Stress distribution maps in polycrystalline materials are needed to reveal stress pathways caused by short-and long-range interactions of crystallites. Stress induced changes to wavenumbers in Raman spectroscopy is a well-known phenomenon that occurs when a crystalline material undergoes elastic strain. Using spatially resolved Raman spectroscopy, we have developed a technique to experimentally measure grain-scale residual stresses across a sample of polycrystal quartz Tiger's Eye. The results of this technique are validated using multiple criteria, including evaluation of the residual stress map itself and the accuracy of the measurements taken. The residual map of Tiger's Eye shows striking similarity to observed characteristics of other polycrystalline residual stress distributions, revealing heterogenous areas of high and low magnitude stresses. The stress magnitudes are consistent with residual stress magnitudes previously measured from polycrystalline quartz. Characterization of Tiger's Eye quartz also revealed the geometric nature of the iron oxide inclusions, not previously observed in Tiger's Eye quartz. With this technique, we present a residual stress map of Tiger's Eye quartz that shows with accuracy a heterogeneous stress state with inter- and intra-granular detail.

Electrodeposition has been used for centuries as a relatively simple, robust, and cost-effective method for applying functional and aesthetic coatings to materials. Fundamental, time-dependent microstructural control remains elusive because systematic relationships between process parameters and resulting coating performance are lacking, due to scattered empirical studies and post-mortem correlations. Here, we aim to use modern techniques in-situ, such as x-ray phase contrast imaging (XPCI) and small angle x-ray scattering (SAXS) to control process-structure relationships of electrodeposited coatings. We will provide results from a range of deposition experiments designed to measure nucleation or growth phenomena directly, allowing connection between physical processes to classical nucleation theory. Complementary SEM and SAXS results will be presented as a means of evaluating utility for high resolution imaging at required time and length scales. Cyclic voltammetry and chronoamperometry will be applied to inferentially approximate relevant nucleation mechanisms. Comparisons to conventional measurements by scanning electron microscopy (SEM) with energy-dispersive x-ray spectroscopy (EDS) are also described. The objective of this work is ultimately to tailor the structure and properties of electrodeposited coatings through real-time parameter variations.

Heterogeneous microstructures in polycrystalline metals can enhance the strength and ductility, outperforming homogeneous structures of similar composition. This study investigates deformed cobalt via friction stir spot processing with varying dwell times to uncover the effects of plastic deformation and heat generation on the formation of morphological, phase, and grain boundary character gradients. A new approach to quantify the morphological gradients in materials, which describes grain morphology in terms of density followed by parametric regression, enables direct quantification of processing depth and gradient sharpness. Results show that longer processing times increase the steepness of morphological gradients and reduce the deformation depth for friction stir spot processing with low plunge depths and high tool rotational speeds. The amount of retained FCC is increased in the shorter processing conditions, primarily due to refined grain size, increased defect content, and reduced heat generation. Crystallographic texture analysis of the HCP phase indicated a dominant B-fiber described by (0001) II shear plane normal in the extreme processing conditions and the formation of a P-fiber, shear direction II (1120) for intermediate dwell times. The texture of the FCC phase for low processing times was a C texture {100}(011) where longer processing times were dominated by a [001] fiber texture with a main {110}(100) orientation and emergence of a slight [111] fiber in the longest processing condition. The approaches outlined in this work give insight into quantifying gradients and improve the understanding of highly deformed cobalt.

Electrochemical polishing of metallic surfaces is a scalable, cost-effective technique to smooth surfaces for functional and/or decorative purposes. In direct current electrochemical polishing increasing electrolyte viscosity is used to mediate current density by controlling diffusion. This approach has significant limitations with the uniquely rough surfaces yielded in additive manufacturing which can lead to an inability to smooth very rough surfaces, lack of shape retention, and inducing corrosion in extreme cases. Pulse electropolishing offers the promise of additional control variables for targeted roughness scales. In this work, we explore the underlying electrochemistry that governs pulse electropolishing. We directly correlate pulse parameters (on/off time and current) with specific scales of asperity dissolution. We demonstrate that designing the electrolyte to be less hazardous and less chemically aggressive shifts the control parameters from electrolyte viscosity to pulse waveform parameters. This shift allows for smoothing surface roughness to typical engineering specifications of ∼ 1 μm, affecting the achievable part dimensions, polishing effectiveness, and corrosion resistance, while enhancing operational safety. The pulse electropolishing effectiveness over very large roughness scales with selective removal of partially melted particles, addressing major challenges related to additively manufactured parts.

