Microfluidic Fuel Cell Research Articles

Numerical and experimental comparative study of microfluidic fuel cells with different flow configurations: Co-flow vs. counter-flow cell

Microfluidic fuel cell (MFC) is a new type of fuel cell which utilizes two laminar flows as electrolyte for both reactant delivery and ionic conduction purposes. According to the flow configuration, two MFC designs, that is, the co-flow cell and the counter-flow cell, have been proposed in the literature, but the specific merits and demerits between them have not been well understood yet. Therefore, in this work both experimental and numerical comparative studies are conducted on this issue. It is found that the counter-flow MFC encounters an inherent drawback on its power output because the outer part of its electrodes contributes much less than the inner part due to the longer ionic transport path. In conclusion, short and wide electrodes are more appropriate for counter-flow MFCs rather than the conventional long and narrow ones. Nevertheless, the counter-flow MFC does exhibit great advantage on low flow rate tolerance, leading to much improved fuel utilization and energy density at the same time. Considering this huge superiority for real applications, structural optimization of the counter-flow MFC is further conducted by reducing the electrode distance and discarding the outer part of the electrodes. The optimized counter-flow cell performance is successfully improved to the same level with its co-flow counterpart.

Design Principles of Current Collectors in Microfluidic Fuel Cell with Flow-through Porous Electrodes

Abstract Computational and experimental studies have been performed to investigate the effects of current collector design on the performance of microfluidic fuel cell (MFC) with flow-through porous electrodes. Characteristics of electron transport in MFC with flow-through porous electrodes are investigated based on a three-dimensional computational model. The lateral electron transport in the porous electrode is found to encounter high resistance. To improve the cell performance, influences of different current collector design parameters on the transport resistances are examined. Physical origins for the influences of different design parameters are also discussed. The results demonstrate that current collector position is the most influential factor due to the non-uniform flow rate distribution. In the experimental study, cell performances revealed maximum power density when current collectors were located at the high flow rate region. An increase of 61% was observed when the current collectors moved from the conventional exposed ends of the electrodes to the high flow rate regions in the electrode active area. Based on the results, some general rules are set for the current collector designs of MFCs.

Optimization of Cathode Flooding in Scaled-up Microfluidic Fuel Cells

Abstract The scaling up of microfluidic fuel cells (MFC) with enlarged electrode area can be very advantageous for their stacking, which will, however, aggravate the cathode flooding problem due to the intensified fuel crossover. In this paper, we first validate the cathode flooding phenomenon in a scaled-up MFC prototype which has a hydrogen-breathing anode and an air-breathing cathode. To optimize the flooding issue, cracking the cathode catalyst layer is found to be remarkably effective. The cathode outer surface is found to be free from water after six polarization cycles, and the degradation rate of current density is as low as 1.3mAcm -2 h -1 when the cell is discharged at 0.4 V for five hours. This is probably attributed to the pressure variation inside the cathode induced by the cracks, which alters the water transport direction from gas diffusion layer to the electrolyte channel.

Fabric‐based alkaline direct formate microfluidic fuel cells

Fabric-based microfluidic fuel cells (MFCs) serve as a novel, cost-efficient alternative to traditional FCs and batteries, since fluids naturally travel across fabric via capillary action, eliminating the need for an external pump and lowering production and operation costs. Building on previous research with Y-shaped paper-based MFCs, fabric-based MFCs mitigate fragility and durability issues caused by long periods of fuel immersion. In this study, we describe a microfluidic fabric-based direct formate fuel cell, with 5 M potassium formate and 30% hydrogen peroxide as the anode fuel and cathode oxidant, respectively. Using a two-strip, stacked design, the optimized parameters include the type of encasement, the barrier, and the fabric type. Surface contact of the fabric and laminate sheet expedited flow and respective chemical reactions. The maximum current (22.83 mA/cm2 ) and power (4.40 mW/cm2 ) densities achieved with a 65% cotton/35% polyester blend material are a respective 8.7% and 32% higher than previous studies with Y-shaped paper-based MFCs. In series configuration, the MFCs generate sufficient energy to power a handheld calculator, a thermometer, and a spectrum of light-emitting diodes.

