gloss and good throwing power in the low current density regime when compared to the electrolytes containing other additives or without MPA. Cross section analyses of the deposits indicate that the MPA is not only acting as a strong brighter, but it also helps in levelling (Fig. 1). XRD measurements indicated the effect of the different additives on the structure of the nickel deposits.

Fig. 1. Cross section of a sample deposited for 72 minutes at 2 A/dm² and 50 °C from a Ni electrolyte containing 240 g/L NiSO4 x 7 H2O, 40 g/L NiCl2 x 6 H2O, 30 g/L H3BO3, 0.5 g/L SDS, 1.5 g/L saccharin, 1.5 g/L ALS, 1.6 mg/L PPS, 7.5 mg/L HPOPS und 5 mg/L MPA

Figure 1
(Invited) Dynamic Plating/Stripping Behavior of Zn Anode in an Operating Aqueous Zn-Ion Battery
Authors: Liu Yijin
Published: July 2022

To circumvent the fossil resource depletion and to reduce the carbon emission, electrochemical energy storage technique undergoes blooming developments over the past few decades. A promising candidate for electrochemical energy storage is the rechargeable Zn aqueous battery, which has the merits of rich Zn abundance, low cost, high safety, and environmental friendliness. Despite of enormous research and engineering investments, the practical implementation and deployment of Zn aqueous battery are still hindered by challenges concerning several different aspects of the electrochemical reaction involving Zn-ions. One of the main obstacles is that the Zn anode suffers from a low Coulombic efficiency, and the underlying mechanism is related with the non-ideal reversibility of the Zn plating/stripping process. The behavior of Zn plating and stripping is sophisticated and can be modulated by several co-existing and intertwined factors, including the electrode configurations, the charging/discharging protocols, and the composition of the electrolyte.

For example, it has been demonstrated that the anode morphology can affect the dendrite growth. By fabricating Zn anode with a 3D sponge structure, the Ni-Zn cells could exhibit an improved cycle performance and a suppressed dendrite formation. Plating with high current density could exacerbate the electrochemical polarization and tends to form Zn dendrites. As a mitigation, the Zn dendrites can be dissolved by applying a small current during the stripping process. In addition, surface chemistry on anode plays a critical role in the Zn plating/stripping process. The reactions involving the solid-liquid interphase are often complicated and may vary depending on the electrolyte used. A holistic investigation of the structural, dynamic, and chemical features in Zn-ion batteries under operating conditions is key to the development of high-performance Zn-ion battery.

In this talk, I will present our recent study using in-situ X-ray tomography and operando X-ray radiography to investigate the Zn plating/stripping behaviors in an in-house developed aqueous zinc-ion battery cell. We electrochemically plate Zn on a three-dimensional Cu foam and reveal how the electrode configuration and the local morphology collectively regulate the Zn plating behavior. Through advanced quantification and analysis of the tomographic data, we uncover that the Zn deposition in ZnSO4 electrolyte exhibits a substrate-curvature dependence. We further investigate how the current density would modulate the Zn plating using operando X-ray radiography. I will also briefly discuss the possibility of utilizing a novel tri-contrast x-ray imaging method to image dendric structures with better sensitivity and contrast.
(Digital Presentation) Magnesium Shot Filled Electrochemical Packed Bed Reactor for Phosphate Recovery
Authors: Sultana Ruhi , Greenlee Lauren F
Published: July 2022

The global food-energy-water nexus encompasses energy efficient recovery and reuse of nutrients. However, limited phosphate sources and pollution from phosphate-rich fertilizers adversely affect global food security, which mandates energy-efficient technologies, like electrochemical struvite (MgNH4PO4.6H2O) production, with nutrient capture and reuse potential. In this study, we report a first-of-its-kind electrochemical struvite precipitation in an electrochemical packed bed reactor filled with pure Mg shots, which achieved shortened retention time and higher phosphate removal efficiency, compared to the previous batch electrochemical system used by our group. Mg loading, equivalent to the weight of the immersed Mg anode in the batch reactor, was fixed in the packed bed reactor at the beginning of each experiment. The feed flow rate (0.5-5 LPM) and Mg shot diameter (0.5-1.5 cm) were varied to study the performance of electrochemical precipitation column in a 10 mM synthetic solution of ammonium dihydrogen phosphate (NH4H2PO4, 10 mM) at neutral pH. The continuous flow system achieved a >40% phosphate removal over 4 h. The experimental results help in understanding the different parameters that affect struvite recovery from a flow-based reactor design, as well as an understanding of the challenges involved in transitioning from a batch reactor to a flow reactor.
(Digital Presentation) On Demand Electrochemical Peroxide Generation for Disinfection
Authors: Vijapur Santosh Hanamant , Hall Timothy , Taylor E. Jennings , Wang Dan , More Santosh R , Liu Danny , Snyder Stephen , Skinn Brian
Published: July 2022

