One-step environmentally friendly exfoliation and functionalization of hexagonal boron nitride by β-cyclodextrin-assisted ball milling

Hexagonal boron nitride nanosheets (BNNs) are gaining much attention owing to their extraordinary performance; however, difficulties remain in achieving their large-scale preparation and dispersion at high concentration in solvents. A facile yet efficient β-cyclodextrin-assisted mechanochemical exfoliation method is proposed to exfoliate and functionalize hexagonal boron nitride (h-BN). The β-cyclodextrin-assisted ball milling process gave a high yield of 60%, with the resultant BNNs being covalently grafted with hydroxyl, and well dispersed in water and other solvents. The concentration of the hydroxyl-functionalized boron nitride nanosheets (OH-BNNs) reached 3 mg/mL, and was stable for several weeks. Next, we fabricated a membrane based on the resulting OH-BNNs to effectively capture Congo red dye. This work not only offers an environmentally friendly, efficient, solvent-less and extremely cost-effective scalable production method, but also assists in our understanding of the mechanism of exfoliation and functionalization in other layered materials.     

High Power Conversion Efficiency of 13.61% for 1 cm2 Flexible Polymer Solar Cells Based on Patternable and Mass-Producible Gravure-Printed Silver Nanowire Electrodes

With the aim of developing high-performance flexible polymer solar cells, the preparation of flexible transparent electrodes (FTEs) via a high-throughput gravure printing process is reported. By varying the blend ratio of the mixture solvent and the concentration of the silver nanowire (AgNW) inks, the surface tension, volatilization rate, and viscosity of the AgNW ink can be tuned to meet the requirements of gravure printing process. Following this method, uniformly printed AgNW films are prepared. Highly conductive FTEs with a sheet resistance of 10.8 Ω sq⁻¹ and a high transparency of 95.4% (excluded substrate) are achieved, which are comparable to those of indium tin oxide electrode. In comparison with the spin-coating process, the gravure printing process exhibits advantages of the ease of large-area fabrication and improved uniformity, which are attributed to better ink droplet distribution over the substrate. 0.04 cm² polymer solar cells based on gravure-printed AgNW electrodes with PM6:Y6 as the photoactive layer show the highest power conversion efficiency (PCE) of 15.28% with an average PCE of 14.75 ± 0.35%. Owing to the good uniformity of the gravure-printed AgNW electrode, the highest PCE of 13.61% is achieved for 1 cm² polymer solar cells based on the gravure-printed FTEs.     

Revealing the Mechanism behind the Catastrophic Failure of n-i-p Type Perovskite Solar Cells under Operating Conditions and How to Suppress It

The n-i-p type perovskite solar cells suffer unpredictable catastrophic failure under operation, which is a barrier for their commercialization. The fluorescence enhancement at Ag electrode edge and performance recovery after cutting the Ag electrode edge off prove that the shunting position is mainly located at the edge of device. Surface morphology and elemental analyses prove the corrosion of the Ag electrode and the diffusion of Ag⁺ ions on the edge for aged cells. Moreover, much condensed and larger Ag clusters are formed on the MoO₃ layer. Such a contrast is also observed while comparing the central and the edge of the Ag/Spiro-OMeTAD film. Hence, the catastrophic failure mechanism can be concluded as photon-induced decomposition of the perovskite film and release reactive iodide species, which diffuse and react with the loose Ag clusters on the edge of the cell. The corrosion of the Ag electrode and the migration of Ag⁺ ions into Spiro-OMeTAD and perovskite films lead to the forming of conducting filament that shunts the cell. The more condensed Ag cluster on the MoO₃ surface as well as the blocking of holes within the Spiro-OMeTAD/MoO₃ interface successfully prevent the oxidation of Ag electrode and suppress the catastrophic failure.     

Optoelectronic platform and technology

Optoelectronic technology is a new technology formed by the combination of photon technology and electronic technology. Photon technology can cause an industrial revolution that supersedes electronic technology, because it will have a deeper impact on industry and society. We review the development of optoelectronic devices and integration technologies. We compare and analyze the development and characteristics of optoelectronic technology platforms, summarize the key manufacturing technologies, introduce several representative optoelectronic devices including flexible devices, and focus on the key breakthrough technologies that need to be achieved. Through a comprehensive review of the development of optoelectronic technology, China should seize the opportunity for a transformation of the optoelectronic technology industry. By drawing on the experiences with advanced optoelectronic platforms and technologies in foreign countries, we should speed up the accumulation and reserves of Chinese industrial talents, pay attention to the accumulation of basic technology, and establish a national optoelectronic technology platform, to greatly enhance domestic levels in these regards and to achieve independent innovations with these devices.

     

Ionic strength directed self-assembled polyelectrolyte single-bilayer membrane for low-pressure nanofiltration

Layer-by-layer assembly is a versatile technique for fabricating nanofiltration membranes, where multiple layers of polyelectrolytes are usually required to achieve reasonable separation performance. In this work, an ionic strength directed self-assembly procedure is described for the preparation of nanofiltration membranes consisting of only a single bilayer of poly(diallyldimethylammoniumchloride) and poly(sodium-4-styrenesulfoate). The influence of background ionic strength as well as membrane substrate properties on the formation of single-bilayer membranes are systematically evaluated. Such a simplified polyelectrolyte deposition procedure results in membranes having outstanding separation performance with permeating flux of 14.2 ± 1.5 L∙m^–2∙h^–1∙bar^–1 and Na₂SO₄ rejection of 97.1% ± 0.8% under a low applied pressure of 1 bar. These results surpass the ones for conventional multilayered polyelectrolyte membranes. This work encompasses an investigation of ionic strength induced coiling of the polyelectrolyte chains and emphasizes the interplay between-polyelectrolyte chain configuration and substrate pore profile. It thus introduces a new concept on the control of membrane fabrication process toward high performance nanofiltration.     

