Jiazang Chen

Synthesis of highly nitrogen-doped hollow carbon nanoparticles and their excellent electrocatalytic properties in dye-sensitized solar cells

Hollow carbon nanoparticles that have been highly doped with nitrogen (N-HCNPs) are directly prepared by a facile one-pot method based on the detonation-assisted chemical vapor deposition of dimethylformamide without the use of metal catalysts. The N-HCNPs exhibit uniform core-shell microstructures with inner cavities encapsulated by graphitic walls, possessing a narrow size distribution of 10–25 nm. The nitrogen content in N-HCNPs is as high as 20.8% atom ratio, and the nitrogen bonds display pyridine-, pyrrole-, and graphite-like configurations. Defects and dislocations are present in the graphene layers due to highly incorporated nitrogen, leading to the creation of micropores on the carbon shell and a large BET surface area of 454 m2 g−1. The unique N-HCNPs with interconnected hierarchical porous structures and nitrogen-containing defects show excellent electrocatalytic activity for triiodide reduction in dye-sensitized solar cells, superior to conventional platinum catalysts.

Nitrogen-doped hollow carbon nanoparticles as efficient counter electrodes in quantum dot sensitized solar cells

The functions of nitrogen-doped hollow carbon nanoparticles (N-HCNPs) as counter electrodes in quantum dot sensitized solar cells (QDSSCs) have been studied in this paper. Electrochemical impedance spectroscopy (EIS) and Tafel-polarization tests reveal a low charge transfer resistance and a high exchange current density between polysulfide electrolyte and the N-HCNPs electrode. Cyclic voltammetry results indicate that the N-HCNPs electrode shows high electrocatalytic activity and excellent tolerance toward the S 2� /Sn 2� electrolyte. A power conversion efficiency of 2.67% is achieved for the QDSSCs based on N-HCNPs counter electrodes, which is clearly higher than those of the QDSSCs based on HCNPs, carbon nanotubes and Pt counter electrodes. The results reveal that the N-HCNPs electrode is a promising counter electrode candidate for QDSSCs.

In Situ Observation of Initial Corrosion of MgAl9Zn1 Magnesium Alloy in Cyclic Wet-Dry Conditions Using Environmental Scanning Electron Microscopy

Abstract The corrosion of a MgAl9Zn1 (UNS M11918, AZ91) alloy in an atmosphere of water vapor with cyclic wet-dry conditions was studied using environmental scanning electron microscopy (ESEM). The...

Electrophoretic deposition of TiO2 nanorods for low-temperature dye-sensitized solar cells

The fabrication of low-temperature photoanodes is essential for flexible dye-sensitized solar cells. Electrophoretic deposition (EPD) represents a potential alternative to form photoanodes at low temperature. To optimize the photoanodes fabricated by EPD, TiO2 nanorod/nanoparticle (labeled as NRP) structures were synthesized. The obtained NRPs have high surface charges and wide size distribution, making them suitable to form binder-free photoanodes with EPD. Compared with reference DSSCs produced with P25 (commercial TiO2 particles), NRP based DSSCs showed enhanced light-scattering property and decreased recombination. Further, under the same total time, the efficiencies of the devices obtained with multiple EPD are above 2.2 times those of one step devices. Without any calcination or compression, the best device (with multiple EPD and a thin layer of nanoparticles) gives a conversion efficiency of 4.35%, having a short circuit current density, open circuit voltage, and filling factor of 8.41 mA cm−2, 0.74 V and 69.75%, respectively.

Highly efficient visible light-driven hydrogen production of precious metal-free hybrid photocatalyst: CdS@NiMoS core–shell nanorods

Well-shaped precious metal-free hybrid photocatalysts with low cost and high efficiency of photocatalytic H2 evolution are of great significance for clean energy. Herein, we report that NiMoS, a non-noble metal co-catalyst used for forming a well-designed one-dimensional (1D) CdS@NiMoS core–shell nanorod photocatalyst system, greatly improves the efficiency and durability for photogeneration of hydrogen in water. The intimate interaction between the CdS nanorod core and the NiMoS thin shell enhances the separation of the photogenerated electron–hole pair, and the large contact surface area improves the utilization efficiency of the photogenerated electrons. Consequently, the optimal loading content of NiMoS is 3 wt% for CdS, giving a photocatalytic H2 production rate of 185.4 mmol g−1 h−1, which is about 16.55, 5.24 and 3.85 times higher than that of 2 wt% Pt/CdS, 3 wt% CdS@MoS2 and 3 wt% CdS@NiS, respectively, and the apparent quantum efficiency at 420 nm over CdS@NiMoS reaches 21.82%. This study provides a simple method for constructing high performance and low cost photocatalysts, which enhance photocatalytic H2 evolution.

Structure-controlled CdS(0D, 1D, 2D) embedded onto 2D ZnS porous nanosheets for highly efficient photocatalytic hydrogen generation

The morphological characteristics of a photocatalyst is central to its photocatalytic activity for solar energy conversion. Herein, Pt–ZnS/CdS composites comprising ZnS nanosheets, embedded via the geometry and size modulation and tuning of band gap of CdS with 0D, 1D or 2D structure, were investigated for solar hydrogen production. The photoactivity results indicate that the shape and morphology of CdS in the Pt–ZnS/CdS heterojunction play a pivotal role in affecting the photocatalytic performance. CdS with a 1D structure deposited on porous Pt–ZnS nanosheets endow the heterojunction with increased efficiency for the separation and transport of photoinduced electron–hole pairs. The proposed mechanism for the boosted suppression of charge recombination was further confirmed by the transient photocurrent response and photoluminescence.

Fabricating efficient CdSe–CdS photocatalyst systems by spatially resetting water splitting sites

Water oxidation and reduction over semiconductor-based photocatalysts intrinsically occur at different spatial sites. Modulation of the reaction sites and charge transfer between them are logically important in speeding up the reaction. Here, we demonstrate that divorcing a CdSe–CdS–Pt donor–acceptor system on different surface sites of TiO2 can significantly increase the H2 generation rate. The increase is derived from an effective reset of water oxidation and reduction sites. Widening of the site distance by employing a TiO2 membraniform acceptor effectively decreases the electron–hole recombination especially for a membrane of TiO2 nanotube arrays. The oriented charge transfer characteristic of TiO2 nanotube arrays benefits long-range electron transport, thereby increasing the electron lifetime and reaction rate. When more conductive carbon nanotube arrays serve as an electron acceptor to replace TiO2, the electron transport is greatly improved, resulting in an ultrahigh H2 generation rate of 1270 mmol g−1 h−1. This work provides a basis for the design and construction of highly efficient photocatalysts through rational modulation of reaction sites and charge transport.

Direct C–C coupling of acetone at α-position into 2,5-hexanedione induced by photochemical oxidation dehydrogenation

Facile carbon–carbon bond formation was achieved through the dehydrogenation coupling of acetone at the α-position. Using the H2O2/UV-light system, the acetonyl radicals that were formed from the selective cleavage of the α-C–H bond of acetone underwent a C–C coupling reaction. By modulating the instantaneous concentration of hydrogen peroxide, the direct C–C coupling of acetone was achieved. Moreover, the selectivity and generation rate of 2,5-hexanedione reached 67.4% and 8.6 mmol h−1, respectively.