Direct Methanol Fuel Cell Power Research Articles

Adaptive Joint Multiobjective Operating Parameters’ Optimization for Active Direct Methanol Fuel Cells

The operating parameters of the active direct methanol fuel cell (DMFC) are essential factors affecting its power delivery performance. Different operating parameters lead to variations in the amount of methanol crossover in a DMFC, which might cause overpotential and cathode catalyst poisoning. Due to the complexity of the DMFC system, changes in operating conditions, and correlations among these parameters, it is challenging to maintain output power density while reducing the negative effects of methanol crossover. This paper proposes an adaptive joint optimization method for fuel cell operating parameters. The principle operating parameters are selected by the orthogonal tests, which include an adaptive numerical simulation and multiobjective optimization regarding cell output power density and methanol crossover. The selected parameter combinations are verified by an evaluation model that quantifies the influences of operating parameters on the active DMFC power density and its methanol crossover, where the nonlinear mapping function for the two optimization objectives is obtained. The nondominated sorting genetic algorithm‐II (NSGA‐II) is applied to rapidly obtain the optimal combination. The results show that with the optimal parameters, the maximum power density is increased by 16.7% and the methanol crossover is reduced by 35.1%.

Effects on the electrochemical performance of surface-modified mordenite in a PTFE Nafion composite membrane for direct methanol fuel cells

Mordenite (MOR)/PTFE Nafion composite membranes were produced by impregnating Nafion solutions in a PTFE porous support with a modified form of MOR. A 3-mercaptopropyl triethoxysilane (MPTES) - MOR mixture is used as a filler in the PTFE Nafion membrane to block methanol crossover and increase water uptake. An experiment was conducted with a membrane without M-MOR (PTFE Nafion membrane) and a membrane with M-MOR at 2, 4, and 10 wt% (2-, 4-, and 10-M-MOR/PTFE Nafion membranes, respectively). In order to improve the interfacial properties, surface modification of the zeolite was conducted with a silane coupling reaction. The MOR samples were analyzed by SEM, SEM-EDS, and BET surface area analysis. The Nafion membrane was analyzed by SEM, according to the water uptake, and by an electrochemical analysis. The 10-M-MOR/PTFE Nafion membrane showed greater water uptake of 75% compared to the PTFE Nafion membrane without M-MOR (28%). It was found that the addition of MOR had a positive effect on the reduction of the methanol permeability of the MOR/PTFE Nafion membrane. The DMFC (Direct Methanol Fuel Cell) power density of MEA with the 4-M-MOR/PTFE Nafion membrane (4-M-MOR MEA) was found to be 71% higher than that of the PTFE Nafion membrane (0-M-MOR MEA).

Boosting DMFC power output by adding sulfuric acid as a supporting electrolyte: Effect on cell performance equipped with platinum and platinum group metal-free cathodes

Direct methanol fuel cells (DMFCs) are promising electrochemical systems capable of producing electricity from the electrochemical oxidation of methanol and the reduction of oxygen. In this work, the effectiveness of the addition of sulfuric acid as a supporting electrolyte for methanol fuel composition was assessed. The results showed that the peak of power curve in DMFCs with Pt/C cathode electrocatalysts increased progressively from 70 mW cm−2 (0 mM of H2SO4) to 115 mW cm−2 with a concentration of 100 mM of H2SO4. These results underlined the positive effect of the addition of a supporting electrolyte in the methanol aqueous solution on the electrochemical output that was enhanced. Platinum group metal-free (PGM-free) electrocatalysts based on Fe-Nx-C type were also tested being insensitive to methanol crossover and oxidation at the cathode. DMFC with Fe–N–C cathode catalysts result in a performance of 21.5 mW cm−2. In these operating conditions, the addition of supporting electrolyte does not seem to bring excessive advantage. Short stability tests are presented and an overall assessment of the resistances within the system is also discussed.

Flexible All-Solid-State Direct Methanol Fuel Cells with High Specific Power Density.

It is vital to create flexible batteries as power sources to suit the needs of flexible electronic devices because they are widely employed in wearable and portable electronics. The direct methanol fuel cell (DMFC) is a desirable alternative portable energy source since it is a clean, safe, and high energy density cell. The traditional DMFC in mechanical assembly and its unbending property, however, prevent it from being employed in flexible electrical devices. In this study, the flexible membrane electrode assembly (MEA) with superior electrical conductivity and nanoscale TiC-modified carbon cloth (TiC/CC) is used as supporting layer. Additionally, solid methanol fuels used in the manufacturing of flexible all-solid-state DMFC have the advantages of being tiny, light, and having high energy density. Furthermore, the DMFC's placement and bending angle have little effect on its performance, suggesting that DMFC is appropriate for flexible portable energy. The flexible all-solid-state DMFC's power density can reach 14.06mWcm-2 , and after 50 bends at 60°, its voltage loss can be disregarded. The flexible all-solid DMFC has an energy density that is 777.78WhKg-1 higher than flexible lithium-ion batteries, which is advantageous for the commercialization of flexible electronic products.

