•Polyamide membranes are modified with graphene oxide layers.•Graphene oxide-coated membranes demonstrate higher water flux.•Water flux reaches the maximum under the condition of pH value of about 6.•Graphene oxide-coated membranes exhibit good chlorine resistance.Improving chlorine resistance of polyamide (PA) reverse osmosis membranes is one of the major challenges in reverse osmosis membrane technology. In this study, few-layered graphene oxide (GO) was assembled onto polyamide thin film composite membrane surfaces through a spin-coating method to address this challenge. The coating solutions were used at different pH values and with different dispersion solvents. It was found that the pH values have great effects on membrane performance including maximizing water flux at a pH value of 6–7. XPS results indicate that the GO layer can protect the PA functional layer by absorbing chlorine radicals to form O–Cl bond. All modified membranes demonstrate a good suppression of membrane degradation in salt rejection upon chlorine exposure, and the degree of resistance to chlorine was enhanced with the increase of the number of GO layers. The GO1-coated membrane with GO nanosheets dispersed in ethanol showed increased water flux and good chlorine resistance. For instance, salt rejection varied from 95.3% to 91.6% for the first two hours, while unmodified membrane dropped to 80%. After 16 h of chlorine exposure, measured salt rejection of GO1-coated membrane was 75% but unmodified membrane was a less effective 63%.

•Ag@MxFe3−xO4 nanoparticles are synthesized via a seed-mediated method.•Ag@MnFe2O4/C performs better over Ag@CoFe2O4/C and other Ag@MnxFe3−xO4/C.•Ag@MFe2O4/C exhibits superior ORR catalytic activity over hollow-MFe2O4/C.•Ag@MnFe2O4/C shows high durability for the ORR in alkaline media.•Ag@MnFe2O4/C is insensitive to methanol.Nanoparticles with core–shell or hollow interiors have immense potential for catalysis. Herein, Ag@MxFe3−xO4 (M = Co, Mn) core–shell nanoparticles were firstly synthesized through a seed-mediated method. These particles were then loaded onto carbon catalyst supports to form Ag@MxFe3−xO4/C. Then, hollow-MxFe3−xO4/C was prepared with the diffusion of Ag from Ag@MxFe3−xO4/C in saturated NaCl solution at room temperature. As a result, Ag@MnFe2O4/C demonstrates better oxygen reduction reaction (ORR) activity than Ag@CoFe2O4/C and other Ag@MnxFe3−xO4/C with various Mn/Fe ratios. Moreover, Ag@MFe2O4/C shows superior ORR catalytic activities over hollow-MFe2O4/C, which can be due to electronic coupling between Ag core and MFe2O4 shell. Furthermore, Ag@MnFe2O4/C catalysts demonstrate high durability for the ORR in alkaline media and insensitivity to methanol. These findings will provide helpful guidance for design and fabrication of carbon-supported core–shell catalysts for ORR in the future.

•N-doped ordered mesoporous carbon/graphene composites is fabricated by evaporation induced self-assembly.•The composites show the high surface area.•The composites exhibit supercapacitor performances and reserve perfect stability as for electrode material.N-doped ordered mesoporous carbon/graphene composites with supercapacitor performance are successful synthesized by evaporation induced self-assembly (EISA). In this procedure, using phenolic resin as carbon source, triblock copolymer (F127) as template, hydrochloric acid as catalyst, tetraethylorthosilicate (TEOS) as structure enhancer agent and urea as additive for improving graphitization and surface wettability, ordered mesoporous carbon is formed by EISA and low temperature carbonization. At the same time, graphene is added into the mixed solution with the carbon source. Transmission electron microscopy (TEM), small-angle X-ray diffraction (XRD) and N2 sorption analysis results illustrate that the samples display two-dimensional ordered mesoporous structure with uniform pore diameter (∼4 nm). The highest surface area could reach to 1801 m2/g and the biggest pore volume can be up to 1.55 cm3/g. The reinforcement of graphitization is implied by the Raman spectroscopy and wide-angle XRD results. The capacitor performance test shows a capacitance of 246 F/g at 1 A/g with excellent stability.N-doped ordered mesoporous carbon/graphene composites with supercapacitor performance are successful synthesized by evaporation induced self-assembly (EISA). The capacitor performance test shows capacitance as high as 246 F/g at 1 A/g and the capacitance is equipped with excellent stability.Download high-res image (278KB)Download full-size image

