Electrochemistry-Induced Restructuring of Tin-Doped Indium Oxide Nanocrystal Films of Relevance to CO2 Reduction

The electrochemical reduction of CO2 into fuels using renewable electricity presents an opportunity to utilize captured CO2. Electrocatalyst development has been the primary focus of research in this area. This is especially true at the nanoscale, where researchers have focused on understanding nanostructure-property relationships. However, electrocatalyst structure may evolve during operation. Indium- and tin-based oxides have been widely studied as electrocatalysts for CO2 reduction to formate, but evolution of these catalysts during operation is not well-characterized. Here, we report the evolution of nanoscale structure of tin-doped indium oxide nanocrystals under CO2 reduction conditions. We show that sparse monolayer nanocrystal films desorb from the electrode upon charging, but thicker nanocrystal films remain, likely due to increased number of physical contacts. Upon applying a cathodic voltage of -1.0 V vs RHE or greater, the original 10-nm diameter nanocrystals are no longer visible, and instead form a larger microstructural network. Elemental analysis suggests the network is an oxygen-deficient indium-tin metal alloy. We hypothesize that this morphological evolution is the result of nanocrystal sintering due to oxide reduction. These data provide insights into the morphological evolution tin-doped indium oxide nanocrystal electrocatalysts under reducing conditions and highlight the importance of post-electrochemical structural characterization of electrocatalysts.

XRD and EDX Analyses on the Formation of MgTiO3 Phase in (Mg0.6Zn0.4)(Ti0.99Sn0.01)O3 Powders Due to Calcination Temperature Variations

MgTiO3-based dielectric ceramics have been recognized as functional materials in the microwave telecommunications industry. Research and development on MgTiO3 dielectric ceramics has therefore developed rapidly. This paper reports x-ray diffraction (XRD) and energy dispersive x-ray (EDX) analyses on the formation of MgTiO3 phase in (Mg0.6Zn0.4)(Ti0.99Sn0.01)O3 powder due to variations in calcination temperature from 550 to 700°C for 2 h. The powder was synthesized via the dissolved metal mixing course using magnesium, zinc, titanium and tin metal powders (Merck) as starting materials. The Rietveld refinement on the XRD patterns of the samples revealed that increasing the calcination temperature reduces the molar% content of MgTiO3 phase of from (97.91±1.51) at 550°C to (87.81±1.29) at 700 °C and causes a decrease in the diffraction peak intensity. The remaining % belongs to TiO2 rutile. The calcination temperature also enlarged the size of MgTiO3 unit cell volume. The EDX data on the atomic% ratio of the elements confirmed the presence of the phases. Discussion of these results is presented in detail in this paper.

The Crystal Structures of Two Hydro-closo-Borates with Divalent Tin in Comparison: Sn(H2O)3[B10H10] · 3 H2O and Sn(H2O)3[B12H12] · 4 H2O

Single crystals of Sn(H2O)3[B10H10] · 3 H2O and Sn(H2O)3[B12H12] · 4 H2O are easily accessible by reactions of aqueous solutions of the acids (H3O)2[B10H10] and (H3O)2[B12H12] with an excess of tin metal powder after isothermal evaporation of the clear brines. Both compounds crystallize with similar structures in the triclinic system with space group P$$\bar{1 }$$ 1 ¯ and Z = 2. The crystallographic main features are electroneutral $${}_{\infty }^{1} \{$$ ∞ 1 { Sn(H2O)3/1[B10H10]3/3} and $${}_{\infty }^{1} \{$$ ∞ 1 { Sn(H2O)3/1[B12H12]3/3} double chains running along the a-axes. Each Sn2+ cation is coordinated by three water molecules of hydration (d(Sn–O) = 221–225 pm for the B10 and d(Sn–O) = 222–227 pm for the B12 compound) and additionally by hydridic hydrogen atoms of the three nearest boron clusters (d(Sn–H) = 281–322 pm for the B10 and d(Sn–H) = 278–291 pm for the B12 compound), which complete the coordination sphere. Between these tin(II)-bonded water and the three or four interstitial crystal water molecules, classical bridging hydrogen bonds are found, connecting the double chains to each other. Furthermore, there is also non-classical hydrogen bonding between the anionic [BnHn]2− (n = 10 and 12) clusters and the crystal water molecules pursuant to B–Hδ−$$\cdots$$ ⋯ δ+H–O interactions often called dihydrogen bonds.

Effect of Sulfurization Time on the Physical Properties of Tin (II) Monosulfide Thin Films

Tin (II) monosulfide (SnS) films were prepared via sulfurization using sputtered Sn precursors of the tin metal layers in the presence of elemental sulfur vapor as a function of sulfurization time (ts) in the range of 30–180 min while keeping other parameters constant. The properties of these sulfurized layers were examined through suitable characterization techniques. The diffraction patterns exhibited various planes with the orientations (110), (120), (021), (101), (111), (211), (131), (210), (141), (002), (112), (122), and (042) corresponding to orthorhombic SnS at ts ≤ 90 min. However, for ts ≥ 120 min, the diffraction patterns showed a single (111) plane and enhanced the intensity of the peak with the increase of ts up to 150 min; with further increase of time, the peak intensity was found to decrease. The Raman spectra of films sulfurized at various ts showed modes at 95, 162, 189, 219, and 284 cm−1 for times were lower than 120 min and 95, 189, and 219 cm−1 for ts ≥ 120 min, related to SnS. In the transmittance spectra of the sulfurized films, it is clear that the film grown at ts = 30 min had higher transmittance, and with the increase of ts to 120 min, transmittance was decreased. For further extension of ts to 150 min, a sharp falling of the absorption edge was observed.