•Very thin SPSf/ZrP composite membranes were prepared by solution casting method.•The viability of SPSf/ZrP membranes for DMFCs was investigated for the first time.•Superior proton conductivity over ...Nafion® 115 was achieved between 45–80°C.•Desired membrane characteristics, along with low manufacturing cost were achieved.•Single cell DMFC performance was improved up to 13%.
Direct methanol fuel cell (DMFC) technology has advanced perceivably, but technical challenges remain that must be overcome for further performance improvements. Thus, in this study, sulfonated polysulfone/zirconium hydrogen phosphate (SPSf/ZrP) composite membranes with various sulfonation degrees (20%, 35%, and 42%) and a constant concentration of ZrP (2.5%) were prepared to mitigate the technical challenges associated with the use of conventional Nafion® membranes in DMFCs. The composite membranes were investigated through Scanning Electron Microscopy (SEM), Electrochemical Impedance Spectroscopy (EIS), Thermogravimetric Analysis (TGA), oxidative stability and water uptake measurements, and single cell testing. Comparison was also made with Nafion® 115. Single cell tests were performed under various methanol concentrations and cell temperatures. Stability characteristics of the DMFCs under charging and discharging conditions were investigated via 1200min short-term stability tests. The response characteristics of the DMFCs under dynamic conditions were determined at the start-up and shut-down stages. Composite membranes with sulfonation degrees of 35% and 42% were found to be highly promising due to their advanced characteristics with respect to proton conductivity, water uptake, thermal resistance, oxidative stability, and methanol suppression. For the whole range of parameters studied, the maximum power density obtained for SPSf/ZrP-42 (119mWcm−2) was found to be 13% higher than that obtained for Nafion® 115 (105mWcm−2).
In an attempt to improve upon conventional flow fields (e.g., serpentine flow field), Murray's Law was applied to design two different bio-inspired, leaf-shaped flow fields. This law governs the ...dimensions of natural networks, such as: the veins within plant leaves and human lungs. In this study, the serpentine, the lung, and the two leaf-shaped flow fields were used to form seven different anode–cathode combinations. The experiments focused on the effects of methanol concentration (0.50 M, 0.75 M, and 1.00 M) and the combined effect of methanol and oxygen flow rates (1.3 ml/min methanol and 400 ml/min oxygen, as well as 2 and 3 times both of these flow rates). An analytical model was also developed to help understand the experimental results. The results show that the highest performance could be achieved when the bio-inspired configurations were used on the cathode. The best configuration was the serpentine (anode) – second leaf design (cathode), with a peak power density of 888 W/m2. For comparison, a peak power density of 824 W/m2 was achieved when the serpentine flow field was used on the anode and cathode. Furthermore, of all the tested configurations, the lung-based flow field provided the lowest performance in all tests.
•Murray's Law-based flow fields operated best as cathode flow field.•Anode serpentine-cathode bio-inspired leaf configuration provided best performance.•Bio-inspired lung design found to be least promising of all tested flow fields.•Analytical model developed, accounting for channel geometry and MEA.
In this study, Direct Methanol Fuel Cells (DMFCs) based on composite membranes (Nafion/SiO2 and Nafion/TiO2) were manufactured; and their performances were compared with that of the DMFC based on ...Nafion® 115 membrane. For this purpose, composite membranes were synthesized applying the recasting method with the inorganic particle loading of 2.5 wt%. The structures of these composite membranes were investigated by Scanning Electron Microscopy (SEM), proton conductivity measurement and water uptake measurement. Ultrasonic coating technique was used in the manufacturing of the Membrane Electrode Assemblies (MEAs). The performance tests of the composite membranes were conducted using in-house experiments. In these tests, the effect of methanol concentration (0.75, 1, and 1.5 M) on the performance of the MEA having Nafion® 115 was investigated at 80 °C to find the value of the methanol concentration that yields the highest power density. This study showed that the MEA operating at 1 M gives the highest performance. Then, the performance of this MEA was compared with that of the MEAs having Nafion/SiO2 and Nafion/TiO2 composite membranes in single cell DMFC setup at 60 °C, 80 °C, and 95 °C. The results of these experiments demonstrated that the MEA having Nafion/TiO2 composite membrane provides much better performance with the maximum power density values of 422.04 W/m2, 641.16 W/m2, and 710.88 W/m2 at 60 °C, 80 °C, and 95 °C, respectively.
•Nafion/TiO2 and Nafion/SiO2 composite membrane based DMFCs were manufactured.•Composite membrane based DMFCs provide better performance than conventional DMFCs at 95 °C.•The peak power density of the DMFC having Nafion/SiO2 yields 26% more power density.•The peak power density of the DMFC having Nafion/TiO2 yields 36% more power density.•Nafion based composite membranes are very promising for high temperature DMFCs.
