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This article presents an output power regulation system for micro fuel cells to help enhance the stability of the fuel cell in a portable micro power system. The structure of an MCU-controlled DC-DC converter is proposed. Then, the output characteristics of a selected fuel cell stack and the DC-DC converter’s power control functions are estimated by a system-level model. Based on the simulation results, the model provides a power regulation system which is implemented, and the test shows that it fulfills its intended function and the output power is regulated to a fixed level of 5 W–40 W with good efficiency.

Constructed wetlands (CWs) are ecosystems artificially designed to mimic natural wetland systems for the treatment of effluents. Its adoption can be given both at a decentralized level and as an economic alternative for a variety of pollution controls: agricultural, industrial, mines and urban drainage effluents. Although a CW has larger area requirements than conventional energy-intensive treatment technologies, they have several advantages: lower costs; energy savings; fewer operating and maintenance requirements; enable wild habitat and natural leisure areas; and allow the use of solar energy. Thus, the treatment of effluents through CWs is highly promising. This review aims to encompass the current literature and state-of-the-art on CWs applied on domestic wastewater in decentralized systems, explaining with visual examples their constructions, processes and modalities. [ABSTRACT FROM AUTHOR]

The main objective of this research study was to assess the energy potential of cocoa residues (pod and mucilage) as a direct energy source. Three dilutions were made per substrate. Crushed pod (< 0.5 mm) diluted in 1:25 (1.20 g), 1:50 (0.60 g), and 1:100 (0.30 g). Mucilage diluted in 1:4 (25%), 1:8 (12.50%), and 1:16 (6.25%). Measurements were performed in microbial fuel cells in three periods: acclimatization (one period) and electrical performance (two periods). During the third period, the highest electrical performance was observed in the 1.20 g pod dilution (voltage: 726 mV; power density: 11.75 mW / m2; coulombic efficiency: 0.33%) and in the 12.50% mucilage dilution (voltage: 474 mV; density power: 6.52 mW / m2; coulombic efficiency: 0.01%). It is concluded that the dilutions of pod (1.20 g) and mucilage (12.50%) showed the highest energy potential. [ABSTRACT FROM AUTHOR]

Highlights • We analyze the effectiveness of support schemes for micro fuel cells in Germany. • Focus on polymer electrolyte membrane fuel cells (PEMFCs) for private households. • Battery storage and latest market conditions taken into consideration. • The hourly simulation and investment decision model is shown to offer new insights. • The combination of PEMFC and battery storage is found not to be economically viable. Abstract In this paper, the effectiveness of support schemes for micro fuel cells in Germany is analyzed with regard to the latest market conditions, technical characteristics, and legislative changes. To this end, a dynamic model is used and applied to high-resolution household demand data. Specifically, we scrutinize whether polymer electrolyte membrane fuel cells are now a feasible investment option for residential usage in Germany or are likely to become so soon. Furthermore, we investigate whether electric energy storage could be a useful extension to the domestic fuel cell system by supplying short-term peak demand, and thus increasing self-consumption and potentially the overall economic merit. We find that the fuel cell technology analyzed is unlikely to become cost-competitive by 2020, and it may take quite some time to achieve a substantial market diffusion. We conclude that for the time being, electric energy storage in combination with a fuel cell system is not a worthwhile investment in a scenario where grid connection is assumed. [ABSTRACT FROM AUTHOR]

[Display omitted] • C-TiO 2 -g-PNIPAM polymer composite was prepared by polymerization method and coated on the fabric electrode surface. • It was observed that polymer composite structures were formed on and inside the fabric surface with SEM-EDX and mapping analysis. • The C-TiO 2 -g-PNIPAM/SC electrodes exhibited the best photocatalytic activity compared to the other electrodes, with a specific activity of 2.80 mA/cm2 under UV illumination. At present, poly N-isopropyl acrylamide (PNIPAM) polymer composites containing titanium dioxide (TiO 2) and carbon-TiO 2 (C-TiO 2) were designed for photocatalytic glucose electrooxidation by coating the textile fabric surface such as wool blended fabrics called Sign Cocana (SC), Valencia (VC), Dante (DT), and Broadway (BW). C-TiO 2 was obtained from TiO 2 in a furnace under hexane gas with a certain temperature and time. Polymer synthesis was realized by a polymerization method. The surface analyses of these polymer composite fabric electrodes were characterized by scanning electron microscopy-energy dispersive X-Ray (SEM-EDX) and mapping analysis. In addition, tear and breaking strengths were examined. Photocatalytic activity of the polymer composite electrodes was examined by cyclic voltammetry (CV). The C-TiO 2 -graft(g)-PNIPAM/SC electrode exhibited the best photocatalytic activity under UV illumination with a specific activity of 2.80 mA/cm2 both in the dark and compared to other fabric electrodes. In addition, it was observed that it exhibited the best stability and resistance by chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) analyses. It could be a promising anode electrode for photocatalytic fuel cells and wearable electronics. [ABSTRACT FROM AUTHOR]

We present two simple methods, with parallel and serial gas flows, for the stacking of microfabricated silicon fuel cells with integrated current collectors, flow fields and gas diffusion layers. The gas diffusion layer is implemented using black silicon. In the two stacking methods proposed in this work, the fluidic apertures and gas flow topology are rotationally symmetric and enable us to stack fuel cells without an increase in the number of electrical or fluidic ports or interconnects. Thanks to this simplicity and the structural compactness of each cell, the obtained stacks are very thin (~1.6 mm for a two-cell stack). We have fabricated two-cell stacks with two different gas flow topologies and obtained an open-circuit voltage (OCV) of 1.6 V and a power density of 63 mW·cm−2, proving the viability of the design.

