Electrochemical performance of a glucose/oxygen microfluidic biofuel cell

A microfluidic glucose/O₂ biofuel cell, delivering electrical power, is developed based on both laminar flow and biological enzyme strategies. The device consists of a Y-shaped microfluidic channel in which fuel and oxidant streams flow laminarly in parallel at gold electrode surfaces without convective mixing. At the anode, the glucose is oxidized by the enzyme glucose oxidase whereas at the cathode, the oxygen is reduced by the enzyme laccase, in the presence of specific redox mediators. Such cell design protects the anode from interfering parasite reaction of O₂ at the anode and works with different streams of oxidant and fuel for optimal operation of the enzymes. The dependence of the flow rate on the current is evaluated in order to determine the optimum flow that would provide little to no mixing while yielding high current densities. The maximum power density delivered by the assembled biofuel cell reaches 110 μW cm⁻² at 0.3 V with 10 mM glucose at 23 °C. This research demonstrates the feasibility of advanced microfabrication techniques to build an efficient microfluidic glucose/O₂ biofuel cell device.     

Biofuel cell nanodevices

Looking at the past decades, intense efforts have been made on one of the flourishing technology called biofuel cells with respect to the power or energy crisis prevailing all over the globe. Global researchers are taking part in the development of biofuels cells by exploiting novel characteristics of unconventional materials at atomic and molecule level like nanotubes (carbon nanotubes), nanosheets, nanoparticles, conducting polymers, etc in order to generate effective electricity from the substrates of biological origin via utilizing various biocatalysts. With the advancement in the field of nanotechnology, significant discoveries with respect to the field of biofuel cells have been accomplished. But till date, there has been a significant challenge regarding the performance and efficiency of the biofuels cells. Nowadays, to generate high power, an efficient and skillful approach which consists of the implementation of nano-based materials and conducting polymers with respect to the assembly of the biofuel cells is being considered by many researchers. Bioenergy and biofuels is a potential contestant for alternative fuel and with regard to this nanotechnology is one such significant weapon to synthesize and modify the production of biofuel and bio-energy. It has been assumed that in the near future with such extensive research biofuel cells will take up the economy of a nation in a sustainable way. This review gives the insights of biofuel cells and their types, brief synopsis of applications of the biofuel cells along with the scrutiny of biofuel cells in the market. Significant discussions have been provided in this review relating to the nanomaterials being employed as an electrode in biofuel cells. Certain examples have been mentioned to justify the concept of biofuel cell nanodevices following the ethical considerations of the same.     

Microfluidic microbial fuel cells: Recent advancements and future prospects

Over the years, there has been a substantial increase in the demands of a portable, green source of energy for powering microelectronics to be used as sensors, medical implants and other lab-on-chip devices. Microfluidic microbial fuel cells have been identified as a genuine option to address these requirements. These cells operating at microscale level are characterised by laminar flow of fuel and oxidant which eradicates the requirement of a membrane ensuring higher performance and improved reaction rates than conventional fuel cells. Owing to these advantages, microsized microbial fuel cells have been extensively used to design micro power sources for environmental biosensors, point-of-care diagnostics, medical implants. However, the microfluidic microbial fuel cell technology suffers from some noteworthy disadvantages which need to be addressed before the commercialization of technology. The review comprehensively discusses the development, and advancements in microfluidic microbial fuel cell technology followed by their current applications, challenges, the possible solutions and future prospects.     

基于微流体技术的生物燃料开发与应用

为了加快生物燃料产业的发展速度,提高生物燃料的产量和质量,微流体技术被引入到了生物燃料领域。文章聚焦于微流体技术在生物燃料领域的应用,重点介绍了微流体技术及装置在生物柴油和生物乙醇生产中的应用,讨论了影响生物燃料微流体反应器性能的相关因素,最后,提出了微流体技术在生物燃料领域的应用过程中所面临的问题并展望了其应用前景。     