Novel technologies with limited earth support are required to enable habitation in microgravity spacecraft habitats such as International Space Station (ISS). Disinfection needs is an area of particular need, which is currently accomplished through the use of pre-packaged, disposable, wetted disinfection wipes. These items represent an appreciable carry-along mass and disposal/replacement burden requiring ground support. Therefore, a system is desired that could utilize onboard utilities to create disinfecting solutions to eliminate storage/disposable problems of the wetted wipes and further reduce the astronaut’s dependence on earth-based supplies.

Faraday Technology Inc. is addressing this challenge by demonstrating an in-situ approach, which utilizes on-board supplies of air and water for on demand electrochemical generation of hydrogen peroxide. Hydrogen peroxide is well-established disinfectant with non-toxic decomposition products (viz., O2 and H2O), that is safe enough for human contact to be sold commercially as a 1-5 w/w% solution, which makes it an ideal disinfecting solution for closed space environments. Faraday has continued to improve the TRL by scaling the electrochemical peroxide generation system from a sub-scale to alpha-scale process in order to deliver 1 L per day of ~2 w/w% hydrogen peroxide for disinfectant applications from DI water feed-stream with air as a feed source
[1],[2],[3],[4]
. These electrolytes were then sent to NASA for microbial control property characterization. Specifically, this talk will discuss the results of these advancements.

Acknowledgements: Financial support of NASA Contracts NNX16CA43P, NNX17CJ12C, and 80NSSC20C0070 is acknowledged.

References:

[1] Vijapur, Santosh H., et al. "Electrochemical peroxide generation." ECS Transactions 77.11 (2017): 947.

[2] Vijapur, Santosh, et al. "In-Situ Resource Utilization for Electrochemical Generation of Hydrogen Peroxide for Disinfection." 49th International Conference on Environmental Systems, 2019.

[3] Nelson, George J., et al. "Electrochemistry for Space Life Support." The Electrochemical Society
Interface 29.1 (2020): 47.

[4] Vijapur, Santosh, et al. "In-Situ Resource Utilization for Electrochemical Generation of Hydrogen Peroxide for Disinfection." 50th International Conference on Environmental Systems, 2021.
An Electro-Reductive Removal of Gaseous Toluene By a Copper-Nickel Complex Mediator at Gas-to-Solid Interface
Authors: Kim Daekeun , Choi Youngyu , Govindan Muthuraman
Published: July 2022

Electrochemical technique is one of the most promising methods for the removal of volatile organic compounds such as toluene. However, the conventional gas electrolysis method has mass transfer limitation, and the homogeneous catalysts are often irrecoverable after the reaction is completed, which leads to inefficient, less environmental-friendly, and uneconomical performance. This study proposes a gas-to-solid electrolysis system employing an electrode coated with heterogenous catalyst as the electron transfer mediator. A CuNi(CN)4 complex was prepared according to a published method and drop-coated on a commercial copper mesh electrode with 5% Nafion solution. The CuNi(CN)4 coated copper electrode was further covered by 10 M of NaOH solution by drop-coating to increase the pH, which in turn widens the potential window. The prepared CuNi(CN)4 electrode was characterized by XRD and SEM-EDS analyses. The XRD and SEM-EDS analyses evidenced the CuNi(CN)4 presence with structural and composition details. Characteristics of electrodes and mediators were also confirmed through various analysis methods. Additionally, an electrochemical confirmation of CuNi(CN)4 presence by its redox behavior was inferred by gas-phase cyclic voltammetry. After confirmation of mediator presence, electrode mounted in a Nafion membrane divided electrolytic cell at the cathodic half-cell for the gas phase reductive electrolysis. A PVA gel was inserted in-between the Nafion membrane and the cathode to serve as a solid electrolyte to facilitate the electron transfer process. The electrochemical reduction of gas-phase toluene was carried out using a continuous flow model and chronoamperometry method. Different experimental parameters such as feed gas flow rates and concentrations were investigated on toluene removal. GC-MS analyses were applied to measure toluene concentration and intermediate compounds identification. A possible reaction mechanism will be discussed in detail at the conference.

