Metal Cation Pre-Intercalated Ti3C2Tx MXene as Ultra-High Areal Capacitance Electrodes for Aqueous Supercapacitors

Two-dimensional transition-metal carbides and nitrides “MXenes” have demonstrated great potential as electrode materials for electrochemical energy storage systems. This is especially true for delaminated Ti3C2Tx, which already shows outstanding gravimetric and volumetric capacitance, with areal capacitance limited by thickness (only a few microns). However, the performance of multilayer Ti3C2Tx has been more modest. Here, we report on using metal cation (viz., Na+, K+, and Mg2+) pre-intercalated multilayer Ti3C2Tx as electrodes for aqueous supercapacitors. These electrodes are scalable and amenable to roll-to-roll manufacturing, with adjustable areal loadings of 5.2 to 20.1 mg/cm2. K–Ti3C2Tx exhibited the highest capacitances at different scan rates. A gravimetric capacitance comparable to that of delaminated MXene of up to 300 F/g was achieved for multilayer K–Ti3C2Tx but with an outstanding ultra-high areal capacitance of up to 5.7 F/cm2, which is 10-fold higher than the 0.5 F/cm2 of delaminated MXene and exceeds the 4.0 F/cm2 of microengineered MXene electrodes

Nanoscale insights into the structure of solution-processed graphene by x-ray scattering

Chemical exfoliation is an attractive approach for the synthesis of graphene due to its low cost and simplicity. However, challenges still remain in the characterization of solution-processed graphene, in particular with atomic resolution. Through this work we demonstrate the x-ray pair distribution function as a novel approach to study solution-processed graphene or other 2D materials with atomic resolution, directly in solution, produced by liquid-phase and electrochemical exfoliations. The results show the disappearance of long-range atomic correlations, in both cases, confirming the production of single and few-layer graphene. In addition, a considerable ring distortion has been observed as compared to graphite, irrespective of the solvent used: the normal surface angle to the sheet of the powder sample should be less than 6°, compatible with ripples formation observed in suspended graphene. We attribute this effect to the interaction of solvent molecules with the graphene nanosheets

Synthesis of 2D anatase TiO₂ with highly reactive facets by fluorine-free topochemical conversion of 1T-TiS₂ nanosheets

Two-dimensional (2D) anatase titanium dioxide (TiO(2)) is expected to exhibit different properties as compared to anatase nanocrystallites, due to its highly reactive exposed facets. However, access to 2D anatase TiO(2) is limited by the non-layered nature of the bulk crystal, which does not allow use of top-down chemical exfoliation. Large efforts have been dedicated to the growth of 2D anatase TiO(2) with high reactive facets by bottom-up approaches, which relies on the use of harmful chemical reagents. Here, we demonstrate a novel fluorine-free strategy based on topochemical conversion of 2D 1T-TiS(2) for the production of single crystalline 2D anatase TiO(2), exposing the {001} facet on the top and bottom and {100} at the sides of the nanosheet. The exposure of these faces, with no additional defects or doping, gives rise to a significant activity enhancement in the hydrogen evolution reaction, as compared to commercially available Degussa P25 TiO(2) nanoparticles. Because of the strong potential of TiO(2) in many energy-based applications, our topochemical approach offers a low cost, green and mass scalable route for production of highly crystalline anatase TiO(2) with well controlled and highly reactive exposed facets

Solution-based synthesis and processing of Sn- and Bi-doped Cu₃SbSe₄ nanocrystals, nanomaterials and ring-shaped thermoelectric generators

