bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Regimes of Reaction-Diffusion Processes Nearby the Plasma-Liquid Interface
Authors: Uner Necip Berker 
Published: September 2023

Plasma-liquid systems are usually comprised of an atmospheric-pressure plasma electrode and a liquid surface, which can have a bubbly and irregular, or a smooth surface. When coupled with a metal counter electrode immersed in the liquid, this configuration has been shown to form capable electrochemical systems that can degrade recalcitrant pollutants, conduct organic chemistry and when reactive gases are used, can create unique gas-liquid reaction pathways for important processes such as N2 fixation and CO2 utilization. Up to date, many different types of plasmas with different frequencies, plasma electrode shapes, gas flow rates and applied powers have been utilized in literature. One common aspect of most plasma sources in plasma-liquid systems is that the current density at the interface is much higher than in conventional electrochemical systems. Consequently, the observed rate constants of some of the plasma-assisted processes mentioned above have been found to fall in a rather narrow range of values, despite the vast differences in plasma sources. This is an indication of mass transport playing a crucial role in the observed kinetics. This argument is supported by experimental results obtained through changing current in continuous plasmas and changing frequency in pulsed plasmas.
When mass transport rate is of the same order with reaction rate or slower, the observed picture for kinetics requires a mathematical description of the interplay of reaction and diffusion to elucidate intrinsic kinetic data. A phenomenological, yet practical and predictive modeling framework has not yet been established for plasma-liquid systems. Despite new kinetics that arise from the unique species produced at the plasma liquid interface, gas-liquid contacting is a well-established field in chemical engineering. In this talk, early chemical engineering studies on gas-liquid contacting will be summarized and the reaction-diffusion models developed through these studies will be applied to plasma-electrochemical systems. According to the theory, multiple regimes of reaction-diffusion processes must exist, and some of these regimes can be reduced to simpler analytical models that allow compact expressions for the observed rate constant and faradaic efficiency. Examples on applying the modeling framework to published experimental data will be given and the criteria that determine the validity of the model equations will be discussed.
Anodic Behaviour of NixFeyCu5 and NixFeyCu20 in Potassium-Rich Naf-KF-AlF3-Al2O3 Melts
Authors: Padamata Sai Krishna , Singh Kamaljeet , Haarberg Geir Martin , Saevarsdottir Gudrun 
Published: September 2023

Using inert anode technology to produce aluminium would substantially reduce the aluminium industry's carbon footprint. Replacing the Hall-Héroult process with an alternative process based on vertical electrode cell (VEC) design using inert anodes and wettable cathodes is a promising alternative, but must be developed to be economically viable at scale. Three material types have been explored as inert anodes: metals, cermets and ceramics. Metallic anodes have been widely studied for their attractive properties, such as superior mechanical strength, high electrical conductivity and ease of fabrication. Of metallic anodes, Cu-Al, Ni-Fe and Ni-Fe-Cu-based alloys are the most commonly examined alloy systems for anode applications. It is also necessary to use low-temperature melts during the electrolysis process to ensure that the anodes are not damaged. In NaF-KF-AlF3 melts, increasing the KF content in the mixture would reduce the liquidus temperature and increase the alumina solubility in the melt.
In this work, we examine the anodic behaviour of NixFeyCu5 and NixFeyCu20 electrodes, without prior surface treatment, in potassium-rich NaF-KF-AlF3 melts at 770°C. The cryolite ratio (xNaF+xKF/xAlF3) and potassium ratio (xKF/xKF+xNaF) of the melt used for the studies are 1.3 and 0.7, respectively. Electrochemical techniques such as chronopotentiometry, chronoamperometry and linear sweep voltammetry were performed to examine the anodic behaviour of these metallic anodes under an N2 atmosphere.
Figure 1 shows the steady-state anodic polarisation curves on NixFeyCu5 and NixFeyCu20 anodes before and after galvanostatic polarisation with an applied current density of 0.5 Acm-2 for 120 minutes. It can be noted that the anodic potential at the same current density is more for the polarised anode compared to the non-polarised in both cases. This is due to the formation of a stable oxide layer during the galvanostatic polarisation of the anode. Oxidation of the anode is expected instead of fluoridation when the melt is saturated with alumina. The stabilisation of anodic current can be seen between 1.9 and 2.4 V. This stabilisation corresponds to the passivation of anodes due to the oxide layer formation. A rapid increase in the current after 2.4 V is due to the oxygen evolution reaction. The anodic current density in the passive region is much lower in anodes with Cu 20%, meaning a more protective layer is formed. After the galvanostatic polarisation of the anode, anodes were examined using scanning electron microscopy to understand the oxide layer composition. Anodes performed stably in potassium-rich melts, and Cu content plays a vital role in the anode's performance.

