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All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Composition-Dependent Photoluminescence Properties and Anti-Counterfeiting Applications of A 2 AgX 3 (A = Rb, Cs; X = Cl, Br, I)

Copper(I) halides are emerging as attractive alternatives to lead halide perovskites for optical and electronic applications. However, blue-emitting all-inorganic copper(I) halides suffer from poor stability and lack of tunability of their photoluminescence (PL) properties. In this work, the preparation of silver(I) halides A 2 AgX 3 (A = Rb, Cs; X = Cl, Br, I) through solid-state synthesis is reported. In contrast to the Cu(I) analogs, A 2 AgX 3 are broad-band emitters sensitive to A and X site substitutions. First-principle calculations show that defect-bound excitons are responsible for the observed main PL peaks in Rb 2 AgX 3 and that self-trapped excitons (STEs) contribute to a minor PL peak in Rb 2 AgBr 3 . This is in sharp contrast to Rb 2 CuX 3 , in which the PL is dominated by the emission by STEs. Moreover, the replacement of Cu(I) with Ag(I) in A 2 AgX 3 significantly improves photostability and stability in the air under ambient conditions, which enables their consideration for practical applications. Thus, luminescent inks based on A 2 AgX 3 are prepared and successfully used in anti-counterfeiting applications. The excellent light emission properties, significantly improved stability, simple preparation method, and tunable light emission properties demonstrated by A 2 AgX 3 suggest that silver(I) halides may be attractive alternatives to toxic lead halide perovskites and unstable copper(I) halides for optical applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Emergence of Moiré Dirac Fermions at the Interface of Topological and 2D Magnetic Insulators

Dirac Fermions on the surface of the topological insulator are spin-momentum locked and topologically protected, making them interesting for spintronics and quantum computing applications. When in proximity to magnetism and superconductivity, these electronic states could result in quantum anomalous Hall effect and Majorana Fermions, respectively. An even more dramatic enrichment of the topological insulators’ physics is expected for moiré superlattices, where, analogously to the twisted graphene layers, electronic correlations could be strongly enhanced, a task previously notoriously difficult to achieve in topological matter. Until now, the experimental confirmation of such moiré properties has remained elusive. Here, we grow the two-dimensional van der Waals magnetic insulators FeX 2 (where X = Cl or Br) on top of the topological insulator Bi 2 Se 3 and establish a moiré superlattice formation at the interface. By means of scanning tunneling microscopy and angle-resolved photoemission spectroscopy, we investigate the electronic properties of the formed moiré superlattice and demonstrate its tunability via the film choice. We reveal replicated Dirac cones and focus on their intersections, which, in the case of FeBr 2 /Bi 2 Se 3 , occur below the Fermi level. We identify the signatures of small gaps at the intersections around the M̅ i points that we attribute to the moiré interaction. These findings point to the specific type of magnetic moiré potential that breaks the time-reversal symmetry at these points but not at the $\barΓ$ point. Our observations provide an intriguing scenario of correlated topological phases induced by moiré superlattice that may result in topological superconductivity, high Chern number phases, and exotic noncollinear magnetic textures.

2D magnets↗
DOE OSTI2022

Preliminary Chlorine Worth Study Benchmark Evaluation

The Chlorine Worth Studies (CWS) experiments with polyvinyl chloride (PVC with chemical formula (C 2 H 3 Cl) n ), chlorinated polyvinyl chloride (CPVC with chemical formula (C 9 H 11 Cl 7 ) n ), and high density polyethylene (HDPE with chemical formula (CH 2 ) n ) were a series of measurements performed at the National Criticality Experiments Research Center (NCERC). The purpose of the CWS experiments was to perform integral experiments that were highly sensitive to the thermal 35 Cl(n,γ) reaction and matched the sensitivities of aqueous chloride operations at the plutonium facility at Los Alamos National Laboratory (LANL). The CWS experiments were performed on the Planet critical assembly machine at NCERC and utilized weapons grade plutonium (WGPu) plates as fuel. The design process and design of the CWS experiment were discussed previously. This paper discusses the benchmark evaluation of the experiment, intended for the International Criticality Safety Benchmark Evaluation Project (ICSBEP). Criticality calculations were performed with MCNP version 6.3. Results presented here are preliminary, as the benchmark has not yet been submitted to the ICSBEP.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

