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This paper focuses on the gradual performance and durability degradation behaviors of a direct methanol fuel cell (DMFC) with more than 3000 h lifetime. This work adopted a new DMFC test strategy and the entire lifetime test consisted of No.1-No.166 single operation. Stage-failure phenomenon occurred in the lifetime test, which indicated the existence of recoverable and non-recoverable degradations during the entire operation process. In-situ electrochemical tests were applied to the DMFC to analyse causes of durability and performance loss. When single cell came to failure, some recoverable methods were conducted to realize the recovery and improvement of DMFC performance and durability. As a result, during each single operation, continuous lifting pressure operation can realize the improvement of catalyst activity and optimization of mass transfer channel. Proton (H+) recovery method and increasing operation temperature can effectively solve the problem of internal resistance enlargement. According to the results of electrochemical monitoring, higher temperature results in the rapid degradation of catalytic layer activity, and lower temperature causes the increase of membrane resistance. N2 purging works as an effective method to eliminate the concentration polarization caused by cathode “water flooding” phenomenon. Based on these results, it can be concluded that the main degradation of DMFC successively changes with operation time, which mainly comes from internal resistance enlargement, cathode concentration polarization and final deactivation of catalyst at different operation stages. This work well explains the real long-term degradation behaviors of DMFC along with operation time, and provides several practicable methods for recovering DMFC performance and durability.

In this study, the deterioration of lithium iron phosphate (LiFePO 4 ) /graphite batteries during cycling at different discharge rates and temperatures is examined, and the degradation under high-rate discharge (10C) cycling is extensively investigated using full batteries combining with post-mortem analysis. The results show that high discharge current results in an instability of electrode/electrolyte interface and unstable solid electrolyte interphase (SEI) layers are expected to form on the newly exposed graphite anode surface, which cause sustainable consumption of active lithium and further lead to the performance degradation of active materials. For LiFePO 4 cathode, the initial capacity is largely recovered under low rate (0.1-0.2C), whereas a decline in the capability is observed at higher rates (0.5-3.0C). For graphite anode, half-cell study shows that considerable capacity loss occurs even at low rates. A small amount of Fe deposition is observed on graphite anode after cycling under 10C discharge at 55 °C. X-ray photoelectron spectroscopy (XPS) analysis confirms that a layer composed of lithium compounds is formed on the surface of anode, which can not participate in the reversible electrochemical reaction again. In addition, electrochemical impedance spectrum (EIS) measurements of half-cell indicate that the increased resistance of the positive electrode is suggested to be the root cause of power fading under high-rate discharge cycling, especially at high temperature.

Solid solution cathode materials 0.6Li[Li1/3Mn2/3]O2-0.4Li[Ni1/3Co1/3Mn1/3]O2 with different morphologies were synthesized by electrospinning and coprecipitation method respectively. The field-emission scanning electron microscope images verified the successful formation of nanofibers for electrospinning and nanoparticles for coprecipitation and the nanofibers showed larger specific surface area according to the Brurauer Emmerr Teller procedure. The X-ray powder diffraction patterns and the corresponding lattice parameter refinements showed that both samples can be indexed to hexagonal α-NaFeO2 layered structure with space group of R-3m. And the material prepared by electrostatic spinning method has a tight atomic arrangement in the layer yet the different dimensions do not influence the intercalation and deintercalation of lithium ion through the interlayer. The discharge capacity of nanofibers electrode is 302.3 mAh g−1 at 0.05 C and the initial columbic efficiency is 76.2%, which are higher than 282.7 mAh g−1 and 68.2% of the nanoparticles electrode. The nanofibers electrode also presented better cycleability and rate capability, especially performed capacity of 126.6 mAh g−1 at 5 C, much higher than that of 109.4 mAh g−1 for nanoparticles electrode. The step-by-step cyclic voltammetry revealed that the nanofibers electrode performs higher discharge voltage platform and enhanced discharge energy density. The excellent electrochemical performance of nanofibers electrode is ascribed to the better conductivity and superior lithium ion diffusion ability according to the electrochemical impedance spectrum measurement.

