An abiotically catalyzed glucose fuel cell for powering medical implants: Reconstructed manufacturing protocol and analysis of performance

Although the first abiotically catalyzed glucose fuel cells have already been developed as sustainable power supply for medical implants in the 1970s, no detailed information concerning the fabrication of these devices has been published so far. Here we present a comprehensive manufacturing protocol for such a fuel cell, together with a detailed analysis of long-term performance in neutral buffer containing physiological amounts of glucose and oxygen. In air saturated solution a power density of (3.3 ± 0.2) μW cm⁻² is displayed after 10 days of operation that gradually decreases to a value of (1.0 ± 0.05) μW cm⁻² in the course of 224 days. A novelty of this work is the characterization of fuel cell performance with individually resolved electrode potentials. Using this technique, we can show that the major part of performance degradation originates from a positive shift of the anode potential, indicating that a more poisoning-resistant glucose oxidation catalyst would improve the degradation behavior of the fuel cell. As further factors influencing performance an incomplete reactant separation and a mass transfer governed cathode reaction under the relatively low oxygen partial pressures of body tissue have been identified. Consequently we propose an oxygen depleting electrode interlayer and the application of more effective oxygen reduction catalysts as promising strategies to further improve the fuel cell performance under physiological concentrations of glucose and oxygen.     

A potentially implantable glucose fuel cell with Raney-platinum film electrodes for improved hydrolytic and oxidative stability

We present an improved abiotically catalyzed glucose fuel cell, intended as energy harvesting tissue implantable power supply for medical implants. The fuel cell is constructed from a Raney-platinum film cathode deposited on a silicon substrate with micro-machined feedholes for glucose permeability, arranged in front of a Raney-platinum film anode. A novelty is the application of platinum for both electrodes and the complete abdication of hydrogel binders. This overcomes the limited stability against hydrolytic and oxidative attack encountered with previous glucose fuel cells fabricated from activated carbon particles dispersed in a hydrogel matrix. During performance characterization in phosphate buffered saline under physiological concentrations of glucose and oxygen the diffusion resistance to be expected from tissue capsule formation was taken into account. Despite the resulting limited oxygen supply, the Raney-platinum fuel cells exhibit a power density of up to (4.4 ± 0.2) μW cm⁻² at 7.0% oxygen saturation. This exceeds the performance of our previous carbon-based prototypes, and can be attributed to the higher catalytic activity of platinum cathodes and in particular the increased oxygen tolerance of the Raney-platinum film anodes.     

Microfluidic fuel cells: A review

A microfluidic fuel cell is defined as a fuel cell with fluid delivery and removal, reaction sites and electrode structures all confined to a microfluidic channel. Microfluidic fuel cells typically operate in a co-laminar flow configuration without a physical barrier, such as a membrane, to separate the anode and the cathode. This review article summarizes the development of microfluidic fuel cell technology, from the invention in 2002 until present, with emphasis on theory, fabrication, unit cell development, performance achievements, design considerations, and scale-up options. The main challenges associated with the current status of the technology are provided along with suggested directions for further research and development. Moreover, microfluidic fuel cell architectures show great potential for integration with biofuel cell technology. This review therefore includes microfluidic biofuel cell developments to date and presents opportunities for future work in this multi-disciplinary field.     

Raney-platinum film electrodes for potentially implantable glucose fuel cells. Part 1: Nickel-free glucose oxidation anodes

We present a novel fabrication route yielding Raney-platinum film electrodes intended as glucose oxidation anodes for potentially implantable fuel cells. Fabrication roots on thermal alloying of an extractable metal with bulk platinum at 200 °C for 48 h. In contrast to earlier works using carcinogenic nickel, we employ zinc as potentially biocompatible alloying partner. Microstructure analysis indicates that after removal of extractable zinc the porous Raney-platinum film (roughness factor ∼2700) consists predominantly of the Pt₃Zn phase. Release of zinc during electrode operation can be expected to have no significant effect on physiological normal levels in blood and serum, which promises good biocompatibility. In contrast to previous anodes based on hydrogel-bound catalyst particles the novel anodes exhibit excellent resistance against hydrolytic and oxidative attack. Furthermore, they exhibit significantly lower polarization with up to approximately 100 mV more negative electrode potentials in the current density range relevant for fuel cell operation. The anodes’ amenability to surface modification with protective polymers is demonstrated by the exemplary application of an approximately 300 nm thin Nafion coating. This had only a marginal effect on the anode long-term stability and amino acid tolerance. While in physiological glucose solution after approximately 100 h of operation gradually increasing performance degradation occurs, rapid electrode polarization within 24 h is observed in artificial tissue fluid. Optimization approaches may include catalyst enhancement by adatom surface modification and the application of specifically designed protective polymers with controlled charge and mesh size.     

