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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
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Autonomous Measurement of Electrochemical Redox Couples for In-Situ Characterization of Enceladus Plume Samples

A 3D-printed microfluidic electrochemical cell with integrated electrodes was developed to demonstrate autonomous in-situ electrochemical characterization of terrestrial seawater samples. The system is designed to extend the capabilities of the 2008 Phoenix Lander’s Wet Chemistry Laboratory (WCL) that analyzed the soluble chemistry of the Martian soil, by miniaturizing its fluidic architecture for analysis of µL-volume samples as expected from an Enceladus fly-by mission. The microfluidic device has a total fluid volume of 48 µL and includes dual channels each populated with 7 electrodes. Measurement of pH was measured using an iridium oxide electrode. Cyclic voltammetry with Au, Pt, and glassy carbon working electrodes was used to measure redox couples in synthetic seawater that contained inorganic and bio-organic molecules. Glassy carbon was found to have minimal risk of interference from constituents of synthetic seawater when measuring molecular organic redox species; however, care must be used to prevent interference due to potential oxidation or dissolution in the case of Au working electrodes. A completely autonomous end-to-end run including sample delivery was performed, to demonstrate the feasibility of microfluidic-based cyclic voltammetry measurements for in-situ characterization of redox couples in Ocean World samples.

Planetary Instruments↗
NASA NTRS2012

Fundamental Investigation of Silicon Anode in Lithium-Ion Cells

Silicon is a promising and attractive anode material to replace graphite for high capacity lithium ion cells since its theoretical capacity is ~10 times of graphite and it is an abundant element on Earth. However, there are challenges associated with using silicon as Li-ion anode due to the significant first cycle irreversible capacity loss and subsequent rapid capacity fade during cycling. Understanding solid electrolyte interphase (SEI) formation along with the lithium ion insertion/de-insertion kinetics in silicon anodes will provide greater insight into overcoming these issues, thereby lead to better cycle performance. In this paper, cyclic voltammetry and electrochemical impedance spectroscopy are used to build a fundamental understanding of silicon anodes. The results show that it is difficult to form the SEI film on the surface of a Si anode during the first cycle; the lithium ion insertion and de-insertion kinetics for Si are sluggish, and the cell internal resistance changes with the state of lithiation after electrochemical cycling. These results are compared with those for extensively studied graphite anodes. The understanding gained from this study will help to design better Si anodes, and the combination of cyclic voltammetry with impedance spectroscopy provides a useful tool to evaluate the effectiveness of the design modifications on the Si anode performance.

Wu, James J.↗
DOE OSTI2021

Influence of the proton relay spacer on hydrogen electrocatalysis by cobalt hangman porphyrins

A cobalt hangman porphyrin system with a phenyl spacer between the porphyrin ring and an internal carboxylic acid group as well as its non-hangman analogue were synthesized and utilized for the study of the proton-coupled electron transfer (PCET) kinetics attendant to electrocatalytic hydrogen evolution. Cyclic voltammetry (CV) together with simulations show that a short distance between the proton relay and the redox active cobalt center as well as the increased proton donating strength results in superior catalytic activity. Here, the mechanism of hydrogen generation is at the nexus of proton transfer–electron transfer (PTET) and concerted proton–electron transfer (CPET), as opposed to an ETPT mechanism that is characteristic of hangman systems with longer proton relay networks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1991

The Nickel(111)/Alkaline Electrolyte Interface

The electrochemical properties of Ni (111) prepared and characterized in ultra high vacuum, UHV, by surface analytical techniques have been examined in alkaline media by cyclic voltammetry using an UHV-electrochemical cell transfer system designed and built in this laboratory. Prior to the transfer, the Ni(111) surfaces were exposed to saturation coverages of CO in UHV in an attempt to protect the surface from possible contamination with other gases during the transfer. Temperature Programmed Desorption, TPD, of CO-dosed Ni (111) surfaces displaying sharp c(4x2), LEED patterns, subsequently exposed to water-saturated Ar at atmospheric pressure in an auxiliary UHV compatible chamber and finally transferred back to the main UHV chamber, yielded CO2 and water as the only detectable products. This indicates that the CO-dosed surfaces react with water and/or bicarbonate and hydroxide as the most likely products. Based on the integration of the TPD peaks, the combined amounts of H2O and CO2 were found to be on the order of a single monolayer. The reacted c(4x2)CO/Ni(111) layer seems to protect the surface from undergoing spontaneous oxidation in strongly alkaline solutions. This was evidenced by the fact that the open circuit potential observed immediately after contact with deaerated 0.1 M KOH was about 0.38 V vs. DHE, drifting slightly towards more negative values prior to initiating the voltametric scans. The average ratio of the integrated charge obtained in the first positive linear scan in the range of 0.35 to 1.5 V vs. DHE (initiated at the open circuit potential) and the first (and subsequent) linear negative scans in the same solution yielded for various independent runs a value of 3.5 +/- 0.3. Coulometric analysis of the cyclic voltammetry curves indicate that the electrochemically formed oxyhydroxide layer involves a charge equivalent to 3.2 +/- 0.4 layers of Ni metal.