A conditionally guided generative latent diffusion process that is trained on a set of experimental processing parameters and their associated resulting electron microscope images of the electrodeposition process is able to interpolate between processing parameters in a physically consistent way. Electrodeposition of rhenium with pulse and pulse-reverse waveforms is used as a model system, and the process is adaptable to other electrodeposition, electropolishing, or corrosion processes. The method is able to extrapolate, predicting estimates of material morphologies for experimental setups unseen in the training data. The results are demonstrated with experimental data.

Cobalt electrodeposition has been studied for various applications ranging from catalysis materials to alloys to low mean-free-path conductors for decreased scale electronic interconnects. Though all of these applications are important from a commercial perspective, it is of general scientific interest in particular because it has been demonstrated that deposition parameters can influence coating shape, morphology, and microstructure; what is unique about cobalt among many more common materials is that the deposition parameters can additionally select between the isomorphic hcp and fcc phases. The ability to select phase is itself of interest to understand, but this feature also allows for an interrelated parameter study that includes phase and microstructure and morphology. Is it possible to select all of these properties at the same time ? If so, it may be possible to create microstructure and phase mixtures and gradients and to achieve unique properties not possible to achieve in other manufacturing methods. Though many studies are available, the breadth of work on cobalt electrodeposition is not nearly as comprehensive as many other more common engineering coatings. There are several possible chemistries to apply with many similarities to widely studied and implemented nickel deposition behavior. These approaches will be discussed. We present a study of cobalt deposition parameters to achieve control of microstructure and phase at the same time. We correlate process variables including electrolyte chemistry, pulse and pulse reverse waveforms, and temperature with the resultant microstructures.

Electrodeposition involves many control parameters. Choices of solvent, electrolytes, complexing agents, adsorbents, temperature, and power settings introduce myriad choices in processing conditions. Though many individual chemical and physical processes that influence choices in these processing conditions are understood at some level, the detailed interdependencies are difficult to unravel. Using experience and wealth of past studies, researchers can hypothesize parameters to use when developing deposition methods for new systems. However, trial and error remain integral to the development process, wherein many parameters are varied, and resulting coatings are characterized. Recent revolutionary advances in pulse and pulse-reverse power and electrolyte developments only add to the complexity; controlled current or voltage, on/off/reverse heights and durations alone add many variables. High throughput methods are being developed to more rapidly screen deposition parameters, in which deposition variables are varied and resulting films are characterized by methods including optical microscopy. In some cases in situ characterization methods have been demonstrated and remain in development, but even so, data is sparse given how much uncertainty there is in the time-dependent processing variables. Deep learning methods of various kinds have demonstrated impressive predictions in several fields in recent years. Examples include (1) real-time control of beamline dynamics, in which input parameters from injectors and magnetic lens controls result in downstream images of beam shape, with limited data on intermediate processes and (2) forward prediction of diffraction or microstructure data, among others. In many ways, these examples are very similar to the electrodeposition problem we have outlined: definitive chemistry and physics processes along with input parameters are known, dependencies and time evolution are not, and outcomes are measured downstream in the form of some characterization of output. Previously, we used high throughput trial and error approaches to optimize parameters for rhenium deposition, and input waveforms can be compared to microscopy characterization of the resulting film. Here, we will describe an approach for deep learning using pulse/pulse-reverse deposition parameters and resulting images for this system. Such approaches may enable much more rapid parameter refinement for electrodeposition of many materials.

