Moni Kanchan Datta

Silicon-based composite anodes for Li-ion rechargeable batteries

Si–C and Si–C–Al composite powders have been synthesized by thermal treatment of high-energy mechanically-milled composite precursors comprising graphite, silicon, aluminium and several types of polymers such as poly(acrylonitrile), poly[(o-cresylglycidyl ether)-co-formaldehyde] resin and poly(methacrylonitrile). The polymers have been used to suppress the interfacial diffusion reactions between graphite, silicon and aluminium, which otherwise lead to the formation of electrochemically-inactive SiC and Al4C3 intermetallics during high-energy mechanical milling. The resultant Si–C composite obtained after thermal treatment of mechanically milled powders of nominal composition [52.5 wt% C]–[17.5 wt% Si]–[8 wt% PAN]–[22 wt% resin] exhibits a reversible capacity of ∼630 mA h g−1 with excellent capacity retention when cycled at a rate of ∼160 mA g−1. On the other hand, the Si–C–Al composite of nominal composition [52.5 wt% C]–[14 wt% Si]–[3.5 wt% Al]–[30 wt% PMAN] exhibits a reversible capacity of ∼650 mA h g−1 up to 30 cycles at a charge/discharge rate of ∼340 mA g−1. Scanning electron microscopy analysis of electrochemically-cycled electrodes indicates that the microstructural stability and the structural integrity of the Si–C and Si–C–Al composite is retained during electrochemical cycling, contributing to the good cyclability demonstrated by the composites.

High performance robust F-doped tin oxide based oxygen evolution electro-catalysts for PEM based water electrolysis

Identification and development of non-noble metal based electro-catalysts or electro-catalysts comprising compositions with significantly reduced amounts of expensive noble metal contents (e.g. IrO2, Pt) with comparable electrochemical performance to the standard noble metal/metal oxide for proton exchange membrane (PEM) based water electrolysis would signify a major breakthrough in hydrogen generation via water electrolysis. Development of such systems would lead to two primary outcomes: first, a reduction in the overall capital costs of PEM based water electrolyzers, and second, attainment of the targeted hydrogen production costs (<

Noble metal-free bifunctional oxygen evolution and oxygen reduction acidic media electro-catalysts

3.00/gge delivered by 2015) comparable to conventional liquid fuels. In line with these goals, by exploiting a two-pronged theoretical first principles and experimental approach herein, we demonstrate for the very first time a solid solution of SnO2:10 wt% F containing only 20 at.% IrO2 [e.g. (Sn0.80Ir0.20)O2:10F] displaying remarkably similar electrochemical activity and comparable or even much improved electrochemical durability compared to pure IrO2, the accepted gold standard in oxygen evolution electro-catalysts for PEM based water electrolysis. We present the results of these studies.

Gold-coated carbon nanotube electrode arrays: Immunosensors for impedimetric detection of bone biomarkers

Identification of low cost, highly active, durable completely noble metal-free electro-catalyst for oxygen reduction reaction (ORR) in proton exchange membrane (PEM) fuel cells, oxygen evolution reaction (OER) in PEM based water electrolysis and metal air batteries remains one of the major unfulfilled scientific and technological challenges of PEM based acid mediated electro-catalysts. In contrast, several non-noble metals based electro-catalysts have been identified for alkaline and neutral medium water electrolysis and fuel cells. Herein we report for the very first time, F doped Cu1.5Mn1.5O4, identified by exploiting theoretical first principles calculations for ORR and OER in PEM based systems. The identified novel noble metal-free electro-catalyst showed similar onset potential (1.43 V for OER and 1 V for ORR vs RHE) to that of IrO2 and Pt/C, respectively. The system also displayed excellent electrochemical activity comparable to IrO2 for OER and Pt/C for ORR, respectively, along with remarkable long term stability for 6000 cycles in acidic media validating theory, while also displaying superior methanol tolerance and yielding recommended power densities in full cell configurations.

