Key Engineering Materials Vols. 645-646

Abstract: A kind of novel wind energy harvesting device with square ZnO piezoelectric thin films array structure has been investigated in the article. It is designed and fabricated for ambient wind energy on high buildings in city blocks particularly. Ordinary elements of wind energy harvesting are various windmills or turbines, they are usually expensive and noisy, and are not suitable to be used in the crowed city. The novel wind energy harvesting device is fabricated by Micro Electro Mechanical System (MEMS) technology in order to avoid the deficiencies mentioned above. The films array has a multilayer structure with five layers, and has a thickness of about 2.5μm. The maximum open circuit output voltage of the device reaches 2.81V, and its maximum output power density is 23.39nW/cm².

Abstract: A Cu doped V₂O₅ film for lithium-ion batteries is prepared by magnetron sputtered using a vanadium target. Coppers are doped in varying proportions to investigate the effect of doping on the electrochemical properties. In comparison, the surface of doped samples is smooth and uniform. And the results of electrochemical tests indicate that the proper doped films (V: Cu=8: 1 by area) exhibit better cycle performance, wider voltage plateaus and higher capacity than other samples.

Abstract: The traditional supercapacitor is made of activated carbon, which shows lower specific capacity and higher resistance. In this paper, we demonstrated preparation of high performance supercapacitor electrode materials based on activated carbon and conducting polymer polypyrrole (ppy). In order to obtain well dispersion of ppy in activated carbon for lower resistance of electrode, a high-speed agate beads milling process was used to mix the ppy and porous carbon powder. By controlling the synergistic effect between ppy and activated carbon, a uniform structure composite electrode was prepared and the performance of this composite based supercapacitor was investigated. Compared with pure activated electrode, the obvious electrochemical performance improvement was achieved in composite electrode after the introduction of ppy. It has been found that electrode based on this composite has a maximum specific capacitance about 159 F/g, which was higher than pure activated carbon, and exhibited low resistance about 3.35 Ohm. The cycle performance results revealed that a 142 F/g (more than 88% of initial capacitance) capacitance was kept in composite electrode after 1000 cycles charge/discharge process. We conclude that the excellent synergistic effect between activated carbon and ppy resulted in superior electrochemical performance of composite electrode. Furthermore, the simple preparing method of composite electrode for supercapacitor assembly has potential commercial applications.

Abstract: A catalyst-coated membrane (CCM) with structure and material gradient variation was deposited layer-by-layer (LbL) using electrohydrodynamic atomization (EHDA) deposition. This CCM contained 7 layers which is C cathode diffusion layer, Pt/C-C cathode transition layer, Pt/C cathode catalyst layer, Nafion membrane, Pt-Ru/C anode catalyst layer, Pt-Ru/C-C anode transition layer and C anode diffusion layer. The cathode and anode side were named as cathode and anode catalyst-diffusion layers, respectively. It was observed that the cathode and anode catalyst-diffusion layers presented the dendritic structure. Within the cathode and anode catalyst-diffusion layers, the Pt/C-C and Pt-Ru/C-C transition layer was more porous compared to the C layer, Pt/C layer and Pt-Ru/C layer. It was also shown that the EHDA LbL deposited CCM still presented close-packed structure after life test.

Abstract: Gallium atoms have been introduced into the framework of Y zeolite by treating the zeolite with an aqueous solution of ammonium hexafluoro gallate. The synthesized Y zeolite ([Ga]AlY) was characterized by means of X-Ray Diffraction (XRD), N₂ adsorption, Infrared spectrophotometer (IR) and Inductively Coupled Plasma (ICP). The results indicated that Ga has been substituted into the faujasitic framework. Hydrodesulfurization (HDS) of various model fuels containing about 500 μg/g sulfur has been studied over the [Ga]AlY. The activity of the [Ga]AlY catalysts on HDS reaction is highly affected by the temperature and kind of sulfide in model fuels. The conversion for thiophene, benzothiophene (BT) and dibenzothiophene (DBT) in model fuel 1, 2 or 3 was 81.2%, 60.7% and 37.2% respectively. Compared with the model fuel 1, 2 and 3, the conversion of every sulfide in model fuel 4 was much lower which can be due to the competitive adsorption between between the three of them.