The electrodeposition of rhenium (Re) has received renewed attention in the past decade as a scalable approach to apply uniform coatings to enable a wide range of applications in aerospace, nuclear, catalysis and biomedical fields. However, Re has traditionally been difficult to deposit by electrolysis using aqueous solutions due to the overpotential for hydrogen evolution coupled with complex electrochemical reactions. Beginning with the perrhenate ion (ReO4-), reduction to metallic rhenium involves the transfer of 7 electrons and 8 protons. A series of proton-coupled electron transfer reactions occur during electrochemical deposition, resulting in a distribution of Re oxides, oxyhydroxides and metallic metal. The inclusion of these undesirable oxides results in a brittle coating with cracks throughout the morphology. Electrochemical deposition of Re is known to occur using water-in-salt electrolytes, enabling room temperature electrodeposition. However, correlations between the electrodeposition parameters and morphology are still lacking. Further, mechanistic insight into the electrochemical reaction pathways is limited. Herein, we present the application of a custom high-throughput electrochemical platform to systematically study the impact of current and pulse parameters (ton, toff) on the obtained Re morphology. A circumscribed central composite design with 3 factors was employed to define the processing window of interest. Standard image processing techniques were employed to quantify the obtained morphologies in terms of crack width and crack area. This work provides new insight into the mechanistic pathways of metallic rhenium deposition. Specially, the initial broad design space was unable to identify processing conditions that produced a crack free coating. However, with insights from the hexavalent chromium literature, design of a pulse reverse procedure can produce homogenous, crack free films.

Laser powder bed fusion (LPBF) of metal produces extremely rough as-printed surfaces, which can negatively impact material quality and performance including corrosion and mechanical response. Depending on the material and the build angle, the arithmetical mean surface roughness (Sa) can range from 5 – 50 um. These values do not meet the typically required roughness specification (Sa » 0.8 um = 32 uin); in many cases, machining or mechanical grinding is impractical due to the complex surface geometries. Our team has focused on using pulse electropolishing methods that have been shown to reduce the overall surface roughness while maintaining the part geometry. Low hazard electrolytes have been identified for 316L stainless steel (SS) and Ti64. In this talk, we will describe how we optimized the pulse electropolishing parameter and electrolyte for 316L SS and Ti64. To achieve this, we have optimized how each pulse parameter affects the surface finish of the material and then used this information to build an electropolishing recipe that could target the different roughness scales of the material. For both 316L SS and Ti64, we have shown that we can significantly reduce the surface roughness of these materials, as shown in Fig. 1. Furthermore, we have demonstrated that this process can be applied to complex geometries. 3D images of samples before and after electropolishing demonstrate the uniformity of this process. Figure 1

Electrodeposition of metallic rhenium (Re) is optimized for crack-free coatings through the use of a high-throughput cell to develop pulse-reverse waveforms. Pulse waveforms were required for metallic rhenium electrodeposition from water in salt electrolytes. Screening experiments were used to understand how flow rate and the inclusion of citric acid impact the film formation process using a consistent pulse sequence. Flow rate has minimal influence on the observed electrodeposition process, indicating that reaction pathways are more important than diffusion depletion in the chosen electrolyte. The addition of citric acid additionally enabled deposition of metallic Re over the hydrogen evolution reaction. Drawing parallels to crack-free chromium (Cr) plating, it was postulated that a tailored pulse sequence would provide additional improvements in the electrodeposition process. A 3-factor circumscribed central composite design was utilized to investigate the impact of pulse on time, off time, and peak current control the formation of cracks during electrodeposition. Application of a minimum charge is required to form a metallic Re film, independent of the pulse sequence, consistent with an intermediate conversion process during deposition. Finally, application of a pulse reverse sequence produced a crack-free, metallic Re coating.

