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In this contribution, we combined electrochemical cycling and X-ray photoelectron spectroscopy (XPS) to understand the nonpassivating behavior of the solid electrolyte interphase (SEI) on Si anodes during the first cycles. Based on galvanostatic measurements, we show that the irreversible capacity loss is reduced after the first cycle, and it stays almost constant from the second cycle onwards. XPS was used to determine the root causes of the Coulombic inefficiency, showing that the rate of decomposition of the organic solvents strongly decreased after the first cycle, whereas the rate of salt decomposition is almost unchanged between cycles. We determine that the inhibition of the decomposition reaction of the organic solvent is responsible for the lower Coulombic loss during the second electrochemical cycle in comparison to the first, whereas the nonpassivating behavior toward the salt decomposition is one of the main causes of capacity loss upon cycling. We further revisit the role of cracking in contributing to capacity loss. Whereas high volumetric expansion remains an issue plaguing the performance of Si anodes, our chronoamperometry studies reveal that the SEI formed on Si anodes does not passivate even when the electrode is fully expanded, and no additional surface is exposed. Overall, our work establishes the need to address the chemical and electrochemical instability of the SEI on the Si anode in addition to the more notorious issue of cracking.

Lepidocrocite-type titanates that reversibly intercalate sodium ions at low potentials (∼0.6 V vs Na/Na+) are promising anode candidates for sodium-ion batteries. However, large amounts of carbon additives are often used to improve their electrical conductivity and overcome poor cycling performance in the electrode composites. To ameliorate electronic transport issues of lepidocrocite titanate (K0.8Ti1.73Li0.27O4, KTL) in sodium-ion batteries, we have designed and synthesized heterostructures of exfoliated lepidocrocite-type titanium oxide (LTO) nanosheets with alternating carbon layers via a solution-based self-assembly approach. Positively charged dopamine (Dopa) was used as the carbon precursor and intercalated between negatively charged exfoliated titania nanosheets through electrostatic interaction. Dopa-intercalated LTO was then annealed under argon to form conductive carbon layers between titania sheets. The carbon content in the heterostructures was controlled by modifying the self-assembly conditions (i.e., pH, stirring duration, and Dopa-to-LTO ratio). Electrodes were prepared using carbonized heterostructures (LTO-C) without adding more carbon to the composites and tested in sodium half-cell configurations. Higher capacities and improved capacity retention over 250 cycles and lower impedance were observed, as the carbon content of LTO-C heterostructures was increased from 0% (LTO nanosheets) to 30%. These results indicate that the self-assembly approach for 2D heterostructured electrode materials is a promising strategy to overcome electronic transport limitations of layered transition-metal oxides and improve their electrochemical performance for next-generation energy storage applications.

Alloying anodes such as silicon are of great interest for lithium-ion batteries due to their high lithium-ion storage capacities, but have only seen minimal commercial deployment due to their limited calendar life. This has been attributed to an intrinsically unstable solid electrolyte interphase (SEI) that is aggravated by mechanical failure. An amorphous structure can mitigate lithiation strains, and amorphous alloys, or metallic glasses, often exhibit exceptional fracture toughness. Additional elements can be added to metallic glasses to improve passivation. Splat quenching was utilized to prepare an amorphous Al64Si25Mn11 Li-ion anode with a specific capacity >900 mAh g-1 that remains amorphous upon cycling. On this metallic glass electrode, parasitic electrolyte reduction is found to be much reduced in comparison to pure Si or Al, and comparable to that on Cu. The SEI is much thinner, more stable, and richer in fluorinated inorganic phases than the SEI formed on Si, while organic carbonate compounds such as lithium ethylene decarbonate (LiEDC) are notably absent. This study indicates that metallic glasses can become a viable new class of Li-ion anode materials with improved surface passivity.