Due to their outstanding structural, transport and electrical characteristics, nickel foams serve as excellent candidate materials for gas diffusion layers (GDLs) in polymer electrolyte fuel cells ...(PEFCs). In this work, a new three-dimensional PEFC model was developed to explore the local and global fuel cell performance with nickel foam-based GDLs. The fuel cell operating with nickel foam GDLs was shown to have, due to its superior mass and charge transport properties, higher oxygen and water concentration and current density compared to that operating with the conventional carbon fibre-based GDLs. The results show that the pumping power should be taken into account when optimising the dimensions of the flow channels and as such the net power density must be the criterion for optimisation. The optimal dimensions of the flow channels for the fuel cell operating with nickel foam based GDLs were found to be 0.25 mm for the channel height and 1 mm for the channel width; the maximum net power density with these dimensions was around 0.95 W/cm2 which is two times higher than that operating with carbon fibre based GDLs. All the results have been presented and critically discussed.
•Nickel foam GDLs demonstrate more uniform concentration and current distributions.•Smaller channels boost the fuel cell performance but demand more pumping power.•Net power output of nickel foam-based PEFC nearly doubles that of carbon-based PEFC.•The performance gain with nickel foam GDL was investigated numerically.
Nickel foams feature superior structural and transport characteristics and are therefore strong candidates to be used as gas diffusion layers (GDLs) in polymer electrolyte fuel cells (PEFCs). In this ...work, the impact of compression on the key structural and transport properties has been investigated, including employing a specially designed compression apparatus and X-ray computed tomography. Namely, 20 equally spaced two-dimensional CT based images and numerical models have been used/developed to investigate the sensitivity of the key properties of nickel foams (porosity, tortuosity, pore size, ligament thickness, specific surface area, gas permeability and effective diffusivity) to realistic compressions normally experienced in PEFCs. Wherever applicable, the anisotropy in the property has been investigated. One of the notable findings is that, unlike porosity and ligament thickness, the mean pore size was found to decrease significantly with compression. The mean pore size is around 175 μm for uncompressed nickel foam and it decreased to around 110 μm for a 20% compression ratio and to around 70 μm for a 40% compression ratio. Further, unlike the effective diffusivity, the gas permeability was shown to be highly anisotropic with compression; this fact is of particular importance for PEFC modelling where the properties of GDLs are often assumed isotropic. All the computationally estimated properties have been presented, validated and discussed.
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•Nickel foam was numerically evaluated as a potential GDL material for PEFCs.•X-ray CT images, 3D-printed compression device and numerical models were employed.•Structural and transport properties of nickel foam under compression were determined.•Anisotropy of nickel foam permeability significantly increases with compression.•Nickel foam has superior properties compared to conventional GDLs.
Nickel foams are excellent candidate materials for gas diffusion layers (GDLs) for polymer electrolyte fuel cells (PEFCs) and this is due to their superior structural and transport properties. A ...highly computationally-efficient framework has been developed to not only estimate the key structural and mass transport properties but also to examine the multi-dimensional uniformity and/or the isotropy of these properties. Specifically, multiple two-dimensional X-ray CT images and/or numerical models have been used to computationally determine the porosity, the tortuosity, the pore size distribution, the ligament thickness, the specific surface area, the gas permeability and the effective diffusivity of a typical nickel foam sample. The results show that, compared to the conventionally used carbon substrate, the nickel foam sample demonstrate a high degree of uniformity and isotropy and that it has superior structural and mass transport properties, thus underpinning its candidacy as a GDL material for PEFCs. All the computationally-estimated properties, which were found to be consistent with the corresponding literature data, have been presented and thoroughly discussed.
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•Nickel foam was numerically evaluated as a candidate GDL material for PEFCs.•Novel two-dimensional X-ray CT images and related numerical models were employed.•Multiple structural and transport properties of nickel foam were determined.•Nickel foam shows excellent uniformity and isotropy as a potential GDL material.•Nickel foam demonstrates superior properties as a potential GDL material.