Rhenium (Re) electrodeposition is a fascinating but challenging system to develop a robust processing procedure that can be implemented at scale. Beginning with the perrhenate anion (ReO 4 - ), reduction from the +7-oxidation state must occur to deposit metallic Re. Traditionally, Re has been difficult to deposit from aqueous solutions due to the over potential for hydrogen evolution so significant efforts have focused on developing alternative electrolytes. A water-in-salt electrolyte using 5M lithium chloride (LiCl) emerged as a cost-effective, viable option. Successful electrodeposition of metallic Re was only observed with the inclusion of citric acid to locally control the pH at the cathodic interface. Electrolyte engineering is only one aspect of the electrodeposition process that needs to be optimized. Early studies indicated that thick coatings (>10 µm) could not be obtained via DC electroplating. Optimization greatly expands the design space to include cathodic peak current (I c, peak ), cathodic on-time (t c, on ), anodic peak current (I a, peak ), anodic on-time (t a, on ), and off-time (t c, off ). A high-throughput electrodeposition platform was designed, and parameters were systematically investigated using a 3-factor, circumscribed central composite (CCC) design with α = ± 1.68. Crack free deposits were only observed when both a cathodic and anodic pulse were included. However, small scale experiments masked the impact of chlorine evolution on the stability of the electrolyte. In the 5 M LiCl electrolyte chlorine evolution is both kinetically and thermodynamically more favorable than oxygen evolution, limiting the lifespan of the electrolyte. A divided cell with a Nafion membrane can effectively mitigate this issue but the anolyte must be appropriately selected to balance pH and ionic strength to limit unwanted ion diffusion across the membrane. Finally, substrate selection and preparation must also be considered to enable scalable electrodeposition. Iron group metals are known to induce co-deposition of Re, presenting an obvious selection of surface material to deposit on. However, trials using aluminum treated with a zincate and thin electroless nickel layer resulted in selective deposition of Re with substantial pitting and dissolution of the aluminum. Our results indicate that the iron-group metal surface must be optimized to enable scalable electrodeposition of Re. Overall, this work presents broad considerations for the scale-up of difficult-to-electroplate metals that are often overlooked when designing new electrodeposition processes.

The objective of this study is to tailor the structure and properties of electrodeposited coatings through real-time parameter variations. Electrodeposition has been used for centuries to apply both functional and aesthetic coatings to a range of materials. This process is, in general, relatively simple, robust, and cost-effective for depositing films of one material onto another. These favorable characteristics though, have resulted in a deficiency in the fundamental understanding of time-dependent microstructural control and key relationships between process parameters and the resulting coating performance. The development of microelectronics and other devices that require increasingly tighter tolerances on coating deposition and performance, pushing the limits of what is currently achievable, has facilitated a resurgence in the advancement of electrodeposition technologies. While it is generally understood how changing parameters (e.g. potential, electrolyte composition, temperature, pH, etc.) affects the developing coating, much of this work has been done through empirical research and post-mortem correlations. Herein, we develop a methodology for tailoring coating structure (size, shape, and texture) to exploit different physical properties (hardness, ductility, electrical conductivity, etc.) of electrodeposited coatings through parameter variation and direct linkage to observable events and physical characteristics in real-time. Modern instruments such as transmission electron microscopy (TEM) and small-angle electron scattering (SAXS) theoretically have the ability to observe these phenomena, with both time and spatial resolution falling in range of physical requirements. However, few studies have developed or demonstrated these techniques for in-situ measurements. In this presentation, preliminary experiments utilizing nickel (Ni) and silver (Ag) salt electrolytes as model systems for the investigation of incipient nucleation and growth behavior of electrodeposited Ni and Ag coatings will be defined, as well as confirmation of SAXS as a complementary technique for characterizing island growth in the first stages of deposition. Electrochemical techniques including cyclic voltammetry and chronoamperometry were applied to study the nucleation mechanisms for these materials. Additionally, potentiostatic electrodeposition was used to deposit the nanoparticle islands. For this study, we artificially promoted instantaneous growth of the coating using an initial “seed” pulse, followed by a subsequent growth pulse. This serves to improve the monodispersity of the islands that are deposited on the substrate surface, simplifying the analysis of the initial SAXS measurements. Utilization of a laboratory-source SAXS and wide-angle x-ray scattering (WAXS) instrument for physical and chemical characterization of island growth allowed us to quickly characterize the deposited particles. A comparison of these measurements to equivalent SEM/EDS imaging of the samples for size, shape, number density, and elemental composition confirmation of the deposited particles will also be described. Additionally, we will briefly discuss the state of the literature and our current plans for transitioning these post-mortem experiments to in-situ measurements, allowing for time resolved data, directly observing nucleation and growth of electrodeposited coatings to be collected.

