Fuel Cell Performance Tests Research Articles

Energy efficiency and electrochemical characteristic assessment of PEMFC-supercapacitor hybridization via railway profile

Electric trains equipped with efficient electric motors and powered by high-capacity hydrogen fuel cells are a choice of the global transportation industry to accelerate the global transition to a low-carbon transportation system. The operation of distinct vehicle types in varying geographical regions is characterized by unique features. Concurrently, the continually fluctuating demand for electricity necessitates the utilization of fuel cells in conjunction with energy storage devices. Thus, this study centers on examining the role of the PEMFC-supercapacitor direct hybridization system within the authentic driving profile of the subway in the Bangkok metropolitan region. The supercapacitor within the hybridization system serves as an energy management device, enhancing the durability of fuel cells when subjected to diverse load demands associated with train propulsion. In order to validate this hypothesis, an MRT (Mass Rapid Transit) protocol was formulated to emulate and serve as the load demand for the investigation, and then the PEMFC-supercapacitor direct hybridization system was operated using the created profile. Subsequently, the hybridization system undergoes electrochemical characterizations and fuel cell performance tests for diagnostic purposes. Empirical findings validated that the supercapacitor operates as a filter, generating a stable voltage response to varying load requirements, and possesses the capability to assimilate energy originating from regenerative braking. The integration of supercapacitors in stabilizing the operational parameters of proton exchange membrane fuel cells (PEMFCs) has markedly prolonged their operational lifespan. This assertion is substantiated by voltage signal analysis, which demonstrated a negligible increase in surface resistance of merely 0.23%, as depicted by Nyquist plots. Furthermore, cyclic voltammetry revealed that the system attained a peak electrochemical surface area (ECSA) of 0.0089 (106 cm2/mg of Pt). The information presented in this article constitutes data that has been minimally explored in existing research. Specifically, the study concentrates on the practical driving pattern of electric trains. Consequently, experimental results were deemed advantageous for the advancement of heavy-duty electric vehicles.

Synthesized and characterized high‐performance and low‐cost zirconium phosphate‐additive sulfonated polyethersulfone membranes for PEMFC

AbstractIn this study, the preparation, characterization, and fuel cell performance tests of high‐performance and low‐cost zirconium phosphate (ZrP)‐additive sulfonated polyethersulfone (sPES) membranes, which may serve as a substitute for the commercial membrane used in proton exchange membrane fuel cell (PEMFC), were carried out. ZrP‐additive sPES membranes were prepared by solution casting method with different weight ratios (2.5%, 5%, and 9%). Fourier transform infrared (FTIR), water uptake capacity (WUc), dynamic mechanical analysis, ion exchange capacity (IEx), degree of hydration, impedance analysis, and oxidative stability were used to characterize the created membranes. Ultimately, single‐cell performance experiments were used to evaluate the membranes' performance in real fuel cell environments. ZrP additive improved the WUc, mechanical properties, IEx, and proton conductivity properties of the membrane. WUc of the membranes enhanced by approximately 94% at 80°C, while the proton conductivity augment by approximately 47% with 9% ZrP by weight. 0.97 meq g−1 IEx was obtained for the sPES, whereas it was obtained as 1.41 meq g−1 for sPES‐9ZrP. Oxidative stability experiments for 120‐h determined that all synthesized membranes had a stable structure, and their weight losses varied between 68% and 85%. The sPES‐9ZrP exhibited very high values at 0.6 V, resulting in a power density of 680 mW cm−2 and a current density of 1100 mA cm−2. The results obtained are quite promising, and sPES and ZrP in composite membrane structures have high synergy.