Acknowledgment

This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education(NRF-2021R1I1A1A01049901) and also from the Grants No. NRF-2020R1A6A1A03042742
(Invited) Advancements in Vertical GaN p-n Junction Structures Via p-Type Ion Implantation
Authors: Goorsky Mark S. , Liao Michael Evan , Huynh Kenny , Wang Yekan , Anderson Travis J. , Tweedie James , Allerman Andrew A.
Published: July 2022

Vertical GaN power devices have emerged to become promising candidates for next-generation high power applications due to superior material properties such as high breakdown voltage, low on-resistance, and high mobility compared to devices based on Si and SiC. GaN-based p-n junction switching devices enable higher voltage power with significantly higher efficiencies with added advantages of reduced size and weight systems. A technological limitation of GaN, however, has been the inability to achieve high p-type doping in a planar, vertical device. Here, we will focus on recent developments to achieve high p-type efficiency though ion implantation, novel high temperature annealing schemes, and the importance of defects and morphology in native substrates and epitaxial layers

GaN epitaxial layers for subsequent p-type ion implantation can be grown on sapphire substrates but vertical devices are optimal when using GaN homoepitaxial structures. Unlike most other semiconductor substrates, GaN substrates are not grown from the melt. Hydride vapor phase epitaxy or ammonothermal growth are predominantly used to produce substrates and these substrates will experience higher temperatures during subsequent epitaxy and ion implant activation annealing than occurs during substrate formation. In both types of substrates, the threading dislocation distribution can vary by orders of magnitude – these variations correlate well with leakage currents in vertical devices.

The activation of the implanted p-type dopants requires high temperature annealing. For most semiconductors, an annealing temperature of ~ 2/3 the melting point leads to a high activation fraction (> 95%) of the implanted species. The implantation process introduces large concentrations of native defects as well as the p-type implant (typically Mg), so it is necessary to remove the defects and for the dopants to locate on substitutional sites (Ga sites for Mg). We demonstrate how the formation of inverted domain defects at temperatures below 1400 °C correlate with Mg-compound formation, whereas annealing temperatures 1400 °C and above do not lead to the formation of such compounds but rather high Mg activation efficiencies.

These recent developments, partly through the ARPA-E PNDIODES program as well as international efforts, have brought understanding of the key processing steps and substrate requirements to achieve high activation efficiency p-type doping for planar, vertical device structures in a scalable framework.
(Invited, Digital Presentation) Thermal Conductance across Heterogeneously Integrated Interfaces for Thermal Management of Wide and Ultra-Wide Bandgap Electronics
Authors: Cheng Zhe
Published: July 2022

Thermal management is important for wide and ultra-wide bandgap power electronics because overheating degrades device reliability and performance. High thermal conductivity substrates such as SiC and diamond facilitate heat dissipation of these devices while the thermal boundary resistance between devices and substrates accounts for a large portion of the total thermal resistance, which prevents devices from taking the full advantage of the high thermal conductivity of the substrates. Recently, heterogeneously integrated wide and ultra-wide bandgap semiconductor interfaces are found to have low thermal boundary resistances, which provides a new degree of freedom to design and fabricate thermally conductive interfaces for thermal management of related power devices. For example, GaN can be bonded with single crystal SiC or single crystal diamond directly at room temperature. β-Ga2O3 can be bonded with SiC with or without Al2O3 interfacial layers. Compared with growth, the bonded interfaces are not limited by lattice mismatch. Moreover, the room-temperature bonding process discussed in this talk can possibly eliminate the effects of thermal stress existed in high temperature growth or bonding techniques. Recent progresses in this sub-area will be discussed in this talk, especially thermal conductance across surface-activated bonded GaN and β-Ga2O3 interfaces measured by time-domain thermoreflectance (TDTR) and the effects of thermal boundary resistance values on device temperatures. Finally, the potential challenges will also be pointed out, for instance, high-throughput thermal measurements of buried interfaces, thermal property-structure relations of interfaces bonded under different conditions, theoretical understanding of interfacial thermal transport, and device demonstrations.
(Invited) Materials Integration, Durability, and Perspectives in Anion Exchange Membrane-Based Low Temperature Electrolysis
Authors: Alia Shaun M , Intikhab Saad , Ha Mai-Anh , Ghoshal Shraboni
Published: July 2022

