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Platinum (Pt)-based alloys are considerably promising electrocatalysts for the reduction of I–/I3– and Co2+/Co3+ redox couples in dye-sensitized solar cells (DSSCs). However, it is still challenging to minimize the dosage of Pt to achieve comparable or even higher catalytic efficiency. Here, by taking full advantages of the Mott–Schottky (M–S) effect at the metal–semiconductor interface, we successfully strategize a low-Pt-based M–S catalyst with enhanced electrocatalytic performance and stability for the large-scale application of DSSCs. The optimized M–S electrocatalyst of Ni3S4–Pt2X1 (X = Fe, Ni) heteronanorods is constructed by rationally controlling the ratio of Pt to transition metal in the hybrids. It was found that the electrons transferred from Ni3S4 to Pt2X1 at their interface under the Mott–Schottky effect result in the concentration of electrons onto Pt2X1 domains, which subsequently accelerates the regeneration of both I–/I3– and Co2+/Co3+ redox shuttles in DSSCs. As a result, the DSSC with N...

Metal-semiconductor based Mott-Schottky (M-S) heterojunctions combining two or more functionalities in one unit can effectively improve their catalytic activity and durability due to the electronic coupling effects between distinct components. Although tremendous progress has been made in structure fabrication, controllable synthesis of one-dimensional (1D) M-S heterojunction and its application as electrocatalysts is still lacking. Herein, uniform and well-defined 1D Ni3S4-PtCo heteronanorods are synthesized via a facile solution method and employed as counter electrode (CE) catalyst in the dye-sensitized solar cells (DSSCs). By exploiting the benefits of both structural and compositional characteristics, namely, the direct electrical pathways of 1D nanostructure, optimized work function of metal alloy as well as the synergistic effect between Ni3S4 and PtCo, the as-designed Ni3S4-PtCo heteronanorods exhibit excellent catalytic activity and stability toward the reduction of triiodide in DSSCs. A DSSC with Ni3S4-PtCo achieves a high power conversion efficiency of 8.66% under AM1.5G illumination (100 mW cm−2), higher than that of pristine Pt-based device (8.12%). Moreover, the fast activity onset and relatively long stability further demonstrate that the Ni3S4-PtCo heteronanorod is a promising alternative to Pt in DSSCs. Considering the diversity of structures and components in heterostructures, the strategy presented here can be extended for synthesizing other well-defined 1D M-S heterojunctions, which may be used in the fields of catalysis, energy conversion and storage.

Hollow heterostructures have tremendous advantages in electrochemical energy storage and conversion areas due to their unique structure and composition characteristics. Here, we report the controlled synthesis of hollow CoSe

Developing conductive polymer binders is a new way to enhance the electric connectivity and mechanical contact of Si based anode material. While the linear structure of commercial PEDOT:PSS cannot effectively alleviate the volume expansion of Si. Herein, glycerol was introduced as a cross-linker to PEDOT:PSS binder for Si anodes, which can further improve the interfacial compatibility between silicon and PEDOT:PSS. After crosslinking, the peel force increased 2 times. As a result, the Si nanoparticles anode with the glycerol-crosslinked binder exhibited a high reversible capacity of 1951.5 mAh g−1 after 200 cycles at 0.5 A g−1 and superior rate capability (804 mAh g−1 at a high current of 8.0 A g−1) for the inherent superior conductivity of PEDOT:PSS.

Electro-induced reduction of redox active esters and N-phthalimidoyl oxalates derived from naturally abundant carboxylic acids and alcohols provides a sustainable and inexpensive approach to radical formation via undivided electrochemical cells. The resulting radicals are trapped by an electron-poor olefin or hydrogen atom source to furnish the Giese reaction or reductive decarboxylation products, respectively. A broad range of carboxylic acid (1°, 2°, and 3°) and alcohol (2° and 3°) derivatives are applicable in this catalyst-free reaction, which tolerated a diverse range of functional groups. This method features simple operation, is a sustainable platform, and has broad application.

Aqueous polysulfide/iodide redox flow batteries are attractive for scalable energy storage due to their high energy density and low cost. However, their energy efficiency and power density are usually limited by poor electrochemical kinetics of the redox reactions of polysulfide/iodide ions on graphite electrodes, which has become the main obstacle for their practical applications. Here, CoS2/CoS heterojunction nanoparticles with uneven charge distribution, which are synthesized in situ on graphite felt by a one-step solvothermal process, can significantly boost electrocatalytic activities of I−/I3− and S2−/Sx2− redox reactions by improving absorptivity of charged ions and promoting charge transfer. The polysulfide/iodide flow battery with the graphene felt-CoS2/CoS heterojunction can deliver a high energy efficiency of 84.5% at a current density of 10 mA cm−2, a power density of 86.2 mW cm−2 and a stable energy efficiency retention of 96% after approximately 1000 h of continuous operation., Polysulfide/iodide redox flow batteries are promising due to low cost and high-solubility components, but are limited by energy efficiency and power density. Here the authors fabricate heterojunction electrocatalysts to achieve improved performance in a polysulfide/iodide redox flow battery.