Wang, Kuilong↗
DOE OSTI2021

Synthesis, structure, electronic characterization, and halogenation of gold(III) phlorin complexes

The metalation chemistry of the phlorin, which is a non-aromatic tetrapyrrole macrocycle containing a single sp 3 -hybridized meso-carbon has remained underdeveloped, as compared to that of more traditional tetrapyrroles such as porphyrins, corroles and phthalocyanines. There have been few prior efforts to prepare metallophlorins, and those that have been reported have relied on either reduction or nucleophilic attack of parent metalloporphyrins, rather than direct metalation of freebase phlorin constructs. In this work, an alternate synthetic approach for preparation of gold(III) phlorin complexes that involves the first direct metalation of two different freebase phlorin derivatives (3H(Phl tBu ) and 3H(Phl F )) with AuBr 3 to produce the stable and fully isolable gold(III) phlorin complexes Au(Phl tBu ) and Au(Phl F ) is reported. The first structural characterization of a metallophlorin bearing geminal dimethyl substituents at the sp 3 -hybridized meso-carbon via X-ray crystallography is also reported. In addition to the preparation of Au(Phl tBu ) and Au(Phl F ), the UV-vis absorption and redox properties of these two gold(III) phlorins in comparison to those of their freebase homologues is also detailed. Notably, the metallophlorins are characterized by panchromatic absorbance profiles and intense and broad bands that span the long-visible and into the near-IR regions, as well as two fully reversible oxidation and reduction waves as probed by cyclic voltammetry. Lastly, the chlorination of Au(Phl tBu ) using PhI(Cl 2 ) was probed and it was found that this regioslective reaction generates monochlorinated (Au(Phl tBu Cl)) and dichlorinated (Au(Phl tBu Cl 2 )) products, which were both structurally characterized by X-ray crystallography.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Diffusion coefficient and nucleation density studies on electrochemical deposition of aluminum from chloroaluminate ionic liquid electrolytes

In this study, aluminum was electrodeposited from ionic liquids comprising a melt of alkyl imidazolium chlorides and aluminum chloride (AlCl 3 ). The ionic liquids utilized in this study were 1-ethyl-3-methyl-imidazolium chloride (EMIC)-AlCl 3 , 1-butyl-3-methylimidazolium chloride (BMIC)-AlCl 3 , and 1-hexyl-3-methyl-imidazolium chloride (HMIC)-AlCl 3 at the AlCl 3 mole fraction of 0.667 (molar ratio of 1:2). The electrochemical behavior of chloroaluminate species in the three ionic liquids was investigated by cyclic voltammetry (CV) and chronoamperometry (CA) techniques at different temperatures. The cyclic voltammograms indicated that the reduction of Al 2 Cl 7 – species to metallic aluminum followed a diffusion-controlled phenomenon. Moreover, even at a less negative applied potential, the higher current density was obtained for EMIC-AlCl 3 ionic liquid. That indicates that EMIC-AlCl 3 favors less energy consumption during the electrodeposition. The chronoamperometric analysis revealed that the onset of aluminum deposition from such ionic liquids proceeds via a three-dimensional instantaneous nucleation process. The concentrations of Al 2 Cl 7 – ions in the ionic liquids were calculated based on the thermodynamic data, which were 2520, 2271, and 2035 mol m –3 for EMIC-AlCl 3 , BMIC-AlCl 3 , and HMIC-AlCl 3 , respectively. The diffusion coefficient (D) values of Al 2 Cl 7 – species in such ionic liquids were also calculated at various temperatures. The D values determined from the CA technique at 363 K are 2.16 × 10 –11 , 1.03 × 10 –11 , and 0.87 × 10 –11 m 2 s –1 for EMIC-AlCl 3 , BMICAlCl 3 , and HMIC-AlCl 3 , respectively. In addition, the D value increased as temperature increased and decreased as the hydrocarbon group in the ionic liquid increased. As a result, the calculated grain sizes of nucleation range from 2 to 4 μm for these ionic liquids and are in good agreement with experimental data obtained from SEM micrographs.