Intrinsic microporous poly(phenyl-alkane)s with pendent piperazinium for high performance anion exchange membrane fuel cells

Exploring anion exchange membranes (AEMs) with high conductivity and satisfactory stability is very meaningful for the advancement of alkaline fuel cells. Herein, a novel class of intrinsic microporous AEMs with pendent piperazinium are systematically fabricated for alkaline fuel cell performance testing. Contorted and rigid spirobisindane backbone structure expands the free volume of AEMs, inducing broad and interconnected ion transport channels. This unique feature endows membranes a leading advantage for the efficient transmission of hydroxide ions. Consequently, the prepared membrane displays excellent normalized hydroxide conductivity of 78.99 mS g cm−1 mmol−1 at 80 °C. Meanwhile, the hydroxide conductivity degrades by only 8.3 % after treatment in 1 M NaOH for 1000 h at 80 °C. Moreover, the peak power density of H2/O2 single cell employing this membrane exhibits 1.06 W cm−2 at 80 °C and the cell can preserve 93.0 % of its initial voltage after operating for 18 h.

Synergistic effect and ionic conductivity of crosslinked imidazole ionic liquids and piperidine cations on poly(biphenyl-piperidine) anion exchange membranes

In order to prepare anion exchange membranes with good performance, and we prepared ether-free bonded poly(biphenyl-piperidine) anion exchange membranes (CQPBP-M-x, x is degree of crosslinking) by introducing cross-linked imidazolium ionic liquids. The introduction of cross-linked imidazolium ionic liquids increases multiple OH− transport sites and establishes a more pronounced microphase-separated structure with the backbone, while acting synergistically with piperidinium cations, resulting in improved membrane conductivity. Meanwhile, the introduction of an ether-free backbone and the construction of a cross-linked structure could promote the chemical stability of the membrane and effectively inhibit membrane swelling. The prepared cross-linked imidazole ionic liquid poly(biphenyl-piperidine) (CQPBP-M-30 %) membrane exhibited relatively good ionic conductivity (88.03 mS/cm), and low swelling (11.75 %) at 80 °C. The H2–O2 fuel cell performance test conducted at 80 °C without back pressure showed a peak power density of 125.7 mW/cm2. Therefore, it is a worthwhile direction to explore to improve the performance of anion exchange membranes by adopting an ether-free backbone and constructing a cross-linked structure contain multiple cationic groups.

Electrospun Sulfonated Silica/P(VDF-TrFE)-Based Composite Membranes for PEM Fuel Cells

Nafion® membranes are the most widely used commercially available membranes for PEM fuel cells due to their good chemical and mechanical stability as well as high ionic conductivity at fully humidified conditions. However, their high cost and inadequate conductivity at lower humidity levels can be addressed as the main drawbacks of Nafion® membranes which needs to be overcome. In this regard new strategies such as complete replacement of these membranes with alternative cost-effective membranes or modifying their properties via synthesizing of Nafion® containing composite membranes by incorporation of some inorganic additives such as silica were extensively investigated previously [1].In this study, we developed two types of electrospun composite membranes: in the first route: membranes were prepared with using P(VDF-TrFE) or PVDF as carrier polymers which are decorated with sulfonated silica (S-SiO2) nanoparticles, as a proton conducting additive. Here S-SiO2 nanoparticles were synthesized via hydrothermal method, then these nanoparticles were added to the electrospinning solutions to prepare the hybrid membranes. The effect of S-SiO2 amount in final properties of these membranes were investigated via preparing samples with three different S-SiO2/ carrier polymer ratios [2]. In the second approach, a combination of sol-gel and dual electrospinning methods were employed to fabricate proton conducting membranes comprising sulfonated silica network, Nafion®, and PVDF or P(VDF-TrFE) as the carrier polymers. For this purpose, the obtained S-SiO2 network via sol-gel method was incorporated into the Nafion®/carrier polymer mixed fibrous-mats during dual electrospinning process [3]. In both approaches after electrospinning all electrospun mats were transformed to compact membranes via hot-pressing process. Then fabricated mats and compact membranes, were characterized by various techniques including FTIR, XPS, SEM, TEM, ionic conductivity, ion exchange capacity (IEC), water uptake and mechanical tests. Finally, membrane-electrode-assemblies (MEAs) were prepared via composite electrospun membranes and fuel cell performance tests were performed. The results showed an enhancement in ionic conductivity for both set of membranes (102 and 132 mS/cm) compared to commercial Nafion® membranes at the same conditions. Moreover, the fuel cell test exhibited that presence of sulfonated silica in the composite membranes improved the performance at lower humidity conditions (344 mW/cm2 at 60% RH) due to enhanced water retention ability of the resultant composite membranes.

