Publications by authors named "Emily Hitz"

26 Publications

  • Page 1 of 1

High-Temperature Pulse Method for Nanoparticle Redispersion.

J Am Chem Soc 2020 Oct 21;142(41):17364-17371. Epub 2020 Sep 21.

Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, United States.

Nanoparticles suffer from aggregation and poisoning issues (e.g., oxidation) that severely hinder their long-term applications. However, current redispersion approaches, such as continuous heating in oxidizing and reducing environments, face challenges including grain growth effects induced by long heating times as well as complex procedures. Herein, we report a facile and efficient redispersion process that enables us to directly transform large aggregated particles into nanoscale materials. In this method, a piece of carbon nanofiber film was used as a heater and high treatment temperature (∼1500-2000 K) is rapidly elevated and maintained for a very short period of time (100 ms), followed by fast quenching back to room temperature at a cooling rate of 10 K/s to inhibit sintering. With these conditions we demonstrate the redispersion of large aggregated metal oxide particles into metallic nanoparticles just ∼10 nm in size, uniformly distributed on the substrate. Furthermore, the metallic states of the nanoparticles are renewed during the heat treatment through reduction. The redispersion process removes impurities and poisoning elements, yet is able to maintain the integrity of the substrate because of the ultrashort heating pulse time. This method is also significantly faster (ca. milliseconds) compared to conventional redispersion treatments (ca. hours), providing a pragmatic strategy to redisperse degraded particles for a variety of applications.
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http://dx.doi.org/10.1021/jacs.0c04887DOI Listing
October 2020

Scalable aesthetic transparent wood for energy efficient buildings.

Nat Commun 2020 07 31;11(1):3836. Epub 2020 Jul 31.

Department of Materials Science and Engineering, University of Maryland, College Park, MD, 20742, USA.

Nowadays, energy-saving building materials are important for reducing indoor energy consumption by enabling better thermal insulation, promoting effective sunlight harvesting and offering comfortable indoor lighting. Here, we demonstrate a novel scalable aesthetic transparent wood (called aesthetic wood hereafter) with combined aesthetic features (e.g. intact wood patterns), excellent optical properties (an average transmittance of ~ 80% and a haze of ~ 93%), good UV-blocking ability, and low thermal conductivity (0.24 W mK) based on a process of spatially selective delignification and epoxy infiltration. Moreover, the rapid fabrication process and mechanical robustness (a high longitudinal tensile strength of 91.95 MPa and toughness of 2.73 MJ m) of the aesthetic wood facilitate good scale-up capability (320 mm × 170 mm × 0.6 mm) while saving large amounts of time and energy. The aesthetic wood holds great potential in energy-efficient building applications, such as glass ceilings, rooftops, transparent decorations, and indoor panels.
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http://dx.doi.org/10.1038/s41467-020-17513-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7395769PMC
July 2020

A High-Performance Self-Regenerating Solar Evaporator for Continuous Water Desalination.

Adv Mater 2019 Jun 16;31(23):e1900498. Epub 2019 Apr 16.

Department of Materials Science and Engineering, University of Maryland, College Park, MD, 20742, USA.

Emerging solar desalination by interfacial evaporation shows great potential in response to global water scarcity because of its high solar-to-vapor efficiency, low environmental impact, and off-grid capability. However, solute accumulation at the heating interface has severely impacted the performance and long-term stability of current solar evaporation systems. Here, a self-regenerating solar evaporator featuring excellent antifouling properties using a rationally designed artificial channel-array in a natural wood substrate is reported. Upon solar evaporation, salt concentration gradients are formed between the millimeter-sized drilled channels (with a low salt concentration) and the microsized natural wood channels (with a high salt concentration) due to their different hydraulic conductivities. The concentration gradients allow spontaneous interchannel salt exchange through the 1-2 µm pits, leading to the dilution of salt in the microsized wood channels. The drilled channels with high hydraulic conductivities thus function as salt-rejection pathways, which can rapidly exchange the salt with the bulk solution, enabling the real-time self-regeneration of the evaporator. Compared to other salt-rejection designs, the solar evaporator exhibits the highest efficiency (≈75%) in a highly concentrated salt solution (20 wt% NaCl) under 1 sun irradiation, as well as long-term stability (over 100 h of continuous operation).
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http://dx.doi.org/10.1002/adma.201900498DOI Listing
June 2019

A nanofluidic ion regulation membrane with aligned cellulose nanofibers.

Sci Adv 2019 Feb 22;5(2):eaau4238. Epub 2019 Feb 22.