Copper-based chalcogenides that comprise abundant, low-cost, and environmental friendly elements are excellent materials for a number of energy conversion applications, including photovoltaics, photocatalysis, and thermoelectrics (TE). In such applications, the use of solution-processed nanocrystals (NCs) to produce thin films or bulk nanomaterials has associated several potential advantages, such as high material yield and throughput, and composition control with unmatched spatial resolution and cost. Here we report on the production of Cu₃SbSe₄ (CASe) NCs with tuned amounts of Sn and Bi dopants. After proper ligand removal, as monitored by nuclear magnetic resonance and infrared spectroscopy, these NCs were used to produce dense CASe bulk nanomaterials for solid state TE energy conversion. By adjusting the amount of extrinsic dopants, dimensionless TE figures of merit (ZT) up to 1.26 at 673 K were reached. Such high ZT values are related to an optimized carrier concentration by Sn doping, a minimized lattice thermal conductivity due to efficient phonon scattering at point defects and grain boundaries, and to an increase of the Seebeck coefficient obtained by a modification of the electronic band structure with Bi doping. Nanomaterials were further employed to fabricate ring-shaped TE generators to be coupled to hot pipes, which provided 20 mV and 1 mW per TE element when exposed to a 160 °C temperature gradient. The simple design and good thermal contact associated with the ring geometry and the potential low cost of the material solution processing may allow the fabrication of TE generators with short payback times

Lightweight Wearable Thermoelectric Cooler with Rationally Designed Flexible Heatsink Consisting of Phase-change Material/Graphite/Silicone Elastomer

In this paper, we propose a lightweight wearable thermoelectric (TE) cooler with a rationally designed flexible heatsink. Heatsinks are commonly designed for use with stationary applications, and are consequently rigid..

Enhanced glass forming ability of Fe-based amorphous alloys with minor Cu addition

A novel approach was reported that allows us to enhance glass-forming ability (GFA) of Fe-based amorphous alloys with high saturation magnetization by minor substitution Cu, which has a large positive heat of mixing and similar atomic radius with the main constituent Fe. The minor Cu substitution (<1 at.%) can substantially increase the GFA of Fe-based amorphous alloys with the primary phase that is not alpha-Fe (110) type phase. Using this strategy, Fe-based amorphous alloys with both high saturation magnetization and good GFA were developed. Our results reveal that the formation of competing crystalline phases is beneficial for the GFA. We anticipate that this work may guide the way for designing new Fe-based amorphous alloys with high saturation magnetization and large GFA concurrently. (C) 2015 Elsevier B.V. All rights reserved

Lightweight Wearable Thermoelectric Cooler with Rationally Designed Flexible Heatsink Consisting of Phase-change Material/Graphite/Silicone Elastomer

In this paper, we propose a lightweight wearable thermoelectric (TE) cooler with a rationally designed flexible heatsink. Heatsinks are commonly designed for use with stationary applications, and are consequently rigid..

Inkjet-printed SnOx as an effective electron transport layer for planar perovskite solar cells and the effect of Cu doping

Inkjet printing is a more sustainable and scalable fabrication method than spin coating for producing perovskite solar cells (PSCs). Although spin-coated SnO2 has been intensively studied as an effective electron transport layer (ETL) for PSCs, inkjet-printed SnO2 ETLs have not been widely reported. Here, we fabricated inkjet-printed, solution-processed SnOx ETLs for planar PSCs. A champion efficiency of 17.55% was achieved for the cell using a low-temperature processed SnOx ETL. The low-temperature SnOx exhibited an amorphous structure and outperformed high-temperature crystalline SnO2. The improved performance was attributed to enhanced charge extraction and transport and suppressed charge recombination at ETL/perovskite interfaces, which originated from enhanced electrical and optical properties of SnOx, improved perovskite film quality, and well-matched energy level alignment between the SnOx ETL and the perovskite layer. Furthermore, SnOx was doped with Cu. Cu doping increased surface oxygen defects and upshifted energy levels of SnOx, leading to reduced device performance. A tunable hysteresis was observed for PSCs with Cu-doped SnOx ETLs, decreasing at first and turning into inverted hysteresis afterwards with increasing Cu doping level. This tunable hysteresis was related to the interplay between charge/ion accumulation and recombination at ETL/perovskite interfaces in the case of electron extraction barriers