Phase-Assisted Tailored Conductivity of Doped Ceria Electrolytes to Boost SOFC Performance.

Efforts to lower the operating temperature of solid oxide fuel cells include producing electrolytes that are sufficiently conductive and stable below 600 °C. Doped ceria is one such electrolyte being considered. During this study, codoped ceria powders (Ce0.8Sm0.2-xMxO2-δ, M = Bi3+, Zn2+ and x = 0, 0.05, 0.1, 0.15, 0.2) were prepared via coprecipitation by the addition of sodium carbonate and annealed at 800 and 1200 °C, respectively. Poor solubility of the codopants in the ceria was observed for samples annealed at 800 °C, resulting in a mixed-phase product including stable phases of the oxides of these codopants. A second-stage partial incorporation of these codopants into the ceria lattice was observed when the annealing temperature was increased to 1200 °C, with both codopants forming cubic-type phases of their respective oxides. Materials were characterized using X-ray diffraction (XRD), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR), as well as scanning electron microscopy (SEM) for structural and morphological investigations. The oxide ion conductivity was evaluated using electrochemical impedance spectroscopy between 550 and 750 °C. Fuel cell performance tests of selected samples (annealed at 1200 °C) showed remarkable improvement in peak power densities when the test temperature was increased from 500 to 600 °C (∼720 mW/cm2 for Ce0.8Sm0.15Bi0.05O2-δ and ∼1230 mW/cm2 for Ce0.8Sm0.15Zn0.05O2-δ), indicating possible contribution from the distinct cubic-type oxide phases of the codopants in performance enhancement.

Sulfonated Polyphenylene-Based Multiblock Membranes with Fluorine Moiety for Fuel Cell Applications

Sulfonated poly(phenylene-co-arylene ether sulfone) multiblock copolymers are synthesized via Colon’s nickel-mediated cross-coupling reaction and are investigated as a proton-exchange membrane fuel cell. To investigate the influence of the fluorine moieties on the membrane properties, two different membranes are prepared, one containing a fluorinated hydrophobic poly(arylene ether) block (6F polymer membrane) and a nonfluorinated biphenyl (BP) polymer membrane. The proton transport, morphology, mechanical properties, and oxidative stabilities of the membranes are examined in relation to the ion-exchange capacity (IEC). 6F polymer membranes show superior proton conductivity and oxidative stability (results of Fenton’s oxidative stability and hydrogen peroxide exposure tests) compared with the BP polymer membranes. In water at 25°C, 6F and BP polymer membranes with IEC 2.0 meq g–1 exhibit proton conductivity of 0.11 S cm–1 with 6F having 16% lower water uptake than BP polymer. Meanwhile, at 30% RH and 80°C, 6F-X5Y9-(2.0) exhibits proton conductivity of 0.0026 S cm–1 that almost 50% higher than BP-X5Y7-(2.0) with 0.0018 S cm–1, while at 90% RH and 80°C, both polymers have an almost similar value of 0.10 S cm–1. Oxidative stability with the Fenton test under harsh conditions demonstrates that 6F-X5Y9-(2.0) has an extent degradation of 26%, almost 19% lower than BP-X5Y7-(2.0) with 32%, and the hydrogen peroxide exposure test demonstrates that 6F has 50% lower extent of degradation than BP with 5 and 9%, respectively. Fuel cell performance test at 80°C and 100% RH show that 6F-X5Y9-(2.0) exhibits a current density of 1.6 A cm–2 at 0.6 V (hydrogen/air) and outperforms Nafion-NR211 and BP-X5Y7-(2.0), 1.4 A cm–2 and 1.2 A cm–2, respectively. Undoubtedly, incorporating fluorinated moieties could enhance proton transport properties and oxidative stability favorable for fuel cell application.