42 ENGINEERING↗
DOE OSTI2020

Differentiating Double-Layer, Psuedocapacitance, and Battery-like Mechanisms by Analyzing Impedance Measurements in Three Dimensions

Electrochemical energy storage arises from processes that are broadly categorized as capacitive, pseudocapacitive, or battery-like. Advanced charge-storing materials that are designed to deliver high capacity at a high rate often exhibit a multiplicity of such mechanisms, which complicates the understanding of their charge-storage behavior. In this paper, we apply a “3D Bode analysis” technique to identify key descriptors for fast Li-ion storage processes, where AC impedance data, such as the real capacitance ($C'$) or phase angle ($Φ$), are represented versus the frequency ($f$) and a third independent variable, the applied DC cell voltage. For double-layer processes, a near-constant $C'$ or $Φ$ is supported across the entire voltage range, and the decrease in these values shows a near-linear decrease at higher $f$. For pseudocapacitance, an increase in $C'$ is delivered, accompanied by high $C'$ retention at higher $f$ compared to double-layer processes. Interestingly, the lower $Φ$ values, where $C'$ is highest, suggest that this is a key descriptor for pseudocapacitance, where high-rate charge storage is still facilitated within a kinetically limited regime. For battery-like processes, a high $C'$ is only observed at the voltage at which the material stores charge, while outside that voltage, $C'$ is negligible. The three-dimensional (3D) Bode analysis allows charge-storage dynamics to be mapped out in great detail with more delineation between mechanisms compared to the more frequently deployed kinetic analyses derived from cyclic voltammetry.

25 ENERGY STORAGE↗
DOE OSTI2020

Investigation of impurity driven corrosion behavior in molten 2LiF-BeF 2 salt

A 1000 -h corrosion experiment of 316H stainless steel at 700 °C investigated the role of metal fluoride impurities CrF 2 and FeF 2 in LiF-BeF 2 (66-34 mole %) (FLiBe) salt. Inductively coupled plasma-optical emission spectroscopy (ICP-OES) demonstrated the ability to measure changes in the concentration of these fluorides in FLiBe salt. Cyclic voltammetry (CV) showed the potential for real-time quantitative concentration measurement of corrosion products in the molten salt. Materials characterization revealed that both impurity species influence the dissolution of Cr from the alloy. The collective results from these analysis methods advance the understanding of the influence impurities have on materials corrosion.

2LiF-BeF2↗
DOE OSTI2022

Deconvoluting sources of failure in lithium metal batteries containing NMC and PEO-based electrolytes

Solid-state lithium metal batteries (SSLMBs) containing polyethylene oxide (PEO)-derived polymer electrolytes and high-voltage (> 4 V vs. Li/Li + ) cathode materials suffer from three sources of failure: (1) instability between the polymer electrolyte and cathode at high voltage, (2) instability of the polymer electrolyte with Li metal, and (3) poorly-designed cathodes. In this study, these three sources of failure are deconvoluted by studying Ni-rich LiNi x Mn y Co 1-x-y O 2 (NMC, x ≥ 0.6) cathodes and a gel polymer electrolyte (GPE) derived from PEO. Initial cycling data reveals that rapid capacity fade occurs regardless of whether soft short circuits form due to Li dendrites. Cyclic voltammetry scans on cells featuring a Li metal electrode, GPE, and a NMC811 electrode free of additives suggest that there are no runaway reactions between the GPE and NMC811 up to 4.5 V vs. Li/Li + . Cathode/cathode symmetric cell cycling demonstrates that Li metal reactivity is a prime source of failure, though a poorly-designed cathode leads to subpar performance. A cathode with single-crystal NMC particles was demonstrated to achieve better initial capacity and longer cycle life, indicating room for improvement in SSLMB cathode design. Therefore, the sources of failure as enumerated may be ranked as follows from most to least concerning: 2 > 3 > 1.