The first examples of electrochemical trifluoromethylation and sulfonylation/semipinacol rearrangements of allylic alcohols were developed using cheap and stable RSO2Na (R = CF3, Ph) as reagents. Various β-trifluoromethyl and sulfonated ketones were obtained in moderate to excellent yields. This strategy provides a facile, direct, and complementary approach to construct all-carbon quaternary stereocenters. In addition, the reaction has the advantages of being chemical oxidant-free and metal-free and has safe and mild reaction conditions.

Heterogeneous photocatalysis has attracted considerable attention for environmental remediations, artificial photosynthesis, and the performance mainly depends on the light absorption, photocarrier dynamics and surface reactions of photocatalysts. Herein, the photocarrier dynamics of hierarchical SnS2 microspheres were studied by surface photovoltage and transient photovoltage spectra, in which the chemical composition, crystallinity, primary building blocks and assembling structures are affected by the light absorption and photocarrier transfer characteristics of SnS2. Further studies revealed that the enhanced visible light absorption and photocatalytic activity of Red-Embroidery-Ball-like microspheres were derived from the synergistic effects of S self-doping, the exciton transitions of surface states and the light trapping effects of porous hierarchical structure.

Inspired by nature, both high-performance Si/C and activated carbon (AC) energy storage materials with a hierarchically biomimetic structure can be prepared from rice husks (RHs), and further serve as promising anode and cathode materials for hybrid lithium-ion capacitors (LICs), respectively. Benefitting from the high capacity and good rate and cycling performances of the Si/C anode material and RH-derived AC (RAC) cathode material, the designed Si/C||RAC LICs give a high energy density of 227 W h kg−1 at a power density of 1146 W kg−1, and ∼181 W h kg−1 can still be retained even at an ultra-high power density of ∼32 595 W kg−1. Furthermore, the RH-derived LICs also show a long-term cycling stability (16 000 cycles at ∼16 800 W kg−1).

Based on the crystal structure and the DFT calculation of Bi2O2CO3, I- can partly replace the CO32-in Bi2O2CO3 to narrow its bandgap and to enhance its visible light absorption. With this in mind, rose-like I-doped Bi2O2CO3 microspheres were prepared via a hydrothermal process. This method can also be extended to synthesize rose-like Cl- or Br-doped Bi2O2CO3 microspheres. Photoelectrochemical test supports the DFT calculation result that I- doping narrows the bandgap of Bi2O2CO3 by forming two intermediate levels in its forbidden band. Further study reveals that I-doped Bi2O2CO3 microspheres with optimized composition exhibit the best photocatalytic activity. Rhodamine B can be completely degraded within 6min and about 90% of Cr(VI) can be reduced after 25min under the irradiation of visible light (λ>400nm).

Of all the novel electrode materials that can be used to enhance the electrochemical performance of supercapacitors, the most promising one is ordered nanoarray structures, which can be used as binder-free electrodes. Honeycomb-like metallic nickel selenide (Ni0.85Se) nanosheet arrays supported on nickel foams were successfully synthesized via a one-step hydrothermal approach. Characterization results reveal that the as-obtained Ni0.85Se nanosheets belong to the hexagonal crystal phase with a thickness of ∼15 nm. By virtue of their intrinsic metallicity, super-hydrophilic surface and unique honeycomb-like structure composed of interconnected ultrathin nanosheets, the Ni0.85Se nanosheet arrays exhibit splendid electrochemical properties, e.g. higher specific capacitance (3105 F g−1 at 1 A g−1 and 1460 F g−1 at 10 A g−1), outstanding cycling stability (90.1% capacitance retention after 5000 cycles), and remarkable conductivity. More importantly, hybrid asymmetric supercapacitors are assembled with Ni0.85Se nanosheet arrays as the binder-free positive electrode and activated carbon as the negative electrode, and show remarkable energy-storage characteristics, including an energy density of 65.02 W h kg−1 at a power density of 103.33 W kg−1, only 6.3% capacitance loss after 10 000 cycles, and a wider voltage window of 0–1.6 V. In addition, two asymmetric supercapacitors based on Ni0.85Se nanoarrays connected in series can be charged and easily drive two light emitting diodes or a mini fan. Such excellent performance evidently proves that Ni0.85Se nanosheet arrays are a promising electrode material for energy storage applications.