Aim ng at improving the high rate capability of spinel lithium manganese oxide (LiMn 2 O 4 ) cathode, ultralong LiMn 2 O 4 nanofibers are prepared by combination of electrospinning and sol-gel techniques. The effect of processing parameters, including the weight ratio of polyvinylpyrrolidone (PVP) to Li and Mn precursor, calcination temperature and time, on the morphology and the resultant cathode performance of spinel LiMn 2 O 4 nanofiber cathodes have been systematically investigated. Thermal behavior of LiMn 2 O 4 precursor nanofibers is performed on a differential scanning calorimetry-differential thermal analysis (DSC-DTA), indicating the spinel LiMn 2 O 4 began forming at 513 °C. The cathode materials appear porous “network-like” morphology with nanosize in diameter (∼170 nm), microsize in length (∼20 μm) and pure spinel structure, confirmed by scanning electron microscopy (SEM) and X-ray diffractometer (XRD). The ultralong LiMn 2 O 4 nanofiber cathode calcined at 700 °C for 8 h shows highest capacity and best rate capability. Its discharge capacity is 146 mAh g −1 at 0.1 C; more importantly, the discharge capacities are 112 mAh g −1 , 103 mAh g −1 and 92 mAh g −1 at high discharge rates of 10 C, 20 C and 30 C, respectively.

Lithium-rich layered cathode material Li1·2Ni0·13Co0·13Mn0·54O2 has attracted extensive attention owing to high specific capacity and energy density from its distinctive anionic redox chemistry. However, the material suffers from low Coulombic efficiency, serious capacity attenuation, severe voltage decay which can be ascribed to the irreversible oxygen loss and phase transformation. Herein, oxygen defects are induced through the pre-extraction of lithium and oxygen from Li2MnO3 component on the surface of the material accompanying with the generation of spinel structure via a facile method of hydrothermal reaction assisted with calcination clarified by X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). The material exhibits excellent electrochemical properties including enhanced initial Coulombic efficiency over 87% and prominent capacity retention of 89.7% after 100 cycles superior to those for the pristine, which are attributed to the fact that oxygen defects inhibit evolution of oxygen, and alleviate the lattice microstrain along consecutive delithiation/lithiation process to improve mechanical property of material. Besides, the Galvanostatic Intermittent Titration Technique (GITT) manifests that the material possesses superior dynamic condition. These results indicate that oxygen defects are beneficial to stabilize the lattice oxygen on the surface of the lithium-rich layered oxides for a high-performance cathode material for lithium-ion batteries.

An ethylene glycol (EG)-based approach has been developed for the synthesis of Pt/C catalysts with uniform Pt nanoparticles. A number of characterization techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical measurements are used to characterize the as-prepared Pt catalysts. The well-dispersed Pt nanoparticles with average size of approximate 2 nm could be obtained in the EG/water mixture with volume ratio of 1/1, which display higher activity for methanol oxidation than that of the Pt/C products prepared at other EG/water volume ratios (0:1, 2:1, and 1:0). In particular, the performance of the Pt nanoparticles prepared at EG/water volume ratio of 1/1 in the membrane electrode assembly for direct methanol fuel cells has also been evaluated and benchmarked by commercial Pt/C catalysts. This study offers a vivid example to synthesize Pt nanoparticles with fine size and good catalytic activity by simply tuning the solvent ratio in colloidal chemistry methods. (C) 2013 Elsevier Ltd. All rights reserved.

