This work proposes a mild and environmentally-friendly approach to prepare a highly efficient functional graphene (termed as AGO-hv) using methods of ozone oxidation, solvothermal synthesis, and photoreduction. The use of ozone oxidation in the first step can effectively increase the interlaminar distance between graphite oxide sheets, and create active sites for nucleophilic attack on the epoxy carbon from ammonia. The amino groups were successfully grafted on the surface of graphene as evidenced by the amidation reaction, with a maximum nitrogen content of 10.46 wt% and a C/N molar ratio of 8.46. After further photoreduction of the aminated graphite oxide (AGO), the residual oxygen functionalities, such as C-OH, were effectively removed and the conductivity of the graphene sheet was further recovered. The dye-sensitized solar cell (DSC) exhibited a power conversion efficiency (PCE) of 7.51% based on AGO-hv counter electrode (CE), close to that of Pt counterpart (7.79%). The experimental results indicated that the amidation and photoreduction processes were significantly facilitated by the initial ozonization of graphene oxide, and this process significantly improved the electrochemical activity and the conductivity of graphene oxide. Density functional theory (DFT) calculations revealed that AGO-hv had the lowest ionization energy (a better electron-donating ability) and also suitable binding energy with I atoms as well. The combination of ozonization, amination and photoreduction is an efficient route to obtain electrocatalysts with desired compositional distributions and performance for triiodide reduction reaction in DSCs.

In this work, a facile one-step approach is reported for using ZIF-67 as a sacrificial template in the synthesis of a counter electrode (CE) catalyst for dye-sensitized solar cells (DSCs). Porous nanocomposites of Co, CoO and N-doped graphitic carbon were synthesized by controlling the carbonization temperature of the templates in a N2 atmosphere. The characterization of the structure of the products indicated that cobalt nanoparticles were embedded in an N-doped graphitic carbon matrix, (a core-shell structure termed Co@NGC) while cobalt and cobalt oxide nanoparticles were exposed on the external surface of the carbon (termed Co/CoO). In particular, the chemical stability of the nanostructure of the Co@NGC was superior to Co/CoO with respect to etching by strong acids such as hydrochloric acid (HCl, 0.1 M). The DSC performance of ZIF-67-850 (pyrolyzed at 850 °C) employed as a CE resulted in a photoelectric conversion efficiency (PCE) of 7.92%, which was close to a Pt CE (8.18%) in the liquid I3−/I− redox couple electrolyte. The excellent performance of ZIF-67-850 can be attributed to the synergetic effects between the Co and CoO coupled with the nitrogen doped graphitic carbon. The cost-effective porous Co/CoO and Co@NGC nanocomposites exhibit great potential for application as high performance CE in solar cells.

Utilization of metal oxide/supports interface structures could generate high- performance electrochemical materials for clean energy storage and conversion. However, designing the metal oxide/supports interfaces with highly enhanced conductivity and cycle durability remains a significant challenge. Here, we demonstrate an in-situ growth technique to synthesize a Sn/SnO2@C composite with nano-Sn species attached on surface of carbon spheres (denoted as Sn/SnO2@C) during the carbonization of a sol-gel precursors of tin (IV) tetrachloride pentahydrate (SnCl4·5H2O) and Resorcinol-Formaldehyde (Sn4+-RF) in N2. We investigate the nucleation and crystal growth of Sn/SnO2 from Sn4+-RF precursor to Sn/SnO2@C composite with the variation of the concentration of acid value and heat-treatment temperature. Sn/SnO2@C-(1.0, 800) composite as supercapacitor electrode achieves a maximum specific capacitance of 906.8 F g−1 at a scan rate of 1 mV s−1 in 6 M KOH solution, and an excellent cycle durability of 2000 cycles at 5 A g−1. The electrochemical performances demonstrate that charge storage occurs in Sn/SnO2@C mainly due to redox reactions between the binary oxidation states: Sn↔Sn(OH)62−(IV) in basic electrolyte, hierarchical porosity and Sn/SnO2@C distinct structure, which is formed in situ. The work provides new insights into the rational design of Sn@C composites electrode materials for pseudocapacitor and other electrochemical devices.