Department of Materials Science and Engineering, University of Maryland College Park, College Park, MD 20742, USA.

The advancement of nanofluidic applications will require the identification of materials with high-conductivity nanoscale channels that can be readily obtained at massive scale. Inspired by the transpiration in mesostructured trees, we report a nanofluidic membrane consisting of densely packed cellulose nanofibers directly derived from wood. Numerous nanochannels are produced among an expansive array of one-dimensional cellulose nanofibers. The abundant functional groups of cellulose enable facile tuning of the surface charge density via chemical modification. The nanofiber-nanofiber spacing can also be tuned from ~2 to ~20 nm by structural engineering. The surface-charge-governed ionic transport region shows a high ionic conductivity plateau of ~2 mS cm (up to 10 mM). The nanofluidic membrane also exhibits excellent mechanical flexibility, demonstrating stable performance even when the membrane is folded 150°. Combining the inherent advantages of cellulose, this novel class of membrane offers an environmentally responsible strategy for flexible and printable nanofluidic applications.
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http://dx.doi.org/10.1126/sciadv.aau4238DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6386557PMC
February 2019

Isotropic Paper Directly from Anisotropic Wood: Top-Down Green Transparent Substrate Toward Biodegradable Electronics.

ACS Appl Mater Interfaces 2018 Aug 15;10(34):28566-28571. Epub 2018 Aug 15.

Department of Materials Science and Engineering , University of Maryland , College Park , Maryland 20742 , United States.

Flexible electronics have found useful applications in both the scientific and industrial communities. However, substrates traditionally used for flexible electronics, such as plastic, cause many environmental issues. Therefore, a transparent substrate made from natural materials provides a promising alternative because it can be degraded in nature. The traditional bottom-up fabrication method for transparent paper is expensive, environmentally unfriendly, and time-consuming. In this work, for the first time, we developed a top-down method to fabricate isotropic, transparent paper directly from anisotropic wood. The top-down method includes two steps: a delignification process to bleach the wood by lignin removal and a pressing process for removing light-reflecting and -scattering sources. The resulting isotropic, transparent paper has high transmittance of about 90% and high haze over 80% and is demonstrated as a nature-disposable substrate for electronic/optical devices. Adjusting the pressing ratio used changes the density of the resulting paper, which tunes the microstructure-related properties of the isotropic, transparent paper. This top-down method is simple, fast, environmentally friendly, and cost-effective, which can greatly promote the development of paper-based green optical and electronic devices.
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http://dx.doi.org/10.1021/acsami.8b08055DOI Listing
August 2018

From Wood to Textiles: Top-Down Assembly of Aligned Cellulose Nanofibers.

Adv Mater 2018 Jul 7;30(30):e1801347. Epub 2018 Jun 7.

Department of Materials Science and Engineering, University of Maryland College Park, College Park, MD, 20742, USA.

Advanced textiles made of macroscopic fibers are usually prepared from synthetic fibers, which have changed lives over the past century. The shortage of petrochemical resources, however, greatly limits the development of the textile industry. Here, a facile top-down approach for fabricating macroscopic wood fibers for textile applications (wood-textile fibers) comprising aligned cellulose nanofibers directly from natural wood via delignification and subsequent twisting is demonstrated. Inherently aligned cellulose nanofibers are well retained, while the microchannels in the delignified wood are squeezed and totally removed by twisting, resulting in a dense structure with approximately two times higher mechanical strength (106.5 vs 54.9 MPa) and ≈20 times higher toughness (7.70 vs 0.36 MJ m ) than natural wood. Dramatically different from natural wood, which is brittle in nature, the resultant wood-textile fibers are highly flexible and bendable, likely due to the twisted structures. The wood-textile fibers also exhibit excellent knitting properties and dyeability, which are critical for textile applications. Furthermore, functional wood-textile fibers can be achieved by preinfiltrating functional materials in the delignified wood film before twisting. This top-down approach of fabricating aligned macrofibers is simple, scalable, and cost-effective, representing a promising direction for the development of smart textiles and wearable electronics.
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http://dx.doi.org/10.1002/adma.201801347DOI Listing
July 2018

Epitaxial Welding of Carbon Nanotube Networks for Aqueous Battery Current Collectors.

ACS Nano 2018 Jun 17;12(6):5266-5273. Epub 2018 May 17.

Department of Materials Science and Engineering , University of Maryland , College Park , Maryland 20742 , United States.