As an energy carrier, hydrogen has unique advantages due to its high energy density, ability for long-term storage, and the ability to convert between chemical bonds and electricity. [1] Although hydrogen currently has a small role in energy pathways, decreasing electricity prices can allow for a significant growth opportunity. Compared to alkaline electrolysis, anion exchange membrane (AEM) systems utilize zero-gap membrane electrode assemblies that improve performance and potentially enable hydrogen compression with back pressure. Compared to proton exchange membrane (PEM) systems, the high pH of AEMs allows for non-platinum group metal (non-PGM) catalysts and component coatings (transport layers, separators) that can reduce system cost and improve long-term durability.

This presentation includes on an overview of NREL efforts in AEM electrolysis, and focuses on operation choices, materials integration, and catalysis. In recent years, membrane advancements have enabled higher AEM performance, particularly in supporting electrolytes. [2] Testing has included supported and unsupported (water) feeds, and operational strategies largely depend on the intended market. Efforts have been made to investigate the role supporting electrolytes play in improving AEM performance and assess the viability of AEM as a PEM replacement through water-only feeds and dry-cathode operation. [3,4]

Materials integration focuses on strategies for incorporating catalysts and ionomers that have improved water performance and allowed for short-term durability testing. [3] These efforts include coating approaches and processing conditions to rearrange catalyst layers, and detail the complications of developing protocol recommendations with component changes. In catalysis, fundamental studies have improved an understanding of materials requirements in the oxygen and hydrogen evolution reactions, and the impact of ionomer interactions on reactivity. Ab-initio simulations have provided feedback into low- and non-PGM catalyst development studies that improve device-level kinetics. Perspectives in AEM electrolysis will be discussed, and include ongoing needs for component development and durability testing, to separate and accelerate relevant degradation mechanisms.

References

[1] B. Pivovar, N. Rustagi, S. Satyapal, The Electrochemical Society Interface
2018, 27, 47.

[2] G. Bender, H. Dinh, HydroGEN: Low-Temperature Electrolysis (LTE) and LTE/Hybrid Supernode, https://www.hydrogen.energy.gov/pdfs/review20/p148a_bender_2020_o.pdf
2020.

[3] S. M. Alia, HydroGEN: Low Temperature Electrolysis, https://www.hydrogen.energy.gov/pdfs/review21/p148a_alia_2021_p.pdf
2021.

[4] S. Ghoshal, B. S. Pivovar, S. M. Alia, J. Power Sources
2021, 488, 229433.
Chromium-Rich Core-Shell Cr
x
Ir1-X
O2 Nanotubes for Highly Efficient Oxygen Evolution Reaction in Alkaline Solution
Authors: Jin Dasol , Kang Jisoo , Lee Youngmi , Kim Myung Hwa , Jin Dasol
Published: July 2022

Considering the growing attention to oxygen evolution reaction (OER) as a key role in clean energy through electrocatalytic water splitting, advanced materials for water oxidation are central to the area of renewable energy. In general, the OER process, involved four electron and four proton coupled electrochemical reaction, demands higher kinetics to overcome an overpotential than HER (hydrogen evolution reaction). For this aspect, significant research efforts have been devoted to developing efficient OER electrocatalyst with enhanced electrocatalytic kinetics and long-term durability.

