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Photocatalytic hydrogen production is recognized as a prospective technology for energy conversion to alleviate the energy shortage. Hence, we propose a convenient method to synthesize two-dimensional (2D) ZnS-propylamine (pa) hybrid complex materials with traditional solvothermal method, demonstrating prominent photocatalytivity under visible light irradiation. Meanwhile, the improvement of hydrogen production has been further investigated by controlling different in-situ ultrasonic times. The optimized hydrogen generation obtained from ZnS(pa)x was up to 1828 μmol/g under 4 h visible light irradiation. The high performance could be contributed by the inorganic-organic coordination effect on optimizing the morphology and structure, which enlarge reaction sites and accelerate carriers migration of the material. This work represents an effective approach to promote and optimize the traditional wide bandgap semiconductors for enlarging visible light photocatalytic performances.

Heterogeneous La-doped CeO2 (LCO)-ZnO nanocomposites have been synthesized via a facile wet-chemical approach for multifunctional applications. It is found that such LCO-ZnO with the Zn/Ce ratio of 9:1 demonstrates the highest photoactivity under visible light irradiation. Apart from the photocatalytic application, this material has also been used as the electrolyte membrane of solid oxide fuel cells (SOFCs). The best device of SOFC composed of 10% LCO-ZnO composite achieved 922 mW cm-2 output along with an open circuit voltage of 1.10 V at 550 °C. Heterogeneous semiconductor-ionic composite of the heterogeneous LCO-ZnO nanocomposite result in high charge-hole pairs separation and ionic conduction which attributes the efficient multifunctional activity of the synthesized material. The built-in field directed at the junction may promote ions (H+ and O2-) transport to pass through the semiconductor-ionic LCO-ZnO membrane layer. This work is the first discovery on the LCO-ZnO semiconductor-ionic materials as a potential candidate for renewable energies to electricity conversions.

A metallic route for protons The operating temperatures of solid oxide fuel cells are usually much higher than needed to drive the uncatalyzed electrochemical reaction to transport oxygen anions or protons through ceramic electrolytes. Wu et al. report that the interface between two semiconductors, Na x CoO 2 and CeO 2 , forms a metallic state that enables proton transport at temperatures below 600°C (see the Perspective by Ni and Shao). The authors constructed a hydrogen fuel cell with this material that delivered 1 watt per centimeter. Science , this issue p. 184 ; see also p. 138

Two-dimensional nanomaterials are attracting attention for cancer therapy. However, high toxicity, insensitivity to external stimuli and single therapeutic modality are still key issues hindering their clinical application. Therefore, the construction of a safe, intelligent and versatile nanocomposite is needed to meet clinical expectations. Herein, we developed a nanocomposite of Bi@RP-PEG-DOX with 2D bismuthene loaded with 0D red phosphorus quantum dots and DOX. The nanocomposite with DOX loading capacity (ca. 250 %) and photothermal conversion efficiency (ca. 54 %) showed both photothermal and photodynamic effects and a sensitive response of drug release to the acidic tumor microenvironment or NIR II laser irradiation. The nanocomposite exhibits good biosafety. Through the X-ray attenuation properties of bismuth, the nanocomposite serves as an excellent CT contrast agent, providing potential to perform CT-guided therapy.

Two-dimensional (2D) photocatalysts have been widely studied due to their short charge carrier migration pathways and tunable electronic structures. Herein, a facile one-pot solvothermal process with ethylamine (ea) constructs a novel 2D nanojunction based on ZnSe. The ea molecules coordinate with Zn2+ to form 2D ZnSe(ea)x, where the consequent 2D ZnSe grows in an epitaxial way resulting in the self-assembled 2D/2D ZnSe/ZnSe(ea)x nanojunctions driven by van der Waals (VDW) force, which largely extend the absorption range. The atomic thickness of the 2D structure offers a short charge migration pathway, low electric resistance and rich active sites for the surface reaction of photocatalysis. All the above favorable factors work synergistically to reach a superior hydrogen evolution of 2875 μmol g-1 h-1 under visible light irradiation (≥420 nm) and a notable quantum yield of 64.5% at 450 nm, which are among the highest recorded values of non-noble metal photocatalysts.