In this paper, the effectiveness of support schemes for micro fuel cells (FC) in Germany is analyzed with regard to the latest market conditions and legislative changes. We analyze whether polymer electrolyte membrane fuel cells (PEMFCs) are a feasible investment option for domestic usage, or whether they are likely to become so soon. Furthermore, electrical energy storage could be a complement to the system by supplying short-term peak demand, and thus increasing self-consumption and potentially the overall economic merit. We find that PEMFCs will not have become a competitive technology by 2020, and it may take even more time to achieve a substantial market diffusion. Also, electric energy storage in combination with an FC system is found not to be a worthwhile investment in a grid-connected scenario. [ABSTRACT FROM AUTHOR]

The annealing temperature effects on nickel on reduced graphene oxide (Ni/rGO) catalysts for urea electrooxidation were investigated. Nickel chloride was directly reduced in an aqueous solution of graphene oxide (GO) followed by annealing under argon at 300, 400, 500, 600, and 700 °C, respectively. X-ray Diffraction (XRD) patterns revealed an increase in the crystallite size of the nickel nanoparticles while the Raman spectra displayed an increase in the graphitic disorder of the reduced graphene oxide at higher annealing temperatures due to the removal of oxygen functional groups. The Ni/rGO catalysts annealed at higher temperatures displayed oxidized nickel surface characteristics from the Ni 2p X-ray Photoelectron Spectra (XPS) due to the oxidation of the nickel from the oxygen functional groups in the graphitic lattice. In the half-cell testing, the onset potential of urea electrooxidation decreased while the urea electrooxidation currents decreased as the annealing temperature was increased. The nickel catalyst annealed at 700 °C displayed a 31% decrease in peak power density while the catalyst annealed at 300 °C displayed a 13% increase compared with the unannealed Ni/rGO catalyst in the micro direct urea/hydrogen peroxide fuel cells tests. [ABSTRACT FROM AUTHOR]

A simple and convenient small-scale fuel-cell test platform was created from a commercial compression fitting and graphite rod current collectors and used to conduct diagnostic tests on disk-shaped membrane-electrode assemblies (MEAs) fabricated from Nafion membranes and Nafion-impregnated platinum-on-carbon-cloth anodes and cathodes. A key advantage of this test platform is that it requires very little material, perhaps just a few milligrams, to conduct a fuel-cell test on a supported catalyst. Electrochemically-active surface area (ECSA) values for supported platinum on carbon-cloth electrodes were obtained by in-situ (in the fuel cell) and ex-situ (in liquid electrolyte) cyclic voltammetry on similarly-prepared electrodes, and values obtained by these methods were compared with each other to estimate the fraction of platinum catalyst contacted by the Nafion ionomer in the fuel-cell cathode. Polarization curves were acquired under controlled-potential conditions using slow-scan cyclic and sampled-current voltammetry and potential-step amperometry methods with conventional electroanalytical instrumentation. Tests performed using this platform are complementary to rotating disk electrode (RDE) voltammetry tests which also allow for catalyst testing on small amounts of material, albeit in the presence of liquid electrolyte, and are commonly used for initial screening of new fuel-cell catalysts. They are also complementary to conventional fuel-cell testing that is commonly performed on MEAs having active areas more than 100 times larger than that in the present cells. [ABSTRACT FROM AUTHOR]

Implantable biosensing is attractive for both medical monitoring and diagnostic applications. It is possible to monitor phenomena such as physical loads on joints or implants, vital signs, or osseointegration in vivo and in real time. Microelectromechanical (MEMS)-based generation techniques can allow for the autonomous operation of implantable biosensors by generating electrical power to replace or supplement existing battery-based power systems. By supplementing existing battery-based power systems for implantable biosensors, the operational lifetime of the sensor is increased. In addition, the potential for a greater amount of available power allows additional components to be added to the biosensing module, such as computational and wireless and components, improving functionality and performance of the biosensor. Photovoltaic, thermovoltaic, micro fuel cell, electrostatic, electromagnetic, and piezoelectric based generation schemes are evaluated in this paper for applicability for implantable biosensing. MEMS-based generation techniques that harvest ambient energy, such as vibration, are much better suited for implantable biosensing applications than fuel-based approaches, producing up to milliwatts of electrical power. High power density MEMS-based approaches, such as piezoelectric and electromagnetic schemes, allow for supplemental and replacement power schemes for biosensing applications to improve device capabilities and performance. In addition, this may allow for the biosensor to be further miniaturized, reducing the need for relatively large batteries with respect to device size. This would cause the implanted biosensor to be less invasive, increasing the quality of care received by the patient.

Silicon micro-hole arrays (Si-MHA) were fabricated as a gas diffusion layer (GDL) in a micro fuel cell using the micro-electro-mechanical-systems (MEMS) fabrication technique. The resistance temperature detector (RTD) sensor was integrated with the GDL on a bipolar plate to measure the temperature inside the fuel cell. Experimental results demonstrate that temperature was generally linearly related to resistance and that accuracy and sensitivity were within 0.5 °C and 1.68×10-3/°C, respectively. The best experimental performance was 9.37 mW/cm2 at an H2/O2 dry gas flow rate of 30/30 SCCM. Fuel cell temperature during operation was 27 °C, as measured using thermocouples in contact with the backside of the electrode. Fuel cell operating temperature measured in situ was 30.5 °C.

