A highly efficient nitrogen and sulfur co-doped graphene (NSG) nanosheet for dye-sensitized solar cells (DSSCs) was synthesized using a simple hydrothermal method, and its electrocatalytic activity towards the I3−/I− redox reaction was investigated. The NSG materials showed a uniform distribution of nitrogen and sulfur heteroatoms throughout the graphene nanosheet. The doped nitrogen was present in the form of pyridinic, pyrrolic and graphitic states, and the doped sulfur was present in the C–S–C configuration. The DSSC with the NSG counter electrode exhibited a high conversion efficiency (7.42%), similar to that of the Pt counter electrode (7.56%) and much higher than that of the only N- or S-doped graphene electrodes. The high catalytic activity of the NSG electrode is attributed to the synergistic effect of the high charge polarization arising from the difference in electronegativity between nitrogen and carbon as well as the structural distortion caused by the bigger atomic size of the sulfur atom. To the best of our knowledge, the synergistic effect of co-doping of graphene on the counter electrode performance in DSSCs is demonstrated for the first time, and co-doping is proposed as a promising approach to enhance the photovoltaic performance of DSSCs.

Nitrogen and sulfur co-doped graphene counter electrodes with synergistically enhanced performance for dye-sensitized solar cells

Replacement of expensive platinum-based catalysts at the cathode of fuel cells by low-cost alternatives represents an important milestone to achieve significant system cost reductions. In this work, single crystal cobalt disulfide (CoS2) octahedral nanoparticles supported on graphene/carbon nanotube composites were prepared as oxygen reduction reaction (ORR) catalysts in acidic electrolyte. During the simplistic, one-pot solvothermal synthesis, the nanostructured carbon supports were also simultaneously doped with nitrogen and sulfur. Time dependent studies elucidated the growth process of the {111} facet encased octahedra that could only be prepared when carbon support materials were incorporated into the reaction mixture. Through computational simulations, the shape directed growth process was found to be driven thermodynamically towards surface energy minimization. Control experiments and spectroscopy characterization were also used to investigate the occurrence and nature of nitrogen and sulfur doping into the graphitic structure of the graphene/carbon nanotube composite support. The impact of carbon support on ORR activity was clear, with the graphene/carbon nanotube composite supported CoS2 octahedra (CoS2-CG) outperforming CoS2 supported on just graphene or carbon nanotubes. Additionally, CoS2-CG provided an on-set potential (0.78 V vs. RHE) and half-wave potential (0.66 V vs. RHE) that was 60 mV and 150 mV higher than the CoS2 particle agglomerates formed when no carbon support was included during catalyst preparation. This improved activity can be attributed to the beneficial properties of the nitrogen and sulfur doped graphene/carbon nanotube composite support, and also may arise due to the more favourable oxygen adsorption on the (111) surface of the octahedral particles predicted by theoretical calculations. By combining the synergistic properties of the graphene/carbon nanotube composite and unique shape controlled single crystal CoS2 nanoparticles, CoS2-CG is presented as an emerging catalyst for the ORR in fuel cells.

Shape-controlled octahedral cobalt disulfide nanoparticles supported on nitrogen and sulfur-doped graphene/carbon nanotube composites for oxygen reduction in acidic electrolyte

Synthesis of nitrogen and sulfur co-doped graphene supported hollow ZnFe2O4 nanosphere composites for application in lithium-ion batteries

Single step combustion synthesis, characterization and photocatalytic application of α-Fe2O3-Bi2S3 heterojunctions for efficient and selective reduction of structurally diverse nitroarenes

We report a facile two-step sequential deposition method to prepare Sb2S3 thin films, where antimony acetate and thiourea are utilized as antimony and sulfur sources, respectively. The sequential deposition of two precursor materials followed by swift annealing at mild temperature leads to high-quality Sb2S3 films. The detailed reaction mechanism is revealed on the basis of structural and compositional analyses. By optimizing the concentration of thiourea and annealing temperature, uniform and flat Sb2S3 thin films are obtained with either sulfur-deficiency or sulfur richness. Finally, a planar heterojunction solar cell based on the as-prepared Sb2S3 film delivers a high power conversion efficiency of 5.69%, which is a top value for planar heterojunction Sb2S3 solar cells fabricated by a solution approach. This research provides a convenient and low-cost approach for the deposition of Sb2S3 films for efficient solar cell applications.

Sequential deposition route to efficient Sb2S3 solar cells

Theoretical study on the thermal decomposition of thiourea

A benchmark comparison for different computational methods and basis sets has been presented. In this study, five computational methods (Hartree–Fock (HF), MP2, B3LYP, MPW1MP91, and PBE1PBE) along with 18 basis sets have been applied to optimize the geometry of carbon disulfide (CS2), and further calculate the vibrational frequencies of the optimized geometries. The differences between the calculated frequencies and corresponding experimental data are used to evaluate the efficiency of each combination of computational method and basis set. The comparison of frequency difference indicates that B3LYP generally gives the best prediction of frequencies for CS2, whereas the other two density functional theory (DFT) methods, i.e., MPW1PW91 and PBE1PBE, often give parallel results. Although MP2 predicts the frequencies with accuracy almost as good as those from DFT methods, in a particular case, HF calculation outperforms MP2 as well as MPW1PW91 and PBE1PBE for prediction of the frequency of asymmetrical stretching for CS2. © 2013 Wiley Periodicals, Inc.

Zerong Daniel Wang

Papers

Theoretical study on the thermal decomposition of thiourea

Theoretical study of the vibrational frequencies of carbon disulfide