Raghuram Chetty

A method for estimating the stack rating of vanadium redox flow batteries (VRFBs) through constant power characterization was developed. A stack of 22 cells, each with 1500 cm2 of nominal electrode area, was constructed and tested using constant current and constant power protocols. Typical ratios of charging to discharging power that prevail in various applications (e.g., peak shaving, wind power/solar photovoltaic power integration) were employed in the test protocols. The results showed that fractional energy storage capacity utilization and round-trip energy efficiency varied linearly with the power at which the energy was charged or discharged. A zero-dimensional electrochemical model was proposed based on the area-specific resistance to account for the energy stored/extracted during constant power discharge in the state of charge (SoC) window of 20% to 80%. It was shown that this could be used to rate a given stack in terms of charging and discharging power from the point of view of its application as a power unit. The proposed method enables stack rating based on a single polarization test and can be extended to flow battery systems in general.

Fuel Cell Hybrid Electric Vehicles (FCHEVs) have the potential for providing a solution for clean transportation. For FCHEVs to be successful, it is important to improve their fuel economy and acceleration performance. One of the important systems to be worked on to achieve these goals is the vehicle's powertrain. This research work aims at providing a systematic procedure for multi-objective optimum sizing of a FCHEV powertrain, with the objectives of minimizing the fuel consumption and maximizing the acceleration performance. The work was carried out for a fuel cell-battery hybrid heavy road vehicle for Indian driving cycle. The design variables in the component sizing process were chosen to be speed ratio (x) of the traction motor and degree of hybridization (H) of the power sources. The values of objective functions and constraints were evaluated using ADVISOR software for a sample set of design variables. Surrogate modelling technique was adopted for constructing models for objective functions and constraints. Then, the optimization was carried out using multi-objective genetic algorithm approach to find the Pareto optimal solutions for the problem. This study provides a framework for component sizing of FCHEV that considers x and H as design variables.

In this article, Box–Behnken experimental design methodology was successfully used to consider the effects of silver (Ag)ion concentration and temperature of reaction together with the interaction between Ag+ and reducing agent (hydrazine)concentration on the yield of Ag nano-rods. The statistical and variance analysis was presented, which indicated the factors with higher influence over the model response. By applying such model, the optimum conditions for effective factors were determined for obtaining Ag nano-rods with yield per volume 0.6–0.7, which was at Ag+ concentration of 0.19 g/ml, molar ratio between surfactants of 1, concentration of hydrazine of 0.5 g/ml and nano-rods formation temperature of 90 °C, and was found to give 0.55 g/ml varied from predicted values which was 0.7g/ml with Ag nano-rod outer diameter of 59–73 nm.

High entropy alloys (HEAs) have drawn considerable attention owing to their unique properties such as high fracture toughness, good strength–ductility combination and enhanced corrosion resistance. In this study, the corrosion resistance dependence on the crystal structure and grain size of AlCoCrFeNi HEA is investigated. AlCoCrFeNi HEA with different mixture of body centered cubic (BCC) and face centered cubic (FCC) phases is produced using sequential alloying and tested for corrosion resistance in 3.5 wt% NaCl solution. CoNi+Fe+Cr+Al (84% BCC), FeCr+Ni+Al+Co (62% BCC) and AlNi+Co+Cr+Fe (38% BCC) alloy sequences have corrosion potential of −454, −299 and −524 mV (vs. SCE), and corrosion current of 14, 0.4 and 12 µA, respectively. FCC is a tight binding lattice with higher packing fraction than BCC which made it better for corrosion resistance, but FCC is rich in elements like Co, Ni, and Fe which are easily corroded. These two competing effects lead to a nearly optimum corrosion resistance for FeCr+Ni+Al+Co alloy sequence with 62% BCC and 32% FCC. It is also observed that an increase in grain size improves corrosion resistance. The influence of different chemical elements, crystal structure and microstructure (coarse vs. nanocrystalline) on corrosion resistance is discussed.

Palladium (Pd) dendrites on carbon black support were synthesized by a simple template/surfactant-free electrochemical deposition. In comparison to Pd spherical deposit obtained on non-activated carbon, Pd deposited on an electrochemically activated carbon displayed a dendritic morphology with increased electrochemical surface area and showed enhanced catalytic activity for formic acid oxidation. The effect of electrochemical activation and deposition cycles were studied in relation to the growth and morphological features of Pd deposit. Scanning electron micrographs and X-ray diffraction studies showed a transition in Pd morphology from spheres to dendrites when the carbon support was subjected to varying cycles of electrochemical activation, prior to Pd deposition. Raman and X-ray photoelectron spectra results showed that the defects induced during electrochemical activation on carbon played a major role in tailoring the Pd morphology.

