Bharat Gattu

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

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.

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

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.

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

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 New Lamination and doping Concepts for Enhanced Li – S Battery Performance

• Objective: The project aims to develop commercially viable lithium battery technologies with a cell level specific energy of 500 Wh/kg through innovative electrode and cell designs that enable the extraction of the maximum capacity from advanced electrode materials. In addition, the project aims to achieve 1000 cycles for the developed technologies Impact: • The results of this project will be used for the development of technologies that will significant increase the energy density, cycle life and reduce the cost of rechargeable batteries for electric vehicles Title of Graph: Battery500 team developed Cryo TEM to study the Li metal anode for high energy density batteries PI/Co-PI Jun Liu (PNNL) and Yi Cui (Stanford University)

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