Organic–inorganic hybrid perovskites are promising candidates for the next-generation solar cells. Many efforts have been made to study their structures in the search for a better mechanistic understanding to guide the materials optimization. Here, we investigate the structure instability of the single-crystalline CH3NH3PbI3 (MAPbI3) film by using transmission electron microscopy. We find that MAPbI3 is very sensitive to the electron beam illumination and rapidly decomposes into the hexagonal PbI2. We propose a decomposition pathway, initiated with the loss of iodine ions, resulting in eventual collapse of perovskite structure and its decomposition into PbI2. These findings impose important question on the interpretation of experimental data based on electron diffraction and highlight the need to circumvent material decomposition in future electron microscopy studies. The structural evolution during decomposition process also sheds light on the structure instability of organic–inorganic hybrid perovskites in solar cell applications.

Designing and constructing bifunctional electrocatalysts is vital for water splitting. Particularly, the rational interface engineering can effectively modify the active sites and promote the electronic transfer, leading to the improved splitting efficiency. Herein, free‐standing and defect‐rich heterogeneous MoS 2 /NiS 2 nanosheets for overall water splitting are designed. The abundant heterogeneous interfaces in MoS 2 /NiS 2 can not only provide rich electroactive sites but also facilitate the electron transfer, which further cooperate synergistically toward electrocatalytic reactions. Consequently, the optimal MoS 2 /NiS 2 nanosheets show the enhanced electrocatalytic performances as bifunctional electrocatalysts for overall water splitting. This study may open up a new route for rationally constructing heterogeneous interfaces to maximize their electrochemical performances, which may help to accelerate the development of nonprecious electrocatalysts for overall water splitting.

No abstract

No abstract

a great deal of research effort has been devoted on high energy density supercapacitors. According to the equation of energy density E = 1/2 CV 2 , the energy density (E) of supercapacitors can be enhanced by increasing either voltage window (V) or specific capacitance (C). [5] For high specific capacitance, one of the research efforts should concentrate on using transition metal oxides (TMO) (e.g., MnO 2 , RuO 2 ) as electrode materials. [6,7] They can provide great specific capacitance due to the pseudocapacitive characteristic. [8,9] Among TMO materials, MnO 2 is one of the most potential materials for supercapacitors due to its high theoretical specific capacitance, environmental friendliness, and the high practical voltage window (about 1 V). [2] However, it has suffered from intrinsically low conductivity and specific surface area, which severely restrict its further development in practical application of supercapacitors. In this regard, integrating nanostructured MnO 2 and conductive carbon materials to fabricate novel hybrid nanostructures is a plausible solution to overcome this obstacle. [4] Further, some research efforts have been accordingly performed to synthesize hybrid nanostructures electroactive materials for constructing supercapacitors with considerable performance. Some researchers accordingly synthesized highperformance nanostructured MnO 2 -carbon materials electrodes, whose specific capacitance is close to theoretical value. However, the undesirable contact resistances that produced by the weak and noncoherent TMO/conductor interfaces lead to sluggish kinetics for charge transport, which requires further improvement. [10,11] In order to further improve the energy density, some researchers have concentrated on enlarging the voltage window of supercapacitors. The applications of aqueous electrolytes have been limited by their theoretical voltage window (≈1.23 V) and the practical voltage window is mostly lower than about 1 V for supercapacitors. [12] To extend the voltage window, various techniques have been applied, such as dual shuttle-ion electrolytes, [13,14] pH adjustment of electrolytes, [15] and concentrated electrolytes. [16][17][18] All of these methods have complex processing technologies and sacrifice capacitance, so being difficult for practical applications. Recently, Zhu and co-workers

No abstract

SnTe is known as an eco-friendly analogue of PbTe without toxic elements. However, the application potentials of pure SnTe are limited because of its high hole carrier concentration derived from intrinsic Sn vacancies, which lead to a high electrical thermal conductivity and low Seebeck coefficient. In this study, Sn self-compensation and Mn alloying could significantly improve the Seebeck coefficients in the whole temperature range through simultaneous carrier concentration optimization and band engineering, thereby leading to a large improvement of the power factors. Combining precipitates and atomic-scale interstitials due to Mn alloying with dense dislocations induced by long time annealing, the lattice thermal conductivity is drastically reduced. As a result, an enhanced figure of merit (ZT) of 1.35 is achieved for the composition of Sn Mn Te at 873 K and the ZT from 300 to 873 K is boosted to 0.78, which is of great significance for practical application. Hitherto, the ZT and ZT of this work are the highest values among all single-element-doped SnTe systems.

Precisely engineering the electrical conductivity represents a promising strategy to design efficient catalysts towards oxygen evolution reaction (OER). Here, we demonstrate a versatile partial cation exchange method to fabricate lamellar Ag-CoSe nanobelts with controllable conductivity. The electrical conductivity of the materials was significantly enhanced by the addition of Ag cations of less than 1.0 %. Moreover, such a trace amount of Ag induced a negligible loss of active sites which was compensated through the effective generation of active sites as shown by the excellent conductivity. Both the enhanced conductivity and the retained active sites contributed to the remarkable electrocatalytic performance of the Ag-CoSe nanobelts. Relative to the CoSe nanobelts, the as-prepared Ag-CoSe nanobelts exhibited a higher current density and a lower Tafel slope towards OER. This strategy represents a rational design of efficient electrocatalysts through finely tuning their electrical conductivities.