Improved performance of nafion membranes by blending ultra-high molecular weight polyvinylidene fluoride

Proton exchange membrane (PEM) is developing towards thin thickness and high mechanical strength for extraordinary performance proton exchange membrane fuel cells (PEMFCs). However, the commercial membrane such as Nafion can hardly satisfy the practical application of PEMFCs because of high gas crossover and low mechanical strength when the thickness is less than 20 μm. Here, a reinforced composite membrane (denoted as P110-PFSA) was synthesized by blending poly(vinylidene fluoride)(PVDF) featured with high molecular weight of Mw= 1100000 g mol-1 into perfluorosulfonic acid resin (PFSA). The P110-PFSA with the thickness of 15 μm exhibits tensile strength of over 33 MPa because the PVDF with high molecular weight forms a higher density of hydrogen bonds with PFSA, resulting in a reinforcement of the bonding strength between PVDF and PFSA. H2/O2 fuel cell performance with the P110-PFSA shows more than 1170 mW cm-2 fed with H2 at 70 °C and 100% RH much better than that with Nafion 211. Direct methanol fuel cell power densities of the blent PEM are 92, 61, 50, 28 and 15 mW cm-2 fed with 2, 6, 10,16 and 20 M methanol solution respectively at the anode.

Passive direct methanol fuel cells acting as fully autonomous electrochemical biosensors: Application to sarcosine detection

This work describes an innovative electrochemical biosensor that advances its autonomy toward an equipment-free design. The biosensor is powered by a passive direct methanol fuel cell (DMFC) and signals the response via an electrochromic display. Briefly, the anode side of the DMFC power source was modified with a biosensor layer developed using molecularly imprinted polymer (MIP) technology to detect sarcosine (an amino acid derivative that is a potential cancer biomarker). The biosensor layer was anchored on the surface of the anode carbon electrode (carbon black with Pt/Ru, 40:20). This was done by bulk radical polymerization with acrylamide, bis-acrylamide, and vinyl phosphonic acid. This layer selectively interacted with sarcosine when integrated into the passive DMFC (single or multiple, in a stack of 4), which acted as a transducer element in a concentration-dependent process. Serial assembly of a stack of hybrid DMFC/biosensor devices triggered an external electrochromic cell (EC) that produced a colour change. Calibrations showed a concentration-dependent sarcosine response from 3.2 to 2000 µM, which is compatible with the concentration of sarcosine in the blood of prostate cancer patients. The final DMFC/biosensor-EC platform showed a colour change perceptible to the naked eye in the presence of increasing sarcosine concentrations. This colour change was controlled by the DMFC operation, making this approach a self-controlled and self-signalling device. Overall, this approach is a proof-of-concept for a fully autonomous biosensor powered by a chemical fuel. This simple and low-cost approach offers the potential to be deployed anywhere and is particularly suitable for point-of-care (POC) analysis.

Optimization of Direct Methanol Fuel Cell Power System

Wydawnictwo SIGMA-NOT wydaje czasopisma fachowe informujące swoich czytelników o najnowszych osiągnięciach naukowych i nowoczesnych rozwiązaniach technicznych w Polsce i na świecie, popularyzuje problemy techniczne oraz poszerza wiedzę i kulturę techniczną.

A Portable Direct Methanol Fuel Cell Power Station for Long-Term Internet of Things Applications

With regard to the best electro-chemical efficiency of an active direct methanol fuel cell (DMFC), the stacks and their balance of plant (BOP) are complex to build and operate. The yield of making the large-scale stacks is difficult to improve. Therefore, a portable power station made of multiple simpler planar type stack modules with only appropriate semi-active BOPs was developed. A planar stack and its miniature BOP components are integrated into a semi-active DMFC stack module for easy production, assembly, and operation. An improved energy management system is designed to control multiple DMFC stack modules in parallel to enhance its power-generation capacity and stability so that the portability, environmental tolerance, and long-term durability become comparable to that of the active systems. A prototype of the power station was tested for 3600 h in an actual outdoor environment through winter and summer. Its performance and maintenance events are analyzed to validate its stability and durability. Throughout the test, it maintained the daily average of 3.3 W power generation with peak output driving capability of 12 W suitable for Internet of Things (IoT) applications.