Hydrogen Flow Controller Applied to Driving Behavior Observation of Hydrogen Fuel Cell Performance Test.

Fuel cell performance tests for automotive applications include static and dynamic tests, and the dynamic load test is typically carried out to investigate the cell operating performance related to driving behavior in the particular use of fuel cell electric vehicles. The automatic hydrogen flow controller, utilized to regulate the hydrogen flow as a function of time, is one of the imperative apparatuses applied for the dynamic test. The driving behavior generally consists of rapid load fluctuations, several loads running at idle, full power, overload circumstances, start-stop repeats, and cold starting, and these dynamic variations are directly related to the power required for propelling a vehicle and the demand for hydrogen volume fluctuation throughout time. The desired automatic hydrogen flow controller was designed and manufactured for the dynamic performance test via the driving simulation protocol of a heavy-duty vehicle. The main experimental activities were performed to observe the responsibility and accuracy of the invented controller. The relation between the reliability of using the automatic hydrogen flow controller and the performance improvement of fuel cell operation was studied to gain ideas for further fuel cell modification. The hydrogen flow rates controlled by the created flow controller presented a data tolerance of approximately 0.84% which was not significantly different from the theoretical figure based on T-test analysis. The controller reacted to variations in flow rates in as little as 1-2 s, which was acceptable for the dynamic test. Regarding the performance enhancement, this automatic hydrogen flow controller assisted a single cell to generate 16% more power and 33% more energy at 45 mA as a minimum current demand in comparison with the results obtained from a test system using a traditional hydrogen controller with a constant flow rate.

Fabrication of PVP/sulfonated PES electrospun membranes decorated by sulfonated halloysite nanotubes via electrospinning method and enhanced performance of proton exchange membrane fuel cells

Composite membranes, which are composed of polyvinylpyrrolidone (PVP)/polyethersulfone (PES)/halloysite nanotubes (HNT), have a high potential to be an alternative candidate for proton exchange membrane fuel cell (PEMFC) applications. In this context, PVP/sulfonated PES matrix decorated by sulfonated HNT was successfully fabricated via the electrospinning method. The fabricated PEMs were characterized by SEM, FT-IR, XRD, TGA, electrochemical impedance spectroscopy (EIS), water uptake capacity, swelling property, ion exchange capacity tests, and fuel cell performance tests. The results of morphological characterization showed that smooth and bead-free alignments with randomly oriented fibers were achieved. It is found that the mass percentage of sHNT increased the thickness, and accordingly, the surface area of swelling and water uptake capacity were enhanced. Therefore, the mechanism of the proton transfer increased, and the proton conductivity values were also increased with temperature. In addition, ion exchange capacity values progressively increased as the content of sHNT enhanced up to 1%. The fabricated sPES/PVP-sHNT-1.0 membrane stood out of among other membranes higher current density of 450 mA cm−2 at 0.6 V. To sum up, these fabricated nanofibrous composite membranes showed a high potential for use as fuel cells.

