On-chip fuel cell: micro direct methanol fuel cell of an air-breathing, membraneless, and monolithic design

This paper proposes a novel design for a microfuel cell as an on-chip power source and demonstrates its fabrication and operation to prove the concept. Its simple design is important from the viewpoints of fabrication (e.g., replication), integration, and compatibility with other microdevices. In testing, the prototype cell was able to generate electric power (maximum: ca. 1.4 microW) on methanol without pumps under both neutral and acidic conditions. As for the size, the electrode part of the cell (two cathodes and one anode) is 400 microns in width and 6 mm in length. The evaluation demonstrated that the proposed design is a promising on-chip power source for miniature devices.     

Preparation of electrolyte membranes for micro tubular solid oxide fuel cells

Yttria-stabilized zirconia (YSZ) micro tubular electrolyte membranes for solid oxide fuel cells (SOFCs) were prepared via the combined wet phase inversion and sintering technique. The as-derived YSZ mi- cro tubes consist of a thin dense skin layer and a thick porous layer that can serve as the electrode of fuel cells. The dense and the porous electrolyte layers have the thickness of 3-5 μm and 70-90 μm, respectively, while the inner surface porosity of the porous layer is higher than 28.1%. The two layers are perfectly integrated together to preclude the crack or flake of electrolyte film from the electrode. The presented method possesses distinct advantages such as technological simplicity, low cost and high reliability, and thus provides a new route for the preparation of micro tubular SOFCs.     

Ash-free coal as fuel for direct carbon fuel cell

This work describes the performance of the direct carbon fuel cell (DCFC) fuelled by ash-free coal. Employing coal in the DCFC might be problematic, mainly because of the ash deposition after the cell reactions. In the study, the carbonaceous ash-free component of coal is obtained, which is then evaluated as the DCFC fuel and compared with raw coal, active carbon, carbon black, and graphite. The electrolyte-supported SOFC structure is adapted to build the DCFC. The DCFC based on the ash-free coal fuel exhibits good performance with regard to the maximum power density, day-by-day measurements, and durability at continuous run. When the carbon fuels are internally gasified to H₂ and CO, the power density is generally much improved, compared to N₂ pyrolysis environment. The power generation is most likely related to the concentration of pyrolyzed gases as well as the electrochemical reactivity of the solid carbon.     

Membrane fluidity sensoring microbial fuel cell

A study has been performed to examine the effect of temperature and ethanolic stresses on the coulombic efficiency of a microbial fuel cell. The conventional-type fuel cell containing Gram-negative bacteria, Proteus vulgaris, was investigated as a model system. From current output measurements, it was found that the coulombic yields were altered by environmental stresses such as temperature shock or ethanol treatment to the bacteria. While high-temperature or ethanolic shock led to a remarkable decrement in coulombic output, the low-temperature shock induced a slight increase in microbial fuel cell efficiency. These results indicate that the membrane fluidity is affected considerably by environmental stress, which in turn affects the electron transfer process through the bacterial cell membrane to and from the electrode. This interpretation was confirmed by the cyclic voltammetric study of a mediator on an electrode surface modified with the lipids extracted from the membrane of P. vulgaris under the given stress. Markedly different electrochemical behaviors were observed depending on the environmental stress. A reciprocal relationship between coulomb output and the ratio of saturation/unsaturation of fatty acids has been observed. This is the first report, to our knowledge, that the structural adaptation of membrane fatty acids in response to the environmental shock can regulate the coulombic efficiency of a microbial fuel cell.     

千瓦级熔融碳酸盐燃料电池堆

1.5kW级熔融碳酸盐燃料电池（molten carbonate fuel cell,MCFC）堆由15个电极面积为250mm×400mm的单电池组成.系统采用内部分配方式供给气体,通过设在电池堆上、下部和四个侧面的电炉丝进行加热.在常压和650℃条件下,分别以氢气和空气作燃料和氧化剂,经过4次热循环,电池堆的开路电压依然保持在16.33V,在运行144h后,电池堆在150mAcm^-2放电时,其峰值输出功率为1.48kW,在工作电压10.5V（平均每个单电池的工作电压为0.7V）条件下输出功率基本不变,达到825W.     