Chitosan/sulfonated graphene oxide/silica nanocomposite membranes for direct methanol fuel cells

Silica nanoparticles on sulfonated graphene oxide (sGO/SiO2) are incorporated with chitosan (CS) in tunable compositions and their performances as ion conductors in direct methanol fuel cells (DMFC) are evaluated. The morphological observations reveal that sGO/SiO2 nanocomposite is homogeneously distributed throughout the CS matrix. The anisotropic and strong bonds created among the carbon atoms of functionalized GO nanosheets and the ceramic characteristic of SiO2 nanofillers promote the thermal stability of CS/sGO/SiO2 composite membrane than that of bare CS membrane. The hydrophilic sites provided via the sulfonated moieties of GO and hygroscopic characteristics of SiO2 nanoparticles improve the water adsorption channels. The hydrogen bonding and acid-base pair interaction exerted between the CS and sGO/SiO2 facilitate the continuous and rapid ion conduction via grotthuss mechanism. The high aspect ratio of sGO and the effectively piled SiO2 nanoparticles generate tortuous channels for methanol diffusion. Thus the selective passage of ions and fuel in CS/sGO/SiO2 composite membrane provides the maximum DMFC power density of 87.18 mW cm−2 with considerable duration, which confers the prosperous light on the utility of environmentally benign and bio-degradable CS membrane in DMFCs.

Cumulative effect of bimetallic alloy, conductive polymer and graphene toward electrooxidation of methanol: An efficient anode catalyst for direct methanol fuel cells

In this article, we report a wet reflux strategy for the synthesis of reduced graphene oxide (rGO)/polyaniline (PANI)/Pt-Pd composite, which was exploited as a potential anode catalyst with enhanced methanol oxidation capacity for direct methanol fuel cells (DMFCs). The construction of rGO/PANI/Pt-Pd involves two steps such as synthesis of PANI on GO and in-situ reduction of GO and metal precursors. The spherical shaped Pt-Pd particles with the average size of 3.5 nm are scattered throughout the surface of rGO/PANI, as observed from transmission electron microscope (TEM). PANI tailors the surface of rGO to allow the uniform scattering of Pt-Pd, which is beneficial for adsorption and decomposition of methanol. Besides, PANI generates strong interaction with Pt-Pd through nitride bond, thereby enhances the durability of composite. The cumulative features of rGO/PANI/Pt-Pd include active carbon support, extended architecture of electron conducting channels and number of methanol oxidation centers endows excellent DMFC power density of 117.45 mW/cm2 and concrete cell durability over 70 h. Therefore, the proposed rGO/PANI/Pt-Pd can be used to address various critical issues associated with commercial Pt/C catalyst.

Polybenzimidazole Supported Monolayer Graphene Membrane for Inexpensive PEM Fuel Cells

One atom thick structure of the two dimensional single layer graphene has distinguished itself as a very promising material due to its unique properties. Excellent in-plane electron conductivity and permeability to proton but barrier to other kinds makes it a very tempting and cost effective membrane material for environment friendly alternative energy devices-proton exchange membrane (PEM) fuel cells. Expensive Nafion and Pt are the commonly used membrane and catalyst for fuel cells, covering 50 % of the total amount of the fuel cell cost [1]. To make them commercially viable, the overall cost needs to be reduced or the performance has to be enhanced at the expense of the same cost. Our work showed that incorporation of monolayer graphene into the membrane electrode assembly with the Nafion enhances the direct methanol fuel cell power density by 45 %, owing to the graphene’s methanol barrier properties [2]. In this work we report inexpensive polybenzimidazole (PBI) membrane as mechanical support for the monolayer graphene substituting Nafion. The composites are tailored with different degrees of graphene coverage. The influence of these ‘defects’ are studied with respect to the fuel cell operation in different conditions. Further functionalization of the composition demonstrated to be a cost effective solution, showing a good prospect as an alternative to Nafion.