Automating Correlative Electron Microscopy for Heavy Duty Fuel Cell Development

The efficiency and durability of proton exchange membrane fuel cells has come to the forefront of research and development efforts as sustainable transportation applications shift from passenger to heavy duty vehicles. Complementary research expertise and advanced instrumentation are required to accelerate materials discovery and degradation mitigation of fuel cell components, with significant attention on catalysts, ionomers and membranes. The scanning transmission electron microscope (STEM) is among the key characterization techniques for accelerating materials and device development, providing key insights into atomic scale structure. Automating STEM data acquisition and analysis enables large data sets with improved statistical relevance and throughput will expand the impact of this method in the rapid materials and accelerated stress test development.We will show how the latest instrument developments in automation and high speed detectors enable new insights into catalyst structure and electrode layer degradation. This includes correlative, multimodal STEM techniques, such as aberration-corrected imaging, secondary electron detection, energy dispersive X-ray spectroscopy, cryogenic microscopy and 4D-STEM, to build a more comprehensive view of the effect of particle size and composition on surface strain and durability. These results will be correlated with information obtained from X-ray scattering techniques and fuel cell performance testing to understand the type and degree of degradation occurring during accelerated stress tests under development for heavy duty applications. The prospect of automated electron tomography coupled with identical location (IL)-STEM to provide detailed three-dimensional information on catalyst-support interactions will also be discussed.This material is based on work performed by the Million Mile Fuel Cell Truck (M2FCT) Consortium, technology managers Greg Kleen and Dimitrios Papageorgopoulus, which is supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office. Electron microscopy research was supported by the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory. The X-ray scattering experiments were performed at beamline 9-ID-C at the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). Use of the APS, an Office of Science user facility operated by ANL, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AS02-06CH11357

Functionalized POSS-Modified SEBS-Based Composite Anion-Exchange Membranes for AEMFCs

Inspired by the strategy of rubber reinforcement, the N-methylpiperidium functionalized POSS was designed and synthesized to improve the ion conductivity as well as the mechanical and thermal properties of SEBS-based anion-exchange membranes (AEMs). A series of Pi-POSSx%/Pi-SEBS AEMs were prepared and assembled into MEAs for the fuel cell performance test. The addition of Pi-POSS fillers significantly enhanced the comprehensive performance of the AEMs. Especially, the Pi-POSS15%/Pi-SEBS composite membrane with the highest IEC value exhibited ion conductivities of 30.70 mS cm–1 at 30 °C and 69.11 mS cm–1 at 80 °C and the best alkaline stability. The Pi-POSS15%/Pi-SEBS composite membrane showed a maximum power density of 219 mW cm–2 at 80 °C, which was higher than the original Pi-SEBS membrane (117 mW cm–2). This work discloses a promising approach for improving the AEM performance with well-designed inorganic–organic composite fillers.

Hybrid Nafion Membranes of Ionic Hydrogen-Bonded Organic Framework Materials for Proton Conduction and PEMFC Applications.

As the high-power density and environmentally friendly energy resources, proton exchange membrane fuel cells (PEMFCs) have a promising future in portable power generation. Herein, the hybrid Nafion membranes of ionic hydrogen-bonded organic frameworks (iHOFs) for PEMFC applications are demonstrated. By adjusting the position of sulfonic groups on naphthalene disulfonic acid compounds, four iHOFs with different types of hydrogen bonds were synthesized successfully based on 1,1'-diamino-4,4'-bipyridylium and naphthalene disulfonic acid. The formation of hydrogen bond interactions between amino and sulfonate groups provides a rich hydrogen bond network, which makes such iHOFs have high conductivity, and the maximum value is 2.76 × 10-3 S·cm-1 at 100 °C and 98% RH. Besides, composite membrane materials were obtained by mixing Nafion and iHOFs, and the maximum proton conductivity values can achieve 1.13 × 10-2 S·cm-1 for 6%-iHOF-3/Nafion and 2.87 × 10-3 S·cm-1 for 6%-iHOF-4/Nafion membranes at 100 °C under 98% RH. Through the H2/O2 fuel cell performance test by using iHOF/Nafion as the solid electrolyte, the maximum power and current density values of hybrid membranes are 0.36 W·cm-2 and 1.10 A·cm-2 for 6%-iHOF-3/Nafion and 0.42 W·cm-2 and 1.20 A·cm-2 for 6%-iHOF-4/Nafion at 80 °C and 100% RH. This work provides a practicable approach for establishing high-performance proton exchange hybrid membranes by doping high proton-conducting iHOFs into the Nafion matrix.