Several nitrogen-doped TiO2/Sepiolite (N-TiO2/Sep) photocatalysts were prepared via microwave-hydrothermal treatment using four different types of nitrogen sources: ammonium hydroxide, urea, ethylenediamine and triethylamine. The obtained nanocomposites were characterized by using XRD, TEM, BET, XPS and UV–vis techniques. The results revealed that the chemical and morphological properties of the nanocomposites were significantly dependent on the nitrogen source. The interstitial N doping occurred in the form of N-O-Ti-O and the surfaces of the samples were modified by carbon species from dopants. As compared to that of the undoped sample, N-doped samples exhibited a red shift in the band gap transition. The results of simulated solar light photocatalytic activities demonstrated that NTS-EDA exhibited better photocatalytic activity than singly N-doped (i.e., no carbon) or undoped TiO2/Sep sample. The enhanced solar-light activity is attributed to the low band gap energy with N-doping, the high adsorption capacity and uniform distribution of titania nanoparticles with sepiolite as support, and the appropriate carbon content of the dopants.

Heterogeneous ZnO–SrTiO3 nanocomposites were synthesized via a facile hydrothermal method. The highest H2 production rate, 1317.44 μmol g−1 within 5 h under solar-light irradiation was achieved for the Zn/Sr ratio of 9:1 of the ZnO–SrTiO3. More interestingly though the ZnO–SrTiO3 is a semiconducting system, it could be used as an electrolyte in the low temperature solid oxide fuel cell without electronic conducting short circuiting problem. This device displayed an open circuit voltage of 1.14 V and reached the maximum power density of 564 mW cm−2 at 550 °C. These results are attributed to the enhanced separation of the charge-hole pairs by the heterogeneous structure of ZnO–SrTiO3 nanocomposites, which possess obvious both heterogeneously ionic and semiconduction. This new discovery indicates a good promising candidate for both solar and hydrogen energy conversions.

Flexible piezoelectric devices are attractive for energy conversion and strain sensing applications, including in the area of wearable electronics and self-powered sensors. Here, we report a piezoelectric nanogenerator/strain sensor based on lead (II) iodide (PbI2) nanosheets with the shape of two-dimensional (2D) structures, of which the piezoelectricity is not affected by the number of layers. A typical 2D piezoelectric device fabricated with 3 layers PbI2 nanosheets has recorded peak values of open-circuit voltage, short-circuit current and loading power as 29.4 mV, 20 pA, and 0.12 pW, respectively, and also possess good charging and integration capabilities. Moreover, these devices can be applied as self-powered strain sensors, with high sensitivity and excellent stability. As such, this study provides new knowledge and strategy for flexible energy harvesting or strain sensing devices based on 2D structures.

The flower-shaped ZnO was synthesized to form composite with the delafossite structure CuFeO2. The composite heterojunction formed for the ZnO-CuFeO2 composite material demonstrates a profound significance for exploring novel materials in solid oxide fuel cell (SOFC) field. At 550 °C, power outputs of 300 mW cm−2 and 468 mW cm−2 were achieved for SOFC devices using pure ZnO and composite with CuFeO2 as the electrolytes, respectively. The composite showed a good performance at low temperatures, for instance, it showed a power output of 148 mW cm−2 at 430 °C. The studies on photocurrent-time curves with visible light on/off irradiation provided an evidence for electron-hole separation. The heterojunctions separate holes and electrons, preventing short-circuiting while used in the SOFC device. These results demonstrate that introducing the heterojunctions in the electrolyte is an innovative approach for advanced SOFCs.

The design and synthesis of efficient non-noble metal catalyst is important for the practical application of hydrogen evolution reaction (HER) from water electrolysis. In this study, molybdenum carbides were prepared by a novel synthetic method, which involved the first exfoliation of 2D MoS2 based on the principle of cold expansion of water below 4 °C and then carburization of exfoliated MoS2. In this method, MoS2 played roles of morphology template and molybdenum source simultaneously. Carbon-coated molybdenum carbide nanosheets were obtained and confirmed by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. The stripping degree of MoS2 was found to have an important influence on physical properties and catalytic performance of molybdenum carbides. Interestingly, Mo2C nanosheets encapsulated in carbon nanotubes were observed when the MoS2 with a high peeling degree was used in the preparation. It showed high activity and good durability towards HER in acid solution.

