Eco-Friendly Cerium-Cobalt Counter-Doped Bi2Se3 Nanoparticulate Semiconductor: Synergistic Doping Effect for Enhanced Thermoelectric Generation.

Metal chalcogenides are primarily used for thermoelectric applications due to their enormous potential to convert waste heat into valuable energy. Several studies focused on single or dual aliovalent doping techniques to enhance thermoelectric properties in semiconductor materials; however, these dopants enhance one property while deteriorating others due to the interdependency of these properties or may render the host material toxic. Therefore, a strategic doping approach is vital to harness the full potential of doping to improve the efficiency of thermoelectric generation while restoring the base material eco-friendly. Here, we report a well-designed counter-doped eco-friendly nanomaterial system (~70 nm) using both isovalent (cerium) and aliovalent (cobalt) in a Bi2Se3 system for enhancing energy conversion efficiency. Substituting cerium for bismuth simultaneously enhances the Seebeck coefficient and electrical conductivity via ionized impurity minimization. The boost in the average electronegativity offered by the self-doped transitional metal cobalt leads to an improvement in the degree of delocalization of the valence electrons. Hence, the new energy state around the Fermi energy serving as electron feed to the conduction band coherently improves the density of the state of conducting electrons. The resulting high power factor and low thermal conductivity contributed to the remarkable improvement in the figure of merit (zT = 0.55) at 473 K for an optimized doping concentration of 0.01 at. %. sample, and a significant nanoparticle size reduction from 400 nm to ~70 nm, making the highly performing materials in this study (Bi2-xCexCo2x3Se3) an excellent thermoelectric generator. The results presented here are higher than several Bi2Se3-based materials already reported.

3D heterostructured cobalt oxide@layered double hydroxide core-shell networks on nickel foam for high-performance hybrid supercapacitor.

High performance of an electrode relies largely on scrupulous design of nanoarchitectures and smart hybridization of bespoke active materials. Here, a 3D heterostructured core-shell architecture was fabricated as a supercapacitor electrode, in which Co3O4 nanowire cores were grown on nickel foam prior to the in situ deposition of layered double hydroxide (LDH) nanosheet shells. Owing to the unique configuration and hybridization, the as-fabricated Co3O4@LDH core-shell electrode exhibited high capacities of 818.6 C g-1 at 2 A g-1 and 479.3 C g-1 at 40 A g-1 (3.2 C cm-2 at 7.8 mA cm-2 and 1.87 C cm-2 at 156 mA cm-2), which were much higher than those of the individual components, namely, Co3O4 and LDH. A hybrid supercapacitor with Co3O4@LDH as the positive electrode and graphene nanosheets as the negative electrode yielded an energy density of 53.2 W h kg-1 and a power density of 16.4 kW kg-1, which outperformed devices reported in the literature; the device also exhibited long-term cycling stability and retained 71% of its initial capacity even after 10 000 cycles at 6 A g-1. The rational design of the core-shell architecture may lead to the development of new strategies for fabricating promising electrode materials for electrochemical energy storage.

Correction: Chatterjee, A.; et al. Transition Metal Hollow Nanocages as Promising Cathodes for the Long-Term Cyclability of Li⁻O2 Batteries. Nanomaterials 2018, 8, 308.

The authors wish to add the following information to this paper [...].

Transition Metal Hollow Nanocages as Promising Cathodes for the Long-Term Cyclability of Li⁻O2 Batteries.

As a step towards efficient and cost-effective electrocatalytic cathodes for Li⁻O2 batteries, highly porous hausmannite-type Mn3O4 hollow nanocages (MOHNs) of a large diameter of ~250 nm and a high surface area of 90.65 m²·g−1 were synthesized and their physicochemical and electrochemical properties were studied in addition to their formation mechanism. A facile approach using carbon spheres as the template and MnCl2 as the precursor was adopted to suit the purpose. The MOHNs/Ketjenblack cathode-based Li⁻O2 battery demonstrated an improved cyclability of 50 discharge⁻charge cycles at a specific current of 400 mA·g−1 and a specific capacity of 600 mAh·g−1. In contrast, the Ketjenblack cathode-based one can sustain only 15 cycles under the same electrolytic system comprised of 1 M LiTFSI/TEGDME. It is surmised that the unique hollow nanocage morphology of MOHNs is responsible for the high electrochemical performance. The hollow nanocages were a result of the aggregation of crystalline nanoparticles of 25⁻35 nm size, and the mesoscopic pores between the nanoparticles gave rise to a loosely mesoporous structure for accommodating the volume change in the MOHNs/Ketjenblack cathode during electrocatalytic reactions. The improved cyclic stability is mainly due to the faster mass transport of the O2 through the mesoscopic pores. This work is comparable to the state-of-the-art experimentations on cathodes for Li⁻O2 batteries that focus on the use of non-precious transition materials.

Gradient-Type Magnetoelectric Current Sensor with Strong Multisource Noise Suppression.