Carbon nanomaterials are desirable candidates for lightweight, highly conductive, and corrosion-resistant current collectors. However, a key obstacle is their weak interconnection between adjacent nanostructures, which renders orders of magnitude lower electrical conductivity and mechanical strength in the bulk assemblies. Here we report an "epitaxial welding" strategy to engineer carbon nanotubes (CNTs) into highly crystalline and interconnected structures. Solution-based polyacrylonitrile was conformally coated on CNTs as "nanoglue" to physically join CNTs into a network, followed by a rapid high-temperature annealing (>2800 K, overall ∼30 min) to graphitize the polymer coating into crystalline layers that also bridge the adjacent CNTs to form an interconnected structure. The contact-welded CNTs (W-CNTs) exhibit both a high conductivity (∼1500 S/cm) and a high tensile strength (∼120 MPa), which are 5 and 20 times higher than the unwelded CNTs, respectively. In addition, the W-CNTs display chemical and electrochemical stabilities in strong acidic/alkaline electrolytes (>6 mol/L) when potentiostatically stressing at both cathodic and anodic potentials. With these exceptional properties, the W-CNT films are optimal as high-performance current collectors and were demonstrated in the state-of-the-art aqueous battery using a "water-in-salt" electrolyte.
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http://dx.doi.org/10.1021/acsnano.7b08584DOI Listing
June 2018

Wood-Based Nanotechnologies toward Sustainability.

Adv Mater 2018 Jan 4;30(1). Epub 2017 Dec 4.

Department of Materials Science and Engineering, University of Maryland College Park, College Park, MD, 20742, USA.

With over 30% global land coverage, the forest is one of nature's most generous gifts to human beings, providing shelters and materials for all living beings. Apart from being sustainable, renewable, and biodegradable, wood and its derivative materials are also extremely fascinating from a materials aspect, with numerous advantages including porous and hierarchical structure, excellent mechanical performance, and versatile chemistry. Here, strategies for designing novel wood-based materials via advanced nanotechnologies are summarized, including both the controllable bottom-up assembly from the highly crystalline nanocellulose building block and the more efficient top-down approaches directly from wood. Beyond material design, recent advances regarding the sustainable applications of these novel wood-based materials are also presented, focusing on areas that are traditionally dominated by man-made nonrenewable materials such as plastic, glass, and metals, as well as more advanced applications in the areas of energy storage, wastewater treatment and solar-steam-assisted desalination. With all recent progress pertaining to materials' design and sustainable applications presented, a vision for the future engineering of wood-based materials to promote continuous and healthy progress toward true sustainability is outlined.
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http://dx.doi.org/10.1002/adma.201703453DOI Listing
January 2018

High temperature thermal management with boron nitride nanosheets.

Nanoscale 2017 Dec;10(1):167-173

Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA.

The rapid development of high power density devices requires more efficient heat dissipation. Recently, two-dimensional layered materials have attracted significant interest due to their superior thermal conductivity, ease of production and chemical stability. Among them, hexagonal boron nitride (h-BN) is electrically insulating, making it a promising thermal management material for next-generation electronics. In this work, we demonstrated that an h-BN thin film composed of layer-by-layer laminated h-BN nanosheets can effectively enhance the lateral heat dissipation on the substrate. We found that by using the BN-coated glass instead of bare glass as the substrate, the highest operating temperature of a reduced graphene oxide (RGO) based device could increase from 700 °C to 1000 °C, and at the same input power, the operating temperature of the RGO device is effectively decreased. The remarkable performance improvement using the BN coating originates from its anisotropic thermal conductivity: a high in-plane thermal conductivity of 14 W m K for spreading and a low cross-plane thermal conductivity of 0.4 W m K to avoid a hot spot right underneath the device. Our results provide an effective approach to improve the heat dissipation in integrated circuits and high power devices.
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http://dx.doi.org/10.1039/c7nr07058fDOI Listing
December 2017

Lightweight, Mesoporous, and Highly Absorptive All-Nanofiber Aerogel for Efficient Solar Steam Generation.

ACS Appl Mater Interfaces 2018 Jan 29;10(1):1104-1112. Epub 2017 Dec 29.

School of Environment and Civil Engineering, Dongguan University of Technology , Guangdong 523808, China.

