Elevated Efficiency and Stability of Hole-Transport-Layer-Free Perovskite Solar Cells Triggered by Surface Engineering.

Surface engineering is one of the important strategies to enhance the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). Herein, 2-chloro-1,3-dimethylimidazolidinium hexafluorophosphate (CIP) was introduced into PSCs to passivate the defects of the perovskite films. There are many F atoms in CIP molecules that have strong electronegativity and hydrophobicity. F groups can interact with Pb2+ defects, inhibit interface recombination, improve the interaction between the CIP ionic liquid and perovskite film, and reduce the defect density of perovskites, thus improving the stability of perovskite devices. Density functional theory calculation reveals that CIP can interact with uncoordinated Pb2+ in perovskites through coordination, reduce the defects of perovskite films, and inhibit nonradiation recombination. The ITO/SnO2/MAPbI3/CIP/carbon devices without hole transport layers possessed the highest PCE of 17.06%. Moreover, the unencapsulated device remains at 98.18% of the initial efficiency stored in 30-40% relative humidity for 850 h. This strategy provides an effective reference for enhancing the performance of PSCs.

Improving the Reaction Kinetics by Annealing MoS2/PVP Nanoflowers for Sodium-Ion Storage.

Under the ever-growing demand for electrochemical energy storage devices, developing anode materials with low cost and high performance is crucial. This study established a multiscale design of MoS2/carbon composites with a hollow nanoflower structure (MoS2/C NFs) for use in sodium-ion batteries as anode materials. The NF structure consists of several MoS2 nanosheets embedded with carbon layers, considerably increasing the interlayer distance. Compared with pristine MoS2 crystals, the carbon matrix and hollow-hierarchical structure of MoS2/C exhibit higher electronic conductivity and optimized thermodynamic/kinetic potential for the migration of sodium ions. Hence, the synthesized MoS2/C NFs exhibited an excellent capacity of 1300 mA h g-1 after 50 cycles at a current density of 0.1 A g-1 and 630 mA h g-1 at 2 A g-1 and high-capacity retention at large charge/discharge current density (80% after 600 cycles 2 A g-1). The suggested approach can be adopted to optimize layered materials by embedding layered carbon matrixes. Such optimized materials can be used as electrodes in sodium-ion batteries, among other electrochemical applications.

Evolution of Stabilized 1T-MoS2 by Atomic-Interface Engineering of 2H-MoS2 /Fe-Nx towards Enhanced Sodium Ion Storage.

Metallic conductive 1T phase molybdenum sulfide (MoS2 ) has been identified as promising anode for sodium ion (Na+ ) batteries, but its metastable feature makes it difficult to obtain and its restacking during the charge/discharge processing result in part capacity reversibility. Herein, a synergetic effect of atomic-interface engineering is employed for constructing 2H-MoS2 layers assembled on single atomically dispersed Fe-N-C (SA Fe-N-C) anode material that boosts its reversible capacity. The work-function-driven-electron transfer occurs from SA Fe-N-C to 2H-MoS2 via the Fe-S bonds, which enhances the adsorption of Na+ by 2H-MoS2 , and lays the foundation for the sodiation process. A phase transfer from 2H to 1T/2H MoS2 with the ferromagnetic spin-polarization of SA Fe-N-C occurs during the sodiation/desodiation process, which significantly enhances the Na+ storage kinetics, and thus the 1T/2H MoS2 /SA Fe-N-C display a high electronic conductivity and a fast Na+ diffusion rate.

Electrodeposited Cobalt Nanosheets on Smooth Silver as a Bifunctional Catalyst for OER and ORR: In Situ Structural and Catalytic Characterization.

Developing earth-abundant, cost-effective, and active bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is key to boosting sustainable energy systems such as electrolyzers and lithium-air batteries. However, the performance of promising cobalt-based materials is impaired by the external effects of binders and carbon additives as well as inhomogeneous electrode fabrication. In this work, binder- and carbon-free flower-like Co-decorated Ag catalytic nanosheets were in situ-synthesized via a simple electrodeposition approach. The morphology, composition, and structure of Co/Ag before and after OER were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Co/Ag thin film electrodes with various Co contents exhibited a bifunctional activity toward ORR and OER due to a synergistic effect. XPS analysis suggested the formation of Co3O4 as the main active species for OER. In particular, Co (83%)/Ag surface revealed a 60 mV lower ORR overpotential than a pure Ag surface and even lower than drop-casted Co3O4 nanoparticles on Ag surface. Only 1.5% peroxide was generated, suggesting a four-electron transfer ORR. In addition, the OER onset potential on Co/Ag is 60 mV less than Co3O4. Tafel slopes of 71 and 75 mV dec-1 were obtained for ORR and OER, respectively. Importantly, the three-dimensional (3D) growth mechanism of a cobalt layer (∼1 nm) on a well-defined atomic smooth Ag surface is unraveled by in situ electrochemical scanning tunneling microscopy (EC-STM). EC-STM suggests that Co prefers to nucleate at the step edges of Ag and grows in a 3D, forming nanoparticles, where the deposition/dissolution process of the Co adlayer on Ag is reversible. This investigation may provide insights into design strategies of efficient oxygen electrocatalysts.

Direct conversion of N2 and O2: status, challenge and perspective.