Elucidating Anomalous Intensity Ratios in Chlorine L-Edge X-ray Absorption Spectroscopy: Multiplet Effects and Core Rydberg Transitions

A relativistic core–valence-separated equation-of-motion coupled cluster (CVS-EOM-CC) study of chlorine L 2,3 -edge X-ray absorption near-edge structure (XANES) spectra using CH 3 Cl and CH 2 ICl as representative molecules is reported. The nearly identical intensity for the main features in the L 2 - and L 3 -edge XANES spectra is attributed to multiplet effects and the overlap between core–valence and core Rydberg transitions. The multiplet effects originating from the interaction between the core hole and the C–Cl σ* orbitals account for around half of the deviation of the L 3 and L 2 intensity ratio from the 2:1 ratio of the numbers of 2p 3/2 and 2p 1/2 electrons. The 2p 3/2 → 4s core Rydberg transitions are shown to overlap with the 2p 1/2 → σ* transitions and contribute to the other half of the intensity anomaly. Here, we demonstrate that triple excitations in CVS-EOM-CC calculations play important roles in accurate simulation of the overlap between the 2p 1/2 → σ* and 2p 3/2 → 4s transitions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Materials Data on Nb3Ga2Cl9 by Materials Project

Nb3Ga2Cl9 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Nb sites. In the first Nb site, Nb is bonded to five Cl atoms to form distorted corner-sharing NbCl5 square pyramids. There are four shorter (2.48 Å) and one longer (2.63 Å) Nb–Cl bond lengths. In the second Nb site, Nb is bonded to five Cl atoms to form distorted corner-sharing NbCl5 square pyramids. There are a spread of Nb–Cl bond distances ranging from 2.47–2.69 Å. Ga is bonded in a distorted trigonal non-coplanar geometry to three Cl atoms. There are one shorter (2.92 Å) and two longer (2.97 Å) Ga–Cl bond lengths. There are six inequivalent Cl sites. In the first Cl site, Cl is bonded in a 2-coordinate geometry to two equivalent Nb atoms. In the second Cl site, Cl is bonded in a 2-coordinate geometry to two Nb atoms. In the third Cl site, Cl is bonded in a 2-coordinate geometry to two equivalent Nb atoms. In the fourth Cl site, Cl is bonded in a distorted trigonal non-coplanar geometry to one Nb and two equivalent Ga atoms. In the fifth Cl site, Cl is bonded in a 2-coordinate geometry to two Nb atoms. In the sixth Cl site, Cl is bonded in a distorted trigonal planar geometry to one Nb and two equivalent Ga atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ta3Tl2Cl9 by Materials Project

Ta3Tl2Cl9 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Ta sites. In the first Ta site, Ta is bonded to five Cl atoms to form distorted corner-sharing TaCl5 square pyramids. There are four shorter (2.48 Å) and one longer (2.60 Å) Ta–Cl bond lengths. In the second Ta site, Ta is bonded to five Cl atoms to form distorted corner-sharing TaCl5 square pyramids. There are a spread of Ta–Cl bond distances ranging from 2.47–2.65 Å. Tl is bonded in a 4-coordinate geometry to four Cl atoms. There are a spread of Tl–Cl bond distances ranging from 3.15–3.28 Å. There are six inequivalent Cl sites. In the first Cl site, Cl is bonded in a 2-coordinate geometry to two equivalent Ta atoms. In the second Cl site, Cl is bonded in a 2-coordinate geometry to two Ta atoms. In the third Cl site, Cl is bonded in a 2-coordinate geometry to two equivalent Ta atoms. In the fourth Cl site, Cl is bonded in a distorted single-bond geometry to one Ta and three equivalent Tl atoms. In the fifth Cl site, Cl is bonded in a 2-coordinate geometry to two Ta atoms. In the sixth Cl site, Cl is bonded in a distorted trigonal planar geometry to one Ta and two equivalent Tl atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