CdSe quantum dots (QDs) hybridized with graphene oxide (GO) are synthesized by a facile chemical precipitation method. The absorption of the CdSe/GO nanocomposite is increased with a significant blue shift with respect to CdSe QDs. The specific surface area of the CdSe/GO nanocomposite is 10.4 m2/g, which is higher than that of CdSe QDs (5 m2/g). The PL intensity of the CdSe/GO nanocomposite is lower than that of the CdSe QDs owing to the inhibition of the recombination of electron-hole pairs in the composite. In Raman analysis, the two bands of the CdSe/GO nanocomposite are shifted to higher wavenumbers with respect to graphene oxide, which is attributed to electron injection that is induced by CdSe QDs into graphene oxide. Using the Brilliant Green dye, the photocatalytic reduction efficiency of CdSe QDs and the CdSe/GO nanocomposite under sunlight irradiation for 90 min are approximately 81.9% and 95.5%, respectively. The calculated photodegradation rate constants for CdSe QDs and the CdSe/GO nanocomposite are 0.0190 min−1 and 0.0345 min−1, respectively. The enhanced photocatalytic activity of the CdSe/GO nanocomposite can be attributed to the high specific surface area and the reduction of electron-hole pair recombination because of the introduction of graphene oxide.

Two-dimensional (2D) ultrathin metal chalcogenides represent a class of promising materials for various applications thanks to attractive physicochemical properties. However, a reliable pathway for fabricating ultrathin metal chalcogenides nanosheets, regardless of the bulk crystals of their 3D counterparts, still remains a challenge. Herein, we present a versatile solution-processed template synthesis strategy, in which a single molecular-level precursor anneals to ultrathin single-crystal nanosheets with the aid of lattice-matching templates, following the Frank–van der Merwe growth mode and featuring high quality, low cost, scalability, and processability. Following this strategy, Sb2S3, MoS2, and ZnS nanosheets are successfully prepared as representatives for materials whose bulk counterparts possess 1D, 2D, and 3D crystal structures, respectively, and the growth mechanism is confirmed by crystal mode analysis. As a proof-of-concept application, MoS2 and Sb2S3 nanosheets are used for gas sensor and fl...

CuSbSe 2 has attracted huge attention as an absorber material for thin-film solar cells due to its attractive optical and electrical properties, as well as earth-abundant, low-cost, and low-toxic constituent elements. However, different from the conventional inorganic absorbers such as CdTe, CuSbSe 2 has a complicated phase space with at least five competitive phases such as Cu 2 Se, CuSe, Sb 2 Se 3 , Cu 3 SbSe 4 , and Cu 3 SbSe 3 and crystallizes in two-dimension (2D) layered structure. Crystal phase and orientation strongly correlate with film properties and thus are crucial for device performance. In this paper, by varying the annealing temperature, we carefully investigated the phase, electrical properties and crystal orientation evolutions of hydrazine solution processed CuSbSe 2 films. Intermediate Cu 3 SbSe 3 secondary phase was identified, and the temperature dependent orientation change was observed, which is driven by the reduced surface energy, as supported by the first-principle calculations. Finally, a prototype thin film solar cell is fabricated, achieving 2.70% efficiency. Our theoretical calculation and experimental investigation demonstrated the importance of controlling phase composition and crystal orientation in the application for photovoltaics.

To date, all the lead halide based full-inorganic or organic–inorganic hybrid perovskites have been synthesized from organic solvent, such as N,N-dimethylformamide (DMF) or dimethyl sulfoxide (DMSO), by a solution method. Herein, water has been utilized as a ‘green’ solvent to develop an efficient synthetic route to grow various kinds of lead halide perovskite nanowires (NWs). By controlling the proportion of the hybrid cations, Csx(CH3NH3)1−xPbI3 perovskite NWs were successfully synthesized. Every Csx(CH3NH3)1−xPbI3 perovskite NW demonstrated single crystal characteristics with uniform stoichiometric element distribution. Because of the controllable cation composition, the NW bandgaps could be finely tuned from 1.5 to 1.7 eV. Transient photoluminescence spectra showed superior NW quality when compared with those of the conventional DMF-based NWs. Based on the abovementioned high quality single Cs0.5(CH3NH3)0.5PbI3 perovskite NW, a reliable single-NW photodetector was fabricated to investigate the optoelectronic application. It demonstrated a responsivity of 23 A/W, exceeding most of the reported values in the perovskite nanowire photoconductive detectors, and the shot-noise normalized detectivity was 2.5 × 1011 Jones comparable to the parameters of the commercial silicon-based nanowires. The green and robust synthesis method, finely tunable NW bandgaps, and superior optoelectronic properties are expected to open a new door for the development of perovskite optoelectronic devices.