Advantages in low cost, and excellent catalytic activity of Fe-based nanomaterials dispersed on nitrogen-doped graphene supports render them to be good electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells. Here, Fe2O3/polypyrrole/graphene oxide (Fe2O3/Ppy/GO) composites with the Fe2O3 embedded in the Ppy modified GO are synthesized using hydrothermal method. With an optimal iron atom content ratio of 1.6% in graphene oxide and heat treatment at 800 °C, the Fe2O3/Ppy/GO exhibited enhanced catalytic performance for ORR with the onset potential of −0.1 V (vs SCE), cathodic potential of −0.24 V (vs SCE), an approximate 4e− transfer process in O2-saturated 0.1 M KOH, and superior stability that only reduced 5% catalytic activity after 5000 cycles. The decisive factors in improving the electrocatalytic and durable performance are the intimate and large contact interfaces between nanocrystallines of Fe2O3 and Ppy/GO, in addition to the high electron withdrawing/storing ability and the high conductivity of GO doped with nitrogen from Ppy during the hydrothermal reaction. The Fe2O3/Ppy/GO showed significantly improved ORR properties and confirmed that Fe-N-C-based electrocatalysts played a key role in fuel cells.Fe2O3/polypyrrole/graphene oxide electrocatalysts for oxygen reduction reaction (ORR) are successfully prepared through one simple polypyrrole-assisted hydrothermal method and possess very high ORR activity and are able to selectively reduce O2 to water through the four-electron transfer reaction mechanism in alkaline electrolyte.

Nanocrystalline SnO2 is successfully assembled into highly-ordered hollow microspheres by a facile procedure consisting of hydrothermal synthesis and assistance of templates, then high temperature calcination. The structures consist of highly crystalline grains with hexagonal shape and about 11 nm mean size. Kirkendall effect directs the diffusion of SnO2 nanocrystals and carbon dioxide and causes the formation of hollow SnO2 spheres. Effect of the concentration of Sn precursor and acid value on the SnO2 morphology and SnO2 electrochemistry properties for pseudocapacitor are employed. Electrochemical measurements demonstrate that the maximum specific capacitance of hollow SnO2 microspheres is 178.86 F g−1 at a scan rate of 1 mV s−1 in 1 M KOH solution and originated from Faradaic redox reactions. Also the specific capacitance only decays 4.8% from 150 cycles to 200 cycles and keeps constant from 200–2000 cycles. The present results clearly indicate that hollow SnO2 spheres with layered crystalline structures are very attractive materials for energy storage because of their ability to intercalate ions into a wide range of sites.Multilayered nanocrystalline SnO2 hollow microspheres (HS-SnO2) were prepared hydrothermally with the assistance of templates formed through in-situ polymerization of resorcinol and formaldehyde. HRTEM image shows that the synthesized particles are perfectly hexagonal in shape and contain a well defined lattice fringe that indicates the high crystallinity of SnO2 materials. Cyclic voltammetric (CVs) showed that a maximum specific capacitance of 178.86 F g−1 at a scan rate of 1 mV s−1 in 1 M KOH solutions. The present study clearly indicated that hollow SnO2 microspheres were indeed promising electroactive materials for improved pseudocapacitor reliability.