The electrodeposition of platinum-based catalysts (PtPd, PtRu, and PtSn) using the pulse current deposition technique was carried out on titanium substrate to prepare electrodes of different compositions to identify a possible catalyst offering high catalytic activity towards methanol oxidation (MOR). Characterization by XRD, SEM, and EDX confirmed the deposition of catalysts with the desired composition with various morphologies of dendritic, spherical, and irregular deposits for PtPd, PtRu, and PtSn, respectively. Among the various compositions and binary metals studied, electrochemical results indicate PtRu/Ti with Pt to Ru ratio of 1:1 (Pt50Ru50/Ti) to be most active with lower onset potentials for CO oxidation (0.381 V) and methanol oxidation (0.545 V) along with higher peak current density of ∼90 mA cm-2 compared to Pt/Ti (with onset potentials of 0.601 V for CO oxidation, 0.659 V for methanol oxidation and ∼68 mA cm-2 peak current density). Moreover, the MOR catalytic activity retention after 1000 accelerated durability test cycles was the highest for Pt50Ru50/Ti at 55% compared to Pt/Ti and commercial Pt/C.

The conventional electrode structure used in the DMFC is generally based on porous carbon-based gas diffusion electrodes, which consists of a catalyst layer, hydrophobic microporous layer and carbon paper or cloth. This structure is not ideal for transport and release of CO2 gas produced during methanol oxidation at the anode, potentially resulting in considerable hydrodynamic and mass transport limitations. To circumvent these problems, an expanded titanium mesh has been adopted as the catalyst substrate material in this study. Titanium mesh was used as the substrate due to its chemical stability and its ability to support a diverse range of electrocatalysts. In the proposed fuel cell application, the mesh-based electrode has several potential advantages in terms of cost, simplicity, size and shape. This work describes the design, fabrication and evaluation of a passive air-breathing direct methanol fuel cell using the mesh-based electrodes. PtRu/Ti and Pt/Ti prepared by electrodeposition onto the Ti mesh were used as anode and cathode, respectively. Methanol is stored in an in-built reservoir and oxygen is taken from the surrounding air. Single cells with an active area of 9 cm2 produced a power density of 9.5 mW cm-2, whereas a cubic four-cell stack with an active area of 24 cm2 produced a maximum power of 180 mW. The effects of experimental parameters such as concentration and temperature on the cell performance were also investigated. © 2009 Nova Science Publishers, Inc. All rights reserved.

The Government of India has implemented Solar PV based microgrid Decentralized Distributed Generation (DDG) projects in different parts of the country. The monitoring of the performance of DDG projects is a manual process with reliance on the data provided by the system integrators who oversee the DDG projects. With the advent of the Internet of Things (IOT), the monitoring evaluation can be improved dramatically by making it objective, and also to monitor the performance of the policy progress on a near real-time basis. The characteristics of an LPWAN technology viz., LoRa that makes it an appropriate communication technology for remote monitoring of DDG projects are: Long-range, Low power, Small data requirements, and flexibility to operate in unlicensed spectrum. An open-source Internet of Things (IOT) solution is proposed here to monitor and evaluate the rural electrification projects. The methodology involves the development of a low-cost prototype and an open-source based solution to monitor the performance of a DC-based stand-alone solar photovoltaic system, which was set up in the IIT Madras campus. The integration across the LoRaWAn architecture was demonstrated, and a visualization dashboard was created in the Ubidots IOT platform to monitor basic parameters such as voltage and current. The goal is to monitor the solar DC system in terms of the objectives set in DDG policy.

Palladium (Pd) dendrites were synthesized on electrochemically activated carbon (Vulcan XC-72R) support by a simple template free potentiostatic (constant voltage) deposition. Scanning electron micrographs displayed a dendritic morphology when deposited at potentials <0.5 V (vs. RHE), whereas spherical aggregates were obtained at potentials >0.5 V. Transmission electron micrographs and X-ray diffraction pattern confirmed the difference in morphological features and growth of Pd dendrites. Pd deposited at 0.4 V showed higher electrochemical surface area of 128.5 m2 g−1 in comparison to 25.1 m2 g−1 obtained for Pd deposited at 0.5 V and also displayed enhanced activity towards formic acid oxidation.