Ceria (CeO2) is a material of significant technological importance. A detailed understanding of the material's defect physics and chemistry is key to understanding and optimizing its properties. Here, we report a hybrid density-functional study of native point defects, hydrogen impurities, and metal dopants in CeO2. We find that electron polarons (eta-Ce) and oxygen vacancies (VO2+) are the dominant native defects under conditions ranging from extreme oxidizing to highly reducing. Hydrogen is stable either in the hydroxyl (H+i ) or hydride (H+O) structure, but the substitutional H+O is energetically more favorable than H+ i only under highly reducing conditions. The interstitial H+ i is highly mobile in the bulk. Yttrium (Y) is energetically most favorable at the substitutional Ce site. Copper (Cu) and nickel (Ni) can be incorporated at the substitutional site and/or an interstitial site, depending on actual conditions during preparation, and the dopants can exist in different charge and spin states. In light of the results, we discuss electronic and ionic conduction and the effects of metal doping on the formation of electron polarons and oxygen vacancies.

The presented family of one-dimensional (1D) polyanionic borophosphates is discussed in the context of a growing class of intermediate temperature electrolytes. The borophosphates are noteworthy for exhibiting high thermal stability under a highly reducing H2 atmosphere. Here, we report the electrolyte characteristics observed in rubidium borophosphate (Rb3H2[BOB-(PO4)3]) and cesium borophosphate (Cs3H2[BOB-(PO4)3]) (a new compound) as newly identified members of the proton-conducting 1D borophosphate polyelectrolyte family. Ab initio molecular dynamics simulations of the compounds suggest extremely high H+ mobility correlated with gyrational mobility of the borophosphate chains, which is similar in character to that of previously reported borosulfate proton electrolytes. Particularly noteworthy is the proton conductivity of the Cs3H2[BOB-(PO4)3] variant, which has the highest conductivity of any of the borophosphates so far, found to be on the order of 10 -5 S·cm -1 (250 °C and 0.2 atm of water). Cs3H2[BOB-(PO4)3] was found to be the best-performing 1D borophosphate electrolyte due to the combination of the highest observed proton conductivity, the greatest thermal stability, and attractive mechanical properties. This represents an important advance for intermediate temperature proton conductors and provides a viable path to improve electrolytes for intermediate temperature hydrogen fuel cells.

Substitution of vanadium into earth-abundant maghemite iron oxide introduces cation vacancies that increase Li+ storage capacity concomitant with a positive shift in its electrochemical potential. Expressing vanadium ferrite (VFe2Ox) as an aerogel offers an opportunity to probe Li+ storage in this inherently defective spinel from highly disordered (X-ray amorphous) to nanocrystalline. To understand the redox sequence of the host cations, we use in situ X-ray absorption near-edge spectroscopy (XANES) obtained using an in-lab X-ray absorption spectrometer in concert with density functional theory calculations to uncover the quantum mechanical-level effects that underpin relevant energy-storage behaviors. The Fe K-edge spectra indicate that upon Li+ insertion, the change in Fe oxidation state occurs primarily at high voltage (average voltage ∼2.9 V), which is ∼0.7 V higher than the average voltage for γ-Fe2O3. Parallel computations using density functional theory show that tetrahedral V and octahedral Fe sites are reduced during lithiation and that the hybridization of Fe and V orbitals imposes a positive shift in voltage for Fe redox. Our combined experimental and computational investigation sheds light on how these complex materials store Li+ and increase cell voltage. These findings point toward future compositional alterations that may further improve their properties.