• A portable power based on a self-breathing µPEMFC with silicon membrane is proposed. • A novel electrical connection method is proposed by rotating series-wound fuel cell array. • Appropriate operating current range and hydrogen pressure of the stack are proposed. • Power matching and discharging time under standard charging power are studied. This study proposes a portable mobile power supply with a self-breathing micro-proton exchange membrane fuel cells (µPEMFCs) stack as the core for the application of µPEMFCs in portable charging power supplies. A porous silicon membrane etched with hydrofluoric acid was used to conduct protons. A series array of single cells was formed on a single printed circuit board (PCB) board. Four PCB boards are connected by rotation to form a PEMFC stack, and the cavity enclosed by the PCB boards was used to store hydrogen. The effects of hydrogen pressure and ambient conditions on stack performance were analyzed, and the discharging time of the stack was investigated at standard charging powers of 5 V and 1 A. The results revealed that the heat dissipation method of the self-breathing stack limits the operating current density of the stack. To ensure that the stack temperature was within 60–80 °C, the current density should be controlled within 600–820 mA·cm−2. The mobile power supply designed in this study can satisfy the standard charging power requirements of 5 V and 1 A for electronic devices. When the hydrogen pressure was 3 atm, the discharging time of the mobile power supply was 420 s, and the discharging time could be extended by increasing the hydrogen pressure. [ABSTRACT FROM AUTHOR]

Fuel cell technology is expected to play an important role in meeting the growing demand for distributed power generation. In an ongoing effort to meet increasing energy demand and to preserve the global environment, the development of energy systems with readily available fuels, high efficiency and minimal environmental impact is urgently required. A fuel cell system is expected to meet such demands because it is a chemical power generation device, which converts the chemical energy of a renewable clean fuel (e.g. Hydrogen) directly into electrical energy. Still a maturing technology, fuel cell technology has already indicated its advantages, such as its high-energy conversion efficiency, modular design and very low environmental intrusion, over conventional power generation equipment. Among all kinds of fuel cells, proton exchange membrane (PEM) fuel cells have many superior advantages. These advantages have sparked development efforts in various quarters of industry to open up new field of applications for PEM fuel cells. Three key issues limiting the widespread commercialization of the PEM fuel cells technology which are better performance, lower cost, and long cell life. The strategy of the Fuel Cell Research Center at the International Energy and Environment Foundation (IEEF) is to develop the PEM fuel cells to improve their lifetime with a much higher power density and lower cost. An overview of innovations in this field is presented using the published results of the center over the last decade. These innovative improvements will show a new scenario for the future fuel cell market of the next years. [ABSTRACT FROM AUTHOR]

The use of microfabricated solid oxide fuel cells (mSOFCs) is a promising technology for a low temperature operation (as low as 300 °C) with reduced start-up time and improved energy density. However, one of the limitations to widespread adoption of this technology has been due to the use of Pt electrodes, which exhibit poor bulk ionic conductivity and suffers from Ostwald ripening. Pt/YSZ is a promising alternative for providing both microstructural and electrochemical stability to the electrode layer. The objective of this research is to investigate the electrochemical performance and long term morphological stability of Pt/YSZ, by tailoring the composition, porosity, thickness, and functional-graded distribution, for use as a high performance mSOFC cathode. The Pt/YSZ cathodes were deposited through a co-sputtering process. An increase in the oxygen reduction reaction (ORR) charge transfer kinetics are observed with the Pt/YSZ cathode versus pure Pt, along with a significantly more stable morphology over a 24hr period. Although the mSOFC performance is found to be sensitive to Pt/YSZ composition at the TPB interface, the mass diffusion of oxygen through the cathode is determined to be the rate limiting step. The increased porosity in the Pt/YSZ led to more efficient oxygen diffusion and higher mSOFC performance. [ABSTRACT FROM AUTHOR]

Micro-fuel cells are considered as promising electrochemical power sources in portable electronic devices. The presence of microelectromechanical system (MEMS) technology makes it possible to manufacture the miniaturized fuel cell systems. The majority of research on micro-scale fuel cells is aimed at micro-power applications. Performance of micro-fuel cells are closely related to many factors, such as designs and operating conditions. CFD modeling and simulation for heat and mass transport in micro PEM fuel cells are being used extensively in researches and industrial applications to gain better understanding of the fundamental processes and to optimize the micro fuel cell designs before building a prototype for engineering application. In this research, full three-dimensional, non-isothermal computational fluid dynamics model of a micro proton exchange membrane (PEM) fuel cell with nature inspired flow field designs has been developed. The design inspired from the existed biological fluid flow patterns in the leaf. This comprehensive model accounts for the major transport phenomena such as convective and diffusive heat and mass transfer, electrode kinetics, transport and phase-change mechanism of water, and potential fields in a micro PEM fuel cell. The model explains many interacting, complex electrochemical, and transport phenomena that cannot be studied experimentally. [ABSTRACT FROM AUTHOR]

We present two simple methods, with parallel and serial gas flows, for the stacking of microfabricated silicon fuel cells with integrated current collectors, flow fields and gas diffusion layers. The gas diffusion layer is implemented using black silicon. In the two stacking methods proposed in this work, the fluidic apertures and gas flow topology are rotationally symmetric and enable us to stack fuel cells without an increase in the number of electrical or fluidic ports or interconnects. Thanks to this simplicity and the structural compactness of each cell, the obtained stacks are very thin (~1.6 mm for a two-cell stack). We have fabricated two-cell stacks with two different gas flow topologies and obtained an open-circuit voltage (OCV) of 1.6 V and a power density of 63 mWcnT2, proving the viability of the design. [ABSTRACT FROM AUTHOR]

