Sn Cations Research Articles

Mixed Tin Valence in the Tin(II/IV)-Nitridophosphate Sn3P8N16.

Sn3P8N16 combines the structural versatility of nitridophosphates and Sn within one compound. It was synthesized as dark gray powder in a high-pressure high-temperature reaction at 800 °C and 6 GPa from Sn3N4 and P3N5. The crystal structure was elucidated from single-crystal diffraction data (space group C2/m (no. 12), a=12.9664(4), b=10.7886(4), c=4.8238(2) Å, β=109.624(1)°) and shows a 3D-network of PN4 tetrahedra, incorporating Sn in oxidation states +II and +IV. The Sn cations are located within eight-membered rings of vertex-sharing PN4 tetrahedra, stacked along the [001] direction. A combination of solid-state nuclear magnetic resonance spectroscopy, 119Sn Mössbauer spectroscopy and density functional theory calculations was used to confirm the mixed oxidation of Sn. Temperature-dependent powder X-ray diffraction measurements reveal a low thermal expansion of 3.6 ppm/K up to 750 °C, beyond which Sn3P8N16 starts to decompose.

Dynamic Lone Pairs and Fluoride-Ion Disorder in Cubic-BaSnF4.

Introducing compositional or structural disorder within crystalline solid electrolytes is a common strategy for increasing their ionic conductivity. (M,Sn)F2 fluorites have previously been proposed to exhibit two forms of disorder within their cationic host frameworks: occupational disorder from randomly distributed M and Sn cations and orientational disorder from Sn(II) stereoactive lone pairs. Here, we characterize the structure and fluoride-ion dynamics of cubic BaSnF4, using a combination of experimental and computational techniques. Rietveld refinement of the X-ray diffraction (XRD) data confirms an average fluorite structure with {Ba,Sn} cation disorder, and the 119Sn Mössbauer spectrum demonstrates the presence of stereoactive Sn(II) lone pairs. X-ray total-scattering PDF analysis and ab initio molecular dynamics simulations reveal a complex local structure with a high degree of intrinsic fluoride-ion disorder, where 1/3 of fluoride ions occupy octahedral "interstitial" sites: this fluoride-ion disorder is a consequence of repulsion between Sn lone pairs and fluoride ions that destabilizes Sn-coordinated tetrahedral fluoride-ion sites. Variable-temperature 19F NMR experiments and analysis of our molecular dynamics simulations reveal highly inhomogeneous fluoride-ion dynamics, with fluoride ions in Sn-rich local environments significantly more mobile than those in Ba-rich environments. Our simulations also reveal dynamical reorientation of the Sn lone pairs that is biased by the local cation configuration and coupled to the local fluoride-ion dynamics. We end by discussing the effect of host-framework disorder on long-range diffusion pathways in cubic BaSnF4.

Study of the structural, optical, and electrical characteristics of Sr2Sn1.6In0.2Cu0.2O6-δ mixed ionic-electronic conductor

A solid state route is used to ensure the synthesis of the oxygen-deficient, mixed-valence double perovskite Sr2Sn1.6In0.2Cu0.2O6-δ. This novel mixed ionic-electronic conductor's (MIEC) structural, morphological, optical, and electrical characteristics were investigated. The arrangement of the Sn, In and Cu cations shows discrete tin/copper-oxygen and tin/indium-oxygen layers in a structure characterized as a √2ap x √2ap x 2ap deformed perovskite, and Rietveld refinement of the XRD data reveals a monoclinic phase under P21/c space group. The elemental analysis with EDX permitted the identification of the elemental composition of the sample, and the average grain size as measured with a scanning electron microscope (SEM) is around 230 nm. Sn–O, In–O, and Cu–O vibrations detected by FTIR spectroscopy analysis near 581 cm-1 further confirm the desordered nature of this perovskite structure. The calculated bandgap of 3.35eV reinforcing the semiconducting nature of the sample increases the potential of studied compound as MIEC. The complex impedance spectroscopy technique was employed in the dielectric investigation and electrical conductivity determination of the sample at different temperatures and frequencies. Nyquist diagrams (- Z″ versus Z′) showed a relaxation of the Cole-Cole type that was not Debye-like. The Correlated Barrier Hopping (CBH) model is the suitable to represent the conductivity of the compound, with two separate behaviors beyond and below T = 260 °C. The conductivity dependence vs temperature follows Arrhenius' law in the two just mentioned temperature domains, with activation energies 0.82 and 0.31 eV respectively.