Air-breathing laminar flow-based microfluidic fuel cell

This communication reports the design and characterization of an air-breathing laminar flow-based microfluidic fuel cell (LFFC). The performance of previous LFFC designs was cathode-limited due to the poor solubility and slow transport of oxygen in aqueous media. Introduction of an air-breathing gas diffusion electrode as the cathode addresses these mass transfer issues. With this design change, the cathode is exposed to a higher oxygen concentration, and more importantly, the rate of oxygen replenishment in the depletion boundary layer on the cathode is greatly enhanced as a result of the 4 orders of magnitude higher diffusion coefficient of oxygen in air as opposed to that in aqueous media. The power densities of the present air-breathing LFFCs are 5 times higher (26 mW/cm2) than those for LFFCs operated using formic acid solutions as the fuel stream and an oxygen-saturated aqueous stream at the cathode ( approximately 5 mW/cm2). With the performance-limiting issues at the cathode mitigated, these air-breathing LFFCs can now be further developed to fully exploit their advantages of direct control over fuel crossover and the ability to individually tailor the chemical composition of the cathode and anode media to enhance electrode performance and fuel utilization, thus increasing the potential of laminar flow-based fuel cells.     

Hierarchical micro/nano structures of carbon composites as anodes for microbial fuel cells

We demonstrate the utility of hierarchical micro/nano structures of electrically conductive carbon composites as anodes for microbial fuel cells (MFCs). To construct the hierarchical structures, carbon nanotubes (CNTs) were directly grown on micro-porous graphite felts at high densities. Using the CNT-modified felts as anodes, power outputs from MFCs were increased ～7 fold compared to those with bare graphite-felt anodes. We also show that this power improvement is sustainable even in MFCs operated with naturally occurring microbial communities. These results suggest the wide utility of the hierarchical micro/nano structures of conductive carbon composites for bio-electrochemical processes.     

Single fuel cell with supported LSM cathode

Single fuel cells with bilayer supported cathodes are manufactured and tested. The cathodes consist of a high-porous La_0.6Sr_0.4MnO₃ support with the thickness of approximately 1 mm and a functional composite layer with the thickness of 13?C15 ??m made of La_0.75Sr_0.2MnO₃ and 8YSZ. Voltammetric and power characteristics of single fuel cells with a supported cathode, thin-film YSZ electrolyte, and platinum cathode are determined. The conclusion as to the significant contribution into the polarization overpotential losses on the cathode is made on the basis of the measurements of electric fuel cell characteristics. It decreases significantly as a result of the supported cathode modification by praseodymium oxide. At 850°C and voltage of 0.81 V, electric power density of a fuel cell was 1.65 W/cm².     

Platinum-palladium catalysts for hydrogen fuel cell electrodes

Five series of Pt–Pd/C catalysts were prepared with different total metal loading and different atomic composition in Pt and Pd. The activity in electrooxidation of hydrogen were measured for all these catalysts. Electrooxidation of hydrogen is a structure insensitive reaction on platinum and a structure sensitive reaction on palladium. For bimetallic catalysts, curves of activity as a function of the composition of the catalyst can exhibit a maximum. Yet, metal loading can alter the atomic composition at which activities are maxima.

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Pt–Pd/C Pt Pd. . - - . . , .

     

Tungsten based electrocatalyst for fuel cell applications

A barrier to the widespread use of fuel cells is their reliance on expensive and scarce platinum and other precious metal catalysts. We present a catalyst for hydrogen oxidation, prepared electrochemically from high-purity aqueous tungstate salt precursors. The 24-electron reduction of ammonium metatungstate ((NH₄)₆[H₂W₁₂O₄₀]) yields a material with electrocatalytic activity towards the oxidation of hydrogen in acid electrolyte which approaches 25% that of platinum. Moreover, the tungstate catalyst is unusually tolerant to CO and H₂S contaminants in the fuel stream.     

Development of a lateral PEM fuel cell

A novel lateral PEM fuel cell was developed. The anodes and cathodes are situated nearby each other on a polymer electrolyte membrane. The transport of the protons takes place in a lateral way in the membrane. All manufacturing steps of the lateral PEM fuel cell were designed to meet the requirements of mass production. The base plate being the central part was made by means of polymer micro injection moulding.     

Supercapacitive operational mode in microbial fuel cell

Supercapacitive microbial fuel cells (SC-MFCs) are an emerging and promising field that has captured the attention of scientists in the past few years. This hybridization consists in the integration of supercapacitive features in the MFC electrodes to boost the performance output. The MFC anaerobic and aerobic enviroments induce self-polarization of the electrodes. The electrodes can be discharged galvanostatically and then self-recharged by the biotic/abiotic environments. During the discharge, two main phenomena named electrostatic and faradaic take place but the separation and quantification of the two contributes seems to be challenging. Galvanostatic discharges of SC-MFC produce at least one order of magnitude higher current/power compared with continuous operations, making it promising for pulsed type applications.     

