Search Results (12)

This review reveals the parameters of next-generation fuel cells for portable applications such as cellular phones, laptops, automobiles, etc. Disputes over issues such as design, fluid dynamics, channel dimensions, thermal management, and water management must be overcome for practical applications. We examine techniques such as microfabrication, material selection for membranes and electrodes, and integration challenges in small-scale devices, in addition to issues like methanol crossover, low efficiency at high methanol concentrations, thermal management, and the cost of materials. The advancements in micro-DMFC stacks and prototype developments are presented, and the challenges relating to micro-DMFCs are also identified and reviewed in detail. The challenges in the development of micro-DMFC applications are also presented, including the need for a better understanding of the anode and cathode catalyst structure and for high catalyst loadings in oxidation-and-reduction reactions. Also, a comprehensive and highly valuable database for advancing innovations and enhancing the understanding of micro-DMFCs for potential applications is provided. Full article

Micro direct methanol fuel cells (μDMFCs) are a promising power source for microelectronic devices and systems. As the operating state and performance of a μDMFC is generally determined by both electrochemical polarization and methanol crossover, it is important to monitor the methanol concentration in μDMFCs. Here, we design and fabricate a microwave sensor and integrate it with a μDMFC for the online detection of methanol concentration in a nonintrusive way. The sensing area is set at the bottom of the anode chamber of a μDMFC which exhibits a maximum output power density of 28.8 mW cm⁻² at 30 °C. With a square ring structure, the dual-mode microwave sensor shows a sensitivity of 9.5 MHz mol⁻¹ L. Furthermore, the importance of methanol concentration monitoring is demonstrated in the long term. A relatively smooth methanol decline curve was obtained, which indicated a normal and stable operating status of the μDMFC. Derived from real-time recording data, fuel utilization was additionally calculated as 28.5%. Full article

The diffusion layer (DL) in the structure of the membrane electrode assembly (MEA) of a micro direct methanol fuel cell (μDMFC) plays an essential role in reactant/product mass transfer and catalyst loading. The material selection and structure design of the μDMFC affects its performance. In this work, a reduced graphene oxide/carbon paper (rGO/CP) was proposed and prepared for the anode DL of a μDMFC. It was prepared using electrophoretic sedimentation combined with an in situ reduction method. The rGO/CP reduced the cell’s ohmic and charge transfer resistances. Meanwhile, it provided more significant mass transfer resistance to reduce the methanol crossover, allowing the cell to operate stably at higher concentrations for a longer duration than conventional μDMFCs. The experimental results showed that the maximum power density increased by 53% compared with the traditional anode DL of carbon paper. Full article

Micro-direct-methanol fuel cells ($\mu$DMFCs) use micro-electro mechanical system (MEMS) technology, which offers high energy density, portable use, quick replenishment, and free fuel reforming and purification. However, the $\mu$DMFC is limited by a short effective service life due to the membrane electrode’s deterioration in electrochemical reactions. This paper presents a health status assessment and remaining useful life (RUL) prediction approach for $\mu$DMFC under dynamic operating conditions. Rather than making external observations, an internal characterization is used to describe the degradation indicator and to overcome intrusive influences in operation. Then, a Markov-process-based usage behavior prediction mechanism is proposed to account for the randomness of real-world operation. The experimental results show that the proposed degradation indicator alleviates the reduction in $\mu$DMFC output power degradation behavior caused by the user loading profile. Compared with the predictions of RUL using traditional external observation, the proposed approach achieved superior prognostic performance in both accuracy and precision. Full article

For micro direct methanol fuel cell (μDMFC), water flooding on the cathode seriously affects the performance stability. Additionally, the effect of material and wettability of the cathode current collector (CCC) on the drainage capacity is studied to improve the μDMFC’s performance. To this end, a CCC with foamed stainless steel was prepared to assemble the μDMFC due to its absorbency. Further, based on analyzing the gas–liquid two-phase flow characteristics of the μDMFC cathode, it was found that the gradient wettability CCC could accelerate the discharge of cathode water. Hence, the foam stainless steel CCC was partially immersed in a KOH solution to complete the gradient corrosion using its capillary force. Then, four different types of gradient wettability CCC were prepared by controlling the time of chemical corrosion. Finally, the performance of the μDMFC with different gradient wettability CCC was tested at room temperature using electrochemical impedance spectroscopy (EIS) and discharge voltage. The experimental results show that the gradient wettability CCC can improve the performance of the μDMFC by slowing down the rate of cathode flooding. The optimum corrosion time is 5 min at a concentration of 1 mol/L. Under these conditions, the CCC has the best gradient wettability, and the μDMFC has the lowest total impedance. The discharge voltage of the μDMFC with corroded CCC is increased by 33.33% compared to the uncorroded CCC μDMFC. The gradient wettability CCC designed in this study is economical, convenient, and practical for water management of the μDMFC. Full article

The micro direct methanol fuel cell ($\mu$DMFC) has attracted more and more attention in the field of new energy due to its simple structure, easy operation, and eco-friendly byproducts. In a $\mu$DMFC’s structure, the current collector plays an essential role in collecting the conduction current, and the rational distribution of gas and water. The choice of its material and flow fields would significantly impact the $\mu$DMFC’s performance. To this end, four different types of cathode current collector were prepared in this study. The materials selected were stainless steel (SS) and foam stainless steel (FSS), with the flow fields of hole-type and grid-type. The performance of the $\mu$DMFC with different types of cathode current collector was investigated by using polarization curves, electrochemical impedance spectroscopy (EIS), and discharging. The experimental results show that the maximum power density of $\mu$DMFC of the hole-type FSS cathode current collector is 49.53 mW/cm² at 70 °C in the methanol solution of 1 mol/L, which is 115.72% higher than that of the SS collector. The maximum power density of the $\mu$DMFC with the grid-type FSS collector is 22.60 mW/cm², which is 27.39% higher than that of the SS collector. The total impedance of the $\mu$DMFC of the FSS collector is significantly lower than that of the $\mu$DMFC of the SS collector, and the total impedance of the $\mu$DMFC with the hole-type flow field collector is lower than that of the grid-type flow field. The discharging of $\mu$DMFC with the hole-type FSS collector reaches its optimal value at 70 °C in the methanol solution of 1 mol/L. Full article