Figure 1. Stationary state polarisation curves of NixFeyCu5 and NixFeyCu20 anodes before and after the polarisation at 0.5 A cm-2

Figure 1
Bubble Behavior and Anode Effect on Different Carbon Anode Designs in Cryolite Melt Applying a See-through Furnace
Authors: Stanic Nikolina , Martinez Ana Maria , Einarsrud Kristian Etienne , Sandnes Espen 
Published: September 2023

Anodic CO2 gas evolution is one of the main processes in the Hall-Héroult electrolysis cell for primary aluminium production. This work is a laboratory scale study of the effect of anode geometry, anode orientation and carbon anode material on bubble behavior and bubble properties in cryolite melt. Increased knowledge of the bubble behavior is important for improved design of industrial cells, but also for laboratory‐scale experiments. The anodes studied in this work are frequently applied for investigation of reaction kinetics and mass transport, anode effect, current efficiency, anode quality properties, etc. It is therefore of interest to study the bubble dynamics of these anodes in more detail because bubble evolution is relevant for all the above-mentioned phenomena.
The anode potential has been shown to be highly dependent on anode geometry and orientation. For this study four different anode designs were made: horizontal (downward-facing), inverted horizontal (upward-facing), vertical, rod (with both vertical and horizontal surface). For most of the designs, characteristics such as bubble noise, bubble size, and wetting were obtained as a function of current density or anode potential/cell voltage. The bubble noise normally went through a maximum, while the bubble size decreased in the whole current density range. The wetting contact angle showed little variation with current density. It was assumed that the current density had a stronger effect on the contact angle through its effect on the bubble size than the polarization and associated surface roughening.
Also, phenomena like nucleation, growth, coalescence, bubble detachment and anode effect were studied for both graphite and industrial carbon as anode material. The nucleation was more pronounced at the industrial carbon due to more active sites confirmed by CT analysis. The coalescence process was found to be independent of current density/potential and carbon anode material and was in the range 16-24 msec. On increased currents anode effect occurred on both anodes, the current being lower for the graphite anode at onset. Video recordings and electrochemical measurements showed more abrupt initiation of the anode effect on the graphite and a strong de-wetting of the anode. With the existence of a (C – F) surface compound on the anode, as long as the anode effect gas could escape the electrode surface, the anode seems to be electrochemically active towards both CO/CO2 and PFC formation during anode effect.
In addition to the bubble characteristics and phenomena described, the impact of the results for better anode design for laboratory scale studies is discussed.
Understanding the Crystal Chemistry of Phosphate Cathode Materials
Authors: Murgu Roxana Nicoleta , Gover Richard K. B. , Payne Julia Louise 
Published: September 2023