Energy management strategy based on fuzzy logic for a fuel cell hybrid bus

Fuel cell vehicles, as a substitute for internal-combustion-engine vehicles, have become a research hotspot for most automobile manufacturers all over the world. Fuel cell systems have disadvantages, such as high cost, slow response and no regenerative energy recovery during braking; hybridization can be a solution to these drawbacks. This paper presents a fuel cell hybrid bus which is equipped with a fuel cell system and two energy storage devices, i.e., a battery and an ultracapacitor. An energy management strategy based on fuzzy logic, which is employed to control the power flow of the vehicular power train, is described. This strategy is capable of determining the desired output power of the fuel cell system, battery and ultracapacitor according to the propulsion power and recuperated braking power. Some tests to verify the strategy were developed, and the results of the tests show the effectiveness of the proposed energy management strategy and the good performance of the fuel cell hybrid bus.     

Energy management of a fuel cell hybrid ultra-energy efficient vehicle

This paper focuses on energy management in an ultra-energy efficient vehicle powered by a hydrogen fuel cell with rated power of 1 kW. The vehicle is especially developed for the student competition Shell Eco-marathon in the Urban Concept category. In order to minimize the driving energy consumption a simulation model of the vehicle and the electric propulsion is developed. The model is based on vehicle dynamics and real motor efficiency as constant DC/DC, motor controllers and transmission efficiency were considered. Based on that model five propulsion schemes and driving strategies were evaluated. The fuel cell output parameters were experimentally determined. Then, the driving energy demand and hydrogen consumption was estimated for each of the propulsion schemes. Finally, an experimental study on fuel cell output power and hydrogen consumption was conducted for two propulsion schemes in case of hybrid and non-hybrid power source. In the hybrid propulsion scheme, supercapacitors were used as energy storage as they were charged from the fuel cell with constant current of 10 A.     

Energy and exergy analysis of microfluidic fuel cell

Microfluidic fuel cell (MFC) is a promising fuel cell type because its membraneless feature implies great potential for low-cost commercialization. In this study, an energy and exergy analysis of MFC is performed by numerical simulation coupling computational fluid dynamics (CFD) with electrochemical kinetics. MFC system designs with and without fuel recirculation are investigated. The effects of micropump efficiency, fuel flow rate and fuel concentration on the MFC system performance are evaluated. The results indicate that fuel recirculation is preferred for MFC to gain higher exergy efficiency only if the efficiency of the micropump is sufficiently high. Optimal cell operating voltage for achieving the highest exergy efficiency can be obtained. Parasitic effect will cause a significant reduction in the exergy efficiency. An increase in the fuel concentration will also lead to a reduction in the exergy efficiency. Increasing the fuel flow rate in a MFC with fuel recirculation will cause a fluctuating variation in the exergy efficiency. On the other hand, in a one-off MFC system, the exergy efficiency decreases with increasing fuel flow rate. The present work enables better understanding of the energy conversion in MFC and facilitates design optimization of MFC.     