Abstract: A micro space power system using micro fuel cell was developed for nano-satellites. The power system was fabricated using microelectromechanical system (MEMS) fabrication technologies. Polymer electrolyte membrane (PEM) fuel cell was selected in consideration of space environment. Sodium borohydride (NaBH4) was selected as a hydrogen source while hydrogen peroxide (H2O2) was selected as an oxygen source. The power system consists of a micro fuel cell, micro-reactor, micro-pump, and fuel cartridges. The micro fuel cell was fabricated on a light-weight and corrosion-resistant glass plates. The micro-reactor was used to generate hydrogen from NaBH4 alkaline solution via a catalytic hydrolysis reaction. All components such as micro-pump, fuel cartridges, and auxiliary battery were integrated for a complete power system. The storability of NaBH4 solution was evaluated at −25°C and the performance of the micro power system was measured at various operating conditions. The power output of micro power system reasonably followed up the given electric load conditions. [Copyright &y& Elsevier]

We present a simple method for microfabricating microfluidic devices by wet etching of bulk aluminum wafers. Aluminum wafers are identical to silicon wafers in terms of dimensions and can easily be processed in standard clean room processes like lithography, etching, and thin film deposition. Aluminum thin film wet etching in phosphoric acid-based etchants is well established. In this paper, it is extended to much greater depths than before. 80 μm deep structures have been fabricated. A hydrogen-fueled micro fuel cell has been microfabricated from bulk aluminum. These fuel cells achieved very high current densities of 1.1 A cm-2 and power density up to 228 mW cm-2. Considering the simplicity of bulk aluminum micromachining, these results are very encouraging. [ABSTRACT FROM AUTHOR]

Micro-fuel cells are considered as promising electrochemical power sources in portable electronic devices. The presence of microelectromechanical system (MEMS) technology makes it possible to manufacture the miniaturized fuel cell systems. The majority of research on micro-scale fuel cells is aimed at micro-power applications. Performance of micro-fuel cells are closely related to many factors, such as designs and operating conditions. CFD modeling and simulation for heat and mass transport in micro PEM fuel cells are being used extensively in researches and industrial applications to gain better understanding of the fundamental processes and to optimize the micro fuel cell designs before building a prototype for engineering application. In this research, full three-dimensional, non-isothermal computational fluid dynamics model of a micro proton exchange membrane (PEM) fuel cell has been developed. This comprehensive model accounts for the major transport phenomena such as convective and diffusive heat and mass transfer, electrode kinetics, transport and phase-change mechanism of water, and potential fields in a micro PEM fuel cell. The model explains many interacting, complex electrochemical, and transport phenomena that cannot be studied experimentally. Three-dimensional results of the species profiles, temperature distribution, potential distribution, and local current density distribution are presented and analysed, with the focus on the physical insight and fundamental understanding. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new and novel planar array module. [•] Easy handling/assembling as well as fast fabrication upon its commercialization. [•] Compact configuration design and geometry could be secured. [ABSTRACT FROM AUTHOR]

Abstract: This paper explores the effects of fuel chemistry and pellet configuration (void fraction, particle size) on MFC reaction rate and yield. Candidate hydrides were evaluated based on their suitability in a MFC using water vapor-driven hydrolysis, and lithium aluminum hydride (LiAlH4) was selected for evaluation. Hydrogen evolution tests were performed in a hydrolysis reactor with three particle size distributions (5 μm, 20 μm, and 50 μm in mean diameter) and at three initial void fractions (86%, 71%, 43%). Void fraction and particle size are found to affect reaction rates, but have no impact on reaction yields (all were ∼100%) within the range tested. Higher void fraction and smaller particle size are correlated with faster reaction rates. Electrical discharge tests are performed on a MFC at a constant potential of 1.2 V at three particle sizes (5 μm, 20 μm, 50 μm) at a 32% initial void fraction. Tests in the MFC reveal the strong impact of particle sizes on reaction rates, and show that reaction rates decrease with increasing particle size. Reaction yields are lower (90–93%) in the MFC, which is attributed to a small hydrogen leak. The energy density of the MFC is 1003 Wh L−1, the highest reported to date. [Copyright &y& Elsevier]

Abstract: Micro fuel cells (MFCs) defined by an average power output of less than 10 W offer the potential to improve the runtime and performance of portable devices by providing significantly higher energy density (energy per unit volume) than batteries. However, despite several decades of intense research and development, MFCs have yet to realize this potential, and no MFC technology has achieved broad market adoption. We report in this article an MFC which utilizes water-vapor-driven hydride hydrolysis, fuel cell water recovery, and a self-regulating pneumatic valve to achieve higher energy density than conventional batteries. Integrated MFC prototypes were developed and tested, and achieved 987 Wh L−1. Further improvements in energy density are possible by optimizing the fuel pellet configuration (density, geometry, particle size and distribution, etc.). Energy density greater than 2000 Wh L−1 may be possible in optimized MFCs discharged at low power. [Copyright &y& Elsevier]

A novel thin‐film direct hydrogen peroxide/borohydride micro fuel cell with a high operating voltage of 1.6 V is fabricated by a facile method. [ABSTRACT FROM AUTHOR]