Ultra-black coatings have served various roles in space instrumentation and hardware. The Ebonol C coating has been used for various missions requiring low reflectivity on aluminum substrates that are electrically conducting. This coating is produced through the formation of a cupric oxide structure on an intermediate layer of copper applied to the aluminum. For many years, this commercial formulation has been used ubiquitously for space instruments. The coating relies upon details of the copper base layer that have been trade secret at various finishing companies, and the availability of the Ebonol C formulated chemistry from the chemical supplier. In recent years, this product has been discontinued at various times, leaving vendors to either rely on expired stock or to formulate their own equivalents. Here, we detail the processing methods, chemistries, and resultant coating structures that produce reflectance performance equivalent to baseline historical reflectance data. This process detail will ensure equivalent performance for such coatings for future missions and link the performance to past and currently deployed instruments.

The upcoming UCNProBe experiment at Los Alamos National Laboratory will measure the beta decay rate of free neutrons with different systematic uncertainties than previous beam-based neutron lifetime experiments. We have tested a new B-10-coated Yttrium Aluminum Perovskite (YAP:Ce) scintillator and present its properties. The advantages of the YAP:Ce scintillator include its high Fermi potential, which reduces the probability for upscattering of ultracold neutrons (UCN), and its short decay time, which increases sensitivity at high counting rates. Birks' coefficient of YAP:Ce was measured to be (5.56(-0.30)(+0.05))x10-4 cm/MeV. The loss of light due to the 120 nm B-10-coating was measured to be about 60%, and the loss of light from YAP:Ce due to transmission through a deuterated polystyrene scintillator was about 50%. The efficiency for neutron capture on the B-10 coating was (86.8 +/- 2.6)%, and a measurement using UCN showed that the YAP:Ce crystal counted 8%-28% more UCN compared to a ZnS:Ag screen. The difference may be due to the uneven coating of B-10 on the rough surface of ZnS:Ag. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial 4.0International (CC BY-NC) license (https://creativecommons.org/licenses/by-nc/4.0/).

Anodized aluminum oxide (AAO) has many beneficial properties leading to its wide use across industries as a surface treatment for many aluminum components, but the wear properties of the coating could be improved significantly. Here, we used an electrochemical method to incorporate molybdenum disulfide (MoS2), a nanomaterial used as a dry lubricant, to modify alloys of aluminum during AAO preparation. Using Raman spectroscopy and tribological scratch measurements, we thoroughly characterized the structure and wear behavior of the films. The MoS2 deposition procedure was optimal on aluminum 5052 anodized in higher acid concentrations, with friction coefficients around 0.05 (~10x better than unmodified AAO). Changing anodization conditions to produce harder films with smaller pores led to worsened wear properties, likely because of lower MoS2 content. Studying a commercial MoS2/AAO film of a different Al alloy (7075) showed that a heat treatment step intended to fully convert all deposited MoSx species to MoS2 can adversely affect wear in some alloys. While Al 6061 and 1100 produced films with worse wear performance compared to Al 5052 or 7075, our results show evidence that acid cleaning after initial anodization likely removes residual alloying elements, affecting MoS2 incorporation. This study demonstrates a nanomaterial modified AAO film with superior wear characteristics to unmodified AAO and relates fabrication procedure, film structure, and practical performance. Methods for production of this enhanced wear coating for several aluminum alloys along with associated wear and scratch performance will be presented.