A membrane electrode assembly (MEA) with a novel trilaminar-catalytic layered structure was designed and fabricated for a micro-direct methanol fuel cell (μ-DMFC). The trilaminar-catalytic layer comprises three porous layers. The medial layer has a lower porosity than the inner and outer layers. The simulation results predicted a lower water content and a higher oxygen concentration in the trilaminar-catalytic layer. The novel trilaminar-catalytic layer enhanced the back diffusion of water from the cathode to the anode, which reduces methanol crossover and improves oxygen mass transportation. The electrochemical results of the half-cell test indicate that the novel MEA has a greatly increased cathode polarization and a slightly increased anode polarization. Thus, this novel μ-DMFC structure has a higher power density and a longer discharging time, and hence may be used in portable systems. Full article

The effect of an anode composite electrode on the performance of a micro direct methanol fuel cell (μDMFC) is analyzed from sample preparation configurations and discussed in detail, with a specific focus on the catalyst layer and the micro-porous layer on the anode composite electrode. This study investigates the effects of Pt content, Pt-Ru molar ratio, Nafion content, catalyst support, and preparation method in the catalyst layer, along with the carbon loading and polytetrafluoroethylene (PTFE) content in the micro-porous layer, on the performance of the anode composite electrode. The results show that the anode composite electrode delivers the best performance with 30% Pt content, a 1:1.5 Pt-Ru molar ratio, 10% Nafion content on reduced graphene oxide as the catalyst support. The synthesis is optimized with the impregnation reduction method using NaBH₄ as the reducing agent, with the addition of 1.5 mg/cm² carbon loading and 5% PTFE. Full article

In order to solve the problem that bolts in traditional packaged direct methanol fuel cells (DMFCs) take up a large area and reduce the specific energy (energy per unit weight) and power density (power per unit area), a new button-type micro direct methanol fuel cell (B-μDMFC) is designed, assembled, and packaged. The cell with four different structures was tested before and after packaging. The results indicate that the button cell with three-dimensional graphene and springs has the best performance. The equivalent circuit and methanol diffusion model was applied to explain the experimental results. The peak volumetric specific power density of the cell is 11.85 mW cm⁻³. This is much higher than traditional packaged DMFC, because the novel B-μDMFC eliminates bolts in the structure and improves the effective area ratio of the cell. Full article

To achieve a self-adaptive fuel supply mechanism for the micro direct methanol fuel cell (μDMFC), we designed and developed a thermal control microvalve channel structure, where we considered the relationship between the temperature characteristics, viscosity, and velocity of the methanol solution. Both the single channel model and three-dimensional cell model for the microvalve were established using the COMSOL Multiphysics program. The results demonstrated that in the microvalve channel, the viscosity of the solution decreased, and the flow rate at the microvalve outlet increased with the increasing temperature. Meanwhile, the geometry structure of the microvalve single channel was optimized, so that the effect of the control speed of the microvalve under temperature changes became more prominent. In the full-cell model analysis, a low-velocity methanol solution at the low current density can significantly inhibit methanol crossover. At the high current densities, an increase in the methanol solution flow rate was beneficial to an increase in the cell reaction output. The μDMFC was fabricated and the experiment was conducted, where the results showed that the power density of the self-adaptive cell reached a maximum value of 16.56 mW/cm² in 2 M methanol solution, which was up to 7% better than conventional cell performance. The proposed microvalve structure can effectively improve the output power of the μDMFC during the whole reaction process, and it may improve the stability of the cell operation. Full article

A dual-chamber anode structure is proposed in order to solve two performance problems of the conventional passive micro direct methanol fuel cell (μ-DMFC). One of the problems is the unstable performance during long time discharge. The second problem is the short operating time. In this structure, low concentration chamber is filled with methanol solution with appropriate concentration for the μ-DMFC. Pure methanol in high concentration chamber diffuses to the low concentration chamber to keep the concentration of methanol solution suitable for long-term discharge of μ-DMFC. In this study, a Nafion-Polytetrafluoroethylene (PTFE) composite membrane is inserted between the two chambers to conduct pure methanol. The experimental results during long-term discharge show that the stable operating time of passive μ-DMFC increases by nearly 2.3 times compared to a conventional one with the same volume. These results could be applied to real products. Full article

Clogging of anode flow channels by CO₂ bubbles is a vital problem for further performance improvements of the micro direct methanol fuel cell (μDMFC). In this paper, a new type anode structure usingthe concept of the non-equipotent serpentine flow field (NESFF) to solve this problem was designed, fabricated and tested. Experiments comparing the μDMFC with and without this type of anode flow field were implemented using a home-made test loop. Results show that the mean-value, amplitude and frequency of the inlet-to-outlet pressure drops in the NESFF is far lower than that in the traditional flow fields at high μDMFC output current. Furthermore, the sequential images of the CO₂ bubbles as well as the μDMFC performance with different anode flow field pattern were also investigated, and the conclusions are in accordance with those derived from the pressure drop experiments. Results of this study indicate that the non-equipotent design of the µDMFC anode flow field can effectively mitigate the CO₂ clogging in the flow channels, and hence lead to a significant promotion of the μDMFC performance. Full article