The global fresh water shortage has driven enormous endeavors in seawater desalination and wastewater purification; among these, solar steam generation is effective in extracting fresh water by efficient utilization of naturally abundant solar energy. For solar steam generation, the primary focus is to design new materials that are biodegradable, sustainable, of low cost, and have high solar steam generation efficiency. Here, we designed a bilayer aerogel structure employing naturally abundant cellulose nanofibrils (CNFs) as basic building blocks to achieve sustainability and biodegradability as well as employing a carbon nanotube (CNT) layer for efficient solar utilization with over 97.5% of light absorbance from 300 to 1200 nm wavelength. The ultralow density (0.0096 g/cm) of the aerogel ensures that minimal material is required, reducing the production cost while at the same time satisfying the water transport and thermal-insulation requirements due to its highly porous structure (99.4% porosity). Owing to its rationally designed structure and thermal-regulation performance, the bilayer CNF-CNT aerogel exhibits a high solar-energy conversion efficiency of 76.3% and 1.11 kg m h at 1 kW m (1 Sun) solar irradiation, comparable or even higher than most of the reported solar steam generation devices. Therefore, the all-nanofiber aerogel presents a new route for designing biodegradable, sustainable, and scalable solar steam generation devices with superb performance.
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http://dx.doi.org/10.1021/acsami.7b15125DOI Listing
January 2018

Three-Dimensional Printed Thermal Regulation Textiles.

ACS Nano 2017 11 1;11(11):11513-11520. Epub 2017 Nov 1.

Department of Materials Science and Engineering and ‡Department of Mechanical Engineering, University of Maryland , College Park, Maryland 20742, United States.

Space cooling is a predominant part of energy consumption in people's daily life. Although cooling the whole building is an effective way to provide personal comfort in hot weather, it is energy-consuming and high-cost. Personal cooling technology, being able to provide personal thermal comfort by directing local heat to the thermally regulated environment, has been regarded as one of the most promising technologies for cooling energy and cost savings. Here, we demonstrate a personal thermal regulated textile using thermally conductive and highly aligned boron nitride (BN)/poly(vinyl alcohol) (PVA) composite (denoted as a-BN/PVA) fibers to improve the thermal transport properties of textiles for personal cooling. The a-BN/PVA composite fibers are fabricated through a fast and scalable three-dimensional (3D) printing method. Uniform dispersion and high alignment of BN nanosheets (BNNSs) can be achieved during the processing of fiber fabrication, leading to a combination of high mechanical strength (355 MPa) and favorable heat dispersion. Due to the improved thermal transport property imparted by the thermally conductive and highly aligned BNNSs, better cooling effect (55% improvement over the commercial cotton fiber) can be realized in the a-BN/PVA textile. The wearable a-BN/PVA textiles containing the 3D-printed a-BN/PVA fibers offer a promising selection for meeting the personal cooling requirement, which can significantly reduce the energy consumption and cost for cooling the whole building.
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http://dx.doi.org/10.1021/acsnano.7b06295DOI Listing
November 2017

Highly Anisotropic Conductors.

Adv Mater 2017 Nov 18;29(41). Epub 2017 Sep 18.

Department of Materials Science and Engineering, University of Maryland, College Park, MD, 20742, USA.

Composite materials with ordered microstructures often lead to enhanced functionalities that a single material can hardly achieve. Many biomaterials with unusual microstructures can be found in nature; among them, many possess anisotropic and even directional physical and chemical properties. With inspiration from nature, artificial composite materials can be rationally designed to achieve this anisotropic behavior with desired properties. Here, a metallic wood with metal continuously filling the wood vessels is developed, which demonstrates excellent anisotropic electrical, thermal, and mechanical properties. The well-aligned metal rods are confined and separated by the wood vessels, which deliver directional electron transport parallel to the alignment direction. Thus, the novel metallic wood composite boasts an extraordinary anisotropic electrical conductivity (σ /σ ) in the order of 10 , and anisotropic thermal conductivity (κ /κ ) of 18. These values exceed the highest reported values in existing anisotropic composite materials. The anisotropic functionality of the metallic wood enables it to be used for thermal management applications, such as thermal insulation and thermal dissipation. The highly anisotropic metallic wood serves as an example for further anisotropic materials design; other composite materials with different biotemplates/hosts and fillers can achieve even higher anisotropic ratios, allowing them to be implemented in a variety of applications.
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http://dx.doi.org/10.1002/adma.201703331DOI Listing
November 2017

Ultrafine Silver Nanoparticles for Seeded Lithium Deposition toward Stable Lithium Metal Anode.

Adv Mater 2017 Oct 18;29(38). Epub 2017 Aug 18.

Department of Materials Science and Engineering, University of Maryland at College Park, College Park, MD, 20742, USA.

