Prashanth Jampani

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 (<

High energy density titanium doped-vanadium oxide-vertically aligned CNT composite electrodes for supercapacitor applications

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.

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

In this study, we provide the first report on the supercapacitance behavior of titanium doped vanadium oxide films grown on vertically aligned carbon nanotubes using a chemical vapor deposition (CVD) technique. The capacitance of CVD derived titanium doped vanadium oxide–carbon nanotube composites was measured at different scan rates to evaluate the charge storage behavior. In addition, the electrochemical characteristics of the titanium doped vanadium oxide thin films synthesized by the CVD process were compared to substantiate the propitious effect of the carbon nanotubes on the capacitance of the doped vanadium oxide. Considering the overall materials loading with good rate capability and excellent charge retention up to 400 cycles, it can be noted that attractive capacitance values as high as 310 F g−1 were reported. Ab initio theoretical studies, demonstrating the substantial improvement in the electronic conductivity of the vanadium oxide due to titanium doping and oxygen vacancies, have also been included corroborating the attractive experimental capacitance response.

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

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.

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

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.

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

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.

Growth of Carbon Nanotubes on Copper Substrates Using a Nickel Thin Film Catalyst

Earth abundant and economical rock salt (NaCl) particles of different sizes (<3 μm and 5–20 μm) prepared by high energy mechanical milling were used as water-soluble templates for generation of Si with novel nanoscale architectures via low pressure chemical vapor deposition (LPCVD). Si nanoflakes (SiNF) comprising largely amorphous Si (a-Si) with a small volume fraction of nanocrystalline Si (nc-Si), and Si nanorods (SiNR) composed of a larger volume fraction of crystalline Si (c-Si) and a small volume fraction of a-Si resulted from modification of the NaCl crystals. SiNF yielded first-cycle discharge and charge capacities of ∼2,830 and 2,175 mAh·g−1, respectively, at a current rate of 50 mA·g−1 with a first-cycle irreversible loss (FIR loss) of ∼15%–20%. SiNR displayed first-cycle discharge and charge capacities of ∼2,980 and ∼2,500 mAh·g−1, respectively, at a current rate of 50 mA·g−1 with an FIR loss of ∼12%–15%. However, at a current rate of 1 A·g−1, SiNF exhibited a stable discharge capacity of ∼810 mAh·g−1 at the end of 250 cycles with a fade rate of ∼0.11% loss per cycle, while SiNR showed a stable specific discharge capacity of ∼740 mAh·g−1 with a fade rate of ∼0.23% loss per cycle. The morphology of the nanostructures and compositions of the different phases/phase of Si influence the performance of SiNF and SiNR, making them attractive anodes for lithium-ion batteries.

A rapid solid-state synthesis of electrochemically active Chevrel phases (Mo6T8; T = S, Se) for rechargeable magnesium batteries

Carbon nanotubes with their attractive properties, one-dimensional geometry, and their large aspect ratio are ideal candidates for a variety of applications including energy storage, sensing, nanoelectronics, among others. We have studied the growth of carbon nanotubes on copper substrates using a nickel thin film as a catalyst. The catalyst was sputtered in a chamber with a base pressure in the ultra-high-vacuum regime. By adjusting the sputtering parameters, the effects of the morphology and the thickness of the nickel catalyst on the growth of carbon nanotubes have also been investigated. Multiple hydrocarbon sources as carbon feedstock (methane, acetylene and m-xylene), corresponding catalyst precursors and varying temperature conditions were used during chemical vapor deposition (CVD) process to understand and determine the best conditions for growth of carbon nanotubes on copper. Correlation between the thickness of the thin film nickel catalyst and the carbon nanotube diameter is also presented in the study. Characterization techniques used to study the morphology of the CNTs grown on copper include SEM, TEM, HRTEM, Raman Spectroscopy. Results of these studies are outlined and discussed.

Amorphous silicon-carbon based nano-scale thin film anode materials for lithium ion batteries

High energy mechanical milling (HEMM) of a stoichiometric mixture of molybdenum and metal chalcogenides (CuT and MoT2; T = S, Se) followed by heat treatment at elevated temperatures was successfully applied to synthesize Chevrel phases (Cu2Mo6T8; T = S, Se) as positive electrodes for rechargeable magnesium batteries. Differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to understand the phase formation following milling and heat treatment. CuS and Mo were observed to react at 714–800 K and formed an intermediate ternary Chevrel phase (Cu1.83Mo3S4), which further reacted with residual Mo and MoS2 to form the desired Cu2Mo6S8. Quantitative XRD analysis shows the formation of a ∼96%–98% Chevrel phase at 30 min following the milling and heat treatment. The electrochemical performance of de-cuprated Mo6S8 and Mo6Se8 phases were evaluated by cyclic voltammetry (CV), galvanostatic cycling, and electrochemical impedance spectroscopy (EIS). The results of the CV and galvanostatic cycling data showed the expected anodic/cathodic behavior and a stable capacity after the first cycle with the formation of MgxMo6T8 (T = S, Se; 1 ≤ x ≤ 2). EIS at ∼0.1 V intervals for the Mo6S8 electrode during the first and second cycle shows that partial Mg-ion trapping resulted in an increase in charge transfer resistance Re. In contrast, the interfacial resistance Ri remained constant, and no significant trapping was evident during the galvanostatic cycling of the Mo6Se8 electrode. Importantly, the ease of preparation, stable capacity, high Coulombic efficiency, and excellent rate capabilities render HEMM a viable route to laboratory-scale production of Chevrel phases for use as positive electrodes for rechargeable magnesium batteries.