In-situ synthesis of needle-like PdO-decorated NiO thin films on Al2O3 substrates for high-performance H2 sensors

Safety is an essential consideration in the utilization of hydrogen energy due to its potential risk of explosion. Thereby, the synthesis of hydrogen sensors with highly sensitive properties is required for the early detection of hydrogen leaks. Here, a low-cost process was applied to fabricate PdO-decorated NiO H₂ sensors capable of detecting sub-ppm H₂ concentration. Unlike the previous two-step noble metal modification strategy, in situ ultrasonic spray pyrolysis was used in this work to directly obtain the needle-like PdO decorated NiO structure. The doped PdO tends to segregate at grain boundaries of NiO in needlelike form and can inhibit crystal growth. The gas-sensing performance was investigated by the means of dynamic gas distribution. The results show that the gas response towards H₂ could be enhanced significantly by PdO doping. Especially, the sprayed 2 at% PdO-decorated NiO film sensor shows the highest response and the lowest detection limit at 250 °C, with a response value of 82% to 50 ppm H₂ and a detection limit of 500 ppb. It can be speculated that the surface state of NiO film could be heavily affected by PdO doping, which leads to the high performance of PdO-decorated NiO sensors.     

Steering the construction of amorphous/crystalline hierarchical structure for accelerating the oxygen evolution reaction rate

As electrochemical water splitting is an extremely promising direction for solving future energy problems and the oxygen evolution reaction (OER) is the key half-reaction in water splitting, it is necessary to develop a new type of highly active and stable non-noble metal catalyst. Herein, we construct a series of hierarchical structure by modifying ZIF-67 on clustered-MnO₂ nanotubes which are used as precursor. The fruit@branch-shaped compounds, marked as X@MnO₂ (X = CoS_x, Co₃O₄ and CoP). Compared with pure MnO₂ nanotubes, the obtained derivatives imaginably result in the unique hierarchical structure and introduce synergistic effect between MnO₂ and Co-based species that result in higher performance. In Particular, owing to the abundant active sites, a facil mass transfer pathway and improved electrical conductivity in amorphous/crystallize hierarchical structure, CoS_x@MnO₂ possesses the highest electrocatalytic activity with a lower overpotential of 329 mV at the current density of 10 mA cm^?2, which is superior to most MnO₂-based catalyst previously reported. Most importantly, to expand this strategy is an effective way to synthesize more high-activity catalysts.     

Recent development of transition metal doped carbon materials derived from biomass for hydrogen evolution reaction

Achieving high catalytic performance with the lowest cost is critical for hydrogen evolution reduction. In recent years, biomass-derived carbon catalysts have triggered huge interest in catalytic reactions owing to the low cost, high energy conversion efficiency and environmental friendliness. A rapid growth of novel electrocatalysts is witnessed especially those based on non-precious metals, some of which approach the activity of precious metals. Synergistic interactions between metals and heteroatoms can significantly improve the electrocatalytic activity, thus transition metal-decorated biomass-based carbon materials were commonly adopted to improve HER performance. The resulting electrocatalytic activities are introduced and compared to conventional Pt/C-based electrocatalysts in present research. Moreover, the remaining challenges in the development process and future prospects of hydrogen evolution reduction catalysts are discussed.     

Ligand and temperature effects of porous palladium nanoparticle ensembles with grain boundaries for highly efficient electrocatalytic CO2 reduction

Journal of Materials Science - Electrocatalytic conversion from carbon dioxide with main products of carbon monoxide and hydrogen provides an economic and sustainable pathway to produce syngas,...     

Investigation of the tarnish on the surface of a panda gold coin

In natural environment, tarnish was observed on the surface of historic and contemporary gold coins in several countries. Few years after the emergence of panda gold coins, several red spots were appeared on the surface. To identify the stains and to examine the spots, optical microscope （OM）, scanning electron microscope （SEM）, electron microprobe analysis （EMPA）, X-ray photoelectron spectroscopy （XPS）, and X-ray diffraction （XRD） were used. It was found by microscopic observation that the stain has a dark blue central area surrounded by a large area with a nuance of colors from brown to red. Red spots usually contain holes in the center, which are distributed along the forging stress zones formed in the struck process. From the surface analyses using EMPA, sulfur and silver are detected besides gold, and the contents of Ag and S at the tarnish part are higher than those at the other part. Furthermore, distributions of Ag and S are correlated with the morphology of stains. XPS shows that components of stains are Ag2S and Ag2SO4 and the former is much predominant. These results are confirmed using XRD analysis. Accelerated tarnish test of gold in an atmosphere containing sulfur compound proves that the similar phenomenon appears when a small amount of silver is present on the surface of gold. It can be concluded that the occurrence of tarnish stains is caused by the presence of Ag and S.