A novel wet method of (NH 4 ) 3 AlF 6 coating was explored to enhance the electrochemical performance of Mn-based solid-solution cathode material 0.5Li 2 MnO 3 ·0.5LiNi 1/3 Co 1/3 Mn 1/3 O 2 . The X-ray powder diffraction patterns show that the coating material is pure-phase (NH 4 ) 3 AlF 6 and both pristine and coated samples can be indexed to hexagonal α-NaFeO 2 layered structure with space group of R-3 m. The field-emission scanning electron microscope images and the energy dispersive X-ray spectroscopy show that (NH 4 ) 3 AlF 6 is successfully coated on the surface of active particle. The (NH 4 ) 3 AlF 6 coated electrodes exhibit improved electrochemical performance, for instance, the initial charge-discharge efficiency was promoted by 5% (NH 4 ) 3 AlF 6 coating, the 1 wt.% and 3 wt.% coated electrodes deliver elevated cycling ability which is ascribed to the lower resistance between electrode and electrolyte as indicated by AC impedance measurement at different cycles. In addition, the coated-electrodes also give enhanced rate capability particularly for 1 wt.% NAF-coated electrode performing surprising capacity of 143.4 mAh g −1 at 5 C higher than that of 109.4 mAh g −1 for pristine electrode. Furthermore, the 1 wt.% NAF-coated electrode also shows improved cycle and rate performance at 55°C.

N,N′-ethylenebis(salicylideneaminato) nickel(II), (Ni(salen)), which is the archetype of Schiff base metal complexes, was easily synthesized onto the surface of activated carbon (AC), mesoporous carbon (MC) and multi-walled carbon nanotube (MWCNT) by the route of linear potential sweep, respectively. The microstructure of the poly[Ni(salen)] homogeneously grown on the different carbon supports was evidenced by field emission scanning electron microscopy (FESEM). Growth parameters such as the apparent surface coverage and the doping level were investigated to confirm the effects of supports on the Ni(salen) polymerization. Diffusion coefficient was calculated from the chronoamperometry test to characterize the charge transport ability with the different pore size distributions of the supports, and the result indicates that MWCNT support with abundant macro porous is more active to the growth of the polymer and the charge diffusion. Capacitance performance of the electrodes was discussed by constant charge/discharge and alternating current impedance tests. A 3.79 times capacitance increase of the poly[Ni(salen)] electrode with MWCNT as a support was observed. The exceptional electrochemical properties make the use of MWCNT an attractive support for poly[Ni(salen)] as a supercapacitor material.

Electrocatalysts made of IrO2/SnO2 were prepared using the Adams method for solid polymer electrolyte (SPE) water electrolysis. The physicochemical properties of the catalyst were characterized via X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical properties of the catalyst were investigated using cyclic voltammetry (CV), electrochemical impendence spectroscopy (EIS), chronopotentiometry and Tafel curve measurements in 0.1 mol L−1 H2SO4 at room temperature. The test results showed that the catalytic properties of IrO2/SnO2 depended on the mass ratio of iridium to tin, and that the optimal mass ratio was 2:1. The optimized catalyst was applied to a membrane electrode assembly (MEA), and the stationary current–potential relationships were determined. With an IrO2/SnO2 (2:1) anode, a 40% Pt/C cathode and a total noble metal (Ir, Pt) loading of 1.2 mg cm−2, the terminal applied potential difference of the water electrolysis was 1.70 V at 2 A cm−2 and 80 °C.

An IrO 2 anode catalyst was prepared by using the Adams method for the application of a solid polymer electrolyte (SPE) water electrolyzer. The effect of calcination temperature on the physical–chemical properties and the electrochemical performance of IrO 2 were examined to obtain a low loading and a high catalytic activity of oxygen evolution at the electrode. The physical–chemical properties were studied via thermogravimetry–differential scanning calorimetry (TG–DSC), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The electrochemical activity was investigated by using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry in 0.1 mol L −1 H 2 SO 4 at room temperature. The optimum condition was found to be at the calcination temperature of 500 °C, where the total polarization reached a minimum at high current densities (>200 mA cm −2 ). The optimized catalyst was also applied to a membrane electrode assembly (MEA) and stationary current–potential relationships were investigated. With an optimized catalytic IrO 2 loading of 1.5 mg cm −2 and a 40% Pt/C loading of 0.5 mg cm −2 , the terminal applied potential difference was 1.72 V at 2 A cm −2 and 80 °C in a SPE water electrolysis cell.

