Functional Materials Letters

The Aerosol Deposition (AD) method is a dry spray coating process for the production of dense ceramic coatings at room temperature directly from the ceramic raw powder. In order to avoid confusion with liquid aerosol technology, the term powder aerosol deposition (PAD) is introduced here, to highlight that the aerosol consists only of ceramic powder and carrier gas. Especially in the field of functional ceramics, PAD is a promising alternative to conventional sinter-based production processes. This review focuses on the PAD of functional ceramics in the field of sensing and energy technology. In this context, especially current developments and trends are presented. On the part of the sensors, gas and temperature sensors are especially considered, whereas in the field of energy technology, the focus is on vibration energy harvesting, thermoelectric generators, superconductors, and solar cells as well as on all solid-state batteries and fuel cells. Besides the different applications of PAD films, this review also highlights opportunities for influencing the film properties by the used powder or the process parameters.

Aqueous zinc-ion batteries (ZIBs) as a new battery technology have received great attention due to the high energy and power density, low cost, high safety and environmental friendliness. However, their practical deployment has been restricted by some serious issues such as corrosion of zinc metal anode in aqueous electrolyte, undesired growth of zinc dendrites, and hydrogen evolution from the water splitting. Therefore, tremendous efforts have been devoted to mitigate these issues and significant progresses have been achieved. In this paper, we review some key recent progresses of aqueous ZIBs, focusing on materials engineering strategies that are able to address the major challenges. Moreover, we provide rational perspectives on the future development of ZIBs.

Alkaline zinc-based rechargeable batteries (AZRBs) are competitive candidates for future electrical energy storage because of their low-cost, eco-friendliness and high energy density. However, plagued by dendrites, the AZRBs suffer from drastic decay in electrochemical properties and safety. This review elucidates fundamentals of zinc dendritic formation and summarizes the strategies, including electrode design and modification, electrolyte optimization and separator improvement, for suppressing zinc dendritic growth.

Trap types of the yellow emitting long-persistent phosphor Ca₂BO₃Cl: ${\text{Eu}}^{2+}$, ${\text{Dy}}^{3+}$ were analyzed in this study. ${\text{Eu}}^{2+}$ acting as luminescent centers produced a broad emission band located at 580nm, which ascribes to the 5d-4f transitions. Four kinds of traps in this afterglow phosphor were detected by thermoluminescence spectra. Electron paramagnetic resonance spectroscopy, which is a considerable testing method, was used to identify the traps caused by different reasons. Based on it, detailed processes and traps analyses were examined and discussed.

This paper investigates the synthesis and enhanced electrochemical behaviors of ZnO and NiO/ZnO nanocomposites for electrode material of supercapacitors. ZnO and NiO/ZnO nanocomposites were produced via sol–gel technique. Transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM) were used to determine the size and structure of as-synthesized nanomaterials, respectively. The capacitive behavior and charge–discharge characteristics of the electrode using ZnO and NiO/ZnO nanocomposites (as active material) were individually probed with the help of cyclic voltammetry (CV) and galvanostatic charge-discharge tests, respectively. The specific capacitance of nanocomposites-based electrode calculated from galvanostatic charge-discharge tests was 469F ${\text{g}}^{-1}$ at the scan rate of 1mA ${\text{g}}^{-1}$ in 1M Na₂SO₄ electrolyte. The power density and energy density at the current density of 1mA ${\text{g}}^{-1}$ were determined as 1458.33W ${\text{kg}}^{-1}$ and 91.14Wh${\text{kg}}^{-1}$, respectively. Hence, NiO/ZnO nanocomposites could be reckoned to be a promising electrode material for supercapacitor while comparing to ZnO-based electrode material.

A porous organic framework as electrode material for supercapacitor was prepared successfully. It exhibited the remarkable specific capacitance of $170.66\mathrm{\text{F}}\cdot {\mathrm{\text{g}}}^{-1}$ at current density of $1.0\mathrm{\text{A}}\cdot {\mathrm{\text{g}}}^{-1}$, and 100% of capacitance retention after successive charge–discharge 10,000 cycles in an alkaline aqueous electrolyte solution. At the same time, we explored the electrochemical performance of porous N-doped carbon derived from the template of porous organic framework as supercapacitor electrode material. Impressively, it possessed the higher specific capacitance and better cycling stability, which showed specific capacitance of $180.88\mathrm{\text{F}}\cdot {\mathrm{\text{g}}}^{-1}$ at the current density of $0.4\mathrm{\text{A}}\cdot {\mathrm{\text{g}}}^{-1}$ and retained 100% of initial capacitance after 30,000 cycles.

