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In this review, the development history, evaluation indexes, structure-types, applications and development trends of quantum dot-based photodetectors are summarized.

Electrocatalytic water splitting is a desirable and sustainable strategy for hydrogen production yet still faces challenges due to the sluggish kinetics and rapid deactivation of catalysts in the oxygen evolution process. Herein, we utilized the metal-catalyzed growth technology and phosphating process to fabricate self-supported electrodes (Co

This study presents the formation mechanism of a layered structure consisting of coherent cellular and columnar solidification microstructure accompanied with the macrosegregation in aluminum dissimilar-filler welding. The filler-depleted zone resulted from the incomplete mixing of the solute; moreover, it solidifies before the surrounding mixed zone, wherein the subsequent dendritic growth is hindered by the pre-solidified microstructure. This solidification sequence leads to a layered solidification microstructure and segregation patterns.

Cost-effective electrodes with high activity for hydrogen evolution reaction (HER) and durability are required to develop clean and renewable hydrogen energy. In this work, a porous Cu supported Ni-P/CeO2 composite coating was fabricated by a facile electrodeposition technique. Owing to the contribution from the 3D porous Cu support and the incorporating agglomeration-free and uniformly distributed CeO2 particles into the Ni-P matrix, the optimal composite coating (porous Cu supported Ni-P/CeO2 (20 g L-1)) exhibits outstanding electrocatalytic performance with small overpotentials (η) of 118 and 320 mV at a cathodic current density of 10 and 100 mA cm2. Moreover, the composite electrode also presents excellent electrochemical stability in the alkaline solution. This work provides a feasible option to fabricate composite electrodes that may have desirable electrochemical properties for HER.

Electrolysis of water to generate hydrogen is an important issue for the industrial production of green and sustainable energy. The best electrocatalyst currently available for the hydrogen evolution reaction (HER) is platinum. We herein show that iridium can be manipulated to achieve a record high HER activity surpassing platinum in every aspect: a lower overpotential at any given current density, a higher current density, and mass activity for all bias potentials applied and a catalyst cost reduction of 50% for the same hydrogen generation rate. The superior HER activity was achieved by a binary Ir/Si nanowire catalyst design in which (as density functional theory calculations show) two distinct strategies act in synergy: (i) decreasing the size of the iridium nanoparticles to ∼2.2 nm and (ii) dividing the H2-generation process to three steps occurring on two different catalysts: H adsorption on iridium, H diffusion to silicon, and H2 desorption from silicon.

We reported a network-like porous amorphous Co-Ni-B grown on carbon cloth (CC) through a facile one-step chemical reduction process which was used as a binder-free three dimension (3D) integrated electrode for hydrogen evolution reaction (HER). The Co-Ni-B/CC with Co/Ni molar ratio about 1:1 (Co-50Ni-B/CC) exhibited the best HER performance in alkaline medium, with a negligible onset overpotential (22 mV), a small Tafel slope (88.2 mV dec−1) and excellent long-term stability. Specially, the HER activity of Co-50Ni-B/CC even exceeds that of commercial Pt/C at sufficiently high overpotential. The excellent HER performance of the Co-Ni-B/CC is attributed to a large number of active sites, the enhanced electron transfer process and the robust contact between catalyst and CC substrate. Keywords: Co-50Ni-B/CC electrode, Network-like porous structure, Amorphous metal borides, Electrocatalysis, Hydrogen evolution reaction

Co-W/CeO2 composite coatings were electrodeposited under galvanostatic conditions from a citrate plating bath containing suspended micro-CeO2 particles. The composition, structure and morphology of the composite coatings were evaluated and compared when different concentrations of micro-CeO2 particles are added. The as-prepared Co-W coating without CeO2 has an amorphous structure. However, embedding CeO2 into the Co-W matrix considerably improved the crystallinity of the Co-W alloy. The surface morphology study revealed that Co-W/CeO2 composite coatings were more compact with fewer microcracks and defects than the Co-W coating. The electrocatalytic performance of these composite coatings for hydrogen evolution reaction (HER) was also investigated by liner sweep voltammetry and electrochemical impedance spectroscopy techniques in alkaline medium. Co-W/CeO2 composite coatings gained remarkable improvement in HER activity which may be attributed to a synergistic eletrocatalytic effect between CeO2 particles and Co-W matrix. The apparent exchange current density value (j0) of the Co-W/CeO2 composite coating was 15.6 times higher than that of the Co-W coating when the concentration of micro-CeO2 particles in the plating bath is 7 gL-1 (denoted as M3), and the j0/Rf ratio (intrinsic catalytic activity) was 3.72 × 10−5 Acm−2. Furthermore, M3 coating also showed good stability and its apparent activation energy (Ea) of HER was calculated to be 24.59 kJmol-1, which was significantly lower than that of the Co-W coating.

