Functional Materials Letters

Pd–Ni/Au nanoshelled microsphere arrays with different Pd–Ni atomic ratios were successfully synthesized using the etched monolayer colloidal spheres as templates. Morphology and composition characterizations indicated that the prepared products consisted of polystyrene cores of Au and Pd–Ni metallic nanoshells with an overall diameter of 450 nm. Electrochemical measurements in an alkaline solution showed that the Pd–Ni/Au catalyst with Pd:Ni = 4:1 atomic ratio demonstrated an optimal catalytic activity with the peak current of 59.4 mA$\cdot {\mathrm{\text{cm}}}^{-2}$, the lower oxidation peak potential and the higher stability. These results could be ascribed to the enhanced surface area which increased the number of electrocatalytic active sites, and the electronic interaction between Pd and Ni. This work provides new opportunities for the rational design of microsphere array catalysts for enhancing the catalytic performance in fuel cells.

${\mathrm{\text{TiO}}}_2$/C aerogel composites are primarily composed of resorcinol-formaldehyde (RF) and low-cost commercial titanium dioxide nanoparticles. These composites are synthesized through a simple process of freeze-drying and high-temperature carbonization under inert gas protection. ${\mathrm{\text{TiO}}}_2$ nanoparticles in the ${\mathrm{\text{TiO}}}_2$/C aerogel composites produce partial oxygen vacancies by high-temperature treatment under anoxic conditions which is beneficial to increase the carrier density of the material. Electrochemical characterizations confirm the excellent specific capacitance, which reaches a maximum of 250 F ${\mathrm{\text{g}}}^{-1}$ at a current density of 0.2 A ${\mathrm{\text{g}}}^{-1}$. Moreover, after 5000 charge/discharge cycles at a current density of 10 A ${\mathrm{\text{g}}}^{-1}$, capacitance retention can be up to 98% or more. These properties are attributed to a synergistic effect of electrical double layer capacitance and pseudo-capacitance.

Herein, precursor assembly of polyanion with pH sensitive molecule, Bis[2-(4-HydroxyPhenyl)BenzImidazole] (BHPBI), was reported to amplify layer-by-layer (LBL) exponential growth. The promoted polyelectrolyte diffusivity was responsible for the amplified LBL deposition efficiency. The release behavior of BHPBI and the anti-oxidant stress function of the film were both evaluated. The constructed multilayer film was tested to be potential drug loading and delivery system for BHPBI.

Flexible strain sensors with highly similar effects to human skin have been given great attention due to their potential application in personal health monitoring, human–computer interaction systems and artificial electronic skin fields. In particular, the self-healing properties of the sensors are important for their long-term and repeated use during the actual operation. Herein, a flexible strain sensor with complete self-healing function is proposed by combining self-healable PDMS film with rich hydrogen bonds and conductive ink based on recoverable liquid metal. By adjusting the contents of different components of self-healing PDMS film and the relative mass fraction of the liquid metal ink in the strain sensor, the tensile stress and resistance of flexible sensor can be changed to match different usage scenarios. The sensor can achieve a maximum tensile stress of 0.83 MPa and an elongation at break of 843%. After self-healing for 24 h at room temperature, its tensile stress can revert to 82% of the original value, while the electrical connection can instantaneously recover to initial situation after fracture surface contacts. This hints its potential advantage as wearable sensors for motion monitoring of the human body and developable applications in medical monitoring, recyclable electronics and artificial skin.

As the environmental issues of organic dyes pollutants are becoming more and more severe, the need to develop emerging technologies to effectively eliminate pollutants is becoming increasingly urgent. In this work, the perovskite-type ${\mathrm{\text{BaCeO}}}_3$/${\mathrm{\text{Fe}}}_2{\mathrm{\text{O}}}_3$ composites were successfully synthesized by a simple ultrasonic water bath. The obtained composite was characterized by various techniques such as XRD, FTIR, SEM and UV-Vis. The photocatalytic performance of the composite was investigated by degrading rhodamine B under 25 W and 254 nm UV irradiation. Moreover, we investigated the optimum preparation conditions of ${\mathrm{\text{BaCeO}}}_3$/${\mathrm{\text{Fe}}}_2{\mathrm{\text{O}}}_3$ photocatalyst with a ${\mathrm{\text{BaCeO}}}_3$ to ${\mathrm{\text{Fe}}}_2{\mathrm{\text{O}}}_3$ mass ratio of 1:1 and a temperature of $50^{\circ }$C for 2 h. In addition, the operating parameters of the photocatalytic reaction were systematically studied such as the initial concentration of solution, catalyst dosage and solution initial pH. The results showed that the photocatalytic decolorization rate of rhodamine B could reach 97.5% by adding 1 g/L ${\mathrm{\text{BaCeO}}}_3$/${\mathrm{\text{Fe}}}_2{\mathrm{\text{O}}}_3$ photocatalyst to 100 mL of 20 mg/L rhodamine B solution at pH 2 for 2 h. What’s more, the ${\mathrm{\text{BaCeO}}}_3$/${\mathrm{\text{Fe}}}_2{\mathrm{\text{O}}}_3$ catalyst was shown to be reusable and stable by cycling tests, and the use of active species trapping agents determined the predominance of •${\mathrm{\text{O}}}_2^{-}$ and ${\mathrm{\text{h}}}^{+}$ in the reaction system. Finally, the possible mechanism of enhancement of photocatalytic activity was initially discussed.