A high-mobility diketopyrrolopyrrole-based copolymer (P) was employed in compact layer free CH3NH3PbI3 perovskite solar cells as a hole-transporting layer (HTL). By using the P-HTL, the 6.62% device efficiency with conventional poly-3-hexylthiophene was increased to 10.80% in the simple device configuration (ITO/CH3NH3PbI3/HTL/MoO3/Ag). With improved short circuit current density, open circuit voltage, and fill factor, the higher power conversion efficiency of P-HTL device is ascribed to the higher carrier mobility, more suitable energy level, and lower interfacial charge recombination. Advantages of applying P-HTL to perovskite solar cells, such as low cost, low-temperature processing, and excellent performance with simple cell structure, exhibit a possibility for commercial applications.Keywords: compact layer free; diketopyrrolopyrrole-based copolymer; hole-transporting layer; low-temperature processing; perovskite solar cells; solution processing

The attractiveness of graphene arises from its low cost, transparency, high electrical conductivity, chemical robustness, and flexibility, as opposed to the rising cost and brittleness of FTO. In particular, graphene is emerging as a possible substitute for FTO in flexible displays, touch screens, and solar cells. The main goal of our work is to develop new conductive oxide free graphene-based counter electrodes for dye sensitized solar cells (DSSCs). Graphene nanoplates are modified by silane coupling agent to introduce vinyl groups, and then mixed with polyurethane adhesive and cast on glass substrate. The film is irradiated by UV source and heat treated under Ar/H2. A network graphene film is formed and tightly bonded on glass substrate with enhanced electrical conductivity. The structure of network graphene is investigated by XPS, TGA and SEM. The DSSCs with network graphene counter electrode exhibit power conversion efficiencies of 9.33%, much better than those with FTO electrodes (4.05%).

•ZnO and AZO were synthesized by a simple low-temperature solution-processed method.•AZO films show high transmittance and conductivity.•The photovoltaic performance can be improved with AZO as ETL.•AZO-based devices demonstrate excellent stability, with 85% retained after 120 days.A simple low-temperature solution-processed zinc oxide (ZnO) and aluminum-doped ZnO (AZO) were synthesized and investigated as an electron transport layer (ETL) for inverted polymer solar cells. A solar cell with a blend of poly(4,8-bis-alkyloxy-benzo[1,2-b:4,5-b′] dithiophene-alt-alkylcarbonyl-thieno [3,4-b] thiophene) and (6,6)-phenyl-C71-butyric acid methyl ester as an active layer and AZO as ETL demonstrates a high power conversion efficiency (PCE) of 7.36% under the illumination of AM 1.5G, 100 mW/cm2. Compared to the cells with ZnO ETL (PCE of 6.85%), the PCE is improved by 7.45% with the introduction of an AZO layer. The improved PCE is ascribed to the enhanced short circuit current density, which results from the electron transport property of the AZO layer. Moreover, AZO is a more stable interfacial layer than ZnO. The PCE of the solar cells with AZO as ETL retain 85% of their original value after storage for 120 days, superior to the 39% of cells with ZnO ETL. The results above indicate that a simple low-temperature solution-processed AZO film is an efficient and economical ETL for high-performance inverted polymer solar cells. Due to its environmental friendliness, good electrical properties, and simple preparation approach, AZO has the potential to be applied in high-performance, large-scale industrialization of solar cells and other electronic devices.

