A new popular transition metal-based catalyst:SmMn_(2)O_(5) mullite-type oxide

Catalyst with high performance has drawn increasing attention recently due to its significant advantages in chemical reactions such as speeding up the reaction,lowering the reaction temperature or pressure,and proceeding without itself being consumed.Despite the superior catalytic performance of precious metal catalysts,transition metal oxides offer a promising route for substitution of precious metals in catalysis arising from their low cost,intrinsic activity and sufficient stability.Mullite-type oxide SmMn_(2)O_(5) exhibits a unique crystal structure containing double crystalline fields,and nowadays is used widely as the catalyst in different chemical reactions,including the reactions of vehicle emissions reduction and oxygen evolution reaction,gas sensors,and metal-air batteries,promoting attention in catalytic perfor-mance enhancement.To our knowledge,there is no review article covering the comprehensive informa-tion of SmMn2 O 5 and its applications.Here we review the recent progress in understanding of the crys-tal structure of SmMn_(2)O_(5) and its basic physical properties.We then summarize the catalytic sources of SmMn_(2)O_(5) and reaction mechanisms,while the strategies to improve catalytic performance of SmMn_(2)O_(5) are further presented.Finally,we provide a perspective on how to make further progress in catalytic applications.

Investigation of weak interlayer coupling in 2D layered GeS_(2) from theory to experiment

Interlayer coupling as a unique feature for two-dimensional(2D)materials may influence their thickness-dependent physical properties,especially the bandgap due to quantum confinement effect.Widely-studied 2D materials usually possess strong interlayer coupling such as most of transition metal dichalcogenides(TMDs),PtS_(2) and so on.However,2D materials with weak interlayer coupling are rarely referred that mainly focus on ReS_(2),as well as its counterpart ReSe_(2).Here we report a new member of weak interlayer coupling 2D materials,germanium disulfide(GeS_(2)).The interlayer interaction in GeS_(2) is investigated from theory to experiment.By density functional theory calculations,we find that this extraordinarily weak interlayer coupling in GeS_(2) originates from the weak hybridization of interlayer S atoms.Thickness-dependent Raman spectra of GeS_(2) flakes exhibit that the Raman peaks remain unchanged when increasing the thickness;and a small first-order temperature coefficient of-0.00857 cm^(-1)·K^(-1) is obtained from the temperature-dependent Raman spectra.These experimental results further confirm the weak interlayer coupling in GeS_(2).

Boosting the efficiency of GeSe solar cells by low-temperature treatment of p-n junction

Germanium monoselenide(GeSe)is an emerging promising photovoltaic absorber material due to its attractive optoelectronic properties as well as non-toxic and earth-abundant constitutes.However,all previously reported GeSe solar cells rely on a superstrate configuration coupled with a CdS buffer layer,and suffer from unsatisfactory performance.Here we demonstrate that this low efficiency arises from the inevitable high-temperature treatment of p-n junction in superstrate configuration.This results in the diffusion of Cd atoms from CdS layer into GeSe film that introduces detrimental deep trap states inside the bandgap of GeSe(~0.34 eV below conduction band minimum).We adopt therefore a substrate configuration that enables the deposition of CdS atop pre-deposited polycrystalline GeSe film at room temperature,avoiding the Cd diffusion.By optimizing the annealing temperature of complete devices via a highthroughput screening method,the resulting substrate solar cells annealed at 150℃achieve an efficiency of 3.1%,two times that of the best previously reported superstrate GeSe results.

Melt-and air-processed selenium thin-film solar cells

Elemental selenium(Se), as the world’s first but long-neglected photovoltaic material, has regained great interest recently in tandem solar cells as top cells due to its wide bandgap(~1.8 eV), simple, non-toxic and earth-abundant composition, and intrinsic environmental stability. In particular, Se possesses the lowest melting point of 217 °C among the photovoltaic absorbers reported so far, endowing Se with a unique advantage of film fabrication by blade coating the Se melt on substrate. However, the poor wettability of Se melt on widely-used photovoltaic functional layers such as TiO_(2) limits its melt processing. Here we introduce a wettability-modification strategy that decreases the contact angle of Se melt on substrate and improves the wettability by appropriately enhancing the heating temperature of molten Se while avoiding Se volatilization. We further reveal the mechanism of the inherent air stability of Se that originates from the high activation energy of oxygen chemisorption on Se(3.21 eV). This enables the realization of compact Se films through melt-based blade coating in ambient air. The resulting Se solar cells exhibit an efficiency of 3.5%. Unencapsulated devices show no efficiency loss after 1,000 h of storage under ambient conditions.