Browsing by Author "Meng, Lijian"
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- Atomic-scale structure and nonlinear optical absorption of two-dimensional GeSPublication . Zhang, Jijun; Sun, Rong; Ge, Yanqi; Wang, Jingyi; Wang, Zexuan; Meng, Lijian; Deepak, Francis Leonard; Zhang, Min; Yin, Peng; Cheng, Faliang; Wang, Zhiming; Wang, Zhongchang
- Bifacial dye-sensitized solar cells: a strategy to enhance overall efficiency based on transparent polyaniline electrodePublication . Wu, Jinhui; Li, Yan; Tang, Qunwei; Yue, Gentian; Lin, Jianming; Huang, Miaoliang; Meng, LijianDye-sensitized solar cell (DSSC) is a promising solution to global energy and environmental problems because of its clean, low-cost, high efficiency, good durability, and easy fabrication. However, enhancing the efficiency of the DSSC still is an important issue. Here we devise a bifacial DSSC based on a transparent polyaniline (PANI) counter electrode (CE). Owing to the sunlight irradiation simultaneously from the front and the rear sides, more dye molecules are excited and more carriers are generated, which results in the enhancement of short-circuit current density and therefore overall conversion efficiency. The photoelectric properties of PANI can be improved by modifying with 4-aminothiophenol (4-ATP). The bifacial DSSC with 4-ATP/PANI CE achieves a light-to-electric energy conversion efficiency of 8.35%, which is increased by ,24.6% compared to the DSSC irradiated from the front only. This new concept along with promising results provides a new approach for enhancing the photovoltaic performances of solar cells.
- Bifunctional atomically dispersed ruthenium electrocatalysts for efficient bipolar membrane water electrolysisPublication . Yu, Zhipeng; Si, Chaowei; Escobar-Bedia, Francisco Javier; LaGrow, Alec P.; Xu, Junyuan; Sabater, Maria J.; Amorim, Isilda; Araujo, Ana; Sousa, Juliana P. S.; Meng, Lijian; Faria, Joaquim Luis; Concepcion, Patricia; Li, Bo; Liu, LifengAtomically dispersed catalysts (ADCs) have recently drawn considerable interest for use in water electrolysis to produce hydrogen, because they allow for maximal utilization of metal species, particularly the expensive and scarce platinum group metals. Herein, we report the electrocatalytic performance of atomically dispersed ruthenium catalysts (Ru ADCs) with ultralow Ru loading (0.2 wt%). The as-obtained Ru ADCs (Ru (0.2)-NC) are active for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), which only require a low overpotential (η) of 47.1 and 72.8 mV to deliver 10 mA cm−2 for HER in 0.5 M H2SO4 and 1.0 M KOH, respectively, and of 300 mV for OER in 1.0 M KOH, showing favorable bifunctionality. Density functional theory (DFT) calculations reveal that the Ru–N bonding plays an important role in lowering the energy barrier of the reactions, boosting the HER and OER activities. Furthermore, the bipolar membrane (BPM) water electrolysis using the bifunctional Ru (0.2)-NC as both HER and OER catalysts can afford 10 mA cm−2 under a low cell voltage of only 0.89 V, and does not show any performance decay upon 100 h continuous operation, showing great potential for energy-saving hydrogen production.
- Combustion synthesis of Ce 2 LuO 5.5:Eu phosphor nanopowders: structure, surface and luminescence investigationsPublication . Shi, Shikao; Wei, Dan; Li, Keyan; Wang, Shuping; Fu, Lianshe; Yang, Tao; Meng, LijianThe spherical shape, uniform size and small degree of agglomeration of the particles play crucial roles in promoting the practical applications of the phosphor powders. In this paper, the novel Eu3+ -doped cerium lutetium Ce2LuO5.5 composite nanopowders with a cubic fluorite structure were prepared via a typical solution combustion route, and their internal structure, surface morphology as well as luminescence properties were investigated. The Eu3+ could substitute in either Lu3+ or Ce4+ sites and the existence of oxygen vacancy was confirmed in the composite by X-ray diffraction and Raman spectra techniques. Without the addition of surfactant, most of the as-prepared particles were bound together, and the luminescence was very weak even after a sintering process. Assisted with appropriate polyvinyl alcohol (PVA) surfactant in the combustion reaction and a subsequent heat-treatment process, the bound-particles were evidently separated and seemed to be nearly spherical shape. The particle size could be controlled to 30-120 nm and the luminescence was enhanced by adjusting the subsequent sintering temperature. Excited with 466 nm blue light, the nanopowders exhibited characteristic 5D0→7FJ (J = 0∼ 4) emission transition of Eu3+ and showed enhanced red luminescence as Eu3+ occupied Ce4+ site rather than Lu3+ site. The maximum emission was obtained as 40 mol% Eu substitutes Ce in the composite. Due to the coincidence of 466 nm excitation light with the emission of InGaN chips in white light-emitting diodes, the surface-morphology improved Eu-doped Ce2LuO5.5 phosphor nanopowders have a potential application in solid state lighting fields.