Emerging photocatalytic applications of cerium dioxide (CeO2) include green hydrogen production, CO2 conversion to fuels, and environmental remediation of various toxic molecules. These applications leverage the oxygen storage capacity and tunable surface chemistry of CeO2 to photocatalyze the chosen reaction, but many open questions remain regarding the fundamental physics of photocatalysis over CeO2. The commonly ascribed 'bandgap' of CeO2 (similar to 3.1 eV) differs fundamentally from other photocatalytic oxides such as TiO2; UV light excites an electron from the CeO2 valence band into a 4f state, generating a polaron as the lattice distorts around the localized charge. Researchers often disregard the distinction between the 4f state and a traditional, delocalized conduction band, resulting in ambiguity regarding mechanisms of charge transfer and visible-light absorption. This review summarizes modern literature regarding CeO2 photocatalysis and discusses commonly reported photocatalytic reactions and visible light-sensitization strategies. We detail the often misunderstood fundamental physics of CeO2 photocatalysis and supplement previous work with original computational insights. The exceptional progress and remaining challenges of CeO2-based photocatalysts are highlighted, along with suggestions for further research directions based on the observed gaps in current understanding.

Vanadium–iron oxides (VFe2Ox) exhibit promising Li+-storage properties when expressed in high-surface-area, disordered/defective forms such aerogels.1 We have also shown that the specific capacity for VFe2Ox can be further increased by compositional substitution with minority amounts of electro-inactive cations such as Al3+ and Zr4+.2 To deconvolve the relative contributions of V- and Fe-based redox and the effects of metal substitution, we turn to X-ray absorption spectroscopy (XAS) as performed with a bench-scale instrument. X-ray absorption near-edge spectroscopy (XANES) provides vital element-specific information on electronic properties and metal oxidation state, while extended absorption fine-structure spectroscopy (EXAFS) produces information on local bonding/coordination, even for amorphous/disordered materials. Using pouch cells designed specifically for the bench-scale spectrometer, we collect in situ spectra on VFe2Ox electrodes as they undergo electrochemical cycling between 2.0 and 3.8 V vs Li/Li+ in conventional nonaqueous electrolyte. We show that the first stages of Li+-insertion are accompanied by Fe3+/2+ redox, with V5+/4+ redox becoming active only at lower cell voltages (<2.5 V). Parallel DFT calculations on a representative spinel-type VFe2Ox structure confirms that V incorporates at tetrahedral sites. The combination of Fe/V tetrahedral occupation and vacancy-induced disorder also lowers the overall energy to open an electronic energy gap that establishes the Fe3+/2+-to-V5+/4+ redox sequence during lithiation, in confirmation of experimental XAS findings. The role of additional metal substitution is also assessed by parallel XAS measurements and DFT computation. 1. C. N. Chervin, J. S. Ko, B. W. Miller, L. Dudek, A. N. Mansour, M. D. Donakowski, T. Brintlinger, P. Gogotsi, S. Chattopadhyay, T. Shibata, J. F. Parker, B. P. Hahn, D. R. Rolison, and J. W. Long, J. Mater. Chem. A 3, 12059 (2015). 2. C. N. Chervin, R.H. DeBlock, J. F. Parker, B. M. Hudak, N. L. Skeele, J. S. Ko, D. R. Rolison, and J. W. Long, RSC Adv. 11, 14495 (2021).

Initiated chemical vapor deposition provides the means to coat thin, conformal polymer films on high surface-area 3D architectures as well as planar substrates.

The ionic conductivity, thermal stability, and general viability for use as electrolytes in fuel cells are examined for two borophosphate polyelectrolyte compounds (e.g., sodium borophosphate (NaBOB, Na5[BOB(PO4)3)]) and ammonium borophosphate (NH4BOB, (NH4)3H2[BOB(PO4)3])). Bulk synthesis methods are presented for laboratory scale reactions (> 5 g) using low-temperature ionic liquid fluxes. Electrochemical impedance spectroscopy (EIS) was used to determine temperature-dependent ionic conductivities of the NH4BOB and NaBOB to be on the order of 2 µS cm−1 and 0.1 µS cm−1 at 200 °C, respectively. Although NH4BOB displays higher ionic conductivity compared to NaBOB at equivalent temperatures, thermal gravimetric analysis (TGA) shows much higher thermal stability for NaBOB, exhibiting no mass loss below 600 °C. The thermal stability of NaBOB was also assessed under reducing ( 1 atm H2) conditions, finding no reductive thermal degradation below 400 °C. Ab initio molecular dynamics (AIMD) simulations show free proton (H+) movement is related to gyrational mobility of the polyanionic borophosphate chains.