To exploit the high energy density of the lithium (Li) metal battery, it is imperative to address the dendrite growth and interface instability of the anode. 3D hosts for Li metal are expected to suppress the growth of Li dendrites. Heterogeneous seeds are effective in guiding Li deposition and realizing spatial control over Li nucleation. Herein, this study shows that ultrafine silver (Ag) nanoparticles, which are synthesized via a novel rapid Joule heating method, can serve as nanoseeds to direct the deposition of Li within the 3D host materials, resolving the problems of the Li metal anode. By optimizing the Joule heating method, ultrafine Ag nanoparticles (≈40 nm) are homogeneously anchored on carbon nanofibers. The Ag nanoseeds effectively reduce the nucleation overpotential of Li and guide the Li deposition in the 3D carbon matrix uniformly, free from the dendrites. A stable and reversible Li metal anode is achieved in virtue of the Ag nanoseeds in the 3D substrate, showing a low overpotential (≈0.025 V) for a long cycle life. The ultrafine nanoseeds achieved by rapid Joule heating render uniform deposition of Li metal anode in 3D hosts, promising a safe and long-life Li metal battery for high-energy applications.
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http://dx.doi.org/10.1002/adma.201702714DOI Listing
October 2017

Protected Lithium-Metal Anodes in Batteries: From Liquid to Solid.

Adv Mater 2017 Sep 24;29(36). Epub 2017 Jul 24.

Department of Materials Science and Engineering, University of Maryland at College Park, College Park, Maryland, 20742, USA.

High-energy lithium-metal batteries are among the most promising candidates for next-generation energy storage systems. With a high specific capacity and a low reduction potential, the Li-metal anode has attracted extensive interest for decades. Dendritic Li formation, uncontrolled interfacial reactions, and huge volume effect are major hurdles to the commercial application of Li-metal anodes. Recent studies have shown that the performance and safety of Li-metal anodes can be significantly improved via organic electrolyte modification, Li-metal interface protection, Li-electrode framework design, separator coating, and so on. Superior to the liquid electrolytes, solid-state electrolytes are considered able to inhibit problematic Li dendrites and build safe solid Li-metal batteries. Inspired by the bright prospects of solid Li-metal batteries, increasing efforts have been devoted to overcoming the obstacles of solid Li-metal batteries, such as low ionic conductivity of the electrolyte and Li-electrolyte interfacial problems. Here, the approaches to protect Li-metal anodes from liquid batteries to solid-state batteries are outlined and analyzed in detail. Perspectives regarding the strategies for developing Li-metal anodes are discussed to facilitate the practical application of Li-metal batteries.
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http://dx.doi.org/10.1002/adma.201701169DOI Listing
September 2017

Super-Strong, Super-Stiff Macrofibers with Aligned, Long Bacterial Cellulose Nanofibers.

Adv Mater 2017 Sep 21;29(35). Epub 2017 Jul 21.

Department of Materials Science and Engineering, University of Maryland College Park, College Park, MD, 20742, USA.

With their impressive properties such as remarkable unit tensile strength, modulus, and resistance to heat, flame, and chemical agents that normally degrade conventional macrofibers, high-performance macrofibers are now widely used in various fields including aerospace, biomedical, civil engineering, construction, protective apparel, geotextile, and electronic areas. Those macrofibers with a diameter of tens to hundreds of micrometers are typically derived from polymers, gel spun fibers, modified carbon fibers, carbon-nanotube fibers, ceramic fibers, and synthetic vitreous fibers. Cellulose nanofibers are promising building blocks for future high-performance biomaterials and textiles due to their high ultimate strength and stiffness resulting from a highly ordered orientation along the fiber axis. For the first time, an effective fabrication method is successfully applied for high-performance macrofibers involving a wet-drawing and wet-twisting process of ultralong bacterial cellulose nanofibers. The resulting bacterial cellulose macrofibers yield record high tensile strength (826 MPa) and Young's modulus (65.7 GPa) owing to the large length and the alignment of nanofibers along fiber axis. When normalized by weight, the specific tensile strength of the macrofiber is as high as 598 MPa g cm , which is even substantially stronger than the novel lightweight steel (227 MPa g cm ).
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http://dx.doi.org/10.1002/adma.201702498DOI Listing
September 2017

Superflexible Wood.

ACS Appl Mater Interfaces 2017 Jul 7;9(28):23520-23527. Epub 2017 Jul 7.

Department of Materials Science and Engineering, University of Maryland , College Park, Maryland 20742, United States.