The expectation to progress towards Terawatts production by solar technologies requires continuous development of new materials to improve efficiency and lower the cost of devices beyond what is currently available at industrial level. At the same time, the turnaround time to make the investment worthwhile is progressively shrinking. Whereas traditional absorbers have developed in a timeframe spanning decades, there is an expectation that emerging materials will be converted into industrially relevant reality in a much shorter timeframe. Thus, it becomes necessary to develop new approaches and techniques that could accelerate decision-making steps on whether further research on a material is worth pursuing or not. In this review, we will provide an overview of the photoemission characterization methods and theoretical approaches that have been developed in the past decades to accelerate the transfer of emerging solar absorbers into efficient devices.

Silicon is a promising alloying anode for lithium-ion batteries because of its high capacity and low cost. However, its use has been hampered by mechanical failure arising from the large volume change upon cycling and by an insufficiently stable solid electrolyte interphase (SEI). SEI formation depends on the Si surface, which is often an oxide (SiOx). In this study we compare three different Si surfaces using Si wafers: 1.3 nm native SiOx, 1.4 nm thermally grown SiO2, and a SiOx-free surface. The oxide-free surface showed the worst electrochemical performance, never exceeding 94% Coulombic efficiency (CE). It also exhibited the thickest SEI and the highest overpotential for lithiation, which correlated with uninhibited electrolyte reduction and the incorporation of P-F species into the SEI. The oxide-coated surfaces performed significantly better, demonstrating a CE above 99% beyond the second cycle, low overpotential for lithiation, and a thinner and more stable SEI. The oxides lower the onset potential for electrolyte reduction and yield an SEI with fewer P-F species. However, it was found that the CE with the native oxide surface decays from the fifth cycle onward and correlates with a resurgence of electrolyte reduction. A 1-2 nm thermal SiO2 coating is optimum for achieving a stable SEI that minimizes side reactions and sustains efficient cycling.

Ternary nitride semiconductors with wurtzite-derived crystal structures are an emerging class of materials for optoelectronic applications compatible with GaN and related III-V compounds. In particular, II-IV-V2 materials such as ZnSnN2 and ZnGeN2 have been very actively studied for applications in photovoltaics and light emitting devices. However, many other possible wurtzite-derived ternary nitrides have not been reported, and hence their optical and electrical properties remain unknown. Here, we report on Zn2SbN3-the first Sb-based nitride and a photoactive semiconductor. Surprisingly, Zn2SbN3 contains Sb in the highest (5+) oxidation state, and in the unusual tetrahedral coordination. This new Zn2SbN3 material has a solar-matched 1.6-1.7 eV band gap and shows near-band-edge room-temperature photoluminescence, demonstrating its promise as an optoelectronic semiconductor. Finally, Zn2SbN3 can be synthesized at low temperature under a wide range of processing conditions, despite being metastable according to theoretical calculations. All these results, as well as the band position measurements, indicate that Zn2SbN3 is a promising emerging semiconductor for applications as an absorber in photovoltaic-and photoelectrochemical solar cells.

Exploratory synthesis in new chemical spaces is the essence of solid-state chemistry. However, uncharted chemical spaces can be difficult to navigate, especially when materials synthesis is challenging. Nitrides represent one such space, where stringent synthesis constraints have limited the exploration of this important class of functional materials. Here, we employ a suite of computational materials discovery and informatics tools to construct a large stability map of the inorganic ternary metal nitrides. Our map clusters the ternary nitrides into chemical families with distinct stability and metastability, and highlights hundreds of promising new ternary nitride spaces for experimental investigation-from which we experimentally realized seven new Zn- and Mg-based ternary nitrides. By extracting the mixed metallicity, ionicity and covalency of solid-state bonding from the density functional theory (DFT)-computed electron density, we reveal the complex interplay between chemistry, composition and electronic structure in governing large-scale stability trends in ternary nitride materials.