Vanadium ferrite (VFe 2 O x ) is a defective spinel system that can incorporate substantial Li+ and exhibits a high charge–discharge rate, particularly when structured as a nanoscale aerogel.1 Cations such as Zr, Zn and Al,2 can readily enter the structure substitutionally and have strong, but differing effects on the charge-storage capacity of the material. These earth abundant, cost- effective constituent elements give this class of materials strong potential as future Li-ion battery cathodes but optimizing the stoichiometry for maximum capacity and stability will require understanding the redox sequence of the host cations (Fe, V) and role of intentional dopants. We use density functional theory calculations in concert with in situ and operando X-ray absorption near-edge spectroscopy (XANES) spectra obtained using an in-lab X-ray absorption spectrometer to uncover the quantum mechanical-level effects that underpin relevant energy- storage behaviors of doped and undoped VFe 2 O x . Our experimental V K-edge and Fe K-edge spectra indicate reduction of both species during discharge but cannot distinguish between tetrahedral and octahedral Fe redox sites or fully resolve the valency of each element as a function of state of charge. Using a hybrid form of density functional theory that accounts for the strong correlation present in 3d elements, we show that both V and Fe are indeed reduced, but that only tetrahedral Fe is redox active until fully converted to Fe 2+ . Furthermore, both octahedral and tetrahedral Fe 3+ are high spin configuration, but the 5μ B moments in the fully filled majority spin channel at each symmetry site are anti-aligned. This arrangement allows for easy exchange of electrons and facilitates conduction. We also calculate XANES spectra based on first principles calculations to be compared directly to those measured in the lab. This cross- check allows us to understand the effect of Al, Zr, and Zn dopants on the redox sequence and relate these results to site preference and capacity. Our combined experimental and calculational investigation sheds light on how these complex materials store Li ions and points toward future alterations that may further improve their properties.

X-ray absorption spectroscopy (XAS) provides important information on metal oxidation state and element-specific coordination, but data collection has historically required the energy specificity and brilliance of a synchrotron facility. Recent developments in detectors and optics are now bringing XAS capabilities to the laboratory setting through multiple commercially available instruments. At the U.S. Naval Research Laboratory, we use laboratory-based XAS to explore the local electronic and atomic structure of a class of disordered vanadium ferrite (VFe 2 O x ) aerogels that exhibit promising performance for electrochemical energy-storage applications such as rechargeable lithium-ion batteries. 1,2 These materials are synthesized by an epoxide-promoted sol– gel reaction of iron chloride and vanadium isopropoxide, with the resulting fluid-filled gels rendered as high surface area aerogels via supercritical-CO 2 drying. During the initial sol–gel synthesis, electroinactive metals such as aluminum, zinc, and zirconium may also be substituted for vanadium and iron to alter the local electronic environment and corresponding electrochemical performance of VFe 2 O x . Heat treatment of as-dried VFe 2 O x aerogels under either O2-containing or inert atmosphere yields disordered or nanocrystalline variants, respectively. The resulting series of native and substituted VFe 2 O x materials are evaluated as powder-composite cathodes versus lithium metal in coin cells with conventional nonaqueous lithium-ion electrolyte. We correlate such critical battery-performance parameters as total specific capacity, high-rate capability, and cycle life as a function of VFe 2 O x composition and its degree of structural order/disorder, as measured with in-situ XANES and EXAFS. In parallel with experimental observations, calculations on VFe 2 O x reveal that V incorporates into the defective spinel structure at tetrahedral sites and that both disorder induced by vacancies and Fe/V tetrahedral occupation lowers the overall energy and opens an electronic energy gap that establishes the redox sequence during lithiation. 1. C. N. Chervin, J. S. Ko, B. W. Miller, L. Dudek, A. N. Mansour, M. D. Donakowski, T. Brintlinger, P. Gogotsi, S. Chattopadhyay, T. Shibata, J. F. Parker, B. P. Hahn, D. R. Rolison, and J. W. Long, J. Mater. Chem. A 3, 12059 (2015). 2. C. N. Chervin, R. H. DeBlock, J. F. Parker, B. M. Hudak, N. L. Skeele, J. S. Ko, D. R. Rolison, and J. W. Long, RSC Adv. 11, 14495 (2021).