Flexible porous membranes have attracted increasing scientific interest due to their wide applications in flexible electronics, energy storage devices, sensors, and bioscaffolds. Here, inspired by nature, we develop a facile and scalable top-down approach for fabricating a superflexible, biocompatible, biodegradable three-dimensional (3D) porous membrane directly from natural wood (coded as flexible wood membrane) via a one-step chemical treatment. The superflexibility is attributed to both physical and chemical changes of the natural wood, particularly formation of the wavy structure formed by simple delignification induced by partial removal of lignin/hemicellulose. The flexible wood membrane, which inherits its unique 3D porous structure with aligned cellulose nanofibers, biodegradability, and biocompatibility from natural wood, combined with the superflexibility imparted by a simple chemical treatment, holds great potential for a range of applications. As an example, we demonstrate the application of the flexible, breathable wood membrane as a 3D bioscaffold for cell growth.
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http://dx.doi.org/10.1021/acsami.7b06529DOI Listing
July 2017

Highly Flexible and Efficient Solar Steam Generation Device.

Adv Mater 2017 Aug 12;29(30). Epub 2017 Jun 12.

Department of Materials Science and Engineering, University of Maryland, College Park, MD, 20742, USA.

Solar steam generation with subsequent steam recondensation has been regarded as one of the most promising techniques to utilize the abundant solar energy and sea water or other unpurified water through water purification, desalination, and distillation. Although tremendous efforts have been dedicated to developing high-efficiency solar steam generation devices, challenges remain in terms of the relatively low efficiency, complicated fabrications, high cost, and inability to scale up. Here, inspired by the water transpiration behavior of trees, the use of carbon nanotube (CNT)-modified flexible wood membrane (F-Wood/CNTs) is demonstrated as a flexible, portable, recyclable, and efficient solar steam generation device for low-cost and scalable solar steam generation applications. Benefitting from the unique structural merits of the F-Wood/CNTs membrane-a black CNT-coated hair-like surface with excellent light absorbability, wood matrix with low thermal conductivity, hierarchical micro- and nanochannels for water pumping and escaping, solar steam generation device based on the F-Wood/CNTs membrane demonstrates a high efficiency of 81% at 10 kW cm , representing one of the highest values ever-reported. The nature-inspired design concept in this study is straightforward and easily scalable, representing one of the most promising solutions for renewable and portable solar energy generation and other related phase-change applications.
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http://dx.doi.org/10.1002/adma.201701756DOI Listing
August 2017

3D-Printed, All-in-One Evaporator for High-Efficiency Solar Steam Generation under 1 Sun Illumination.

Adv Mater 2017 Jul 4;29(26). Epub 2017 May 4.

Department of Materials Science and Engineering, University of Maryland College Park, College Park, MD, 20742, USA.

Using solar energy to generate steam is a clean and sustainable approach to addressing the issue of water shortage. The current challenge for solar steam generation is to develop easy-to-manufacture and scalable methods which can convert solar irradiation into exploitable thermal energy with high efficiency. Although various material and structure designs have been reported, high efficiency in solar steam generation usually can be achieved only at concentrated solar illumination. For the first time, 3D printing to construct an all-in-one evaporator with a concave structure for high-efficiency solar steam generation under 1 sun illumination is used. The solar-steam-generation device has a high porosity (97.3%) and efficient broadband solar absorption (>97%). The 3D-printed porous evaporator with intrinsic low thermal conductivity enables heat localization and effectively alleviates thermal dissipation to the bulk water. As a result, the 3D-printed evaporator has a high solar steam efficiency of 85.6% under 1 sun illumination (1 kW m ), which is among the best compared with other reported evaporators. The all-in-one structure design using the advanced 3D printing fabrication technique offers a new approach to solar energy harvesting for high-efficiency steam generation.
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http://dx.doi.org/10.1002/adma.201700981DOI Listing
July 2017

Encapsulation of Metallic Na in an Electrically Conductive Host with Porous Channels as a Highly Stable Na Metal Anode.

Nano Lett 2017 06 9;17(6):3792-3797. Epub 2017 May 9.

Department of Materials Science and Engineering, ‡Department of Mechanical Engineering, University of Maryland , College Park, Maryland 20742, United States.