Sn-alloying of BaZrS3 chalcogenide perovskite as eco-friendly material for photovoltaics: First principle insight

This paper focuses mainly on investigating the effects of partial substitution of Zr cations by Sn cations on the structural, opto-electronic and photovoltaic properties of the chalcogenide perovskite BaZr1−xSnxS3 (x ≤ 0.25). For this purpose, we have used first-principles calculations. Through this approach, we show that the lattice constants and the gap energy (Eg) decrease as the Sn content (x) increases. Furthermore, the Eg values obtained decrease from 1.55 to 0.96 eV. our calculated decomposition energies suggest that it will be difficult to synthesize BaZr1−xSnxS3 alloys for higher Sn contents under thermal equilibrium conditions. Also, the calculated dielectric functions and absorption coefficient show a red shift for higher Sn content. Besides, our theoretical approach, indicate that, the compound BaZr0.815Sn0.125S3 presents a maximum photovoltaic efficiency η of 32.5% for a thickness L = 500 nm, which is close to the Shockley–Queisser limit (33.7%), which makes it a promising candidate for the production of high power conversion efficiency solar cells with ultra-thin absorption layers. sulfide alloys for lead-free perovskite solar cells.

Conversion‐Type Organic‐Inorganic Tin‐Based Perovskite Cathodes for Durable Aqueous Zinc‐Iodine Batteries

AbstractAqueous metal‐iodine batteries have recently attracted widespread attention, but their intrinsic issues such as the undesired shuttle effect and volatility of iodine hinder their reliable long‐term performance. Herein, organic–inorganic MXDA2SnI6 (MXDA2+ denotes protonated m‐xylylenediamine cation) perovskite microcrystals with a zero‐dimensional arrangement of octahedral perovskite units offering high content of elemental iodine (46 wt% in the whole cathode) are proposed as conversion‐type cathode materials for aqueous ZnI2 batteries. Iodide anions deliver reliable electrochemical activity and are effectively immobilized on the cathode to relieve the shuttle process by both physical steric hindrance and chemical adsorption offered by long‐chain organic matrix and the presence of B‐site Sn(II) cations in the MXDA2SnI6 perovskite, respectively. Moreover, the formation of triiodide anions is alleviated in favor of a significant proportion of pentaiodide ions during the end of the charging process, enabled by increased formation energy of I3− and effective confinement via SnI…I halogen bonds and NH…I hydrogen bonds, as revealed by density functional theory calculations. As a result, rechargeable aqueous ZnI2 batteries are realized that achieve a champion capacity of over 206 mAh g−1I at 0.5 A g−1 (close to the theoretical limit), and outstanding rate capability with a capacity retention of 87% at 3 A g−1. Suppressed shuttle of polyiodide anions endows aqueous ZnI2 batteries with prolonged cyclic stability, namely high capacity retention of 95% after 5700 cycles at 1 A g−1. This study promotes the development of high‐performance cathode materials for metal‐I2 batteries by revealing the feasibility of using ionic perovskites as conversion‐type cathodes.

Utilization of a Tris(carbene)borate Ligand for Umpolung Reactivity of a Nucleophilic Tin(II) Cation Salt.

We show that a tris(carbene)borate (TCB) ligand, namely [PhB(tBuIm)3]- ([PhB(tBuIm)3]- = phenyltris(3-tert-butylimidazol-2-ylidene)borato), is capable of stabilizing an unprecedented nucleophilic Sn(II) cation salt. Unlike known Sn(II) cations, the strong electron-donating ability of [PhB(tBuIm)3]- makes the cationic tin atom electron-rich, σ-donating yet slightly π-accepting, which allows for the ensuing facile oxidation with o-chloranil and S8 as well as coordination with coinage metals. The former oxidations give the Sn(IV) cation salts, while the latter reactions produce the metal complexes. The electronic structures of these species are thoroughly probed by quantum chemical computations. These results uncover an added role for TCB ligands in isolating unprecedented p-block species.

Hydrogen-Doping-Enabled Boosting of the Carrier Mobility and Stability in Amorphous IGZTO Transistors.

