Sulfonated poly(ether ether ketone)/poly(vinylidene fluoride)/graphene (S/P/G) composite membrane was prepared through a solution-casting method for a vanadium redox flow battery (VRB), and the weight ratio of high sulfonated poly(ether ether ketone) (SPEEK), polyvinylidene fluoride (PVDF), and graphene was optimized. The preferred S/P/G-7 composite membrane showed the lowest VO2+ permeability and highest ion selectivity compared with other four kinds of cation exchange membranes SPEEK75, heterogeneous PSSA-PE, Nafion 117, and recast Nafion (r-Nafion). The VRB with S/P/G-7 membrane exhibited the higher coulombic efficiency of ∼8% and energy efficiency of ∼4%, but lower capacity loss and self-discharge than that of VRB with Nafion117 membrane during cycling tests, which further indicated the promising prospects of S/P/G-7 composite membrane in VRB application.

It is significantly challenging to collect more light and simultaneously avoid dye aggregation in dye-sensitized solar cells (DSSCs). This work addresses the significance of the intensity, rather than just the traditionally emphasized broadness, of the absorption band in developing DSSC sensitizers. With the assistance of calculating the oscillator strength of the first transition, the indoline-conjugated porphyrin sensitizer CM-b is screened out to have an impressively large Qx molar absorptivity and thus an improved light harvesting ability together with suppressed aggregation in DSSCs. As a result, an overall efficiency of 10.7% for iodine-based DSSCs is achieved, which is a record for non-ruthenium iodine-based DSSCs in the absence of a cosensitizer and a coabsorbate.

This paper presents a facile approach for the synthesis of a novel Pt/graphene-nickel foam (Pt/GNF) electrode composed of flower-like Pt nanoparticles (NPs) and 3D graphene. The fabrication process involved the chemical vapor deposition of graphene onto Ni foam as a substrate and the subsequent growth of Pt NPs via a galvanic replacement reaction without using any seed and organic solvent. The surface morphology and composition of the prepared materials were characterized. Meanwhile, cyclic voltammetry and electrochemical impedance spectroscopy were employed to confirm their typical electrochemical characteristics. The as-prepared nanocomposites displayed enhanced catalytic activity and kinetics toward methanol electro-oxidation. Such an excellent performance can be ascribed to the high dispersion of flower-like Pt NPs and to the exposure of more sites provided by the flower-like structure. The improved stability, decreased charge transfer resistance, and enhanced reaction rate of the nanocomposites promise new opportunities for the development of direct methanol fuel cells.A novel Pt/graphene-nickel foam (Pt/GNF) electrode composed of flower-like Pt nanoparticles and three-dimensional graphene was easily synthesized and used as an promising electrocatalyst material for methanol oxidation reaction.

A novel three-dimensional graphite-coated nickel foam (GNF) was synthesized by the chemical vapor deposition (CVD) method, and palladium nanoparticles (Pd NPs) were successfully synthesized on a GNF support by metal atomic layer deposition (ALD) technology for the first time. The physicochemical properties of the as-prepared catalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma-atomic emission spectrometry (ICP). Results showed that the Pd NPs with ultralow loading (below 50 μg cmPd−2) were uniformly dispersed on the GNF support, and the as-prepared catalysts presented the highest catalytic activity toward ethanol electro-oxidation (the peaking current density was about 39.97 mA cm−2) in alkaline media. In particular, it was found that the morphology and content of graphite of the GNF will greatly affect the dispersion of the ALD Pd NPs. When the CVD time for preparing the GNF was 10 min, the as-prepared catalyst presented a higher dispersity of Pd NPs and catalytic activity toward ethanol electro-oxidation than that of other as-prepared catalysts. The effect of the ALD cycle for Pd NPs growth and its performance was also investigated. When the cycle of ALD Pd was 450, the peaking current density of the as-prepared catalysts was about 2.64 times as high as that of commercial Pd/C to ethanol electro-oxidation. Herein, there is a promising application prospect for the prepared Pd/GNF nanocomposite as an electrocatalyst toward ethanol electro-oxidation in alkaline media.