Improved performance of direct methanol fuel cells with the porous catalyst layer using highly-active nanofiber catalyst

PtRu supported on TiO2-embedded carbon nanofibers (PtRu/TECNF), which was recently reported as a highly-active catalyst for methanol oxidation, was applied to a direct methanol fuel cell (DMFC), and the power generation performance was compared to that using the commercial PtRu/C. Before the comparison, the effect of the catalyst loading on the power density of the DMFC was investigated using PtRu(18 wt%)/TECNF. The DMFC power density showed a maximum at about a 1.5 mg cm−2 PtRu loading that corresponds to about an 80 µm layer thickness. A catalyst layer thicker than this value reduced the power density probably due to the concentration overvoltage. The PtRu content in the PtRu/TECNF was then increased to 30 wt% or more to reduce the layer thickness and to increase the power density. The DMFC performance was compared to that of different anode catalysts at a 1 mg cm−2 PtRu loading. The power density was maximized using the PtRu30 wt%/TECNF, which showed a 173 mW cm−2 at 353 K and had 66 µm layer thick, that was 26% higher than that of commercial PtRu/C. The current–voltage curve of the DMFC with the PtRu/TECNF suggested an improved mass transport overvoltage, but a little improvement in the activation one despite using the catalyst with about a 2 times higher activity compared to that of the commercial PtRu/C. This was attributed to the lower Pt utilization of the nanofiber catalyst layer.

Functionalized fullerene embedded in Nafion matrix: A modified composite membrane electrolyte for direct methanol fuel cells

Methanol permeability is a major concern for Nafion® membranes used as polymer electrolyte in direct methanol fuel cells (DMFCs). In the present study, composite membranes are formed by incorporation of functionalized fullerene (FF) in Nafion® ionomer for its use as electrolytes in direct methanol fuel cells at various methanol concentrations. Fullerene was functionalized by 4-benzene diazonium sulfonic acid precursor formed via diazotization reaction of sulfanilic acid. Surface functionalization and sulfonation of fullerene is confirmed by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and elemental analysis. Structural changes in fullerene are determined by transmission electron microscopy (TEM) analysis. The composite membranes of Nafion®-FF are prepared by solvent casting technique and characterized for their physico-chemical properties in terms of water uptake, proton conductivity and methanol permeability. The morphological changes are observed by field emission scanning electron microscopy (FE-SEM) suggesting the FF distribution in Nafion® and atomic force microscopy (AFM) explaining the presence of FF in the ionic clusters of Nafion® thereby increasing the surface roughness. Nafion®-FF composite membranes show improved proton conductivity due to the presence of surface functional –SO3H groups. Composite membranes exhibit better electrochemical selectivity and as a result enhanced DMFC power output in comparison to recast Nafion®. In addition, methanol permeability and DMFC polarization for the optimized composite membrane are carried out at different methanol concentration. The peak power density of 146mWcm−2 in DMFC is obtained for Nafion®-FF (1wt.%) at 2M methanol which is higher than the performance observed for Nafion-117. Open circuit voltage change is minimal with respect to time for Nafion®-FF (1wt.%) confirming its better stability in comparison with recast Nafion® and on par with Nafion-117.

Optimum design parameters and operating condition for maximum power of a direct methanol fuel cell using analytical model and genetic algorithm

It is well known that anode and cathode pressures, cell temperature and channel geometry are the effective parameters in the performance of DMFC (direct methanol fuel cell). In the present paper, the GA (genetic algorithm) as one of the most powerful optimization tools is applied to determine the optimal values for these parameters which result in maximum power density of a DMFC. The predominant part of the genetic algorithm is the fitness function. For the fitness function calculation, calculation of more than one thousand cases is necessary. Unfortunately, large numbers of experiments are needed, which is very time-consuming and costly. To overcome this challenge, a quasi two dimensional, isothermal model is used to obtain the power of DMFC as the fitness function of GA. For validation of this model, the results of the model are compared with experimental results and literature and shown to be in good agreement with them.

Novel O2-enhanced methanol oxidation performance at Pt–Ru–C sputtered anode in direct methanol fuel cell

We have developed a novel anode catalyst for the direct methanol fuel cell (DMFC). A Pt–Ru–C electrode was prepared by a co-sputtering technique and compared with Pt and Pt–Ru sputtered electrodes for the methanol electro-oxidation reaction. The prepared Pt–Ru–C electrode with a specific atomic ratio showed a remarkable O2-enhanced methanol oxidation performance by O2 addition to methanol as a fuel. For practical utilization, the relationship between the O2-enhanced methanol oxidation activity and the thermal stability of the Pt–Ru–C sputtered electrode was evaluated using a post-annealing treatment. It is found that the O2-enhanced methanol oxidation activity of the Pt–Ru–C electrodes is retained if the annealing temperature is less than or equal to 100 °C. Finally, the DMFC performance was assessed using a single DMFC cell incorporating a membrane electrode assembly with Pt–Ru–C which was hot-pressed at 100 °C. The O2-enhanced methanol oxidation was observed at a single DMFC cell also. Moreover, the enhanced reaction was recognized in DMFC power generation by feeding methanol and oxygen to the anode and oxygen to the cathode.

