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In this perspective, we outline that a space borne gravitational wave detector network combining LISA and Taiji can be used to measure the Hubble constant with an uncertainty less than 0.5% in ten years, compared with the network of the ground based gravitational wave detectors which can measure the Hubble constant within a 2% uncertainty in the next five years by the standard siren method. Taiji is a Chinese space borne gravitational wave detection mission planned for launch in the early 2030 s. The pilot satellite mission Taiji-1 has been launched in August 2019 to verify the feasibility of Taiji. The results of a few technologies tested on Taiji-1 are presented in this paper. Gravitational wave astronomy has opened the door to test general relativity and the effect of gravity in the Universe. The authors present the capabilities of an overlap between space gravitational wave detectors LISA and Taiji to constrain the Hubble constant to 0.5%, in 10 years, and what can be learned from the satellite pilot Taiji-1 launched in 2019.

Harvesting energy from water movement has aroused extensive and intensive interest because of its great potential in both energy-related field and wearable electronics. In this work, simply bridging two carbon nanotube (CNT) electrodes by HCl/polyvinyl alcohol (PVA) electrolyte gel with CaCl2 in one side, a novel moisture induced self-charging device (MISD) was successfully fabricated. The MISD can be directly charged to 0.348 V in a humid environment without any complex experimental configuration and the harvesting energy can be effectively stored. The self-charging behaviors under various humid conditions have been explored. The self-charging property is based on the automatic electrolyte diffusion, which is driven by water absorption from moisture by CaCl2. The diffusion can reorient and dislocate conductive ions and induce a potential across the bridge. The application possibility was demonstrated by scaling up MISDs in series to power a timer. Output improvement of a single MISD is also available based on a sandwich like structure, which can reach 0.243 mW cm−2. Besides its application potential in wearable and smart electronics, the MISD also provides a reference for the novel utilization of moisture in energy harvesting and storage.

Based on porous carbon nanotube/polyaniline composite (CNT/PANI) and poly(vinyl alcohol) gel, we fabricated centimeter-sized hydrocapacitors with dual functions of energy conversion and storage with an efficient low-cost method. Owning to excellent hydrophily and large specific capacitance of CNT/PANI, the hydrocapacitors can easily convert energy from water movement induced by capillarity, gravity, or air pressure difference into electricity and store the generated electricity. Especially, sandwich-like hydrocapacitors outputted large current of 1.65 mA through an external load of 100 Ω, and hydrocapacitors showed good extendibility by connecting in series. To explain the mechanism of hydrocapacitors in this work, a possible model based on capillarity and traditional streaming potential was proposed and discussed. Hydrocapacitors here also provide a reference for future integration of nanogenerators and energy storage parts.

Carbon nanotubes (CNTs) and other related CNT-based materials with a high thermal conductivity can be used as promising heat dissipation materials. Meanwhile, the miniaturization and high functionality of portable electronics, such as laptops and mobile phones, are achieved at the cost of overheating the high power-density components. The heat removal for hot spots occurring in a relatively narrow space requires simple and effective cooling methods. Here, an auxiliary passive cooling approach by the aid of a flat plate (aluminum-magnesium alloy) is investigated to accommodate heat dissipation in a narrow space. The cooling efficiency can be raised to 43.5%. The cooling performance of several CNT-based samples is compared under such circumstances. Heat dissipation analyses show that, when there is a nearby plate for cooling assistance, the heat radiation is weakened and natural convection is largely improved. Thus, improving heat radiation by increasing emissivity without reducing natural convection can effectively enhance the cooling performance. Moreover, the decoration of an auxiliary cooling plate with sprayed CNTs can further improve the cooling performance of the entire setup.

Transition metal dichalcogenides (TMDs) are van der Waals layered materials with sizable and tunable bandgaps, offering promising platforms for two-dimensional electronics and optoelectronics. To this end, the bottleneck is how to acquire high-quality single crystals in a facile and efficient manner. As one of the most widely employed method of single-crystal growth, conventional chemical vapor transport (CVT) generally encountered problems including the excess nucleation that leads to small crystal clusters and slow growth rate. To address these issues, a seed crystal is introduced to suppress the nucleation and an inner tube is adopted as both a separator and a flow restrictor, favoring the growth of large-size and high-quality TMD single crystals successfully. Three examples are presented, the effective growth of millimeter-sized MoSe2 and MoTe2 single crystals, and the greatly shortened growth period for PtSe2 single crystal, all of which are synthesized in high quality according to detailed characterizations. The mechanism of seeded CVT is discussed. Furthermore, a phototransistor based on exfoliated multi-layered MoSe2 displays excellent photoresponse in ambient conditions, and considerably rapid rise and fall time of 110 and 125 us are obtained. This work paves the way for developing a facile and versatile method to synthesize high-quality TMD single crystals in laboratory, which could serve as favorable functional materials for potential low-dimensional optoelectronics.

It is known that carbon nanotubes (CNTs) possess a high light absorption coefficient with a very broad spectrum, showing good potential for solar-thermal conversion. Bi2Te3 is a typical thermoelectric material with high thermoelectric conversion efficiency. In this study, we first fabricated several simple elements based on p- and n-type Bi2Te3 respectively. By integrating p- and n-type elements in series, we constructed a novel solar thermoelectric conversion device covered with 0.32 g/m2 CNT sheets, which showed a high light absorption coefficient and generated a large short-circuit current (Isc) of 200 mA. The size of the cross section of each series element was 0.19×0.19 cm2. Thus, the short-circuit current density (Jsc) was as high as 5520 mA/cm2. The open-circuit voltage (Voc) of the device reached 400 mV. Each element of the device displayed a power conversion efficiency (PCE) of 2.1% in the near-infrared (NIR) region by a narrow band diode laser source with light flux of 100 mW/cm2 without using any optical or thermal concentrator. Furthermore, the device is stable, durable and capable of operating at high temperatures and thus is promising for converting sunlight into electricity. This work provides a simple and convenient approach to prepare solar-energy conversion devices for large-scale applications in the future.

The zinc-based primary batteries have various merits including the low cost, high-security and reasonable energy, but their one-time use and low power performance limit the wider applications. Compared with the primary batteries, the supercapacitor has an extra higher cycling performance and power capability, but its specific energy is lower. Here we originally achieve a novel hybrid battery combined of a zinc-based primary battery and a supercapacitor through a unique assembly method. In this new structure, two symmetrical carbon nanotube/polyaniline nanoporous composites as supercapacitor electrodes are inserted in a zinc–manganese dioxide primary battery system with a way in series. Meanwhile, a special technique is used to form excellent conductive connections between the supercapacitor electrodes and the primary battery cathode and anode, respectively. This hybrid battery shows both a high specific power similar to that of the supercapacitor and a high specific energy comparable to that of the primary battery. It is more striking that the rechargeable character of this hybrid battery is much more excellent. Its specific capacity retained 75% after 500 cycles of charge–discharge at the high current density of 2 A g−1 while the coulombic efficiency kept at 100%. These notable improvements are attributed to the special design on the structure and chemistry system of the hybrid battery combining the merits of both the primary battery and the supercapacitor.