Thermal batteries are primary reserve batteries that can achieve high power output in a short period of time by melting an insulating salt electrolyte with a pyrotechnic heat source and converting it into a highly conductive eutectic salt electrolyte. The thermal battery exhibits no self-discharge before activation, and the initial capacity of the thermal battery is maintained after long-term storage. Thermal batteries are an attractive option for emergency power supplies in aircraft, ejector seats, space landings and helicopters due to their outstanding robustness, high reliability, and long-term storage properties.
FeS2 or CoS2 are the most common cathode materials for thermal batteries.1 However, their high cost and relatively low discharge voltage makes it desirable to find new materials that have higher voltage discharges, higher specific capacities, low cost and that are environmentally friendly. Polyanion cathode materials have attracted much attention in the field of both Li-ion and Na-ion batteries,2–4 as they can be regarded as low-cost materials and environmentally friendly. However, to the best of our knowledge, there have been no studies on polyanion cathode materials for thermal batteries. These materials are formed by tetrahedral units (XO4)n- (X = P, S, Si or B) bonded to MO6 polyhedra (M = transition metal). The tetrahedral anion presents a very strong covalent bond between X-O, giving rise to higher voltages versus Li+/Li or Na+/Na via the inductive effect and their very stable framework and open structure facilitates ion diffusion. Thus, polyanion materials present high structural stability and enable the tuning of the operating potential, making them an excellent choice for developing new cathode materials for thermal batteries. Here we report some of our latest work on the synthesis, structure and electrochemistry of polyanionic cathode materials for thermal batteries.

1 R. Li, W. Guo and Y. Qian, Front. Chem., 2022, in press, doi: 10.3389/fchem.2022.832972

2 Z. Gong and Y. Yang, Energy Environ. Sci., 2011, 4, 3223–3242.

3 C. Masquelier and L. Croguennec, Chem. Rev., 2013, 113, 6552–6591.

4 Q. Ni, Y. Bai, F. Wu and C. Wu, Adv. Sci., 2017, 4, 1600275.
(Invited) Aerosol Jet and Laser Assisted Electrochemical Deposition for Advanced Metallization
Authors: Gibertini Eugenio , Bernasconi Roberto , Magagnin Luca 
Published: September 2023

The inkjet printing technology for conductive patterns is commonly conducted with inks that are made of metal nanoparticles or based on metal-organic decomposition. An additional step of sintering, which is usually done in oven or on a hot plate, is required after inkjet printing to obtain metallic patterns with desired electrical conductivity [1]. Laser-induced selective metal deposition on metallic and non-metallic substrates has been the subject of much attention recently. An induced deposition rate several orders of magnitude greater than conventional rates is claimed to occur at points where a laser beam impinges the electrode surface [2].
In this work, electrolytic and electroless deposition processes are combined with aerosol jet technology and laser assisted setups to induce local metallization on metallic and non-metallic substrates. Single metals and alloys deposition will be discussed according to compatibility with the substrates, selectivity and achievable feature size. Examples of microfabrication and selective decorative applications will be provided, together with an evaluation of the properties of the produced deposits.

J-J. Chen, Fabrication of conductive copper patterns using reactive inkjet printing followed by two-step electroless plating, Applied Surface Science 396 (2017) 202–207.

R. Khan, Laser-Induced Selective Deposition on Metal Using Electroless Gold, NASF SURFACE TECHNOLOGY WHITE PAPERS 84 (2019) 6-13.
Electrohydrodynamic Redox Printing: A Swiss Army Knife of Metals Microfabrication?
Authors: Nydegger Mirco , Porenta Nikolaus , Reiser Alain , Spolenak Ralph 
Published: September 2023

