Nano-metal diborides-supported anode catalyst with strongly coupled TaOx/IrO2 catalytic layer for low-iridium-loading proton exchange membrane electrolyzer.

The sluggish kinetics of oxygen evolution reaction (OER) and high iridium loading in catalyst coated membrane (CCM) are the key challenges for practical proton exchange membrane water electrolyzer (PEMWE). Herein, we demonstrate high-surface-area nano-metal diborides as promising supports of iridium-based OER nanocatalysts for realizing efficient, low-iridium-loading PEMWE. Nano-metal diborides are prepared by a novel disulphide-to-diboride transition route, in which the entropy contribution to the Gibbs free energy by generation of gaseous sulfur-containing products plays a crucial role. The nano-metal diborides, TaB2 in particular, are investigated as the support of IrO2 nanocatalysts, which finally forms a TaOx/IrO2 heterojunction catalytic layer on TaB2 surface. Multiple advantageous properties are achieved simultaneously by the resulting composite material (denoted as IrO2@TaB2), including high electrical conductivity, improved iridium mass activity and enhanced corrosion resistance. As a consequence, the IrO2@TaB2 can be used to fabricate the membrane electrode with a low iridium loading of 0.15 mg cm-2, and to give an excellent catalytic performance (3.06 A cm-2@2.0 V@80 oC) in PEMWE-the one that is usually inaccessible by unsupported Ir-based nanocatalysts and the vast majority of existing supported Ir-based catalysts at such a low iridium loading.

Hybrid artificial muscle: enhanced actuation and load-bearing performance via an origami metamaterial endoskeleton.

Owing to their compliance, soft robots demonstrate enhanced compatibility with humans and the environment compared with traditional rigid robots. However, ensuring the working effectiveness of artificial muscles that actuate soft robots in confined spaces or under loaded conditions remains a challenge. Drawing inspiration from avian pneumatic bones, we propose the incorporation of a lightweight endoskeleton into artificial muscles to augment the mechanical integrity and tackle load-bearing environmental difficulties. We present a soft origami hybrid artificial muscle that features a hollow origami metamaterial interior with a rolled dielectric elastomer exterior. The programmable nonlinear origami metamaterial endoskeleton significantly improves the blocked force and load-bearing capability of the dielectric elastomer artificial muscle and an increased actuation strain. The origami hybrid artificial muscle demonstrates a maximum strain of 8.5% and a maximum actuating stress of 12.2 mN mm-2 at 30 V µm-1 while preserving its actuating ability, even under a 450 mN load, which is equivalent to 155 times its own weight. We further investigate the dynamic responses and demonstrate the potential use of the hybrid artificial muscle in flapping-wing actuation applications.

Research on the relationship between the centerline velocity, aspect ratio and exhaust airflow rate for a slot and a rectangular capture hood in an local exhaust ventilation system.

When using a local exhaust hood to remove harmful substances from the production process, the exhaust airflow rate must be calculated according to the capturing velocity specified by the relevant regulations. The Numano and American Conference of Governmental Industrial Hygienists (ACGIH) equations are used in Japan and the US, respectively, for estimating the exhaust airflow rate of slot hoods. However, these equations differ from each other, and when using these equations to calculate the exhaust airflow rate of the capture hood, whether using Japan's equation or ACGIH, the hood type (slot or rectangular hood) should be distinguished at first. Therefore, this study performs experiments and a computational fluid dynamics (CFD) simulation to investigate the relationship between the centerline velocity and the aspect ratio for five types of capture hoods. The results showed good agreement between simulated and experimental centerline velocities when the distance from the hood face. A dimensionless velocity was introduced and a significant difference in the relationship between the centerline velocity and the distance from the hood face with different aspect ratios was found. A unified equation was obtained that can express the relationship between exhaust airflow rate and centerline velocity regardless of the aspect ratio of the hood face of the free-standing capture hood.

A Highly Active, Long-Lived Oxygen Evolution Electrocatalyst Derived from Open-Framework Iridates.

The acidic oxygen evolution reaction underpins several important electrical-to-chemical energy conversions, and this energy-intensive process relies industrially on iridium-based electrocatalysts. Here, phase-selective synthesis of metastable strontium iridates with open-framework structure and their unexpected transformation into a highly active, ultrastable oxygen evolution nano-electrocatalyst are presented. This transformation involves two major steps: Sr2+ /H+ ion exchange in acid and in situ structural rearrangement under electrocatalysis conditions. Unlike its dense perovskite-structured polymorphs, the open-framework iridates have the ability to undergo rapid proton exchange in acid without framework amorphization. The resulting protonated iridates further reconstruct into ultrasmall, surface-hydroxylated, (200) crystal plane-oriented rutile nanocatalyst, instead of the common amorphous IrOx Hy phase, during acidic oxygen evolution. Such microstructural characteristics are found to benefit both the oxidation of hydroxyls and the formation of OO bonds in electrocatalytic cycle. As a result, the open-framework iridate derived nanocatalyst gives a comparable catalytic activity to the most active iridium-based oxygen evolution electrocatalysts in acid, and retains its catalytic activity for more than 1000 h.

