Aqueous Zn/MnO2 batteries (AZMOB) with mildly acidic electrolytes hold promise as potential green grid-level energy storage solutions for clean power generation. Mechanistic understanding is critical to advance capacity retention needed by the application but is complex due to the evolution of the cathode solid phases and the presence of dissolved manganese in the electrolyte due to a dissolution–deposition redox process. This work introduces operando multiphase extended X-ray absorption fine structure (EXAFS) analysis enabling simultaneous characterization of both aqueous and solid phases involved in the Mn redox reactions. The methodology was successfully conducted in multiple electrolytes (ZnSO4, Zn(CF3SO3)2, and Zn(CH3COO)2) revealing similar manganese coordination environments but quantitative differences in distribution of Mnn+ species in the solid and solution phases. Complementary Raman spectroscopy was utilized to identify the less crystalline Mn-containing products formed under charge at the cathodes. This was further augmented by transmission electron microscopy (TEM) to reveal the morphology and surface condition of the deposited solids. The results demonstrate an effective approach for bulk-level characterization of poorly crystalline multiphase solids while simultaneously gaining insight into the dissolved transition-metal species in solution. This work provides demonstration of a useful approach toward gaining insight into complex electrochemical mechanisms where both solid state and dissolved active materials are important contributors to redox activity.

interface was shown to be tunable by an electric-field effect, [10,11] leading to the discovery of gate-tunable exotic properties such as superconductivity, [11][12][13][14] magnetism, [15] and Rashba interaction, [16][17][18] which can be exploited in novel electronic and spintronic devices. [19] The intriguing conductivity arising between LAO and STO-both of which are wide band gap insulators with band gaps of 5.6 and 3.2 eV, respectively-was initially explained by the polar catastrophe model. [4,20] According to this model, a charge of 0.5 e − per square STO lattice parameter is transferred from the LAO surface to the STO side of the interface to prevent the electrical potential from diverging due to the polar stacking of LaO + and AlO 2 − layers. Figure 1a illustrates this behavior, in which a downward bending of STO bands near the interface creates a narrow potential well that accommodates and confines the transferred charge at the interface, forming the 2DEG. However, numerous reports have proposed alternative explanations for the origin of the 2DEG, including charge doping by oxygen vacancies and cation intermixing. [21][22][23][24][25][26] Interestingly, angle-resolved photoemission spectroscopy (ARPES) studies showed that a similar 2DEG can be stabilized on the bare surface of STO (001) cleaved under ultrahigh vacuum (UHV) conditions following ultraviolet (UV)-light irradiation. [27][28][29] The 2DEG in this case is an electron accumulation layer that screens the positively charged oxygen vacancy defects ( O 2 V + or O V ⋅⋅ in Kröger-Vink notation) formed near the surface. The positively charged oxygen vacancies donate charge (e − ) while also inducing downward band bending at the STO surface, providing a confining potential well for the doped electrons. This is illustrated schematically in Figure 1b and also in Figure 1c, where the 2DEG is shown to form from Ti 3d t 2gderived quantized states (subbands).Recent studies have employed a variety of techniques to generate a 2DEG on the STO surface, also based on oxygen vacancy formation, including in situ sputtering, [30] vacuum annealing, [31,32] and metal deposition. [33] However, the quantitative relationship between the surface and bulk electronic structures remains unclear in some of these studies, especially given that n-type conducting (Nb-doped) STO substrates are often used to permit ARPES measurements. [30][31][32] In these The emergence of a 2D electron gas (2DEG) on the (001) surface of oxygendeficient strontium titanate (SrTiO 3−δ ) is investigated. Using in situ soft X-ray spectroscopy and effective mass modeling, a series of quantitative band diagrams are developed to describe the evolution of near-surface and bulk carrier concentrations, downward band bending, and Fermi level along a lateral gradient of oxygen vacancies formed on SrTiO 3−δ by direct-current resistive heating under ultrahigh vacuum conditions. Electrons are accumulated over a 3 nm region near the surface, confined within a potential well with saturated 300 meV downward band be...

Gadolinium scandate (GdScO) has been synthesized at 300 °C through the decomposition of a mixed cation hydroxide hydrogel in a humid environment. Increasing the reaction temperature produced larger particles that better adopted the Wulff shape. A lack of water vapor during the synthesis caused the solid network of the hydrogel to collapse upon heating so an amorphous xerogel was produced. Water vapor in the system imbibed the hydrogel and allowed for greater diffusion of the atomic species to allow for crystallization into the perovskite phase at temperatures lower than typical sol-gel processes. Temperatures less than 300 °C, or an excess of water vapor, promoted the formation of Gd(OH) and ScOOH in addition to or in lieu of GdScO.

A general approach to the formation of well-faceted nanoparticles is discussed and successfully applied to the production of several rare-earth scandates. Two steps were used, with higher temperatures first to nucleate the perovskite phase, followed by lower temperatures to smooth the particle surfaces. Exploiting these two different regimes led to smaller nanoparticles with more faceting. This general approach may be tailored to other material systems as a step towards producing shape-controlled nanoparticles for a desired application.

There has been extensive work on the equilibrium shape of isolated nanoparticles with internal boundaries and also single crystals on substrates. Surprisingly, almost shockingly, there has been very little work on the equilibrium shape of particles with internal boundaries on substrates. Here, the general solution is given for the configuration of particles containing twin and other grain boundaries on a flat substrate, which can be applied to any polycrystalline or multiphase nanoparticle configuration. The solution is based upon combining the established modified Wulff construction that has been extensively validated for twinned particles with the Winterbottom construction for single particles on a substrate. The solution is illustrated for the specific case of five-fold multiply twinned particles (MTPs). Good agreement is observed between both existing experimental data in the literature as well as some experimental data included within this work.

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Some catalytic oxide supports are more equal than others, with numerous variable properties ranging from crystal symmetry to surface chemistry and electronic structure. As a consequence, it is often very difficult to determine which of these act as the driver of performance changes observed in catalysis. In this work, we hold many of these variable properties constant with structurally similar LnScO3 (Ln = La, Sm, and Nd) nanoparticle supports with cuboidal shapes and a common Sc-rich surface termination. Using CO oxidation over supported Au nanoparticles as a probe reaction, we observe higher activation energy and a slower rate using NdScO3 as the support material. This change is found to correlate to the strength of CO2 binding to the support surface, identified by temperature-programmed desorption measurements. The change is due to differences in the 4f electrons of the lanthanide cations, the cations’ Lewis acidity, and the inductive effect they impose.