Transition metal sulfides are a kind of potential candidates for efficient and stable CE materials in DSSCs due to their good electrocatalytic ability and stability towards I3− reduction. However, the low conductivity of sulfides is harmful for the electron collection and transfer process, and the absorption/desorption and diffusion process of I−/I3− should be optimized to achieve high electrocatalytic activity over Pt. Herein, a hierarchical CoFeS2/reduced graphene oxide (CoFeS2/rGO) composite was rationally designed and prepared via the in situ conversion of CoFe layer double hydroxide anchored on rGO. Due to the synergistic effects of Co and Fe, unique 3D hierarchical structures formed by nanosheets, and the conductivity of rGO, the CoFeS2/rGO CEs exhibited good electrocatalytic activity and stability towards the reduction of I3− to I−, and the DSSCs could also achieve a high efficiency of 8.82%, higher than those of the devices based on Pt (8.40%) and pure CoFeS2 (8.30%) CEs. Moreover, the devices also showed the characteristics of fast activity onset, good stability, and high multiple start/stop capability. The results indicated that the developed CoFeS2/rGO composite could be a promising alternative for Pt in DSSCs.

Transition metal sulfides with high specific capacity have received increasing research interest in lithium storage. However, the low reversibility of metal sulfides usually leads to the oxidation of Li2S into polysulfides. The dissolution of polysulfides will suppress the regeneration of sulfides due to the loss of Li2S, which usually leads to poor cycling stability of sulfides. Herein, Al2O3 coated Ni3S4 nanoparticles (Ni3S4@Al2O3) have been rationally designed and fabricated via a one-pot hydrothermal process. The regeneration of nickel sulfides, which is the key to cycling stability of sulfides, can be promoted by the localized conversion from metal to metal sulfides because the Al2O3 layer can prevent the diffusion and dissolution of polysulfides. The conversion of Al2O3 to ion-conductive AlF3 can enhance the quick charge transfer process of the lithium ion insertion/extraction reaction. Furthermore, the Al2O3/AlF3 layer can also prevent the growth and aggregation of Ni3S4 nanoparticles to retain the structure of the electrodes during the cycling process. The as-prepared Ni3S4@Al2O3 exhibits a high reversible capacity of 651 mA h g−1 at 500 mA g−1 even after 400 cycles. This method can also be extended to other metal sulfides for improving electrochemical performances.

LDHs in atomic thickness (mono-/bi-layers) usually exhibit novel physicochemical properties, especially in surface-dependent energy storage and catalysis areas. However, the thickness of the commonly reported 2D LDHs is in nanoscale and the bottom-up synthesis of atomically thin LDHs is rarely reported. Herein, high-quality atomically thin layered NiFe-LDHs assembled 3D microspheres were synthesized via a rational designed reaction system, where the formation of atomically thin building blocks was controlled by the synergetic effects of released carbonate anions and butanol. Furthermore, the complexant and solvents played important effects on the process of coprecipitation and the assembling of LDHs. Due to the nature of atomically thin LDHs nanosheets and unique 3D hierarchical structures, the obtained microspheres exhibited excellent electrocatalytic oxygen evolution reaction (OER) activity in alkaline medium with an onset overpotential (0.435 V, which is lower than that of common LDHs) and good durability. The as-prepared 3D NiFe-LDHs microspheres were also firstly used as supercapacitor materials and displayed a high specific capacitance of 1061 F g −1 at the current density of 1 A g −1 .

Si/C yolk-shell structures have been developed to deal with the major issues associated with Si anodes: the huge volume changes and the low electrical conductivity. However, the fabrication process often involves expensive starting materials and/or simultaneously generates insulated SiC, which is harmful for Si anodes. Here, silica wastes from the optical fibers industry are used as starting materials to prepare high performance Si/C materials with Si@void@C yolk-shell structure via a rational designed Al2 O3 coating assisted magnesiothermic process. The obtained yolk-shell Si@void@C materials have a capacity of more than 1450 mA h g-1 after 100 cycles at 0.4 A g-1 . Thanks to the easily coated and removed Al2 O3 layer, the general formation of SiC can be avoided which is beneficial for improving the rate performances, and a capacity of ≈800 mA h g-1 is still kept after 200 cycles at a high rate of 10 A g-1 with a low capacity loss of 0.08% per cycle.

Aqueous polysulfide/iodide redox flow battery (RFB) with highly soluble active species are attractive candidates for scalable energy storage, offering noticeable reduced RFB cost. Though, poor reversibility and electrochemical activity of the redox reaction of polysulfide couples on graphite felt electrode restricts its energy efficiency. Herein, a facile method to improve the electrocatalytic activity by fabrication of skeletal Cu7S4 hollow nanocages with copper vacancies is presented. Cu7S4 nanoparticles can selectively boost the electrocatalytic activities of S2−/Sx2- redox reactions and suppress the hydrogen evolution side reaction. In addition, the hollow opening structure of skeletal Cu7S4 served as the catalytic active site (both the inner side and outer surface), accelerating the electrolyte transport and promoting the charge transfer process. A sandwiched electrode was constructed by coating Cu7S4 nanocages into the interlayer of graphite felt. The polysulfide/iodide flow battery with SKE-Cu7S4 sandwich structure electrode can generate high energy efficiency of 78.5% at 20 mA cm−2, power density of 30.6 mW cm−2 and a stable energy efficiency retention of 92% after approximately 200 continuous cycles suggesting their potential use for future scalable RFBs. The developing of highly efficient and stable electrocatalyst for the electro-conversion of polysulfides will boost the performance and application of polysulfide-based flow batteries and other energy devices involved with polysulfides such as, quantum dots sensitized solar cells, Li–S batteries.