All-temperature zinc batteries with high-entropy aqueous electrolyte

Electrification of transportation and rising demand for grid energy storage continue to build momentum around batteries across the globe. However, the supply chain of Li-ion batteries is exposed to the increasing challenges of resourcing essential and scarce materials. Therefore, incentives to develop more sustainable battery chemistries are growing. Here, in this paper, we show an aqueous ZnCl 2 electrolyte with introduced LiCl as supporting salt. Once the electrolyte is optimized to Li 2 ZnCl 4 ∙9H 2 O, the assembled Zn–air battery can sustain stable cycling over the course of 800 hours at a current density of 0.4 mA cm -2 between -60 °C and +80 °C, with 100% Coulombic efficiency for Zn stripping/plating. Even at -60 °C, >80% of room-temperature power density can be retained. Advanced characterization and theoretical calculations reveal a high-entropy solvation structure that is responsible for the excellent performance. The strong acidity allows ZnCl 2 to accept donated Cl - ions to form ZnCl 4 2- anions, while water molecules remain within the free solvent network at low salt concentration or coordinate with Li ions. Our work suggests an effective strategy for the rational design of electrolytes that could enable next-generation Zn batteries.

25 ENERGY STORAGE↗
DOE OSTI2022

Dark Energy Survey Year 3 results: Cosmology from cosmic shear and robustness to modeling uncertainty

Here, this work and its companion paper, Amon et al. [Phys. Rev. D 105, 023514 (2022)], present cosmic shear measurements and cosmological constraints from over 100 million source galaxies in the Dark Energy Survey (DES) Year 3 data. We constrain the lensing amplitude parameter 𝑆 8 ≡𝜎 8 ⁢$\sqrt{Ω_{m}/0.3}$ at the 3% level in Λ⁢ CDM: 𝑆 8 =0.75⁢9$^{+0.025}_{−0.023}$ (68% CL). Our constraint is at the 2% level when using angular scale cuts that are optimized for the Λ⁢ CDM analysis: 𝑆 8 =0.77⁢2$^{+0.018}_{−0.017}$ (68% CL). With cosmic shear alone, we find no statistically significant constraint on the dark energy equation-of-state parameter at our present statistical power. We carry out our analysis blind, and compare our measurement with constraints from two other contemporary weak lensing experiments: the Kilo-Degree Survey (KiDS) and Hyper-Suprime Camera Subaru Strategic Program (HSC). We additionally quantify the agreement between our data and external constraints from the Cosmic Microwave Background (CMB). Our DES Y3 result under the assumption of Λ⁢ CDM is found to be in statistical agreement with Planck 2018, although favors a lower 𝑆 8 than the CMB-inferred value by 2.3⁢𝜎 (a 𝑝-value of 0.02). This paper explores the robustness of these cosmic shear results to modeling of intrinsic alignments, the matter power spectrum and baryonic physics. We additionally explore the statistical preference of our data for intrinsic alignment models of different complexity. The fiducial cosmic shear model is tested using synthetic data, and we report no biases greater than 0.3⁢𝜎 in the plane of 𝑆 8 ×Ω m caused by uncertainties in the theoretical models.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Search for a light sterile neutrino with 7.5 years of IceCube DeepCore data

We present a search for an eV-scale sterile neutrino using 7.5 years of data from the IceCube DeepCore detector. The analysis uses a sample of 21,914 events with energies between 5 and 150 GeV to search for sterile neutrinos through atmospheric muon neutrino disappearance. Improvements in event selection and treatment of systematic uncertainties provide greater statistical power compared to previous DeepCore sterile neutrino searches. Our results are compatible with the absence of mixing between active and sterile neutrino states, and we place constraints on the mixing matrix elements |U μ⁢4 | 2 < 0.0534 and |U $\tau$⁢4 | 2 < 0.0574 at 90% CL under the assumption that Δ⁢m$^{2}_{41}$ ≥ 1 eV 2 . These null results add to the growing tension between anomalous appearance results and constraints from disappearance searches in the 3+1 sterile neutrino landscape.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Materials Data on Ta3In2Cl9 by Materials Project

