Functional Materials Letters

NASICON-type Li${}_{1.5}$Al${}_{0.5}$Ge${}_{0.5}$P₃O${}_{12}$(LAGP) is one of the most promising inorganic solid-state electrolytes (SSEs). However, its practical applications have been hindered due to the high grain boundary resistance and poor sintering performance. In this work, we introduce a novel LiBF₄ sintering aid into LAGP to promote the growth of grains, decrease grain boundary resistance, and supplement the loss of lithium. The experimental results show that the ionic conductivity of LAGP-0.5 wt% LiBF₄ has the highest ionic conductivity (3.21 × 10${}^{-4}$S/cm), grain boundary impedance decreases from 162.2 $\mathrm{\Omega }$ to 35.2 $\mathrm{\Omega }$, the relative density increases from 93.6% to 96.5%, and no impurity phase is observed in LAGP–0.5 wt% LiBF₄. At the same ionic conductivity, the sintering temperature of LAGP without LiBF₄ and with a small amount of LiBF₄ decreases from 800${}^{\circ }$C to 700${}^{\circ }$C. The Li/LAGP-LiBF₄/LiFePO₄ cell presents excellent cyclic stability (capacity retention of the discharge capacity is still 117.5 mAhg${}^{-1}$ after 100 cycles) and a high initial discharge capacity of 164.2 mAhg${}^{-1}$ at 0.2 C.

After self-assembly and thermal treatment at low temperature (350^∘C), reduced graphite oxide membranes (RGOM) with a specific surface area of 10.6 m²g${}^{-1}$ and average interlayer distance of 0.372 nm were obtained. When used as free-standing electrodes for sodium ion battery (SIB), the RGOM could not show good electrochemical performances at high current density ($\sim$52 mAh g${}^{-1}$ at 200 mA g${}^{-1}$ and $\sim$22 mAh g${}^{-1}$ at 500 mA g${}^{-1}$), which may be attributed to dense structure and low specific surface area. Cyclic voltammetry (CV) results showed that the energy storage of RGOM in SIB was ions’ diffusion-dependent. Thus, when the RGOM electrodes went through repeated charge/discharge cycles at 200 mA g${}^{-1}$, an obvious improvement of specific capacity was found due to increase of Na${}^{+}$ diffusion speed. After $\sim$300 times charge/discharge cycles, the specific capacity of RGOM was $\sim$120 mAh g${}^{-1}$. Additionally, after the current activation at 200 mA g${}^{-1}$, the electrodes also showed better performances at higher current density (from $\sim$85 mAh g${}^{-1}$ to $\sim$68 mAh g${}^{-1}$ at a current density of 500 mA g${}^{-1}$ during 500 times charge/discharge cycles). The current activation phenomenon maybe a promising method for using RGOM as SIB electrodes on a large scale.

The field emission tip arrays with sub-100 nm apices (nanoFEAs) on single crystal cerium hexaboride (CeB₆) surface were fabricated by the focused ion beam (FIB) milling microtechnology. The surface morphologies and field emissions of the nanoFEAs are systematically characterized. FIB milling, similar to the physical stripping process, can fabricate the nanoFEAs single crystal CeB₆ with uniform morphologies. The nanoFEAs with sharp tips of size about 50 nm demonstrate the lowest turn-on electric fields (2.0 V/$\mu$m), as well as a high current ($>$1 mA) at the field of 6.7 V/$\mu$m and a high stable emission current. Such excellent performances make CeB₆ nanoFEAs promising candidates for application in field emission electronics.

Herein, we report that self-assembled surface modification of 4-hydroxy thiophenol and gold nanoparticles imparted trititanate nanotubes (TiNTs) with stable, highly efficient hydrogen production and Photoelectrochemical (PEC) properties. After gold nanoparticles decoration, the modified TiNTs exhibited the photocurrent density of 232 $\mu$A/cm² at 0 V versus Ag/AgCl, with onset potentials ($V_{\mathrm{\text{op}}}$) of −0.4 V versus Ag/AgCl. Our process uses 4-hydroxy thiophenol to achieve control over the bond between gold particles and TiNTs, and improves the distribution uniformity of gold nanoparticles on the surface of TiNTs, which leads to above 90% Faradaic efficiency during 3 h water splitting reaction for hydrogen production.