The dissolution and deposition of metals in solvents is widely known and used in a large range of applications, from electroplating to electro-machining. More recently, it has also been used for additive manufacturing (AM) at the sub-micron scale, since electroplated metals offer as-deposited high-quality metals (in terms of porosity and contamination) compared to other small scale AM techniques [1,2]. These intricate, high-quality metal structures have a range of applications in microelectromechanical systems, photonics or micro-robotics. However, the nature of the deposition process requires a conductive substrate to provide the electrons necessary for the localized reduction of metal ions. This requirement renders the direct fabrication of microelectronic devices using electrochemical small scale AM a challenge, as often deposition on electrically insulating substrates is required.
Here, we present our work on electrohydrodynamic redox printing (EHD-RP), an electrochemical small scale AM technique, and our efforts towards deposition on various substrates. We’ll first introduce EHD-RP with a focus on our recent work on the deposition from aqueous metal salt solutions onto conductive substrates. We’ll then discuss strategies to expand the concept of EHD-RP towards deposition on non-conductive substrates and how electrically floating structures can be fabricated. These strategies render EHD-RP a versatile technique for metals microfabrication.
[1] M. Nydegger, A. Pruška, H. Galinski, R. Zenobi, A. Reiser and R. Spolenak. Additive Manufacturing of Zn with Submicron Resolution and its Conversion into Zn/ZnO core-shell structures. Nanoscale, 2022
[2] L. Hirt, A. Reiser, R. Spolenak and T. Zambelli. Additive Manufacturing of Metal Structures at the Micrometer Scale. Adv. Mater., 29(17), 2017
Electroplating on Unconventional Ultra-Compliant Substrates for Travelling Wave Tube Amplifiers
Authors: Chaudhary Anjali , Prakash Divya J. , Jacobson R B , A Scott Shelley , E Savage Donald , van der Weide Daniel , Lagally Max , Cavallo Francesca 
Published: September 2023

We report gold electroplating on ultra-compliant substrates comprising helical slow wave structures (SWSs) for traveling wave tube amplifiers (TWTAs) [1]. The novel ultra-compliant substrates are composed of edge-tethered tri-layer metal ribbons with a helical geometry of microscale diameter. After electroplating with gold, we obtain overall thicknesses of a few um. We discuss different controllable electroplating conditions that influence thickness, uniformity, roughness, and related properties of deposited gold films on helical ribbons. In addition to increasing conductance of the electroplated helical ribbons, electroplating stabilizes the helix at its equilibrium diameter, with the pitch predicted by Prakash et al.[1].
Our method of fabrication of ultra-compliant helical ribbons starts with defining strips of width 5 µm to 10 µm by optical lithography, metal evaporation, and lift-off, deposited on Si substrates coated with a sacrificial layer of Ge or GeOx,. We use Cr/Au/Cr tri-layers to create an inherent stress gradient that causes the strip to self-assemble into a helix, after etching with XeF2 for selective removal of a sacrificial layer. Diameter and pitch of the released helices are controlled by varying the thickness, the elastic modulus, the residual stress, and the in-plane geometry of the deposited tri-layer metal strips. The gold electroplating process uses a sulphate-based gold solution in a two-electrode electrochemical setup with the helix as the cathode and a platinized mesh as the anode [2]. We deposit gold to a thickness of a few um, using a pulsed current source with variable parameters. Direct current can also be used with smaller deposition times. Our results demonstrate the application of electroplating to unconventional ultra-compliant helix of nanoscale dimensions.

Reference

[1] Divya J. Prakash,., Matthew M. Dwyer, Marcos Martinez Argudo, Mengistie L. Debasu, Hassan Dibaji, Max G. Lagally, Daniel W. van der Weide, and Francesca Cavallo. 2020. “Self-Winding Helices as Slow-Wave Structures for Sub-Millimeter Traveling-Wave Tubes.” ACS Nano, 2021, 15, 1229-1239. doi:10.1021/acsnano.0c08296.
[2] Max G. Lagally, Anjali Chaudhary, Daniel van der Weide, Divya J. Prakash, and Francesca Cavallo, Improved Self-assembly of Helices via Electrodeposition on Freestanding Nanoribbons for TWT Application, provisional US patent application (P220249US01)
Work supported by U.S. AFOSR-Award No FA9550-22-1-0086.
Electrodeposition of Ag-Ni and Pd-Ni Thin Films on Ni-P from a DMSO Solution
Authors: Eyraud Marielle , Bahramian Ahmad , Vacandio Florence , Knauth Philippe 
Published: September 2023

