Santimoy Khilari

Graphene supported α-MnO2 nanotubes as a cathode catalyst for improved power generation and wastewater treatment in single-chambered microbial fuel cells

Microbial fuel cells (MFC) are a promising system to simultaneously accomplish the goal of energy production and wastewater treatment. In the MFC, the cathode plays an important role in achieving high power density and thereby improving the cell performance. In the cathode, an allotrope of carbon [activated carbon, graphite, multi-walled carbon nanotubes (MWCNTs)] is commonly used as a support material for catalysts, such as Pt. Here we show the improved performance of single-chambered MFC (sMFC) using hydrothermally synthesized α-manganese dioxide nanotubes (MnO2-NTs) as the catalyst and graphene as the support in the cathode. With a fixed MnO2-NTs loading, a maximum volumetric power density of 4.68 W m−3 was achieved from the sMFC with MnO2-NTs/graphene, which is higher than that of MnO2-NTs/MWCNTs (3.94 W m−3) and MnO2-NTs/Vulcan XC (2.2 W m−3) composite cathodes, but marginally lower than that of the benchmark Pt/C cathode (5.67 W m−3). The MnO2-NTs/graphene composite also showed a higher oxygen reduction reaction (ORR) activity than the MnO2-NTs/MWCNTs and MnO2-NTs/Vulcan XC composites implying that the former is a better catalyst than the later two. This study demonstrates the high ORR activity and high power generation ability of the cost-effective MnO2-NTs/graphene composite and makes it a potential cathode material for the replacement of expensive Pt in constructing large-scale MFC for wastewater treatment and bioelectricity production.

Manganese cobaltite/polypyrrole nanocomposite-based air-cathode for sustainable power generation in the single-chambered microbial fuel cells

Manganese cobaltite nanorods (MnCo2O4 NRs) were prepared and tested as potential air-cathode catalyst for the single-chambered microbial fuel cells (sMFC). The power generation of sMFC increases with MnCo2O4 NRs loading to the cathode. The Polypyrrole (PPy) and Vulcan XC were used as conducting support to the MnCo2O4 NRs to form composites either by in situ or by mechanical mixing in the cathode fabrication. The cyclic voltammetry, linear sweep voltammetry and electrochemical impedance studies reveal that the in situ-MnCo2O4 NRs/PPy composite has higher catalytic activity than that of mechanically mixed-MnCo2O4NRs/PPy composite because of higher interfacial contact between MnCo2O4 NRs and PPy. The maximum volumetric power density with in situ-MnCo2O4 NRs/PPy, mechanically mixed-MnCo2O4 NRs/PPy, MnCo2O4 NRs/Vulcan XC and catalyst-free (only Vulcan XC) cathode was measured to be 6.11, 5.05, 4.22, and 1.77 W/m(3), respectively, in the sMFC. This suggests that PPy is not only a better conducting support than that of conventionally used Vulcan XC but also the cathode composite fabrication process is important for enhanced performance. The synergetic effect of MnCo2O4 NRs and PPy was found to play an important role for the improved energy recovery and it could be applied as an efficient and inexpensive cathode catalyst for the sMFC.

Bifunctional Manganese Ferrite/Polyaniline Hybrid as Electrode Material for Enhanced Energy Recovery in Microbial Fuel Cell

Microbial fuel cells (MFCs) are emerging as a sustainable technology for waste to energy conversion where electrode materials play a vital role on its performance. Platinum (Pt) is the most common material used as cathode catalyst in the MFCs. However, the high cost and low earth abundance associated with Pt prompt the researcher to explore inexpensive catalysts. The present study demonstrates a noble metal-free MFC using a manganese ferrite (MnFe2O4)/polyaniline (PANI)-based electrode material. The MnFe2O4 nanoparticles (NPs) and MnFe2O4 NPs/PANI hybrid composite not only exhibited superior oxygen reduction reaction (ORR) activity for the air cathode but also enhanced anode half-cell potential upon modifying carbon cloth anode in the single-chambered MFC. This is attributed to the improved extracellular electron transfer of exoelectrogens due to Fe(3+) in MnFe2O4 and its capacitive nature. The present work demonstrates for the first time the dual property of MnFe2O4 NPs/PANI, i.e., as cathode catalyst and an anode modifier, thereby promising cost-effective MFCs for practical applications.

