In Situ Characterization of Metastable Pb3O5 and Pb2O3 Phases During Thermal Decomposition of PbO2 to PbO

Nonstoichiometric lead oxides play a key role in the formation and cycling of the positive electrodes in a lead acid battery. These phases have been linked to the underutilization of the positive active material but also play a key role in the battery's cycle life, providing interparticle adhesion and the connection to the underlying lead grid. Similar phases have previously been identified by mass loss or color change during thermal annealing of PbO2 to PbO, suggesting that at least two intermediate PbOx phases exist. Using multiple, in situ analysis techniques (powder diffraction, X-ray absorption, X-ray photoelectron spectroscopy) and ex situ nuclear magnetic resonance measurements, the structural conversion and changes in the lead oxidation state were identified during this process. Isolation of the PbOx phases enabled confirmation of Pb3O5 and Pb2O3 by diffraction and the first 207Pb NMR measurement of these intermediates. The thermodynamic and kinetic stability of these intermediates and other reported polymorphs were determined by density functional theory, providing key insight into their origins and variation of PbOx structures found in previous studies.

Enhanced Performance of Carbon-Selenide Composite with La0.9Ce0.1NiO3 Perovskite Oxide for Outstanding Counter Electrodes in Platinum-Free Dye-Sensitized Solar Cells

For large-scale applications, dye-sensitized solar cells (DSSCs) require the replacement of the scarce platinum (Pt)-based counter electrode (CE) with efficient and cheap alternatives. In this respect, low-cost perovskite oxides (ABO₃) have been introduced as promising additives to composite-based CEs in Pt-free DSSCs. Herein, we synthesized composites from La_0.9Ce_0.1NiO₃ (L) perovskite oxide and functionalized-multiwall-carbon-nanotubes wrapped in selenides derived from metal-organic-frameworks (f-MWCNT-ZnSe-CoSe₂, “F”). L and F were then mixed with carbon black (CB) in different mass ratios to prepare L@CB, F@CB, and L@F@CB composites. The electrochemical analysis revealed that the L@F@CB composite with a mass ratio of 1.5:3:1.5 exhibits better electrocatalytic activity than Pt. In addition, the related DSSC reached a better PCE of 7.49% compared to its Pt-based counterpart (7.09%). This improved performance is the result of the increase in the oxygen vacancy by L due to the replacement of La with Ce in its structure, leading to more active sites in the L@F@CB composites. Moreover, the F@CB composite favors the contribution to the high electrical conductivity of the hybrid carbon nanotube–carbon black, which also offers good stability to the L@F@CB CE by not showing any obvious change in morphology and peak-to-peak separation even after 100 cyclic voltammetry cycles. Consequently, the corresponding L@F@CB-based device achieved enhanced stability. Our work demonstrates that L@F@CB composites with a low cost are excellent alternatives to Pt CE in DSSCs.

Selective SnO x Atomic Layer Deposition Driven by Oxygen Reactants

SnO _x thin films were successfully deposited by the thermal atomic layer deposition (ALD) method using N, N'- tert-butyl-1,1-dimethylethylenediamine stannylene(II) as a precursor and ozone and water as reactants. The growth of SnO and SnO₂ films could be easily controlled by employing different reactants and utilizing different ozone and water concentrations, respectively. The formation of both SnO and SnO₂ films exhibited typical surface-limiting reaction characteristics, although their growth behaviors differ from one another. The combined studies of density functional theory calculations and experimental analyses showed that the difference in growth behavior of the SnO and SnO₂ films can be attributed to the stability of ozone and water on the SnO₂ and SnO films. SnO and SnO₂ films have different crystal structures and both films were crystallized from the amorphous to polycrystalline states following an increase in the deposition temperature. The absorbance and refractive index of the thin films were investigated using ultraviolet-visible spectroscopy (UV-vis) and spectroscopic ellipsometry (SE), respectively. SnO _x films formed using ozone and water as a reactant showed an optical band gap of 3.60-3.17 eV and 2.24-2.30 eV and refractive indices of ∼2.0 and ∼2.6, respectively, which correspond to values typical of SnO₂ and SnO. The bilayer structure of SnO/SnO₂ was successfully fabricated on indium tin oxide (ITO) glass with nickel as a top electrode at 100 °C. The SnO/SnO₂ bilayer exhibited diode characteristics with a current rectification ratio of 15. Our results present a simple but highly versatile growth method for producing multilayer oxide films with electronic properties that can be finely controlled.

