Showing papers by "Zhifeng Ren published in 2023"

A multifunctional highway system incorporating superconductor levitated vehicles and liquefied hydrogen

Abstract: Magnetic levitation for the transport of people and goods using bulk superconductors and electrical power transmission using superconductors have both been demonstrated, but neither has been developed for daily use due to technological deficiencies and high costs. We envision combining the transport of people and goods and energy transmission and storage in a single system. Such a system, built on existing highway infrastructure, incorporates a superconductor guideway, allowing for simultaneous levitation of vehicles with magnetized undercarriages for rapid transport without schedule limitations and lossless transmission and storage of electricity. Incorporating liquefied hydrogen additionally allows for simultaneous cooling of the superconductor guideway and sustainable energy transport and storage. Here, we report the successful demonstration of the primary technical prerequisite, levitating a magnet above a superconductor guideway.

High-field critical current density enhancement in GdBCO coated conductors by cooperative defects

Abstract: Irradiation can precisely control defects in, and improve the superconducting properties of, REBa2Cu3O7−δ (REBCO, RE: rare earth) coated conductors (CCs). Here we report an effective approach for enhancing the in-field performance of GdBCO CCs. The critical current density (J c) of GdBCO films was significantly improved through cooperative defects created by co-irradiation with O ions and protons, especially at low temperatures and high magnetic fields. Surprisingly, the in-field J c of commercial CCs can be nearly doubled. The cooperative irradiation-induced defects are uniformly distributed throughout the GdBCO layer, which promotes the overall performance of the CC. Moreover, the dimensions of these irradiation-induced defects closely match the coherence length of REBCO. This simple and efficient method is a practical post-production solution to improve the in-field performance of commercial REBCO CCs.

Near‐Room‐Temperature Thermoelectric Performance Enhancement Via Phonon Spectra Mismatch in Mg3(Sb, Bi)2‐Based Material by Incorporating Multi‐Walled Carbon Nanotubes

Abstract: Although a high figure of merit (zT) over a wide range of temperatures has been shown in n‐type Zintl Mg3(Sb, Bi)2, further improvement of its near‐room‐temperature performance is still required to promote its application in next‐generation thermoelectric coolers and power generators. Here, a novel strategy of phonon spectra mismatch for enhancing the thermoelectric performance of Mg3(Sb, Bi)2 is reported by incorporating multi‐walled carbon nanotubes (MWCNT). The introduction of very small amounts of MWCNT generates a large interfacial thermal resistance and thus significantly reduces the lattice thermal conductivity of the resulting composites, while maintaining a high power factor. As a result, a zT of ≈1.5 at 573 K and an average zT of 1.14 between 323 and 573 K can be achieved in the 0.5 wt% MWCNT composite. Moreover, a high conversion efficiency of ≈8.1% under a temperature difference of 283 K is realized in a resulting single‐leg device, making it a promising candidate material for low‐grade heat recovery. This study provides not only a material with a high near‐room‐temperature zT but also a unique insight into the design of high‐performance thermoelectric materials via compositing to exploit the large difference in phonon spectra between the components of the composite.

Hierarchical Interconnected NiMoN with Large Specific Surface Area and High Mechanical Strength for Efficient and Stable Alkaline Water/Seawater Hydrogen Evolution

Abstract: NiMo-based nanostructures are among the most active hydrogen evolution reaction (HER) catalysts under an alkaline environment due to their strong water dissociation ability. However, these nanostructures are vulnerable to the destructive effects of H2 production, especially at industry-standard current densities. Therefore, developing a strategy to improve their mechanical strength while maintaining or even further increasing the activity of these nanocatalysts is of great interest to both the research and industrial communities. Here, a hierarchical interconnected NiMoN (HW-NiMoN-2h) with a nanorod-nanowire morphology was synthesized based on a rational combination of hydrothermal and water bath processes. HW-NiMoN-2h is found to exhibit excellent HER activity due to the accomodation of abundant active sites on its hierarchical morphology, in which nanowires connect free-standing nanorods, concurrently strengthening its structural stability to withstand H2 production at 1 A cm-2. Seawater is an attractive feedstock for water electrolysis since H2 generation and water desalination can be addressed simultaneously in a single process. The HER performance of HW-NiMoN-2h in alkaline seawater suggests that the presence of Na+ ions interferes with the reation kinetics, thus lowering its activity slightly. However, benefiting from its hierarchical and interconnected characteristics, HW-NiMoN-2h is found to deliver outstanding HER activity of 1 A cm-2 at 130 mV overpotential and to exhibit excellent stability at 1 A cm-2 over 70 h in 1 M KOH seawater.