Ta3In2Cl9 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Ta sites. In the first Ta site, Ta is bonded to five Cl atoms to form distorted corner-sharing TaCl5 square pyramids. There are a spread of Ta–Cl bond distances ranging from 2.47–2.66 Å. In the second Ta site, Ta is bonded to five Cl atoms to form distorted corner-sharing TaCl5 square pyramids. There are a spread of Ta–Cl bond distances ranging from 2.47–2.62 Å. In is bonded in a 3-coordinate geometry to three Cl atoms. There are a spread of In–Cl bond distances ranging from 3.07–3.15 Å. There are six inequivalent Cl sites. In the first Cl site, Cl is bonded in a distorted trigonal non-coplanar geometry to one Ta and two equivalent In atoms. In the second Cl site, Cl is bonded in a 2-coordinate geometry to two equivalent Ta atoms. In the third Cl site, Cl is bonded in a distorted trigonal planar geometry to one Ta and two equivalent In atoms. In the fourth Cl site, Cl is bonded in a 2-coordinate geometry to two Ta atoms. In the fifth Cl site, Cl is bonded in a 2-coordinate geometry to two Ta atoms. In the sixth Cl site, Cl is bonded in a 2-coordinate geometry to two equivalent Ta atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Selective Removal of Perfluorobutyric Acid Using an Electroactive Ion Exchanger Based on Polypyrrole@Iron Oxide on Carbon Cloth

Perfluorabutyric acid (PFBA) is one classify of perfluoroalkyl and polyfluoroalkyl substances (PFASs), which is applied to wide-spread industry compounds. The removal of PFBA has attracted considerable scientific interest in recent decades because it caused environmental pollutions and human diseases. For removing PFASs from wastewater, the adsorption method has been commonly used for the remediation of PFASs. However, it is usually limited by the inevitable “secondary waster” produced in this treatment process. In this work, PFBA can be removed effectively by synergizing the electrically switched ion exchange (ESIX) and a novel nanostructured ion exchanger. Herein, the nanostructured ion exchanger is designed by coating polypyrrole (PPy) @ Fe 2 O 3 nanoneedle on carbon cloth (PPy@Fe 2 O 3 NN-CC). Overall, results show that PPy@Fe 2 O 3 NN-CC film enhances ion exchange speed and efficiency, which endures its high-capacity adsorption ability and rapid regeneration property, thereby reducing secondary waste. Moreover, ESIX based on PPy@Fe 2 O 3 NN-CC has high selectivity for adsorption of PFBA over Cl - , SO 4 2- and NO 3 - .

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

Reactivities of Interstitial Hydrides in a Cu 11 Template: En Route to Bimetallic Clusters

In sharp contrast to surface hydrides, reactivities of interstitial hydrides are difficult to explore. When treated with a metal ion (Cu + , Ag + , and Au + ), the stable CuI dihydride template [Cu 11 H 2 {S 2 P(OiPr) 2 } 6 (C≡CPh) 3 ] (H 2 Cu 11 ) generates surprisingly three very different compounds, namely [CuH 2 Cu 11 {S 2 P(OiPr) 2 } 6 (C≡CPh) 3 ] + (1), [AgH 2 Cu 14 {S 2 P(OiPr) 2 } 6 ((C≡CPh) 6 ] + (2), and [AuCu 11 {S 2 P(OiPr) 2 } 6 (C≡CPh) 3 Cl] (3). Compounds 1 and 2 are both MI species and maintain the same number of hydride ligands as their H 2 Cu 11 precursor. Neutron diffraction revealed the first time a trigonal-pyramidal hydride coordination mode in the AgCu 3 environment of 2. 3 has no hydride and exhibits a mixed-valent [AuCu 11 ] 10+ metal core, making it a two-electron superatom.

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

F and N Rich Solid Electrolyte for Stable All-Solid-State Battery

We report the instability of sulfide solid electrolytes to Li anode and high-voltage LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) cathodes limits the cyclic performance of all-solid-state lithium battery (ASSLB). Herein, the stability of Li 6 PS 5 Cl against Li anode is enhanced by mixing a small amount (0.32 wt%) of CuF 2 -LiNO 3 (CL) into Li 6 PS 5 Cl electrolyte layer to in-situ form a mixed-conductive-lithiophobic and self-healing LiF-Li 3 N-Cu solid electrolyte interphase (SEI) at Li 6 PS 5 Cl-CL/Li interface. The critical current density (CCD) of Li 6 PS 5 Cl-CuF 2 -LiNO 3 increases to 1.4 mA cm –2 /1.4 mAh cm –2 at room temperature, which is much higher than that of pristine Li 6 PS 5 Cl (0.4 mA cm –2 /0.4 mAh cm –2 ) even though mixing 0.32 wt% CL into Li 6 PS 5 Cl slightly reduces the ionic conductivity from 2.9 × 10 –3 to 1.5 × 10 –3 S cm –1 . The compatibility of Li 6 PS 5 Cl-CL electrolyte to single-crystalline NMC811 (S-NMC811) is further enhanced by adding a small amount (0.02 wt%) of AlF 3 into Li 6 PS 5 Cl-CL forming Li 6 PS 5 Cl-CuF 2- LiNO 3 -AlF 3 (Li 6 >PS 5 Cl-CLA) as a cathode electrolyte and by doing Cl – on S-NMC811 (Cl@S-NMC811) surface. The Cl@S-NMC811-Li 6 PS 5 Cl-CLA|Li 6 PS 5 Cl-CL|Li cells with areal capacity of 2.55 mAh cm -2 achieve a capacity retention of 69.4% after 100 cycles at 1C (1C = 200 mAh g -1 ). Adding a small amount of SEI and cathode/electrolyte interphase (CEI) former into the sulfide electrolytes with minimal reduction (48.3%) of ionic conductivity is an effective method to enhance the performance of ASSLB.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Direct neutrino-mass measurement with sub-electronvolt sensitivity