In this paper, a functional ternary slurry consisting of polyurethane (PU) microspheres, graphene oxide (GO) nano platelets and silicon oxide (SiO₂) abrasives was used to carry out the polishing process on Si face of 4H-SiC wafers. The processing parameters of the slurry include graphene weight fraction in slurry GO1–GO7 (0.1–0.7wt.%), pH value (3–5), and sonication time T5–T15 (5–15min). Polishing process is conducted with two kinds of polishing pads A and B, PU and PC (polycarbonate). Results show that material removal rate (MRR) increases with increasing GO weight fraction up to GO5; besides, MRR also increases with increasing sonication time up to T10, and with increasing pH value. Using PU pad, the GO5-T10-pH5-A slurry leads to highest MRR 102.220nm/h of the polished SiC wafer. On the other hand, surface roughness improvement rate (SRIR) increases with increasing GO weight fraction up to GO5, and increases with increasing sonication time up to T15. But SRIR is not affected by pH value. Regarding effect of pad type, on average the PU pad results in higher MRR and better SRIR compared with the PC pad. Using PC pad, GO5-T10-pH5-B leads to lower MRR of 87.627nm/h. The addition of GO as the ternary slurry demonstrates its better effect on polishing SiC wafers by comparing with the counterpart binary slurry without GO. For example, MRR by the counterpart slurry SiO₂12-pH5-A is 58.411nm/h, which is lower than 102.220nm/h by the ternary slurry GO5-T10-pH5-A. Both XPS and Raman spectra demonstrate that the wafer polished by the functional ternary slurry can effectively produce the softer SiO₂ reactant layer on SiC wafer, and result in better polishing performance.

Octahedron-shaped ZnFe₂O₄ was fabricated through a facile process, where the ZnFe₂O₄ showed yolk-shell-structured. Hollow mesoporous SiO₂ spheres were used as template in the process. The SiO₂ spheres changed to nanosheets assembled at the surface of the as-formed octahedron-shaped ZnFe₂O₄. The ZnFe₂O₄/SiO₂ composite exhibits higher surface area (154.03m²/g) than those reported. The composite showed excellent catalytic activity in Fenton and photo-Fenton processes, for which the rate constants reached 0.034 and 0.063${\text{min}}^{-1}$, respectively. And the composite exhibited stable catalytic activity for three cycles. These results demonstrate that the composite shows potential applications in environmental treatment.

The composite of ZnO/CsxWO₃ with heterojunction was prepared by a two-step solvothermal method and the degradation of ofloxacin solution under full-spectrum light irradiation was carried out to evaluate the performance. The composites were characterized by XRD, SEM, EDS and UV-Vis-NIR reflectance. The result shows that the prepared composite has an ideal optical absorption in the spectral region of 200–2500nm and higher photocatalytic performance compared with ZnO and CsxWO₃. Moreover, ${\text{h}}^{+}$, $\cdot$OH and $\cdot$${\text{O}}^{2-}$ radicals are determined to be the active species. It is suggested that the heterojunction between ZnO and CsxWO₃ for ZnO/CsxWO₃ composite is important for improving the charge separation and thus restraining the recombination of photogenerated electrons and holes. Photodegradation of ofloxacin catalyzed by ZnO/CsxWO₃ followed the first-order kinetics and the degradation rate of ZnO/2CsxWO₃ was about two times higher than those of CsxWO₃ and ZnO.

Exfoliation/restacking route was utilized to investigate layer-by-layer self-assembly of FeTMPyP/TaWO₆ [5, 10, 15, 20-tetrakis (N-methylpyridinium-4-yl) porphyrinato iron (III)] nanocomposite in this paper. The colloidal suspension of ${\text{TaWO}}_6^{-}$ nanosheet was tested by Zeta potential and proved to be in a well-dispersed statement. Analysis technologies such as X-ray diffraction Scanning electron microscope (SEM) infrared UV-Vis were used to characterize the final product. The results showed that FeTMPyP molecules were introduced into the lamellar space of host material successfully. The electrochemical behaviors of FeTMPyP-TaWO₆ nanocomposite were tested by cyclic voltammetry method, and the nanocomposite showed excellent electrocatalytic properties to the oxidation of nitrite with the anodic peak shifts from 0.122 to 0.860V. Besides, the detection limit of nitrite can be calculated to be $7.2\times 10^{-5}$M with the concentration of nitrite ranging from 0.1 to 3.61mM by different pulse voltammetry (DPV) analyzation.