Determining how the intrinsic kinetics of photo-generated charge carriers affect extrinsic photovoltaic performance is difficult yet essential work for the optimization of novel types of solar cells. However, contributions of several coexistent internal reactions can rarely be differentiated from one to another solely by means of experimental approaches. In this contribution, we propose the optimization of all-solid-state dye-sensitized solar cells by applying the inorganic hole-transport material (HTM) CsSnI2.95F0.05, experimentally focusing on enhancement of the interconnection between electrolyte precursor and the TiO2 nanorod array. More importantly, by taking advantage of a physics-based device-level model that describes the diverse kinetics occurring among active TiO2/dye/HTM junctions, we quantified the correlation between electrolyte precursor adsorbed onto the TiO2 electrode and hole injection from dye to HTM. We attribute the significant impact of hole injection rate (khi) on non-linear charge carrier density-dependent photovoltaic response to one physical interpretation of experimental observations concerning abnormal photovoltaic responses following variable intensity illumination. Eventually, we achieved an average power conversion efficiency of approximately 7.7% over a large number of fabricated cells, the best one of which attained 9.8%.

•Functionalized graphene (FG) was synthesized via a simple two-step method.•FG with 40.17 at.% of oxygen was studied as anode buffer layer for OSC devices.•FG shows higher JSC and PCE for OSCs with various active layers than PEDOT:PSS.•As anode buffer layer, FG demonstrates better stability than PEDOT:PSS.Interface material is a must for highly efficient and stable organic solar cells (OSCs) and has become a significant part of OSC research today. Here, low-cost and oxygen functionalized graphene (FG) was synthesized via a simple two-step method for applications in OSCs as anode buffer layer. The FG shows excellent dispersion in aqueous solution and great process compatibility with spin coating process. The introduction of work-function-tunable FG can effectively improve short current density of the devices. The power conversion efficiency of FG-based devices (4.13%, 4.49%, and 7.11% for P3HT:PC61BM, P3HT:PC71BM and PBDTTT-C:PC71BM, respectively) outperforms PEDOT:PSS-based devices (3.67%, 4.17%, and 6.46%, respectively). Moreover, the stability of the devices was improved with FG as anode buffer layer compared to PEDOT:PSS. The results indicate that simple synthesized FG is a promising solution-processed anode buffer layer material for high-efficiency and stable OSCs.

•For the first time, CZTS/Se films were synthesized by an ethanol-thermal method.•Sulfurization/selenization process greatly impacts physical properties of films.•Energy gap can be tuned between 1.43 eV and 1.1 eV via tailoring annealing process.This contribution reports, for the first time, the successful synthesis of kesterite Cu2ZnSn(S1−x,Sex)4 films by a simple ethanol-thermal method, followed by sulfurization/selenization annealing treatments for stoichiometric control of the products. The annealing processes under various experimental conditions have a significant impact on microscopic properties of the films, such as morphology and crystallinity. In particular, the energy band gap of obtained nanocrystal films was tuned from 1.43 eV to 1.1 eV after the implementation of different annealing treatments. Correspondingly, a preliminary evaluation of photovoltaic response was conducted, and the measurements indicated that the Se/S ratio, controlled by sulfurization/selenization processes, can be a decisive factor in the optoelectronic performance of Cu2ZnSn(S1−x,Sex)4 films.

A facile synthesis of Ag2S-hollow Fe2O3 nanocomposites with NIR photoluminescence was firstly demonstrated by the sulfidation of Ag–Fe2O3 core–shell nanoparticles. Characteristic morphology transformations along with color changes were recorded and a mechanism was proposed for the sulfidation process, which can provide new possibilities to fabricate other complex nanostructures.

Carbon fibers with multi-branched structures were synthesized by chemical vapor deposition method using cupric chloride as catalyst precursor and acetylene as carbon source at different reaction temperatures. Effects of water vapor and reaction temperature on the growth mode of carbon fibers were investigated. Experimental results demonstrate that initial reaction conditions and temperature are key factors for the formation of different carbon materials. Carbon fibers with typical multi-branched structures can be obtained at 450 °C when cupric chloride solution was used as catalyst precursor. X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy are used to characterize carbon materials, and the growth mechanisms of multi-branched carbon fibers were discussed.