This study investigated the effect of hydrogen (H) on the performance of amorphous In-Ga-Zn-Sn oxide (a-In0.29Ga0.35Zn0.11Sn0.25O) thin-film transistors (TFTs). Ample H in plasma-enhanced atomic layer deposition (PEALD)-derived SiO2 can diffuse into the underlying a-IGZTO film during the postdeposition annealing (PDA) process, which affects the electrical properties of the resulting TFTs due to its donor behavior in the a-IGZTO. The a-In0.29Ga0.35Zn0.11Sn0.25O TFTs at the PDA temperature of 400 °C exhibited a remarkably higher field-effect mobility (μFE) of 85.9 cm2/Vs, a subthreshold gate swing (SS) of 0.33 V/decade, a threshold voltage (VTH) of -0.49 V, and an ION/OFF ratio of ∼108; these values are superior compared to those of unpassivated a-In0.29Ga0.35Zn0.11Sn0.25O TFTs (μFE = 23.3 cm2/Vs, SS = 0.36 V/decade, and VTH = -3.33 V). In addition, the passivated a-In0.29Ga0.35Zn0.11Sn0.25O TFTs had good stability against the external gate bias duration. This performance change can be attributed to the substitutional H doping into oxygen sites (HO) leading to a boost in ne and μFE. In contrast, the beneficial HO effect was barely observed for amorphous indium gallium zinc oxide (a-IGZO) TFTs, suggesting that the hydrogen-doping-enabled boosting of a-IGZTO TFTs is strongly related to the existence of Sn cations. Electronic calculations of VO and HO using density functional theory (DFT) were performed to explain this disparity. The introduction of SnO2 in a-IGZO is predicted to cause a conversion from shallow VO to deep VO due to the lower formation energy of deep VO, which is effectively created around Sn cations. The formation of HO by H doping in the IGZTO facilitates the efficient connection of atomic states forming the conduction band more smoothly. This reduces the effective mass and enhances the carrier mobility.

First-principles calculations of phosphorus-doped SnO2 transparent conducting oxide: Structural, electronic, and electrical properties

The structural and electronic properties of phosphorus-doped tin oxide (PTO) were investigated by density functional theory (DFT). The lattice parameters computed with the Perdew-Burke-Ernzerhof (PBE) functional were decreased as phosphorus (P) impurities were substituted for Sn cations. The band structure of PTO computed with the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional showed an optical energy bandgap widening effect, because of a large Moss-Burstein shift and a small exchange–correlation-induced bandgap narrowing. Also, the P impurities in SnO2 induced shallow donor P-3s states in the conduction band minimum near Fermi level. The electron effective mass of the systems was calculated to be 0.25 m0. DFT calculations also predicted a 5.9 × 1020 cm−3 electron density for PTO, which could increase the electrical conductivity of SnO2. These features make PTO a promising material for transparent conducting applications.

O,N,S-tris-chelating ligand scaffolds flanked with cyclohexyl or adamantyl substituents anchored with diorganotin(IV) moieties: synthesis, structures and cytotoxicity

The O,N,S-tris-chelating ligand, H2NSCN-N-C(H)ArO− constitutes an attractive scaffold in coordination chemistry and we have expanded this scaffold by installing an alkyl group of different steric hindrance. Thus, the ligand scaffolds containing O,N,S (Ln) differ with respect to the chemical link between the coordinating O atoms, which is either a phenol or a naphthol moiety and carrying a cyclohexyl or a adamantyl groups (L1, phenol and cyclohexyl; L2, naphthol and cyclohexyl; L3, phenol and adamantyl; L4, naphthol and adamantyl). Six novel diorganotin(IV)-Ln compounds 1–6 were synthesized and structurally characterized. The solid-state structures were deduced from single crystal X-ray diffraction data, and revealed the Sn(IV) cations adopting square pyramid (in 2, 3 and 4) or trigonal bipyramid (in 1, 5 and 6) geometries with coordination spheres comprising κ-N,O,S (κ-N,S in 1) ligand chelators and two methyl or phenyl groups (plus a hydrosulfide in 1) co-ligands. Solution state characterizations were achieved by detailed 1H, 13C, 15N and 119Sn NMR analysis including selected 2D experiments. In vitro cytotoxic activities of the compounds were assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay against human histiocytic lymphoma U-937 cells. The IC50 values revealed better activities of diphenyltin(IV) compounds 4–6 as compared to the respective pro-ligands and doxorubicin. More importantly, compounds 4–6 demonstrated maximum inhibition in U-937 cells (IC50 = 0.47–0.99 μM), with negligible effect on human peripheral blood mononuclear cells (PBMC). Compounds 4–6 effectively inhibited cell viability event, which was confirmed by detecting cytotoxicity, Live & Dead and Lactate dehydrogenase (LDH) release assays.