Room-temperature Na ion batteries (NIBs) have attracted great attention because of the widely available, abundant sodium resources and potentially low cost. Currently, the challenge of the NIB development is due primarily to the lack of a high-performance anode, while the Na metal anode holds great promise considering its highest specific capacity of 1165 mA h/g and lowest anodic potential. However, an uneven deposit, relatively infinite volume change, and dendritic growth upon plating/stripping cycles cause a low Coulombic efficiency, poor cycling performance, and severe safety concerns. Here, a stable Na carbonized wood (Na-wood) composite anode was fabricated via a rapid melt infusion (about 5 s) into channels of carbonized wood by capillary action. The channels function as a high-surface-area, conductive, mechanically stable skeleton, which lowers the effective current density, ensures a uniform Na nucleation, and restricts the volume change over cycles. As a result, the Na-wood composite anode exhibited flat plating/stripping profiles with smaller overpotentials and stable cycling performance over 500 h at 1.0 mA/cm in a common carbonate electrolyte system. In sharp comparison, the planar Na metal electrode showed a much shorter cycle life of 100 h under the same test conditions.
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http://dx.doi.org/10.1021/acs.nanolett.7b01138DOI Listing
June 2017

High-capacity, low-tortuosity, and channel-guided lithium metal anode.

Proc Natl Acad Sci U S A 2017 04 20;114(14):3584-3589. Epub 2017 Mar 20.

Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742

Lithium metal anode with the highest capacity and lowest anode potential is extremely attractive to battery technologies, but infinite volume change during the Li stripping/plating process results in cracks and fractures of the solid electrolyte interphase, low Coulombic efficiency, and dendritic growth of Li. Here, we use a carbonized wood (C-wood) as a 3D, highly porous (73% porosity) conductive framework with well-aligned channels as Li host material. We discovered that molten Li metal can infuse into the straight channels of C-wood to form a Li/C-wood electrode after surface treatment. The C-wood channels function as excellent guides in which the Li stripping/plating process can take place and effectively confine the volume change that occurs. Moreover, the local current density can be minimized due to the 3D C-wood framework. Therefore, in symmetric cells, the as-prepared Li/C-wood electrode presents a lower overpotential (90 mV at 3 mA⋅cm), more-stable stripping/plating profiles, and better cycling performance (∼150 h at 3 mA⋅cm) compared with bare Li metal electrode. Our findings may open up a solution for fabricating stable Li metal anode, which further facilitates future application of high-energy-density Li metal batteries.
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http://dx.doi.org/10.1073/pnas.1618871114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5389307PMC
April 2017

Conformal, Nanoscale ZnO Surface Modification of Garnet-Based Solid-State Electrolyte for Lithium Metal Anodes.

Nano Lett 2017 01 16;17(1):565-571. Epub 2016 Dec 16.

Department of Materials Science and Engineering and ‡University of Maryland Energy Research Center, University of Maryland College Park , College Park, Maryland 20742, United States.

Solid-state electrolytes are known for nonflammability, dendrite blocking, and stability over large potential windows. Garnet-based solid-state electrolytes have attracted much attention for their high ionic conductivities and stability with lithium metal anodes. However, high-interface resistance with lithium anodes hinders their application to lithium metal batteries. Here, we demonstrate an ultrathin, conformal ZnO surface coating by atomic layer deposition for improved wettability of garnet solid-state electrolytes to molten lithium that significantly decreases the interface resistance to as low as ∼20 Ω·cm. The ZnO coating demonstrates a high reactivity with lithium metal, which is systematically characterized. As a proof-of-concept, we successfully infiltrated lithium metal into porous garnet electrolyte, which can potentially serve as a self-supported lithium metal composite anode having both high ionic and electrical conductivity for solid-state lithium metal batteries. The facile surface treatment method offers a simple strategy to solve the interface problem in solid-state lithium metal batteries with garnet solid electrolytes.
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http://dx.doi.org/10.1021/acs.nanolett.6b04695DOI Listing
January 2017

A Solution-Processed High-Temperature, Flexible, Thin-Film Actuator.

Adv Mater 2016 Oct 22;28(39):8618-8624. Epub 2016 Aug 22.

Department of Materials Science and Engineering, University of Maryland College Park, College Park, MD, 20742, USA.

A bilayer actuator made of carbon nanotubes (CNTs) and boron nitride (BN) is developed that can withstand high temperatures. The bilayer actuator can be powered quickly to a temperature up to 2000 K within 100 ms and can operate at frequencies from sub-Hertz to about 30 Hz due to the low heat capacity of the thin CNT layer.
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http://dx.doi.org/10.1002/adma.201602777DOI Listing
October 2016

Three-Dimensional Printable High-Temperature and High-Rate Heaters.

ACS Nano 2016 05 10;10(5):5272-9. Epub 2016 May 10.

Department of Materials Science and Engineering, University of Maryland College Park , College Park, Maryland 20742, United States.