High-performance lead-free piezoelectric materials are environmentally friendly and in great demand for electronic devices. In this study, the phase diagram and properties of Hf, Ca co-doped BaTiO₃ (BHT-BCT) were investigated. A triple-point morphotropic phase boundary separating the rhombohedral, tetragonal and cubic phases for the (1-$x$)Ba(Ti_0.85Hf_0.15)O₃-$x$(Ba_0.7Ca_0.3)TiO₃ system exited at $x=0.3.$ High piezoelectric properties with piezoelectric coefficients $d_{33}$ (572pC/N) and Curie temperature $T_c$ (90^∘C) of 0.55Ba(Ti_0.85Hf_0.15)O₃-0.45(Ba_0.7Ca_0.3)TiO₃ are achieved in the BaTiO₃-based ceramics.

It remains a challenge to evaluate the Li-ions diffusion coefficients of LiMn${}_{1-x}$Fe_xPO₄ due to the presence of two voltage platforms upon charge/discharge. In this paper, a new single-particle model based on Butler–Volmer (BV) equation and one-dimensional diffusion equation is established. Using this model, the cyclic voltammogram curves of LiMn${}_{1-x}$Fe_xPO₄ single-particle electrodes are successfully fitted and their Li-ion diffusion coefficients in organic electrolyte are obtained. Through analyzing the diffusion coefficients, it is found that the Li-ions diffusion coefficients for both Fe and Mn redox processes in LiMn${}_{1-x}$Fe_xPO₄ reach the maximum when $x=0.4$. In addition, the values for oxidation processes are much larger than those for reduction processes.

Undoped and Dy${}^{3+}$-doped SrS nano-powders were synthesized by a solid-state diffusion method (SSDM). The nano-powders are then examined by the use of characterization tools as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM) including selected area electron diffraction (SAED). The emission spectra of SrS: Dy${}^{3+}$ powders are composed of a broadband and the characteristic emission of Dy${}^{3+}$ peaking at 482nm (blue region), 581nm (yellow region), 676nm (light red region) and 750nm (dark red region) bands corresponding to the transitions of ⁴F${}_{9∕2}$-⁶H${}_{15∕2}$, ⁴F${}_{9∕2}$-⁶H${}_{13∕2}$, ⁴F${}_{9∕2}$-⁶H${}_{11∕2}$ and ⁴F${}_{9∕2}$-⁶H${}_{9∕2}$, respectively. The resultant nano-powders can be used to fabricate thin films for the applications of efficient optoelectronic devices.

Rechargeable aqueous Zinc-ion batteries (ZIBs) are highly desirable for meeting ever-growing demands from large-scale energy storage fields due to their high energy density, high safety, low cost and environmental friendliness. Here, we report a binder-free porous MnO₂ film achieved by cathodic electrodeposition coupled with subsequent high temperature heat treatment as cathode for aqueous ZIBs. Benefiting from the binder-free and porous structure, this electrode exhibits a stable capacity of about 94mAhg${}^{-1}$ at 1.8A g${}^{-1}$ over 1500 cycles. The capacity at 6.0Ag${}^{-1}$ remains 61mAhg${}^{-1}$, which is 36% of that at 0.3Ag${}^{-1}$. Electrochemical impedance spectroscopy (EIS) results indicate the MnO₂ film after heat treatment has minor charge transfer impedance and high ions diffusion coefficient. The morphology revolution upon cycling suggests that the MnO₂ film after heat treatment is easily transformed into nanosheet arrays with abundant voids facilitating ions transport and possess better structure stability. This work may offer an efficient pathway to explore a promising cathode for aqueous ZIBs.

Novel Pt/La${}_{10}$Si₅CoO${}_{27-\delta }∕\gamma$-Al₂O₃ catalysts were developed for complete toluene combustion, and their catalytic activities were investigated. The introduction of the La${}_{10}$Si₅CoO${}_{27-\delta }$ promoter enhanced the reducibility and the catalytic activity due to its oxygen release ability. Among the samples prepared in this study, the 10wt.% Pt/10wt.% La${}_{10}$Si₅CoO${}_{27-\delta }∕\gamma$-Al₂O₃ catalyst showed the highest catalytic activity, allowing the complete toluene combustion at 120^∘C. In addition, the catalyst possesses high water durability.

Zeolite NaA was successfully synthesized from low-grade kaolin via hydrothermal synthesis method. The properties of the zeolite NaA were characterized by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray fluorescence (XRF), scanning electron microscopy (SEM)-energy-dispersive spectrometry (EDS), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), and thermogravimetry (TG)-differential thermal analysis (DTA). TEM analysis indicated the formation of body-centered cubic crystal zeolite NaA and the polycrystallinity of the zeolite NaA structure. The textural properties of the zeolite NaA were further studied by N₂ adsorption-desorption technique. In addition, the TG-DTA study confirmed that the heat treatment temperature of the zeolite NaA should be controlled below 600^∘C.