Solid electrolyte membranes based on polybenzimidazole containing graphitic carbon nitride moiety (PBICN) for high-temperature fuel cell applications

Polybenzimidazole containing graphitic carbon nitride moiety (PBICN) is prepared by in situ polymerization of 3,3′-diaminobenzidine (DAB), isophthalic acid (IPA), and graphitic carbon nitride (g-CN) for the application in high-temperature fuel cell membrane. Since g-CN has a nanosheet structure and lots of amine end groups, it can be involved in the polymerization process producing PBI-grafted g-CN. The PBICN membrane shows much improved thermal property, oxidative stability, mechanical strength, and proton conductivity compared to pristine PBI membrane and the PBI composite membrane prepared simply by mixing PBI and g-CN. In addition, it is confirmed that the PBI-grafted g-CN structure formed during the in situ polymerization can contribute to the increase of the dimensional stability for the PBICN membrane. Especially, PBICN membrane prepared by the in situ polymerization using g-CN exhibits much improved fuel cell performance. For example, the power density value of the membrane electrode assembly (MEA) fabricated using PBICN membrane prepared using 0.5 wt% of g-CN is 400 mW cm−2, which is much larger than those of MEA fabricated using PBI membrane (241 mW cm−2) and the PBI composite membrane containing 0.5 wt% of g-CN (326 mW cm−2) membrane during the fuel cell performance test performed at 160 °C without humidification.

States of water in recast Nafion® films

The amount and states of water in a polymer electrolyte significantly affect the material's morphology as well as its mechanical and transport properties, and thus determine performance in many important applications such as fuel cells, electrolyzers, and other electrochemical energy conversion devices. In this study, recast H+-Nafion® films were characterized using attenuated total internal reflection FTIR (ATR-FTIR) spectroscopy before and after thermal annealing and subsequent rehydration. The states of water in the hydrated films were determined by analyzing the O–H stretching band of water using principle component analysis and multivariate curve resolution. It was found that annealing at a temperature above the glass transition temperature caused the water hydrogen-bonding networks in the water-ionic clusters to become restricted, suggesting that annealing forms a robust polymer matrix confining the water-ionic clusters. The evolution of film morphology with increasing thermal-annealing temperature was confirmed with small-angle X-ray scattering (SAXS) and CO2 diffusion measurements. Fuel cell performance tests using annealed and unannealed Nafion® in the cathode catalyst layer found improved stability when the cathode catalyst was annealed, indicating that thermal history is an important design parameter in electrochemical energy conversion device fabrication.

CeO2 nanorod decorated NrGO additives for boosting PEMFC performance

This study presents a novel and highly efficient CeO2-based type of additives to improve the performance of PEM fuel cells. Cerium(IV) oxide (CeO2) nanorods and CeO2 nanorod decorated nitrogen-doped reduced graphene oxide (NrGO) (CeO2/NrGO) were synthesized and utilized to enhance the ORR performance of PEMFCs. With a low energy transition between Ce+3 to Ce+4 and its high catalytic activity, CeO2 could promote O2 reduction. The structural properties of CeO2 nanorods and the CeO2/NrGO composite were investigated using XRD, RAMAN, SEM, TEM, TGA, BET, and XPS. The synthesized CeO2 nanorods and CeO2/NrGO composite were mixed with a low platinum loading (0.09 mgPt.cm−1), and ex-situ electrochemical characterizations were performed (CV and LSV) to evaluate their catalytic activities. Fuel cell performance tests and in-situ impedance analyses were also conducted to confirm the electrochemical results. Compared to commercial Pt/C-based MEA (269 mW.cm−2), the addition of both CeO2 nanorods (382 mW.cm−2) and CeO2/NrGO (389 mW.cm−2) to the catalyst layer showed a significant enhancement in fuel cell performance, due to the unique oxygen buffer ability of the synthesized additives.

Side-Chain-Type Anion Exchange Membranes Based on Poly(arylene ether sulfone)s Containing High-Density Quaternary Ammonium Groups.