Composite membranes for direct methanol fuel cells (DMFCs) were prepared by using Nafion115 membrane modification with polyvinyl alcohol (PVA), polyimide (PI) and 8-trimethoxysilylpropyl glycerin ether-1,3,6-pyrenetrisulfonic acid (TSPS). The performance of the composite membranes was evaluated in terms of water sorption, dimensional stability, thermal stability, proton conductivity, methanol permeability and cell performance. The proton conductivity was slightly decreased by 1–3% compared with Nafion115, which still kept the high proton conduction of Nafion115. The methanol permeability of Nafion/PI–PVA–TSPS composite membranes was remarkably reduced by 35–55% compared with Nafion115. The power density of DMFCs with Nafion/PI–PVA–TSPS composite membranes reached to 100 mW/cm 2 , exceeding that with Nafion115 (68m W/cm 2 ).

The effect of carbon type, carbon loading and microporous layer structure in the microporous layer on the performance of a direct methanol fuel cell (DMFC) at low temperature was investigated using electrochemical polarization techniques, electrochemical impedance spectroscopy, scanning electron microscope and other methods. Vulcan XC-72 carbon was found to be most suitable as a microporous layer for low temperature DMFC. Maximum fuel cell performance was obtained utilizing a microporous layer with carbon loading of 1.0 mg cm −2 when air was used as an oxidant. A membrane electrode assembly with 1.0 mg cm −2 Vulcan XC-72 carbon with 20 wt.% Teflon in the cathode and no microporous layer in the anode showed a maximum power density of 36.7 mW cm −2 at 35 °C under atmospheric pressure. The AC impedance study proved that a cell with a dissymmetrical microporous layer structure had lower internal resistance and mass transfer resistance, thus obtaining better performance.

By using a potentiostatic electrodeposition method, well-aligned ZnO nanorod arrays (ZNAs) were synthesized under different conditions. The effects of preparing conditions on the electrodeposition of ZNAs were systematically studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and absorbance spectroscopy. It is indicated that the electrodeposition parameters, such as electrodeposition potential, electrolyte pH, concentration of precursors, temperature of solution and electrodeposition time, have significant influence on the morphology, diameter, density and growth rate of ZNAs. The ZNAs, with well-defined crystallization, can be only obtained when the applied potential is controlled from −0.4 to −1.0 V. The growth temperature has great impact on the morphology of ZnO nanostructure but it is weakly related to the band gap (Eg) of ZNAs. The rod diameters can be monitored to some extent only by changing the concentration of the precursors. The electrolyte pH value has relative influence on the diameter of ZNAs. With the growth time increasing, ZNAs with high aspect ratio can be gained.

A simple impregnation-reduction method introducing Nd2O3 as dispersing reagent has been used to synthesize PtRu/C catalysts with uniform Pt-Ru spherical nanoparticles. X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analysis have been used to characterize the composition, particle size and crystallinity of the catalysts. Well-dispersed catalysts with average particle size about 2 nm are achieved. The electrochemically active surface area of the different PtRu/C catalysts is determined by the COad-stripping voltammetry experiment. The electrocatalytic activities of these catalysts towards methanol electrooxidation are investigated by cyclic voltammetry measurements and ac impedance spectroscopy. The in-house prepared PtRu/C catalyst (PtRu/C-03) in 0.5 M H2SO4 + 1.0 M CH3OH at 30 °C display a higher catalytic activity and lower charge-transfer resistance (Rt) than that of the standard PtRu/C catalyst (PtRu/C-C). It is mainly due to enhanced electrochemically active specific surface, higher alloying extent of Ru and the abundant Pt0 and Ru oxides on the surface of the PtRu/C catalyst.