A microfabricated low cost enzyme-free glucose fuel cell for powering low-power implantable devices

In the past decade the scientific community has showed considerable interest in the development of implantable medical devices such as muscle stimulators, neuroprosthetic devices, and biosensors. Those devices have low power requirements and can potentially be operated through fuel cells using reactants present in the body such as glucose and oxygen instead of non-rechargeable lithium batteries. In this paper, we present a thin, enzyme-free fuel cell with high current density and good stability at a current density of 10 μA cm⁻². A non-enzymatic approach is preferred because of higher long term stability. The fuel cell uses a stacked electrode design in order to achieve glucose and oxygen separation. An important characteristic of the fuel cell is that it has no membrane separating the electrodes, which results in low ohmic losses and small fuel cell volume. In addition, it uses a porous carbon paper support for the anodic catalyst layer which reduces the amount of platinum or other noble metal catalysts required for fabricating high surface area electrodes with good reactivity. The peak power output of the fuel cell is approximately 2 μW cm⁻² and has a sustainable power density of 1.5 μW cm⁻² at 10 μA cm⁻². An analysis on the effects of electrode thickness and inter electrode gap on the maximum power output of the fuel cell is also performed.     

Raney-platinum film electrodes for potentially implantable glucose fuel cells. Part 2: Glucose-tolerant oxygen reduction cathodes

We report the fabrication and characterization of glucose-tolerant Raney-platinum cathodes for oxygen reduction in potentially implantable glucose fuel. Fabricated by extraction of aluminum from 1 μm thin platinum-aluminum bi-layers annealed at 300 °C, the novel cathodes show excellent resistance against hydrolytic and oxidative attack. This renders them superior over previous cathodes fabricated from hydrogel-bound catalyst particles. Annealing times of 60, 120, and 240 min result in approximately 400-550 nm thin porous films (roughness factors ∼100-150), which contain platinum and aluminum in a ratio of ∼9:1. Aluminum release during electrode operation can be expected to have no significant effect on physiological normal levels, which promises good biocompatibility. Annealing time has a distinct influence on the density of trenches formed in the cathode. Higher trench densities lead to lower electrode potentials in the presence of glucose. This suggests that glucose sensitivity is governed by mixed potential formation resulting from oxygen depletion within the trenches. During performance characterization the diffusion resistance to be expected from tissue capsule formation upon electrode implantation was taken into account by placing a membrane in front of the cathode. Despite the resulting limited oxygen supply, cathodes prepared by annealing for 60 min show more positive electrode potentials than previous cathodes fabricated from hydrogel-bound activated carbon. Compared to operation in phosphate buffered saline containing 3.0 mM glucose, a potential loss of approximately 120 mV occurs in artificial tissue fluid. This can be reduced to approximately 90 mV with a protective Nafion layer that is easily electro-coated onto the Raney-platinum film.     

Energy,equity and the future of the fuel poor

A warm and adequately-lit home is considered a basic need, together with access to energy-consuming appliances ranging from a fridge to a TV. An underlying tenet of sustainable energy is that such basic needs should be affordably met.     

Energy control of supercapacitor/fuel cell hybrid power source

This paper deals with a flatness based control principle in a hybrid system utilizing a fuel cell as a main power source and a supercapacitor as an auxiliary power source. The control strategy is based on regulation of the dc bus capacitor energy and, consequently, voltage regulation. The proposed control algorithm does not use a commutation algorithm when the operating mode changes with the load power variation and, thus, avoids chattering effects. Using the flatness based control method, the fuel cell dynamic and its delivered power is perfectly controlled, and the fuel cell can operate in a safe condition. In the hybrid system, the supercapacitor functions during transient energy delivery or during energy recovery situations. To validate the proposed method, the control algorithms are executed in dSPACE hardware, while analogical current loops regulators are employed in the experimental environment. The experimental results prove the validity of the proposed approach.     

Enhancement of glucose electro-oxidation by an external electromagnetic field in direct-mode fuel cells

In this study a direct-mode fuel cell in which the fuel and electrolyte are mixed with each other is tested. An alkaline electrolyte is used. The direct-mode fuel cell is exposed to an externally generated electromagnetic field between electrodes to cause both the splitting of the fuel molecule into smaller units (i.e. electrochemical reforming) and an increase in the activity of catalyst materials on the fuel before electrochemical oxidation. The target is to create a fuel cell with a capacity range of a few mW cm⁻² with glucose as a fuel. In the selected fuel cell type with glucose as the fuel, a maximum current density of 13 mA cm⁻² was obtained. On the basis of the tests it seems to be possible to use the glucose-fuelled cell in small-scale applications, e.g. in small electronic devices.     