Structure, Stability, and Photocatalytic Activity of a Layered Perovskite Niobate after Flux-Mediated Sn(II) Exchange.

A new strategy to incorporate the Sn(II) cation and its stereoactive lone pair into the structure of a photocatalytic oxide has been achieved by leveraging the asymmetric coordination environments within the (111)-oriented perovskite-type layers of Ba5Nb4O15. This layered perovskite represents one of the few known photocatalysts capable of efficiently splitting water, but its activity is restricted to ultraviolet radiation owing to its large band gap. By reacting this layered niobate at 350 °C for 24 h within a low-melting SnCl2/SnF2 salt, the new (Ba1-xSnx)Nb4O15 (x = 0-0.5; P3̅m1; a = 5.79650(5) Å, c = 11.79288(8) Å; Z = 2) has been prepared in high purity with up to ∼50% Sn(II) cations. Statistical disordering of the Sn(II) cations was probed by neutron diffraction Rietveld refinements and found to occur predominantly over the asymmetric cation sites, Ba2 and Ba3, for the 40% Sn(II) composition of x = 0.4. An increasing Sn(II) amount significantly red-shifts the band gap (Eg) from 0% Sn for x = 0 (3.78 eV; ultraviolet, indirect) to 40% Sn for x = 0.4 (Eg = 2.35 eV; visible, indirect), as found by UV-vis diffuse reflectance. Density functional theory calculations show an increasing metastability, i.e., a thermodynamic instability toward decomposition to the simpler oxides SnO, Nb2O5, and SnNb2O6. A synthetic limit of ∼50% Sn(II) cations can be kinetically stabilized under these reaction conditions. For the highest Sn(II) amounts, photocatalytic rates are observed for the production of molecular oxygen from water of up to ∼77 μmol O2 h-1 g-1 (visible irradiation) and ∼159 μmol O2 h-1 g-1 (UV-vis irradiation), with apparent quantum yields of ∼0.35 and 0.52%, respectively. By comparison, pure Ba5Nb4O15 exhibits no measurable photocatalytic activity under visible-light irradiation. Electronic structure calculations show that the decreased band gap stems from the introduction of the Sn(II) cations and the formation of a higher-energy valence band arising from the filled 5s2 valence orbitals. Thus, visible-light bandgap excitation occurs from electronic transitions predominantly involving the Sn(II) (5s2) to Nb(V) (4d0) cations. This study demonstrates the new and powerful utility of low-temperature Sn(II)-exchange reactions to sensitize layer-type oxide photocatalysts to the visible region of the solar spectrum, which is facilitated by exploiting their asymmetric cation environments.

Static and dynamic components of Debye-Waller coefficients in the novel cubic polymorph of low-temperature disordered Cu2ZnSnS4.

Cu2ZnSnS4 (CZTS) is an attractive material for sustainable photovoltaics and thermoelectrics, and several properties originate from its marked polymorphism. High-energy mechanical alloying is found to lead to a disordered phase that possesses a sphalerite-like cubic structure. This is investigated in detail with the aid of laboratory and synchrotron radiation X-ray diffraction, Raman spectroscopy, electron microscopy and ab initio molecular dynamics. The disordered cubic polymorph is preserved below 663 K. With thermal treatments above 663 K, the tetragonal kesterite phase forms, used here as a reference for structural and microstructural features. Particular attention is paid to the stacking arrangement: a significant fraction of twin faults was found in the disordered cubic samples, which then progressively annealed with domain growth and with the transition to the ordered tetragonal phase. This study also focuses on Debye-Waller coefficients, which were found to be considerably larger for the disordered cubic than the tetragonal sample. Indeed, disorder leads to an ∼1 Å2 upward shift through the temperature range 100-700 K, a feature confirmed by ab initio calculations, which points to a particularly high contribution from disordered Sn cations. This supports the general understanding that structural disorder introduces a temperature-independent static contribution to the atomic mean-square displacement. Debye-Waller coefficients are found to be a good measure of this disorder, known to have a critical effect on transport properties.