- Defective Ru-doped α-MnO2 nanorods enabling efficient hydrazine oxidation for energy-saving hydrogen production via proton exchange membranes at near-neutral pHPublication . Yu, Zhipeng; Si, Chaowei; Sabaté, Ferran; LaGrow, Alec P.; Tai, Zhixin; Diaconescu, Vlad Martin; Simonelli, Laura; Meng, Lijian; Sabater, Maria J.; Li, Bo; Liu, LifengProton exchange membrane water electrolysis (PEMWE) showes substantial advantages over the conventional alkaline water electrolysis (AWE) for power-to-hydrogen (PtH) conversion, given the faster response and wider dynamic current range of the PEMWE technology. However, PEMWE is currently still expensive due partly to the high voltage needed to operate at high current densities and inevitable usage of precious iridium/rutheniumbased catalysts to expedite the slow kinetics of the oxygen evolution reaction (OER) and to ensure sufficient durability under strongly acidic conditions. Herein, we report that ruthenium doped α-manganese oxide (Ru/ α-MnO2) nanorods show outstanding electrocatalytic performance toward the hydrazine (N2H4) oxidation reaction (HzOR) in near-neutral media (weak alkaline and weak acid), which can be used to replace the energydemanding OER for PEMWE. The as-prepared Ru/α-MnO2 is found to comprise abundant defects. When used to catalyze HzOR in the acid-hydrazine electrolyte (0.05 M H2SO4 + 0.5 M N2H4), it can deliver an anodic current density of 10 mA cm 2 at a potential as low as 0.166 V vs. reversible hydrogen electrode (RHE). Moreover, Ru/ α-MnO2 exhibits remarkable corrosion/oxidation resistance and remains electrochemically stable during HzOR for at least 1000 h. Theoretical calculations and experimental studies prove that Ru doping elongates the Mn–O bond and produces abundant cationic defects, which induces charge delocalization and significantly lowers material’s electrical resistance and overpotential, resulting in excellent HzOR catalytic activity and stability. The introduction of N2H4 significantly reduces the energy demand for hydrogen production, so that PEMWE can be accomplished under remarkably low voltages of 0.254 V at 10 mA cm 2 and 0.935 V at 100 mA cm 2 for a long term without notable degradation. This work opens a new avenue toward energy-saving PEMWE with earthabundant OER catalysts.
- Defective Ru-doped α-MnO2 nanorods enabling efficient hydrazine oxidation for energy-saving hydrogen production via proton exchange membranes at near-neutral pHPublication . Yu, Zhipeng; Si, Chaowei; Sabaté, Ferran; LaGrow, Alec P.; Tai, Zhixin; Diaconescu, Vlad Martin; Simonelli, Laura; Meng, Lijian; Sabater, Maria J.; Li, Bo; Liu, LifengProton exchange membrane water electrolysis (PEMWE) showes substantial advantages over the conventional alkaline water electrolysis (AWE) for power-to-hydrogen (PtH) conversion, given the faster response and wider dynamic current range of the PEMWE technology. However, PEMWE is currently still expensive due partly to the high voltage needed to operate at high current densities and inevitable usage of precious iridium/ruthenium-based catalysts to expedite the slow kinetics of the oxygen evolution reaction (OER) and to ensure sufficient durability under strongly acidic conditions. Herein, we report that ruthenium doped α-manganese oxide (Ru/α-MnO2) nanorods show outstanding electrocatalytic performance toward the hydrazine (N2H4) oxidation reaction (HzOR) in near-neutral media (weak alkaline and weak acid), which can be used to replace the energy-demanding OER for PEMWE. The as-prepared Ru/α-MnO2 is found to comprise abundant defects. When used to catalyze HzOR in the acid-hydrazine electrolyte (0.05 M H2SO4 + 0.5 M N2H4), it can deliver an anodic current density of 10 mA cm−2 at a potential as low as 0.166 V vs. reversible hydrogen electrode (RHE). Moreover, Ru/α-MnO2 exhibits remarkable corrosion/oxidation resistance and remains electrochemically stable during HzOR for at least 1000 h. Theoretical calculations and experimental studies prove that Ru doping elongates the Mn–O bond and produces abundant cationic defects, which induces charge delocalization and significantly lowers material’s electrical resistance and overpotential, resulting in excellent HzOR catalytic activity and stability. The introduction of N2H4 significantly reduces the energy demand for hydrogen production, so that PEMWE can be accomplished under remarkably low voltages of 0.254 V at 10 mA cm−2 and 0.935 V at 100 mA cm−2 for a long term without notable degradation. This work opens a new avenue toward energy-saving PEMWE with earth-abundant OER catalysts.