A Roadmap to Low-Cost Hydrogen with Hydroxide Exchange Membrane Electrolyzers.

Hydrogen is an ideal alternative energy carrier to generate power for all of society's energy demands including grid, industrial, and transportation sectors. Among the hydrogen production methods, water electrolysis is a promising method because of its zero greenhouse gas emission and its compatibility with all types of electricity sources. Alkaline electrolyzers (AELs) and proton exchange membrane electrolyzers (PEMELs) are currently used to produce hydrogen. AELs are commercially mature and are used in a variety of industrial applications, while PEMELs are still being developed and find limited application. In comparison with AELs, PEMELs have more compact structure and can achieve higher current densities. Recently, however, an alternative technology to PEMELs, hydroxide exchange membrane electrolyzers (HEMELs), has gained considerable attention due to the possibility to use platinum group metal (PGM)-free electrocatalysts and cheaper membranes, ionomers, and construction materials and its potential to achieve performance parity with PEMELs. Here, the state-of-the-art AELs and PEMELs along with the current status of HEMELs are discussed in terms of their positive and negative aspects. Additionally discussed are electrocatalyst, membrane, and ionomer development needs for HEMELs and benchmark electrocatalysts in terms of the cost-performance tradeoff.

Carbon nanotube thin film transistors fabricated by an etching based manufacturing compatible process.

Carbon nanotube thin film transistors (CNT-TFTs) have been regarded as strong competitors to currently commercialized TFT technologies. Though much progress has been achieved recently, CNT-TFT research is still in the stage of laboratory research. One critical challenge for commercializing CNT-TFT technology is that the commonly used device fabrication method is a lift-off based process, which is not suitable for mass production. In this paper, we report an etching based fabrication process for CNT-TFTs, which is fully manufacturing compatible. In our process, the CNT thin film channel was patterned by dry etching, while wet etching was used for patterning the layers of metal and insulator. The CNT-TFTs were successfully fabricated on a 4 inch wafer in both top-gate and buried-gate geometries with low Schottky barrier contact and pretty uniform performance. High output current (>1.2 µA µm-1), high on/off current ratio (>105) and high mobility (>30 cm2 V-1 s-1) were obtained. Though the fabrication process still needs to be optimized, we believe our research on the etching fabrication process pushes CNT-TFT technology a step forward towards real applications in the near future.

Carbon Nanotube Thin Film Transistors for Flat Panel Display Application.

Carbon nanotubes (CNTs) are promising materials for both high performance transistors for high speed computing and thin film transistors for macroelectronics, which can provide more functions at low cost. Among macroelectronics applications, carbon nanotube thin film transistors (CNT-TFT) are expected to be used soon for backplanes in flat panel displays (FPDs) due to their superior performance. In this paper, we review the challenges of CNT-TFT technology for FPD applications. The device performance of state-of-the-art CNT-TFTs are compared with the requirements of TFTs for FPDs. Compatibility of the fabrication processes of CNT-TFTs and current TFT technologies are critically examined. Though CNT-TFT technology is not yet ready for backplane production line of FPDs, the challenges can be overcome by close collaboration between research institutes and FPD manufacturers in the short term.

Metal contact effect on the performance and scaling behavior of carbon nanotube thin film transistors.

Metal-tube contact is known to play an important role in carbon nanotube field-effect transistors (CNT-FETs) which are fabricated on individual CNTs. Less attention has been paid to the contact effect in network type carbon nanotube thin film transistors (CNT-TFTs). In this study, we demonstrate that contact plays an even more important role in CNT-TFTs than in CNT-FETs. Although the Schottky barrier height at the metal-tube contact can be tuned by the work function of the metal, similar to the case in CNT-FETs, the contact resistance (Rc) forms a much higher proportion of the total resistance in CNT-TFTs. Interestingly, the contact resistivity was found to increase with channel length, which is a consequence of the percolating nature of the transport in CNT films, and this behavior does not exist in CNT-FETs and normal 2D Ohmic conductors. Electrical transport in CNT-TFTs has been predicted to scale with channel length by stick percolation theory. However, the scaling behavior is also impacted, or even covered up by the effect of Rc. Once the contact effect is excluded, the covered scaling behavior can be revealed correctly. A possible way of reducing Rc in CNT-TFTs was proposed. We believe the findings in this paper will strengthen our understanding of CNT-TFTs, and even accelerate the commercialization of CNT-TFT technology.