Interface-dependent activity and selectivity for CO2 hydrogenation on Ni/CeO2 and Ni/Ce0.9Sn0.1Ox

To study the importance of interface microstructure on reactivity for CO2 hydrogenation, Ni/CeO2, Ni/Ce0.9Sn0.1Ox and Ni/0.1SnO2-0.9CeO2 catalysts were prepared, whose support is pristine CeO2, Sn-doped CeO2-based solid solution, and the mixture of SnO2 and CeO2 in sequence with a Sn/Ce molar ratio of 1:9 in the latter two supports. The intrinsic activity of the catalysts for CO2 hydrogenation followed the order: Ni/CeO2 > Ni/0.1SnO2-0.9CeO2 > Ni/Ce0.9Sn0.1Ox. Ni/CeO2 and Ni/0.1SnO2-0.9CeO2 showed CH4 selectivity, while Ni/Ce0.9Sn0.1Ox CO selectivity. The strong interaction between Sn cations and Ni species in Ni/Ce0.9Sn0.1Ox resulted in the immigration of Sn cations to Ni species to form the Ni-O-Sn-O-Ce interface, distinctly differing from the Ni-O-Ce interface in Ni/CeO2 and the Ni-O-Ce plus Ni-O-Sn interfaces in Ni/0.1SnO2-0.9CeO2. The enrichment of Sn cations as acidic sites on the Ni/Ce0.9Sn0.1Ox surface decreased evidently the chemisorption of CO2 and inhibited the generation of HCO3*, thus inhibiting the formate path for CH4. Conversely, the presence of Sn cations in the interface favored the generation of carbonates, thus promoting CO yield. This work shows the activity and selectivity for CO2 hydrogenation are highly dependent on microstructure of an interface in oxide-supported Ni catalysts.

Understanding Ir(III) Photocatalyst Structure-Activity Relationships: A Highly Parallelized Study of Light-Driven Metal Reduction Processes.

High-throughput synthesis and screening methods were used to measure the photochemical activity of 1440 distinct heteroleptic [Ir(C^N)2(N^N)]+ complexes for the photoreduction of Sn(II) and Zn(II) cations to their corresponding neutral metals. Kinetic data collection was carried out using home-built photoreactors and measured initial rates, obtained through an automated fitting algorithm, spanned between 0-120 μM/s for Sn(0) deposition and 0-90 μM/s for Zn(0) deposition. Photochemical reactivity was compared to photophysical properties previously measured such as deaerated excited state lifetime and emission spectral data for these same complexes; however, no clear correlations among these features were observed. A formal photochemical rate law was then developed to help elucidate the observed reactivity. Initial rates were found to be directly correlated to the product of incident photon flux with three reaction elementary efficiencies: (1) the fraction of light absorbed by the photocatalyst, (2) the fraction of excited state species that are quenched by the electron donor, and (3) the cage escape efficiency. The most active catalysts exhibit high efficiencies for all three steps, and catalyst engineering requirements to maximize these elementary efficiencies were postulated. The kinetic treatment provided the mechanistic information needed to decipher the observed structure/function trends in the high-throughput work.

Resonant x-ray scattering method for measuring cation stoichiometry in BaSnO3 thin films

We develop a resonant scattering technique to measure cation stoichiometry of lanthanum-doped BaSnO3 (BSO) thin films on a DyScO3 substrate. Samples are grown by a hybrid molecular beam epitaxy method and display high room-temperature carrier mobilities. The measured thin films are grown with widely differing cation arrival rates, with Ba being evaporated from an elemental source and Sn from a SnO2 source. Differences in mobilities in these films may arise from differences in Ba/Sn cation stoichiometry. Owing to the similar scattering strength of the Ba and Sn cations, odd-order Bragg peaks of BSO are particularly sensitive to the material's cation stoichiometry, i.e., the Ba/Sn ratio. Sensitivity to cation stoichiometry is further enhanced using the technique of resonant x-ray scattering, which changes the scattering strength of a single element across the Ba L absorption edges. We determine that the Ba/Sn cation stoichiometry varies from unity by less than 1% for films of mobility ranging from 84.8 to 144 cm2/(V s) and conclude that the mobility of these films scales with film thickness and growth rate rather than stoichiometry.

