Search

Zintl compounds such as n‐type Mg3(Sb,Bi)2 show promising thermoelectric applications benefiting from their high valley degeneracy and low lattice thermal conductivity. However, the heavier p‐type AMg2X2 (A = Ca, and Yb; X = Bi and Sb) Zintl counterparts even exhibit a higher κlat due to strong chemical bonding. Reducing κlat of AMg2X2 is an important route for improving thermoelectric performance. Herein, it is found that Cd doping at the Mg site in CaMg2Bi2 can weaken intralayer covalent bonds and soften acoustic phonons, as well as fill the optical phonon gap. These effects result in large atomic displacement, low phonon group velocity, and strong lattice vibration anharmonicity. Doping 10% Cd leads to a reduction of 56% in the κlat of CaMg2Bi2. Moreover, Cd doping promotes orbital alignment and thus increases the density‐of‐states effective mass and Seebeck coefficient. Eventually, in conjunction with carrier concentration optimization by Na doping and band structure engineering by Ba doping, a high ZT of ≈1.3 at 873 K in (Ca0.85Ba0.15)0.995Na0.005Mg1.85Cd0.15Bi2 sample is realized. This work highlights the significant role of manipulating chemical bonding in suppressing phonon propagation of semiconductors. [ABSTRACT FROM AUTHOR]

The Bi2Te3 family has been considered a state‐of‐the‐art thermoelectric material for room‐temperature applications for over half a century. However, scarcity of the material Te has been a persistent issue. Recently, the discovery of n‐type Mg3(Bi, Sb)2‐based materials provides new hope for replacing traditional Bi2Te3, but their thermoelectric properties near room temperature still need improvement for application to practical devices. Herein, a competitive figure of merit of ≈0.8 at 300 K and a high power factor greater than 30 µW cm−1 K−2 at 300 K in n‐type Mg3.14Mn0.06Bi1.4Sb0.59Se0.01 is reported, benefiting from the rationally tuned carrier concentration of 2.29×1019 cm−3 at room temperature. Substituting the Mg site with Mn in Mg3.2Bi1.4Sb0.59Se0.01 changes the dominant carrier scattering mechanism from a mixed scattering of acoustic phonons and ionized impurities to acoustic phonon scattering. Mn doping in Mg3.2Bi1.4Sb0.59Se0.01 also enhances the mobility to 180 cm2 V−1 s−1, reduces the thermal conductivity, and significantly increases the quality factor β of the material. The high room temperature thermoelectric performance of n‐type Mn&Se co‐doped Mg3(Bi, Sb)2‐based materials makes them a highly competitive substitute for commercialized n‐type Bi2Te3. [ABSTRACT FROM AUTHOR]

The increasing development of biomedicine and bioelectronics has highlighted the requirement for smart materials that can respond to changes in physical and chemical properties under external environments, such as magnetic fields, electric fields, and temperature. Accordingly, hydrogels have been widely evaluated as promising candidates for smart materials owing to their intriguing structures comprising a cross‐linked network of polymer chains with interstitial spaces filled with solvent water. This feature endows hydrogels with soft and wet characteristics, which not only induce high tissue affinity but also allow the introduction of environmentally responsive nanoparticles to release specific smart properties. Herein, we reviewed novel smart hydrogels that can be applied in biomedicine and bioelectronics, and highlighted and discussed existing challenges in current technologies and research. [ABSTRACT FROM AUTHOR]

Nanoscale composites for high‐performance electrodes employed in flexible, all‐solid‐state supercapacitors are being developed. A series of binder‐free composites, each consisting of a transition bimetal oxide, a metal oxide, and a metal nitride grown on N‐doped reduced graphene oxide (rGO)‐wrapped nickel foam are obtained by using a universal strategy. Three different transition metals, Co, Mo, and Fe, are separately compounded with nickel ions, which originate from the nickel foam, to form three composites, NiCoO2@Co3O4@Co2N, NiMoO4@MoO3@Mo2N, and NiFe2O4@Fe3O4@Fe2N, respectively. These as‐prepared active materials have similar regular variation patterns in their properties, including better conductivity and battery‐mimicking pseudocapacitance, which result in their high whole‐electrode capacitance performance [2598.3 F g−1 (39.85 F cm−2), 3472.6 F g−1 (41.43 F cm−2) and 1907.5 F g−1 (3.41 F cm−2) for the composites incorporating Co, Mo, and Fe, respectively]. The as‐assembled flexible, all‐solid‐state NiCoO2@Co3O4@Co2N//KOH/PVA//NiCoO2@Co3O4@Co2N device can be easily bent and exhibits high energy density and power density of 92.8 Wh kg−1 and 1670.4 W kg−1, respectively. The universality of this design strategy could allow it to be employed in producing hybrid materials for high‐performance energy‐storage devices. [ABSTRACT FROM AUTHOR]

