K.S. Dhathathreyan

Hydrogen storage in carbon nanotubes and related materials

Adsorption of hydrogen at 300 K has been investigated on well-characterized samples of carbon nanotubes, besides carbon fibres by taking care to avoid many of the pitfalls generally encountered in such measurements. The nanotube samples include single- and multi-walled nanotubes prepared by different methods, as well as aligned bundles of multi-walled nanotubes. The effect of acid treatment of the nanotubes has been examined. A maximum adsorption of ca. 3.7 wt% is found with aligned multi-walled nanotubes. Electrochemical hydrogen storage measurements have also been carried out on the nanotube samples and the results are similar to those found by gas adsorption measurements.

Humidification studies on polymer electrolyte membrane fuel cell

Two methods of humidifying the anode gas, namely, external and membrane humidification, for a polymer electrolyte membrane fuel (PEMFC) cell are explained. It is found that the water of solvation of protons decreases with increase in the current density and the electrode area. This is due to insufficient external humidification. In a membrane-based humidification, an optimum set of parameters, such as gas flow rate, area and type of the membrane, must be chosen to achieve effective humidification. The present study examines the dependence of water pick-up by hydrogen on the temperature, area and thickness of the membrane in membrane humidification. Since the performance of the fuel cell is dependent more on hydrogen humidification than on oxygen humidification, the scope of the work is restricted to the humidification of hydrogen using Nafion® membrane. An examination is made on the dependence of water pick-up by hydrogen in membrane humidification on the temperature, area and thickness of the membrane. The dependence of fuel cell performance on membrane humidification and external humidification in the anode gas is also considered.

Evaluation of current distribution in a proton exchange membrane fuel cell by segmented cell approach

A technique is developed for the determination of the distribution of current density in operating fuel cells using a segmented cell structure concept. Real-time current density distribution data are presented and it is shown that they can contribute to an improved understanding of the reactant distribution over the active fuel cell area, for optimization of fuel cell performance. The technique also offers an alternative to a commercial polymer electrolyte membrane fuel cell stack in the small power range. When stacking several segmented structure electrodes, the resulting volume can be considerably reduced compared with a state-of-the-art stack.

A PEDOT-reinforced exfoliated graphite composite as a Pt- and TCO-free flexible counter electrode for polymer electrolyte dye-sensitized solar cells

Herein, we have demonstrated a highly efficient, flexible, and low-cost (Pt-free and TCO-free) counter electrode made of a highly conductive poly(3,4-ethylene dioxythiophene) (PEDOT)/exfoliated graphite (EFG) composite in solid state dye-sensitized solar cells (DSSCs) employing polymer electrolytes. Electropolymerized one-dimensional PEDOT nanofibers were firmly attached to a flexible EFG sheet affording high catalytic activity and electron conductivity. PEDOT/EFG counter electrode-based DSSCs showed an energy conversion efficiency of 5.7% with a solid polymer electrolyte, which is significantly higher than conventional Pt electrodes (4.4%) under similar device architecture conditions.

Development of polymer electrolyte membrane fuel cell stack

Abstract The proton exchange membrane fuel cell (PEMFC) is one of the strongest contenders as a power source for space, electric vehicle and domestic applications. Since 1988 intensive research is being carried out at our centre to develop PEMFCs. The main RandD activities are: (i) to develop a method for the electrode preparation (ii) to enhance platinum utilisation using low platinum loading and (iii) to design multicell stacks. The results of RandD development of the above activities are discussed in this paper.

Analysis of Flow Maldistribution of Fuel and Oxidant in a PEMFC

The flow of fuel and oxidant through a PEMFC is analyzed for prediction of maldistribution. Flow distribution of both fuel and oxidant from the port to the individual cells critically control the performance of a PEMFC stack in combination. The distribution of fluids was simulated by analytical approach utilizing flow channeling model of a manifold. A detailed numerical modeling is also carried out considering flow in each cell between the electrodes as flow through an equivalent porous medium offering identical resistance. The results show a close match between the analytical and numerical results. The parametric study reveals that flow rate and port size plays major role determining maldistribution of the fluids, which can be considerably skewed when large numbers of cells are stacked for larger power output.

Identification and characterization of parameters for external humidification used in polymer electrolyte membrane fuel cells

Abstract Retention of the water content of the membrane in the polymer electrolyte membrane fuel cell is critical for obtaining the maximum power density. Humidification of the reactants is a must to keep the membrane in a wet condition. The present paper identifies the parameters to achieve the maximum humidification of the reactants. Optimization of humidification is also discussed with respect to the pressure drop of the reactants while trying to achieve the theoretical relative humidity (RH), especially for the requirements of a multi-kilowatt stack.

Polymer Electrolyte Membrane Fuel Cell

The polymer electrolyte membrane fuel cell (PEMFC) also known as proton exchange membrane fuel cell, polymer electrolyte fuel cell (PEFC) and solid polymer fuel cell (SPFC) was first developed by General Electric in the USA in the 1960’s for use by NASA in their initial space applications. The electrolyte is an ion conducting polymer membrane, described in more details in Section 2.2. Anode and cathode are bonded to either side of the membrane. This assembly is normally called membrane electrode assembly (MEA) or EMA which is placed between the two flow field plates (bipolar plates) (Section 2.5) to form what is known as “stack”. The basic operation of the PEMFC is the same as that of an acid electrolyte cell as the mobile ions in the polymer are H+ or proton.

Nafion based amperometric hydrogen sensor

A Nafion based amperometric hydrogen sensor that operates at room temperature has been developed. The electrolyte used in the sensor is Nafion 117, which is a proton conducting solid polymer electrolyte. Palladium catalyst was used on the sensing side and platinum supported on carbon on the air side. The sensor functions as fuel cell, H2/Pd//Nafion//Pt/O2 and the short circuit current is measured. The short circuit current is found to be linear with respect to concentration of hydrogen on the sensing side. The sensor is able to detect the concentration of hydrogen in argon down to ppb level. Details of assembly of the sensor, response behavior and applications are discussed.

Thermal rearrangement reactions of methoxycyclophosphazenes

Alkoxycyclophosphazenes find use as flame retardants for textile fibres (1). The thermal rearrangement of alkoxycyclophosphazenes (2) merits a detailed study in view of its relevance to understanding the transformations asso- Ciated with this flame retardant behaviour. We report here our preliminary results on the thermal behaviour of some methoxycyclophosphazenes and the 1H, 31p and 13C ~IR spectro-scopic data for the products.