- A detailed study on the Fe-doped TiO 2 thin films induced by pulsed laser deposition routePublication . Meng, Lijian; Wang, Zhenhua; Yang, Liang; Ren, Weijun; Liu, Wei; Zhang, Zhidong; Yang, Tao; Santos, M.P. dosFe-doped TiO2 thin films are deposited both on the (100) oriented Si and glass substrates by pulsed laser deposition technique using Fe powder doped TiO2 ceramic target. The structural and optical properties of the film have been studied in detail. The degree of film crystallinity is investigated by X-ray diffraction and confirmed by Raman scattering measurements. The stoichiometry and chemical states of Fe, Ti and O are probed by X-ray photoelectron spectroscopy. The surface morphologies are observed by Scanning electron microscopy. The optical properties are studied by measuring the transmittance and the optical constants, the refractive index and the extinction coefficient. It is found that the substrate temperature is a key factor in determining the thin film structure which further influences the refractive index and the optical band gap of the film. An anatase structure emerges above 300 ºC while the rutile structure appears when the substrate temperature is higher than 500 ºC. Another result is that Fe exists in the deposited films as Fe3+ and the atomic concentration of Fe in the films is much lower than that in the source target.
- Effect of the compact Ti layer on the efficiency of dye-sensitized solar cells assembled using stainless steel sheetsPublication . Meng, Lijian; Ma, TingliTitanium films have been deposited on stainless steel metal sheets using dc magnetron sputtering technique at different substrate temperatures. The structure of the titanium films strongly depend on the substrate temperature. The titanium film deposited at the substrate temperature lower than 300 ◦C has a loose flat sheet grains structure and the titanium film prepared at the substrate temperature higher than 500 ◦C has a dense nubby grains structure. The DSSC assembled using stainless steel sheet coated with titanium film deposited at high substrate temperature has a low charge transfer resistance in the TiO2/Ti interface and results in a high conversion efficiency. The DSSC assembled using stainless steel sheet coated with titanium film deposited at temperature higher than 500 ◦C has higher conversion efficiency than that assembled using titanium metal sheet as the substrate. The maximum conversion efficiency, 2.26% is obtained for DSSC assembled using stainless steel sheet coated with titanium film deposited at 700 ◦C substrate temperature, which is about 70% of the conversion efficiency of the FTO reference cell used in this study.
- Efficient hydrogen production by saline water electrolysis at high current densities without the interfering chlorine evolutionPublication . Yu, Zhipeng; Xu, Junyuan; Meng, Lijian; Liu, LifengSeawater electrolysis powered by renewable energy sources has been proposed to be a potentially cost-effective approach to green hydrogen production. However, the long-standing issue regarding the chlorine evolution reaction (CER) that deteriorates the performance of electrocatalysts and other components of electrolyzers has been impeding the market adoption of direct seawater electrolyzers. Herein, we demonstrate that coupling the cathodic hydrogen evolution reaction (HER) with the hydrazine oxidation reaction (HzOR) taking place at the anode enables the alkaline–saline water electrolysis to occur at a high current density without the unfavorable, interfering CER. Using bifunctional carbon paper supported Co–Ni–P nanowires (Co–Ni–P/CP) as the cathode and anode, we have accomplished hydrogen production in the alkaline–saline–hydrazine electrolyte at 500 mA cm−2 with a small cell voltage of only 0.533 V and outstanding stability of 80 hours with minimal degradation.
- Evaluation of the CO2 Tolerant Cathode for Solid Oxide Fuel Cells: Praseodymium Oxysulfates/Ba0.5Sr0.5Co0.8Fe0.2O3-δPublication . Yang, Tao; Su, Chao; Wang, Wei; Meng, Lijian; Deng, Jiguang; Liu, Yu; Rathore, Shambhu; Shao, ZongpingAn effective praseodymium oxysulfate/Ba0.5Sr0.5Co0.8Fe0.2O3-δ composite cathode with high stability in 10% CO2/air was investigated. The addition of 50 vol.% of the praseodymium oxysulfate shows much better tolerance to CO2, and reduced the polarization resistance of the cathode to 1/3 comparing with that of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF). The CO2–temperature programmed desorption (TPD) and the electrochemical impedance spectroscopy (EIS) proved the effectiveness of the praseodymium oxysulfate phase to reduce the electrode resistance and to improve the CO2 resistance. The coefficient thermal expansion (CTE) rate along with the different volume percentage of praseodymium oxysulfate was also measured and it was found that the praseodymium oxysulfate helps to regulate the total CTE of the composite to match with doped-ceria electrolyte. It is proposed the higher acidity of Pr3+/4+ cations inhibited the reaction of alkaline earth metal oxide to form carbonates on the surface of the BSCF particles. The above results proved praseodymium oxysulfate/Ba0.5Sr0.5Co0.8Fe0.2O3-δ to be a highly active and stable cathode for solid oxide fuel cells.