Abstract: Epitaxial model-type platinum (Pt) film electrodes with a high three-phase boundary (tpb) density on single crystalline yttria-stabilized zirconia electrolyte, YSZ(111), are characterized electrochemically in air at a temperature of 673K – which is comparatively low for the system Pt(O2)/YSZ. By combining different electrochemical measurements including impedance spectroscopy (EIS) with and without applied potential bias, cyclic voltammetry (CV), and ‘steady state’ current-overpotential characteristics (I–η curves) with different sample starting conditions, the impact of annealing time and pre-polarization on the polarization resistance and on the oxygen exchange rate are investigated in detail. A model, based on the electrochemical control of thermally grown Pt oxide, is suggested to explain the experimental results. It is assumed that Pt oxide passivates the electrode and decreases the electrocatalytic activity of Pt for the oxygen exchange reaction. Additionally, it is suggested that Pt oxide has a similar passivating effect as in aqueous electrochemistry, despite the higher temperature. Additionally, blocking impurities at the tpb and activating morphological changes are discussed. Together with the experimental results the model provides new insights in the observed electrode processes and offers routes to improve the electrode performance of Pt(O2)/YSZ at low temperature. This might be of significant interest e.g. for μ-solid oxide fuel cells (micro-SOFCs). [Copyright &y& Elsevier]

Abstract: A micro fuel cell system designed to power complex autonomous systems with dynamic pulse-shaped loads like wireless sensor nodes is presented in this work. The requirements posed by the corresponding pulse load profiles are considered for the design of the passive self-breathing micro fuel cell. The performance of the fuel cell is mainly affected by the oxygen and water management which is influenced by the openings in the cathodic current collector. Due to the comparatively low average cell current the performance can be strongly improved by retaining water within the cell using a reduced opening ratio and thus improving the ionic conductivity of the electrolyte. The impact of the opening ratio is studied in the range between 54% and 0.007%. The total active area of the fuel cell is only 0.1 cm2. Prototypes are realized using printed circuit board technology and wet chemical etching of the micro-structured current collectors. The cells were characterized with an exemplary load profile with a 10 ms load pulse and a 1 s pulse period. Successful operation was demonstrated for all cells for different current densities. A significant power improvement was achieved by reducing the opening ratio down to 0.3%. Under these circumstances a power density of 220 mW cm−2 could be generated during the pulse. This is more than twice in comparison to cells with large opening ratios of 54% where only approx. 100 mW cm−2 was obtained. [Copyright &y& Elsevier]

Abstract: This paper reports a novel assembly method using multi-layer bonding technique for micro direct methanol fuel cells (μDMFCs) and their stacks. The new approach shows considerable merit on maneuverability and reliability, and is beneficial to decreasing the internal resistance of the μDMFC. The prototype of μDMFC assembled generates a high power density of 20.29mW/cm2 and a power of 45.6mW with high methanol concentration at room temperature. Benefiting from the assembly process, a new μDMFC tri-cell stack with an expandable cell amount is designed, fabricated and assembled, which has a maximum power of 86.92mW with 2M methanol concentration at room temperature. Moreover, this work presents a promising strategy for the assembly of microfluidic devices with laminated structures. [Copyright &y& Elsevier]

Abstract: Since the 90''s, porous silicon has been studied and implemented in many devices, especially in MEMS technology. In this article, we present a new approach to build miniaturized proton exchange membrane micro-fuel cells using porous silicon as a hydrogen diffusion layer. In particular, we propose an innovative process to build micro fuel cells from a “corrugated iron like” 3D structured porous silicon substrates. This structure is able to increase up to 40% the cell area keeping a constant footprint on the silicon wafer. We propose here a process route to perform electrochemically 3D porous gas diffusion layers and to deposit fuel cell active layers on such substrates. The prototype peak power performance was measured to be 90 mW cm−2 in a “breathing configuration” at room temperature. These performances are less than expected if we compare with a reference 2D micro fuel cell. Actually, the active layer deposition processes are not fully optimized but this prototype demonstrates the feasibility of these 3D devices. [Copyright &y& Elsevier]

Abstract: A new proton conducting membrane was prepared by confining sub-nanoliter volumes of perfluorosulfonic acid (PFSA) polymer within rigid pores cladded with zeolite layers. Tests showed membrane-electrode assembly (MEA) made of confined Nafion PFSA-HZSM-5/Sil-1 structured composite membrane delivered an order of magnitude higher MPD (maximum power density) compared to a standard Nafion 117 MEA in a hydrogen PEMFC at high temperature operation under dry feed conditions. Similarly, 900% higher MPD was obtained from direct methanol fuel cell (DMFC) made of the new membrane. The zeolites are believed to play an active role in the water and methanol managements through adsorption and transport, and the confinement of the PFSA within zeolite environment changes its microstructure resulting in the improved thermal stability. [Copyright &y& Elsevier]

Abstract: A micro PEM fuel cell system with a NaBH4 hydrogen generator is presented. The micro PEM fuel cell contained glass bipolar plates and a microreactor that initiated a catalytic hydrolysis reaction in the NaBH4 solution. The entire system was developed using MEMS technology. The total system comprised the micro PEM fuel cell, a catalytic microreactor, hydrogen separator, micropump, and a NaBH4 solution cartridge. The microreactor generated a hydrogen flow rate of 16.1ml/min from a NaBH4 feeding rate of 60μl/min. The conversion efficiency was 98.8% and the reactor temperature was 41°C during the operation. The maximum power output of micro fuel cell was 174.6mW for a current of 0.45A. Cyclic performance tests were conducted in order to assess the practical operation of the micro fuel cell system. [Copyright &y& Elsevier]