We report on the theoretical prediction and experimental realization of new ternary zinc molybdenum nitride compounds. We used theory to identify previously unknown ternary compounds in the Zn-Mo-N systems, Zn3MoN4 and ZnMoN2, and to analyze their bonding environment. Experiments show that Zn-Mo-N alloys can form in broad composition range from Zn3MoN4 to ZnMoN2 in the wurtzite-derived structure, accommodating very large off-stoichiometry. Interestingly, the measured wurtzite-derived structure of the alloys is metastable for the ZnMoN2 stoichiometry, in contrast to the Zn3MoN4 stoichiometry, where ordered wurtzite is predicted to be the ground state. The formation of Zn3MoN4-ZnMoN2 alloy with wurtzite-derived crystal structure is enabled by the concomitant ability of Mo to change oxidation state from +VI in Zn3MoN4 to +IV in ZnMoN2, and the capability of Zn to contribute to the bonding states of both compounds, an effect that we define as "redox-mediated stabilization". The stabilization of Mo in both the +VI and +IV oxidation states is due to the intermediate electronegativity of Zn, which enables significant polar covalent bonding in both Zn3MoN4 and ZnMoN2 compounds. The smooth change in the Mo oxidation state between Zn3MoN4 and ZnMoN2 stoichiometries leads to a continuous change in optoelectronic properties-from resistive and semitransparent Zn3MoN4 to conductive and absorptive ZnMoN2. The reported redox-mediated stabilization in zinc molybdenum nitrides suggests there might be many undiscovered ternary compounds with one metal having an intermediate electronegativity, enabling significant covalent bonding, and another metal capable of accommodating multiple oxidation states, enabling stoichiometric flexibility.

Compared to oxides, the nitrides are relatively unexplored, making them a promising chemical space for novel materials discovery. Of particular interest are nitrogen-rich nitrides, which often possess useful semiconducting properties for electronic and optoelectronic applications. However, such nitrogen-rich compounds are generally metastable, and the lack of a guiding theory for their synthesis has limited their exploration. Here, we review the remarkable metastability of observed nitrides, and examine the thermodynamics of how reactive nitrogen precursors can stabilize metastable nitrogen-rich compositions during materials synthesis. We map these thermodynamic strategies onto a predictive computational search, training a data-mined ionic substitution algorithm specifically for nitride discovery, which we combine with grand-canonical DFT-SCAN phase stability calculations to compute stabilizing nitrogen chemical potentials. We identify several new nitrogen-rich binary nitrides for experimental investigation, notably the transition metal nitrides Mn3N4, Cr3N4, V3N4, and Nb3N5, the main group nitride SbN, and the pernitrides FeN2, CrN2, and Cu2N2. By formulating rational thermodynamic routes to metastable compounds, we expand the search space for functional technological materials beyond equilibrium phases and compositions.

Palladium nanoparticles stabilised by aniline modified polymer immobilised ionic liquid is a remarkably active catalyst for the hydrogenation of CO2 to formate; the initial TOF of 500 h−1 is markedly higher than either unmodified catalyst or its benzylamine and N,N-dimethylaniline modified counterparts and is among the highest to be reported for a PdNP-based catalyst. [ABSTRACT FROM AUTHOR]

Zinc tin nitride ( ZnSnN 2) is an emerging ternary nitride semiconductor studied for applications in solar cells, light-emitting diodes, and other optoelectronic devices. For all of these applications, the charge carrier mobility is an important property. However, the dominant electron scattering mechanisms in ZnSnN 2 are unclear, especially in the presence of oxygen that is often incorporated during thin film sputter deposition of this material. In addition, there are no experimental reports on the concentration of defects in such polycrystalline sputtered zinc tin oxynitride Zn 1 + x Sn 1 − x N 2 − 2 x O 2 x (ZTNO) thin films. Here, we address both of these questions using temperature-dependent Hall effect measurements of sputtered ZTNO thin films as a function of Zn composition and O content. The measured temperature dependence of the mobility is fitted to scattering on ionized and neutral defects and to grain boundary scattering. The results indicate that ZTNO is a heavily compensated semiconductor, with a high density of neutral defects dominating the electron scattering processes. First principles theoretical calculations indicate that these neutral defects are likely to originate from the abundant Zn Sn − 2 O N complexes in the ZTNO material. Overall, these results establish the dominant electron scattering mechanisms in polycrystalline sputtered ZTNO and help position this material for future use in optoelectronic devices. [ABSTRACT FROM AUTHOR]