Nanostructured robust cobalt metal alloy based anode electro-catalysts exhibiting remarkably high performance and durability for proton exchange membrane fuel cells

C-terminal telopeptide (cTx), a fragment generated during collagen degradation, is a key biomarker of bone resorption during the bone remodeling process. The presence of varying levels of cTx in the bloodstream can hence be indicative of abnormal bone metabolism. This study focuses on the development of an immunosensor utilizing carbon nanotube (CNT) electrodes coated with gold nanoparticles for the detection of cTx, which could ultimately lead to the development of an inexpensive and rapid point-of-care (POC) tool for bone metabolism detection and prognostics. Electrochemical impedance spectroscopy (EIS) was implemented to monitor and detect the antigen-antibody binding events occurring on the surface of the gold-deposited CNT electrode. Type I cTx was used as the model protein to test the developed sensor. The sensor was accordingly characterized at various stages of development for evaluation of the optimal sensor performance. The biosensor could detect cTx levels as low as 0.05 ng/mL. The feasibility of the sensor for point-of-care (POC) applications was further demonstrated by determining the single frequency showing maximum changes in impedance, which was determined to be 18.75 Hz.

Effects of grain refinement on the biocorrosion and in vitro bioactivity of magnesium

In recent years, the development of durable and electrochemically active electro-catalyst alloys with reduced noble metal content exhibiting similar or better electrochemical performance than pure noble metal electro-catalysts has gathered considerable momentum particularly, for proton exchange membrane fuel cell (PEMFC) application. Engineering such reduced noble metal containing electro-catalyst alloys in nano-scale dimensions with highly active electrochemical surface area (ECSA) will ultimately translate to reduced noble metal loadings to ultra-low levels which will eventually lead to an overall reduction in the capital cost of PEMFCs. Herein we report the development of nanostructured Co–Ir based solid-solution electro-catalyst alloys for the hydrogen oxidation reaction (HOR) further validated by first principles theoretical calculation of the d band center of the transition metal in the solid solution alloys. The theoretical and experimental studies reported herein demonstrate that the nanostructured alloy electro-catalysts comprising 70 at% Co (Co0.7Ir0.3) and 60 at% Co (Co0.6Ir0.4) of crystallite size ∼4 nm with a high electrochemically active surface area (ECSA) (∼56 m2 g−1) exhibit improved electrochemical activity (reduction in overpotential and improved reaction kinetics) for the HOR combined with outstanding durability in contrast to pure Ir nanoparticles (Ir-NPs) as well as state of the art commercial Pt/C system. Moreover, an optimized alloy containing 60 at% Co (Co0.6Ir0.4) showed a remarkable ∼156% and 92% higher electro-catalytic activity for the HOR than Ir-NPs and commercial 40% Pt/C, respectively, with similar loading and ECSA. The single PEMFC full cell study also shows ∼85% improved maximum power density for the Co0.6(Ir0.4) electro-catalyst compared to 40% Pt/C and excellent electrochemical stability/durability comparable to 40% Pt/C.

A simple and scalable approach to hollow silicon nanotube (h-SiNT) anode architectures of superior electrochemical stability and reversible capacity

Magnesium is a new class of biodegradable metals potentially suitable for bone fracture fixation due to its suitable mechanical properties, high degradability and biocompatibility. However, rapid corrosion and loss in mechanical strength under physiological conditions render it unsuitable for load-bearing applications. In the present study, grain refinement was implemented to control bio-corrosion demonstrating improved in vitro bioactivity of magnesium. Pure commercial magnesium was grain refined using different amounts of zirconium (0.25 and 1.0 wt.%). Corrosion behavior was studied by potentiodynamic polarization (PDP) and mass loss immersion tests demonstrating corrosion rate decrease with grain size reduction. In vitro biocompatibility tests conducted by MC3T3-E1 pre-osteoblast cells and measured by DNA quantification demonstrate significant increase in cell proliferation for Mg-1 wt.% Zr at day 5. Similarly, alkaline phosphatase (ALP) activity was higher for grain refined Mg. Alloys were also tested for ability to support osteoclast differentiation using RAW264.7 monocytes with receptor activator of nuclear factor kappa-β ligand (RANKL) supplemented cell culture. Osteoclast differentiation process was observed to be severely restricted for smaller grained Mg. Overall, the results indicate grain refinement to be useful not only for improving corrosion resistance of Mg implants for bone fixation devices but also potentially modulate bone regeneration around the implant.