The PVA/GO film prepared by vacuum-assisted self-assembly exhibits quick thermo-/water- responsive shape memory effect. The anisotropic lamellar structure of GO sheets and plenty of chemical groups containing oxygen in the PVA/GO film facilitate rapid recovery in water. The lamellar structure of GO sheets improves the recovery stress of composite and results in a 16-fold increase in Young’s modulus. PVA molecular chain slides along the direction of the laminated GO sheets, consistent with the extension direction, ensuring that the composite film maintains a large fracture strain. The straight film is programmed into a spiral shape by the plasticization of water on PVA instead of ordinary heating and the spiral film can drive a weight 160 times its own weight to rotate in water at room temperature (about 25${}^{\circ }$C).

Misfit strain, lattice parameter, polarization, permittivity, and tunability of Ba${}_{0.6}$Sr${}_{0.4}$TiO₃ thin films onto Ba${}_x$Sr_1−xTiO₃-buffered stainless steel (SS) substrates are computed via a modified phenomenological model. When the Ba/Sr ratio of Ba${}_x$Sr_1−xTiO₃ buffer layer grows, the permittivity and tunability first increase and then decrease with the maximum at $x$ = 0.75. The highest tunability of such films prepared by the sol-gel technique can reach 32.5% at the electric field of 320 kV/cm when $x$ = 0.8. The strains are qualitatively analyzed through combining XRD, Raman, and theoretical calculation. The computed data are generally supported by experimental lattice parameters, permittivities, and tunabilities, which show that polycrystalline BST thin films with smaller compressive strain obtain higher dielectric response, and that inserting buffer layer could regulate the strains and dielectric properties of BST thin films.

Developing photosensitizers with high durability is desirable to boost the practical application of photocatalytic hydrogen evolution. Herein, referring to the successful strategy in the field of light-emitting electrochemical cells, the reported Ir(III) complex with intramolecular $\pi –\pi$ interaction, Ir2, is used as a photosensitizer to explore its durability. Photocatalytic hydrogen evolution experiment exhibits that the durability of Ir2 is significantly improved with the duration of 39 h, which is three times longer than that of the classical Ir(III) complex Ir1 (ca. 13 h) under the same condition. As revealed by theoretical calculation, the incorporation of intramolecular $\pi –\pi$ interaction inhibits the rupture of metal–ligand bond in the excited state, thereby reducing the possibility of complex degradation. This is a novel approach to achieve a durable Ir(III) photosensitizer, which stimulates new molecular engineering endeavors. The finding proves the applicability of molecular design strategy in the field of light-emitting electrochemical cells to the photocatalytic hydrogen evolution system, thus boosting the cross integration of different disciplines.

Multicolor nitrogen-doped graphene quantum dots (NGQDs) were prepared via one-pot method and purified by column chromatography to obtain three NGQDs with different emission colors, i.e. blue emission (B-NGQDs), cyan emission (C-NGQDs), and yellow emission (Y-NGQDs). The multicolor NGQDs were combined with InGaN chip to fabricate light-emitting diode (LED) that emitted blue, cyan, and yellow light, respectively. Moreover, reducing the amount of Y-NGQDs used could construct a white LED (WLED) with color coordinate of (0.324, 0.334).

In this study, ${\mathrm{\text{WS}}}_2–{\mathrm{\text{WO}}}_3$ particles were successfully synthesized by a solvothermal liquid-phase oxidation process under various conditions and their gas sensing performance was evaluated at room temperature. The sample synthesized in ethanol-rich solvent at 210${}^{\circ }$C showed excellent gas sensing performance. It is suggested that the crystalline phase and the particle morphology, which are essential for improving gas sensing performance, are effectively controllable by the present liquid phase oxidation process.

Iron disulfide (FeS₂) has attracted extensive research interest due to its excellent catalytic efficiency. In this work, FeS₂ was composited with carbon matrix to prepare a highly efficient electrocatalyst for hydrogen evolution. Two uniformly composites, namely, FeS₂ @carbon nanotube (FeS₂@CNT) and FeS₂@carbon particle (FeS₂@CP), were successfully prepared by pyrolysis and sulfuration processes. The structures of the synthesized composites were characterized by powder X-ray diffraction (PXRD), scanning electron microscope, transmission electron microscope, and X-ray photoelectron spectroscopy. It was found that the catalytic performances of the composites were obviously improved compared to pure FeS₂. Moreover, compared to FeS₂@CP, the FeS₂@CNT nanotubes achieved a much lower overpotential and a smaller Tafel slope. The enhanced HER kinetics and hydrogen generation rate of FeS₂@CNT may be due to its more efficient charge transport, uniform distribution of active sites, and higher surface areas. This work provides a new clue for the preparation of FeS₂-based composite for hydrogen evolution.