ZnO is one of the most popular materials in UV photodetectors, but its low switching and long attenuation time seriously hinder its practical application. In this work, the performance of PZT/ZnO planar photodetectors is optimized by using the ferroelectric polarization of PZT thin films. The results show that the residual polarization field of PZT affects the electron arrangement in ZnO film, making ZnO in a depleted state, reducing the dark current of resulted photodetectors, and influencing the carrier life. By inhibiting recombination, the photocurrent is increased, and the switching ratio of the ZnO photodetector is increased by 5 times, and more importantly, the optical responsivity increases by 7 times to 1.015 A/W. This work provides a simple and feasible method for ferroelectric polarization to control the performance of two-dimensional material photodetectors.

A model of a heterophase sample with interlayers is proposed to describe coexistence of tetragonal and orthorhombic phases in lead-free perovskite-type ferroelectric solid solutions. Versions of phase coexistence are analyzed at variations of unit-cell parameters of (Ba, Ca)(Ti, Zr)${\mathrm{\text{O}}}_3$ and (K, Na)(Nb, Sb)${\mathrm{\text{O}}}_3$-(Ba, Ca)${\mathrm{\text{ZrO}}}_3$ with compositions near morphotropic phase boundaries. Large regions of the tetragonal and orthorhombic phases are split into $90^{\circ }$ and $120^{\circ }$ domains, respectively. The interlayer of the orthorhombic phase is either single-domain or split into $90^{\circ }$ domains. A complete stress relief can be achieved at an elastic matching of the polydomain/single-domain or polydomain/polydomain phases. It is shown that different phase contents in (${\mathrm{\text{Ba}}}_{0.85}{\mathrm{\text{Ca}}}_{0.15}$)$\cdot \cdot$(${\mathrm{\text{Ti}}}_{0.9}{\mathrm{\text{Zr}}}_{0.1}$)${\mathrm{\text{O}}}_3$ powder and ceramic are caused by different non-${180}^{\circ }$ domain structures in the phases. The interlayer of the orthorhombic phase plays an important role in forming the phase content in solid solutions. Agreement is shown when comparing the evaluated volume fractions of the orthorhombic phase to experimental data.

Li battery has been widely used in mobile electronic devices such as mobile phones and laptop computers and is currently expected as a power source for electric vehicles. Due to high cost and limited supply of Li sources, post-Li batteries like Na, K, Mg and Zn batteries have been researched intensively. However, the post-Li batteries face issues of low-energy density in monovalent ion (Na, K) batteries and slow ion diffusion in multivalent ion (Mg, Zn) batteries. The hybrid metal ion battery (HMIB) contains two different cations which can combine the benefits of fast ion diffusion of monovalent ions and high capacity of multivalent ions. Various types of HMIBs such as Na–Mg, Li–Mg, Li–Zn and so on have been studied. Among them, Li–Na HMIBs composed of Li-based cathodes and Na metal anode are the most promising as the post-Li battery owing to the application of matured Li technology and electrochemical/chemical similarity of Li to Na. In addition, dendric deposition of Na metal is suppressed by the shielding effect, allowing to employ Na metal anode in the Li–Na HMIB system. Na metal anode can provide higher capacity and reduce the material cost. Additionally, commercial Li cathode does not require further investment for manufacturing cathode materials, resulting in a significant reduction of development cost and rapid commercialization of the Li–Na HMIBs. Thus, in this review article, studies on the Li–Na HMIBs are summarized and analyzed, then future challenges for the development of Li–Na HMIBs are suggested.

${\mathrm{\text{NH}}}_2$-MIL-101(Al) material containing phenazine groups, i.e. 1-metal-organic framework (MOF) has been prepared and characterized via FT-IR, PXRD, TGA, SEM and ${\mathrm{\text{N}}}_2$ adsorption and desorption isotherm in this work. 1-MOF can exhibit emission peaks at 447 nm (in pure aqueous solvent) and 595 nm (in pure organic solvents) under 327 nm ultraviolet excitation, respectively. Based on this interesting feature, 1-MOF has been effectively used as a ratiometric fluorescent probe to detect water content in organic solvents. The luminescence color of 1-MOF changed obviously from red to blue with the increasing of water content in organic solvents, which can be observed by the naked eyes. The route to detect water content in organic solvents is fast, accurate and possessing great application potential.

${\mathrm{\text{BaTiO}}}_3$/${\mathrm{\text{SrTiO}}}_3$ (BTO/STO) multilayer films were successfully prepared on (La, Sr)${\mathrm{\text{CoO}}}_3$-coated (100) ${\mathrm{\text{SrTiO}}}_3$ substrates by using a radio-frequency (RF) magnetron sputtering process at $700^{\circ }$C. Benefiting from the flexible deposition configuration of a multi-target sputtering system, we were able to tune the dielectric properties of the multilayer film by varying the number of multilayer periods $N$ and the individual layer thickness $d$. It was found that, in a superlattice-like structure ($d_{\mathrm{\text{BTO}}}=d_{\mathrm{\text{STO}}}$=4 nm, $\sim$ 10 unit cells), the dielectric constant increased and the loss tangent decreased with an increasing $N$, especially in the high frequency range ($10^4–10^6$Hz). This can be attributed to a reduced volumetric contribution to the dielectric property from the leaky interface capacitor layer, which lies between the multilayer film and the (La, Sr)${\mathrm{\text{CoO}}}_3$ electrode. On the other hand, as the individual layer thickness $d$ exceeds the superlattice limit ($d_{\mathrm{\text{BTO}}}=d_{\mathrm{\text{STO}}}$=8 nm, $\sim$ 20 unit cells), the superlattice strain effect disappeared and the dielectric constant value dropped by $\sim$50%. However, owing to the reduced number of interfaces and associated defects, the dielectric loss of the multilayer film with a larger period was reduced significantly, as compared to its superlattice counterpart with the same thickness and more periods. The dielectric loss power density of the former was about one order of magnitude lower than that of the latter. These observations provide a solid foundation for using RF magnetron sputtering as an effective method to prepare various forms of multilayer film capacitors for integrated device applications.