Nafion/zirconium hydrogen phosphate (ZrP) composite membranes containing 2.5 wt.% ZrP (NZ-2.5) or 5 wt.% ZrP (NZ-5) were prepared to improve the performance of a direct methanol fuel cell (DMFC). The ...influence of ZrP content on the Nafion matrix is assessed through characterization techniques, such as Thermogravimetric Analysis (TGA), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Electrochemical Impedance Spectroscopy (EIS), and water uptake measurement. Performance testings of the DMFCs based on these composite membranes as well as commercial Nafion® 115 membrane were performed using a computer aided fuel cell test station for different values of cell temperature (40 °C, 60 °C, 80 °C, and 100 °C) and methanol concentration (0.75 M, 1.00 M, and 1.50 M). Characterization studies indicated that incorporation of ZrP into polymer matrix enhanced the water uptake and proton conductivity values of Nafion membrane. The results of the performance tests showed that the Membrane Electrode Assembly (MEA) having NZ-2.5 provided the highest performance with the peak power density of 551.52 W/m2 at 100 °C and 1.00 M. Then, the performances of the MEAs having the same NZ-2.5 membrane but different cathode catalysts were investigated by fabricating two different MEAs using cathode catalysts made of Pt/C–ZrP and Pt/C (HiSPEC® 9100). According to the results of these experiments, the MEA having NZ-2.5 membrane and Pt/C (HiSPEC® 9100) cathode catalyst containing 10 wt.% of ZrP exhibited the highest performance with the peak power density of 620.88 W/m2 at 100 °C and 1.00 M. In addition, short-term stability tests were conducted for all the MEAs. The results of the stability tests revealed that introduction of ZrP to commercial (HiSPEC® 9100) cathode catalyst improves its stability characteristics.
•Different cathode catalysts and membranes were investigated for DMFC applications.•Introduction of ZrP enhances water uptake and proton conductivity of Nafion membrane.•Introduction of ZrP to the cathode improves the stability and performance of DMFC.•An improved catalytic activity was achieved via inclusion of ZrP to the cathode.•ZrP based composite membranes were found to be suitable for high temperature DMFCs.
The performance impact of using bio-inspired interdigitated and non-interdigitated flow fields (I-FF and NI-FF, respectively) within a DMFC is investigated. These two flow fields, as well as a ...conventional serpentine flow field (S-FF, used as a reference), were examined as possible anode and cathode flow field candidates. To examine the performance of each of these candidates, each flow field was manufactured and experimentally tested under different anode and cathode flow rate combinations (1.3 mL/min methanol and 400 mL/min oxygen, as well as 2 and 3 times these flow rates), and different methanol concentrations (0.50 M, 0.75 M, and 1.00 M). To help understand the experimental results and the underlying physics, a three dimensional numerical model was developed. Of the examined flow fields, the S-FF and the I-FF yielded the best performance on the anode and cathode, respectively. This finding was mainly due to the enhanced under-rib convection of both of these flow fields. Although the I-FF provided a higher mean methanol concentration on the anode catalyst layer surface, its distribution was less uniform than that of the S-FF. This caused the rate of methanol permeation to the cathode to increase (for the anode I-FF configuration), along with the anode and cathode activation polarizations, deteriorating the fuel cell performance. The NI-FF provided the lowest pressure drops of the examined configurations. However, the hydrodynamics within the flow field made the reactants susceptible to traveling directly from inlet to outlet, leading to several low concentration pockets. This significantly decreased the reactant uniformity across its respective catalyst layer, and caused this FFs performance to be the lowest of the examined configurations.
•Serpentine and interdigitated designs best used on anode and cathode, respectively.•Poor under-rib convection and performance obtained with non-interdigitated design.•Interdigitated design improved with additional parent and collector channels.•Performance improved if pressure difference between channel branches increased.
In this study, the effect of introduction of titania (TiO2) material into PtRu/C anode electrocatalyst on the performance of direct methanol fuel cells (DMFCs) was investigated. TiO2 materials were ...first synthesized applying a sol–gel method and then incorporated directly into commercial PtRu/C anode electrocatalyst with different TiO2 weight ratios (5, 15, and 25 wt.%) to improve the performance of the DMFC. For comparison, the anode electrocatalysts with the same TiO2 weight ratios were also prepared using commercial TiO2 materials. The performance tests of the DMFCs based on these composite anode electrocatalysts were conducted and their performances were also compared to that of a DMFC based on a traditional anode electrocatalyst (PtRu/C) under various operating conditions. In addition, 4 h short-term stability tests were conducted for all the manufactured DMFCs. The highest power densities were found as 705.12 W/m2 and 709.32 W/m2 at 80 °C and 1 M for the DMFCs based on PtRu/CTiO2 anode electrocatalysts containing 5 wt.% of commercial and in-house TiO2, respectively. The results of the short-term stability tests showed that introduction of 5 wt.% of commercial TiO2 into commercial PtRu/C anode electrocatalyst improved its stability characteristics significantly.
•The conventional DMFC's performance is improved up to 27.9%.•Introduction of 5 wt.% of TiO2 improves the stability of the conventional DMFC.•Increasing weight ratio of TiO2 leads to significant performance deteriorations.•In-house synthesized TiO2 seems more promising in terms of performance.•Commercial TiO2 has superiority in terms of stability over in-house synthesized TiO2.
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