Fabrication of multi-doped catalysts generally involves complex and energy-intensive processes including the preparation of special precursor, solvent evaporation, and post separation or treatment. Herein, we have developed an eco-friendly one-step process to effectively regulate the electronic structure of products by combining the concepts of alloy, heteroatoms doping, phase controlling and heterostructures. The obtained CoFe and Co2P nanoparticles encapsulated in multi-doped nanoporous carbon (NPSC-Co2Fe1) exhibits a small potential gap between Ej=10 and E1/2 of 0.75 V for bifunctional electrocatalytic O2 redox reactions. It is revealed that defect-rich multi-doped carbon-based nanoarchitecture and electronic redistribution provide more donor-acceptor active sites with reduced energy barrier. Notably, ZABs using NPSC-Co2Fe1 as air electrodes exhibit outstanding charge-discharge performances and cycling stability superior to those of ZABs with Pt/C-IrO2. The flexible all-solid-state ZABs with NPSC-Co2Fe1 operate stably even under bending state. Moreover, these batteries are implemented to power mini-fans and LED panels.

The enormous volume expansion during cycling and poor electron conductivity of SnS2 limit its cycling stability and high rate capability. Herein, flower-like SnS2 anchored on 3D carbon nanofiber structures were designed and synthesized by a simple hydrothermal method. Pyrolyzed bacterial cellulose as 3D carbon nanofibers can not only offer a continuous pathway of Li+ and electrons, but can also migrate the serious volume change of SnS2 during charging and discharging. The obtained composite shows a specific capacity of 408.8 mA h g-1 even after 1500 cycles at 10 A g-1, and almost no specific capacity decay after 20 cycles with a retention of 97.5%.

Fe

Wurtz-stannite Cu2CdGeS4 nanocrystals were synthesized via a facile hot-injection method at a low temperature. They exhibited low charge transfer resistance at the electrolyte-electrode interface and high electrocatalytic activity for the reduction of I3(-) in dye-sensitized solar cells (DSSCs). Moreover, this DSSC showed a power conversion efficiency of 7.67%, comparable to the Pt-based device (7.54%).

Tremendous volume expansion of germanium during cycling limits its wide applications in lithium ion batteries. Na2Ge4O9 nanoparticles encapsulated in 3D carbon networks have been designed and fabricated via a salt-templating method. The unique 3D interconnected carbon networks and sodium in Na2Ge4O9 effectively buffer volume expansion and prevent the aggregation of active materials. Furthermore, the thin carbon networks (3–4 nm in thickness) can improve the conductivity of anodes and enhance the diffusion of Li+. Thus, the obtained material shows a high specific capacity of ∼800 mA h g−1 in the range of 0.2–1 A g−1 and a retention of 81.2% after 1000 cycles. And it can still maintain a specific capacity of ∼500 mA h g−1 even at 20 A g−1.

Hierarchical Cu2−XSe nanotubes, constructed by nanosheets with a thickness of two unit cells (1.2 nm), have been fabricated with Cu(OH)2 nanorod arrays as self-sacrificial templates at room temperature, with a high surface area of 72.3 m2 g−1. The unique structure of the Cu2−XSe nanotubes leads to high electrocatalytic activity towards the reduction of polysulfides, given their enlarged active surface area, rapid transportation of electrons and mass. As a result, quantum dot-sensitized solar cells (QDSSCs) with the obtained Cu2−XSe nanotubes as the counter electrode material exhibit long-term stability and a high power conversion efficiency of 5.14% (1 sun irradiation simulation), better than those of the commonly-used Cu2S/brass (3.38%) and reference Pt (1.78%) electrodes.

We have significantly improved the performance of dye-sensitized solar cells (DSSCs) by incorporating plasmonic Au nanostars into the TiO2 photoanode. Gold nanostars were synthesized and used as localized surface plasmons (LSPs) to enhance the light absorption of DSSCs. The Au nanostars exhibit near infrared (NIR) light absorption at ∼785 nm. The N719 and N749 dye based DSSC devices were fabricated with and without the incorporation of Au nanostars. The power conversion efficiency (PCE) of DSSCs using Au nanostars was increased by ∼20% from 7.1% to 8.4% for N719 cells and by ∼30% from 3.9% to 5.0% for N749 devices. The incident photon-to-current conversion efficiency (IPCE) was improved and the spectral response was broadened over the wavelength range of 380–1000 nm. Electrochemical impedance spectroscopy (EIS) showed that by incorporating Au nanostars, the charge recombination resistance Rct value decreased under both open-circuit and illumination conditions, which indicated high electron density generated in the device photoanode.

