Effect of Fe incorporation on electrical properties of (NixCoyMn3-x-y)O4 (NMC) spinel compound is investigated for the application to a negative temperature coefficient (NTC) thermistor. Cation ...distribution of the Fe doped NMC (FNMC) is calculated based on the size of ions located at tetragonal A sites and octahedral B sites in spinel structure, which can be closely related with temperature dependent electrical properties of the FNMC. With change of Fe contents, the ratio of Mn3+/Mn4+ in octahedral B site of FNMC is changed which can determine the temperature sensitivity factor (B-value). Hopping conduction mode relating with activation energy and hopping distance was also discussed depending on Fe contents, based on the small polaron hopping theory.
•Hopping mode in FNMC occurs through nearest neighboring hopping (NNH) motion when Fe content increases above 0.5.•Variable range hopping (VRH) motion was determined as hopping conduction mechanism for FNMC with Fe content lower than 0.5.•Cation distribution in FNMC with different Fe content is proposed based on the theoretical model.
The development of earth‐abundant and efficient oxygen evolution reaction (OER) electrocatalysts is necessary for green hydrogen production. The preparation of efficient OER electrocatalysts requires ...both the adsorption sites and charge transfer on the catalyst surface to be suitably engineered. Herein, the design of an electrocatalyst is reported with significantly enhanced water oxidation performance via dual‐phase engineering, which displays a high number of adsorption sites and facile charge transfer. More importantly, a simple chemical etching process enables the formation of a highly metallic transition boride phase in conjunction with the transition metal hydroxide phase with abundant adsorption sites available for the intermediates formed in the OER. In addition, computational simulations are carried out to demonstrate the water oxidation mechanism and the real active sites in this engineered material. This research provides a new material design strategy for the preparation of high‐performance OER electrocatalysts.
A novel material design concept of dual‐phase engineering is developed via facile chemical etching toward a highly efficient and robust oxygen evolution reaction electrocatalyst. High number of adsorption sites and facile charge transfer are simultaneously secured through the dual‐phase engineering concept.
The pulsed laser fragmentation in liquid (PLFL) process is a promising technique for the synthesis of carbon‐based functional materials. In particular, there has been considerable attention on ...graphene quantum dots (GQDs) derived from multiwalled carbon nanotubes (MWCNTs) by the PLFL process, owing to the low cost and rapid processing time involved. However, a fundamental deep understanding of the formation of GQDs from MWCNTs by PLFL has still not been achieved despite the high demand. In this work, a mechanism for the formation of GQDs from MWCNTs by the PLFL process is reported, through the combination of experimental and theoretical studies. Both the experimental and computational results demonstrate that the formation of GQDs strongly depends on the pulse laser energy. Both methods demonstrate that the critical energy point, where a plasma plume is generated on the surface of the MWCNTs, should be precisely maintained to produce GQDs; otherwise, an amorphous carbon structure is favorably formed from the scattered carbons.
The pulsed laser fragmentation in liquid (PLFL) process is a promising technique for the synthesis of carbon‐based functional materials. A mechanism for the formation of graphene quantum dots from carbon precursor by the PLFL process is reported, through the combination of experimental and theoretical studies.
Nb and In co-doped rutile TiO
2
nanoceramics (n-NITO) were successfully synthesized through a chemical-solution route combined with a low temperature spark plasma sintering (SPS) technique. The ...particle morphology and the microstructure of n-NITO compounds were nanometric in size. Various techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric (TG)/differential thermal analysis (DTA), Fourier transform infrared (FTIR), and Raman spectroscopy were used for the structural and compositional characterization of the synthesized compound. The results indicated that the as-synthesized n-NITO oxalate as well as sintered ceramic have a co-doped single phase of titanyl oxalate and rutile TiO
2
, respectively. Broadband impedance spectroscopy revealed that novel colossal permittivity (CP) was achieved in n-NITO ceramics exhibiting excellent temperature-frequency stable CP (up to 10
4
) as well as low dielectric loss (∼5%). Most importantly, detailed impedance data analyses of n-NITO compared to microcrystalline NITO (μ-NITO) demonstrated that the origin of CP in NITO bulk nanoceramics might be related with the pinned electrons in defect clusters and not to extrinsic interfacial effects.