25 ENERGY STORAGE↗
DOE OSTI2023

Spin-dependent charge transmission through chiral 2T3N self-assembled monolayer on Au

In this study, a gold surface is functionalized by chemisorption of the enantiopure N,N'-bis-[2,2';5',2"]tert-thiophene-5-yl methylcyclohexane-1,2-diamine (2T3N), a chiral oligothiophene derivative, via overnight incubation in a 2T3N ethanol solution. The Au|2T3N interface is characterized by x-ray photoelectron circular dichroism and comparing x-ray photoemission spectroscopy and electro-desorption results. Charge transmission at the Au|2T3N| solution interface is characterized by recording the cyclic voltammetry of the Fe(III)/Fe(II) reversible redox couple, finding a charge transfer rate constant, k°, variation from 1 × 10 -1 to 3.3 × 10 -2 cm s -1 , when comparing the bare Au and the Au|2T3N interfaces, respectively. The “anomalous” high value of k° found for the chiral Au|2T3N interface can be rationalized on the basis of the chiral-induced spin selectivity effect, as further proved by magnetic–conductive atomic force microscopy measurements at room temperature. A spin polarization of about 30% is found.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Imaginary admittance and charge transfer resistance correlate to the physiological status of Shewanella oneidensis cultures in real time

Monitoring microbial activity is essential for industrial and environmental applications to proceed efficiently. To minimize time and labor-intensive monitoring, a new paradigm is required for in-situ, real time analysis. Since bioconversion of organics is accomplished by microorganisms through the oxidation of feedstocks linked to the reduction of electron acceptors, microorganisms can be viewed as electrochemical catalysts. In this respect, cell membranes have an electrical potential, which is analogous to a conventional capacitor and linked dynamically to cellular activity. Here, in this study, we demonstrate the use of electrochemical impedance spectrometry (EIS) and cyclic voltammetry (CV) for monitoring microbial metabolic activity in real time, in-situ. The effect of organic electron donors as a function of concentration to the physiological status of strains of Shewanella oneidensis was determined. In this study, the pyomelanin overproducer (S. oneidensis ΔhmgA) and the pyomelanin deficient mutant (S. oneidensis ΔmelA) were chosen due to different surface electrochemical characteristics along with differences in oxygen utilization efficiency. CV, relative admittance, phase shift and permittivity changed with growth status and correlated with electron flow from organic carbon sources and terminal electron acceptor availability. This work offers a novel and inexpensive approach to real time monitoring with the advantage of abundant data.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Chiral Recognition: A Spin-Driven Process in Chiral Oligothiophene. A Chiral-Induced Spin Selectivity (CISS) Effect Manifestation

In this paper it is experimentally demonstrated that the electron-spin/molecular-handedness interaction plays a fundamental role in the chiral recognition process. This conclusion is inferred comparing current versus potential (I-V) curves recorded using chiral electrode surfaces, which are obtained via chemisorption of an enantiopure thiophene derivative: 3,3'-bibenzothiophene core functionalized with 2,2'-bithiophene wings (BT 2 T 4 ). The chiral recognition capability of these chiral-electrodes is probed via cyclic voltammetry measurements, where, Ag nanoparticles (AgNPs) capped with enantiopure (BT 2 T 4 ) (BT 2 T 4 )@AgNP) are used as the chiral redox probe. Then, the interface handedness is explored by recording spin-polarized (I-V) curves in spin-dependent electrochemistry (SDE) and magnetic-conductive atomic force microscopy (mc-AFM) experiments. The quality of the interfaces is thoroughly cross-checked using X-ray photoemission spectroscopy, Raman, electrodesorption measurements, which further substantiate the metal(electrode)-sulfur(thiophene) central role in the chemisorption process. Spin-polarization values of about 15% and 30% are obtained in the case of SDE and mc-AFM experiments, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Effect of Electrode/Electrolyte Coupling on Birnessite (δ-MnO 2 ) Mechanical Response and Degradation