Here we present the synthetic processes and physical/electrochemical characterization of Cr
x
Ir1-x
O2 nanotubes (NTs). Those NTs are synthesized through electrospinning, a simple way to facilitate 1D nanostructure, and post-thermal annealing process with different annealing speed (°C /min). As-prepared Cr
x
Ir1-x
O2 NTs at the optimized conditions have shown outstanding OER electrocatalytic activity in alkaline media from the viewpoints of overpotential and Tafel slope as well as durability. The morphology and compositions of Cr
x
Ir1-x
O2 were characterized by a field emission scanning electron microscope (FESEM) equipped with an energy dispersive X-ray spectrometer (EDS), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The crystalline structures of the prepared Cr
x
Ir1-x
O2 are investigated through high-resolution X-ray diffraction (XRD). Electrochemical activities for oxygen evolution reaction (OER) are studied with rotating disk electrode (RDE) voltammetry in N2-saturated 1.0 M KOH (aq); and compared with those of iridium single component oxides (IrOx and IrO2) and commercial iridium (cIr, counterparts in OER electrocatalysts).

This work was financially supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT or by the Ministry of Education (NRF-2019R1F1A1059969, NRF-2018R1A6A1A03025340, NRF-2020R1A2B5B01001984, and NRF-2019R1F1A1062799).
Surface Reconstruction of Iridium Nanoparticles for Enhanced Oxygen Evolution Reaction in Alkaline Medium
Authors: Kim Myeong-Geun , Yoo Sung Jong
Published: July 2022

An electrochemical water splitting is a promising technology that can generate green hydrogen using renewable energy sources. However, the sluggish oxygen evolution reaction (OER) in an anodic side hinders their large scale applications. Many efforts have been focused on developing efficient electrocatalysts; iridium-based catalysts have gained much attentions due to remarkable intrinsic activities and high stability. Technically, however, the properties are derived from amorphous iridium oxide (IrOx) rather than metallic Ir. During an electrochemical activation process, the Ir metal is easily converted into oxidized species with multiple oxidation states of iridium, which are highly active toward OER. Similarly, many catalysts undergo changes during OER process (e.g., oxidation of precatalysts), resulting in enhancement of activities for OER beyond corresponding original catalysts. Accordingly, the reconstruction process involving surface oxidation and leaching of metal cations should be investigated to develop efficient OER electrocatalysts.

Herein, we prepared chalcogen atom modified Ir/IrOx core/shell nanoparticles for enhanced alkaline OER performances (electrolyte: 1M KOH). The S-modified Ir/IrOx exhibited remarkable OER performances with current density of 10 mA cm−2 at overpotentials as low as 180 mV. Incorporation of chalcogen atoms induce surface reconstruction of the Ir/IrOx nanoparticles during OER measurements. It was observed that electrocatalytic activities of Ir/IrOx were varied depending on the type and concentration of chalcogen atoms. There were no observable morphological and structural changes in Ir/IrOx electrocatalyst, whereas the atomic ratio of chalcogen atoms noticeably decreased after OER tests. The result suggests that incorporated chalcogen atoms play a role in modifying the surface of Ir nanoparticles, rather than participating OER as active sites. In addition, XPS measurements were conducted in order to detect changes in chemical states of the catalysts during electrochemical process. We thus believe that the chalcogen atom induced surface reconstruction can be the strategy to efficiently improve the various electrochemical reactions.
Hydrogen Evolution Reaction Electrodes Using Highly Dispersed Ionomer Solutions for Proton Exchange Membrane Water Electrolysis
Authors: Park Jong Hyeok , Kim Beom-Seok , Park Jin Soo
Published: July 2022

Green hydrogen production is importance in the upcoming hydrogen economy era. Proton exchange membrane (PEM) water electrolysis is one of the most important technology to produce the green hydrogen that requires only water and extra electricity supplied from renewable energy. Large amount of hydrogen production and low production cost is most important for hydrogen economy and we need to find out how to decrease hydrogen production cost, which can be come true with high performance and high durability of the component of PEM water electrolysis. The hydrogen production rate is affected by performance of the HER electrode and production cost is affected by material cost and durability of electrode in the PEM water electrolysis. HER electrode is composed of an electrocatalyst (Pt/C) and proton conducting ionomer (PFSI), among them, proton conducting ionomer directly affects to the performance and durability of the electrode. So, designing of the electrode structures through ionomers is essential. In this study, for reduction of hydrogen production cost, highly dispersed ionomers were developed. Effect of dispersing solvents for ionomer on the performance and durability of catalyst layers was investigated. Developed ionomer dispersion shows higher performance and durability in the PEM water electrolysis, which result was made by the electrochemical characterization such as I-V polarization, voltage increasing rate during durability test, and so on as well as the microscopic characterization such as SEM and TEM were carried out to evaluate the effect of ionomer dispersions on the performance and durability of HER electrode in PEM water electrolysis.

