Enhanced Gas-Flow-Induced Voltage in Graphene

We show by systemically experimental investigation that gas-flow-induced voltage in monolayer graphene is more than twenty times of that in bulk graphite. Examination over samples with sheet resistances ranging from 307 to 1600 {\Omega}/sq shows that the induced voltage increase with the resistance and can be further improved by controlling the quality and doping level of graphene. The induced voltage is nearly independent of the substrate materials and can be well explained by the interplay of Bernoulli's principle and the carrier density dependent Seebeck coefficient. The results demonstrate that graphene has great potential for flow sensors and energy conversion devices

Electricity Harvested from Ambient Heat across Silicon Surface

We report that electricity can be generated from limitless thermal motion of ions by two dimensional (2D) surface of silicon wafer at room temperature. A typical silicon device, on which asymmetric electrodes with Au and Ag thin films were fabricated, can generate a typical open-circuit voltage up to 0.40 V in 5 M CuCl2 solution and an output current over 11 {\mu}A when a 25 k{\Omega} resistor was loaded into the circuit. Positive correlation between the output current and the temperature, as well as the concentration, was observed. The maximum output current and power density are 17 {\mu}A and 8.6 {\mu}W/cm2, respectively. The possibility of chemical reaction was excluded by four groups of control experiments. A possible dynamic drag mechanism was proposed to explain the experimental results. This finding further demonstrates that ambient heat in the environment can be harvested by 2D semiconductor surfaces or low dimensional materials and would contribute significantly to the research of renewable energy. However, this finding does not agree with the second law of thermal dynamatics. A lot of future work will be needed to study the mechanism behind this phenomenon

Borophene-based materials for energy, sensors and information storage applications

Borophene, as a rising-star monoelemental two-dimensional (2D) material, has motivated great interest because of its novel properties, such as anisotropic plasmonics, high carrier mobility, mechanical compliance, optical transparency, ultrahigh thermal conductance, and superconductivity. These properties make it an ideal candidate for use in the field of energy, sensors, and information storage. Stimulated by the realization of pioneering experimental works in 2015 and the follow-up synthesis experiments, a series of high-performance borophene-based devices in the fields, including supercapacitors, batteries, hydroelectric generators, humidity sensors, gas sensors, pressure sensors, and memories, have been experimentally reported in recent years, which are beneficial to the transition of borophene-based materials from experimental synthesis to practical application. Therefore, in addition to paying attention to the experimental preparation of borophene, significant efforts are needed to promote the advancement of related applications of borophene. In this review, after providing a brief overview of borophene evolution and synthesis, we mainly summarize the applications of borophene-based materials in energy storage, energy conversion, energy harvesting, sensors, and information storage. Finally, based on the current research status, some rational suggestions and discussions on the issues and challenges in the future research direction are proposed

Enhanced Actuation Response of Nafion-Based Ionic Polymer Metal Composites by Doping BaTiO₃ Nanoparticles

Nafion-based composite membranes by doping BaTiO₃ nanoparticles were prepared to fabricate high-performance ionic polymer metal composite (IPMC) actuators. BaTiO₃/Nafion nanocomposites were evaluated in terms of their static mechanical properties, water uptake, surface resistivity, electrochemical impedance, and actuation behaviors. The results show that the BaTiO₃/Nafion-based IPMCs have higher ionic conductivity and capacitance and better actuator behavior in comparison with the pure Nafion-based counterpart. The membrane with 3 wt % BaTiO₃ nanoparticles exhibits the best overall property under a 3 V dc or ac voltage excitation: exceptional deflections are obtained up to 101.4% under the dc input and 250% under the ac input at a frequency of 1 Hz; the blocking force is increased over 375% at the dc input, in sharp contrast to the pure Nafion sample. The improvements are attributed to the double-layer electrostatic effect which is induced by the broad dispersion of penetrated nanoparticles into electrodes. This study provides an innovative approach to develop high-performance IPMC actuators

The Application of Highly Doped Single-Layer Graphene as the Top Electrodes of Semitransparent Organic Solar Cells

A single-layer graphene film with high conductance and transparency was realized by effective chemical doping. The conductance of single-layer graphene was increased for more than 400% when it was doped with Au nanoparticles and poly(3,4-ethylenedioxythiophene): poly(styrene sulfonic acid). Then semitransparent organic solar cells based on poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) were fabricated with single-layer graphene and indium tin oxide (ITO) as the top and bottom electrodes, respectively. The performance of the devices was optimized by tuning the active layer thickness and doping the single-layer graphene electrodes. The maximum efficiency of 2.7% was observed in the devices with the area of 20 mm² illuminated from graphene electrode under the AM1.5 solar simulator. It is notable that all of the devices showed higher efficiency from the graphene than ITO side, which was attributed to the better transmittance of the graphene electrodes. In addition, the influence of the active area of the organic solar cell on its photovoltaic performance was studied. We found that, when the active areas increased from 6 to 50 mm², the power conversion efficiencies decreased from 3% to 2.3% because of the increased series resistances and the decreased edge effect of the devices

Oxidation-Sulfidation Approach for Vertically Growing MoS₂ Nanofilms Catalysts on Molybdenum Foils as Efficient HER Catalysts

Molybdenum disulfide (MoS₂) has emerged as a promising electrocatalyst for hydrogen evolution reaction (HER). However, the performance of the catalyst suffers from the scarce active sites and poor electrical conductivity. Here we grow vertical MoS₂ films on Mo foils to achieve highly catalytic active sites and enhanced electrical conductivity for facilitating high efficient HER catalysis. The ultrathin nanofilm with a thickness of around 4 nm on molybdenum foils is grown by a two-step method: (1) the molybdenum oxide (MoO₂) nanofilm is achieved by oxidizing the surface of the Mo foil under a low pressure condition and (2) a MoS₂ nanofilm is obtained by sulfurizing the MoO₂ nanofilm in sulfur vapor at 700 °C within 1 min. Furthermore, the vertically aligned MoS₂ nanofilm on Mo foils exhibit excellent stability in acidic solution and the electrochemical measurements show an onset overpotential of as low as 18 mV and a small Tafel slope of 55 mV/dec. The excellent HER catalysis originates from the synergistic effect of the dense catalytic active sites at the vertical MoS₂ surface and superior electron transport along the Mo foil. This study opens a novel avenue for the development of earth-abundant, low-cost electrocatalysts with high HER activities

Measurements of sulfur dioxide,ozone and ammonia concentrations in Asia,Africa,and South America using passive samplers

Measurements of gaseous SO2,NH3,and O3 using IVL passive sampler technology were obtained during a pilot measurement program initiated as a key component of the newly established WMO/GAW Urban Research Meteorology and Environment (GURME) project. Monthly measurements were obtained at 50 stations in Asia,Africa, South America,and Europe. The median SO2 concentrations vary from a high of 13 ppb at Linan,China,to o0.03 ppb at four stations. At 30 of 50 regional stations,the observed median concentrations are o1 ppb. Median ammonia concentrations range from 20 ppb at Dhangadi,India,to o1 ppb at nine stations. At 27 of regional stations,the ambient ammonia levels exceed 1 ppb. The median ozone concentrations vary from a maximum of 45 ppb at Waliguan Mountain,China,to 8 ppb in Petit Saut,French Guiana. In general,the highest ozone values are found in the mid- latitudes,with the Northern hemisphere mid-latitude values exceeding the Southern hemisphere mid-latitude levels,and the lowest values are typically found in the tropical regions