Evaluation of hybrid and enzymatic nanofluidic fuel cells using 3D carbon structures

Membraneless nanofluidic fuel cells are devices that utilize fluid flow through nanoporous media which serve as three-dimensional electrodes. In the case of hybrid fuel cells (HFC) an enzymatic and an abiotic catalyst are incorporated on the electrodes. Here we compared two different HFC. In the first one (HFC-1), glucose oxidase- and Pt-based electrodes were used as bioanode and cathode respectively. This cell reached an open circuit voltage (OCV) of 0.55 V and a maximum power density of 5.7 mWcm^?2. In the second one (HFC-2), AuAg- and laccase-based electrodes were used as anode and biocathode respectively. This cell exhibited an OCV of 0.91 V and a maximum power density of 17 mWcm^?2. Finally, enzymatic electrodes were used to develop a high performance biofuel cell (3.2 mWcm^?2) that exhibited high stability over 4 days. These preliminary results indicate that the incorporation of enzymes into the 3D carbon structures is an efficient alternative for miniaturized nanofluidic power sources.     

Energy harvesting from a piezoelectric biomimetic fish tail

Understanding fish migratory patterns and movements often relies on tags that are externally or internally implanted. Energy harvesting from fish swimming may benefit the state of the art of fish-tags, by increasing their battery lifetime and expanding their sensory capabilities. Here, we investigate the feasibility of underwater energy harvesting from the vibrations of a biomimetic fish tail though piezoelectric materials. We propose and experimentally validate a modeling framework to predict the underwater vibration of the tail and the associated piezoelectric response. The tail is modeled as a geometrically tapered beam with heterogeneous physical properties, undergoing large amplitude vibration in a viscous fluid. Fluid-structure interactions are described through a hydrodynamic function, which accounts for added mass and nonlinear hydrodynamic damping. To demonstrate the practical benefit of energy harvesting, we assess the possibility of powering a wireless communication module using the underwater vibration of the tail hosting the piezoelectrics. The electrical energy generated by the piezoelectrics during the undulations of the tail is stored and used to power the wireless communication device. This preliminary test offers compelling evidence for future technological developments toward self-powered fish-tags.     

Direct hybrid glucose-oxygen enzymatic fuel cell based on tetrathiafulvalene-tetracyanoquinodimethane charge transfer complex as anodic mediator

TTF-TCNQ has been used for the first time as a mediator in a direct glucose fuel cell operating on gas-phase oxygen. It has been shown that TTF-TCNQ forms highly irregular porous structure, which emphasizes the importance of optimization of mass transport and kinetic resistance in the catalyst layer. Kinetics resistance can be optimized by variation of the mediator and/or enzyme loading, while mass transport resistance mainly by the variation of other structural parameters such as electrode thickness. The optimized anode reached limiting current densities of nearly 400 μA cm⁻² in presence of 5 mM glucose under rotation. The enzymatic fuel cell exhibited unexpectedly high OCV values (up to 0.99 V), which were tentatively ascribed to different pH conditions at the anode and the cathode. OCV was influenced by glucose crossover and was decreasing with an increase of glucose concentration or flow rate. Although the performance of the fuel cell is limited by the enzymatic anode, the long-term stability of the fuel cell is mainly influenced by the Pt cathode, while the enzymatic anode has higher stability. The fuel cell delivered power densities up to 120 μW cm⁻² in presence of 5 mM glucose, depending on the glucose flow rate.     

Performance study of a PEM fuel cell

This paper presents the installation, maintenance and the efficiency of a Polymer Electrolyte Membrane (PEM) fuel cell, Ballard Trade Mark that use pure hydrogen as fuel and air as an oxidant. A study of the overall efficiency, considering the co-generation of electrical and thermal energies, is performed. The system consists of the cell, a CC/CC converter, a battery, a DC/AC inverter and the load. The behavior of the system is experimentally analyzed for different load states (cases) by measuring and controlling all the parameters registered by the communication software of the cell. The software can adjust limit values for current intensity, hydrogen flow, pressure and the temperature.     