Development of glycerol/O2 biofuel cell

Glycerol is an attractive fuel for a fuel cell, because it is non-toxic, non-volatile, non-flammable, has high energy density, and is abundant due to the fact that it is a byproduct of biodiesel production. However, it has not been an effective fuel for low temperature, precious metal catalyzed fuel cells. In this paper, we describe the use of glycerol as a fuel in an enzymatic biofuel cell. An alcohol dehydrogenase and aldehyde dehydrogenase-based bioanode has been developed that oxidizes glycerol, a safe high energy density fuel. Glycerol/O₂ biofuel cells employing these bioanodes have yielded power densities of up to 1.21 mW cm⁻², and have the ability to operate at 98.9% fuel concentrations. Previous biofuel cells could not operate effectively at high fuel concentrations due to the nature of the solid fuel such as sugar or the solvent characteristics of fuels such as lower aliphatic alcohols. The glycerol/O₂ biofuel cell provides improved power densities compared to ethanol biofuel cells due to ability to more completely oxidize the fuel.     

Planar and three-dimensional microfluidic fuel cell architectures based on graphite rod electrodes

We propose new membraneless microfluidic fuel cell architectures employing graphite rod electrodes. Commonly employed as mechanical pencil refills, graphite rods are inexpensive and serve effectively as both electrode and current collector for combined all-vanadium fuel/oxidant systems. In contrast to film-deposited electrodes, the geometry and mechanical properties of graphite rods enable unique three-dimensional microfluidic fuel cell architectures. Planar microfluidic fuel cells employing graphite rod electrodes are presented here first. The planar geometry is typical of microfluidic fuel cells presented to date, and permits fuel cell performance comparisons and the evaluation of graphite rods as electrodes. The planar cells produce a peak power density of 35 mW cm⁻² at 0.8 V using 2 M vanadium solutions, and provide steady operation at flow rates spanning four orders of magnitude. Numerical simulations and empirical scaling laws are developed to provide insight into the measured performance and graphite rods as fuel cell electrodes.     

Technology exploration and forecasting of biofuels and biohydrogen energy from patent analysis

The status and activity of technological development in the field of biofuel and biohydrogen energy from the year 2000–2011 were investigated utilizing patent bibliometric analysis. Based on the reports, the current status indicates that the key technologies for biofuel energy have reached technological maturity in the United States. However, the principal or predominant technologies for biohydrogen energy need a great deal of work to accelerate the development of biohydrogen technology. In addition, three important subjects were found from citation techniques, which are related to biodiesel fuel, biological fuel cell, and the biohydrogen. These patents described that the focus of key techniques of energy production should be established towards low energy demand technologies, and biohydrogen was found to be a potential candidate of the future. Finally, this proposed model can be applied to all high-technology cases, and particularly to green energy field.     

Miniaturized additively manufactured co-laminar microfluidic glucose biofuel cell with optimized grade pencil bioelectrodes

Miniaturization of enzymatic biofuel cell has become a crucial factor especially towards device fabrication and integrated bioelectrode system. When successful in a cost-effective manner, it can be used as a source of qualitative electric power for portable and implantable devices. The present work demonstrates the design and fabrication of cost-effective, portable, miniaturized microfluidic enzymatic biofuel cell (M-EBFC) using rapid prototyping 3D printing (3DP) technique. The low cost, radially available, non-toxic Pencil Graphite Electrodes (PGE's) were used as the electrode material. Various grades of PGE's were rigorously studied, by screening separately and cohesively for both anodic and cathodic sides, and the optimized ones (B and 5H for anodic and cathodic sides respectively) have been utilized. These PGE's successively encapsulated into Y-shaped microchannel, fabricated using a commercial 3D Printer. This platform, integrating 3D printing technology and PGE's, delivers simplistic, cost-effective and quick fabrication method, which eradicates the necessity of any further amendment and post-processing. Furthermore, the enhancement of the surface area and electrochemical sensing, PGE's were coated with carboxylated multiwalled carbon nanotube followed by the covalent immobilization enzymes. The electrochemical and polarization performance was compared between both HB and the optimized PGEs. The optimized PGE based 3D printed microfluidic membraneless enzymatic biofuel cell (3DP-MM-EBFC) showed open circuit potential (OCP) of 0.433 V and with a maximum power density of 18 μW cm⁻² at a current density of 60 μA cm⁻². This rapidly prototyped 3D printed fabrication technology demonstrates the viability of simple and advanced microfabrication techniques to build well-organized plug-and-play devices to power several portable low-power microelectronic devices and sensors.     