Synthesis and stability of Sn(II)-containing perovskites: (Ba,SnII)HfIVO3 versus (Ba,SnII)SnIVO3

While Sn(II)-containing perovskite oxides have long drawn attention as Pb(II) substitutes in technologically-relevant dielectric materials, they are also highly thermodynamically unstable and potentially impossible to prepare. Investigations into the new flux-mediated syntheses of metastable Sn(II)-containing hafnate and stannate perovskites were aimed at understanding the key factors related to their synthesizability. The BaHfO3 perovskite was reacted with SnClF from 250 to 350 ​°C for 12–72 ​h, yielding an unprecedented Sn(II) concentration on the A-site of up to ~70 ​mol%, i.e., (Ba0.3Sn0.7)HfO3 in high purity. Elemental mapping using EDS shows the Sn(II) cations diffuse gradually throughout the crystallites, with two reaction cycles needed to give a nearly homogeneous distribution. In contrast, similar reactions with BaSnO3 and as little as 10 ​mol% Sn(II) result in decomposition to SnO, SnO2, and BaSnO3. The (Ba1-xSnx)HfO3 compositions exhibit a primary cubic perovskite structure (Pm3¯m; for x ​= ​1/3, 1/2 and 2/3) by powder X-ray diffraction (XRD) methods, with the Sn(II) cations substituted on the A-site. Total energy calculations show the thermodynamic instability versus the ground state (i.e., metastability) for (Ba1-xSnx)HfO3 increases with Sn(II) substitution, reaching a maximum of ~446 ​meV atom−1 at ~70 ​mol% Sn(II). The decomposition pathway of (Ba1/3Sn2/3)HfO3 was probed by ex situ XRD as well as in situ electron microscopy methods. An onset of thermally-induced decomposition begins at ~350–400 ​°C to give the more stable oxides which are found to segregate out in surface layers. These results help to elucidate the factors underpinning the synthesizability of highly metastable Sn(II)-containing perovskites, which increases with their cohesive energy and with the absence of lower-energy polymorphs or other ground states that can be reached without significant ion diffusion.

Impacts of Sn(II) doping on the Keggin heteropolyacid-catalyzed etherification of glycerol with tert-butyl alcohol

In this work, phosphomolybdic acid salts were synthesized exchanging their protons by the Sn(II) cations (i.e., H3-xSnx/2PMo12O40; x = 0.0, 1.0, 2.0, 3.0), and evaluated in the etherification reactions of glycerol with tert-butyl alcohol (TBA). The catalytic activity of the phosphomolybdate salts containing a variable load of Sn(II) ions was further compared to phosphotungstic and silicotungstic acid salts (i.e., H3-xSnx/2PW12O40; x = 0.0, 1.0, 2.0, 3.0 and H4-xSnx/2PW12O40; x = 0.0, 1.0, 2.0, 4.0, respectively). The integrity of the Keggin anion after the synthesis was confirmed by infrared spectroscopy analysis. Physical properties were determined through thermal analyses, powder X-Rays diffraction patterns, N2 adsorption-desorption isotherms, and scanning electron microscopy. The acidity properties were analyzed by adsorbed pyridine FT-IR spectroscopy, NH3-programmed-temperature desorption, and potentiometric titration. Among all the Sn(II) heteropoly salts tested, the Sn3PMo12O40 was the most active and selective catalyst toward glyceryl ethers. The highest activity of Sn3PMo12O40 was assigned to the greater Lewis acidity strength. Modeling, simulation, and economic analysis allowed to evaluate the viability of the process. An annual capacity of 30,000 metric tons was developed, and the process is feasible with a return on investment (ROI) of 30.7%.

Highly selective Sn/HZSM-5 catalyst for ethane ammoxidation to acetonitrile and ethylene

The ammoxidation of ethane over the conventional metal oxide and Co/zeolite catalysts faces the challenge of inadequate selectivity owing to the formation of CO2, N2, and NOx. Here we report that Sn modified ZSM-5 catalyst is highly selective for ethane ammoxidation. The C- and N-based acetonitrile selectivities are up to 80 % and 70 % over the Sn/HZSM-5, but they are below 60 % and 20 %, over the Co/HZSM-5. We suggested that the Sn (IV) cations are the critical active sites for acetonitrile formation, and the presence of nanosized SnOx particles favors CO2 formation. Transient kinetics analysis suggested that ethane ammoxidation over the Sn/HZSM-5 follows the same reaction pathways as that over the Co/HZSM-5. However, the surface abundancy of the reaction intermediates over these two catalysts is different, which could be the reason for the enhanced selectivity over the Sn (IV) cations in contrast to the Co (II) cations in the ZSM-5 zeolite.