FC energy harvesting using the MPP tracking based on advanced extremum seeking control

In this paper is proposed a Maximum Power Point (MPP) tracking technique for the Fuel Cell (FC) stacks based on advanced Extremum Seeking (aES) control that improves the basic performances of the ES control schemes: a guaranteed convergence and proved internal robustness. Other features such as higher search speed and improved tracking accuracy are demonstrated for the proposed aES control, besides these features that are necessary in case of unmodeled dynamics. The analysis on the frequency domain reveals the relationships between the main aES control parameters, the values of closed loop gain and dither amplitude, and the design performance indicators, the speed of search and accuracy of MPP finding, respectively. If the dither amplitude is set to be proportional with the magnitude of first harmonics of the processed FC power, then the reference current used in the FC current control loop will have an insignificant ripple after the MPP is caught. Thus, a reduced FC power ripple will appear. Therefore, if the search speed is set to be the same for all ES control schemes, then the proposed aES control outperforms all classical ES control schemes in overall power efficiency. Moreover, the aES search speed will proportionally increase with the loop gain and the dither amplitude. Note that here the dither has the amplitude set by the first harmonic of the FC power, being a time variable that have high value during the searching phase. This accelerates MPP searching up to the FC safe limits. Finally, this means a controllable time to shortly find the next MPP on dynamical operation of the FC stack. First harmonic of the FC power becomes almost zero after MPP is caught. Thus, higher tracking accuracy that means an economy on fuel consumption is obtained. The simulations performed show that above mentioned performances are effective for the aES control operating in both ripple- and dither-based modes of the grid connected FC inverters.     

Energy management of fuel cell/solar cell/supercapacitor hybrid power source

This study presents an original control algorithm for a hybrid energy system with a renewable energy source, namely, a polymer electrolyte membrane fuel cell (PEMFC) and a photovoltaic (PV) array. A single storage device, i.e., a supercapacitor (ultracapacitor) module, is in the proposed structure. The main weak point of fuel cells (FCs) is slow dynamics because the power slope is limited to prevent fuel starvation problems, improve performance and increase lifetime. The very fast power response and high specific power of a supercapacitor complements the slower power output of the main source to produce the compatibility and performance characteristics needed in a load. The energy in the system is balanced by d.c.-bus energy regulation (or indirect voltage regulation). A supercapacitor module functions by supplying energy to regulate the d.c.-bus energy. The fuel cell, as a slow dynamic source in this system, supplies energy to the supercapacitor module in order to keep it charged. The photovoltaic array assists the fuel cell during daytime. To verify the proposed principle, a hardware system is realized with analog circuits for the fuel cell, solar cell and supercapacitor current control loops, and with numerical calculation (dSPACE) for the energy control loops. Experimental results with small-scale devices, namely, a PEMFC (1200 W, 46 A) manufactured by the Ballard Power System Company, a photovoltaic array (800 W, 31 A) manufactured by the Ekarat Solar Company and a supercapacitor module (100 F, 32 V) manufactured by the Maxwell Technologies Company, illustrate the excellent energy-management scheme during load cycles.     

Comparative assessments of two integrated systems with/without fuel cells utilizing liquefied ammonia as a fuel for vehicular applications

In the current study, two different integrated systems for vehicular applications are presented and thermodynamically analyzed. The first system consists of liquefied ammonia tank, dissociation and separation unit (DSC) for decomposition of ammonia and an internal combustion engine (ICE) to power the vehicle. The second system is a hybrid system consisting of liquefied ammonia tank, DSC unit, a small ICE and a fuel cell system. In the second system, the main power unit is fuel cell and a supplementary internal combustion engines is also utilized. The exhaust gasses emitted from the ICE are used to provide the required heat for the thermal decomposition process of ammonia. The ICE is fueled with a mix of ammonia and hydrogen generated from the DSC unit that is installed in the two systems. Hydrogen generated from DSC unit will be utilized to operate fuel cell installed in system 2. The proposed systems are analyzed and assessed both energetically and exergetically. A comprehensive parametric study is carried out for comparative assessments to determine the influence of altering design and operating parameters such as the amount of ammonia fuel supplied to the two systems on the performance of the two systems. The overall energy and exergy efficiencies for system 1 and system 2 are found to be 61.89%, 63.34%, 34.73% and 38.44% respectively. The maximum exergy destruction rate in the two systems occurred in the ICE.