Oxygen vacancies confined in SnO2 nanoparticles for glorious photocatalytic activities from the UV, visible to near-infrared region

For the purpose of effectively utilizing solar energy, tailoring of the energy band configuration represents an effective approach to the exploration and development of full-spectrum-responsive photocatalysts with advanced performance.

Encapsulating CoS2–CoSe2 heterostructured nanocrystals in N-doped carbon nanocubes as highly efficient counter electrodes for dye-sensitized solar cells

The CoS₂–CoSe₂@N-doped carbon nanocubes were synthesized through simultaneous sulfurization and selenization of polydopamine coated Prussian blue analogs.

Synergistically Enhanced Electrochemical Performance of Ni3S4-PtX (X = Fe, Ni) Heteronanorods as Heterogeneous Catalysts in Dye-Sensitized Solar Cells

Platinum (Pt)-based alloys are considerably promising electrocatalysts for the reduction of I^-/I₃^- and Co²⁺/Co³⁺ redox couples in dye-sensitized solar cells (DSSCs). However, it is still challenging to minimize the dosage of Pt to achieve comparable or even higher catalytic efficiency. Here, by taking full advantages of the Mott-Schottky (M-S) effect at the metal-semiconductor interface, we successfully strategize a low-Pt-based M-S catalyst with enhanced electrocatalytic performance and stability for the large-scale application of DSSCs. The optimized M-S electrocatalyst of Ni₃S₄-Pt₂X₁ (X = Fe, Ni) heteronanorods is constructed by rationally controlling the ratio of Pt to transition metal in the hybrids. It was found that the electrons transferred from Ni₃S₄ to Pt₂X₁ at their interface under the Mott-Schottky effect result in the concentration of electrons onto Pt₂X₁ domains, which subsequently accelerates the regeneration of both I^-/I₃^- and Co²⁺/Co³⁺ redox shuttles in DSSCs. As a result, the DSSC with Ni₃S₄-Pt₂Fe₁ manifests an impressive power conversion efficiency (PCE) of 8.79% and 5.56% for iodine and cobalt-based electrolyte under AM1.5G illumination, respectively. These PCEs are obviously superior over those with Ni₃S₄-Pt, PtFe, Ni₃S₄, and pristine Pt electrodes. The strategy reported here is able to be further expanded to fabricate other low-Pt-alloyed M-S catalysts for wider applications in the fields of photocatalysis, water splitting, and heterojunction solar cells.

WB crystals with oxidized surface as counter electrode in dye-sensitized solar cells

Tungsten boride (WB) crystals, whose surface tends to be oxidized when exposed to air, were demonstrated to have a comparable activity to platinum as counter electrode material in dye-sensitized solar cells. The synergistic effect of both catalytically active surface layer WO_x and electronically conductive internal WB is considered to be responsible for the high activity of the WB crystals.

A strategy to design novel structure photochromic sensitizers for dye-sensitized solar cells

Two sensitizers with novel structure were designed and synthetized by introducing photochromic bisthienylethene (BTE) group into the conjugated system. Thanks to the photochromic effect the sensitizers have under ultraviolet and visible light, the conjugated bridge can be restructured and the resulting two photoisomers showed different behaviors in photovoltaic devices. This opens up a new research way for the dye-sensitized solar cells (DSSCs).

Two carboxyethyltin functionalized polyoxometalates for assembly on carbon nanotubes as efficient counter electrode materials in dye-sensitized solar cells

Two new POM-carboxyethyltin derivatives increased the electrocatalytic activity of single-walled carbon nanotubes toward triiodide reduction as counter electrodes in DSSCs.