Polymer separator and low fuel concentration to minimize crossover in microfluidic direct methanol fuel cells

Microfluidic direct methanol fuel cell (DMFC) has some key issues, such as fuel crossover and water management, which typically hamper the development of conventional polymer electrolyte‐based fuel cells. Here a method of minimizing fuel crossover in microfluidic DMFC is reported. A polymer separator at the interface of the fuel and electrolyte streams in a single‐channel microfluidic DMFC is used to reduce the cross‐sectional area across where methanol can diffuse. Based on the optimized fuel rate, fuel concentration and pore radius, a maximum power density of 7.4 mW cm^?2 was obtained with the separator using 2 M methanol. This simple design improvement reduces the voltage loss at the cathode and leads to better performance. Copyright © 2014 John Wiley & Sons, Ltd.     

Overview on nanostructured membrane in fuel cell applications

Fuel cells are expected to soon become a source of low- to zero-emission power generation for applications in portable technologies and electric vehicles. Allowing development of high quality solid electrolytes and production of smaller fuel cells, significant progress has been made in the development of fuel cell membranes using nanotechnology. Nanostructures have been recognized as critical elements to improve the performance of fuel cell membranes. This paper provides an overview of research and development of nanostructured membranes for different fuel cell applications and focuses on improvement of fuel cell membranes by these nanostructures. Theoretical studies using molecular-scale modeling and simulation of fuel cell membranes have also been included in this review. Other issues regarding the technology limitations, research challenges and future trends are also reviewed.     

Computational modeling of microfluidic fuel cells with flow-through porous electrodes

In the current work, a computational model of a microfluidic fuel cell with flow-through porous electrodes is developed and validated with experimental data based on vanadium redox electrolyte as fuel and oxidant. The model is the first of its kind for this innovative fuel cell design. The coupled problem of fluid flow, mass transport and electrochemical kinetics is solved from first principles using a commercial multiphysics code. The performance characteristics of the fuel cell based on polarization curves, single pass efficiency, fuel utilization and power density are predicted and theoretical maxima are established. Fuel and oxidant flow rate and its effect on cell performance is considered and an optimal operating point with respect to both efficiency and power output is identified for a given flow rate. The results help elucidate the interplay of kinetics and mass transport effects in influencing porous electrode polarization characteristics. The performance and electrode polarization at the mass transfer limit are also detailed. The results form a basis for determining parameter variations and design modifications to improve performance and fuel utilization. The validated model is expected to become a useful design tool for development and optimization of fuel cells and electrochemical sensors incorporating microfluidic flow-through porous electrodes.     

Innovation of vapor-feed microfluidic fuel cell with novel geometric configuration and operation parameters optimization

The harmless reaction process makes the fuel cells possess the environment-friendly characteristic, but the application of fuel cells is limited by their low fuel utilization. To improve this, a model of vapor-feed microfluidic fuel cell with a novel geometric configuration is established in present study, and the effects of various parameters on cell performance are investigated in detail. Simulation results show that structural parameters contribute significantly to the improvement in cell performance. After a series of optimizations, the maximum power density of 47.43 mW/cm² is achieved, the fuel utilization and exergy efficiency are increased to 46.03% and 5.24%, respectively. This indicates that the structural optimization measures such as tower-type gas chamber and embedded electrode are significant for improving the performance of the vapor-feed microfluidic fuel cell.     