In this work, a series of nano- and microcrystals of anatase TiO2 including well-defined truncated tetragonal bipyramids (TTBs) (15–20 nm) and hierarchical hollow microspheres (HHMs) (1.5 μm) were successfully synthesized using a facile sol-hydrothermal approach free from surfactants and templates. The latter HHMs also consisted of similar TTBs but bigger in size. The conversion pathway to TiO2 mainly depended on the volume ratio of H2O2 to NH3. In the presence of NH4F, small TTBs were generated as a result of inhibited growth along both [100] and [001] directions. The formation of HHMs through gradual depletion of the yolk followed a typical Ostwald ripening process. Their photovoltaic activities were investigated on dye-sensitized solar cells (DSSCs) using bilayer photoanodes made of typical TTBs and HHMs. The cells delivered a power conversion efficiency (PCE) of 9.06%, corresponding to a 51.5% increment over those fabricated in the same way using P25 and 400 nm TiO2 (CCIC). Meanwhile, the short-circuit current density (JSC) reached up to 18.38 mA cm−2, which was 1.46 times that of the P25 + CCIC cells. They were also superior to previously reported DSSCs based on highly crystalline nanooctahedra and agglutinated mesoporous microspheres. The small particle size of TTBs and micrometer size and hierarchical structure of HHMs endowed the bilayer photoanodes with a synergetic effect of dye loading and light scattering. Moreover, their exposed {001} and {101} facets, which could facilitate spontaneous charge separation through preferential carrier flow towards specific facets, and highly crystalline anatase phase rendered the cells efficient in charge collection.

As a kind of promising generation solar cells, the catalytic properties of counter electrodes (CEs) play a key factor on the performance of QDSSCs (quantum dot-sensitized solar cells) at present. Here, hierarchical Cu7S4 nanotubes (Cu7S4-HNT) assembled by hexagonal nanoplates have been prepared by an in-situ growth route and etching process at room temperature. The formation mechanism of the unique morphology is also proposed. Because of the rapid diffusion of electrons and electrolyte, abundant catalytic sites and high stability, the as-prepared Cu7S4-HNT combined the characteristics of nanotube and hierarchical structure can improve the catalytic performance of CEs. QDSSCs based on the Cu7S4-HNT CEs possess a high power conversion efficiency of 4.53%, superior to those with the commonly used Cu2S/brass (3.3%) or the referenced Pt (1.79%) CEs. What's more, the Cu7S4-HNT CE still shows excellent stability in electrolyte after 1000 CV cycles.

We report effects of an interface between TiO2-perovskite and grain-grain boundaries of perovskite films prepared by single step and sequential deposited technique using different annealing times at optimum temperature. Nanoscale kelvin probe force microscopy (KPFM) measurement shows that charge transport in a perovskite solar cell critically depends upon the annealing conditions. The KPFM results of single step and sequential deposited films show that the increase in potential barrier suppresses the back-recombination between electrons in TiO2 and holes in perovskite. Spatial mapping of the surface potential within perovskite film exhibits higher positive potential at grain boundaries compared to the surface of the grains. The average grain boundary potential of 300-400 mV is obtained upon annealing for sequentially deposited films. X-ray diffraction (XRD) spectra indicate the formation of a PbI2 phase upon annealing which suppresses the recombination. Transient analysis exhibits that the optimum device has higher carrier lifetime and short carrier transport time among all devices. An optimum grain boundary potential and proper band alignment between the TiO2 electron transport layer (ETL) and the perovskite absorber layer help to increase the overall device performance.

Mastery over the structures at nano/microscale can effectively tailor the catalytic activity and durability of materials. Herein, three dimension (3D) hierarchical iron diselenide (FeSe2) microspheres have been successfully synthesized via a hot-injection method. The morphologies of building blocks and final products can be simply controlled by the amount and/or the type of alkythiols, from irregular micro/nanoparticles to uniform 3D hierarchical microspheres made of ultrathin nanosheets or rhombus-like nanorods. A formation mechanism has been understood based on the inherent crystal structure of FeSe2 and the selective adsorption of alkythiols. The as-obtained FeSe2 samples were employed as counter electrode (CE) materials in dye-sensitized solar cells (DSSCs). Electrochemical characterizations indicated that the 3D hierarchical FeSe2 microspheres composed of ultrathin nanosheets (FeSe2 NSs) exhibited low charge transfer resistance at the electrolyte–electrode interface, high electrocatalytic activity and fast reaction kinetics for the I−/I3− redox reaction. A DSSC with FeSe2 NSs CE achieved a high power conversion efficiency of 8.39% under a simulated solar illumination of 100 mW cm−2 (AM 1.5), comparable to that of Pt based devices (8.20%). Moreover, the fast activity onset and relatively long stability demonstrated that the FeSe2 NSs is a promising alternative to Pt in DSSC.

