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Han L.,Gansu Academy of science | Ma Z.,Gansu Academy of science | Luo Z.,Northwest Yongxin Coatings Company Ltd | Liu G.,Gansu Academy of science | And 2 more authors.
RSC Advances | Year: 2016

Protonated titanate nanotubes were chosen as a precursor in a hydrogenation process. Owing to the high capacity for molecular hydrogen storage of nanotubes, TiO2 nanotubes can be hydrogenated through thermal treatment under N2 and H2 mixed flow at lower temperature. A series of hydrogenated TiO2 nanotubes and nanobelts were synthesized and characterized by XRD, UV-vis, TEM, EPR and XPS. The results showed that the hydrogenated TiO2 nanotubes possess tiny and uniform diameters of 8-10 nm and walls thicknesses of 2-3 nm, and were mainly anatase. The anatase TiO2 nanotubes transformed to TiO2-B nanobelts when the hydrothermal temperature was higher than 150 °C. The light absorption of hydrogenated TiO2 nanotubes was expanded to visible light. However, air-TiO2 and hydrogenated TiO2 nanobelts only absorbed ultraviolet light. According to XPS and EPR analysis, hydrogenated TiO2 nanotubes displayed stable core-shell structures, in which the surface was mainly stoichiometric TiO2 and the core was non-stoichiometric TiO2 with Ti3+ and oxygen vacancies. The adsorption and photocatalytic performance were evaluated by the removal rate of phenol. Based on a pseudo-first order kinetic model, the degradation rate constant was obtained with the regression analysis. The highest degradation rate constant of hydrogenated TiO2 nanotubes was 5.2 times higher than air-TiO2. In comparison, the degradation rate constants of hydrogenated TiO2 nanobelts were much lower than air-TiO2. The results showed that the precursor with nanotube structure can be hydrogenated easily at lower temperature compared with nanobelts, resulting in the photocatalytic activity of hydrogenated TiO2 nanotubes being enhanced drastically. © The Royal Society of Chemistry 2016. Source


Li X.,Lanzhou University | Fang Y.,Lanzhou University | Wen L.,Northwest Yongxin Coatings Company Ltd | Li F.,Lanzhou University | And 5 more authors.
Dalton Transactions | Year: 2016

Cobalt-based nanomaterials are promising candidates as efficient, affordable, and sustainable alternative electrocatalysts for the oxygen evolution reaction (OER). However, the catalytic efficiency of traditional nanomaterials is still far below what is expected, because of their low stability in basic solutions and poor active site exposure yield. Here a unique hybrid nanomaterial comprising Co@Co3O4 core-shell nanoparticle (NP) encapsulated N-doped mesoporous carbon cages on reduced graphene oxide (denoted as Co@Co3O4@NMCC/rGO) is successfully synthesized via a carbonization and subsequent oxidation strategy of a graphene oxide (GO)-based metal-organic framework (MOF). Impressively, the special carbon cage structure is very important for not only leading to a large active surface area, enhanced mass/charge transport capability, and easy release of gas bubbles, but also preventing Co@Co3O4 NPs from aggregation and peeling off during prolonged electrochemical reactions. As a result, in alkaline media, the resulting hybrid materials catalyze the OER with a low onset potential of ∼1.50 V (vs. RHE) and an over-potential of only 340 mV to achieve a stable current density of 10 mA cm-2 for at least 25 h. In addition, metallic Co cores in Co@Co3O4 provide an alternative way for electron transport and accelerate the OER rate. © 2016 The Royal Society of Chemistry. Source


Li F.,Lanzhou University | Li J.,Lanzhou University | Cao Z.,Lanzhou University | Lin X.,Lanzhou University | And 6 more authors.
Journal of Materials Chemistry A | Year: 2015

Active, stable and cost-effective electrocatalysts are the key to water splitting for hydrogen production through electrolysis. In this work, we report MoS2 quantum dots (MoS2 QDs) decorated on reduced graphene oxide (RGO) synthesized by a facile sonication method as highly effective electrocatalysts for the hydrogen evolution reaction (HER). Compared with MoS2 sheets, the zero-dimensional MoS2 QDs have a defect-rich structure rendering these quantum dots with plentiful active sites, which can further enhance the catalytic activity by a synergistic effect with RGO. Electrochemical experiments demonstrated that the catalyst exhibited large cathode currents (a small overpotential of 64 mV for 10 mA cm-2 current density) and a Tafel slope as small as 63 mV per decade, achieving high stability simultaneously. This work opens up possibilities for preparing non-noble metal electrocatalysts while achieving high HER performance similar to commercial Pt catalysts (Pt/C). © The Royal Society of Chemistry 2015. Source


Li F.,Lanzhou University | Li J.,Lanzhou University | Lin X.,Lanzhou University | Li X.,Lanzhou University | And 6 more authors.
Journal of Power Sources | Year: 2015

Design and synthesis of non-precious-metal catalyst for efficient electrochemical transformation of water to molecular hydrogen in acid environments is of paramount importance in reducing energy losses during the water splitting process. Here, the hybrid material of MoS2-coated Cu loaded on the multi-walled carbon nanotubes (MWCNTs@Cu@MoS2) was synthesized using chemical process and hydrothermal method. It was found that the participation of MWCNTs and Cu nanoparticles not only improved the electrical conductivity of the catalyst, but also further enhanced the catalytic activity by synergistic effect with edge-exposed MoS2-coating. Electrochemical experiments demonstrated that the catalyst exhibited excellent hydrogen evolution reaction (HER) activity with large cathode currents (small overpotential of 184 mV for 10 mA cm-2 current density) and a Tafel slope as small as 62 mV per decade. Furthermore, it was discovered that the current density of this composite catalyst had a little decrease after the continual 1000 cycling, which showed the catalyst had a high stability in the recycling process. These findings confirmed that this catalyst was a useful and earth-abundant material for water splitting. © 2015 Elsevier B.V. All rights reserved. Source


Li X.,Lanzhou University | Fang Y.,Lanzhou University | Lin X.,Lanzhou University | Tian M.,Lanzhou University | And 5 more authors.
Journal of Materials Chemistry A | Year: 2015

Highly efficient and non-precious metal electrocatalysts for oxygen evolution reactions (OERs) and oxygen reduction reactions (ORRs) are at the heart of key renewable-energy technologies. Nevertheless, developing highly active bi-functional catalysts at low cost for both OER and ORR still remains a huge challenge. In this paper, Co3O4 nanocrystals embedded in N-doped mesoporous graphitic carbon layer/multiwalled carbon nanotube (MWCNT) hybrids are prepared by a facile carbonization and subsequent oxidation process of MWCNT-based metal-organic frameworks (MOFs). As a result, in alkaline media, the hybrid material catalyzes OER with an onset potential of 1.50 V (vs. reversible hydrogen electrode) and an over-potential only of 320 mV to achieve a stable current density of 10 mA cm-2 for at least 25 h. The same hybrids also exhibit similar catalytic activity but superior stability to the commercial 20 wt% Pt/C catalyst for ORR, making it a high-performance cheap bi-catalyst for both OER and ORR. The design concept of nonmetal-doped and precious-metal-free electrocatalysts from MOFs can be extended to fabricate other novel, stable and easy to use catalyst systems for advanced applications. © The Royal Society of Chemistry 2015. Source

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