Raghuram Chetty

Nitrogen-doped Fe-based carbon electrocatalyst (Fe–N–C) is developed by a one-pot pyrolysis method, using a solid-state Fe-EDTA coordination complex. The synthesized catalyst was analytically evaluated by various physical and electrochemical measurements. The effect of various synthetic parameters such as sucrose and EDTA and the effect of metal contents were systematically evaluated. The synthesized Fe–N–C shows significant oxygen reduction activity with half-wave potential of 0.81 V, closer to the commercial Pt/C catalyst, with a nearly 3.9 e− transferred per oxygen molecule. The developed catalyst also shows admirable stability under repeated potential cycling conditions, when compared to the Pt/C catalyst. In a single-cell fuel cell performance analysis, the Fe–N–C catalyst exhibited a peak power density of 118 mW cm−2. Moreover, the Fe–N–C showed remarkable durability during the accelerated stress test (AST) at highly corrosive conditions.

An air breathing direct methanol fuel cell (AB-DMFC) with a unique architecture was designed and fabricated to hold cell components together firmly, avoid fuel leakage and limit cell resistance. Pt and PtRu catalysts prepared by pulse electrodeposition on Ti mesh-based electrodes were employed and compared to traditional carbon-based electrodes. Results showed that Ti mesh can be a suitable catalyst support without the need for a gas diffusion layer (GDL) at the anode, while the absence of a GDL at the cathode drastically reduces cell performance, which can be attributed to the diffusion limitation of oxygen to the cathode. Among the various Ti mesh-based cell configurations explored, the optimum configuration was found with PtRu on an 80 mesh (47% open ratio) Ti anode and a Pt/C coated GDL with 40 mesh (71% open ratio) Ti as a cathode. The single cell AB-DMFC architecture was extended to 2-cell and 6-cell mini-stacks. The 6-cell stack, offering an OCV of 2.9 V and a maximum power of 60 mW using 2 M methanol and ambient air, was used to run a small portable device.

In this investigation, the effect of embedding nanocomposite with different morphology in a polymer-based reverse osmosis (RO) membrane was studied. Thin-film-nanocomposite (TFN) RO membrane was prepared with graphene oxide (GO) and amino-functionalized zinc oxide (ZnO) having different morphologies, i.e. spherical (ZnO-S), flower (ZnO-F) and rod (ZnO-R) shaped nanostructure. The surface properties of the fabricated TFN-RO membrane were investigated using SEM, TEM, XRD, FTIR, AFM, XPS and contact angle measurement. The membrane performance was evaluated using a cross-flow filtration set-up at 25 °C and 20 bar pressure for 2000 mg/L NaCl solution. The experimental results indicated that 0.02 wt% GO-ZnO composite membranes (regardless of their shape) exhibited enhanced hydrophilicity, flux, and permeability. A comparison of different GO-ZnO morphology highlighted that the GO-ZnO-S TFN-RO membrane exhibited superior performance due to the smaller size of ZnO-S, which effectively prevented GO nanosheets from stacking together. The modified membrane with an optimum GO-ZnO-S concentration of 0.02 wt% showed higher solute water flux (31.42 L/m2·h) compared to the pristine TFC membrane (14.28 L/m2·h) with a good salt rejection. Moreover, the modified membranes were found to be chlorine resistant and showed better anti-fouling performance compared to the pristine membrane.

The perceived attraction of nanotubular TiO2 in diverse applications has brought the researchers attention to focus on various aspects of nanotube synthesis and modification. In this work, the visible light activity of dye sensitized TiO2 nanotubes obtained in powder form via rapid breakdown anodization was investigated. Tetra (4-carboxy phenyl) porphyrin (TCPP) was used as a visible light sensitizing component on phase pure anatase TiO2 nanotubes (ATiNT). The effect of introducing two different anchoring groups between the dye and TiO2 nanotubes on photocatalytic activity was investigated. The visible light photocatalytic efficiency of the prepared ATiNT/TCPP composites was tested on a pharmaceutical compound, famotidine (FAM) in order to avoid degradation through photosensitization. For the given amount of TCPP load on ATiNT, the presence of a lengthy anchoring group between TCPP and ATiNT had a negative influence on the photocatalytic activity. Direct oxidation through visible-light-generated holes in the ATiNT/TCPP composite appeared to be the most significant pathway for FAM photocatalysis.

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.