Two-dimensional (2D) photocatalysts have been widely studied due to their short charge carrier migration pathways and tunable electronic structures. Herein, a facile one-pot solvothermal process with ethylamine (ea) constructs a novel 2D nanojunction based on ZnSe. The ea molecules coordinate with Zn2+ to form 2D ZnSe(ea)x, where the consequent 2D ZnSe grows in an epitaxial way resulting in the self-assembled 2D/2D ZnSe/ZnSe(ea)x nanojunctions driven by van der Waals (VDW) force, which largely extend the absorption range. The atomic thickness of the 2D structure offers a short charge migration pathway, low electric resistance and rich active sites for the surface reaction of photocatalysis. All the above favorable factors work synergistically to reach a superior hydrogen evolution of 2875 μmol g-1 h-1 under visible light irradiation (≥420 nm) and a notable quantum yield of 64.5% at 450 nm, which are among the highest recorded values of non-noble metal photocatalysts.

Two-dimensional atomic crystals, such as two-dimensional oxides, have attracted much attention in energy storage because nearly all of the atoms can be exposed to the electrolyte and involved in redox reactions. However, current strategies are largely limited to intrinsically layered compounds. Here we report a general strategy that uses the surfaces of water-soluble salt crystals as growth templates and is applicable to not only layered compounds but also various transition metal oxides, such as hexagonal-MoO3, MoO2, MnO and hexagonal-WO3. The planar growth is hypothesized to occur via a match between the crystal lattices of the salt and the growing oxide. Restacked two-dimensional hexagonal-MoO3 exhibits high pseudocapacitive performances (for example, 300 F cm−3 in an Al2(SO4)3 electrolyte). The synthesis of various two-dimensional transition metal oxides and the demonstration of high capacitance are expected to enable fundamental studies of dimensionality effects on their properties and facilitate their use in energy storage and other applications., Two-dimensional atomic crystals are known to be effective electrode materials for energy storage applications. Here, the authors report the preparation of various two-dimensional metal oxides, including those which do not have a layered parent structure, via a salt templating strategy.

Bi2S3 is a promising inorganic material for thin film photovoltaic application with optimum direct band gap of ~1.3 eV, strong absorption coefficient, nontoxic and simple composition. Here we introduce rapid thermal evaporation (RTE), a method with simple facility and extremely fast deposition speed, to produce high quality Bi2S3 films. By optimizing the substrate temperature and post-annealing process, well-crystalline, smooth and compact Bi2S3 films were obtained. The band gap, doping type and density, and photosensitivity of as-produced Bi2S3 films were revealed by a combined X-ray diffraction, Scanning electron microscopy (SEM), Raman spectrum, X-ray photoelectron spectroscopy (XPS), Energy dispersive spectroscopy (EDS), Hall effect and photoresponse measurements. Finally, a prototypical ITO/NiO/Bi2S3/Au solar cell with 0.75% power conversion efficiency was obtained, manifesting the promise of Bi2S3 as the absorber layer for thin film photovoltaics.

Sodium (Na) has been identified as a benign contaminant in some thin film solar cells. Here, we have studied the impact of sodium on the properties of CdS/Sb2Se3 superstrate thin film solar cells. NaF deposited at the CdS/Sb2Se3 heterojunction severely degraded the device performance, yet NaF introduced into the Sb2Se3 film after the completion of the heterojunction showed a negligible influence on the film conductivity and device performance. We concluded that sodium could easily diffuse into the Sb2Se3 film and probably locates in the gap between (Sb4Se6)n ribbons, being inert in Sb2Se3 solar cells.