Integrated Microfluidic Flow-Through Microbial Fuel Cells

This paper reports on a miniaturized microbial fuel cell with a microfluidic flow-through configuration: a porous anolyte chamber is formed by filling a microfluidic chamber with three-dimensional graphene foam as anode, allowing nutritional medium to flow through the chamber to intimately interact with the colonized microbes on the scaffolds of the anode. No nutritional media flow over the anode. This allows sustaining high levels of nutrient utilization, minimizing consumption of nutritional substrates, and reducing response time of electricity generation owing to fast mass transport through pressure-driven flow and rapid diffusion of nutrients within the anode. The device provides a volume power density of 745 μW/cm3 and a surface power density of 89.4 μW/cm2 using Shewanella oneidensis as a model biocatalyst without any optimization of bacterial culture. The medium consumption and the response time of the flow-through device are reduced by 16.4 times and 4.2 times, respectively, compared to the non-flow-through counterpart with its freeway space volume six times the volume of graphene foam anode. The graphene foam enabled microfluidic flow-through approach will allow efficient microbial conversion of carbon-containing bioconvertible substrates to electricity with smaller space, less medium consumption, and shorter start-up time.

Application of electrospun CNx nanofibers as cathode in microfluidic fuel cell

Abstract Carbon nitride (CNx) nanofibers is successfully utilised as cathode catalyst in microfluidic fuel cell (MFC) using electrospinning technique. The electrochemical measurement for CNx nanofibers as cathode catalyst in MFC is studied and compared with that of Pt and Au cathodes. Formic acid is employed as fuel, KMnO4 as oxidant and H2SO4 as supporting electrolyte. CNx nanofibers is shown to be not active towards formic acid oxidation and as a result, is tolerant to fuel crossover effect as compared to Pt and Au cathode. CNx nanofibers enable MFC to operate at a wider range of flow rates of fuel and oxidant as compared to Pt and Au conventionally used. MFC utilising CNx nanofibers gives higher power density of 3.43 mW cm−2 and the current density of 9.79 mAcm−2, as compared to that utilizes pure Au (2.72 mW cm−2, 6.04 mA cm−2) and Pt (3.09 mW cm−2, 6.18 mA cm−2) as anode.

Electrooxidation study of NaBH4 in a membraneless microfluidic fuel cell with air breathing cathode for portable power application

A microfluidic fuel cell (MFC) is constructed at laboratory for NaBH4 electrooxidation using varying operating conditions. The temperatures of anode and cathode were varied from 40 °C to 70 °C, and the pressure was maintained at 1 bar. The anode and cathode electrocatalyst used was Pt (40 wt. %)/High Surface Area Carbon (CHSA) with loading in the range of 0.5 mg/cm2 to 2 mg/cm2. The oxidant at cathode was atmospheric oxygen (21 mol % O2). The commercial gas diffusion layer (GDL) was used as substrate at anode and air breathing cathode side. The cell voltage and current density were measured for different fuel (NaBH4) concentration, electrolyte (KOH) concentration, temperature and electrocatalyst loading at anode and cathode, respectively. The maximum open circuit voltage (OCV) of 1.079 V and power density of 24.09 mW/cm2 at a current density of 54.97 mA/cm2 were obtained for anode (Pt/CHSA) and cathode (Pt/CHSA) loading of 1 mg/cm2 using 0.1 M NaBH4 as fuel mixed with 1 M KOH as electrolyte at a temperature of 70 °C. Whereas the maximum power density of 8.47 mW/cm2 at a current density of 34.04 mA/cm2 was obtained at the temperature of 40 °C. Although similar cell conditions were used, the cell performance in terms of power density is significantly enhanced (about 65%) due to increase in temperature from 40 °C to 70 °C. These results were validated using cyclic voltammetry at single electrodes under similar conditions to those of the single microfluidic fuel cell.