Chip-embedded thin film current collector for microfluidic fuel cells

Microfluidic fuel cells are an attractive candidate for low-power applications and provide a unique advantage over traditional fuel cells by elimination of the membrane. More importantly, microfluidic fuel cells enable a simple single-layer structure similar to common lab-on-chip devices, which makes conventional microfabrication or micromachining techniques readily applicable. Microfabrication is a preferable fabrication tool for microscale devices due to the benefits of high precision and repeatability at relatively low cost. However, the performance of most microfluidic fuel cells reported to date was negatively influenced by intrinsic contact resistances arising due to the highly porous nature of the electrodes. In the present work, a chip-embedded thin film current collector for vanadium fueled microfluidic fuel cells is proposed, fabricated, and evaluated as a potential mitigation strategy. The micromachining based thin film process is compatible with the overall cell fabrication, comprising photolithography and soft lithography, and does not require a substantial modification of the original cell design. Cells with and without current collectors are directly compared experimentally: the cell with current collectors demonstrates a 79% increase in peak power density, indicating that the contact resistance is significantly reduced by this approach. A volume specific peak power density of 6.2 W cm⁻³ is achieved, which is significantly higher than for previously reported microfluidic fuel cells. Electrochemical impedance spectroscopy (EIS) analysis is carried out to measure the combined ohmic cell resistance and confirmed a 32% reduction using the current collectors, which shows a good agreement with slope decrements in the polarization curves.     

Glycerol oxidation in a microfluidic fuel cell using Pd/C and Pd/MWCNT anodes electrodes

Pd/C and Pd/MWCNT based electro-catalysts were prepared by impregnation and used as anodes for glycerol electro-oxidation in a microfluidic fuel cell. Average particle size and lattice parameters of the catalysts were determined by X-ray diffraction, resulting in 7.5 and 3.5 nm for Pd/C and Pd/MWCNT respectively. The electro-catalytic activity of Pd/C and Pd/MWCNT was investigated in 0.1 M glycerol. The results obtained by electrochemical studies in half cell configuration showed that the onset potential for glycerol oxidation on Pd/MWCNT was characterized by a negative shift ca. 40 mV compared to Pd/C. The maximum power density obtained was 0.51 and 0.7 mW cm⁻² for Pd/C and Pd/MWCNT respectively. These results are comparable with those obtained for a microfluidic fuel cell that uses glucose as fuel. The results of this work not only show that glycerol can be used as fuel in a microfluidic fuel cell but also its performance is similar to that obtained with others fuels.     

A membraneless microscale fuel cell using non-noble catalysts in alkaline solution

This paper presents the development of a novel liquid-based microscale fuel cell using non-noble catalysts in an alkaline solution. The developed fuel cell is based on a membraneless structure. The operational complications of a proton exchange membrane lead the development of a fuel cell with the membraneless structure. Non-noble metals with relatively mild catalytic activity, nickel hydroxide and silver oxide, were employed as anode and cathode catalysts to minimize the effect of cross-reactions with the membraneless structure. Along with nickel hydroxide and silver oxide, methanol and hydrogen peroxide were used as a fuel at anode and an oxidant at cathode. With a fuel mixture flow rate of 200 μl min⁻¹, a maximum output power density of 28.73 μW cm⁻² was achieved. The developed fuel cell features no proton exchange membrane, inexpensive catalysts, and simple planar structure, which enables high design flexibility and easy integration of the microscale fuel cell into actual microfluidic systems and portable applications.     

A membraneless microfluidic fuel cell stack

A membraneless microfluidic fuel cell stack architecture is presented that reuses reactants from one cell to a subsequent one, analogous to PEMFC stacks. On-chip reactant reuse improves fuel utilization and power densities relative to single cells. The reactants flow separately through porous electrodes and interface with a non-reacting and conductive electrolyte which maintains their separation. The reactants remain separated downstream of the interface and are used in subsequent downstream cells. This fuel cell uses porous carbon for electrocatalysts and vanadium redox species as reactants with a sulfuric acid supporting electrolyte. The overall power density of the fuel cell increases with reactant flow rate and decreasing the separating electrolyte flow rate. The peak power, maximum fuel utilization, and efficiency nearly double when electrically connecting the cells in parallel.     