Since the discovery of neutrino oscillations, we know that neutrinos have non-zero mass. However, the absolute neutrino-mass scale remains unknown. Here we report the upper limits on effective electron anti-neutrino mass, m ν , from the second physics run of the Karlsruhe Tritium Neutrino experiment. In this experiment, m ν is probed via a high-precision measurement of the tritium β-decay spectrum close to its endpoint. This method is independent of any cosmological model and does not rely on assumptions whether the neutrino is a Dirac or Majorana particle. By increasing the source activity and reducing the background with respect to the first physics campaign, we reached a sensitivity on m ν –2 at a 90% confidence level (CL). The best fit to the spectral data yields m$^2_ν$ = (0.26 ± 0.34) eV 2 c –4 , resulting in an upper limit of m ν < 0.9 eV c –2 at 90% CL. By combining this result with the first neutrino-mass campaign, we find an upper limit of m ν < 0.8 eV c –2 at 90% CL.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

The stability of Cl-, Br-, and I-passivated Si(100)-(2 × 1) in ambient environments for atomically-precise pattern preservation

Abstract Atomic precision advanced manufacturing (APAM) leverages the highly reactive nature of Si dangling bonds relative to H- or Cl-passivated Si to selectively adsorb precursor molecules into lithographically defined areas with sub-nanometer resolution. Due to the high reactivity of dangling bonds, this process is confined to ultra-high vacuum (UHV) environments, which currently limits its commercialization and broad-based appeal. In this work, we explore the use of halogen adatoms to preserve APAM-derived lithographic patterns outside of UHV to enable facile transfer into real-world commercial processes. Specifically, we examine the stability of H-, Cl-, Br-, and I-passivated Si(100) in inert N 2 and ambient environments. Characterization with scanning tunneling microscopy and x-ray photoelectron spectroscopy (XPS) confirmed that each of the fully passivated surfaces were resistant to oxidation in 1 atm of N 2 for up to 44 h. Varying levels of surface degradation and contamination were observed upon exposure to the laboratory ambient environment. Characterization by ex situ XPS after ambient exposures ranging from 15 min to 8 h indicated the Br– and I–passivated Si surfaces were highly resistant to degradation, while Cl–passivated Si showed signs of oxidation within minutes of ambient exposure. As a proof-of-principle demonstration of pattern preservation, a H–passivated Si sample patterned and passivated with independent Cl, Br, I, and bare Si regions was shown to maintain its integrity in all but the bare Si region post-exposure to an N 2 environment. The successful demonstration of the preservation of APAM patterns outside of UHV environments opens new possibilities for transporting atomically-precise devices outside of UHV for integrating with non-UHV processes, such as other chemistries and commercial semiconductor device processes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Heteroleptic Square Planar Cobalt(I/II) Complexes

Reduction of the cobalt(II) chloride complex, Ph 2 B( t BuIm) 2 Co(THF)Cl (1) in the presence of t BuN≡C affords the diamagnetic, square planar cobalt(I) complex Ph 2 B( t BuIm) 2 Co(C≡N t Bu) 2 (2). This is a rare example of a 16-electron cobalt(I) complex that is structurally related to square planar noble metal complexes. Accordingly, the electronic structure of 2, as calculated by DFT, reveals that the HOMO is largely d z 2 in character. Complex 2 is readily oxidized to its cobalt(II) congener [Ph 2 B( t BuIm) 2 Co(C=N t Bu) 2 ]BPh 4 (3-BPh 4 ), whose EPR spectral parameters are characteristic of low-spin d 7 with an unpaired electron in an orbital of d z 2 parentage. Further, this is also consistent with the results of DFT calculations. Despite its 16-electron configuration and the d z 2 parentage of the HOMO, the only tractable reactions of 2 involve one electron oxidation to afford 3.