Abstract: Zeolites are increasingly used in fuel cell, from fuel conversion and conditioning to membrane additives as well as support for electrocatalysts. Zeolites’ ionic conductivity and capacity for water adsorption and retention were exploited to create zeolite and zeolite-PFSA proton conducting membranes for PEMFC. HZSM-5 micromembranes of different Si/Al ratios (from ∞ for Sil-1 to 30) were fabricated in a regular array on silicon followed by assembly and test for fuel cell performance. HZSM-5 with high aluminum content exhibits good proton conductivity and better PEMFC performance that approaches that of Nafion MEA. A rational approach in the design of structured HZSM-5-PFSA composite membrane was demonstrated. The PFSA was confined in subnanoliter volumes within zeolite sleeves to obtain self-humidifying membrane and enhanced PEMFC performance (i.e., up to nine-fold in MPD) at elevated temperatures (i.e., up to 100°C) and dry conditions. Higher water retention and improved membrane thermomechanical properties are believed to be responsible. [Copyright &y& Elsevier]

An ever increasing demand for packaging more energy on-board to meet the needs of power hungry microsystems is driving the miniaturization of power generators. We report a fully integrated Power MEMS, in the 10-μL size, designed to deliver high energy and power densities. On-board hydrogen production and an efficient control scheme that facilitates integration with a fuel cell membrane electrode assembly are key elements for micro energy conversion. A millimeter-scale reactor produces hydrogen by hydrolysis of CaH and LiAlH, to yield energy densities of the order of 200 Whr/L. A passive microfluidic control scheme, incorporating surface tension to pump water in a microchannel for hydrolysis and microvalve control using hydrogen backpressure, facilitates delivery and regulation and eliminates bulky auxiliaries that consume parasitic power. We tested the ability of this control scheme to improve uniformity of power delivery during long periods of lower demand, with fast switching to mass transport regime on the order of seconds, and realized peak power density of up to 391.85 W/L. Prototypes have been tested for duty periods from 2-48 h, with multiple switching of power demand in order to establish performance across multiple regimes. Critical to the realization of the integrated power MEMS, and its energy and power density, are effects of water transport and byproduct hydrate swelling on hydrogen production in the microreactor. While CaH showed superior hydrogen release kinetics that enhances power density, LiAlH provided greater energy density due to reduced byproduct expansion that permitted increased hydrogen production. [ABSTRACT FROM AUTHOR]

Abstract: A fully-integrated micro PEM fuel cell system with a NaBH4 hydrogen generator was developed. The micro fuel cell system contained a micro PEM fuel cell and a NaBH4 hydrogen generator. The hydrogen generator comprised a NaBH4 reacting chamber and a hydrogen separating chamber. Photosensitive glass wafers were used to fabricate a lightweight and corrosion-resistant micro fuel cell and hydrogen generator. All of the BOP such as a NaBH4 cartridge, a micropump, and an auxiliary battery were fully integrated. In order to generate stable power output, a hybrid power management operating with a micro fuel cell and battery was designed. The integrated performance of the micro PEM fuel cell with NaBH4 hydrogen generator was evaluated under various operating conditions. The hybrid power output was stably provided by the micro PEM fuel cell and auxiliary battery. The maximum power output and specific energy density of the micro PEM fuel cell system were 250 mW and 111.2 W h/kg, respectively. [Copyright &y& Elsevier]

Abstract: In this study, we demonstrate the possibility of using macroporous silicon as a hydrogen diffusion layer in integrated planar and 3D proton exchange membrane micro fuel cells (PEMFC). In this context, silicon electrochemical etching is presented as an interesting alternative to costly deep reactive ion etching techniques. In the case of planar PEMFC, a maximum density power of 250mW/cm2 was measured. The second objective of our work is to enhance the fuel cell active surface. One way to increase power densities is to chemically texture the surface of the GDL supporting the fuel cell. Then, the porous silicon electrochemical etching process is applied to these 3D silicon substrates. Flow rates measured through these fully porous 3D structures are compared with planar diffusion layers. [Copyright &y& Elsevier]

Abstract: In recent years, integrated fuel cell (FC) type primary and secondary batteries attracted a great deal of attention as integrated on-chip power sources due to their high theoretical power densities. Unfortunately, the costs of these devices have been rather high. This is partially due to the involved clean-room processes, but also due to the fact that these devices generally rely on expensive precious-metals such as Pd and Pt. Therefore we developed a novel integrated FC type accumulator that is based on non-precious-metals only. The key component of the presented accumulator is its alkaline polymer electrolyte membrane that allows not only the usage of a low-cost AB5 type hydrogen storage electrode, but also the usage of La0.6Ca0.4CoO3 as a precious-metal free bifunctional catalyst for the air-breathing electrode. Additionally the presented design requires only comparatively few cleanroom processes which further reduces the overall production costs. Although abdicating precious-metals, the presented accumulator shows an open circuit voltage of 0.81V and a maximum power density of 0.66mWcm−2 which is comparable or even superior to former precious-metal based cells. [Copyright &y& Elsevier]