Porous hollow tin oxide (SnO2) nanofibers and their composite with titanium dioxide (TiO2) particles (Degussa P25) were investigated as a photoanode for dye-sensitized solar cells. Incorporation of TiO2 particles in porous hollow SnO2 fibers enhanced the power conversion efficiency ( $\eta )$ from 4.06% to 5.72% under 100-mW/cm $^{2}$ light intensity. The enhancement of efficiency was mainly attributed to increase in current density ( $J_{\rm sc}$ ) and improvement in fill factor (FF). Increase in $J_{\rm sc}$ was caused by higher dye loading as indicated by UV–Vis absorption spectra and the improvement in FF was attributed to faster charge transport time as obtained from transient analysis. The microstructure of SnO2 fibers was studied using transmission electron microscope, scanning electron microscope, and X-ray diffraction. The electron transfer and recombination life times were studied using transient analysis, whereas interfacial charge transfer was studied using electrochemical impedance spectroscopy.

The widely used brass based Cu 2 S counter electrodes (CEs) cannot stand the continuing corrosion in polysulfide electrolyte, which has limited the development of quantum dot-sensitized solar cells. Here, skeletal Cu 7 S 4 nanocages (SKE-Cu 7 S 4 ) with symmetric opening windows were rational designed and synthesized by kinetic roughening processes, and a possible formation mechanism had been proposed. Furthermore, SKE-Cu 7 S 4 onto fluorine-doped tin oxide glass substrates were designed and deposited to function as new efficient, stable and low cost CEs. Thanks to the 3D opening structure of SKE-Cu 7 S 4 CEs, the assembled QDSSCs exhibited a power conversion efficiency of 4.43% under 1 sun (100 mW cm −2 ) irradiation, while those of preformed 18 facet-Cu 7 S 4 , Pt and brass/Cu 2 S CEs are of 3.87%, 1.73% and 3.32%, respectively. Further studies by cyclic voltammetry measurements indicate the SKE-Cu 7 S 4 CEs still remain good cyclability after 600 cycles, demonstrating a super stable capability, while the commonly used brass/Cu 2 S CEs show obvious fluctuation.

Hexagonal CuInSe2 (CISe) nanoplates with a size of about 200 nm have been synthesized by a two-step solvothermal method, in which Sex2− precursor stabilized by HCO(CH3)2NH+ cations (hydrolysis product of the solvent) was prepared from Se powder and vitamin C. Further study indicated that the pre-reduction process of Se powder could control the concentration of Sex2− ions, which played a key role in the phase formation and morphologies of CISe. Furthermore, poly(vinyl pyrrolidone) was beneficial to form CISe nanoplates and could help CISe nanoplates disperse in ethanol and water to form stable inks. CISe films prepared by drop-coating showed a good photoelectric response under visible light irradiation and better electrocatalytic activity for the reduction of polysulfides than Pt.

Well-defined uniform pyramidal Ag-Ag8SnS6 heterodimers are prepared via a one-pot method. A plausible formation mechanism for the unique structures based on a seed-growth process and an etching effect due to oleylamine is proposed. The formed metal-semiconductor Mott-Schottky heterojunction promotes electron transfer from semiconducting Ag8 SnS6 to metallic Ag, which catalyzes the reduction of I3 (-) to I(-). When used as counter electrode in dye-sensitized solar cells, the heterodimers show comparable performance to platinum.

N-type hedgehog-like CuBi2O4 hierarchical microspheres assembled by prismatic nanorods have been prepared by a simple co-precipitation process at room temperature. Controlled experiments indicate that the formation and morphological evolution of CuBi2O4 architectures can be tuned by the activity of cations via changing the concentration, surfactants and solvent. Furthermore, the obtained CuBi2O4 architectures show a good photoelectric response to visible light irradiation because of the enhanced light trapping properties derived from the omni-directionally grown nanorods in the hedgehog-like hierarchical microspheres.

Because of the huge energy and environmental problems caused by the use of fossil fuels, R&D on innovative energy storage systems has never become so important as today. Although there are still some safety, energy, power and cost issues because of which electric vehicles are becoming more and more common in our daily life, such as E-bikes or E-cars. This paper provides an overview of the recent progress on three dimensional (3D) metal oxides–graphene (MOs–G) composites as advanced electrode materials in lithium ion batteries (LIBs). Beginning with a brief description of the importance and preparation methods of 3D MOs–G composites, the effects of the morphology and size of metal oxides (MOs) or graphene on composites for LIBs are then systematically reviewed and discussed. Additionally, important effects of composition and interactions between metal oxides and graphene are also pointed out. Finally, the future challenges of MOs–G composites for lithium ion batteries are discussed.