•Nitrogen-doped graphene (NG) was synthesized by a solvothermal method.•NG was used for the investigation on direct electrochemistry of hemoglobin with carbon ionic liquid electrode.•The Hb modified electrode exhibited excellent electrocatalytic activity toward different substrates.Nitrogen-doped graphene (NG) was synthesized and used for the investigation on direct electrochemistry of hemoglobin (Hb) with a carbon ionic liquid electrode as the substrate electrode. Due to specific characteristics of NG such as excellent electrocatalytic property and large surface area, direct electron transfer of Hb was realized with enhanced electrochemical responses appearing. Electrochemical behaviors of Hb on the NG modified electrode were carefully investigated with the electrochemical parameters calculated. The Hb modified electrode exhibited excellent electrocatalytic reduction activity toward different substrates, such as trichloroacetic acid and H2O2, with wider dynamic range and lower detection limit. These findings show that NG can be used for the preparation of chemically modified electrodes with improved performance and has potential applications in electrochemical sensing.The utilization of N-doped graphene enables direct electrochemistry of hemoglobin with a pair of well-defined redox peaks appearing.

Freestanding graphene membranes were successfully functionalized with platinum nanoparticles (Pt NPs). High-resolution transmission electron microscopy revealed a homogeneous distribution of single-crystal Pt NPs that tend to exhibit a preferred orientation. Unexpectedly, the NPs were also found to be partially exposed to the vacuum with the top Pt surface raised above the graphene substrate, as deduced from atomic-scale scanning tunneling microscopy images and detailed molecular dynamics simulations. Local strain accumulation during the growth process is thought to be the origin of the NP self-organization. These findings are expected to shape future approaches in developing Pt NP catalysts for fuel cells as well as NP-functionalized graphene-based high-performance electronics.Keywords: fuel cells; graphene; molecular dynamics; platinum; self-organization; STM; TEM

Through the redox reaction between Cu(NH3)42+ and H2O2, copper quantum dots (QDs) were deposited onto the surface of single-crystal rutile TiO2 nanorod arrays that were grown directly on transparent, conductive fluorine-doped tin oxide substrates by a facile hydrothermal process. Compared with pristine TiO2 nanorods, the top facets of TiO2 nanorods decorated with Cu QDs became flattened and adherent to each other, and the lateral facets were rough and covered with vast amounts of extremely small particles. The QDs were tightly attached on the surface of the nanorods, and the nanoparticle size measured from high resolution transmission electron microscopy images was around 6 nm, which is comparable with the Bohr exciton radius. X-ray photoelectron spectroscopy measurements showed that the QDs existed in the form of Cu(II)O and Cu(I)2O after the deposition process, and the Cu(0) QDs were unstable on the TiO2 surface. Furthermore, under the irradiation of a solar simulator, the photocurrent response of the QD sensitized TiO2 nanorods was improved dramatically with a small amount of QDs, and the optimal photocurrent density (98 μA/cm2) was much greater than that of the undecorated sample (16 μA/cm2). Likewise, external quantum efficiency (EQE) characterization demonstrated the superiority of the surface modification with Cu QDs, by which the highest EQE value of the photoanode was enhanced nearly ten times. In addition, a red shift of the peak in EQE measurement was found from the Cu QD sensitized samples, suggesting a quantum size effect caused by small QD particles.Keywords: Copper quantum dots; Photoelectrical conversion; Surface sensitization; TiO2 nanorod arrays

TiO2 has been extensively investigated due to its unique photoelectric properties. In this study, oriented single-crystal rutile TiO2 nanorod arrays were synthesized and then calcined at different temperatures in the atmosphere. The morphology and crystalline characterization indicated that the length of TiO2 nanorods increased rapidly and the nanorods became aggregated and fragile after calcination, yet the sintering treatment seemed to have almost no effect on the crystallinity. To obtain the all-solid-state, dye-sensitized solar cells (DSSCs), a newly reported solid inorganic semiconductor, CsSnI2.95F0.05, was employed as the electrolyte, and the Pt deposited on the conductive side of the fluorine-doped tin oxide (FTO) glass substrate was used as the counter-electrode. The effects of the calcination treatment on the photoelectric properties of the solar cells, including external quantum efficiency (EQE), open circuit voltage (VOC), short-circuit current (JSC), and photoelectric conversion efficiency (η), were investigated under the illumination of a solar simulator. As a result, all of the EQE, VOC, JSC, and η values of the cells first increased and then declined with the increase of calcination temperatures, and the highest η of 2.81% was obtained by the cell assembled with its TiO2 electrode sintered at 450 °C for 3 h, a value almost 2.5 times that of the non-sintered sample (1.1%).