X-ray absorption spectroscopy (XAS) is a critical tool for investigating new materials for electrochemical energy storage, providing important information on metal oxidation state and element-specific coordination. Historically, XAS measurements had required the energy specificity and brilliance of a synchrotron facility, but recent advances in detectors and optics are bringing XAS capabilities to the laboratory setting with multiple commercial instruments available. At the Naval Research Laboratory, we use laboratory-based XAS to study a class of disordered vanadium ferrite (VFe 2 O x ) aerogels that exhibit promising performance for electrochemical energy-storage applications such as rechargeable lithium-ion batteries. 1,2 The structure and composition of these materials are readily varied via modifications to the epoxide-promoted sol–gel reaction of iron chloride and vanadium isopropoxide (e.g., substitution with other cations such as Al 3+ ), 2 as well as post-synthesis thermal treatments that render disordered, defective, or nanocrystalline forms of a given composition. The resulting series of VFe 2 O x materials are evaluated by XAS in both ex situ and in situ configurations, including as powder-composite cathodes versus lithium metal in pouch cells with conventional nonaqueous lithium-ion electrolyte. X-ray Absorption Near-edge Spectroscopy (XANES) at the V K-edge and Fe K-edge is used to track V and Fe oxidation state, respectively, permitting the assignment of metal-centered redox across the broad potential range over which these materials are electrochemically active (2–3.4 V vs Li/Li + ). Extended X-ray Absorption Fine Structure (EXAFS) analysis provides information on V- or Fe-specific coordination as a function of composition, structure, and state-of-charge. Parallel computation efforts using Density-Functional Theory offer a complementary feedback loop with experimental XANES and EXAFS to achieve a sophisticated description of these complex battery materials. 1. C. N. Chervin, J. S. Ko, B. W. Miller, L. Dudek, A. N. Mansour, M. D. Donakowski, T. Brintlinger, P. Gogotsi, S. Chattopadhyay, T. Shibata, J. F. Parker, B. P. Hahn, D. R. Rolison, and J. W. Long, J. Mater. Chem. A 3 , 12059 (2015). 2. C. N. Chervin, R. H. DeBlock, J. F. Parker, B. M. Hudak, N. L. Skeele, J. S. Ko, D. R. Rolison, and J. W. Long, RSC Adv. 11 , 14495 (2021).

The nature of the Fermi surface observed in the recently discovered family of unconventional insulators starting with SmB 6 is a subject of intense inquiry. Here we shed light on this question by accessing quantum oscillations in the high magnetic field-induced metallic regime above ≈47 T in YbB 12 , which we compare with the unconventional insulating regime. In the field-induced metallic regime, we find prominent quantum oscillations in the electrical resistivity characterised by multiple frequencies and heavy effective masses. The close similarity in Lifshitz-Kosevich low-temperature growth of quantum oscillation amplitude in insulating YbB 12 to field-induced metallic YbB 12 , points to an origin of quantum oscillations in insulating YbB 12 from in-gap neutral low energy excitations. Higher frequency Fermi surface sheets of heavy quasiparticle effective mass emerge in the field-induced metallic regime of YbB 12 in addition to multiple heavy Fermi surface sheets observed in both insulating and metallic regimes. f -electron hybridisation is thus observed to persist from the unconventional insulating to the field-induced metallic regime of YbB 12 , in contrast to the unhybridised conduction electron Fermi surface observed in unconventional insulating SmB 6 . Our findings thus require an alternative model for YbB 12 , of neutral in-gap low energy excitations, wherein the f -electron hybridisation is retained.