Decoupling the electric conductivity, Seebeck coefficient, and thermal conductivity is a core issue to improve the properties of thermoelectric materials by tuning the electron and phonon transport properties. Herein, Bi2Te2.7Se0.3/Bi2S3 heterostructure is successfully synthesized by a simple anion exchange method with Bi2Te2.7Se0.3 as the starting material. The Bi2Te2.7Se0.3/Bi2S3 heterointerfaces can achieve an effective phonon scattering and significant decrease in thermal conductivity, while maintaining a high power factor, resulting in an enhanced figure of merit (ZT). By controlling the concentration of Bi2Te2.7Se0.3/Bi2S3 heterointerfaces, the carrier‐transporting and phonon‐scattering behaviors can be simultaneously optimized. A maximum ZT of 0.7 is obtained at 473 K, which is 23% higher than that of pure Bi2Te2.7Se0.3. In addition, the average ZT at 300–548 K increases from 0.49 to 0.61, which is 25% higher than that of pure Bi2Te2.7Se0.3. [ABSTRACT FROM AUTHOR]

The advantage of using composite electrode materials for energy storage is, to a large extent, the synergistic role of their components. Our work focuses on the investigation of the interactions of each phase, exploring the patterns found with the change of materials to provide theoretical or experimental foundations for future study. Here, conductive polymers (CPs), including polyaniline (PANi), polypyrrole (PPy), and polythiophene (PTh), as well as reduced graphene oxide (rGO), and TiO2 with the different crystalline phases of anatase and rutile were applied to form a series of free‐standing and flexible binary or ternary composite electrodes. The electrochemical behaviors of these composite electrodes are presented. The results indicate that the synergistic improvement in electrochemical performance is due to the incorporation of the different components. CPs significantly increase the current density of these composite films and contribute their pseudocapacitance to improve the specific capacitance, but lead to a decline in cycle stability. After introducing TiO2, both the specific capacitance and the cycle‐stability of rGO‐TiO2‐CP were synergistically improved. A CP can magnify the pseudocapacitance behavior of any of the TiO2 crystalline phases, and interactions vary with the specific CP and the specific TiO2 crystalline phase employed. The synergistic effects of the as‐prepared composites were theoretically predicted and explored. [ABSTRACT FROM AUTHOR]

Pd‐based alloy nanomaterials normally crystallize in the conventional face‐centered cubic (fcc) crystal phase. Here, 2H‐Au nanosheets (NSs), possessing 2H crystal phase (2H: hexagonal close‐packed with a stacking sequence of “AB”), are used as templates for the growth of PdFe, during which the 2H‐to‐fcc phase transformation in Au NSs happens, leading to the formation of 2H/fcc Au@PdFe core–shell NSs. By changing the Pd/Fe atomic ratio, the 2H/fcc phase ratio in 2H/fcc Au@PdFe NSs can be tuned accordingly. As a proof‐of‐concept application, the as‐synthesized 2H/fcc Au@Pd0.66Fe0.34 NSs are used as an electrocatalyst for methanol oxidation reaction (MOR) in alkaline media, exhibiting a remarkable mass activity of 4.39 A mg−1Pd, which is 1.7, 5.4 and 12.9 times that of 2H/fcc Au@Pd0.56Fe0.44 NSs (2.57 A mg−1Pd), 2H/fcc Au@Pd0.40Fe0.60 NSs (0.81 A mg−1Pd), and Pd black (0.34 A mg−1Pd), respectively, placing it among the best of reported Pd‐based MOR electrocatalysts. This strategy, based on phase engineering of nanomaterials (PEN), paves an efficient way to the rational design and controlled synthesis of noble multimetallic nanostructures with unconventional phases for exploring the phase‐dependent properties and applications. [ABSTRACT FROM AUTHOR]

Supercapacitors are of great importance for energy storage and have been the subject of intensive research in recent years, in which conductive polymers are used to make flexible and freestanding electrodes. However, their insufficient access to the electrolytes and the low chemical stability of these conductive polymers lead to their poor performance. To solve these issues, a facile method that can be used to synthesize freestanding composite film electrodes of reduced graphene oxide–cobalt oxide–polypyrrole (RGO—Co3O4—PPy) as supercapacitors is demonstrated. They exhibit a high specific capacitance of 532.8 F g−1 and nearly no degradation after 700 cycles of charging and discharging. The synergistic effect of Co3O4, RGO, and PPy is responsible for the superior property. The three‐phase composite electrode utilizes the RGO nanosheet as a substrate to provide a large surface area for loading Co3O4 nanoparticles and also to enhance the electron transfer. Furthermore, the deposition of PPy largely reduces the resistivity of RGO—Co3O4—PPy, and the introduction of Co3O4 nanoparticles significantly improves cycle stability. New composite electrode materials are synthesized and studied for use as supercapacitors in energy storage applications. [ABSTRACT FROM AUTHOR]