Solving slow kinetics of oxygen reduction reaction is critically important for the development of hydrogen fuel cells and direct methanol/ethanol fuel cells. In this study, graphene and nitrogen (N)-doped graphene were synthesized by a solvothermal method and investigated as catalysts as well as catalyst supports for oxygen reduction reactions. In comparison to graphene, N-doped graphene demonstrated higher electrocatalytic activity in both acidic and alkaline solutions. N-doped graphene can act directly as a catalyst to facilitate four-electron oxygen reductions in alkaline solution and two-electron reductions in acidic solution. On the other hand, when used as catalyst supports for Pt and Pt–Ru nanoparticles, N-doped graphene can contribute to four-electron oxygen reductions in acidic solution, yet demonstrate much slower reaction kinetics in alkaline solution. Our findings conclude that N-doped graphene can be developed as an efficient catalyst for oxygen reductions to replace the use of precious Pt catalysts in alkaline solution but not in acidic solution.Highlights► Electrocatalytic activity of N-doped graphene in both acidic and alkaline solution. ► N-doped graphene can be directly used as a catalyst for ORR in alkaline solution. ► N-doped graphene is a two-electron oxidation catalyst for ORR in acidic solution. ► N-doped graphene activates Pt and Pt–Ru nanoparticles for ORR in acidic solution.

A facile synthesis of Ag2S-hollow Fe2O3 nanocomposites with NIR photoluminescence was firstly demonstrated by the sulfidation of Ag–Fe2O3 core–shell nanoparticles. Characteristic morphology transformations along with color changes were recorded and a mechanism was proposed for the sulfidation process, which can provide new possibilities to fabricate other complex nanostructures.

TiO2 has been extensively investigated due to its unique photoelectric properties. In this study, oriented single-crystal rutile TiO2 nanorod arrays were synthesized and then calcined at different temperatures in the atmosphere. The morphology and crystalline characterization indicated that the length of TiO2 nanorods increased rapidly and the nanorods became aggregated and fragile after calcination, yet the sintering treatment seemed to have almost no effect on the crystallinity. To obtain the all-solid-state, dye-sensitized solar cells (DSSCs), a newly reported solid inorganic semiconductor, CsSnI2.95F0.05, was employed as the electrolyte, and the Pt deposited on the conductive side of the fluorine-doped tin oxide (FTO) glass substrate was used as the counter-electrode. The effects of the calcination treatment on the photoelectric properties of the solar cells, including external quantum efficiency (EQE), open circuit voltage (VOC), short-circuit current (JSC), and photoelectric conversion efficiency (η), were investigated under the illumination of a solar simulator. As a result, all of the EQE, VOC, JSC, and η values of the cells first increased and then declined with the increase of calcination temperatures, and the highest η of 2.81% was obtained by the cell assembled with its TiO2 electrode sintered at 450 °C for 3 h, a value almost 2.5 times that of the non-sintered sample (1.1%).

Determining how the intrinsic kinetics of photo-generated charge carriers affect extrinsic photovoltaic performance is difficult yet essential work for the optimization of novel types of solar cells. However, contributions of several coexistent internal reactions can rarely be differentiated from one to another solely by means of experimental approaches. In this contribution, we propose the optimization of all-solid-state dye-sensitized solar cells by applying the inorganic hole-transport material (HTM) CsSnI2.95F0.05, experimentally focusing on enhancement of the interconnection between electrolyte precursor and the TiO2 nanorod array. More importantly, by taking advantage of a physics-based device-level model that describes the diverse kinetics occurring among active TiO2/dye/HTM junctions, we quantified the correlation between electrolyte precursor adsorbed onto the TiO2 electrode and hole injection from dye to HTM. We attribute the significant impact of hole injection rate (khi) on non-linear charge carrier density-dependent photovoltaic response to one physical interpretation of experimental observations concerning abnormal photovoltaic responses following variable intensity illumination. Eventually, we achieved an average power conversion efficiency of approximately 7.7% over a large number of fabricated cells, the best one of which attained 9.8%.