WO3 based solid solution oxide – promising proton exchange membrane fuel cell anode electro-catalyst

Strain engineered unique architectures of silicon nanotubes have garnered tremendous attention as high capacity and stable lithium-ion battery (LIB) anodes. However, the expensive nature of the hitherto synthesis techniques used to produce the silicon nanotubes combined with the inferior yield and poor loading densities have rendered these unique morphologies unattractive for commercial LIB systems. In this study, we report for the first time, a simple, facile, and more importantly, recyclable sacrificial template based approach involving magnesium oxide (MgO) nanorods for producing scalable quantities of hollow silicon nanotubes (h-SiNTs) architectures. Electrodes fabricated from these h-SiNTs derived from this novel scalable approach exhibit equitable loadings and reversible capacities in excess of 1000 mA h g−1 at a high current density of 2 A g−1 for nearly 400 cycles, combined with a very low fade rate of only 0.067% loss per cycle. The high capacity, good current rate characteristics combined with excellent charge-transfer kinetics as well as the long cycle life of these engineered h-SiNTs render this approach viable for industry scale while also boding promise for practical applications.

Fluorine substituted (Mn,Ir)O2:F high performance solid solution oxygen evolution reaction electro-catalysts for PEM water electrolysis

There is a vital need to develop novel non-noble metals based electro-catalyst or reduced noble metal containing electro-catalyst with excellent electrochemical activity and stability fostering economic commercialization of proton exchange membrane fuel cells (PEMFCs). It is hence of paramount importance to identify and generate reduced noble metal containing electro-catalyst with high electrochemical active surface area, offering noble metal loadings in the ultra-low levels thus reducing the overall capital cost of PEMFCs. Using theoretical first principles d-band center calculations of tungsten trioxide (WO3) based electro-catalysts containing IrO2 as a solute for hydrogen oxidation reaction (HOR), we have identified, synthesized and experimentally demonstrated a highly active nanostructured (W1−xIrx)Oy (x = 0.2, 0.3; y = 2.7–2.8) electro-catalyst for HOR. Furthermore, experimental studies validate superior electrochemical activity of nanostructured (W0.7Ir0.3)Oy for HOR exhibiting improved/comparable stability/durability contrasted to pure WO3 nanoparticles (WO3-NPs), IrO2 nanoparticles (IrO2-NPs) as well as state of the art commercial 40% Pt/C system. Optimized composition of (W0.7Ir0.3)Oy was identified exhibiting ∼33% higher and almost similar electro-catalytic activity for HOR compared to IrO2-NPs and commercial 40% Pt/C catalyst, respectively. Additionally, (W0.7Ir0.3)Oy showed significant enhancement in electrochemical activity for HOR compared to pure WO3-NPs. Long-term life cycle test of (W0.7Ir0.3)Oy for 24 h also showed comparable electrochemical stability/durability compared to that of 40% Pt/C and pure WO3-NPs. The results of half and full cell electrochemical characterization bode well with the theoretical first principles studies demonstrating the promise of the WO3 based solid solution electro-catalyst.

Water-soluble-template-derived nanoscale silicon nanoflake and nano-rod morphologies: Stable architectures for lithium-ion battery anodes

Identification and development of high performance with reduced overpotential (i.e. reduced operating electricity cost) oxygen evolution reaction (OER) electrocatalysts for proton exchange membrane (PEM) based water electrolysis with ultra-low noble metal content (i.e. reduced materials cost) is of significant interest for economic hydrogen production, thus increasing the commercialization potential of PEM water electrolysis. Accordingly, a novel electrocatalyst should exhibit low overpotential, excellent electrochemical activity and durability superior to state of the art noble metal based electro-catalysts (e.g. Pt, IrO2, RuO2). Herein, for the very first time to the best of our knowledge, exploiting first-principles theoretical calculations of the total energies and electronic structures, we have identified a reduced noble metal content fluorine doped solid solution of MnO2 and IrO2, denoted as (Mn1−xIrx)O2:F (x = 0.2, 0.3, 0.4), OER electrocatalyst system exhibiting lower overpotential and higher current density than the state of the art IrO2 and other previously reported systems for PEM water electrolysis. The doped solid solution displays an excellent electrochemical performance with a lowest reported onset potential to date of ∼1.35 V (vs. RHE), ∼80 mV lower than that of IrO2 (∼1.43 V vs. RHE) and ∼15 fold (x = 0.3 and 0.4) higher electrochemical activity compared to pure IrO2. In addition, the system displays excellent long term electrochemical durability, similar to that of IrO2 in harsh acidic OER operating conditions. Our study therefore demonstrates remarkable, ∼60–80% reduction in noble metal content along with lower overpotential and excellent electrochemical performance clearly demonstrating the potential of the (Mn1−xIrx)O2:F system as an OER electro-catalyst for PEM water electrolysis.