A novel sulfonated poly(ether ether ketone) (SPEEK)/TiO2 double-deck membrane which consists of a layer of SPEEK and a layer of TiO2 was prepared and investigated for vanadium redox flow battery (VRB) application for the first time. The physicochemical properties of the SPEEK/TiO2 membrane, including the water uptake, swelling ratio, ion exchange capacity, proton conductivity, VO2 + permeability and ion selectivity are evaluated in detail, compared to the pristine SPEEK membrane and Nafion 117 membrane. The scanning electron microscopy images reveal its double-deck structure and the structural stability with no delamination, and thermogravimetric analysis (TG) identifies its thermal stability. Among all membranes, the SPEEK/TiO2 double-deck membrane possesses lowest vanadium ion permeability (6.66 × 10− 7 cm2 min− 1) and highest ion selectivity (9.46 × 104 S min cm− 3). The VRB single cell with SPEEK/TiO2 double-deck membrane shows higher coulombic efficiency (97.0% vs 93.3%) and energy efficiency (85.8% vs 83.7%) compared to that with Nafion 117 membrane at 60 mA cm− 2. Furthermore, the SPEEK/TiO2 double-deck membrane exhibits highly stable cell performance after 60 times of cycling tests at 60 mA cm− 2 and lower capacity decay rate than that of Nafion 117 membrane. Therefore, the SPEEK/TiO2 double-deck membrane exhibits good potential usage in VRB systems.

•The V(V) electrolytes with the addition of organic amines CTS, SA and NPAM and inorganic ammonium ATC, FAS and AFS remained stable from − 5 °C to 45 °C.•The electrochemical activity for V(V) electrolytes with the addition of CTS, ATC, AFS and FAS was improved compared with the pristine one.•Overall, the effect of the organic amines on the V(V) solution was better than the inorganic ammoniums.•The VRB with CTS performed well with an energy efficiency of more than 80% and good cycling stability at a current density of 50 mAcm− 2.Several organic amines with –NH2 functional groups and inorganic ammoniums with –NH4+ functional groups have been comparatively investigated as stabilizers of the V(V) electrolyte for vanadium redox flow battery (VRB) to improve its stability and electrochemical performance. Thermal stability tests showed that chitosan (CTS) and nonionic-type polyacrylamide (NPAM) additives with –NH2; ammonium thiocyanate (ATC), ferrous ammonium sulfate (FAS) and ammonium ferric sulfate (AFS) additives with –NH4+ could significantly improve the thermal stability of the V(V) electrolyte over a wide temperature range of − 5 °C to 45 °C. The electrochemical behavior of the V(V) electrolyte with these preferred additives was further studied by cyclic voltammetry (CV), steady state polarization, electrochemical impedance spectroscopy (EIS) and charge–discharge test. The results indicated that the electrochemical activity and reversibility for the V(V) electrolyte with the best additive CTS with –NH4+ was significantly improved compared with the additives with –NH2 and pristine one. In addition, the VRB employing the positive electrolyte with CTS exhibited excellent cycling stability and charge–discharge behavior with a high energy efficiency of 82.5%. The N-containing and O-containing functional groups of CTS in the V(V) electrolyte could modify the electrode and further improve the electrochemical performance and cycling stability of VRB.

•Using the simple technique to combine the wide and narrow band gap materials.•The formed composite appears the broad light absorption in the visible range.•The formed composite exhibits the effective photo-induced carriers separation.•The hydrogen evolution was improved more than 100% compared with pure g-C3N4.•The article provide a new route to use the narrow band gap materials.The CuO micro-sphere combined with the g-C3N4 to form the p-n heterojunction was first prepared by the simple impregnation–calcination technique. The SEM and XPS revealed the tight combination between CuO micro-sphere and g-C3N4. The UV spectra and PL spectra confirmed the obvious red shift to improve visible light absorption and effective light-induced carriers separation. The hydrogen evolution rate was improved more than 100% compared with pure g-C3N4. It is revealed that the more broad visible light absorption range and the p-n heterojuction mechanism was the key factor to facilitate the photocatalytic performance of hydrogen evolution.

