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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 NiOx@Fe3O4 structure decorated on surface-modified carbon nanotubes. Experimental results exhibit outstanding OER performance, including an overpotential (η10) 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 Fe3O4 catalysts (η10: 1266 mV, Tafel plot slope: 246.2 mV dec−1). Also, computational simulations reveal that the electronic structure modifications in NiOx@Fe3O4 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. [ABSTRACT FROM AUTHOR]

Poly-(dimethylsiloxane) (PDMS) has been used as a negative friction layer in triboelectric nanogenerators (TENGs) owing to its high electronegativity and flexibility. With the advantage of PDMS, the design of various materials to further enhance the energy output of a PDMS-based TENG system have been suggested for practical applications. Herein, we report a high-efficiency PDMS-based TENG wherein surface-modified carbon nanotubes (SMCs), fabricated by one-step pulsed laser ablation, were used as a PDMS additive. SMCs possess oxygen-rich functional groups on the surface that enhance their permittivity and dispersibility in PDMS. Consequently, improvements in the triboelectric performance and capacitance of an SMC-PDMS-based TENG device (SMC-PDMS) were observed, owing to the synergistic effects of the enhanced permittivity and dispersibility of SMCs. Compared to a pristine PDMS-based TENG, SMC-PDMS containing 0.05 wt% SMCs showed an output voltage of 382.12 V and a current of 29.44 μA, which correspond to 170% and 243% enhancements, respectively. In addition, a facile radio frequency plasma treatment was performed to further improve the performance of SMC-PDMS, resulting in an output voltage of 414.63 V, a current of 40.03 μA, and a power density of 7.69 W m−2. [ABSTRACT FROM AUTHOR]

Development of an efficient and stable electrocatalyst for the oxygen evolution reaction (OER) is crucial to generate hydrogen via water splitting as a sustainable fuel. Nickel iron layered double hydroxides (NF-LDHs) are considered the most promising electrocatalysts for alkaline water oxidation among various low-cost transition metal-based electrocatalysts although exact mechanisms are still on debate. Herein, we disclose that quaternary multimetallic Ni–Fe–Al–Co LDHs (NFAC-MELDHs) function as one of the best catalysts for alkaline as well as seawater oxidation due to the synergetic effects among the four different redox-flexible metals. The multimetallic Ni–Fe–Al–Co LDHs are prepared via the metal–organic framework (MOF)-derived electrochemical incorporation of fourth transition metal (Co) into ternary Ni–Fe–Al LDHs grown by a hydrothermal reaction. Moreover, we reveal an exact electrocatalytic mechanism for the OER in NFAC-MELDHs via ex situ spectroscopies in combination with density functional theory (DFT) calculations. Redox-flexible Fe is identified with a real active site in synergy with the neighboring metals stabilizing adsorption of oxygen intermediates and simultaneously facilitating charge transfer. In consequence, NFAC-MELDHs exhibit one of the lowest overpotentials of 220 and 280 mV for affording a current density of 100 mA cm−2 in alkaline and simulating seawater solutions, respectively. More importantly, activity and stability merits in electrocatalysis for the OER are improved in the sequence of unary, binary, ternary, and quaternary LDHs, implying that catalyst design using multimetals for LDHs is a highly promising strategy. [ABSTRACT FROM AUTHOR]