A circular stacking strategy for microfluidic fuel cells with volatile methanol fuel

Microfluidic fuel cell (MFC) stacking is a prerequisite to improve its power output for practical applications. Unlike the stacking of membrane-based fuel cells, MFC stacking generally involves complex fluidic management, such as anolyte and catholyte distribution, and spent electrolyte collection, which greatly increases the system’s complexity. In addition, the operational robustness of MFC stacks is generally sensitive to the electrolyte flow rate, which imposes stringent requirements on the precision of the electrolyte distributor and the stability of the environment where the MFC stack works. To deal with these issues, a circular MFC stacking strategy is proposed in this paper, which is especially suitable for volatile hydrocarbon fuels. In such an MFC stack, anolyte is no longer needed because fuel is stored outside the MFC in neat form, which evaporates into vapor form and diffuses into the MFC anodes, while oxidant is directly obtained from the ambient air. In this manner, only one electrolyte flow is needed for each single cell, which greatly simplifies the fluidic management system. Moreover, the stack performance is also found to be flow rate insensitive, ensuring a much improved operational robustness. Experimental results of a six-cell stack prototype (connected in series) have demonstrated an OCV of 5–5.5V, indicating a very effective electrolyte distribution and, therefore, fuel crossover suppression. A peak power density of 108.7mWcm−2 can be achieved at 60°C with 3M KOH as electrolyte. Moreover, stacking efficiency as high as 98.4% was obtained, which could be attributed to both the effective inhibition of shunt currents and the limited performance difference among the single cells.

A high-performance aluminum-feed microfluidic fuel cell stack

Abstract In this paper, a six-cell microfluidic fuel cell (MFC) stack is demonstrated. Low-cost aluminum is fed directly to the stack, which produces hydrogen fuel on site, through the Al-H 2 O reaction. This design is not only cost-efficient, but also eliminates the need for hydrogen storage. Unlike the conventional MFC stacks which generally require complex electrolyte distribution and management, the present Al-feed MFC stack requires only a single electrolyte stream, flowing successively through individual cells, which is finally utilized for hydrogen generation. In this manner, the whole system is greatly simplified while the operational robustness is also improved. With 2 M sodium hydroxide solution as electrolyte and kitchen foil Al as fuel, the present six-cell stack (in series) exhibits an open circuit voltage of nearly 6 V and a peak power density of 180.6 mWcm −2 at room temperature. In addition, an energy density of 1 Whg −1 (Al) is achieved, which is quite high and comparable with its proton exchange membrane-based counterparts. Finally, pumpless operation of the present stack, together with its practical applications are successfully demonstrated, including lightening LED lights, driving an electric fan, and cell phone charging.

Toward the scaling up of microfluidic fuel cells, investigation and optimization of the aggravated cathode flooding problem

The scaling up of microfluidic fuel cells (MFC) with enlarged electrode areas can be very advantageous for their power output and further stacking, which may, however, aggravate the cathode flooding problem due to intensified fuel crossover. In this paper, we first validate this phenomenon in a scaled-up MFC prototype, which has a hydrogen-breathing anode and an air-breathing cathode. Possible influential factors on the flooding extent are studied next, including the electrode area, electrolyte flow rate, and ambient temperature. Furthermore, three different strategies are proposed to improve cathode flooding, which is achieved either by adding an interlayer inside the channel to suppress hydrogen crossover, by adding hydrophilic water remover on the cathode surface to wick the generated water, or by cracking the cathode catalyst layer (CL) to manipulate the water transport direction. Among all these methods, the cracking of cathode CL is found to be remarkably effective especially with acid electrolyte, which exhibits the lowest current density degradation rate of 1.3mAcm−2h−1 when discharged at the peak power point for five hours.

Fabrication and Evaluation of an Air-Breathing Microfluidic Fuel Cell Employed Enzymatic Electrodes for Lactate Oxidation