Improvement of power generation using Shewanella putrefaciens mediated bioanode in a single chambered microbial fuel cell: Effect of different anodic operating conditions

Three different approaches were employed to improve single chambered microbial fuel cell (sMFC) performance using Shewanella putrefaciens as biocatalyst. Taguchi design was used to identify the key process parameter (anolyte concentration, CaCl₂ and initial anolyte pH) for maximization of volumetric power. Supplementation of CaCl₂ was found most significant and maximum power density of 4.92 W/m(3) was achieved. In subsequent approaches, effect on power output by riboflavin supplementation to anolyte and anode surface modification using nano-hematite (Fe₂O₃) was observed. Volumetric power density was increased by 44% with addition of 100 nM riboflavin to anolyte while with 0.8 mg/cm(2) nano-Fe₂O₃ impregnated anode power density and columbic efficiency increased by 40% and 33% respectively. Cyclic voltammetry revealed improvement in electrochemical activity of Shewanella with nano-Fe₂O₃ loading and electrochemical impedance depicted inverse relationship between charge transfer resistance and nano-Fe₂O₃ loading. This study suggests anodic improvement strategies for maximization of power output.

CoFe2O4-decorated carbon nanotubes for the dehydration of glucose and fructose

Multi-walled carbon nanotubes (CNTs) decorated with different ferrites have been synthesized and successfully used under heterogeneous conditions in the dehydration of fructose. In addition, inverse spinels, such as cobalt ferrite (CoFe2O4) and magnetite (Fe3O4), decorated on CNTs showed better performance than normal spinel such as zinc ferrite (ZnFe2O4)-decorated CNTs. The catalyst could be easily recycled and the protocol was simple. Moreover, functionalized CNTs were characterized using various methods, including Raman spectroscopy, X-ray diffraction and Transmission Electron Microscope analysis. The crystallite size of CoFe2O4-decorated CNTs was nearly 20 nm.

Surface modification of polyhedral nanocrystalline MgO with imidazolium carboxylates for dehydration reactions: a new approach

The surface modification of nanomaterials with organic molecules and the utilization of modified materials in various applications is equally important. Here we demonstrate, the surface modification of polyhedral nano MgO with imidazolium carboxylate, which generates the NHC stabilized material MgO–[NHC]. The resultant material was successfully utilized in the catalytic dehydration of glucose under heterogeneous conditions. Furthermore, it was used in the dehydration of nitro alcohol to olefins in high yields. In addition, the surface modified catalyst was characterized by using various techniques like XRD, FE-SEM, TEM, FT-IR, XPS and AES analysis.

MnFe2O4@nitrogen-doped reduced graphene oxide nanohybrid: an efficient bifunctional electrocatalyst for anodic hydrazine oxidation and cathodic oxygen reduction

The direct hydrazine fuel cell (DHFC) emerges as a promising tool to produce electricity without any carbon emission. The electrocatalyst plays a role central to the performance of the DHFC. Thus, development of cost-effective bifunctional electrocatalysts remains a key to make this technology practically viable. Herein, we report a single-step hydrothermal synthesis route to couple MnFe2O4 nanoparticles (NPs) with nitrogen-doped reduced graphene oxide (h-MnFe2O4 NPs/N-rGO) and demonstrate its bifunctional role as an electrocatalyst for both anodic hydrazine electrooxidation and cathodic reduction of molecular oxygen. The as-synthesized h-MnFe2O4 NPs/N-rGO composite not only catalyzes hydrazine electrooxidation via a quasi-4-electron pathway (n = 3.94) with a small Tafel slope (106 mV decade−1) but is also capable of reducing molecular oxygen through an efficient 4-electron pathway. The oxygen reduction performance of the present composite is found to be comparable to that of the state-of-the-art Pt/C catalyst. In addition, the bifunctional electrocatalytic behavior of the h-MnFe2O4 NPs/N-rGO composite is found to be superior to those of MnFe2O4 NPs/rGO, pristine MnFe2O4 NPs, N-rGO alone, and the physical mixture of MnFe2O4 NPs and N-rGO. The improved electrocatalytic efficiency of the h-MnFe2O4 NPs/N-rGO composite originates from the synergetic physicochemical properties of MnFe2O4 NPs and N-rGO, which facilitates analyte diffusion, reduces charge transfer resistance, and offers a greater number of active sites for the catalytic reactions.