Acknowledgments

This research was supported in part by the Hydrogen Energy Innovation Technology Development Program of the National Research Foundation (NRF) funded by the Ministry of Science, ICT ＆ Future Planning (NRF-2019M3E6A1063677) and by 2021 Green Convergence Professional Manpower Training Program of the Korea Environmental Industry and Technology Institute funded by the Ministry of Environment.
(Digital Presentation) Tuning Oxygen Reduction on Monoclinic and Tetragonal Zirconia Surfaces Using Oxygen Vacancy and Nitrogen Doping: A Density-Functional Study
Authors: Muhammady Shibghatullah , Haruyama Jun , Kasamatsu Shusuke , Sugino Osamu
Published: July 2022

The proton exchange membrane fuel cell (PEMFC) shows the interesting properties,1 where oxygen reduction reaction (ORR) is rate-determining.2 For the PEMFC, Pt-based materials are effective to be its ORR catalyst but their expensive cost and the limited availability are unavoidable,3 motivating to searching non-Pt materials. Zirconia (ZrO2) becomes a considerable candidate for the ORR catalyst since it has a higher chemical stability than that of Pt in an acidic environment,4 where tetragonal ZrO2 (t-ZrO2) (101) and monoclinic ZrO2 (m-ZrO2) (-111) surfaces have been observed to be the most stable.5

In this study, oxygen reduction reaction (ORR) on m-ZrO2 (-111), (-101), (110) and t-ZrO2 (101) surfaces is investigated using the density-functional theory. Each surface is divided into two regimes, that are pristine and defective surfaces, containing defects as two nitrogen impurities and an oxygen vacancy (2NO + VO). Then, the effect of the defects on free energy diagrams and bonding characteristics of an adsorbed oxygen (O*) is investigated. The free energy diagrams correspond to elementary ORR steps involving four intermediates, that are O2*, O2H*, O*, and OH*.

As the results, the free energy diagrams show that the first electron transfer, corresponding to the formation of O2H*, is rate-determining on the pristine surfaces. It is modified to the third and fourth electron transfers, corresponding to the formation and removal of OH*, on the defective t-ZrO2 and m-ZrO2 surfaces, respectively. Furthermore, the defects provide a significant effect on the bonding of O*, leading to a slight improvement of ORR catalytic activity on t-ZrO2 but an apparent decrease on m-ZrO2 surfaces. Moreover, due to the defects, adsorption free energies for the defective m-ZrO2 surfaces, ΔG
O, ΔG
OH, and ΔG
OOH, are moving away from the universal scaling curve and the ideal catalyst point. On the other hand, for the defective t-ZrO2 surface, ΔG
O, ΔG
OH, and ΔG
OOH are off the universal scaling curve, heading to the ideal catalyst point. Our result presents the significant effect of the defects, providing a new insight into the oxide-based catalysts.

References

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Electrochemical Investigations of Ionic Transport through Synthetic Nanopore Membranes
Authors: Volta Thomas T. , Bush Stevie N , Martin Charles R
Published: July 2022

Multiporous membrane systems have created a way for scientists to efficiently separate unwanted contaminates from wastewater and drinking water. In ion-exchange membranes the selectivity is typically governed by the surface charge. The ability for a membrane to reject ions of the same sign while simultaneously transporting ions of opposite sign is called permselectivity. In this work, 30 nm polycarbonate membranes are gold-plated using a well-known template synthesis method. The gold-plating time can be precisely controlled to give nanopores as small as 1 nm. By exposing this membrane to a chloride containing salt, a layer of adsorbed chloride will form along the pore walls and membrane faces. The adsorbed chloride gives this membrane a net negative surface charge which will reject anions and transport cations. Using a varying concentration cell, the permselectivity of these membranes can be obtained potentiometrically. The membrane is exposed to various chloride salt solutions to determine how the chemical identity of the cation affects permselectivity. The diameter of these nanopores is also changed to probe how the pore radius affects the permselectivity of these cations. These membranes show ideal cation permselectivity so long as the pore radius is smaller than the thickness of the electrical double layer. Membranes investigated in this work have effective diameters smaller than 10 nm.