On the irreversible sodiation of tin disulfide

Tin disulfide is considered as a promising electrode material for sodium-ion batteries because of its two-dimensional layered structural characteristics allowing the intercalation of Na ions. Understanding the underlying reaction mechanisms and the decisive step of the reaction reversibility is critical for its applications. Herein, we investigate the sodiation and desodiation processes of SnS2 by employing in situ transmission electron microscopy (TEM). After the initial intercalation reaction, a rock-salt NaySnS2 phase with disordering Na and Sn cations is observed, followed with a conversion reaction and an alloying reaction. The disordering reaction occurs along < 1–10 > direction of pristine SnS2 phase which is correlated with local bonding rearrangements induced by the exchange of Sn and Na cations. In-situ TEM studies and first-principles calculations indicate that the original 2D SnS2 structure could not be recovered during desodiation. Instead, the disordered NaySnS2 phase is finally formed, which indicates that the irreversible disordering transition is the determining step of irreversible cycling. This work probes the structural evolution of sodiation, providing a fundamental understanding of the electrochemical properties of metal sulfides and inspiring rational designs of high performance electrodes for sodium-ion batteries.

SnO2/ZnO heterostructured nanorods: Structural properties and mechanistic insights into the enhanced photocatalytic activity

Restricting electron-hole recombination addresses a bottleneck in photocatalytic processes, namely, low quantum efficiency. One way to restrict recombination is by constructing a heterostructure to spatially separate photoproduced electrons from corresponding holes. In this study, a SnO2–ZnO binary system is constructed hydrothermally to clarify the enhancement mechanism of photocatalytic activity in a heterostructure. XPS analysis confirms that the chemical state of Sn cations remains intact, while that of Zn cations gradually changes upon heterostructuring. Further in-depth analyses with XANES and EXAFS at the Zn K-edge reveal that the oxidation state of Zn cations decreases and their local structure gradually changes. The sensitivity of the oxidation state, local environment around Zn cations, and SnO2 loading amount suggest the partial replacement of Zn cations on the surface region by a small portion of Sn cations. Heterostructuring with SnO2 beneficially affects the photocatalytic activity of ZnO for mineralizing refractory organic compounds under ultraviolet light irradiation (200 < λ < 400 nm). The enhanced photocatalytic activity is caused by the efficient restriction of electron-hole recombination, as is evidenced by light-induced infrared absorption spectroscopy. The electron population is increased by up to 17 times after the heterostructuring.

Nanoscale charge transport and local surface potential distribution to probe the defect passivation in Cr-substituted earth abundant CZTS absorber layer

The non-stochiometric deviations in CZTS often results in certain detrimental point defects that act as trap centers causing non-radiative recombination and potential fluctuations, eventually results in large open circuit voltage (VOC) deficit in CZTS solar cells. Cationic substitution in CZTS layer is one of the leading approaches to capture the great potential of kesterite solar cells for future cost-effective photovoltaic technology. Here, chromium incorporation in CZTS is studied for cationic substitution in CZTS layer, as it renders multiple chemical states including +1, +2 and + 4 of Cu, Zn and Sn cations in CZTS. The CZTS films determine to have good crystallinity and morphology with no significant disparity among pristine and Cr-doped CZTS films, apart from slight shift of XRD (112) peak indicating partial cation substitution by smaller Cr atoms. However, the Zn content is found to be decreased with increasing Cr content in CZTS layer. Substantial enhancement in the absorption of Cr-doped CZTS films indicate intermediate band (IB) within the band gap. Photoluminescence (PL) emission spectra strongly suggests reduced non-radiative recombination and potential fluctuations in Cr-CZTS films. X-ray photoelectron spectroscopy investigations reveal Zn substitution by Cr in CZTS crystal geometry. Using nanoscale Kelvin Probe Force Microscopy (KPFM) and Conducting Atomic Force Microscopy (CAFM), we verify the surface potential variation and nanoscale electrical conductivity in pristine and Cr-CZTS films. Additionally, Zn substitution by Cr eventually lead to suppression of ZnSn deep level defects segregated at grain boundaries (GBs). CAFM strongly confirms the GB passivation in Cr-CZTS films. This work widens the opportunity of exploring potential cationic substitution in CZTS for developing high efficiency CZTS solar cells.