Two efficient ruthenium sensitizers with a phenothiazine-modified bipyridine as an ancillary ligand, coded SCZ-1 and SCZ-2, have been developed as dyes in dye-sensitized solar cells (DSSCs). Both sensitizers exhibit low-energy metal-to-ligand charge transfer (MLCT) bands centered at 539 nm with high molar extinction coefficients of 1.77 × 104 M–1 cm–1 for SCZ-1 and 1.66 × 104 M–1 cm–1 for SCZ-2, which are significantly higher than the corresponding value for the reference N719 (1.27 × 104 M–1 cm–1), indicating that the light-harvesting capacity of ruthenium sensitizers can be reinforced by introducing phenothiazine moieties into the bipyridine ligand. Under AM 1.5G irradiation (100 mW cm–2), SCZ-1 and SCZ-2 sensitized DSSC devices show impressive power conversion efficiencies (PCE) up to 10.4% by using of iodide-based electrolytes, which exceeds that of N719 (9.9%) under the same conditions. Both of the open circuit voltage (VOC) and fill factor (FF) of SCZ-sensitized solar cells approximate to those of N719-sensitized cell. The relatively higher efficiencies of the SCZ-sensitized cells than that of N719-sensitized cell come from their higher short-circuit photocurrent density (JSC), which may be mainly attributed to the high absorption coefficient. The absorption spectrum and device efficiency of SCZ-1 are both quite close to those of SCZ-2, suggesting that the difference in alkyl chains on the N atom of phenothiazine is not a decisive factor in affecting the photovoltaic performance of dyes.Keywords: dye-sensitized solar cell; high-efficiency; light-harvesting capacity; phenothiazine; ruthenium sensitizer

•Core–shell like Ir/C@Pd catalyst was prepared by a two-stage route.•The Ir/C@Pd shows ultrahigh activity for formic acid electro-oxidation.•The mass activity of Ir/C@Pd catalyst is about 3.38 times as large as PdIr/C.•The mass activity of Ir/C@Pd is about 4.16 times as large as commercial Pd/C.•The interaction of Pd shell with Ir core was confirmed by XPS results.A core–shell like Ir/C@Pd catalyst with ultrahigh activity toward formic acid electro-oxidation (FAEO) was prepared by decorating Pd shell on the Ir NPs for the first time. The structure has been demonstrated by XRD, XPS, TEM, EDS and electrochemical techniques. The mass-normalized current density at 0.08 V (vs. SCE) of Ir/C@Pd for FAEO is 3756 mA mg− 1Pd, which is about 3.38 and 4.16 times higher than that of the PdIr/C and commercial Pd/C, respectively. The remarkable performance of Ir/C@Pd should be attributed to its unique core–shell like structure and the enhanced electronic coupling between the Ir and Pd, which was confirmed by XPS results.

Carbon-supported platinum (Pt/C) catalysts were prepared via reduction in three different routes: Sodium borohydride (NaBH4), ethylene glycol (EG), and EG with NaBH4 (EG-NaBH4). The reduction conditions of each procedure were systematically optimized to achieve maximum Pt/C catalytic activity for methanol electro-oxidation as determined via cyclic voltammetry (CV). The EG-NaBH4 process showed greater activity for methanol oxidation than those prepared by the NaBH4 and EG processes and the Johnson Matthey 40 wt.% Pt/C catalyst with the support of carbon black (Pt-JM). The average size of the particles for each of the three preparation processes determined from the XRD data was 4.8, 4.1, and 2.5 nm, respectively. The average surface area of the catalyst particles was determined to be 58, 68, and 112 m2·gPt−1, respectively. Analysis by X-ray diffraction (XRD), transmission electron microscopy (TEM), and CV suggest that the greater activity for methanol oxidation of the Pt/C catalyst prepared by the EG-NaBH4 process is due to the smaller particle size, better cluster dispersion, and an increase in the number of Pt(110) surface sites achieved using this method.