Colloidal quantum dots (CQDs) are solution-synthesized semiconductor nanocrystals with size typically below 10 nm. Their large surface-to-volume ratio and abundant active surface sites, combined with the grain size effect and solution-processability make CQDs promising building blocks for low-cost and high-performance gas sensors. Here we employed the ligand exchange strategy to develop low-power and highly sensitive H 2 S gas sensors based on PbS CQDs. Following the layer-by-layer spin-coating of PbS CQDs capped with long-chain oleic acid ligands from synthesis, a surface treatment using different inorganic salts was conducted for ligand exchange in air ambient at room temperature. Upon exposure to 50 ppm of H 2 S at 135 °C, the resistance of all those sensors decreased shown as the response and the Pb(NO 3 ) 2 treatment yielded highest response (4218 at 135 °C) with shortest response/recovery time. We tentatively proposed a H 2 S-induced and temperature-promoted p-to-n transition of PbS CQDs as the sensing mechanism and the role of Pb(NO 3 ) 2 treatment was attributed to an n-type remote doping effect realized by the ligand exchange, which was further supported by the energy dispersive spectrometry (EDS) and ultraviolet photoelectron spectroscopy (UPS) analysis.

2D materials, particularly those bearing in-plane anisotropic optical and electrical properties such as black phosphorus and ReS

To date, all the lead halide based full-inorganic or organic-inorganic hybrid perovskites have been synthesized from organic solvent, such as N,N-dimethylformamide (DMF) or dimethyl sulfoxide (DMSO), by a solution method. Herein, water has been utilized as a 'green' solvent to develop an efficient synthetic route to grow various kinds of lead halide perovskite nanowires (NWs). By controlling the proportion of the hybrid cations, Cs

The new emerging organometal trihalide perovskite holds great potential for high-efficiency, low-cost solar cells because of its high solar to electricity conversation efficiency (>16%) achieved within 4 years of research and its low-temperature solution processing. In this Letter we introduce NiO as the hole-collecting and -conducting layer in perovskite solar cells. Through a modified sequential deposition strategy, we successfully fabricated high-quality CH3NH3PbI3 onto a planar NiO layer and built a planar inverted ITO/NiO/CH3NH3PbI3/PCBM/Al photovoltaic device. A device efficiency of 7.6% was achieved with an impressively high open-circuit voltage (Voc) of 1.05 V. Our study demonstrates the potential application of a deep work function NiO layer for perovskite solar cells.

Recently, CuSbS2 has been proposed as an alternative earth-abundant absorber material for thin film solar cells. However, no systematic study on the chemical, optical, and electrical properties of CuSbS2 has been reported. Using density functional theory (DFT) calculations, we showed that CuSbS2 has superior defect physics with extremely low concentration of recombination-center defects within the forbidden gap, espeically under the S rich condition. It has intrinsically p-type conductivity, which is determined by the dominant Cu vacancy (VCu) defects with the a shallow ionization level and the lowest formation energy. Using a hydrazine based solution process, phase-pure, highly crystalline CuSbS2 film with large grain size was successfully obtained. Optical absorption investigation revealed that our CuSbS2 has a direct band gap of 1.4 eV. Ultraviolet photoelectron spectroscopy (UPS) study showed that the conduction band and valence band are located at 3.85 eV and −5.25 eV relative to the vacuum level, re...

Compact thin film of antimony sulfide (Sb2S3) as a promising absorber layer was obtained by rapid thermal evaporation (RTE) rather than conventional chemical bath deposition or atomic layer deposition based methods. The systematical characterizations of Sb2S3 film demonstrated the pure phase, void free and high crystallization. The large grain and preferential growth of Sb2S3 thin film were implemented by crystallization and cooling techniques, respectively. The corresponding devices were gradually optimized with a power conversion efficiency of ~3.5%, almost three times of planar devices fabricated by vacuum method. Both the non-oxide buffer layer (CdS layer) and free of hole transport layer enabled the high stability of the non-encapsulated planar devices. The high throughput and reliable RTE fabrication technique, environment-friendly and earth-abundant Sb2S3 materials, stable and superior device performances were expected to drive the research progress of Sb2S3 thin film photovoltaics.