Homogenously hexagonal prismatic AgBiS2 nanocrystals with sizes of about 7.6 nm have been synthesized by the selective absorption of oleylamine and anisotropic growth in a mixed solvent system. Quantum dot-sensitized solar cells with the as-prepared AgBiS2 nanocrystals as counterelectrode materials showed a conversion efficiency of 2.09% compared with that of Pt (1.73%).

Ternary metal sulfides could provide more alternatives and tune physicochemical properties due to the presence of two cations. However, only Co/Ni-based ternary sulfides have been explored as counter electrode (CE) materials for dye-sensitized solar cells (DSSCs). Herein, CEs fabricated using Ag8GeS6 nanocrystal ink exhibited efficient electrocatalytic activity in the reduction of I3− to I− in DSSCs. The DSSC with the Ag8GeS6 CE displayed a higher power conversion efficiency of 8.10% than that with the Pt CE (8.02%). Moreover, the devices also showed the characteristics of fast activity onset, high multiple start/stop capability and good irradiation stability. The results indicated that the developed Ag8GeS6 CE could be a promising alternative to Pt CEs in DSSCs.

Dye-sensitized solar cells (DSCs) have attracted incredible attention in recent years as relatively inexpensive alternative to silicon solar cells. Conventionally, a transparent fluoride-doped tin oxide (FTO) conductive glass with a thin layer coating of platinum (Pt) is used as counter electrode in DSCs. The widespread use of Pt as counter electrode in DSCs is due to its catalytic capability for I3- reduction in electrolyte. However, Pt is costly and can be affected by the corrosive nature of I-/I3- redox couple, which makes it a less desirable candidate for use in industrial scale manufacturing. In this study, carbon nanofibers with surface-attached Pt nanoparticles were prepared by stabilization and carbonization of electrospun polyacrylonitrile (PAN) nanofibers and subsequent controllable Pt nanoparticle growth on the obtained carbon nanofiber surface through redox reaction. The hierarchical carbon nanofibers with surface-attached Pt nanoparticles (ECNFs-PtNPs) were then employed as cost-effective counter electrode in DSCs. The effects of size, morphology, and loading of Pt nanoparticles on performance of DSCs were investigated. Compared to conventional counter electrode, the counter electrode that was made of ECNFs-PtNPs exhibited larger open circuit voltage (Voc). The DSCs that were made with ECNFs-PtNPs counter electrode demonstrated excellent solar energy conversion efficiencies in the range of 7% to 8%.

Platinum (Pt)-based alloys are considerably promising electrocatalysts for the reduction of I

Transition metal sulfides are a kind of potential candidates for efficient and stable CE materials in DSSCs due to their good electrocatalytic ability and stability towards I

AgInxGa1−xS2 (x = 0, 0.3, 0.5, 0.7 and 1) solid solutions with a size of 25–100 nm have been synthesized in a mixed solvent system via a solvothermal process. The crystal structure of the solid solutions gradually transforms from tetragonal to orthorhombic, along with the chemical composition (x value changes from 0 to 1), and the band gap of the solid solutions can be tuned from 2.37 eV to 1.62 eV. Further studies revealed that the obtained AgInxGa1−xS2 solid solutions show improved photocatalytic activities under visible light irradiation compared with AgGaS2 and AgInS2, and the AgIn0.3Ga0.7S2 solid solution exhibits the best photocatalytic performance for its optimized band gap and energy structure.

Urchin-like SnO2 microspheres have been grown for use as photoanodes in dye-sensitized solar cells (DSSCs). We observed that a thin layer coating of TiO2 on urchin-like SnO2 microsphere photoanodes greatly enhanced dye loading capability and light scattering ability, and achieved comparable solar cell performance even at half the thickness of a typical nanocrystalline TiO2 photoanode. In addition, this photoanode only required attaching ∼55% of the amount of dye for efficient light harvesting compared to one based on nanocrystalline TiO2. Longer decay of transient photovoltage and higher charge recombination resistance evidenced from electrochemical impedance spectroscopy of the devices based on TiO2 coated urchin-like SnO2 revealed slower recombination rates of electrons as a result of the thin blocking layer of TiO2 coated on urchinlike SnO2. TiO2 coated urchin-like SnO2 showed the highest value (76.1 ms) of electron lifetime (τ) compared to 2.4 ms for bare urchin-like SnO2 and 14.9 ms for nanocrystalline TiO2. TiO2 coated SnO2 showed greatly enhanced open circuit voltage (V oc), short-circuit current density (J sc) and fill factor (FF) leading to a four-fold increase in efficiency increase compared to bare SnO2. Although TiO2 coated urchin-like SnO2 showed slightly lower cell efficiency than nanocrystalline TiO2, it only used a half thickness of photoanode and saved ∼45% of the amount of dye for efficient light harvesting compared to normal nanocrystalline TiO2.

