Papers Published in High Impact Factor Journals

Years

As of May. 25th, 2024, Dr. Ren has published 630 peer-reviewed papers.

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Tuning the carrier scattering mechanism to improve the thermoelectric power factor

High thermoelectric power factor not only enables potentially high figure of merit ZT but also leads to large output power density, hence it is critical to find an effective route to improve power factor. Previous reports on manipulation of carrier scattering mechanisms (e.g., ionization scattering) were mainly focused on enhancing the Seebeck coefficient. On the contrary, here we demonstrate that by tuning carrier scattering mechanism in n-type Mg3Sb2-based materials, it is possible to noticeably improve the Hall mobility (from ~19 V cm-1 s-2 to ~77 V cm-1 s-2) and hence substantially increasing the power factor by a factor of 3, from ~5 to ~15 µW cm-1 K-2. The enhancement in mobility is mainly due to the reason that ionization scattering has been shifted into mixed scattering between ionization scattering and acoustic phonon scattering, which less effectively scatter the carriers. The strategy of tuning carrier scattering mechanism to improve the mobility should be widely applicable to various materials systems for achieving better thermoelectric performance. (Published by Jing et al. in Energy & Environmental Science, 2017)

Capillary-Force-Induced Cold Welding in Silver-Nanowire-Based Flexible Transparent Electrodes

Silver nanowire (AgNW) films have been studied as the most promising flexible transparent electrodes for flexible photoelectronics. The wire−wire junction resistance in the AgNW film is a critical parameter to the electrical performance, and several techniques of nanowelding or soldering have been reported to reduce the wire−wire junction resistance. However, these methods require either specific facilities, or additional materials as the “solder”, and often have adverse effects to the AgNW film or substrate. In this study, we show that at the nanoscale, capillary force is a powerful driving force that can effectively cause self-limited cold welding of the wire−wire junction for AgNWs. The capillary-force-induced welding can be simply achieved by applying moisture on the AgNW film, without any technical support like the addition of materials or the use of specific facilities. The moisture-treated AgNW films exhibit a significant decrease in sheet resistance, but negligible changes in transparency. We have also demonstrated that this method is effective to heal damaged AgNW films of wearable electronics and can be conveniently performed not only indoors but also outdoors where technical support is often unavailable. The capillary-force-based method may also be useful in the welding of other metal NWs, the fabrication of nanostructures, and smart assemblies for versatile flexible optoelectronic applications. (Published by Liu et al. in Nano Letters, 2017)

Solar thermoelectric generators with a peak efficiency of 7.4%

Concentrating solar power normally employs mechanical heat engines and is thus only used in large-scale power plants; however, it is compatible with inexpensive thermal storage, enabling electricity dispatchability. Concentrating solar thermoelectric generators (STEGs) have the advantage of replacing the mechanical power block with a solid-state heat engine based on the Seebeck e ect, simplifying the system. The highest reported e ciency of STEGs so far is 5.2%. Here, we report experimental measurements of STEGs with a peak e ciency of 9.6% at an optically concentrated normal solar irradiance of 211kWm􀀀2, and a system e ciency of 7.4% after considering optical concentration losses. The performance improvement is achieved by the use of segmented thermoelectric legs, a high-temperature spectrally selective solar absorber enabling stable vacuum operation with absorber temperatures up to 600  C, and combining optical and thermal concentration. Our work suggests that concentrating STEGs have the potential to become a promising alternative solar energy technology. (Published by Kraemer et al. in Nature Energy, 2016)

3D Porous WSSe/NiSe2 Foam for Hydrogen Evolution Catalysis

Improvements in thermoelectric material performance over the past two decades have largely been based on decreasing the phonon thermal conductivity. Enhancing the power factor has been less successful in comparison. In this work, a peak power factor of ∼106 μW·cm^−1·K^−2 is achieved by increasing the hot pressing tem- perature up to 1,373 K in the p-type half-Heusler Nb0.95Ti0.05FeSb. The high power factor subsequently yields a record output power density of ∼22 W·cm^−2 based on a single-leg device operating at between 293 K and 868 K. Such a high-output power density can be beneficial for large-scale power generation applications. (Published by He et al. in Proceedings National Academy of Science U.S.A., 2016)

