Kingshuk Dutta

Utilization of Conducting Polymers in Fabricating Polymer Electrolyte Membranes for Application in Direct Methanol Fuel Cells

Search for suitable materials for fabricating polymer electrolyte membranes (PEMs) for application in polymer electrolyte membrane fuel cells, and particularly in direct methanol fuel cells (DMFCs), has been an important field of research for the last several decades. Notable candidates that have emerged from this extensive and seemingly exhaustive research are Nafion®, poly(vinylidenefluoride), sulfonated poly(etheretherketone), poly(benzimidazole), Dow XUS®, Flemion® R, 3P-energy, Aciplex-S®, Gore-Tex®, Gore-Select®, and their different blends, copolymers and interpenetrating networks with compounds, such as poly(hexafluoropropylene), poly(acrylonitrile), poly(styrenesulfonate), and poly(methylmethacrylate). Nevertheless, the objective of achieving a much reduced methanol crossover, while maintaining a substantial level of proton conductivity, has remained by and large elusive. However, a ray of hope has been provided by conducting polymers (CPs), and this has led to a considerable number of researchers to plunge into the exploitation of this possibility. This review focuses on the application of CPs, mainly polyaniline and polypyrrole, as PEM constituents. Detailed comparisons between their functioning, and their respective utility in terms of achieving this objective have been provided. We have also discussed the following critical points: first, the effect of CPs on methanol crossover, proton conductivity, and gas diffusion, and second, thermal stability of CPs in the temperature range within which DMFC operates.

Concomitant synthesis of highly crystalline Zn–Al layered double hydroxide and ZnO: Phase interconversion and enhanced photocatalytic activity

Metal oxide/hydroxide with hierarchical nanostructures has emerged as one of the most promising materials for their unique, attractive properties and feasibility of applications in various fields. In this report, a concomitant synthesis of crystalline zinc aluminum layered double hydroxide (ZnAl-LDH) nanostructure and ZnO is presented using Al substrate as template. Studies on interconversion of ZnO to LDH phase in bulk solution under hydrothermal conditions produced Al-doped ZnO (AZO) in one case, and in other, it improves the crystallinity of LDH film templated on Al substrate. In presence of Al salt, the self-limiting growth nature of plate LDH turned to non-self-limiting. Materials obtained during phase transition, AZO in bulk solution and crystalline porous ZnAl-LDH on substrate, have been demonstrated as effective photocatalysts for decomposition of congo red in aqueous medium.

Enhancements of Catalyst Distribution and Functioning Upon Utilization of Conducting Polymers as Supporting Matrices in DMFCs: A Review

Fuel cells (FCs) have evolved as a potential alternative energy harnessing device, with direct methanol fuel cell (DMFC) as one of the front-runners. Although it has achieved significant progress, and is currently getting available in the commercial market; however, from a broader perspective, DMFCs, like most other devices, suffer from certain critical drawbacks. This, in turn, demands considerable progress to be made in order to realize ultimate commercialization, i.e., cheap, reliable, durable, and portable DMFCs with easily accessible fuel. In this respect, one important area of real concern is the DMFC electrodes, consisting of catalysts and catalyst-supporting matrices. Sluggish reaction rates and use of highly expensive and scarce catalysts are two critical drawbacks. Conducting polymers (CPs) have found extensive use in the fabrication of these matrices and have resulted in better dispersion, distribution and anchoring of catalysts, which is important to enhance their reaction efficiencies. This review attempts to summarize the potential contributions of CPs, their critical roles, and possible future trends toward fabricating catalyst-supporting matrices in DMFCs.

A Review on Aromatic Conducting Polymers-Based Catalyst Supporting Matrices for Application in Microbial Fuel Cells

Polymer electrolyte membrane fuel cells (PEMFCs) are being considered as a very important source of alternative energy for powering present and next generation electrical and electronic devices. Microbial fuel cell (MFC) is an important member of the PEMFC family. Compared to other members, such as hydrogen/oxygen and direct methanol fuel cells, MFC is a relatively new entity and is still largely in the research and developmental stage. In terms of fuel, MFC enjoys a huge advantage over other prospective competitors due to large availability of waste water and sludge. In addition, the prospect of waste water and sludge treatment, along with the production of electricity, in an MFC operation is an added bonus. Nevertheless, like most other devices, MFC also suffers from certain critical drawbacks. For example, sluggish electrode reaction rates are source of real concern. This necessitates considerable progress to be made in terms of catalyst and catalyst supports. In this respect, the use of aromatic conducting polymers (ACPs) based catalyst supports have resulted in realizing better dispersion, distribution, and anchoring of catalysts, which is important to enhance their performances towards electrode reactions. This review summarizes the potential roles of ACPs in the capacity as a catalyst-supporting matrix in MFCs.