In high pressure physics applications, a shock wave can be modified by tuning the acoustic impedance of an impactor. The acoustic impedance is influenced by the sound speed of the material and the density. Forming structures that have a gradation in these properties enables a range of experiments to better understand materials under extreme conditions. Polymers are some of the lowest density materials with densities around 1 g/cc. The density of metals extends from ~1 g/cc to ~ 20 g/cc. Thus, being able to create graded polymer / metal structures maximizes the gradation of density. Electropolymerization can be used to deposit polymer films on a surface. Polypyrrole can be synthesized from pyrrole in nitric acid via the electrochemical formation of the oxidizing nitrosyl ion. Metallic electrodeposition occurs via the reduction of metal salts. Therefore, careful control of the applied currents using pulse electrodeposition methods can be used to co-deposit both species. The challenge is in controlling the growth mechanisms. Early observations indicated that polymers could nucleate from existing polymer chains or metallic surfaces. Metallic nucleation could only occur from metal sites, resulting in dendritic metallic structures decorated with polymers. Efforts to control the nucleation and growth dynamics to encourage more layer-by-layer growth are currently on-going. Herein, we will present our findings in controlling the microstructures of electrodeposited polymer / metal composites.

Perfluorosulfonic Acid (PFSA)/Polytetrafluoroethylene (PTFE) copolymer and cation-exchange membranes were used to elongate the use water-in-salt electrolytes for rhenium electrodeposition. Water-in-salt electrolytes are a common technique used to minimize the amount of free water in solution by including high concentrations of salts, thus solvating the water molecules and lowering activity of the solution. This expands the electrochemical window in which deposition is possible and minimizes unnecessary hydrogen evolution reactions (HER) in the electrodeposition system by reducing available protons. Lithium chlorine (LiCl) is a common salt for this purpose due to low costs. However, in the LiCl electrolyte, the necessary oxygen evolution reaction (OER) competes with chlorine evolution, which increases water activity and is visually identifiable with a color change from clear to yellow. When chloride ions are depleted, further deposition is no longer possible, and the electrolyte breaks down. A solution to this issue is using membranes to isolate the anode and cathode, thus preventing the chlorine evolution reaction from occurring. Since rhenium is a system with a small electrochemical window, possible oxide intermediates, and an overpotential for hydrogen evolution, the system requires the use of a stable water-in-salt electrolyte for elongated deposition. In this experiment, three membranes were examined to compare the impact on rhenium depositions in an H-cell. To compare the impact of each membrane, the change of pH of the DI side of the H-cell was monitored across time alongside the volume changes on both sides of the H-cell as a function of time due to LiCl inclusion. The quality and thicknesses of the coatings was examined by SEM as well as the impact on the morphologies of the rhenium of the deposits between each of the membranes.

Impact physics provide equation of state information for material performance in extreme environments. There is some evidence that the underlying microsctructure impacts the response at some velocities1. One way to probe the microstructure is through controlled electrodeposition. Both pulse plating and chemical additives are known to modify the grain structure during electrodeposition. However, additives can be incorporated in the coating and influence the resulting properties such as hardness and mechanical properties. Therefore, we aim to control electroformed coatings through exclusively using square wave pulses. There are some preliminary studies indicating control of grain size of electroplated coatings, however, process control has, so far, only been studied by post characterization analysis on often limited subsets2–5. A methodical approach leads to a deeper mechanistic understanding of isolating plating parameters to control the grain structure. In this work, we explore the impact of current density, duty cycle, frequency and pulse widths/heights and their impacts on the grain structure. We show uniform grain structure through thick films (>3mm), and control over the texture and orientation of grains (Fig. 1). (1) Escobedo, J. P.; Dennis-Koller, D.; Cerreta, E. K.; Patterson, B. M.; Bronkhorst, C. A.; Hansen, B. L.; Tonks, D.; Lebensohn, R. A. Effects of Grain Size and Boundary Structure on the Dynamic Tensile Response of Copper. J. Appl. Phys. 2011, 110 (3), 033513. https://doi.org/10.1063/1.3607294. (2) Marro, J. B.; Darroudi, T.; Okoro, C. A.; Obeng, Y. S.; Richardson, K. C. The Influence of Pulse Plating Frequency and Duty Cycle on the Microstructure and Stress State of Electroplated Copper Films. Thin Solid Films 2017, 621, 91–97. https://doi.org/10.1016/j.tsf.2016.11.047. (3) Chan, K. C.; Qu, N. S.; Zhu, D. Crystallographic Textures and Magnetic Properties of Electroformed Nickel. J. Appl. Electrochem. 1998, 28 (10), 1095–1099. https://doi.org/10.1023/A:1003452615814. (4) Sivasakthi, P.; Sekar, R.; Bapu, G. N. K. R. Pulse Electrodeposited Nickel Using Sulphamate Electrolyte for Hardness and Corrosion Resistance. Mater. Res. Bull. 2015, 70, 832–839. https://doi.org/10.1016/j.materresbull.2015.06.019. (5) El-Sherik, A. M.; Erb, U.; Page, J. Microstructural Evolution in Pulse Plated Nickel Electrodeposits. Surf. Coat. Technol. 1997, 88 (1), 70–78. https://doi.org/10.1016/S0257-8972(96)02928-3. Figure 1