Hydrogen evolution by electrocatalysis is an attractive method of supplying clean energy. However, it is challenging to find cheap and efficient alternatives to rare and expensive platinum based catalysts. Pt provides the best hydrogen evolution performance, because it optimally balances the free energies of adsorption and desorption. Appropriate control of these quantities is essential for producing an efficient electrocatalyst. We demonstrate, based on first principles calculations, a stepwise designed Rh-Au-Si ternary catalyst, in which adsorption (the Volmer reaction) and desorption (the Heyrovsky reaction) take place on Rh and Si surfaces, respectively. The intermediate Au surface plays a vital role by promoting hydrogen diffusion from the Rh to the Si surface. Theoretical predictions have been explored extensively and verified by experimental observations. The optimized catalyst (Rh-Au-SiNW-2) has a composition of 2.2:28.5:69.3 (Rh:Au:Si mass ratio) and exhibits a Tafel slope of 24.0 mV·dec–1. Its electrocatalytic activity surpasses that of a commercial 40 wt.% Pt/C catalyst at overpotentials above 0.19 V by exhibiting a current density of greater than 108 mA·cm–2. At 0.3 V overpotential, the turnover frequency of Rh-Au-SiNW-2 is 10.8 times greater than that of 40 wt.% Pt/C. These properties may open new directions in the stepwise design of highly efficient catalysts for the hydrogen evolution reaction (HER).

Nano-sized gold has been recognized as a potential catalyst in methanol fuel cells for both low cost and no formation of poisoning species compared with Pt. Previous techniques to prepare highly effective pure gold catalysts for methanol fuel cells are dealloying, which needs stern conditions. In this paper, cauli-flower shape gold nanoparticles with exposed high-index facets were obtained by a mild hydrothermal method. During the reaction process, sodium dodecyl sulfonate selectively protected high-index facets of gold, and H 2 O 2 kept etching low-index ones and growing new ones at the same time. A possible growth mechanism for high-index facets was proposed. The as-prepared gold nanoparticles were employed as electrocatalysts in the methanol oxidation. The results show enhanced anode current of 1249.8 μA cm −2 at 0.18 V in solutions with 0.5 M KOH and 1.0 M CH 3 OH, which is 10.68-fold larger than the previous reported value based on nanoporous gold catalysts. The preparation method of cauli-flower shape gold was easy to be operated and controlled, which is also universal in the synthesis of other materials with high-index facets.

Nickel compounds have been particularly explored for their excellent electrochemical properties. Attention is now placed on adding conductive materials to improve its electrochemical performance. Here, Ag/NiO composites are prepared from AgNiO 2 nanoparticle precursors through one galvanostatic charge/discharge cycle. The obtained Ag and NiO are grown epitaxially, producing large contact area, increasing the stability of the structure and decreasing the resistance between them. When Ag/NiO composites are employed as electrode materials and performed in the electrochemical experiments, they deliver a high capacity of 1166 C g −1 at 2 A g −1 , which is larger than that of the simple mixture of Ag and NiO. An excellent cyclic stability is also testified. Only 10% of the specific capacity lost is tested after 2000 galvanostatic charge/discharge cycles. Our study suggests that Ag/NiO composites with epitaxial-growth structure are an excellent candidate for high-performance hybrid asymmetric supercapacitors.

Surface tension of calcium aluminate refining slag was measured by the Slide method at 1823 K. Based on different levels of the MgO content and the mass ratio of CaO to Al2O3, the effects of MgO content and the mass ratio of CaO to Al2O3 on surface tension were investigated. The results indicate that surface tension decreased with increasing MgO content (from 0 to 4.86%), followed by an increase with further increasing MgO content up to 11.33%. The trend that surface tension changed with the mass ratio of CaO to Al2O3 was the same as the trend that surface tension changed with the MgO content. The surface tension was varied from 0.617 N/m to 0.710 N/m, for the mass ratio of CaO to Al2O3 varying between 0.60 and 1.28. An attempt was made to estimate surface tension of CaO−Al2O3−MgO slag and its sub-system, and the application showed that the model worked well.