Hollow SnO2 microspheres are prepared from resorcinol–formaldehyde gel and different tin compound precursors, including stannous sulfate (SnSO4), stannous chloride dihydrate (SnCl2·2H2O), and stannic chloride pentahydrate (SnCl4·5H2O) via chemically induced self-assembly in hydrothermal environment. Morphological and structural characterizations of as-prepared hollow SnO2 microspheres are carried out using scanning electron microscopy, X-ray diffraction, and nitrogen adsorption–desorption method. Their electrochemical properties as the supercapacitor electrode materials for application are also investigated using cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) measurement in 1 M H2SO4 electrolyte. There are redox peaks in CV curves and a large number of Faradic plateaus in GCD curves. At different scan rates, all the obtained samples have excellent electrochemical properties. The hollow SnO2 microspheres obtained from SnSO4 and SnCl2·2H2O as precursors show relatively lower specific capacitances of 395 and 347 F g−1, respectively. However, the specific capacitance of SnO2 from SnCl4·5H2O is up to 663 F g−1. The high specific surface area and hollow structure of SnO2 microspheres are due to facilitating the rapid transport of electrolyte ions and improving the electrochemical performance. It is expected that hollow SnO2 microspheres are the promising redox supercapacitor materials.

•Fine controlled core shell structure of sPS@SnO2 particles.•Hollow SnO2 microspheres are prepared via template assisted method in hydrothermal environment and high-temperature calcination treatment for removal of sPS.•SnO2@C composite hollow spheres were fabricated.•SnO2@C composite leads to an improved electrochemical performance in supercapacitors due to a suitable carbon coating.In the presence of sulfonated polystyrene (sPS) template, sPS@SnO2 core shell particles formed via the interaction between the functional group of -SO3H on the template surface and ions of Sn2+ from the precursor of SnSO4 which were in ethanol-aqueous medium. After high-temperature calcination treatment for removal of sPS, the sPS@SnO2 changed into SnO2 hollow spheres. With the further carbonization of the sPS@SnO2@glucose composite microspheres, SnO2@C composite hollow spheres were fabricated. Using SEM, TEM, and N2 adsorption - desorption technology, the structure, specific surface area, and the core-shell structure formation mechanism were determined. Cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) properties of SnO2 hollow spheres and SnO2@C composites were investigated, respectively, in the foam nickel electrode under alkaline condition. The specific capacitance of SnO2@C composite hollow spheres could reach 25.8 F g−1 in 1 mol L−1 KOH aqueous solution and showed excellent charge-discharge behavior.

The kinetics of CO oxidation in hydrogen-rich gas on Pt/mordenite (Pt/MD) or Pt/Al2O3 were investigated over a wide range of CO (0.4–1.8%) and O2 concentrations (0.26–1.14%). The integral flow measurements showed that both the catalysts that could remove CO from 1% to ppm-level Pt/MD had a wider operation temperature range than Pt/Al2O3, especially towards lower temperatures.

One of the major challenges associated with fuel cells is the design of highly efficient electrocatalysts to reduce the high overpotential of the oxygen reduction reaction (ORR). Here we report Polyaniline (PANI) based micro/nanomaterials with or without transition metals, prepared by the emulsion polymerization and subsequent heat treatment. PANI microspheres with the diameter of about 0.7 µm have been prepared in basic (NH3 solution) condition, using two different types of surfactant (CTAB, SDS) as the stabilizer, ammonium persulphate (APS) as oxidant with aniline/surfactants molar ratio at 1/1 under the hydrothermal treatment. PANI nanorods, FePANI, and FeCoPANI have been synthesized in acidic (HCl) medium with aniline/surfactants molar ratio at 1/2 and polymerization carried out without stirring for 24 h. Products mainly FeCoPANI have shown high current density with increasing sweep rate and excellent specific capacitance 1753 F/g at the scan rate of 1 mV/s. Additionally, it has shown high thermal stability by thermogravimetric analysis (TGA). FePANI has been investigated for excellent performance toward ORR with four electron selectivity in the basic electrolyte. The PANI-based catalysts from emulsion polymerization demonstrate that the method is valuable for making non-precious metal heterogeneous electrocatalysts for ORR or energy storage and conversion technology.Polyaniline-based microspheres, nanorods with or without Fe, Fe–Co have been prepared through emulsion polymerization, and showed good interfacial contact and demonstrated high supercapacity and electrocatalytic activity especially for Fe–Co–PANI sample.Download high-res image (179KB)Download full-size image