The recently discovered kagome net compounds AV3Sb5 (A = K, Rb, and Cs) become superconducting on cooling, in addition to displaying interesting topological features in the electronic structure. They also exhibit charge density wave ordering, which manifests as a breathing-mode distortion in the kagome layers. It has been suggested that such ordering derives from nesting between saddle points on the Fermi surface. In aid of the evolving understanding of this intriguing materials class, we present calculations of Fermi surface nesting and Lindhard susceptibility of CsV3Sb5. The breathing mode distortions appear to not display a simple link with Fermi surface nesting (FSN) and do not display the signatures of a Peierls-like transition. The FSN is agnostic to changes along kz and is only mildly impacted by small shifts of the Fermi level. The results suggest that FSN is largely independent of specific features in the saddle point.

Understanding the transport of hydroxide ion through polymer films designed to function as alkaline exchange membranes in fuel cells or solid-state alkaline electrolytes in batteries is critical to optimizing these materials for high power performance in these devices. We use molecular dynamics (MD) simulations to interrogate solid polymer electrolytes comprising methylated poly(dimethylaminomethyl styrene) (“pDMAMS+”) bearing hydroxide counterions to counterbalance the positively charged quaternized amino moiety. We elucidate the effects on hydroxide ion diffusivity of ion exchange capacity (IEC, 1.5–5.2 mEq g−1), hydration level (λ = 0–3 water molecules per ion), and co-polymerization with 4-butylstyrene (0–75 mol %), a charge-neutral monomer with similar properties to DMAMS. At 300 K, MD simulations yield a hydroxide ion self-diffusion coefficient in anhydrous pDMAMS+ of ∼ 0.02 μm2 s−1 and a glass-transition temperature (Tg) of ∼ 800 K, values that remain relatively unchanged for films with up to 50% 4-butylstyrene content. Increasing the 4-butylstyrene content to 75% results in a polymer with a lower Tg, ∼500 K, and a corresponding three-fold increase in the hydroxide ion diffusion coefficient to ∼ 0.06 μm2 s−1. As expected, increasing the hydration level increases both hydroxide diffusivity and conductivity across the entire range of compositions. 4-butylstyrene content lowers the available ion content, eventually decreasing overall hydroxide conductivity. MD simulations provide a powerful method to estimate the ion and co-monomer contents that will maximize hydroxide conductivity for a given range of polymer compositions and hydration, greatly reducing the need to synthesize and test the full range of compositions experimentally.

Nickel-based heterogeneous catalysts are economical alternatives to traditional Pt or Au-based materials, but their specific activity and stability fall short of these precious metals. Many questions remain regarding the active Ni phase for CO oxidation and how the supporting oxide affects its activity and stability under operating conditions. We demonstrate that CeO2 aerogel-supported Ni(OH)(2) nanoparticles (NPs) show superior activity compared to Ni(OH)(2) NPs supported by commercial, nanometric CeO2 powder or TiO2 aerogels. Ex situ X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy reveal that intimate contact between Ni(OH)2 NPs and the bonded nanoparticulate CeO2 network prevents the conversion to NiO seen with larger aerogel-supported aggregates of Ni(OH) 2 NPs and unsupported Ni(OH)(2) NPs. The best stability and activity per mole of Ni is achieved at 2.5 wt % Ni(OH)(2) on the CeO2 aerogel, which converts 95% of CO at 200 degrees C and maintains activity after 12 h of continuous reaction under dry or humid feedstreams. Computational analysis indicates that CO has far lower adsorption energy on Ni(OH)(2) compared to NiO, resulting in less poisoning of the active surface sites.

Current-generated spin arising from spin-momentum locking in topological insulator (TI) surface states has been shown to switch the magnetization of an adjacent ferromagnet (FM) via spin-orbit torque (SOT) with a much higher efficiency than heavy metals. However, in such FM/TI heterostructures, most of the current is shunted through the FM metal due to its lower resistance, and recent calculations have also shown that topological surface states can be significantly impacted when interfaced with an FM metal such as Ni and Co. Hence, placing an insulating layer between the TI and FM will not only prevent current shunting, therefore minimizing overall power consumption, but may also help preserve the topological surface states at the interface. Here, we report the van der Waals epitaxial growth of β-phase In2Se3 on Bi2Se3 by molecular beam epitaxy and demonstrate its spin sensitivity by the electrical detection of current-generated spin in Bi2Se3 surface states using a Fe/In2Se3 detector contact. Our density functional calculations further confirm that the linear dispersion and spin texture of the Bi2Se3 surface states are indeed preserved at the In2Se3/Bi2Se3 interface. This demonstration of an epitaxial crystalline spin-sensitive barrier that can be grown directly on Bi2Se3, and verification that it preserves the topological surface state, is electrically insulating and spin-sensitive, is an important step toward minimizing overall power consumption in SOT switching in TI/FM heterostructures in fully epitaxial topological spintronic devices.