Nickel nanocatalysts supported on sulfonated polyaniline: potential toward methanol oxidation and as anode materials for DMFCs

The development of potential anode catalysts and catalyst supporting matrices for application in direct methanol fuel cells (DMFCs) has been an active area of research for the last couple of decades. The conventionally used Pt catalyst suffers from (a) high cost, (b) limited abundance and (c) the catalyst poisoning effect induced by the in situ generated carbon monoxide. In this work, a comparatively less expensive and more abundant Ni metal catalyst [supported on Vulcan carbon, polyaniline (PAni) and partially sulfonated PAni (SPAni)] has been utilized as a potential alternative to the Pt metal catalyst for the oxidation of methanol. SPAni emerged as the best matrix for the deposited Ni catalyst nanoparticles. This combination generated a peak current density of 306 μA cm−2 at +0.57 V. In addition, the Ni/SPAni catalyst produced a higher IF/IB ratio compared to the commercial Pt–Ru/C catalyst. Furthermore, a current density of 135 mA cm−2 (at +0.2 V potential) and a maximum power density of 27 mW cm−2 were obtained at 60 °C upon utilizing Ni/SPAni as the anode catalyst for DMFCs. The results, thus obtained, were better than those obtained for the commercial Pt–Ru/C, as well as, the Ni/C and Ni/PAni catalysts.

Morphology control of ZnO with citrate: a time and concentration dependent mechanistic insight

The effect of citrate as a crystal habit modifier on the morphology of zinc oxide has been explored in a wide range of citrate/Zn ratio from 0 to 0.67. With an increase in concentration of citrate at the lower range of the ratio, the aspect ratio of the hexagonal prismatic crystals of ZnO decreases, forming flatter disks with a progressive increase of roughness on the hexagonal face. At intermediate ratios, the otherwise smooth rectangular faces also become rough, with progressive formation of porous spherical aggregates. At a high concentration of citrate, solid spherical particles form with very low crystallinity, eventually forming plate-like zinc citrate. Thermal and spectroscopic studies confirm a progressive increase in the adsorbed citrate concentration in the particles. Evidence in support of citrate being adsorbed first on the hexagonal face, followed by the other rectangular faces is presented, and a scheme has been proposed. This adsorbed citrate can be removed by calcination and the morphology remains intact, and so this procedure can be used to make pure ZnO with various morphologies. It was found that the ZnO morphologies synthesized in the presence of citrate show novel photoluminescent and enhanced photocatalytic activities compared with ZnO synthesized in the absence of citrate.

Reversible assembly and disassembly of amphiphilic assemblies by electropolymerized polyaniline films: effects rendered by varying the electropolymerization potential.

Polymer films that respond to a variety of stimuli are attractive candidates for location-specific guest molecule delivery. These systems release the guest molecules by polymer erosion; thus, these are mono-use systems. If a polymer film is used to disassemble amphiphilic assemblies containing sequestered guest molecules, the polymer erosion issue can be circumvented. However, charge-bearing vinyl polymers, upon interaction with amphiphilic assemblies, are known to adapt to a conformation that results in encapsulating guest molecules instead of releasing them. On the contrary, it has earlier been reported that a rigid, charge-bearing, and water-insoluble conjugated polyaniline film can effectively disassemble amphiphilic assemblies without causing much harm to the film. Herein, we demonstrate the effect rendered by varying the electropolymerization potential on the interaction efficiency between the positive charge-bearing polyaniline film and oppositely charged amphiphilic assemblies. In addition, it is also demonstrated that a film of oxidized polyaniline can be regenerated for repetitive disassembly of the amphiphilic assemblies, and concomitant guest molecule delivery.