Rechargeable all-solid-state batteries have better safety and higher energy density than the commercial rechargeable Li-ion batteries with organic liquid electrolytes. However, it is still quite challenging to develop a thin, flexible and high Li-ion conductive solid electrolyte for all-solid-state batteries. Here we develop a flexible poly(ethylene oxide) (PEO)-based composite electrolyte with high ionic conductivity of 1.3 × 10−4 S cm−1 at 30 °C. Fast Li-ion conductive NASICON Li1.3Al0.3Hf1.7(PO4)3 (LAHP) powders with a high bulk ionic conductivity of 7 × 10−4 S cm−1 at 25 °C are added into PEO-LiTFSI electrolyte to increase the total Li-ion conductivity of the electrolyte. Solid nuclear magnetic resonance (NMR) has been employed to analyze the Li-ion conducting mechanism of the electrolyte. Moreover, the composite electrolyte PEO-LiTFSI-20LAHP with a more amorphous component shows better electrochemical stability than the PEO-LiTFSI electrolyte. The performance of the electrolyte PEO-LiTFSI-20LAHP is also tested in different all-solid-state cells; the composite membrane blocked lithium-dendrite growth, which increases the cycling life of all-solid-state cells.

Three-dimensional ZnO/CdSe heterostructure (ZnO/CdSe HS) was fabricated with large scale and its gas-sensing application with low operating temperature was explored. Combining cost-effective chemical vapor deposition with solution growth methods, ZnO nanorods were grown on the surface of CdSe nanoribbons. Scanning electron microscopy, X-ray diffraction and transmission electron microscopy were employed to confirm the formation of ZnO/CdSe HS. The ZnO/CdSe HSs were fabricated as gas sensors in the detection of ethanol at the optimum operating temperature of 160 °C. Compared with ZnO-based gas sensors, the optimum operating temperature of the ZnO/CdSe HS-based sensor was approximately 100 °C lower, while the sensitivity was 20-fold higher in the dark and 3-fold higher under visible light illumination condition. The enhancement of sensing properties was attributed to the advanced heterostructure and visible light activated CdSe.

Tremendous efforts have been investigated in enhancing the catalytic activity of 3d-transition metal based materials (especially cobalt-based catalysts), which are regarded as promising candidates for non-noble catalysts in electrocatalytic water splitting. Herein, a facile one-step hydrothermal method is utilized to fabricate CoWO4/CoP2 nanoflakes (CTCP) on carbon nanotube film (CNTF), which constructs self-supported CTCP/CNTF composite electrocatalyst for water splitting. Benefitting from the well-configured structure, CTCP/CNTF possesses more active sites for reactions along with quicker interfacial charge transfer and better electrical conductivity. Meanwhile, embedding CoP2 in CoWO4 yields obvious synergistic effect to improve the intrinsic catalytic activity for OER and HER. In 1.0 M KOH, the optimized CTCP/CNTF-3 electrode requires a low overpotential of 252 mV at 10 mA cm−2 (anodic current density) for OER, and 133 mV at −10 mA cm−2 (cathodic current density) for HER. When employing CTCP/CNTF as both anode and cathode, the cell voltage for overall water splitting is only 1.605 V at jcell = 10 mA cm−2, which value is extremely close to that of Pt/C/CNTF (−) // RuO2/CNTF (+). Remarkably, the electrolyzer (CTCP/CNTF(−) // CTCP/CNTF(+)) shows better stability for water splitting than Pt/C/CNTF (−) // RuO2/CNTF (+) over a duration of 32 h at jcell = 10 mA cm−2.

Ruthenium nanoparticles modified on silicon nanowires (Ru/SiNWs) were prepared by directly reducing Ru ions with Si–H bonds. The composites with different contents of Ru (denoted as Ru/SiNW-x, x means the relative molar ratio of Ru to SiNW) were evaluated as electrocatalysts for the hydrogen evolution reaction (HER). Ru/SiNW-42.9 showed an excellent electrocatalytic activity in the oxygen-free 0.5 M H2SO4 medium. The Tafel slope of Ru/SiNW-42.9 was 81 mV/decade, indicating that its catalytic effect was even better than pure Ru particles. SiNWs modified with proper content of Ru may be a promising electrocatalyst for HER. Keywords: Hydrogen evolution reaction, Electrocatalysis, Ruthenium, Silicon nanowires, Nanostructure

In this paper, pure metastable phase iron vanadate (FeVO4-II) ultrathin nanosheets (50 nm in thickness) with exposed {010} facets were obtained by a mild hydrothermal process, without the use of any template or organic surfactant. The photocatalytic rate of the FeVO4-II {010} facets was measured taking advantage of their unique morphology. Furthermore, the FeVO4-II catalyst could be easily separated and reused, simply by applying an external magnetic field. In addition, with their n-type semiconductor structure, FeVO4 ultrathin nanosheets exhibited gas-sensing for an ethanol trace.

