Surface Functionalization of Carbon Nanotubes for Energy Applications

Carbon nanotubes (CNTs) are receiving a great deal of attention as a catalyst support for different energy applications, due to their high surface area and high conductivity. Recent literature studies have shown that the application of CNTs mainly depends on their surface functionalization process. Typically, pristine CNTs (as produced) have no functional groups, which is usually considered as an obstacle to their widespread application. In this chapter, we highlight the different techniques used to functionalize the surface of CNTs, including physical and chemical functionalization processes. We show the advantages and the drawbacks of the different functionalization processes. Additionally, we explain in detail the different techniques used to characterize the CNTs before and after functionalization processes. Furthermore, we focus on polymer wrapping techniques of CNTs to create active nanocomposite materials for energy applications, in particular the applications in the agriculture field to fight pollution and make farming activity easier and more efficient

Current Advances of Polymer Composites for Water Treatment and Desalination

Over the past five years, a lot of research activities in polymer composites were done in order to improve environmental sustainability and to present advantages for commercial applications of water treatment and desalination. Polymers offered tunable properties, improved processability, remarkable stability, high surface area for fast decontamination, selectivity to eliminate different pollutants, and cost-cutting of water treatment. Hence, the development of polymeric materials is one of the future directions to meet the environmental water standards and to supply the water requirements of the growing populations. This review highlighted the very recent achievements in fabrication, characterization, and applications of polymeric composites used for water treatment and desalination. The polymeric modifications, the addition of functional groups, and the assemblies of nanomaterials were also discussed in detail. In particular, great attention was paid to the recent advances in polymer/polymer composites, polymer/carbon composites, and polymer/clay composites, presenting their usage in the removal of various types of contaminants, e.g., metal ions, dyes, and other toxic pollutants. The review also summarized the main advantages and disadvantages of the different adsorbent materials. Specific attention was paid to the mechanism of adsorption, including chemisorption and physisorption mechanisms. In addition, the challenges and the future perspectives were identified to reach the optimal performance of the different adsorbents

Poly[2,2′-(4,4′-bipyridine)-5,5′-bibenzimidazole] functionalization of carbon black for improving the oxidation stability and oxygen reduction reaction of fuel cells

The rapid oxidation of carbon black (CB) is a major drawback for its use as a catalyst support in polymer electrolyte fuel cells. Here, we synthesize poly[2,20 -(4,40 -bipyridine)-5,50 -bibenzimidazole] (BiPyPBI) as a conducting polymer and use it to functionalize the surface of CB and homogenously anchor platinum metal nanoparticles (Pt-NPs) on a CB surface. The as-prepared materials were confirmed by different spectroscopic techniques, including nuclear magnetic resonance spectroscopy, energy-dispersive X-ray, thermal gravimetric analysis, and scanning-transmittance microscopy. The as-fabricated polymer-based CB catalyst showed an electrochemical surface area (ECSA) of 63.1 cm2 mgPt1 , giving a catalyst utilization efficiency of 74.3%. Notably, the BiPyPBI-based CB catalyst exhibited remarkable catalytic activity towards oxygen reduction reactions. The onset potential and the diffusion-limiting current density reached 0.66 V and 5.35 mA cm2 , respectively. Furthermore, oxidation stability testing showed a loss of only 16% of Pt-ECSA for BiPyPBI-based CB compared to a 36% loss of Pt-ECSA for commercial Pt/CB after 5000 potential cycles. These improvements were related to the synergetic effect between the nitrogen-rich BiPyPBI polymer, which promoted the catalytic activity through the structural nitrogen atoms, and demolished the degradation of CB via the wrapping process

Fully-developed laminar flow in trapezoidal ducts with rounded corners: a numerical solution and case study

Purpose: This paper aims to numerically solve fully developed laminar flow in trapezoidal ducts with rounded corners which result following forming processes. Design/methodology/approach: A two-dimensional model for a trapezoidal duct with rounded corners is developed and conservation of momentum equation is solved. The flow is assumed to be steady, fully developed, laminar, isothermal and incompressible. The key flow characteristics including the Poiseuille number and the incremental pressure drop have been computed and tabulated for a wide range of: sidewall angle (θ); the ratio of the height of the duct to its smaller base (α); and the ratio of the fillet radius of the duct to its smaller base (β). Findings: The results show that Poiseuille number decreases, and all the other dimensionless numbers increase with increasing the radii of the fillets of the duct; these effects were found to amplify with decreasing duct heights or increasing sidewall angles. The maximum axial velocity was shown to increase with increasing the radii of the fillets of the duct. For normally used ducts in hydrogen fuel cells, the impact of rounded corners cannot be overlooked for very low channel heights or very high sidewall angles. Practical implications: The data generated in this study are highly valuable for engineers interested in estimating pressure drops in rounded trapezoidal ducts; these ducts have been increasingly used in hydrogen fuel cells where flow channels are stamped on thin metallic sheets. Originality/value: Fully developed laminar flow in trapezoidal ducts with four rounded corners has been solved for the first time, allowing for more accurate estimation of pressure drop