To obtain anion exchange membranes with both high ionic conductivity and good dimensional stability, a series of side-chain-type poly(arylene ether sulfone)s (PAES-QDTPM-x) were designed and synthesized. Quaternary ammonium (QA) groups were densely aggregated and grafted onto the main chain via flexible hydrophobic spacers. Well-defined microphase separation was confirmed by small-angle X-ray scattering. PAES-QDTPM-0.30 exhibited reasonably high conductivity (39.4 mS cm-1 at 20 °C and 76.1 mS cm-1 at 80 °C) and excellent dimensional stability at 80 °C (11.9% in length, 11.2% in thickness) due to the concentration of ion clusters and the side-chain-type structure. All membranes maintained over 82% of the conductivity after alkali treatment for 14 days. In the H2/O2 fuel cell performance test, the maximum power density of PAES-QDTPM-0.30 at 60 °C was 225.8 mW cm-2.

Effect of Mesopores in the Marimo nanocarbon anode material on the power generation performance of direct glucose fuel cell

In this study, the effect of mesopores in the Marimo nanocarbon (MNC) anode material on the power generation performance of a direct glucose fuel cell was investigated. Three types of MNC with different mesopore distributions were used for the catalyst support material; Pt was used as the loaded metal. In the glucose fuel cell performance test, MNC containing many pores of approximately 35 nm showed the highest maximum output density of 0.72 mW cm−2 at 5 wt% metal loading and 0.3 M Glucose aqueous solution. The pores of approximately 30 nm may promote ion diffusion and rapid mass transport of reactants and products. These results indicated that MNC was an effective anode material for the direct glucose fuel cell.

Raw and pyrolyzed (with and without melamine) graphene nanoplatelets with different surface areas as PEM fuel cell catalyst supports

Platinum (Pt) catalysts dispersed on carbon-based support materials are generally used in the polymer electrolyte membrane (PEM) fuel cells. In this study, commercial graphene nanoplatelets (GNPs), with different surface areas (320, 530, 800 m2 g−1), were used as catalyst supports in PEM fuel cells. These GNPs were also pyrolyzed under the inert atmosphere, with and without melamine, as the nitrogen (N) source. Various characterizations (Elemental analysis, FTIR, Raman spectroscopy, BET, TEM, HRTEM, SAED, XRD, TGA, ICP-MS, contact angle measurement, CV, ORR, chronoamperometry, EIS, PEM fuel cell performance test) were performed for the detailed analysis of Pt/GNPs. Based on the three-electrode cell system, the lowest electrochemical surface area (ECSA) loss (29.9%), Pt mass activity loss (20.3%) and overall (charge and mass) resistance (42.2 Ω) were obtained with the Pt/M-530 catalyst. According to the in-situ PEM fuel cell performance results, the specific peak power density was recorded as (450 mW mg Pt−1) for the Pt/R-530 catalyst, which has also the second most hydrophobic catalyst layer surface with the 146.5° ± 1.28° contact angle value. On the heels of Pt/R-530, the two best performances also belong to the Pt/M-530 (391 mW mg Pt−1) and Pt/P-530 (378 mW mg Pt−1) catalysts of the same group.

Simultaneously deposited Pt-alloy nanoparticles over graphene nanoplatelets via supercritical carbon dioxide deposition for PEM fuel cells

