Mohamed R. Berber

Remarkably Durable High Temperature Polymer Electrolyte Fuel Cell Based on Poly(vinylphosphonic acid)-doped Polybenzimidazole

Low durability of polymer electrolyte fuel cell (PEFC) is a major drawback that should be solved. Recent studies have revealed that leaching of liquid phosphoric acid (PA) from both polymer electrolyte membrane and catalyst layers causes inhomogeneous PA distribution that results in deterioration of PEFC performance during long-term operation. Here we describe the finding that a novel PEFC free from acid leaching shows remarkable high durability (single cell test: >400,000 cycling) together with a high power density at 120°C under a non-humidified condition. This is achieved by using a membrane electrode assembly (MEA) with Pt on poly(vinylphosphonic acid)-doped polybenzimidazole wrapped on carbon nanotube and poly(vinylphosphonic acid)-doped polybenzimidazole for the electrocatalst and electrolyte membrane, respectively. Such a high performance PEFC opens the door for the next-generation PEFC for “real world” use.

A polymer-coated carbon black-based fuel cell electrocatalyst with high CO-tolerance and durability in direct methanol oxidation

The design and fabrication of a highly durable and carbon monoxide (CO) tolerant catalyst for direct methanol fuel cells (DMFCs) is highly required since the DMFCs are promising power sources in the near future. Here we describe the finding that a fuel cell catalyst composed of carbon black, poly[2,2′-(2,6-pyridine)-5,5′-bibenzimidazole] and platinum that was coated by a polymer acid, poly(vinylphosphonic acid), shows a high durability and CO tolerance in the methanol oxidation reaction, which has been revealed by electrochemical methods together with a transmission electron microscopy study.

Nanocomposites of 2-arylpropionic acid drugs based on Mg–Al layered double hydroxide for dissolution enhancement

Naproxen (NP) and flurpibrofen (FB) as non-steroidal anti-inflammatory drugs (NSAIDs) of 2-arylpropionic acid derivatives have been used as host organic drugs to be intercalated into layered double hydroxide (LDH) applying reconstruction and co-precipitation techniques. The obtained NP-LDH and FB-LDH nanocomposites were characterized by X-ray powder diffraction, infrared and thermogravimetric analyses. From drug loading, thermal analysis and X-ray measurements we can decide that coprecipitaion technique is better than reconstruction technique to obtain intercalated monophase nanocomposites. In acidic medium LDH dissolved and the intercalated drug starts to release in a molecular form which is suitable for adsorption. The drug solubility has been investigated before and after intercalation. It has been found that LDH improves the drug solubility and its dissolution rate.

Enhancement of Platinum Mass Activity on the Surface of Polymer-wrapped Carbon Nanotube-Based Fuel Cell Electrocatalysts

Cost reduction and improved durability are the two major targets for accelerating the commercialization of polymer electrolyte membrane fuel cells (PEFCs). To achieve these goals, the development of a novel method to fabricate platinum (Pt)-based electrocatalysts with a high mass activity, deposited on durable conductive support materials, is necessary. In this study, we describe a facile approach to grow homogeneously dispersed Pt nanoparticles (Pt) with a narrow diameter distribution in a highly controllable fashion on polymer-wrapped carbon nanotubes (CNTs). A PEFC cell employing a composite with the smallest Pt nanoparticle size (2.3 nm diameter) exhibited a ~8 times higher mass activity compared to a cell containing Pt with a 3.7 nm diameter. This is the first example of the diamter control of Pt on polymer-wrapped carbon supporting materials, and the study opens the door for the development of a future-generation of PEFCs using a minimal amount of Pt.

An Enhanced Anode based on Polymer‐Coated Carbon Black for use as a Direct Methanol Fuel Cell Electrocatalyst

Sluggish methanol oxidation reaction and low durability are the main obstacles for commercialization of direct methanol fuel cells (DMFCs). In this study, we describe the fabrication of 4 different carbon black (CB)‐based electrocatalysts for the DMFC by changing the weight ratio between the Pt feed and polymer wrapped carbon support. In all the fabricated electrocatalysts, CB was coated with poly[2,2′‐(2,6‐pyridine)‐5,5′‐bibenzimidazole] on which the Pt nanoparticles were deposited, which were further coated with poly(vinylphosphonic acid). We found that a decrease in the Pt particle size produced higher catalytic activity. The electrochemical surface area (ECSA) of the electrocatalyst with the smallest Pt particle size was 120.8±12.0 m2 gPt−1. The mass activity of the methanol oxidation reaction reached 1860 mA mgPt−1, which is, to the best of our knowledge, the highest value among the recorded catalytic activities of the CB‐based electrocatalysts. Moreover, after 100 000 cycles the electrocatalyst displayed only 38 % and 10.7 % decrease in ECSA and methanol oxidation activity, respectively. Such an obtained durability was ≈10 times higher than that of the commercial CB/Pt electrocatalyst.