A novel gradient-type magnetoelectric (ME) current sensor operating in magnetic field gradient (MFG) detection and conversion mode is developed based on a pair of ME composites that have a back-to-back capacitor configuration under a baseline separation and a magnetic biasing in an electrically-shielded and mechanically-enclosed housing. The physics behind the current sensing process is the product effect of the current-induced MFG effect associated with vortex magnetic fields of current-carrying cables (i.e., MFG detection) and the MFG-induced ME effect in the ME composite pair (i.e., MFG conversion). The sensor output voltage is directly obtained from the gradient ME voltage of the ME composite pair and is calibrated against cable current to give the current sensitivity. The current sensing performance of the sensor is evaluated, both theoretically and experimentally, under multisource noises of electric fields, magnetic fields, vibrations, and thermals. The sensor combines the merits of small nonlinearity in the current-induced MFG effect with those of high sensitivity and high common-mode noise rejection rate in the MFG-induced ME effect to achieve a high current sensitivity of 0.65-12.55 mV/A in the frequency range of 10 Hz-170 kHz, a small input-output nonlinearity of <500 ppm, a small thermal drift of <0.2%/℃ in the current range of 0-20 A, and a high common-mode noise rejection rate of 17-28 dB from multisource noises.

Magnetoelectric Transverse Gradient Sensor with High Detection Sensitivity and Low Gradient Noise.

We report, theoretically and experimentally, the realization of a high detection performance in a novel magnetoelectric (ME) transverse gradient sensor based on the large ME effect and the magnetic field gradient (MFG) technique in a pair of magnetically-biased, electrically-shielded, and mechanically-enclosed ME composites having a transverse orientation and an axial separation. The output voltage of the gradient sensor is directly obtained from the transverse MFG-induced difference in ME voltage between the two ME composites and is calibrated against transverse MFGs to give a high detection sensitivity of 0.4-30.6 V/(T/m), a strong common-mode magnetic field noise rejection rate of <-14.5 dB, a small input-output nonlinearity of <10 ppm, and a low gradient noise of 0.16-620 nT/m/ Hz in a broad frequency range of 1 Hz-170 kHz under a small baseline of 35 mm. An analysis of experimental gradient noise spectra obtained in a magnetically-unshielded laboratory environment reveals the domination of the pink (1/f) noise, dielectric loss noise, and power-frequency noise below 3 kHz, in addition to the circuit noise above 3 kHz, in the gradient sensor. The high detection performance, together with the added merit of passive and direct ME conversion by the large ME effect in the ME composites, makes the gradient sensor suitable for the passive, direct, and broadband detection of transverse MFGs.

Smart elasto-magneto-electric (EME) sensors for stress monitoring of steel cables: design theory and experimental validation.

An elasto-magnetic (EM) and magneto-electric (ME) effect based elasto-magneto-electric (EME) sensor has been proposed recently by the authors for stress monitoring of steel cables with obvious superiorities over traditional elasto-magnetic sensors. For design optimization and engineering application of the EME sensor, the design theory is interpreted with a developed model taking into account the EM coupling effect and ME coupling effect. This model is able to approximate the magnetization changes that a steel structural component undergoes when subjected to excitation magnetic field and external stress, and to simulate the induced ME voltages of the ME sensing unit located in the magnetization area. A full-scale experiment is then carried out to verify the model and to calibrate the EME sensor as a non-destructive evaluation (NDE) tool to monitor the cable stress. The experimental results agree well with the simulation results using the developed model. The proposed EME sensor proves to be feasible for stress monitoring of steel cables with high sensitivity, fast response, and ease of installation.

Structure and electromagnetic properties of single-crystalline Fe3O4 hollow nanospheres.

Magnetite (Fe3O4) hollow nanospheres with an average diameter of 300 nm and an average shell thickness of 40 nm were synthesized by a surfactant-free solvothermal reduction method, and their structure and electromagnetic (EM) properties were investigated. The Fe3O4 hollow nanospheres showed single-crystalline features along the [111] crystal growth direction and a ferrimagnetic behavior at room temperature. The Fe3O4 hollow nanosphere/paraffin composites exhibited a flatter response in the real complex relative permittivity (epsilon') and a lower value of -0.5 in the imaginary complex relative permittivity (epsilon") in comparison with other Fe3O4-based nanomaterials because of the enhanced electrical resistivity. Their imaginary complex relative permeability (mu") displayed a resonance peak at -4 GHz and a negative value up to -0.03 in the 17.2-18 GHz range due to the dissipation of EM energy in the cavity of the hollow nanospheres. Their reflection loss (RL) exceeded -10 dB from 3.1 to 10.1 GHz at a thickness of 2.6-5 mm and attended an optimal value of -43.5 dB at 4 GHz at 5 mm thickness as a result of an effective complementation between the dielectric and magnetic losses.

Direct current force sensing device based on compressive spring, permanent magnet, and coil-wound magnetostrictive/piezoelectric laminate.