Over the past decade, the direct methanol fuel cell (DMFC) has been considered as a potential candidate of power sources for portable electronics due to its high energy density and environmental friendly operation. However, the use of diluted fuel loading and active fuel mixer/pump limits the DMFC's efficiency and operating time dramatically. The disadvantages become more severe in microscale DMFCs which require high conversion efficiency within a small physical space to meet the strict working specifications. In this paper, a low-power micro fuel supplier with programmable concentration regulation was designed and fabricated by using microelectromechanical system technology. The prototype adopted surface-tension pumping as the primary driving force to deliver fuel at zero power consumption. In addition, a well-arranged microfluidic capillary network was used to regulate the fuel concentration. A pulse-power actuated bubbler switch was embedded in the capillary network to achieve the liquid flow control dynamically and to adjust the fuel concentration for micro-DMFC ( \muDMFC) reaction. Both electrolysis and thermal bubble actuations were investigated in this paper for their effective operations in the prototype. The advantage of precise and low-power fuel regulation within a compact system volume makes the proposed fuel delivery subsystem a suitable candidate for future on-chip \muDMFC development. [ABSTRACT FROM AUTHOR]

Implantable biosensing is attractive for both medical monitoring and diagnostic applications. It is possible to monitor phenomena such as physical loads on joints or implants, vital signs, or osseointegration in vivo and in real time. Microelectromechanical (MEMS)-based generation techniques can allow for the autonomous operation of implantable biosensors by generating electrical power to replace or supplement existing battery-based power systems. By supplementing existing battery-based power systems for implantable biosensors, the operational lifetime of the sensor is increased. In addition, the potential for a greater amount of available power allows additional components to be added to the biosensing module, such as computational and wireless and components, improving functionality and performance of the biosensor. Photovoltaic, thermovoltaic, micro fuel cell, electrostatic, electromagnetic, and piezoelectric based generation schemes are evaluated in this paper for applicability for implantable biosensing. MEMS-based generation techniques that harvest ambient energy, such as vibration, are much better suited for implantable biosensing applications than fuel-based approaches, producing up to milliwatts of electrical power. High power density MEMS-based approaches, such as piezoelectric and electromagnetic schemes, allow for supplemental and replacement power schemes for biosensing applications to improve device capabilities and performance. In addition, this may allow for the biosensor to be further miniaturized, reducing the need for relatively large batteries with respect to device size. This would cause the implanted biosensor to be less invasive, increasing the quality of care received by the patient. [ABSTRACT FROM AUTHOR]

Abstract: A microreactor for hydrogen generation from sodium borohydride was designed and fabricated in the present study. The microreactor has three photosensitive glasses, including the cover, the reactor layer and the base. A nickel form was inserted in the reactor layer as a catalyst support. A Co–P–B catalyst for sodium borohydride hydrolysis was coated on the nickel form by electroless plating. The characteristics of the catalyst were studied using SEM and EDS analysis. The hydrogen generation rate of the microreactor was measured under a variety of conditions and made up 15.6 ml/min at a temperature of 40 °C. The generated hydrogen was supplied to a micro fuel cell with a maximum power output of 157 mW at a current of 0.5 A. [Copyright &y& Elsevier]

Abstract: There is an ever – increasing demand for more powerful, compact and longer – life power modules for portable electronic devices for leisure, communication and computing. Micro fuel cells have the potential to replace battery packs for portable electronic appliances because of their high power density, longer operating and standby times, and substantially shorter recharging times. However, fuel cells have stringent operating requirements, including no fuel leakage, water formed in the electrochemical reactions, heat dissipation, robustness, easy and safe use, and reliability. Due to the large market potential, several companies are currently involved in the development of micro fuel cells. For application of fuel cells as a battery charger or in a battery replacement market, the cells require simplification in terms of their construction and operation and must have volumetric power densities equivalent to or better than those of existing battery power packs. This paper discusses results of investigation on methods and materials for direct hydrogen micro fuel cells as well as the lifetime performance of single cells and 2 We arrays. The paper also reviews the global technology development status for the direct hydrogen micro fuel cell and compares its salient features with other types of micro fuel cells. [Copyright &y& Elsevier]

Abstract: The effects of electrode and electrolyte materials used in single-chamber micro solid oxide fuel cells (SC-μSOFCs) with coplanar electrodes on the cell performance have been little investigated so far. In this study, different combinations of conventional SOFC materials such as NiO–YSZ (ZrO2 doped with 8mol% Y2O3) and NiO–GDC (Ce0.9Gd0.1O1.95) anodes as well as (La0.8Sr0.2)0.98MnO3 (LSM)–YSZ and (La0.6Sr0.4)0.995(Fe0.8Co0.2)O3 (LSCF) cathodes in the form of coplanar interdigitated electrode patterns on YSZ electrolytes were compared at 700°C in methane–air mixtures with a methane-to-oxygen ratio of R mix =2. The best cell performance was obtained for coplanar NiO–YSZ anodes combined with LSM–YSZ cathodes, whereas the NiO–GDC//YSZ//LSCF cell delivered the lowest power output. Chemical interaction between LSM–YSZ cathodes and adjacent anodes during sintering was identified to cause blackening of the anode parts in close vicinity to the cathode, and manganese was detected in the anode, probably through diffusion from the LSM cathode into the anode. In addition to cell performance, the proper choice of electrode materials for coplanar electrodes appears to be important because of the possible chemical interactions between the closely-spaced electrodes. [Copyright &y& Elsevier]