A scalable new method for the synthesis of borosulfate compounds in sulfuric acid providing control over product crystallite size is reported as an alternative to traditional methods requiring slow growth from oleum. This new synthetic approach is used to prepare three isostructural, 1D borosulfates: one containing only ammonium cations, another containing only potassium cations, and the third sample with a solid solution of 1:1 ammonium–potassium. Proton conduction in polycrystalline pellets of these borosulfate electrolytes is compared by electrochemical impedance spectroscopy (EIS) and ab initio molecular dynamics (AIMD) simulations. For a given cation (e.g., NH 4 + ), conductivity decreases by three orders of magnitude with decreasing particle size while maintaining constant activation energy, indicating that proton conduction is not primarily a grain‐boundary process. AIMD simulations show that excess proton mobility in K[B(SO 4 ) 2 ] is in line with that of NH 4 [B(SO 4 ) 2 ], being a backbone (not cation) mediated process. Although K[B(SO 4 ) 2 ] exhibits higher activation energy (60.6 ± 2.0 kJ mol −1 ) than NH 4 [B(SO 4 ) 2 ] (33.8 ± 1.0 kJ mol −1 ), at 200 °C it achieves comparable conductivity to NH 4 [B(SO 4 ) 2 ] samples, which is attributable to hydrolytic B–O–H defects being the common source of mobile protons in these materials.

Achieving both high energy and power density, two traditionally opposed battery metrics, requires moving away from the 200+ years-old 2D layered battery configuration to a three-dimensional all solid-state battery (3D SSB) configuration. The enhanced power and energy benefits bestowed by a 3D SSB design have been demonstrated in the Li-ion 3D SSB literature. 1 However, due to limitations in thermal and electronic conductivity of Li-Ion active materials, 3D Li-ion SSBs are limited to microscale dimensions. A potential means around this limitation is to switch to conductive metal electrodes such as Zn and Ag, for which 3D architectures have been demonstrated. 2 In such a case, the remaining roadblock to a macroscale 3D SSB is the submicron-thick solid-state electrolyte, which requires a non-line-of-sight deposition method for incorporation into the complex 3D base electrode. Initiated chemical vapor deposition ( i CVD) is a non–line-of-sight method that is ideal for generating conformal polymer coatings on complex 3D architectures. We focus on polymers amenable to i CVD protocols that can be modified post-deposition to introduce anion conduction pathways that can facilitate Ag and Zn redox. Submicron-thick coatings of poly-dimethylaminomethylstyrene (pDMAMS) that are pinhole-free and electronically insulating on both 2D planar and complex 3D electrode architectures are prepared via i CVD. The pDMAMS coatings are rendered anion-conducting through a vapor-phase methylation process and subsequent ion exchange to yield desirable anion species (e.g., OH – , Br – , or HCO 3 – ). X-ray photoelectron spectroscopy, ATR-IR spectroscopy, and solid-state magic-angle spinning NMR spectroscopy confirm the structure of the pDMAMS film before and after quaternization, while atomic force microscopy and cyclic voltammetry with redox probes confirm conformality and absence of pinholes in the submicron film. With the use of cyclic voltammetry and AC electrochemical impedance spectroscopy, the electronic and ionic conductivities of the polymer films are measured before and after quaternization. Molecular dynamics simulations of pDMAMS as a function of anion and H2O content in the film are used to generate computational results (e.g., glass-transition temperature Tg, anion conductivity) for comparison to experimental results. 1. Long, J.W.; Dunn, B.; Rolison, D.R.; White, H.S. Chem. Rev. 2004, 104, 10, 4463–4492. 2. Parker, J.F.; Chervin, C.N.; Nelson, E.S.; Rolison, D.R.; Long, J.W. Energy Environ Sci. 2014, 7 , 1117-1124.