Determination of time constants of diffusion and electrochemical processes in Polymer Electrolyte Membrane Fuel Cells

Article number 119833This work presents an experimental analysis of the time constants associated to diffusion and electro chemical processes in a 50 cm2 Polymer Electrolyte Membrane (PEM) fuel cell. The experimental tech niques and results include polarization curves and Electrochemical Impedance Spectroscopy (EIS) analysis of the fuel cell, where the time constants are determined from the analysis of the Distribution of Relaxation Times (DRT). EIS results are also used to determine the cell ohmic resistance, where High Frequency Resistance (HFR) values are calculated from the Nyquist plots. A wide range of operating conditions of the fuel cell are analysed, including back pressure (0.5 bare1 bar), cell temperature (55 C, 65 C, 75 C), reactant gases relative humidity (30%, 60%, 90%), cathode stoichiometry (lc 2.5e3.5), and oxygen concentration (air and pure oxygen). The effect of the operating conditions on the time constants are discussed, and Damkohler number is introduced and discussed.Ministerio de Economía y Competitividad (España) UNSE15-CE2962Junta de Andalucía PY20 RE026 AICIAFeder (UE) 375213500Ministerio de Ciencia, Innovación y Universidades (España) ENE2017-91159-EXPMinisterio de Ciencia, Innovación y Universidades (España) PID2019-104441RB-I0

Improved Durability of Electrocatalyst Based on Coating of Carbon Black with Polybenzimidazole and their Application in Polymer Electrolyte Fuel Cells

Improvement of durability of the electrocatalyst has been the key issue to be solved for the practical application of polymer electrolyte membrane fuel cells. One of the promising strategies to improve the durability is to enhance the oxidation stability of the carbon-supporting materials. In this report, we describe in detail the mechanism of the stability improvement of carbon blacks (CBs; Vulcan and Ketjen) by coating with polybenzimidazole (PBI). Nitrogen adsorption experiments reveal that the PBI coating of CBs results in the capping of the gates of the CB-micropores by the PBI. Since the surface of the micropores inside the CBs are inherently highly oxidized, the capping of such pores effectively prevents the penetration of the electrolyte into the pore and works to avoid the further oxidation of interior of the micropore, which is proved by cyclic voltammogram measurements. Above mechanism agrees very well with the dramatic enhancement of the durability of the membrane electrode assembly fabricated using Pt on the PBI-coated CBs as an electrocatalyst compared to the conventional Pt/CB (PBI-non coated) catalyst

Tailoring of a Potential Nanoformulated Form of Gibberellic Acid: Synthesis, Characterization, and Field Applications on Vegetation and Flowering

Nanoformulation of agrochemicals has become a potential choice to improve the physicochemical properties, enhance the utilization efficiency, and reduce the side effects and ecotoxicity of many hazardous chemicals. Here, we tailored a new formulation platform for gibberellic acid (GA) using the layered double hydroxides (LDH) as a potential carrier. Typically, we synthesized, characterized, and potentially applied the newly nanoformulated form of GA on the quantity and quality properties of <i>Dendranthema grandiflorum</i> cultivar. We also evaluated the synergetic effect of the carrier LDH on the release behavior of GA, showing a remarkable impact on the utilization efficiency of GA. The nanohybrid structure of GA also showed an enhanced thermal stability and safe preservation for the incorporated moieties. Taking into account the hazardous effect of free GA on the environment and human health, the hybrid technique of GA is one of the best choices among all of the studied protocols

Influence of the dwell time in the polarization hysteresis of polymer electrolyte membrane fuel cells

The extent of the cell voltage hysteresis observed in polarization curves of PEM fuel cells and the origins causing this effect are investigated by performing experimental polarization curves with different dwell times for a 50 cm2 PEM fuel cell. Electrochemical Impedance Spectroscopy measurements are carried out in order to determine the relative contributions of the different polarizations (ohmic, activation, and concentration polarization). Equivalent circuits were obtained from the impedance spectra, where the interpretation of the circuit parameters enabled the analysis of the origin and extent of the cell voltage hysteresis. It was identified that the cause of the cell voltage hysteresis is actually dominated by the changes in the concentration polarization at low current densities, and by the changes in the activation polarization at high current densities. The cell ohmic resistance (and consequently the membrane hydration) presents a minor effect on the cell voltage hysteresis. The effect of the dwell time in the cell voltage hysteresis (with values ranging from 15 to 25 mV) presents a mixed trend, with an initial decrease for increasing dwell times from 120 to 600 s, and a later increase and a final almost constant hysteresis for longer dwell times