Shape-Dependent Photocatalytic Activity of Hydrothermally Synthesized Cadmium Sulfide Nanostructures

The effective surface area of the nanostructured materials is known to play a prime role in catalysis. Here we demonstrate that the shape of the nanostructured materials plays an equally important role in their catalytic activity. Hierarchical CdS microstructures with different morphologies such as microspheres assembled of nanoplates, nanorods, nanoparticles, and nanobelts are synthesized using a simple hydrothermal method by tuning the volume ratio of solvents, i.e., water or ethylenediamine (en). With an optimum solvent ratio of 3:1 water:en, the roles of other synthesis parameters such as precursors ratio, temperature, and precursor combinations are also explored and reported here. Four selected CdS microstructures are used as photocatalysts for the degradation of methylene blue and photoelectrochemical water splitting for hydrogen generation. In spite of smaller effective surface area of CdS nanoneedles/nanorods than that of CdS nanowires network, the former exhibits higher catalytic activity under visible light irradiation which is ascribed to the reduced charge recombination as confirmed from the photoluminescence study.

Reduction of start-up time through bioaugmentation process in microbial fuel cells using an isolate from dark fermentative spent media fed anode

An electrochemically active bacteria Pseudomonas aeruginosa IIT BT SS1 was isolated from a dark fermentative spent media fed anode, and a bioaugmentation technique using the isolated strain was used to improve the start-up time of a microbial fuel cell (MFC). Higher volumetric current density and lower start-up time were observed with the augmented system MFC-PM (13.7 A/m(3)) when compared with mixed culture MFC-M (8.72 A/m(3)) during the initial phase. This enhanced performance in MFC-PM was possibly due to the improvement in electron transfer ability by the augmented strain. However, pure culture MFC-P showed maximum volumetric current density (17 A/m(3)) due to the inherent electrogenic properties of Pseudomonas sp. An electrochemical impedance spectroscopic (EIS) study, along with matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) analysis, supported the influence of isolated species in improving the MFC performance. The present study indicates that the bioaugmentation strategy using the isolated Pseudomonas sp. can be effectively utilized to decrease the start-up time of MFC.

The Design of a New Cobalt Sulfide Nanoparticle Implanted Porous Organic Polymer Nanohybrid as a Smart and Durable Water-Splitting Photoelectrocatalyst

Development of an inexpensive, efficient and robust nanohybrid catalyst as a substitute for platinum in photoelectrocatalytic hydrogen production has been considered intriguing and challenging. In this study, the design and sequential synthesis of a novel cobalt sulfide nanoparticle grafted Porous Organic Polymer nanohybrid (CoSx @POP) is reported and used as an active and durable water-splitting photoelectrocatalyst in the hydrogen evolution reaction (HER). The specific textural and relevant chemical properties of as-synthesised nanohybrid materials (Co3 O4 @POP &CoSx @POP) were investigated by means of XRD, XPS, FTIR, 13 C CP MAS NMR, spectroscopy, HR-TEM, HAADF-STEM with the corresponding elemental mapping, FE-SEM and nitrogen physisorption studies. CoSx @POP has been evaluated as a superior photoelectrocatalyst in HER, achieving a current density of 6.43 mA cm-2 at 0 V versus the reversible hydrogen electrode (RHE) in a 0.5 m Na2 SO4 electrolyte which outperforms its Co3 O4 @POP analogue. It was found that the nanohybrid CoSx @POP catalyst exhibited a substantially enhanced catalytic performance of 1.07 μmol min-1 cm-2 , which is considered to be ca. 10 and 1.94 times higher than that of pristine POP and CoSx , respectively. Remarkable photoelectrocatalytic activity of CoSx @POP compared to Co3 O4 @POP toward H2 evolution could be attributed to intrinsic synergistic effect of CoSx and POP, leading to the formation of a unique CoSx @POP nanoarchitecture with high porosity, which permits easy diffusion of electrolyte and efficient electron transfer from POP to CoSx during hydrogen generation with a tunable bandgap, that straddles between the reduction and oxidation potential of water.