Lactate is an important biomarker due to its excessive production by the body during anerobic metabolism. Existing methods for electrochemical lactate detection require the use of an external power source. This work present a light air-breathing bio-microfluidic fuel cell (BµFC) operated with 20 mM lactate in phosphate buffer pH 6.5 as fuel and the integration of an air-exposed electrode as cathode enabling oxygen delivery directly from air. FcMe2-LPEI/LOx (dimethylferrocene-modified linear poly(ethylenimine) hidrogel to simultaneously immobilize and mediate electron transfer from lactate oxidase) and An-CNT/BOD (anthracene-modified multi-walled carbon nanotubes, Bilirubine oxidase, 50mM phosphate buffer at pH 6.5, and TBAB-modified Nafion) were employed as electrocatalyst for anode and cathode respectively. An open circuit potential and maximum power density of 0.855V and 0.125mW cm-2 (at 0.3V) were obtained respectively, meanwhile the maximum current density was 1.01 mA cm_2. Although this air-breathing BµFC requires technological improvements before being tested in a biomedical device, show potential possibilities, it represents the best performance to date for a microfluidic fuel cell using lactate as fuel.

An improved alkaline direct formate paper microfluidic fuel cell.

Paper-based microfluidic fuel cells (MFCs) are a potential replacement for traditional FCs and batteries due to their low cost, portability, and simplicity to operate. In MFCs, separate solutions of fuel and oxidant migrate through paper due to capillary action and laminar flow and, upon contact with each other and catalyst, produce electricity. In the present work, we describe an improved microfluidic paper-based direct formate FC (DFFC) employing formate and hydrogen peroxide as the anode fuel and cathode oxidant, respectively. The dimensions of the lateral column, current collectors, and cathode were optimized. A maximum power density of 2.53 mW/cm(2) was achieved with a DFFC of surface area 3.0 cm(2) , steel mesh as current collector, 5% carbon to paint mass ratio for cathode electrode and, 30% hydrogen peroxide. The longevity of the MFC's detailed herein is greater than eight hours with continuous flow of streams. In a series configuration, the MFCs generate sufficient energy to power light-emitting diodes and a handheld calculator.

Dimensionless parametric sensitivity analysis of microfluidic fuel cell with flow-through porous electrodes

A dimensionless steady-state computational model was developed for microfluidic fuel cell (MFC) with flow-through porous electrodes. The dimensionless nature of the model featured with high versatility as a single set of modeling analysis could interpret a wide range of MFCs in terms of fuel cell properties, physical dimensions and scales. Based on the model, statistical Multi-Parametric Sensitivity Analysis (MPSA) was implemented to evaluate the effects of different parameters on the cell output. Eleven major parameters, grouped in terms of cell operation, charge transport, mass transport and porous structure, were investigated under different working conditions. These parameters were consequently classified into strong-, moderate- and weak-influencing factors. The results showed that the charge transfer coefficient and the equilibrium potential were the most influencing factors. The results indicated that the relationship between charge transfer coefficient and porous electrode properties needed to be further specified and the commonly used uniform equilibrium potential assumption of the porous electrode was questionable. Based on the results, guidance for the future modeling and experimental research on MFC was provided.

The Effects of Electrode and Catalyst Selection on Microfluidic Fuel Cell Performance

AbstractA fuel cell can be best defined as an electrochemical converter of fuel and oxidant of chemical energy to electrical energy. The important components of micro fuel cells are the electrodes and catalysts because the kinetics and rates of the electrochemical reactions depend on their materials. All fuel cells consist of two electrodes: the anode, where fuel oxidation takes place, and the cathode, which is used to reduce the oxidants. The present review article highlights the use of a range of electrodes made up of different materials, a variety of catalysts that have been used in previous studies, and their fabrication materials and approaches. In this article, electrodes and catalysts are classified into two types based on the design approach applied to produce the micro fuel cell: micro fuel cell design and conventional assembly design. Most previous studies on fuel cells have demonstrated that the construction and position of the electrodes play crucial roles in improving the performance of micro fuel cells.

A Counter-flow Microfluidic Fuel Cell Achieving Concentrated Fuel Operation

Abstract Microfluidic fuel cell (MFC) is a considered as a promising energy source for powering portable electronic devices due to low cost and easy control. However, the energy density of MFC is much lower than conventional batteries like lithium battery. Due to the fuel crossover, the optimized operation concentration remains 1-2 M. In this paper, a counter-flow MFC is presented to achieve concentrated fuel. Density mismatch between fuel and electrolyte is the key cause for fuel crossover. Experimental and modeling study confirms that through adjusting different channel design according to fuel concentration, fuel crossover can be prevented.