Abstract: A 3D all-solid-state thin film lithium-ion microbattery (TFLM) with inverted pyramid arrays is fabricated by microfabrication technology. Compared with 2D TFLMs, the effective area of this 3D TFLM increases more than 30%. The 3D TFLM prepared by magnetron sputtering is composed of LiCoO₂ cathode, LiPON solid electrolyte, and copper doped SnO_x anode. The 3D TFLM is tested by electrochemical measurements, and the results show that it has reliable capacity and excellent performance.

Abstract: In this work, a quaternized polysulfone/PTFE/H₃PO₄ composite membrane was prepared and used to a high temperature sustainable proton exchange membrane (HTPEM). This HTPEM was prepared based on a porous PTFE membrane, which can sustainable for 200 °C. Pt/C nano-suspension was prepared and deposited layer-by-layer on the gas diffusion layer (GDL) using electrohydrodynamic atomization (EHDA) deposition technique for the formation of cathode and anode catalyst layers (CLs). The CLs presented well packed and porous features. This EHDA deposited cathode and anode CLs, GDL and HTPEM were assembled to a membrane electrode assembly (MEA) and high temperature methanol fuel cell (HTMFC). The results showed that low concentration and high flow rate of methanol aqueous solution led to the loss of phosphoric acid on HTPEM, which resulted in the decline of the HTPEM. When the concentration and the flow rate of the methanol aqueous solution was increased and reduced, respectively, the cell can work properly at a temperature of 170 °C.

Abstract: This paper studied the combined effect of anode and cathode current collectors on the behavior of water and methanol crossover in micro direct methanol fuel cells (μDMFC). A two-phase, two-dimensional, isothermal model was built to analyze the mass transport behavior in the membrane electrolyte assembly (MEA). The results show that the distribution of methanol exhibits uniform concentration feature over the anode porous area with the asymmetric anode and cathode current collectors. Also, lower water content gradient across the membrane is found. Comparing experiments were conducted to verify the simulation results. Two passive μDMFCs were fabricated and tested. The cells presents almost the same performance at relatively low methanol concentration. However, an increase of 10% cell performance (from 27.5 mW.cm^-2 for symmetric current collectors to 30.3 mW.cm^-2 for asymmetric current collectors) at 5 mol.L^-1 methanol solution was observed. This reveals that the couple of asymmetric current collectors induced the methanol to distribute uniformly and largely suppressed the water and methanol crossover.

Abstract: Harvesting ambient vibration energy through piezoelectric (PE) means is a popular energy harvesting technique. The merit of applying PE means to supply energy for microelectronic devices is that they can reduce the battery weight and possibly make the device self-powered by harvesting mechanical energy. This investigation will examine the energy generating performance of miniature PE cantilever beam through theoretical modeling, simulation and experiment testing. Through the theoretical analysis of the piezoelectric energy harvesting structure, the expression of open circuit voltage output is obtained. Using ANSYS software, the working performance of piezoelectric cantilever beam is analyzed. On the basis of theoretical analysis and simulation optimization, a set of experimental system is established to test the energy harvesting performance of the piezoelectric cantilever beam. The testing result shows that the harvested energy by the piezoelectric cantilever beam could supply electrical power to some micro electrical devices.

Abstract: By finite element simulation and experiment, this paper compares the performance of generators with magnetic material to generators without magnetic material (Fe) in its coil and analyzes the reason why there is difference between simulation results and experimental results. Experimental results present that under the same rotational speed, output voltage improves 60% with the addition of magnetic material in coil compared to generator without magnetic material in coil. We further discuss the feasibility to add magnetic material in coil, present the existed problems and improvement methods.