One of the main barriers to the commercialization of polymer electrolyte membrane fuel cell (PEMFC) systems is the cost, which is largely due to the need of platinum (Pt)-containing catalysts. In order to overcome this issue, several methods have been developed. One of them is the supported electrocatalysts prepared by combining a low cost second metal with Pt. Motivated by this idea, in this study, nano-sized Pt-M (M = Ni, Fe, Cu) binary electrocatalysts were synthesized on the graphene nanoplatelets (GNPs) via supercritical fluid deposition (SFD) technique in order to decrease the cost and increase the activity of the catalysts. Because, the unusual properties of supercritical fluids (SFs), including tunable solvent strength, high diffusivity, low viscosity, and low surface tension, offer significant advantages over conventional techniques for materials processing. In this regard, compared to the other SFs, carbon dioxide (CO2) has received much more attention due to its easy accessibility to the supercritical state, relative benignity to the environment, chemical inertness, low toxicity, low cost. The supercritical carbon dioxide (scCO2) deposition technique involves firstly the dissolution of the metal precursor onto the support material, and then conversion of the metal precursor to its metallic form by means of thermal or chemical conversion. Synthesis of supported bimetallic nanoparticles (NPs) via scCO2 can be sequentially or simultaneously. Herein, we investigated the development of Pt-M (PtCu, PtNi, PtFe) alloy NPs on GNPs by scCO2 deposition via simultaneous addition of metal precursors. Subsequently, these catalysts were characterized by employing various characterization techniques and systems such as X-Ray Diffaction (XRD), Thermogravimetric Analysis (TGA), Inductively Coupled Plasma Mass Spectrometer (ICP-MS), Transmission Electron Microscopy (TEM), Raman Spectroscopy, Cyclic Voltammetry (CV), Rotating Disk Electrode (RDE) and PEM Fuel Cell performance tests. The obtained results revealed the formation of bimetallic catalysts within the size ranges from 1.6 to 2.1 nm. Furthermore, CV results demonstrate that PtNi/GNPs catalyst exhibit significantly high catalytic activity toward the PEM fuel cell reaction in comparison with the PtFe/GNPs and PtCu/GNPs. Also, PtNi/GNPs catalyst show about 2–4 times higher durability than the PtFe/GNPs and PtCu/GNPs catalysts in the accelerated degradation tests (ADTs). All results suggested that the PtNi/GNPs catalyst has great potential for PEM fuel cell applications.

Platinum/graphene nanoplatelets/silicone rubber composites as polymer electrolyte membrane fuel cell catalysts

The importance of carbonaceous catalyst support materials in polymer electrolyte membrane (PEM) fuel cell is well known. In this study, we used two different types of commercial graphene nanoplatelets (GNPs) that have respectively 181 m2/g (G1) and 745 m2/g (G2) surface areas and their pyrolyzed forms with and without melamine as platinum (Pt) catalyst support. The GNPs pyrolyzed with melamine were called as M-G1, M-G2; while pyrolyzed without melamine were called as P-G1, P-G2 through the study. Solely, M-G2 sample was nitrogen (N)-doped (2.3%) via pyrolysis by means of melamine. Pt nanoparticles (NPs) were loaded on these support materials by using microwave irradiation technique. PEM fuel cell performance tests were conducted in order to determine the electrochemical activity of the Pt/GNPs catalysts along with polydimethylsiloxane (PDMS) polymer as catalyst binder. Pt/G2 and Pt/M-G2 provided the better PEM fuel cell performance results according to the Pt/G1 and Pt/M-G1 with PDMS polymer. Both of Pt/M-G1/PDMS and Pt/M-G2/PDMS composites gave the lower performance values compared to their pristine cases. Beside, conventional Nafion solution was also used as catalyst binder in the content of catalyst inks of the best two catalysts (Pt/G2, Pt/M-G2). PDMS and Nafion were compared with each other in terms of PEM fuel cell performance. Based on the results (@0.6 V), Pt/G2/PDMS (531.8 mA/cm2) prevailed the Pt/G2/Nafion (473.7 mA/cm2). However, performance sequence changed inversely for the Pt/M-G2/PDMS (62.6 mA/cm2) and Pt/M-G2/Nafion (329.9 mA/cm2). The highest current density value belongs to the Pt/G2/PDMS composite. The higher surface area (for the well distribution of Pt NPs) and the larger pore volume (for the better transfer of reactant gases) provided by the G2 are effective in its superiority. Under catalyst binder mission, the high oxygen permeability and hydrophobicity of the PDMS polymer is also thought to be beneficial for the improved PEM fuel cell performance. Consequently, Pt/G2/PDMS composite is the best candidate for being high-performance catalyst/binder couple in order to be used in the cathode catalyst layer (CL) of PEM fuel cell.