一种无膜的自呼吸式直接醇燃料电池

采用液相化学还原法制备出多壁碳纳米管（MWCNT）负载的双金属PdNi纳米颗粒（PdNi／MWCNT）;采用水热法,在乙醇为溶剂和还原剂的体系中,制备出MWCNT负载的双金属AgCo纳米颗粒（AgCo／MWCNT）．碱性溶液中,PdNi／MWCNT对甲醇、乙醇、丙醇和丁醇的氧化具有稳定而强的电催化活性;AgCo／MWCNT对氧还原反应也表现出强的电活性,且对上述高浓度的醇具有较强的耐受力．以PdNi／MWCNT催化剂为阳极,同时将AgCo／MWCNT催化剂制备成气体扩散电极,组装成无离子交换膜的自呼吸式直接醇燃料电池．分别以甲醇、乙醇、丙醇和丁醇为燃料时,这种无膜的燃料电池均能稳定放电,且具有较高的功率密度及较大的输出电压．     

Combinatorial electrochemical screening of fuel cell electrocatalysts

Combinatorial methods have been applied to the preparation and screening of fuel cell electrocatalysts. Hardware and software have been developed for fast sequential measurements of cyclic voltammetric and steady-state currents in 64-element half-cell arrays. The arrays were designed for the screening of high-surface-area supported electrocatalysts. Analysis software developed allowed the semiautomated processing of the large quantities of data, applying filters that defined figures of merit relevant to fuel cell catalyst activity and tolerance. Results are presented on the screening of carbon-supported platinum catalysts of varying platinum metal loading on carbon (and thus, particle size) in order to demonstrate the speed and sensitivity of the screening methodology. CO electro-oxidation, oxygen reduction, and methanol oxidation on a series of such catalysts reveal clear trends in characteristics and activities. Catalysts with smaller particle sizes reveal structure in the CO stripping voltammetry that can be associated with edge sites in addition to the closely packed planes, and this is concomitantly reduced as particle size is increased. Specific activity for steady-state methanol oxidation and oxygen reduction at room temperature in H(2)SO(4) electrolyte is found to be a maximum for the largest particle sizes, in agreement with the literature. These trends in activity are significantly smaller than the differences in activities of promoted platinum-based alloy catalysts for the same reaction.     

以椰壳生物质炭为燃料的直接炭固体氧化物燃料电池

通过热裂解制得椰壳炭,表征了其结构和组成,并将其用于电解质为钇稳定化氧化锆（YSZ）、电极材料为银和钆掺杂氧化铈（Ag-GDC）的固体氧化物燃料电池（SOFC）的燃料,对所构成的直接炭固体氧化物燃料电池（DC-SOFC）的性能进行了测试研究。结果表明,所制得的椰壳炭颗粒粒径在微米级别,具有介孔结构,而且椰壳炭中含有K、Ca等元素,可用作Boudouard反应催化剂。当使用椰壳炭作为DC-SOFC燃料时,在800 ℃下电池最大功率密度为255 mW/cm²;负载Fe催化剂后,最大功率密度提升为274 mW/cm²。以0.5 A/cm²的恒电流放电,0.5 g负载Fe椰壳炭燃料电池能够连续工作17.6 h,燃料利用率为39%,表明椰壳炭作为DC-SOFC燃料具有优异的性能和潜力。     

Zeolite micromembranes

Free-standing silicalite-1 (Sil-1) zeolite micromembranes have been successfully fabricated onto silicon substrate. Gas permeation test using permanent gases (i.e., helium, hydrogen, argon and nitrogen) and hydrocarbons (i.e., methane and n-butane) indicates that the micromembranes have excellent permeance flux and high permselectivity.     

Characterization of a micro spiral flow cell for chemiluminescence detection

A 5.5 μl spiral micro-flow cell, mounted in front of a photomultiplier, is made from Teflon capillary (75 cm×100 μm ID) with two inlets for the CL reagent and carrier buffer and a waste outlet. It allows the rapid mixing of CL reagent and analyte and simultaneous detection of the emitted light. Using a flow rate of 25 μl/min for a 0.4 mM luminol-8 μM hemin solution (pH 11.6) and 50 μl/min of carrier buffer (pH 11.6), the slight exponential calibration curve for the flow injection–chemiluminescence (FI–CL) determination of H₂O₂ is 2.5–10 μM and the detection limit is 1.5 μM. The detection limit achieved by using a spiral flow cell is 24 times lower than that obtained from a conventional FI system with a low dead volume tee mixer and a 12 μl flow cell in a HPLC fluorometer with the source lamp off. This luminol CL detection method is successfully applied to the enzymatic determination of -lactate by FI. The lactate sample is mixed with polyethylene glycol (PEG)-stabilized lactate oxidase (LO) enzyme and then injected into the buffered (pH 7.5) carrier stream for CL detection of the H₂O₂ product. Using the optimal conditions of reaction temperature set to 37.5 °C and flow rates of 45 μl/min for the CL reagent and 60 μl/min for the carrier buffer, the calibration range for lactate is 5–50 μM and the detection limit is 2.9 μM. This method is applied to the determination of -lactate in beer.