3D Porous MoSSe/NiSe2 Foam for Hydrogen Evolution Catalysis

Here we report an active and durable earth-abundant transition metal dichalcogenide-based hybrid catalyst that exhibits high hydrogen evolution activity approaching the state-of-the-art platinum catalysts, and superior to those of most transition metal dichalcogenides (molybdenum sulfide, cobalt diselenide and so on). Our material is fabricated by growing ternary molybdenum sulfoselenide particles on self-standing porous nickel diselenide foam. (Published by Zhou et al. in Nature Communication, 2016)

High Thermoelectric Performance in Zintl Phase (Ca, Yb, Eu)Mg2Bi2

Here, we report the rarely studied p-type bismuth (Bi)-based Zintl phases (Ca,Yb,Eu)Mg2Bi2 with a record thermoelectric performance. Phase-pure EuMg2Bi2 is successfully prepared with suppressed bipolar effect to reach ZT ∼ 1. Further partial substitution of Eu by Ca and Yb enhanced ZT to ∼1.3 for Eu0.2Yb0.2Ca0.6Mg2Bi2 at 873 K. Density-functional theory (DFT) simulation indicates the alloying has no effect on the valence band, but does affect the conduction band. Such band engineering results in good p-type thermoelectric properties with high carrier mobility. Using transmission electron microscopy, various types of strains are observed and are believed to be due to atomic mass and size fluctuations. Point defects, strain, dislocations, and nanostructures jointly contribute to phonon scattering, confirmed by the semiclassical theoretical calculations based on a modified Debye–Callaway model of lattice thermal conductivity.(Published by Jing et al. in Proceedings National Academy of Science, 2016)

Quad-Band Solar Spectral Spliter 

We proposed a quad-band solar spectral splitter with both spectral splitting and solar absorption func- tions, which also suppresses radiative heat loss. The splitter is integrated on a single planar substrate, and is based on a combination of a multilayer interference filter and a selective solar thermal absorber. We experimentally demonstrated the quad-band splitting characteristics with SiO2/TiOx multilayer stacks deposited on the WNS selective absorption layer on Cu substrate. The quad-band solar spectrum splitter with WNS absorber exhibits good stability up to 400 °C in vacuum. (Published by Cao et al. in Advanced Materials, 2016)

Graphene-based Nanosheets for Oil Recovery

We have designed and produced a nanofluid of graphene-based amphiphilic nanosheets that is very effective at low concentration. Our nanosheets spontaneously approached the oil–water interface and reduced the interfacial tension in a saline environment (4 wt % NaCl and 1 wt % CaCl2), regardless of the solid surface wettability. A climbing film appeared and grew at moderate hydrodynamic condition to encapsulate the oil phase. With strong hydrodynamic power input, a solid-like interfacial film formed and was able to return to its original form even after being seriously disturbed. The film rapidly separated oil and water phases for slug-like oil displacement. The unique behavior of our nanosheet nanofluid tripled the best performance of conventional nanofluid flooding methods under similar conditions. (Published by Luo et al. in Proceedings National Academy of Science, 2016)

Fatigue-free, Superstretchable, Transparent, and Biocompatible Metal Electrodes

Next-generation flexible electronics require highly stretchable and transparent electrodes. Few electronic conductors are both transparent and stretchable, and even fewer can be cyclically stretched to a large strain without causing fatigue. Fatigue, which is often an issue of strained materials causing failure at low strain levels of cyclic loading, is detrimental to materials under repeated loads in practical applications. Here we show that optimizing topology and/or tuning adhesion of metal nanomeshes can significantly improve stretchability and eliminate strain fatigue. The ligaments in an Au nanomesh on a slippery substrate can locally shift to relax stress upon stretching and return to the original configurationwhen stress is removed. The Au nanomesh keeps a low sheet resistance and high transparency, comparable to those of strain-free indium tin oxide films, when the nanomesh is stretched to a strain of 300%, or shows no fatigue after 50,000 stretches to a strain up to 150%. Moreover, the Au nanomesh is biocompatible and penetrable to biomacromolecules in fluid. (Published by Guo et al. in Proceedings National Academy of Science, 2015)