The most used electrical contact system in electronics and microelectronics is Cu/Ni(Ni-P)/Au, which offers an interesting combination of high electrical conductivity, corrosion resistance, and wear resistance. However, the top Au thin layer being porous, a galvanic coupling between NiP and Au, and then Cu and Au appears that renders the system unusable. Au being highly expensive, the development of more inexpensive and reliable plating materials such as Ag or Pd can be experimented. Ag is widely considered as an economical alternative to Au. Ag and Au top-coats are traditionally obtained from highly toxic cyanide baths. Therefore, recent studies focused on developing non-cyanide electrolytes, Dimethyl sulfoxide (DMSO) being a promising solution for noble metal deposition.
Hard noble coatings, i.e. alloying the noble metal with Ni, Fe, or Co, have a lower content of the noble metal and offer a higher hardness and thus a superior wear resistance. The electrodeposition of Ag-Ni and Pd-Ni layers on Ni-P from a non-cyanide DMSO based electrolyte was investigated, which was especially challenging for Ag deposits given the fact that Ag and Ni are totally immiscible in all the states. The chemical composition and morphology of these systems were highly affected by the applied potential. Therefore, the pulse deposition was used to form films on Ni-P coatings, i.e. a high cathodic potential (-1 V vs. Ag/AgCl) for the preferential deposition of Ni, and a lower value for the preferential deposition of the noble metal (here Ag or Pd). The obtained coatings showed a good adhesion to Ni-P. The Ag-Ni top-coats showed a nanocrystalline structure and presented a higher concentration in noble metal than Pd-Ni. This result was attributed to the formation of stronger DMSO complexes with Pd than with Ag.
Optical Characterisation of Plasmonic Indium Lattices Fabricated Via Electrochemical Deposition
Authors: Valenti Marco , Wobben Merlinde D , Bleiji Yorick , Cordaro Andrea , Tabernig Stefan Wil , Aarts Mark , Buijs Robin D. , Rodriguez Said Rahimzadeh-Kalaleh , Polman Albert , Alarcón Lladó Esther 
Published: September 2023

Indium is an emerging plasmonic material that offers to extend the plasmonic applications given by gold and silver from the visible to the ultraviolet spectral range, with applications in imaging, sensing, and lasing. However, due to the high-vapor pressure/low melting temperature of indium, nanofabrication of pre-defined metallic indium nanostructures is non-trivial.
In this work, we show the potential of selective area electrochemical deposition for the manufacturing of large-area arrays of indium pillars, which can be used for plasmonic applications. We combine electrochemical deposition with substrate-conformal imprint lithography to realize these large-scale indium nanoparticle arrays, having well-defined dimensions. This template growth results into well-defined hexagonal array of pillars with a mean height of 235 nm having a standard deviation of 60 nm.
To highlight the potential of this electrochemical-based technique for plasmonic applications, we have performed angle-dependent extinction measurements using s-polarized light and using a RI matching oil. We found that these indium nanopillar arrays exhibit a strong plasmonic response due to the coupling to the plasmonic surface lattice resonances (SLRs). Furthermore, we have simulated the optical response of this indium nanopillar array using finite difference time domain (FDTD) simulations. In these simulations, we included the morphology obtained from SEM and the electrical permittivity of elemental indium. We found that the simulated extinction spectra agree well with the experimentally obtained spectra at 0˚ and 8˚ incidence, despite the polydispersity of the indium pillar height and defects in the hexagonal array.
Our results therefore demonstrate the possibility of realizing large-area fabrication of indium plasmonic nanoparticles, which can be used for plasmonic applications. Given the low-cost and scalable nature of this technique, this work opens new possibilities in the design and fabrication of large-area plasmonic metasurfaces that operate in the UV spectral range. Future extensions of this work may leverage the indium mask-constrained growth to tailor even further the shape of the nanoparticle and hence give a powerful tuning knob to tailor plasmonic resonances.