Synthesis, Preparation, and Performance of Blends and Composites of π-Conjugated Polymers and their Copolymers in DMFCs

π-conjugated aromatic polymers (π-CPs) are a class of high performance materials used in fabrication of a number of devices. Their use in direct methanol fuel cells (DMFCs) has resulted in improving the performance of this prospective alternative energy harnessing device. This review focuses on these aspects of π-CPs, from fabrication techniques to structure-property relationships and finally performance evaluation and comparison with other potential candidates. Along with an overview of the step-by-step progress that has been made in the last two decades, this review consists of a separate section dedicated to the advancements made in the last five years. This period has seen considerable progress in terms of preparation techniques, such as fabrication of layer-by-layer assembly and core-shell assembly; materials used, such as variety of dopants for π-CPs and sulfonated polymers in case of PEMs and π-CP composites with carbon nanotubes and graphenes in case of catalyst supporting matrices; and surface morphology, such as use of nanofibers, nanotubes, and nanowires. In addition, different polymerization strategies and solubility aspects of π-CPs have also been discussed. All these modifications have resulted in yielding high power and current densities, mass specific activity, stability, durability, and judicious utilization of costly materials, like Pt and Nafion.

Progress in Developments of Inorganic Nanocatalysts for Application in Direct Methanol Fuel Cells

Significant progress has been made in the last few years toward synthesizing highly dispersible inorganic catalysts for application in the electrodes of direct methanol fuel cells. In addition, research toward achieving an efficient catalyst supporting matrix has also attracted much attention in recent years. Carbon black- (Vulcan XC-72) supported Platinum and Platinum-Ruthenium catalysts have for long served as the conventional choice as the cathode and the anode catalyst materials, respectively. Oxygen reduction reaction at the cathode and methanol oxidation reaction at the anode occur simultaneously during the operation of a direct methanol fuel cell. However, inefficiencies in these reactions result in a generation of mixed potential. This, in turn, gives rise to reduced cell voltage, increased oxygen stoichiometric ratio, and generation of additional water that is responsible for water flooding in the cathode chamber. In addition, the lack of long-term stability of Pt-Ru anode catalyst, coupled with the tendency of Ru to cross through the polymer electrolyte membrane and eventually get deposited on the cathode, is also a serious drawback. Another source of potential concern is the fact that the natural resource of Pt and the rare earth metal Ru is very limited, and has been predicted to become exhausted very soon. To overcome these problems, new catalyst systems with high methanol tolerance and higher catalytic activity than Pt need to be developed. In addition, the catalyst-supporting matrix is also witnessing a change from traditionally used carbon powder to transition metal carbides and other high-performance materials. This article surveys the recent literature based on the advancements made in the field of highly dispersible inorganic catalysts for application in direct methanol fuel cells, as well as the progress made in the area of catalyst-supporting matrices.

Materials for Electrodes of Li-Ion Batteries: Issues Related to Stress Development

ABSTRACT Presently, rechargeable Li-ion batteries, possessing highest energy densities among all batte-ries, are used in a major fraction of all portable electronic devices. However, for bestowing the Li-ion batteries suitable for such advanced applications, further improvements in the energy densities (Li-capacities) and in the cycle life are essential. In a broader sense, this can be achieved by replacing the presently used electrode materials by materials possessing higher Li-capacities and minimization of the degradation of such materials with electrochemical cycling. It has been realized that the major reason for degradation in battery performance in terms of capacity with cycling is the disintegration/fragmentation of the active electrode materials due to stresses generated during Li-intercalation/de-intercalation in every cycle. Such stresses arise from the reversible volume changes of the active electrode materials during Li-insertion and removal. In quest of higher energy densities, replacement of the presently used graphitic carbon by potentially higher capacity metallic anode materials (like Si, Sn, and Al) is likely to further accrue this stress related disintegration due to ∼30 times higher volume changes experienced by such materials. It has also been recently realized that passivating layer formed on the surface of the electrodes also contributes toward the stress development. After briefly introducing the mechanistic aspects of Li-ion batteries, this article focuses on the reasons and consequences associated with stress developments in different electrode materials, highlighting the various strategies, in terms of designing new electrode com-positions or reducing the microstructural scale, that are being presently adopted to address the stress-related issues. Considering that experimental determination of such stresses is essential toward further progress in Li-ion battery research, this article introduces a recently reported technique developed for real-time measurement of such stresses. It finally concludes by raising some critical issues that need to be resolved through further research in this area.