Polydopamine (PDA) functionalized graphene/NiFe 2 O 4 (GNSs–PDA–NiFe 2 O 4 ) nanocomposite has been successfully synthesized through an in-situ ultrasonic method. The obtained GNSs–PDA–NiFe 2 O 4 nanocomposite shows a reversible capacity up to 947 mAh g −1 and much improved rate capability, e.g. delivering a capacity of 562 mAh g −1 at 5 A g −1 , about 7 times higher than that of graphene/NiFe 2 O 4 nanocomposite. The improvement in the rate capability of the obtained GNSs–PDA–NiFe 2 O 4 nanocomposite can be attributed to the improved interactions between graphene and NiFe 2 O 4 derived from PDA, and a high conductive network fabricated by PDA functionalized graphene, which can be supported by TEM images and EIS measurements. Further studies reveal the strong graphene–NiFe 2 O 4 interactions are also beneficial for retaining the high conductive network after the charge–discharge processes, and further beneficial for its cyclic stability.

Silicon has been regarded as one of the most promising alternatives to the current commercial graphite anode for Li-ion batteries due to its high theoretical capacity and abundance. Although high gravimetric capacity (mAh/g) of Si-based materials can be achieved, areal capacity (mAh/ cm 2 ), an indication of the energy stored at the electrode level, has rarely been discussed.

The development of cost-effective, highly efficient and robust multi-functional electrode materials can dramatically reduce the overall cost of electrochemical devices. We here report the controlled synthesis of NiS2/FeS2 nanoparticles encapsulated in N-doped carbon nanorods (NiS2/FeS2/NC) through carbonization and sulfurization of Fe/Ni-based bimetallic metal-organic frameworks. Benefiting from both structural and compositional characteristics, the resulting NiS2/FeS2/NC nanorods possess abundant active sites, high electrical conductivity and rapid mass transfer, thereby delivering 10 and 20 mA cm−2 at overpotential of 172 mV and 231 mV towards the hydrogen evolution reaction and oxygen evolution reaction with robust stability in 1.0 M KOH solution, respectively. When employed as a bifunctional electrocatalyst for overall water splitting, it requires only 1.58 V to deliver a current density of 10 mA cm−2 in 1.0 M KOH, outperforming that of the commercial Pt/C || RuO2. Additionally, lithium-ion batteries tests also show high reversible capacity (718 mA h g−1 at 100 mA g−1) and excellent cycling stability and rate performance. The work in this paper not only provides a promising strategy for designing efficient multi-functional electrode materials with similar morphology and structure, but also can be extended to the synthesis of other mixed metal sulfides for energy conversion and storage.

Biomorphic SnO2/C composites were synthesized by a facile biotemplating method using natural cotton as the structure template and the bio-carbon source. The content of carbon in the composites could be easily adjusted by varying the sintering temperature. Electrochemical tests demonstrated that the content of carbon in the obtained composites had great effects on their electrochemical performances, such that the biomorphic SnO2/C composites prepared at 300 °C exhibited a reversible capacity of 530 mAh g−1 after 100 cycles at a current density of 100 mA g−1. The results suggest that the obtained biomorphic SnO2/C composites prepared by the facile approach may be used as anode materials in practical lithium-ion batteries.

Hollow cubic-like CuInS 2 cages were prepared with cubic Cu 2 O nanocrystals as self-sacrificing template through solvothermal process. The formation of these hollow structures could be attributed to the migration of copper ions and the copy of cubic Cu 2 O template based on the Kirkendall effect and the Ostwald ripening process. Such process and mechanism might be extended to synthesize other hollow ternary chalcogenide materials.

We report a novel strategy to enhance the rate capability of Si–C composite by facile boron doping. Boron doping was confirmed by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The boron-doped Si–C composite shows much improved rate capability, delivering a capacity of 575 mAh/g at 6.4 A/g without any external carbon additive, 80% higher than that of undoped composite. Electrochemical impedance spectroscopy (EIS) measurement shows that boron-doped Si–C composite has lower charge transfer resistance, which helps improve its rate capability. Keywords: Boron doping, Si–C composite, Rate capability, Anode, Lithium-ion battery

A NiFe2O4/expanded graphite (NiFe2O4/EG) nanocomposite was prepared via a simple and inexpensive synthesis method. Its lithium storage properties were studied with the goal of applying it as an anode in a lithium-ion battery. The obtained nanocomposite exhibited a good cycle performance, with a capacity of 601 mAh g−1 at a current of 1 A g−1 after 800 cycles. This good performance may be attributed to the enhanced electrical conductivity and layered structure of the EG. Its high mechanical strength could postpone the disintegration of the nanocomposite structure, efficiently accommodate volume changes in the NiFe2O4-based anodes, and alleviate aggregation of NiFe2O4 nanoparticles.

Transition metal sulfides with high specific capacity have received increasing research interest in lithium storage. However, the low reversibility of metal sulfides usually leads to the oxidation of Li