X-ray absorption spectroscopy (XAS) is a powerful technique for exploring the electronic and structural characteristics of battery materials. Historically, XAS measurements require synchrotron-based photon sources to achieve necessary sensitivity and energy control, but with breakthroughs in X-ray optics, laboratory-based XAS systems are now available on the commercial market. The Chemistry Division at the Naval Research Laboratory recently acquired an easyXAFS™ system, a laboratory-scale spectrometer that is capable of collecting XANES (X-ray Absorption Near-Edge Spectroscopy) and EXAFS (Extended X-ray Absorption Fine Structure) measurements in the 5–18 keV energy window. This energy range covers K-edge absorptions for the first-row transition metals that are of primary interest for electrochemical energy storage. In order to demonstrate the utility of such a laboratory-based XAS, we perform operando measurements on pouch-cell batteries containing the common lithium-ion battery cathode, LiFePO 4 (LFP; lithium iron phosphate), tracking Fe oxidation state and bonding environment as a function of state-of-charge. X-ray absorption spectra collected with the easyXAFS™ compare favorably to those from prior investigations of LFP cells analyzed at synchrotron sources [1]. In parallel with XAS measurements, we perform DFT (Density Functional Theory) computation of the LFP structure. Calculations of LFP show that hole-polaron formation during charging alters the local environment around the Fe ion, decreasing the Fe–O bond length. Bond contraction increases with the addition of the Hubbard "U", which also increases the valence difference (formally 2 + /3 + ). We further refine the computational model for the LFP system by tuning the DFT input parameter “U” to correlate with experimental XAS data. [1] C. T. Love, A. Korovina, C. J. Partridge, K. E. Swider-Lyons, M. E. Twigg, and D. E. Ramaker, J. Electrochem. Soc. 160 (2013) A3153.

Disordered vanadium ferrite (VFe2Ox) materials exhibit promising performance for electrochemical energy-storage applications such as rechargeable lithium-ion batteries.1,2 We employ an epoxide-promoted sol–gel reaction of iron chloride and vanadium isopropoxide to form nanostructured vanadium ferrite gels. Subsequent supercritical-CO2 extraction of the pore fluid yields high surface–area aerogels. Heat treatment under either O2-containing or inert atmosphere yields disordered or nanocrystalline variants, respectively. Electroinactive metal cations such as aluminum, zinc, and zirconium are substituted during the initial sol–gel synthesis to alter the local electronic environment of VFe2Ox. The resulting series of native and substituted VFe2Ox materials are evaluated as powder-composite cathodes versus lithium metal in coin cells with conventional nonaqueous lithium-ion electrolyte. We correlate such critical battery-performance parameters as total specific capacity, high-rate capability, and cycle life as a function of MVFe2Ox composition and its degree of structural order/disorder. In-lab X-ray absorption spectroscopy also provides important information on metal oxidation state and element-specific coordination for these VFe2Ox aerogels, including during operando electrochemical lithiation/delithiation. In parallel with experimental advancements, calculations on VFe2Ox reveal that V incorporation into the defect-induced spinel structure occurs at tetrahedral sites. Further, both disorder of vacancies and Fe/V tetrahedral occupation lower the overall energy, opening an electronic energy gap that establishes the redox sequence during lithiation. N. Chervin, J. S. Ko, B. W. Miller, L. Dudek, A. N. Mansour, M. D. Donakowski, T. Brintlinger, P. Gogotsi, S. Chattopadhyay, T. Shibata, J. F. Parker, B. P. Hahn, D. R. Rolison, and J. W. Long, J. Mater. Chem. A 3, 12059 (2015). C. N. Chervin, R.H. DeBlock, J. F. Parker, B. M. Hudak, N. L. Skeele, J. S. Ko, D. R. Rolison, and J. W. Long, RSC Adv. 11, 14495 (2021).