MoO2 nanospheres are successfully synthesized by a simple ethylene glycol-assisted hydrothermal route. The formation process is associated with the dissolution-recrystallization mechanism under the ethylene glycol reduction, resulting in a unique structure of that solid MoO2 nanospheres assembled by many ultrafine primary nanoparticles. Benefiting from the hierarchical structural features, the MoO2 nanospheres electrode displays a higher specific capacitance (204.7 and 197.4 Fg−1 at 1 and 6 A g−1, respectively) and exhibits a significant superior cycling stability (the specific capacitance maintains 90.6% after 1000 cycles at 1 A g−1).

In this paper, Ni-Co coatings were electrodeposited onto carbon steel substrates with the aid of ultrasonic agitation. The coatings were analyzed by energy dispersive X-ray analysis (EDX), X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The effects of the ultrasonic frequency on the roughness, hardness and corrosion resistance of the Ni-Co coatings were also investigated. The results indicated that the increase of the ultrasonic frequency from 20 to 120 kHz reduced the Ni content and the grain size of Ni-Co coatings. Moreover, the phase structure of the electrodeposited coatings was influenced by the ultrasonic frequency. Under 55 kHz ultrasonic agitation, the Ni-Co coating was single fcc phase and showed the finest roughness and the strongest corrosion resistance in 5 wt.% NaCl solution at the ambient temperature. Under ultrasonic agitation with frequency of 90 kHz, the coating was a mixture of fcc and hcp structure and showed the maximal hardness of about 420 HV. Therefore, ultrasonic agitation helped decrease the roughness, and enhance hardness and corrosion resistance of Ni-Co coatings.

Currently, platinum-based electrocatalysts show the best performance for hydrogen evolution. All hydrogen evolution reaction catalysts should however obey Sabatier's principle, that is, the adsorption energy of hydrogen to the catalyst surface should be neither too high nor too low to balance between hydrogen adsorption and desorption. To overcome the limitation of this principle, here we choose a composite (rhodium/silicon nanowire) catalyst, in which hydrogen adsorption occurs on rhodium with a large adsorption energy while hydrogen evolution occurs on silicon with a small adsorption energy. We show that the composite is stable with better hydrogen evolution activity than rhodium nanoparticles and even exceeding those of commercial platinum/carbon at high overpotentials. The results reveal that silicon plays a key role in the electrocatalysis. This work may thus open the door for the design and fabrication of electrocatalysts for high-efficiency electric energy to hydrogen energy conversion., Design of hydrogen evolution catalysts needs to balance the hydrogen adsorption energy to facilitate easy adsorption and desorption. Here, the authors report a composite catalyst where hydrogen adsorption occurs on rhodium and desorbs from silicon which has a lower adsorption energy.

Mott–Schottky analysis, electrochemical impedance spectroscopy in conjunction with the Point Defect Model (PDM), were performed to characterize the semi-conductor property of passive films formed on Cu–Ni alloys in 1 mol/L NaOH solution. The acceptor density, flat potential and vacancy diffusion coefficient in the passive films formed on Cu–Ni alloys were determined. Results indicated that the passive films displayed p-type semi-conductive characteristics, where metal vacancies (over oxygen vacancies and interstitials) preponderated. With the increase of Cu, the flat potential moved towards positive, while the acceptor density and impedance of passive films decreased due to its steady oxidation-from Cu(I) to Cu(II), which increased the susceptibility to corrosion. In addition, the acceptor density and flat potential increased when the formation potential moved towards negative. The calculated value obtained for D 0 was around 10 −14 cm −2 s −1 .

In this paper, nano-SiO2 was used as an accelerator for improving the microstructure and the corrosion resistance of phosphate coating on carbon steel. The chemical composition and microstructure of the coatings were analyzed by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The effects of nano-SiO2 on weight, roughness and corrosion resistance of the phosphate coatings were also investigated. Results show that the compositions of phosphate coating were Zn3(PO4)2·4H2O (hopeite), and Zn2Fe(PO4)2·4H2O (phosphophylite). The phosphate coatings became denser due to the addition of nano-SiO2 which reduced the size of the crystal clusters. The average weight of phosphate coatings approximately linearly increased with the nano-SiO2 content in the bath from 0 to 4 g/L, and the phosphate coatings formed in bath containing 2 g/L nano-SiO2 showed the highest corrosion resistance in 5 wt.% sodium chloride solution at ambient temperature. Nano-SiO2 would be widely utilized as a phosphating additive to replace the traditional nitrite, due to its less pollutant and its better quality of the coating.