High temperature heaters are ubiquitously used in materials synthesis and device processing. In this work, we developed three-dimensional (3D) printed reduced graphene oxide (RGO)-based heaters to function as high-performance thermal supply with high temperature and ultrafast heating rate. Compared with other heating sources, such as furnace, laser, and infrared radiation, the 3D printed heaters demonstrated in this work have the following distinct advantages: (1) the RGO based heater can operate at high temperature up to 3000 K because of using the high temperature-sustainable carbon material; (2) the heater temperature can be ramped up and down with extremely fast rates, up to ∼20 000 K/second; (3) heaters with different shapes can be directly printed with small sizes and onto different substrates to enable heating anywhere. The 3D printable RGO heaters can be applied to a wide range of nanomanufacturing when precise temperature control in time, placement, and the ramping rate are important.
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http://dx.doi.org/10.1021/acsnano.6b01059DOI Listing
May 2016

Reduced Graphene Oxide Films with Ultrahigh Conductivity as Li-Ion Battery Current Collectors.

Nano Lett 2016 06 11;16(6):3616-23. Epub 2016 May 11.

Department of Materials Science and Engineering and ‡Department of Mechanical Engineering, University of Maryland , College Park, Maryland 20742, United States.

Solution processed, highly conductive films are extremely attractive for a range of electronic devices, especially for printed macroelectronics. For example, replacing heavy, metal-based current collectors with thin, light, flexible, and highly conductive films will further improve the energy density of such devices. Films with two-dimensional building blocks, such as graphene or reduced graphene oxide (RGO) nanosheets, are particularly promising due to their low percolation threshold with a high aspect ratio, excellent flexibility, and low cost. However, the electrical conductivity of these films is low, typically less than 1000 S/cm. In this work, we for the first time report a RGO film with an electrical conductivity of up to 3112 S/cm. We achieve high conductivity in RGO films through an electrical current-induced annealing process at high temperature of up to 2750 K in less than 1 min of anneal time. We studied in detail the unique Joule heating process at ultrahigh temperature. Through a combination of experimental and computational studies, we investigated the fundamental mechanism behind the formation of a highly conductive three-dimensional structure composed of well-connected RGO layers. The highly conductive RGO film with high direct current conductivity, low thickness (∼4 μm) and low sheet resistance (0.8 Ω/sq.) was used as a lightweight current collector in Li-ion batteries.
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http://dx.doi.org/10.1021/acs.nanolett.6b00743DOI Listing
June 2016

Electrochemical Intercalation of Lithium Ions into NbSe2 Nanosheets.

ACS Appl Mater Interfaces 2016 05 2;8(18):11390-5. Epub 2016 May 2.

Department of Materials Science and Engineering, University of Maryland , College Park, Maryland 20742, United States.

Transition metal dichalcogenides (TMDCs) have been known for decades to have unique properties and recently attracted broad attention for their two-dimensional (2D) characteristics. NbSe2 is a metallic TMDC that has been studied for its charge density wave transition behavior and superconductivity but is still largely unexplored for its potential use in engineered devices with applications in areas such as electronics, optics, and batteries. Thus, we successfully demonstrate and present evidence of lithium intercalation in NbSe2 as a technique capable of modifying the material properties of NbSe2 for further study. We demonstrate successful intercalation of Li ions into NbSe2 and confirm this result through X-ray diffraction, noting a unit cell size increase from 12.57 to 13.57 Å in the c lattice parameter of the NbSe2 after intercalation. We also fabricate planar half-cell electrochemical devices using ultrathin NbSe2 from platelets to observe evidence of Li-ion intercalation through an increase in the optical transmittance of the material in the visible range. Using 550 nm wavelength light, we observed an increase in optical transmittance of 26% during electrochemical intercalation.
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http://dx.doi.org/10.1021/acsami.5b11583DOI Listing
May 2016

Carbonized-leaf Membrane with Anisotropic Surfaces for Sodium-ion Battery.

ACS Appl Mater Interfaces 2016 Jan 13;8(3):2204-10. Epub 2016 Jan 13.

Department of Materials Science and Engineering, University of Maryland , College Park, Maryland 20742, United States.

A simple one-step thermal pyrolysis route has been developed to prepare carbon membrane from a natural leaf. The carbonized leaf membrane possesses anisotropic surfaces and internal hierarchical porosity, exhibiting a high specific capacity of 360 mAh/g and a high initial Coulombic efficiency of 74.8% as a binder-free, current-collector-free anode for rechargeable sodium ion batteries. Moreover, large-area carbon membranes with low contact resistance are fabricated by simply stacking and carbonizing leaves, a promising strategy toward large-scale sodium-ion battery developments.
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http://dx.doi.org/10.1021/acsami.5b10875DOI Listing
January 2016