The activity of bimetallic catalyst is predominantly determined by its composition and its shape. In this work, Pt–Pd bimetallic catalysts were codeposited using cyclic voltammetry on a carbon black-coated carbon paper at two different potential ranges (0 to 1.3 V and − 0.2 to 1.3 V vs. SHE) and with two different Pt precursors (H2PtCl6 and K2PtCl4). SEM analysis revealed that the deposit obtained from both K2PtCl4 and H2PtCl6 precursor resembled the shape of a flower-like dendrite when the deposition potential window was in the range of 0 to 1.3 V. However, shifting the lower potential limit from 0 to − 0.2 V resulted in a leaf-like dendritic structure, irrespective of the Pt precursor used. Leaf-like dendritic structures showed enhanced formic acid oxidation activity with high mass activity and superior stability compared to flower-like structures. The superior performance of the leaf-like structure was clearly evident from fuel cell polarization studies carried out at 70 °C, which showed a maximum power density of 49 mW cm−2, whereas flower-like structures showed a power density of 20 mW cm−2.

Abstract: Manganese oxide-based nitrogen-doped reduced graphene oxide (MnO/N-rGO) electrocatalyst was developed by a simple sol–gel process with aqueous KMnO4 and sucrose by adding nitrogen-doped reduced graphene oxide. The physical characterizations were systematically evaluated by X-ray diffraction, field emission scanning electron microscope, transmission electron microscope, and X-ray photoelectron spectroscopy. The electrochemical and oxygen reduction properties of the electrocatalyst and support were studied by employing cyclic voltammetry and linear sweep voltammetry techniques on a rotating-disk electrode in alkaline (0.1 M KOH) solution and compared with commercial Pt/C catalysts. The synthesized catalyst possesses a high oxygen reduction activity and the rotating ring-disk electrode results illustrate a 3.8 e− transfer process. Stability tests performed for 10,000 potential cycles exhibited that the MnO/N-rGO catalyst is more durable than Pt/C catalyst. MnO/N-rGO as cathode catalyst in a single alkaline fuel cell studies gave a peak power density of 44 mW cm− 2 at 40 °C. Durability by accelerated stress test (AST) in fuel cell mode demonstrated MnO/N-rGO as alternative hybrid cathode catalyst which has excellent stability and durability of 67% more than commercial Pt/C. Graphical Abstract: [Figure not available: see fulltext.].

Chemical modification of different morphologies of ZnO nanoparticles (spherical, flowers). Modification of thin-film composite (TFC) using ZnO nanoparticles by surface coating. Measured flux, NaCl rejection and hydrophilicity. Fouling resistance studies on unmodified and modified membrane. Best membrane performance was observed with 0.02 wt% ZnO-S-modified membrane.

In this chapter, preliminary discussion on the need for mitigation of greenhouse gas emissions in today’s scenario is emphasized, followed by the foundation to the conversion of CO2 into useful chemicals. Various techniques employed for CO2 sequestration are introduced, and in the midst of these approaches, electrochemical reduction of CO2 is emphasized, owing to its advantages in product selectivity, operation at ambient conditions without supplementary chemical requirements, environmental compatibility, relatively simple modularity and quick scalability. Different types of catalysts reported in the literature for activating and reducing CO2 are critically analysed. To start with, metallic electrodes in aqueous solutions and nanoporous materials are discussed. The reaction mechanism and effect of supporting electrolytes, pressure, and temperature are summarized. Combination of various techniques such as bio-electrochemical reduction and photocatalytic technologies have been accentuated. Furthermore, limitations and outlook of electrochemical reduction of CO2 are presented, in which development of modules similar to that of commercially available H2O electrolysers could pave the way for commercialization of electrocatalytic reduction of CO2.

The present study reports an energy efficient electrochemical strategy to remediate hexavalent chromium Cr(VI) to less toxic Cr(III). The novelty in this system is the use of titania nanotubes (TNT) synthesized by anodization as cathode for the reduction of Cr(VI) with alkaline urea as an anolyte additive. The electrochemical reduction of Cr(VI) was evaluated using bare Ti and porous TNT/Ti cathodes, both with and without urea as an anolyte additive. The experimental results showed that the dual combination of alkaline urea oxidation at anode and acidic Cr(VI) reduction on TNT cathode showed the best performance, with enhanced degradation efficiency up to 97% at 5 V within 15 min for an initial concentration of 100 mg L−1 Cr. The optimized urea-TNT combination was evaluated for the effect of catholyte pH, temperature, initial metal ion concentration and the effect of other anions, such as Cl−, NO3−, PO42− and CO32−, which are commonly present in wastewater discharged from tannery or electroplating industries. Furthermore, the performance when evaluated with cow urine as an anolyte additive confirmed that the dual combination could be a promising in-situ treatment technique for simultaneous urine oxidation and Cr(VI) reduction.