High-Temperature Polymer Electrolyte Fuel Cell Using Poly(vinylphosphonic acid) as an Electrolyte Shows a Remarkable Durability

The development of a high‐performance, durable, and less expensive membrane electrode assembly (MEA) composed of a polymer electrolyte membrane and electrocatalysts is important for developing fuel cells. Herein, we described the design and fabrication of an electrocatalyst with carbon black, polybenzimidazole doped with poly(vinylphosphonic acid) (PVPA), and platinum nanoparticles as an electron‐conducting support material, an electrolyte, and a metal catalyst, respectively. Most importantly, we used PVPA in place of phosphoric acid, which is a widely used acid dopant, as the acid dopant for both the electrocatalyst and the polymer electrolyte membrane. We reported that the use of PVPA is crucial for the high performance of the MEA because it prevented the leaching of acid molecules from the MEA, which led to high durability compared to that of the phosphoric acid‐doped MEAs.

Durability analysis of polymer-coated pristine carbon nanotube-based fuel cell electrocatalysts under non-humidified conditions

A polymer electrolyte fuel cell (PEFC) that shows high durability at elevated temperature and under non-humidified conditions is strongly demanded for the next generation PEFCs. Here we show the importance of using pristine carbon nanotubes (CNTs) as catalyst supports for fuel cell (FC) durability. For that purpose, two different membrane electrode assemblies (MEAs) using pristine CNTs and commercial carbon black (CB) as carbon supports were coated by polybenzimidazole on which platinum (Pt) nanoparticles were deposited. Notably, the CNT-based MEA exhibited ∼4 times higher durability compared to the CB-based MEA. The ex situ monitoring of the fabricated electrocatalysts before and after the durability testing based on transmission electron microscopy and X-ray diffraction measurements revealed higher structural stability of the CNTs compared to the CB in their MEAs. The pristine structure of the CNTs has been revealed to be very important for the high PEFC durability. This is the first report that shows the durability of the pristine CNT-based PEFC at high operating temperature and under non-humidified conditions, which are the targets of the next generation PEFCs with very high performance.

Unusually Large Hysteresis of Temperature-Responsive Poly(N-ethyl-2- propionamidoacrylamide) Studied by Microcalorimetry and FT-IR

We reported here the full characterization of the hysteresis of the phase transition behavior of an aqueous solution of poly(N-ethyl-2-propionamidoacrylamide) (PNEPA), which has a unique alpha,alpha-disubstituted structure, by using microcalorimetry and FT-IR. Phase transition temperatures near the thermodynamic equilibrium were determined by extrapolating the scanning rate of the microcalorimetry to zero. The calculated hysteresis from the phase transition temperature was unusually very large (approximately 8 degrees C). FT-IR analysis indicated that the large hysteresis of PNEPA resulted from a coupling of intra-/intermonomeric unit hydrogen bonds, which is known to occur in a beta-sheet of proteins but has never been reported in temperature-responsive polymers. The effects of the molecular weight and polymer concentration on the hysteresis were studied by using fractionated PNEPAs and it was found that a low molecular weight and a low concentration enhanced the hysteresis.

Design of a multifunctional nanohybrid system of the phytohormone gibberellic acid using an inorganic layered double-hydroxide material.

To offer a multifunctional and applicable system of the high-value biotechnological phytohormone gibberellic acid (GA), a nanohybrid system of GA using the inorganic Mg-Al layered double-hydroxide material (LDH) was formulated. The ion-exchange technique of LDH was applied to synthesize the GA-LDH hybrid. The hybrid structure of GA-LDH was confirmed by different spectroscopic techniques. The nanohybrid size was described by SEM to be ∼0.1 μm. The GA-LDH nanohybrid structure was the key parameter that controlled GA properties. The layered molecular structure of LDH limited the interaction of GA molecules in two-dimensional directions. Accordingly, GA molecules did not crystallize and were released in an amorphous form suitable for dissolution. At various simulated soil solutions, the nanohybrids showed a sustained release process following Higuchi kinetics. The biodegradation process of the intercalated GA showed an extended period of soil preservation as well as a slow rate of degradation.

A highly durable fuel cell electrocatalyst based on double-polymer-coated carbon nanotubes.

Driven by the demand for the commercialization of fuel cell (FC) technology, we describe the design and fabrication of a highly durable FC electrocatalyst based on double-polymer-coated carbon nanotubes for use in polymer electrolyte membrane fuel cells. The fabricated electrocatalyst is composed of Pt-deposited polybenzimidazole-coated carbon nanotubes, which are further coated with Nafion. By using this electrocatalyst, a high FC performance with a power density of 375 mW/cm2 (at 70 ˚C, 50% relative humidity using air (cathode)/H2(anode)) was obtained, and a remarkable durability of 500,000 accelerated potential cycles was recorded with only a 5% loss of the initial FC potential and 20% loss of the maximum power density, which were far superior properties compared to those of the membrane electrode assembly prepared using carbon black in place of the carbon nanotubes. The present study indicates that the prepared highly durable fuel cell electrocatalyst is a promising material for the next generation of PEMFCs.