Understanding the deformation of energy storage electrodes at a local scale and its correlation to electrochemical performance is crucial for designing effective electrode architectures. In this work, the effect of electrolyte cation and electrode morphology on birnessite (δ-MnO 2 ) deformation during charge storage in aqueous electrolytes was investigated using a mechanical cyclic voltammetry approach via operando atomic force microscopy (AFM) and molecular dynamics (MD) simulation. In both K 2 SO 4 and Li 2 SO 4 electrolytes, the δ-MnO 2 host electrode underwent expansion during cation intercalation, but with different potential dependencies. When intercalating Li + , the δ-MnO 2 electrode presents a nonlinear correlation between electrode deformation and electrode height, which is morphologically dependent. Further, these results suggest that the stronger cation–birnessite interaction is the reason for higher local stress heterogeneity when cycling in Li 2 SO 4 electrolyte, which might be the origin of the pronounced electrode degradation in this electrolyte.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Highly Reversible Lithiation of Additive Free T‐Nb 2 O 5 for a Quarter of a Million Cycles

Abstract Fast energy storage via intercalation requires quick ionic diffusion and often results in pseudocapacitive behavior. The cycling stability of such energy storage materials remains understudied despite the relevance to lifetime cost. Orthorhombic niobium oxide (T‐Nb 2 O 5 ) is a rapid ion intercalation material with a theoretical capacity of 201.7 mAh g −1 (Li 2 Nb 2 O 5 ) and good cycling stability due to the minimal unit cell strain during (de)intercalation. Prior reports of T‐Nb 2 O 5 cycling between 1.3–3.1 V versus Li/Li + noted a 50% loss in capacity after 10 000 cycles. Here, cyclic voltammetry is used to identify the role of the voltage window, state of charge, and potentiostatic holds on the cycling stability of mesoporous T‐Nb 2 O 5 thin films. Films cycled between 1.2–3.0 V versus Li/Li + without voltage holds (Li 1.1 Nb 2 O 5 ) exhibited extreme cycling stability with 90.8% capacity retention after 0.25 million cycles without detectable morphological/crystallographic changes. In contrast, the inclusion of 60 s voltage holds (Li 2.18 Nb 2 O 5 ) led to rapid capacity loss with 61.6% retention after 10 000 cycles with corresponding X‐ray diffraction evidence of amorphization. Cycling with other limited voltage windows identifies that most crystallographic degradation occurs at higher extents of lithiation. These results reveal remarkable stability over limited conditions and suggest that T‐Nb 2 O 5 amorphization is associated with high extents of lithiation.

25 ENERGY STORAGE↗
DOE OSTI2022

Electrochemical Proton Insertion Modulates the Hydrogen Evolution Reaction on Tungsten Oxides

Development of new electrocatalysts for the hydrogen evolution reaction (HER) could reduce dependence on Pt and other rare metals and enable large-scale production of hydrogen with near-zero carbon emissions. Mechanistic insight into the electrocatalytic activity of a material helps to accelerate the development of new electrocatalysts. Alternative electrocatalyst materials such as transition metal oxides and sulfides can undergo insertion reactions that change their properties. Recent reports indicate that the presence of inserted ions can influence electrocatalytic activity. In this work, we utilized a materials chemistry approach to understand the role of proton insertion on the HER activity of layered tungsten oxide hydrates (WO 3 ∙xH 2 O, x = 1, 2). We synthesized a series of tungsten oxide hydrates along with an octylamine-pillared tungsten oxide (OA-WO 3 ). We used cyclic voltammetry to study the electrochemical reactivity of each material and performed ex situ X-ray diffraction and Raman spectroscopy to understand bulk and surface structural changes during electrochemical cycling. We show an inverse relationship between the degree of proton insertion and HER overpotential in tungsten oxides: the lack of proton insertion leads to a high overpotential for the HER. We discuss three hypotheses for how proton insertion leads to HER activity in WO 3 ∙xH 2 O: 1) proton insertion changes the electronic band structure of WO 3 ∙xH 2 O, 2) the presence of bulk protons can influence ΔG H,ads at the surface sites, and 3) inserted protons may participate in the HER mechanism on WO 3 ∙xH 2 O. Overall, this work shows the critical role of proton insertion in enabling high HER activity in tungsten oxides.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Exciton Binding Energy in Organic Polymers: Experimental Considerations and Tuning Prospects