The aqueous colloid of mercapto ligand-functionalized silver nanorod was successfully synthesized by citric acid reduction method. The bigger silver nanospheres were preferably stabilizing in nanorod structure due to the presence of very high concentrations of both silver salts as well as mercapto ligand stabilizer. The properties and stability of the mercapto ligand-functionalized silver nanorod in aqueous colloid was investigated from standard characterizations. These types of surface functionalization silver nanorod conjugated with various biomolecules have been considered as interesting probe in electrochemical bioassay with improved sensitivity, selectivity for biomedical application and clinical analysis purpose.

Lanthanum hydroxycarbonate (LaCO₃OH), a kind of fluorescence materials, was less studied in application for photocatalysis. In this paper, LaCO₃OH/In(OH)₃/In₂S₃ (LCO/IO/IS) heterostructures were firstly synthesized by a mild two-step hydrothermal method and investigated by various technologies. The activity of as-prepared samples was evaluated by the degradation of Rhodamine B (RhB) under visible light ($\lambda \ge 420$nm). When the content of LaCO₃OH is 15mol.% (La/In), the obtained sample exhibits the highest performance, beyond two times as high as that of In(OH)₃/In₂S₃. The improved photodegradation activity might be ascribed to higher adsorption capability and photosensitization of RhB due to proper energy structures of the heterostructures, which prompts the effective separation of electrons and holes. This work extends the application of rear earth salts (lanthanum hydroxycarbonate) for purification of dye waste water.

Passivated emitter and rear cell (PERC) has the advantage of higher short circuit current and open circuit voltage, which are generally claimed to be related to the reduction of rear side recombination and the increase of rear surface reflection. However, few works have focused on exploring the internal conducting mechanism about it. Herein, the influence of PERC technique on improving the short circuit current is investigated by comparing a PERC with a single crystalline silicon (sc-Si) solar cell. The surface potential results measured by Kelvin probe force microscopy show a higher surface potential step at the Al–Si interface of PERC than that of sc-Si cell, indicating a severe energy band variation and a better carrier collecting ability of PERC. Moreover, by using advanced microstructure characterization techniques, the relationship among the surface potential step, morphology and element distribution is fully studied, which proposes a new viewpoint to explain the enhanced performance of PERC.

Ca_xBi${}_{1.7-x}$W${}_{0.3}$O${}_{3.45-0.5x}$ (CBW) ($x=0.00$, 0.05, 0.10, 0.15, 0.20, 0.30) electrolyte material were synthesized by sol–gel self-combustion method. The samples were characterized by thermogravimetric-differential thermogravimetric analysis(TG-DSC), X-ray diffraction, scanning electron microscopy (SEM), porosity and electrochemical impedance spectroscopy (EIS). The results show the powders Ca_xBi${}_{1.7-x}$W${}_{0.3}$O${}_{3.45-0.5x}$ (CBW) with fluorite crystal structure can be obtained after the precursor was calcined at 760^∘C. When sintered at 780^∘C for 2h, the compact ceramic sintered with relative density higher than 97% can be obtained. The electrochemical studies showed that Ca_xBi${}_{1.7-x}$W${}_{0.3}$O${}_{3.45-0.5x}$ (CBW) have high ionic conductivity after 780^∘C sintering. The sample Ca${}_{0.20}$Bi${}_{1.50}$W${}_{0.3}$O${}_{3.35}$ exhibits a conductivity of 0.07978 S$\cdot$cm${}^{-1}$ at 750^∘C, and the activation energy is 0.845eV, which is expected to be applied to the electrolyte materials for intermediate temperature solid oxide fuel cells (SOFC).

A series of glass cathode materials $x$Li₂O–50V₂O₅–(50−$x$)P₂O₅ ($x=20$, 25, 30, 35 and 40) have been synthesized by a simple melting–quenching method. 30Li₂O–50V₂O₅–20P₂O₅ glass (LVP30) shows the best cycling performance with a preferable capacity retention after 50 cycles. Then, we prepared a series of carbon-coated LVP30 glass-ceramic cathode materials by carbon coating and heat treatment. The carbon-coated LVP30 samples consist of the crystalline phase V₂O₃, VO₂ and Li₂O–V₂O₅–P₂O₅ glass. Among the carbon-coated LVP30 samples, LVP30-15C sample exhibits the best cycling and rate performance. It can retain a discharge capacity of 140mAh$\cdot$g${}^{-1}$ after 100 cycles. This unique glass-ceramic structure can result in good conductivity and structural ductility.