Abstract: Multi walled carbon nanotubes (MWNTs) have been synthesized by chemical vapour deposition technique using AB3 alloy hydride catalyst. Platinum supported MWNTs (Pt/MWNTs) and platinum-tin supported MWNTs (Pt–Sn/MWNTs) electrocatalysts have been prepared by chemical reduction method. MWNTs and electrocatalysts have been characterized by powder X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), high resolution TEM (HRTEM) and Energy dispersive X-ray analysis (EDAX). The anode and cathode electrodes for DEFC have been fabricated using Pt–Sn/MWNTs and 1:1 Pt/MWNTs + Pt/C electrocatalyst respectively. Performances of Direct Ethanol Fuel Cell (DEFC) with these electrodes have been studied at different temperatures of the membrane electrode assembly at ambient fuel conditions and the results have been discussed. A maximum power density of 38.6 mW/cm2 at a current density of 130mA/cm2 is obtained. A six cell planar Micro Direct Ethanol Fuel Cell (μ-DEFC) stack was also constructed using these electrocatalysts and etched printed circuit boards as anode and cathode current collectors. A maximum power density of 2 mW/cm2 was achieved when the μ-DEFC was operated in air breathing mode at room temperature. This enhancement of the performance may be attributed to dispersion and accessibility of MWNTs support and Pt–Sn in the electrocatalyst mixture for ethanol oxidation reaction. [Copyright &y& Elsevier]

Abstract: In this paper, the influence of current collector open ratio on the performance of a passive micro direct methanol fuel cell is evaluated. The device is based on a hybrid approach consisting of two microfabricated silicon current collectors assembled together with a commercial membrane electrode assembly. The characterization was performed by measuring polarization curves of the fuel cell using current collectors with different open ratios on anode and cathode. Results show that the way in which the open ratio of current collectors is combined has an effect not only on the output power but also on the repeatability of polarization curves. This study allows the setting of some general design rules for current collectors of passive micro direct methanol fuel cells. [Copyright &y& Elsevier]

Abstract: MEMS fuel cell system was designed and fabricated for a portable power source in the present study. The system consists of a methanol–steam reformer, catalytic combustor, preferential oxidation (PROX) reactor, and polymer electrolyte membrane fuel cell (PEMFC). Methanol reformer is an essential part for hydrogen supply, in which a pre-heater, vaporizing/reforming channels and catalytic combustor were integrated. All components were fabricated using MEMS fabrication technologies combined with catalyst loading processes. Performance of the MEMS fuel cell system was measured with the optimal conditions of the reformer and PROX. Power density was 195mW/cm2 when the potential was 0.64V. The performance was low compared to the result for pure hydrogen because the feed at the fuel cell included undesired CO, CO2, and N2. MEMS fuel cell system with a weight specific energy density of 225Wh/kg was accomplished as an alternative micro power source. [Copyright &y& Elsevier]

Abstract: Miniature high-performance micro fuel cells (μFC) operating at room temperature have been fabricated using microsystems technologies. The smallest μFCs have a reaction surface of 0.11 cm2 (volume ∼18.6 mm3; mass ∼35.6 mg) and produce an output power density of 22.9 mW/cm2. The insertion of a hydrophilic macroporous layer into the anode diffusion layer stack, an input fuel flow rate as low as 550 nL min−1 produces 9.25 mW/cm2 at a fuel use efficiency of ∼75%. By optimizing the microfluidic architecture, e.g. the microchannel dimensions and the diffusion layer stack, we demonstrate of the smallest, highest performance μFCs reported to date. [Copyright &y& Elsevier]

Silicon micro-hole arrays (Si-MHA) were fabricated as a gas diffusion layer (GDL) in a micro fuel cell using the micro-electro-mechanical-systems (MEMS) fabrication technique. The resistance temperature detector (RTD) sensor was integrated with the GDL on a bipolar plate to measure the temperature inside the fuel cell. Experimental results demonstrate that temperature was generally linearly related to resistance and that accuracy and sensitivity were within 0.5 °C and 1.68×10-3/°C, respectively. The best experimental performance was 9.37 mW/cm2 at an H2/O2 dry gas flow rate of 30/30 SCCM. Fuel cell temperature during operation was 27 °C, as measured using thermocouples in contact with the backside of the electrode. Fuel cell operating temperature measured in situ was 30.5 °C. [ABSTRACT FROM AUTHOR]

Zeolites were incorporated as membrane and catalyst in chemical microsystems for portable energy generation and fine chemical synthesis. Microfabricated HZSM-5 micromembrane was used as a proton-exchange membrane in a miniature direct methanol fuel cell (μ-DMFC). The good proton conductivity of HZSM-5 micromembrane was attributed to a Grotthus-like diffusion of protons along the water molecules bridging neighboring aluminum sites in the hydrated HZSM-5. The 6-μm thick HZSM-5 micromembrane exhibited comparable proton flux as Nafion® 117 and delivered a Pmax of 2.9 mW cm−2 ( E = 0.33 V) at room temperature. This is smaller compared to 16.5 mW cm−2 ( E = 0.23 V) for a Nafion®-based μ-DMFC and was believed to be caused by adsorbed methanol molecules interrupting the proton transport along the water bridge. A Cs-exchanged NaX on NaA bilayer catalyst-membrane incorporated in microreactor channels was used for the Knoevenagel condensation reactions between benzaldehyde and (1) ethyl cyanoacetate, (2) ethyl acetoacetate (EAA) and (3) diethyl malonate. Microreactor and membrane microreactor gave higher conversion compared to fixed-bed and batch reactors, but the reaction of benzaldehyde and EAA in the microreactor had poorer selectivity due to the slow diffusion of the product molecules in the microchannel that allowed their further reactions to form undesired byproducts. [ABSTRACT FROM AUTHOR]