Partial modification of flow-through porous electrodes in microfluidic fuel cell

The use of flow-through porous electrodes is identified as a promising approach to enhance the performance of microfluidic fuel cell (MFC). In this study, a dimensionless computational model is developed to analyze the distribution characteristics of the electrochemical reactions in flow-through porous electrodes of MFC. One important finding is that the electrochemical reactions mainly occur in the vicinity of the anode and cathode outlets. Based on this observation, the new design of partial modification at reactive sites is proposed to reduce the MFC cost. It is found that MFC with partial modification can achieve comparable performance with that of conventional full electrode modification, demonstrating the feasibility of partial modification method. The partial modification also offers a promising alternative to avoid unwanted secondary reaction, such as hydrogen evolution.

Fabrication and Test of an Air-Breathing Microfluidic Fuel Cell

An air-breathing direct formic acid microfluidic fuel cell, which had a self-made anode electrode of 10 mg/cm2 Pd loading and 6 mg/cm2 Nafion content, was fabricated and tested. The microfluidic fuel cell was achieved by bonding a PDMS microchannel that was fabricated by a soft-lithography process and a PMMA sheet that was machined by a CO2 laser for obtaining 50 through holes of 0.5 mm in diameter. Formic acid of 0.3 M, 0.5 M, and 1.0 M, mixed with 0.5-M H2SO4, was supplied at a flow rate ranging from 0.1 to 0.7 mL/min as fuel. The maximum power density of the fuel cell fed with 0.5-M HCOOH was approximately 31, 32.16, and 31 mW/cm2 at 0.5, 0.6, and 0.7 mL/min, respectively. The simultaneous recording of the flow in the microchannel and the current density of the fuel cell at 0.2 V, within a 100-s duration, showed that the period and amplitude of each unsteady current oscillation were associated with the bubble resident time and bubble dimension, respectively. The effect of bubble dimension included the longitudinal and transverse bubble dimension, and the distance between two in-line bubbles as well.

Counter-flow formic acid microfluidic fuel cell with high fuel utilization exceeding 90%

Microfluidic fuel cell (MFC) is a promising energy source for portable applications, which draws lots of R&D attention. However, MFCs fed with hydrocarbon fuel like formic acid suffers low fuel utilization problem because of sluggish kinetics, complicate reaction condition and dilemma on cell control. In this work, a formic acid MFC based on counter-flow design is proposed. This counter-flow structure is verified a promising design for high Graetz number operation, which is especially beneficial for high fuel utilization manipulation of MFC. A breakthrough in fuel utilization is achieved and the highest fuel utilization of 91.4% is obtained at 1μLmin−1. It is revealed that counter-flow MFC is capable for low flow rate operation, which is significant for reduce the pump energy consumption and improve the energy efficiency of MFC system. Each potential loss involved in counter-flow MFC is categorized and it is found that potential loss caused by internal resistance hinders performance mostly.

Direct Formic Acid Microfluidic Fuel Cell with Pd Nanocubes Supported on Flow-Through Microporous Electrodes

crystallographicplanes and flow-through microporous electrodes with high surface area. The high performance is attributed to the favorable sizeand shape of the catalyst, the high surface-to-volume ratio, and the high localized mass transport rates inside the flow-throughmicroporous electrodes. These results open up the opportunity to utilize oxygen as oxidant in miniaturized electrochemical cellswithout the constraints imposed by integration of air-breathing cathodes exposed to surrounding air.© The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative CommonsAttribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/),whichpermitsnon-commercialreuse,distribution,andreproductioninanymedium,providedtheoriginalworkisnotchangedinanyway and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0031504eel]All rights reserved.Manuscript submitted October 29, 2014; revised manuscript received January 26, 2015. Published February 5, 2015.

Membraneless Microfluidic Fuel Cell with Silver Electrode Fabricated by Low Temperature Co-fired Ceramic Combined with Photolithography

Membraneless Microfluidic Fuel Cell with Silver Electrode Fabricated by Low Temperature Co-fired Ceramic Combined with Photolithography