Rapid fabrication of microfluidic polymer electrolyte membrane fuel cell in PDMS by surface patterning of perfluorinated ion-exchange resin

In this paper we demonstrate a simple and rapid fabrication method for a microfluidic polymer electrolyte membrane (PEM) fuel cell using polydimethylsiloxane (PDMS), which has become the de facto standard material in BioMEMS. Instead of integrating a Nafion sheet film between two layers of a PDMS device in a traditional “sandwich format,” we pattern a perfluorinated ion-exchange resin such as a Nafion resin on a glass substrate using a reversibly bonded PDMS microchannel to generate an ion-selective membrane between the fuel-cell electrodes. After this patterning step, the assembly of the microfluidic fuel cell is accomplished by simple oxygen plasma bonding between the PDMS chip and the glass substrate. In an example implementation, the planar PEM microfluidic fuel cell generates an open circuit voltage of 600–800 mV and delivers a maximum current output of nearly 4 μA. To enhance the power output of the fuel cell we utilize self-assembled colloidal arrays as a support matrix for the Nafion resin. Such arrays allow us to increase the thickness of the ion-selective membrane to 20 μm and increase the current output by 166%. Our novel fabrication method enables rapid prototyping of microfluidic fuel cells to study various ion-exchange resins for the polymer electrolyte membrane. Our work will facilitate the development of miniature, implantable, on-chip power sources for biomedical applications.     

Decision support system integrating GIS with simulation and optimisation for a biofuel supply chain

A range of economic and societal issues has resulted from fossil fuel consumption in the transportation sector in the U.S. These include health related air pollution, climate change, dependence on imported oil, and other oil related national security concerns. Biofuels production from various lignocellulosic biomass types, such as wood, forest residues, and agriculture residues, have the potential to replace a portion of the total fossil fuel consumption. This study focused on locating biofuel facilities and designing the biofuel supply chain to minimise the overall cost. For this purpose, an integrated methodology was proposed by combining the Geographic Information System technology with simulation and optimisation modelling methods. The GIS-based method was used as a precursor for selecting biofuel facility locations by employing a series of decision factors. The identified candidate sites for biofuel production served as inputs for simulation and optimisation modelling. The simulation/optimisation model and identified locations provided an integrated decision support system for decision makers to determine the optimal cost, energy consumption, and emissions for candidate locations. This novel methodology development extends prior research.     

Use of a bilayer platinum-silver cathode to selectively perform the oxygen reduction reaction in a high concentration mixed-reactant microfluidic direct ethanol fuel cell

Microfluidic direct ethanol fuel cells are a promising technology for powering electronic portable devices in the future, and the use of efficient electrocatalysts, both anodic and cathodic are crucial for the development of this type of fuel cells. In this work, an Ag-Pt ethanol-tolerant cathode, synthesized by pulsed laser deposition is studied in the presence of high concentration of ethanol. The cathode exhibited similar catalytic activity to Pt towards the oxygen reduction reaction, performing the reaction through a 4 e⁻ pathway but it showed practically no activity towards the ethanol oxidation reaction. Furthermore, the cathode was successfully tested in a microfluidic direct ethanol fuel cell under mixed-reactant conditions, delivering a maximum cell voltage of 0.75 V and maximum power density of 10 mW cm⁻², thus demonstrating its capability to selectively accomplish the oxygen reduction reaction in presence of ethanol concentration as high as 2 M.     

Lignocellulosic biomass for bioethanol production: Current perspectives,potential issues and future prospects

During the most recent decades increased interest in fuel from biomass in the United States and worldwide has emerged each time petroleum derived gasoline registered well publicized spikes in price. The willingness of the U.S. government to face the issues of more heavily high-priced foreign oil and climate change has led to more investment on plant-derived sustainable biofuel sources. Biomass derived from corn has become one of the primary feedstocks for bioethanol production for the past several years in the U.S. However, the argument of whether to use food as biofuel has led to a search for alternative non-food sources. Consequently, industrial research efforts have become more focused on low-cost large-scale processes for lignocellulosic feedstocks originating mainly from agricultural and forest residues along with herbaceous materials and municipal wastes. Although cellulosic-derived biofuel is a promising technology, there are some obstacles that interfere with bioconversion processes reaching optimal performance associated with minimal capital investment. This review summarizes current approaches on lignocellulosic-derived biofuel bioconversion and provides an overview on the major steps involved in cellulosic-based bioethanol processes and potential issues challenging these operations. Possible solutions and recoveries that could improve bioprocessing are also addressed. This includes the development of genetically engineered strains and emerging pretreatment technologies that might be more efficient and economically feasible. Future prospects toward achieving better biofuel operational performance via systems approaches such as risk and life cycle assessment modeling are also discussed.