Sb2(S1−xSex)3 (0 ≤ x ≤ 1) compounds have been proposed as promising light-absorbing materials for photovoltaic device applications. However, no systematic study on the synthesis and characterization of polycrystalline Sb2(S1−xSex)3 thin films has been reported. Here, using a hydrazine based solution process, single-phase Sb2(S1−xSex)3 films were successfully obtained. Through Raman spectroscopy, we have investigated the dissolution mechanism of Sb in hydrazine: 1) the reaction between Sb and S/Se yields [Sb4S7]2-/[Sb4Se7]2- ions within their respective solutions; 2) in the Sb-S-Se precursor solutions, Sb, S and Se were mixed on a molecular level, facilitating the formation of highly uniform polycrystalline Sb2(S1−xSex)3 thin films at a relatively low temperature. UV-vis-NIR transmission spectroscopy revealed that the band gap of Sb2(S1−xSex)3 alloy films had a quadratical relationship with the Se concentration x and it followed the equation "Equation missing", where the bowing parameter was 0.118 eV. Our study provides a valuable guidance for the adjustment and optimization of the band gap in hydrazine solution processed Sb2(S1−xSex)3 alloy films for the future fabrication of improved photovoltaic devices.

Antimony selenide (Sb2Se3) emerges as a very promising non-toxic absorber material for thin film photovoltaics, and most of the devices, either in the superstrate or substrate configuration, employed CdS as the buffer layer. Due to the peculiar one-dimensional crystal structure of Sb2Se3, severe interfacial diffusion would be expected. In this letter, the interfacial diffusion in CdS/Sb2Se3 photovoltaics was carefully characterized from a combined material and device physics characterization. The results indicated that a buried homojunction located deep inside the Sb2Se3 absorber layer due to Cd diffusion, instead of the apparent CdS/Sb2Se3 heterojunction, dictated charge separation and device performance in Sb2Se3 thin film solar cells. Cd diffusion converted p-type Sb2Se3 into n-type by introducing a donor level with an activation energy of 0.22 eV. Our studies deepen the understanding of Sb2Se3 photovoltaics and shed light on their further performance optimization.

2D materials, particularly those bearing in-plane anisotropic optical and electrical properties such as black phosphorus and ReS2, have spurred great research interest very recently as promising building blocks for future electronics. However, current progress is limited to layered compounds that feature atomic arrangement asymmetry within the covalently bonded planes. Herein, a series of highly anisotropic nanosheets (Sb2Se3, Sb2S3, Bi2S3, and Sb2(S, Se)3), which are composed of 1D covalently linked ribbons stacked together via van der Waals force, is introduced as a new member to the anisotropic 2D material family. These unique anisotropic nanosheets are successfully fabricated from their polymer-like bulk counterparts through a gentle water freezing-thawing approach. Angle-resolved polarized Raman spectroscopy characterization confirms the strong in-plane asymmetry of Sb2Se3 nanosheets, and photodetection study reveals their high responsivity and anisotropic in-plane transport. This work can enlighten the synthesis and application of new anisotropic 2D nanosheets that can be potentially applied for future electronic and optoelectronic devices.

We report low-temperature chemiresistive gas sensors based on tin oxide colloidal quantum dots (CQDs), in which the benefits of CQDs such as extremely small crystal size, solution-processability, and tunable surface activity are exploited to enhance the gas-sensing effect. The sensor fabrication is simply employing spin-coating followed by a solid-state ligand exchange treatment at room temperature in air ambient. The optimal gas sensor exhibited rapid and significant decrease in resistance upon H2S gas exposure when operated at 70 °C, and it was fully recoverable upon gas release. We observed a power law correlation between the sensor response and H2S gas concentration, and the sensing mechanism was discussed using the completely depletion model with a flat band diagram.

Y. Zhou, M. Leng, Z. Xia, Dr. J. Zhong, H. Song, X. Liu, B. Yang, J. Chen, K. Zhou, Prof. Y. Cheng, Prof. J. Tang Wuhan National Laboratory for Optoelectronics (WNLO) Huazhong University of Science and Technology (HUST) Wuhan 430074 , P. R. China E-mail: jtang@mail.hust.edu.cn J. Zhang, J. Han Wuhan National High Magnetic Field Center Huazhong University of Science and Technology Wuhan 430074 , P. R. China