A force sensing device capable of sensing dc (or static) compressive forces is developed based on a NAS106N stainless steel compressive spring, a sintered NdFeB permanent magnet, and a coil-wound Tb(0.3)Dy(0.7)Fe(1.92)/Pb(Zr, Ti)O3 magnetostrictive∕piezoelectric laminate. The dc compressive force sensing in the device is evaluated theoretically and experimentally and is found to originate from a unique force-induced, position-dependent, current-driven dc magnetoelectric effect. The sensitivity of the device can be increased by increasing the spring constant of the compressive spring, the size of the permanent magnet, and/or the driving current for the coil-wound laminate. Devices of low-force (20 N) and high-force (200 N) types, showing high output voltages of 262 and 128 mV peak, respectively, are demonstrated at a low driving current of 100 mA peak by using different combinations of compressive spring and permanent magnet.

Broadband ultrasonic linear array using ternary PIN-PMN-PT single crystal.

Ternary Pb(In(1/2)Nb(1/2))O(3)-Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PIN-PMN-PT) single crystal was investigated for potential application in ultrasonic linear array. Orientation and temperature dependences of height extensional electromechanical coupling coefficient k'(33) for PIN-PMN-PT single crystal were studied. It was found that the [001] poled PIN-PMN-PT diced along the [100] direction would achieve a maximum k'(33) (~87%) and the service temperature was up to 110 °C. Ultrasonic linear arrays using PIN-PMN-PT single crystal and PZT ceramic were fabricated and compared. The bandwidth at -6 dB, two-way insertion loss and pulse length of the PIN-PMN-PT array were 98.6%, -45.1 dB, and 0.28 µs, respectively, which were about 25% broader, 3.7dB higher, and 0.08 µs shorter than those of the PZT array. The experimental results agreed well with the theoretical simulation. These superior performances were attributable to the excellent piezoelectric properties of PIN-PMN-PT single crystal.

Enhanced magnetoelectric effect in heterostructure of magnetostrictive alloy bars and piezoelectric single-crystal transformer.

We report an enhanced magnetoelectric (ME) effect in a heterostructure consisting of a long-type, longitudinally-longitudinally polarized 0.71Pb(Mg(1∕3)Nb(2∕3))O(3)-0.29PbTiO(3) (PMN-PT) piezoelectric single-crystal transformer with its input part sandwiched between two longitudinally magnetized Tb(0.3)Dy(0.7)Fe(1.92) (Terfenol-D) magnetostrictive alloy bars. The observed ME effect has two independent operational modes: namely, ME sensing mode and ME transduction mode. The ME sensing mode features a large ME voltage coefficient (α(V)) of ∼0.32 V∕Oe over a flat frequency range of 1-50 kHz, while the ME transduction mode possesses two colossal resonance α(V) of 7.6 and 7.9 V∕Oe, corresponding to the first and second longitudinal resonances, at 56.2 and 127.9 kHz, respectively. This enhanced dual-mode ME effect not only enables the application potential of the heterostructure, but also advances the technology of power-free ME sensors and transducers.

Magnetic field-induced strain and magnetoelectric effects in sandwich composite of ferromagnetic shape memory Ni-Mn-Ga crystal and piezoelectric PVDF polymer.

A sandwich composite consisting of one layer of ferromagnetic shape memory Ni-Mn-Ga crystal plate bonded between two layers of piezoelectric PVDF polymer film was fabricated, and its magnetic field-induced strain (MFIS) and magnetoelectric (ME) effects were investigated, together with a monolithic Ni-Mn-Ga crystal, as functions of magnetic fields and mechanical load. The load-free dc- and ac-MFISs were 0.35 and 0.05% in the composite, and 5.6 and 0.3% in the monolithic crystal, respectively. The relatively smaller load-free MFISs in the composite than the monolithic crystal resulted from the clamping of martensitic twin-boundary motion in the Ni-Mn-Ga plate by the PVDF films. The largest ME coefficient (α(E)) was 0.58 V/cm·Oe at a magnetic bias field (H(Bias)) of 8.35 kOe under load-free condition. The mechanism of the ME effect originated from the mechanically mediated MFIS effect in the Ni-Mn-Ga plate and piezoelectric effect in the PVDF films. The measured α(E)-H(Bias) responses under different loads showed good agreement with the model prediction.

Piezoelectric energy harvesting based on shear mode 0.71Pb(Mg(1/3)Nb(2/3))O3-0.29PbTiO3 single crystals.

In this paper we theoretically and experimentally present a nonresonant vibration energy harvesting device based on the shear mode of 0.71Pb(Mg(1/3)Nb(2/3))O3-0.29PbTiO3 single crystals. The electrical properties of the energy harvesting device were evaluated using an analytical method. Good consistency was obtained between the analytical and experimental results. Under a mass load of 200 g, a peak voltage of 11.3 V and maximum power of 0.70 mW were obtained at 500 Hz when connecting a matching load resistance of 91 komega. A high output could always be obtained within a very wide frequency range. The results demonstrate the potential of the device in energy harvesting applied to low-power portable electronics and wireless sensors.