A Direct Methanol Fuel Cell Power System for the Battery Charging in Electric Vehicle

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Effect of Porosity in Catalyst Layers on Direct Methanol Fuel Cell Performances

AbstractEffects of porosity of catalyst layers (CLs) on direct methanol fuel cell (DMFC) performances are investigated using silicon dioxide (SiO2) particles as a pore former. The pore size and volume of CLs are controlled by changing the size and content of SiO2. As the size of pore formed by removal of SiO2 increases, DMFC performances are enhanced. The augmentation in performances can be explained by facilitation of fuel transport to catalyst particles, increase of utilization efficiency of catalysts, diminishment in methanol crossover, reduction in activation loss and facilitation of water discharging out of CLs of cathode due to the controlled porosity in CLs. The enhanced fuel transport, accessibility of fuels to Pt catalyst surface, is proved by the active areas of Pt catalyst. In addition to the active area of Pt catalyst, porous CLs exhibit a decline in methanol crossover, leading to increase of open circuit voltage (OCV). The porous CLs also show improvements in activation loss due to high porosity, causing enhancement in DMFC performances. In aspect of pore volume contribution to cathode performance, the SiO2 content is optimized. Based on the DMFC performances, it can be suggested that the optimum conditions of SiO2 are 500 nm in size and 20 wt.% in content. The porosity effect on both electrodes appears as follows: the pores in cathode are more effective on DMFC performances (55.5%) than those of anodes (44.5%) based on the maximum power of DMFC, indicating that the pores in CLs facilitate removal of water from electrodes.

In situ activation procedures applied to a DMFC: Analysis and optimization study

A direct methanol fuel cell (DMFC) needs to be activated to achieve its maximum performance. The activation procedure includes a pre-treatment and an in situ activation procedure. Along the activation procedure the membrane electrode assembly (MEA) experiments significant changes that are studied by electrochemical impedance spectroscopy (EIS), polarization curves and methanol crossover measurements. It is shown that the activation procedure makes the proton conductivity of the PEM to increase as well as the catalyst area and activity. The DMFC power density increases from 8.8mWcm−2 to 22.4mWcm−2 at 55°C along the activation procedure. The Design of Experiments (DoE) methodology was then applied to optimize the in situ activation, where loading cycles were employed. The factors considered for the experimental design were the temperature, the loading and the cathode air pressure. The maximum power density response was optimized using a central composite design (CCD). It was also verified that the potential was the most significant factor. Finally, the in situ loading cycles procedure was critically compared with other in situ activation procedures reported in the literature. It was concluded that the hydrogen conditioning and the in situ loading cycles procedure led to the best performance of the DMFC.

Water Management in Micro Direct Methanol Fuel Cells: Using Integrated Passive Micromixer

In a DMFC (direct methanol fuel cell), water management is a critical issue for enhancing DMFC power per- formance and lifetime. However, the methanol-water mixing tank for water management is difficult to be miniaturized and integrated into a micro-DMFC. This paper proposes an in-fuel cell micromixer, the self-vortical micromixer, which belongs to a passive micromixer, to perform methanol and water mixing inside a micro-DMFC. Experimental results demonstrate the design, fabrication, and testing results of the self-vortical micromixer integrated with the micro-DMFC, showing that the self-vortical micromixer has high fluidic mixing performance and can be oper- ated in the micro-DMFC as a methanol-water mixing tank for water management of the micro-DMFC. The power performance testing results demonstrate that the single cell of micro-DMFC, with the included self-vortical micromixer, exhibits a maximum power density of 21.27 mW/cm 2 .

Electrochemical Impedance Spectroscopy of Direct Methanol Fuel Cell Having Ag/Ag2SO4 Reference Electrode

In this study, we succeeded in measuring the impedance spectra at the anode and cathode during the direct methanol fuel cell power generation using a single cell having a Ag/Ag2SO4 reference electrode. When the anode impedance is measured at 20 mA cm−2, two semicircles are observed in the high and middle frequency ranges, and the magnitude of the latter one increases with the increasing methanol concentration. At the cathode, the impedance spectra at 20 mA cm−2 show three semicircles, of which the magnitudes decrease with the increasing methanol concentration from 1 mol dm−3 to 5 mol dm−3, and increase again at 10 mol dm−3. These results demonstrate that the increased methanol concentration magnifies the methanol oxidation reaction resistance at the anode and affects the total resistance at the cathode.