Alloying degree, particle size and the level of dispersion are the key structural parameters of Pt-Ru/C catalyst in fuel cells. Solvent(s) used in the preparation process can affect the particle size and alloying degree of the object substance, which lead to a great positive impact on its properties. In this work, three types of solvents and their mixtures were used in preparation of the Pt-Ru/C catalysts by chemical reduction of metal precursors with sodium borohydride at room temperature. The structure of the catalysts was characterized by X-ray diffraction (XRD) and Transmission electron microscopy (TEM). The catalytic activity and stability for methanol electro-oxidation were studied by Cyclic Voltammetry (CV) and Chronoamperometry (CA). Pt-Ru/C catalyst prepared in H2O or binary solvents of H2O and isopropanol had large particle size and low alloying degree leading to low catalytic activity and less stability in methanol electro-oxidation. When tetrahydrofuran was added to the above solvent systems, Pt-Ru/C catalyst prepared had smaller particle size and higher alloying degree which resulted in better catalytic activity, lower onset and peak potentials, compared with the above catalysts. Moreover, the catalyst prepared in ternary solvents of isopropanol, water and tetrahydrofuran had the smallest particle size, and the high alloying degree and the dispersion kept unchanged. Therefore, this kind of catalyst showed the highest catalytic activity and good stability for methanol electro-oxidation.

In this work, γ-Al2O3 and hydrogen peroxide treated g-C3N4 (O-g-C3N4) were combined through a novel in-situ hydrothermal method to form heterojunction structured photocatalysts. These photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy and photoluminescence spectroscopy (PL). FT-IR results indicate that oxygen functional groups can be grafted on the surface of O-g-C3N4 by hydrogen peroxide treatment. The visible light photocatalytic hydrogen evolution rate was investigated in 10 vol% TEOA aqueous solution. The optimal Al2O3 mass content is set to be 20 wt% and the corresponding hydrogen evolution rate is 1288 µmol/h/g which is approximately 6, 3 folds that of pristine g-C3N4 and O-g-C3N4 respectively and 1.6 folds that of mechanical mixed composite with the same Al2O3 mass content. The photocurrent density–time curves were carried out under visible light illumination for four on–off cycles. The electrochemical impedance spectroscopy (EIS) measurements verified the enhanced separation efficiency of electron–hole pairs. This work raised a new method to form the heterojunction structured photocatalysts and achieved a remarkable improvement of the photocatalytic activity in water splitting for hydrogen under visible light irradiation.Different mass ratios of γ-Al2O3/O-g-C3N4 heteojunctions are prepared through a novel one step hydrothermal method and the photocatalytic activity of the heterojunctions under visible light irradiation is significantly enhanced.Download high-res image (149KB)Download full-size image

Several acid compounds have been employed as additives of the V(V) electrolyte for vanadium redox flow battery (VRB) to improve its stability and electrochemical activity. Stability of the V(V) electrolyte with and without additives was investigated with ex-situ heating/cooling treatment at a wide temperature range of −5 °C to 60 °C. It was observed that methanesulfonic acid, boric acid, hydrochloric acid, trifluoroacetic acid, polyacrylic acid, oxalic acid, methacrylic acid and phosphotungstic acid could improve the stability of the V(V) electrolyte at a certain range of temperature. Their electrochemical behaviors in the V(V) electrolyte were further studied by cyclic voltammetry (CV), steady state polarization and electrochemical impedance spectroscopy (EIS). The results showed that the electrochemical activity, including the reversibility of electrode reaction, the diffusivity of V(V) species, the polarization resistance and the flexibility of charge transfer for the V(V) electrolyte with these additives were all improved compared with the pristine solution.A series of CV curves and a good linear relationship curves for V(V) electrolyte with 0.5% CH3SO3H on the graphite electrode verified the one-electron quasi-reversible process for V(V)/V(IV) redox reaction.Download full-size image

It is significantly challenging to collect more light and simultaneously avoid dye aggregation in dye-sensitized solar cells (DSSCs). This work addresses the significance of the intensity, rather than just the traditionally emphasized broadness, of the absorption band in developing DSSC sensitizers. With the assistance of calculating the oscillator strength of the first transition, the indoline-conjugated porphyrin sensitizer CM-b is screened out to have an impressively large Qx molar absorptivity and thus an improved light harvesting ability together with suppressed aggregation in DSSCs. As a result, an overall efficiency of 10.7% for iodine-based DSSCs is achieved, which is a record for non-ruthenium iodine-based DSSCs in the absence of a cosensitizer and a coabsorbate.