p-Type transparent conductors and semiconductors still suffer from remarkably low performance compared to their more widespread n-type counterparts, despite extensive investigation into their development. In this contribution, we present a comparative study on the defect chemistry of potential p-type transparent conducting oxides Mg-doped and Ni-doped Cr2O3. Conductivities as high as 28 S cm−1 were achieved by Ni-doping. By benchmarking crystallography and spectroscopy characterization against density functional theory calculations, we show that the incorporation of Ni into Cr2O3 contributes to the composition of the valence band, making the formed holes more delocalized, while Mg states do not interact with the valence band in Mg-doped Cr2O3. Furthermore, it is experimentally proven that Ni has a higher solubility in Cr2O3 than Mg, at least in the highly non-thermodynamic deposition conditions used for these experiments, which directly translates into a higher acceptor concentration. The combination of these two effects means that Ni is a more effective acceptor in Cr2O3 than Mg and explains the improved conductivity observed for the former. [ABSTRACT FROM AUTHOR]

Palladium nanoparticles stabilised by aniline modified polymer immobilised ionic liquid is a remarkably active catalyst for the hydrogenation of CO 2 to formate; the initial TOF of 500 h -1 is markedly higher than either unmodified catalyst or its benzylamine and N , N -dimethylaniline modified counterparts and is among the highest to be reported for a PdNP-based catalyst.

Silicon is a promising anode material for lithium-ion batteries because of its high capacity, but its widespread adoption has been hampered by a low cycle life arising from mechanical failure and the absence of a stable solid-electrolyte interphase (SEI). Understanding SEI formation and its impact on cycle life is made more complex by the oxidation of silicon materials in air or during synthesis, which leads to SiO x coatings of varying thicknesses that form the true surface of the electrode. In this paper, the lithiation of SiO 2 -coated Si is studied in a controlled manner using SiO 2 coatings of different thicknesses grown on Si wafers via thermal oxidation. SiO 2 thickness has a profound effect on lithiation: below 2 nm, SEI formation followed by uniform lithiation occurs at positive voltages versus Li/Li + . Si lithiation is reversible, and SiO 2 lithiation is largely irreversible. Above 2 nm SiO 2 , voltammetric currents decrease exponentially with SiO 2 thickness. For 2-3 nm SiO 2 , SEI formation above 0.1 V is suppressed, but a hold at low or negative voltages can initiate charge transfer whereupon SEI formation and uniform lithiation occur. Cycling of Si anodes with an SiO 2 coating thinner than 3 nm occurs at high Coulombic efficiency (CE). If an SiO 2 coating is thicker than 3-4 nm, the behavior is totally different: lithiation at positive voltages is strongly inhibited, and lithiation occurs at poor CE and is highly localized at pinholes which grow over time. As they grow, lithiation becomes more facile and the CE increases. Pinhole growth is proposed to occur via rapid transport of Li along the SiO 2 /Si interface radially outward from an existing pinhole, followed by the lithiation of SiO 2 from the interface outward.

One of the current challenges faced by material scientists is the development of a p-type transparent conducting oxide with levels of optical transparency and electronic conductivity to equal those of the universally n-type industry leaders such as Sn-doped In2O3. The discovery of a p-type analogue would allow for the combination of both polarities into a heterojunction, accessing the potential for transparent electronics. In this study, an insulating material, Cr2O3, is investigated both experimentally and computationally to determine if it is a viable p-type host matrix as has been recently proposed in the literature. The geometric and electronic structure are examined by high resolution x-ray diffraction, x-ray photoelectron spectroscopy, and periodic density functional theory (specifically, PBE  +  U). By incorporating Mg and performing a comprehensive defect analysis, the dominant intrinsic and extrinsic carriers in the material are determined, and it is shown that Cr2O3 has the potential to display p-type conductivity when appropriately doped.