Homogeneous electrical properties of Nb and In co-doped NITO nanoceramic over the microstructure.
Transition metal layered double hydroxides (LDHs) have received much attention as high-performance oxygen evolution reaction (OER) catalysts due to their large number of active sites with favorable ...adsorption/desorption energies for intermittent reactants. However, the relatively sluggish charge transfer kinetics of transition metal LDHs due to their intrinsically low conductivity often hinders their use in practical applications as high-performance water oxidation catalysts. Here, we disclose a novel strategy of metalloid incorporation into transition metal LDHs, allowing us to simultaneously optimize surface electronic configuration and charge transfer between adsorbed reactants and catalyst surface. Importantly, incorporated metalloid can enhance the density of states (DOS) near the Fermi level and alter the nature of the chemical bonds in the catalytically active atoms, resulting in fast reaction kinetics. Thus, metalloid incorporation into transition metal LDHs can substantially improve the overall reaction kinetics and thermodynamics for water oxidation due to a large number of active sites and high conductivity, boosting OER performance of transition metal LDHs. The metalloid-incorporated transition metal LDHs far outperform their counterpart transition metal LDHs and even the noble metal catalyst RuO2.
Metalloid incorporation into transition metal LDHs can be a promising strategy for designing highly efficient and robust electrocatalysts for alkaline OER. Display omitted
•Atomic scale engineering using metalloid elements for transition metal layered double hydroxides (LDHs) is firstly developed.•Strategic tellerium (Te) incorporation at the atomic level on edge cobalt (Co) sites is found to be crucial for the improvement of electrical conductivity.•Tailored d-band electronic structure occured via p-d hybridization when Te incorporates into NiCo-LDHs leading to enhanced water oxidation properties.•Te-NiCo LDHs shows very low overpotential of 190 mV at a current density of 10 mA cm-2, respectively, with the lowest Tafel slope of 23.38 mVdec-1 for water oxidation.•Density functional theory (DFT) calculations revealed individual roles of elements in Te-NiCo LDHs for water oxidation.
Alkaline water electrolysis is a vital technology for sustainable and efficient hydrogen production. However, the oxygen evolution reaction (OER) at the anode suffers from sluggish kinetics, ...requiring overpotential. Precious metal-based electrocatalysts are commonly used but face limitations in cost and availability. Carbon nanostructures, such as carbon nanotubes (CNTs), offer promising alternatives due to their abundant active sites and efficient charge-transfer properties. Surface modification of CNTs through techniques such as pulsed laser ablation in liquid media (PLAL) can enhance their catalytic performance. In this study, we investigate the role of surface-modified carbon (SMC) as a support to increase the active sites of transition metal-based electrocatalysts and its impact on electrocatalytic performance for the OER. We focus on Co
O
@SMC heterostructures, where an ultrathin layer of Co
O
is deposited onto SMCs using a combination of PLAL and atomic layer deposition. A comparative analysis with aggregated Co
O
and Co
O
@pristine CNTs reveals the superior OER performance of Co
O
@SMC. The optimized Co
O
@SMC exhibits a 25.6% reduction in overpotential, a lower Tafel slope, and a significantly higher turnover frequency (TOF) in alkaline water splitting. The experimental results, combined with density functional theory (DFT) calculations, indicate that these improvements can be attributed to the high electrocatalytic activity of Co
O
as active sites achieved through the homogeneous distribution on SMCs. The experimental methodology, morphology, composition, and their correlation with activity and stability of Co
O
@SMC for the OER in alkaline media are discussed in detail. This study contributes to the understanding of SMC-based heterostructures and their potential for enhancing electrocatalytic performance in alkaline water electrolysis.