It has recently been demonstrated that the OER activity of transition metal sulfides (TMSs) could be enhanced by the introduction of a thin amorphous layer on a pristine surface. We report here a novel strategy to enhance the OER by developing cobalt nickel sulfide (CoxNi1−xS2, CNS) with a high density of crystalline and amorphous phase boundaries. Electrochemical activation (ECA) can partially amorphize hollow CNS nanoparticles derived from surface-selective sulfidation. The ECA-treated CNS (ECA-CNS) electrocatalyst, which is comprised of CNS nanodots separated by thin amorphous layers, shows high densities of crystalline and amorphous phase boundaries. This catalyst shows superior OER catalytic performance with a current density of 10 mA cm−2 at a small overpotential of 290 mV, a low Tafel slope of 46 mV dec−1, a high mass activity of 217 A g−1, a high turnover frequency of 0.21 s−1 at an overpotential of 340 mV, and excellent stability in alkaline media. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO2) with exposed (001) facets (TiO2(001)) has attractive photocatalytic properties. However, the high recombination rate of the photo-excited charge carriers on this surface often limits its application. Here, we report that a few-layered 1T-MoS2 coating on TiO2(001) nanosheets (abbreviated as MST) can be a promising candidate that overcomes some of the challenges of TiO2(001). Computational and experimental results demonstrate that MST as a photocatalyst exhibits a significantly low-charge recombination rate as well as excellent long-term durability. The synthesized MST 2D nanocomposites show a 31.9% increase in photocatalytic activity for hydrogen (H2) production relative to the counterpart TiO2(001). MST offers a new route for further improvement of the photocatalytic activity of TiO2 with exposed high energy facets. [ABSTRACT FROM AUTHOR]

Dielectric spectroscopy was performed on a Nb and In co-doped rutile TiO2 nano-crystalline ceramic (n-NITO) synthesized by a low-temperature spark plasma sintering (SPS) technique. The dielectric properties of the n-NITO were not largely affected by the metal electrode contacts. Huge dielectric relaxation was observed at a very low temperature below 35 K. Both the activation energy and relaxation time suggested that the electronic hopping motion is the underlying mechanism responsible for the colossal dielectric permittivity (CP) and its relaxation, instead of the internal barrier layer effect or a dipolar relaxation. With Havriliak–Negami (H–N) fitting, a relaxation time with a large distribution of dielectric relaxations was revealed. The broad distributed relaxation phenomena indicated that Nb and In were involved, controlling the dielectric relaxation by modifying the polarization mechanism and localized states. The associated distribution function is calculated and presented. The frequency-dependent a.c. conductance is successfully explained by a hopping conduction model of the localized electrons with the distribution function. It is demonstrated that the dielectric relaxation is strongly correlated with the hopping electrons in the localized states. The CP in SPS n-NITO is then ascribed to a hopping polarization. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO 2 ) with exposed (001) facets (TiO 2 (001)) has attractive photocatalytic properties. However, the high recombination rate of the photo-excited charge carriers on this surface often limits its application. Here, we report that a few-layered 1T-MoS 2 coating on TiO 2 (001) nanosheets (abbreviated as MST) can be a promising candidate that overcomes some of the challenges of TiO 2 (001). Computational and experimental results demonstrate that MST as a photocatalyst exhibits a significantly low-charge recombination rate as well as excellent long-term durability. The synthesized MST 2D nanocomposites show a 31.9% increase in photocatalytic activity for hydrogen (H 2 ) production relative to the counterpart TiO 2 (001). MST offers a new route for further improvement of the photocatalytic activity of TiO 2 with exposed high energy facets.

Dielectric spectroscopy was performed on a Nb and In co-doped rutile TiO 2 nano-crystalline ceramic (n-NITO) synthesized by a low-temperature spark plasma sintering (SPS) technique. The dielectric properties of the n-NITO were not largely affected by the metal electrode contacts. Huge dielectric relaxation was observed at a very low temperature below 35 K. Both the activation energy and relaxation time suggested that the electronic hopping motion is the underlying mechanism responsible for the colossal dielectric permittivity (CP) and its relaxation, instead of the internal barrier layer effect or a dipolar relaxation. With Havriliak-Negami (H-N) fitting, a relaxation time with a large distribution of dielectric relaxations was revealed. The broad distributed relaxation phenomena indicated that Nb and In were involved, controlling the dielectric relaxation by modifying the polarization mechanism and localized states. The associated distribution function is calculated and presented. The frequency-dependent a.c. conductance is successfully explained by a hopping conduction model of the localized electrons with the distribution function. It is demonstrated that the dielectric relaxation is strongly correlated with the hopping electrons in the localized states. The CP in SPS n-NITO is then ascribed to a hopping polarization.

Nb and In co-doped rutile TiO2 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 TiO2, 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.