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

Selective cobalt and nickel electrodeposition for lithium-ion battery recycling through integrated electrolyte and interface control

Abstract Molecularly-selective metal separations are key to sustainable recycling of Li-ion battery electrodes. However, metals with close reduction potentials present a fundamental challenge for selective electrodeposition, especially for critical elements such as cobalt and nickel. Here, we demonstrate the synergistic combination of electrolyte control and interfacial design to achieve molecular selectivity for cobalt and nickel during potential-dependent electrodeposition. Concentrated chloride allows for the speciation control via distinct formation of anionic cobalt chloride complex (CoCl 4 2- ), while maintaining nickel in the cationic form ([Ni(H 2 O) 5 Cl] + ). Furthermore, functionalizing electrodes with a positively charged polyelectrolyte (i.e., poly(diallyldimethylammonium) chloride) changes the mobility of CoCl 4 2- by electrostatic stabilization, which tunes cobalt selectivity depending on the polyelectrolyte loading. This strategy is applied for the multicomponent metal recovery from commercially-sourced lithium nickel manganese cobalt oxide electrodes. We report a final purity of 96.4 ± 3.1% and 94.1 ± 2.3% for cobalt and nickel, respectively. Based on a technoeconomic analysis, we identify the limiting costs arising from the background electrolyte, and provide a promising outlook of selective electrodeposition as an efficient separation approach for battery recycling.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Understanding the Dissolution and Passivation of an Aluminum Electrode during Electrocoagulation of Groundwater Using Neutron and X-ray Reflectometry

An aluminum (Al)-based electrocoagulation (EC) system can effectively remove dissolved silica and hardness in groundwater. The effectiveness of Al-EC in terms of pollutant removal, Faradaic efficiency, and energy consumption depends on the interfacial electrolysis or passivation of the electrode in water. Thus, understanding the electrolysis reaction at the liquid/electrode interface during operation is important for sustainable EC deployment. Here, a continuous flow-through Al-EC system was tested with various groundwater simulants, i.e., chloride (Cl – )-based, sulfate (SO 4 2– )-based, and mixed solutions. High pollutant removal with low energy consumption was observed in Cl – -based groundwater treatment, while low pollutant removal with high energy consumption was observed in SO 4 2– -based groundwater. For example, the required energy per unit mass of Al dosing in SO 4 2– -based groundwater is three times higher than that in Cl – -based groundwater at 10 mA/cm 2 . However, increasing the Cl – concentration significantly reduces this energy demand. In SO 4 2– -based groundwater, the silicate removal efficiency drops from 85.1% to 24.0% compared to that for Cl – -based groundwater, while Mg 2+ and Ca 2+ removal efficiencies decrease to 0.6% from 15.8% and 5.7% from 44.8%, respectively. To better understand this EC performance, we used in situ neutron reflectometry (NR) to examine the interfacial dynamics of Al dissolution and passivation at a 100 nm scale occurring on the surface of the sacrificial Al electrodes during EC. Ex situ X-ray reflectometry (XRR) was also used to support the in situ NR results. Both NR and XRR results revealed that Al dissolution is influenced by the presence of Cl – in the simulants, while a passivating layer forms on the electrode in a SO 4 2– -based solution. In the Cl – -based solution, anodic Al dissolution occurred locally and inhomogeneously across the surface of the Al anode film, resulting in a localized thickness reduction over time. In the SO 4 2– -based solution, no apparent dissolution of the Al anode was identified. Instead, Al underwent oxidation, forming an amorphous Al 2 O 3 surface layer within the Al electrode film that increased in thickness over time. In the mixed solution, both anodic Al dissolution and surface Al 2 O 3 layer formation occurred, indicating that Al dissolution and surface Al 2 O 3 layer formation are attributable to the Cl – and SO 4 2– ions, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