The use of water-in-salt electrolytes has been a transformational advancement in electrochemistry. Water-in-salt electrolytes rely on a super high concentration of salts in aqueous electrolytes to lower the activity of water. The water is occupied in the solvation of the salts, leaving minimal ‘free water’ in the system. In the context of electrodeposition, this results in a widened cathodic window as the limited quantity of protons suppresses the hydrogen evolution reaction (HER). Seldom discussed is the impact on anodic reactions that are also limited by the transport of water for the oxygen evolution reaction (OER). Lithium chloride (LiCl) has been used as a cost effective and readily available support salt in water-in-salt electrolytes. However, in this system OER competes with chlorine evolution. At low pH chlorine evolution is more thermodynamically and kinetically favorable. This reaction depletes the system of chlorine atoms required to solvate excess water and saturates the electrolyte with dissolved chlorine. As a result, the electrolyte has a limited lifetime. One solution to this problem is the use of proton exchange membranes to separate the anode from the cathode. The use of these membranes will be discussed focused on our interest in rhenium (Re) electrodeposition. Rhenium has traditionally been difficult to deposit by electrolysis from aqueous solutions due to the over potential for hydrogen evolution and complex electrochemical reactions. Further, many intermediate rhenium oxides catalyze HER, so maintaining a stable water-in-salt electrolyte is crucial. Herein, we present systematic studies investigating various proton exchange membranes in an H-cell confirmation on the electrodeposition of rhenium. Perfluorosulfonic acid and hydrocarbon polymer backbones are explored, both with sulfonic acid functional groups. As these membranes are semipermeable, membrane thickness is also explored. Both volume changes in the two H-cell components and pH are monitored as a function of time. The impact on the morphology and electrodeposition kinetics of rhenium will be presented as a function of membrane properties.

Wear performance is integral to component longevity, minimizing industrial waste and excess energy costs in a wide variety of applications. Anodized aluminum oxide (AAO) has many beneficial properties leading to its wide use across industries as a surface treatment for many aluminum components, but the wear properties of the coating could be improved significantly. Here, we used an electrochemical method to incorporate molybdenum disulfide (MoS2), a nanomaterial used as a dry lubricant, to modify alloys of aluminum during AAO preparation. Using Raman spectroscopy and tribological scratch measurements, we thoroughly characterized the structure and wear behavior of the films. The MoS2 deposition procedure was optimal on aluminum 5052 anodized in higher acid concentrations, with friction coefficients at around 0.05 (~10× better than unmodified AAO). Changing anodization conditions to produce harder films with smaller pores led to worsened wear properties, likely because of lower MoS2 content. Studying a commercial MoS2/AAO film of a different Al alloy (7075) showed that a heat treatment step intended to fully convert all deposited MoSx species to MoS2 can adversely affect wear in some alloys. While Al 6061 and 1100 produced films with worse wear performance compared to Al 5052 or 7075, our results show evidence that acid cleaning after initial anodization likely removes residual alloying elements, affecting MoS2 incorporation. This study demonstrates a nanomaterial modified AAO film with superior wear characteristics to unmodified AAO and relates fabrication procedure, film structure, and practical performance.