As key components of air, nitrogen (N2) and oxygen (O2) are the vital constituents of lives. Synthesis of NO2, and C-N-O organics direct from N2 and O2, rather than from an intermediate NH3 (known as the Haber-Bosch process), is tantalizing. However, the extremely strong N≡N triple bond (945 kJ mol-1) and the nonpolar stable electron configuration of dinitrogen lead to its conversion being extensively energy demanding. The further selective synthesis of high-value C-N-O organics directly from N2, O2 and C-containing molecules is attractive yet greatly challenging from both scientific and engineering perspectives. Enormous efforts have been dedicated to the direct conversion of N2 and O2 via traditional and novel techniques, including thermochemical, plasma, electrochemical, ultrasonic and photochemical conversion. In this review, we aim to provide a thorough comprehension of the status and challenge of the direct conversion of N2, O2 and C-containing molecules (particularly N2 and O2). Moreover, we will propose some future perspectives to stimulate more inspiration from the scientific community to tackle the scientific and engineering challenges.

Characterization of lithium zinc titanate doped with metal ions as anode materials for lithium ion batteries.

With the aim of improving the ionic and electronic conductivities of Li2ZnTi3O8 for high performance lithium ion battery applications, Li2Zn0.9M0.1Ti3O8 (M = Li+, Cu2+, Al3+, Ti4+, Nb5+, Mo6+) compounds are successfully fabricated using facile high temperature calcination at 800 °C. Physical characterization and lithium ion reversible storage demonstrate that Zn-site substitution by multivalent metal ions is beneficial for improving the migration rate of ions and electrons of Li2ZnTi3O8. X-ray diffraction analysis and scanning electron microscopy reveal that the crystal structure and microscopic morphology of bare Li2ZnTi3O8 do not change by introducing a small amount of foreign metal ions. As a result, Li2Zn0.9Nb0.1Ti3O8 retains a reversible capacity as high as 198 mA h g-1 at the end of the 500th cycle among all samples. Even when cycled at high temperatures, Li2Zn0.9Nb0.1Ti3O8 still maintains excellent reversible discharge capacities of 210 mA h g-1 and 196 mA h g-1 at 1000 mA g-1 for the 100th cycle at 50 °C and 60 °C, respectively. All the conclusions indicate that Li2Zn0.9Nb0.1Ti3O8 is a high-performance anode material for large-scale energy storage devices.

Giant improvement of performances of perovskite solar cells via component engineering.

The absorption layer is a crucial factor for high-performance perovskite solar cells. In this work, the influence of the two components, methylammonium iodide (MAI) and formamidinium iodide (FAI) on the morphology, optical absorption and photovoltaic performances was systematically investigated. The results revealed that the surface morphologies of MAI/FAI based perovskite films were rougher, and the grain sizes became larger with increasing the FAI concentration. UV-Vis and photoluminescence spectra showed that there was a red shift with enhancing the FAI concentration. By the effective doping of FAI into the pristine MAI based perovskite film, the formation of a δ-FAPbI3 was successfully inhibited. As a result, the power conversion efficiency (PCE) of the perovskite solar cells based on mixed absorption layers was improved by about 27% compared to the pristine MAI based perovskite device.

Antimony deposition onto Au(111) and insertion of Mg.

Magnesium-based secondary batteries have been regarded as a viable alternative to the immensely popular Li-ion systems owing to their high volumetric capacity. One of the largest challenges is the selection of Mg anode material since the insertion/extraction processes are kinetically slow because of the large ionic radius and high charge density of Mg2+ compared with Li+. In this work, we prepared very thin films of Sb by electrodeposition on a Au(111) substrate. Monolayer and multilayer deposition (up to 20 monolayers) were characterized by cyclic voltammetry (CV) and scanning tunneling microscopy (STM). Monolayer deposition results in a characteristic row structure; the monolayer is commensurate in one dimension, but not in the other. The row structure is to some extent maintained after deposition of further layers. After dissolution of the Sb multilayers the substrate is roughened on the atomic scale due to alloy formation, as demonstrated by CV and STM. Further multilayer deposition correspondingly leads to a rough deposit with protrusions of up to 3 nm. The cyclic voltammogram for Mg insertion/de-insertion from MgCl2/AlCl3/tetraglyme (MACC/TG) electrolyte into/from a Sb-modified electrode shows a positive shift (400 mV) of the onset potential of Mg deposition compared to that of a bare Au electrode. From the charge of the Mg deposition, we find that the ratio of Mg to Sb is 1:1, which is somewhat less than expected for the Mg3Sb2 alloy.

Surface morphology and adlayer structure of Se on Rh(111).

The deposition of Se from SeO32- solutions was examined in the submonolayer regime by cyclic voltammetry, scanning tunneling microscopy and atomic force microscopy. Up to a coverage of ca. 0.5 (Se atoms to substrate atoms) a smooth adlayer is obtained with a 2 × âˆš3 structure. When the coverage is increased, at around 0.55 V further deposition is paralleled by a roughening starting at the monoatomic steps. The adsorbed Se is stable in the SeO32- free solution. For coverages below 0.25, separate domains for the Se covered regions and Se free regions were observed for potentials above 0.6 V. Since this is the potential of the spike corresponding to adsorption of OH at the clean Rh(111) surface in HClO4, we have to assume that Se and OH adsorb in separate domains. At lower potentials, where OH is desorbed, Se spreads over the complete surface which then appears completely smooth in the STM images. When the coverage is about 0.25 or above, the roughening is also observed in SeO32- free solution, demonstrating that the rough structures are not due to disordered deposition, but really due to a roughening by place exchange.