Discrepancies in reported values of exciton binding energy (E b ) for organic semiconductors (OSs) necessitate a comprehensive study. Traditionally, E b is defined as the difference between the transport gap (E t ) and the optical gap (E opt ). Here, the E b values of PBnDT‐TAZ polymer variants are determined using two commonly employed methods: a combination of ultraviolet photoemission spectroscopy and low‐energy inverse photoemission spectroscopy (UPS‐LEIPS) and solid‐state cyclic voltammetry (CV). E b values obtained by UPS‐LEIPS show low dispersion and no clear correlation with the polymer structure and thedielectric properties. In contrast, CV reveals a larger dispersion (200 meV‐1 eV) and an apparent qualitative E b ‐molecular structure correlation, as the lowest E b values are observed for oligo‐ethylene glycol side chains. This discrepancy is discussed by examining the implications of the traditional definition of E b . Additionally, the impact of both intrinsic and extrinsic factors contributing to the derived experimental values of E t is discussed. The differences in intrinsic and extrinsic factors highlight the context‐dependent nature of measurement when drawing global conclusions. Notably, the observed E b trend derived from CV is not intrinsic to the pure materials but likely linked to electrolyte swelling and associated changes in dielectric environment, suggesting that high‐efficiency single‐material organic photovoltaics with low E b may be possible via high dielectric materials.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Influence of solvents on electrochemical stability window of ionic liquid solutions

The electrochemical stability window (ESW) defines the voltage range within which an electrolyte remains stable against oxidation and reduction, serving as a key descriptor for ionic liquid (IL)-based systems. The ESWs of 15 ILs with diverse cation-anion combinations were systematically investigated, both in their neat forms and as binary mixtures with three representative solvents, i.e., propylene carbonate (PC), ethylene glycol (EG), and tetrahydrofuran (THF). Cyclic voltammetry on a glassy carbon electrode determined anodic and cathodic stability limits, revealing that ESW protection in IL-solvent mixtures strongly depends on solvent polarity, proticity, and IL compatibility. PC, with a high dielectric constant and aprotic character, broadened anodic limits and moderately stabilized cathodic limits. THF maintained compact interfacial structure, offering additional cathodic protection, whereas EG, being protic, reduced ESWs via proton-coupled electron transfer and hydrogen evolution. The solvent protection trend followed by PC > THF > EG, with bulky, hydrophobic cations ([HMIM] + , [BMPYRR] + ) and weakly coordinating anions ([NTF 2 ] - , [DCA] - , [DEP] - ) showing the highest ESW protection for 50 mol% IL in these solvents. Among the neat ILs, [EMIM][DEP], [HMIM][PF 6 ], and [BMPYRR][DCA] showed wide ESWs of ∼5.5 V. These results provide valuable insight into solvent-modulated electrochemical stability, enabling rational design of IL-based electrolytes for energy storage and electrosynthesis.

25 ENERGY STORAGE↗
DOE OSTI2026

Electrochemical behavior of SnCl 2 and influence of Cu and Ni ions in molten LiCl−KCl−CaCl 2 eutectic

Reliable transport and thermodynamic data for multivalent ions in complex molten salts are scarce, limiting model fidelity for electrorefining and impurity control. Here, we report a comprehensive electrochemical characterization of SnCl₂ in LiCl–KCl–CaCl₂ (50.5–44.2–5.3 mol%) at 685 K, including the effects of Ni 2+ and Cu + impurities. Using cyclic voltammetry (CV), chronoamperometry (CA), and chronopotentiometry (CP), we quantified Sn 2+ and Ni 2+ diffusion with exceptional agreement across methods: Sn 2+ averaged (1.03 ± 0.10) × 10 −5 cm 2 s −1 , and Ni 2+ averaged (0.75 ± 0.19) × 10 −5 cm 2 s −1 . The tight confidence-interval overlap across CV, CA, and CP strengthens confidence in these values and is uncommon in molten chloride studies. Open-circuit-potential measurements provided standard apparent reduction potentials that closely match LiCl–KCl literature, indicating minimal shift with CaCl₂ present. The Sn 2+ /Sn couple behaves as a reversible two-electron soluble–insoluble process at 685 K; the Sn 4+ /Sn 2+ couple transitions to soluble–soluble behavior near 788 K, which may correlate with the decomposition of surface bound chlorostannates, though direct characterization remains to be established. In mixed systems, Cu+/Cu overlaps Sn 2+ /Sn, limiting Cusingle bondSn electroseparation, whereas the larger potential gap between Ni 2+ /Ni and Sn 2+ /Sn supports selective Ni removal. These internally consistent transport and thermodynamic data establish a validated basis for process modeling and optimization of Sn electrorefining and impurity management in LiCl–KCl–CaCl₂.

Berzins-Delahay↗