Deep level donor's ionization behavior of passive film formed on the surface of stainless steel was investigated by Mott-Schottky plots. It is indicated that transformation process of deep level donors' ionization behavior of passive film on surface of stainless steel can be divided into 4 stages with rising immersion time. At the initial immersion stage (10 min), Fe(Ⅱ) located in the octahedral sites of the unit cell is not ionized and the deep level does not appear in Mott-Schottky plots. At the second stage (9−38 h), Fe(Ⅱ) located in the octahedral sites starts to be ionized, which results in deep level donors' generation and density of deep level donors almost is constant with augmenting immersion time but the thickness of space charge layer is more and more thicker with rising immersion time. At the third stage (48 h−12 d), density of deep level donors rises with increasing immersion time and the thickness of passive films space charge layer decreases. At last stage (above 23 d), both the space charge layer's thickness and density of deep level donors are no longer changed with increasing immersion time. In the overall immersion stage, the shallow level donors' density is invariable all the time. The mechanism of deep level donor's ionization can be the generation of metal vacancies, which results in crystal lattice's aberration and the aberration energy urges the ionization of Fe(Ⅱ) in octahedral sites.

The influence of dissolved ozone (O3) and its concentrations on the formation of phosphate coatings on carbon steel in phosphate bath, as well as the protective properties of phosphate coatings in a 5 wt% NaCl solution have been studied. The structure, surface morphologies, and phase compositions of the phosphate coating on the carbon steel substrate was investigated by SEM, XRD. It is shown that the phosphate coating became more dense with fewer microholes and an increasing concentration of ozone in phosphate bath in the range of 0.0 to 1.62 mg/L. The coating compositions were Zn3(PO4)2 · 4H2O (hopeite) and Zn2Fe(PO4)2 · 4H2O. Potentiodynamic polarization and immersion tests were used to evaluate the corrosion properties of the treated samples. The coating showed good corrosion resistance properties.

Ni–W–Al2O3 nanocomposite coatings were deposited on the low-carbon steel substrates from aqueous sulfate-citrate electrolytes containing various amounts of Al3O2 nanoparticles. Their surface morphology, element and phase composition were carried out using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). The corrosion resistance was carried out using the potentiodynamic polarization (Tafel) and electrochemical impedance spectroscopy (EIS). It is shown that incorporation of Al2O3 nano-particles into amorphous Ni–W coating would transform its structure to being crystalline and influence its properties. The hardness sharply increases and corrosion resistance performance significantly decreases even after few Al2O3 nanoparticles (2 g/L) were added into the bath. In addition, with increase of Al2O3 addition in the bath, a tendency of increase in hardness and corrosion resistance performance is observed.

In this paper, ultrasonic irradiation was utilized for improving the corrosion resistance of phosphate coatings on aluminum alloys. The chemical composition and morphology of the coatings were analyzed by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The effect of ultrasonic irradiation on the corrosion resistance of phosphate coatings was investigated by polarization curves and electrochemical impedance spectroscopy (EIS). Various effects of the addition of Nd(2)O(3) in phosphating bath on the performance of the coatings were also investigated. Results show that the composition of phosphate coating were Zn(3)(PO(4))(2).4H(2)O(hopeite) and Zn crystals. The phosphate coatings became denser with fewer microscopic holes by utilizing ultrasonic irradiation treatment. The addition of Nd(2)O(3) reduced the crystallinity of the coatings, with the additional result that the crystallites were increasingly nubby and spherical. The corrosion resistance of the coatings was also significantly improved by ultrasonic irradiation treatment; both the anodic and cathodic processes of corrosion taking place on the aluminum alloy substrate were suppressed consequently. In addition, the electrochemical impedance of the coatings was also increased by utilizing ultrasonic irradiation treatment compared with traditional treatment.

A visible light-enhanced gas sensor based on cadmium selenide (CdSe) nanoribbons has been successfully developed. These nanoribbons were synthesized by a gold-catalyzed vapor–liquid–solid method and employed as visible-light-activated gas sensors for 50 to 1000 ppm ethanol at 200 °C. Visible light illumination on the surface of CdSe nanoribbons could produce more holes and increase the conductance of the sensor which significantly enhanced the gas response.