This work presents the effect of oxynitriding process at different temperature on the corrosion resistance and wear behavior of the quenching‐and‐tempering‐treated AISI 4140 steel. The AISI 4140 was ...plasma nitrided at 500°C. Subsequently, the plasma oxynitriding was performed on the nitrided AISI 4140 at different temperatures under H2O atmosphere. Microstructure and phases of the plasma‐oxynitrided samples are investigated, indicating that phase formation of the oxide layer is strongly dependent on processing temperature during plasma oxynitriding: Formation of Fe3O4 is preferred over Fe2O3 at lower processing temperature. Also, it is believed that ε‐Fe2–3N phase formed by nitriding process plays an important role to promote the formation of Fe3O4 phase during plasma oxynitriding. In order to investigate the mechanical, wear, and corrosion properties of the plasma‐oxynitrided samples, Vickers hardness, friction coefficient, and potentiodynamic curves are evaluated, respectively. Compared to a plasma‐nitrided sample, the Vickers hardness of the plasma‐oxynitrided sample at optimal processing temperature shows a slight decrease of the hardness, but, improved wear and corrosion resistances were observed. It is suggested that wear and corrosion resistance of the oxynitrided sample is strongly dependent on the volume fraction of Fe3O4 phase in the oxide layer.
Advanced core@shell structures have emerged as an important strategy for enhancing performance and introducing novel functionalities across diverse scientific and engineering domains, facilitated by ...synergistic interactions between the core and shell. Particularly, when core@shell electrocatalysts are applied to the oxygen evolution reaction (OER) in alkaline water splitting, they are promising for improving OER kinetics using economically feasible and readily available compounds, previously overlooked as electrocatalysts. As a representative study to demonstrate the synergistic effect of the core@shell structure on OER performance, we have developed a NiO x @Fe 3 O 4 structure decorated on surface-modified carbon nanotubes. Experimental results exhibit outstanding OER performance, including an overpotential ( η 10 ) of 286 mV, a Tafel slope of 32 mV dec −1 , and a faradaic efficiency of 97.2% during an 18-hour chronoamperometry test. Remarkably, this performance surpasses that of Fe 3 O 4 catalysts ( η 10 : 1266 mV, Tafel plot slope: 246.2 mV dec −1 ). Also, computational simulations reveal that the electronic structure modifications in NiO x @Fe 3 O 4 promote electron transfer while significantly reducing the reaction energy barrier for boosting OER performance. This study offers scientific insights into the rational design of core@shell structures for enhanced OER performance, which have remained relatively unexplored.
High-performance energy harvesting for human-sensing applications has been achieved through recent progress in piezoelectric-based wearable devices. Piezoelectric nanomaterials can be leveraged for ...flexibility and biocompatibility while also enhancing piezoelectricity. However, such nanomaterials exhibit low piezoelectricity, limits the industrial-scale development of highly efficient piezoelectric devices. Hence, design of novel materials to significantly enhance piezoelectricity is necessitated. Herein, we demonstrate that a peapod-inspired design in which ZnSnO3 anchored on surface-modified carbon nanotubes (CNT) allows significant enhancement of the piezoelectricity produced by poly(vinylidene fluoride-co-trifluoroethylene)-based (P(VDF-TrFE)-based) nanofibers (a piezoelectric material). The piezoelectric properties were exploited for the application of the as-prepared nanofibers (NFs) in flexible NFs in energy-harvesting and pulse-sensing systems, which demonstrated high output power ((97.5 V and 1.16 μA) as well as imperceptible pulse detection even in posterior tibial arteries. This work provides the scientific and engineering framework for delivering ZnSnO3-surface-modified CNT-P(VDF-TrFE) NFs excellent piezoelectric performance for use in piezoelectric devices.
Display omitted
•ZnSnO3 nanoparticles were anchored on the surface modified CNT (ZnSnO3-SMC) by pulsed laser ablation process.•ZnSnO3-SMC were reinforced within P(VDF-TrFE) nanofibers.•ZnSnO3-SMC-P(VDF-TrFE) nanofibers show excellent piezoelectric performance as well as imperceptible pulsed detection.
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