Shubhadeep Pal

Fluorographene based Ultrasensitive Ammonia Sensor

Single molecule detection using graphene can be brought by tuning the interactions via specific dopants. Electrostatic interaction between the most electronegative element fluorine (F) and hydrogen (H) is one of the strong interactions in hydrogen bonding, and here we report the selective binding of ammonia/ammonium with F in fluorographene (FG) resulting to a change in the impedance of the system. Very low limit of detection value of ~0.44 pM with linearity over wide range of concentrations (1 pM–0.1 μM) is achieved using the FG based impedance sensor, andthisscreen printed FG sensor works in both ionized (ammonium) and un-ionized ammonia sensing platforms. The interaction energies of FG and NH3/NH4+ are evaluated using density functional theory calculations and the interactions are mapped. Here FGs with two different amounts of fluorinecontents −~5 atomic% (C39H16F2) and ~24 atomic% (C39H16F12) - are theoretically and experimentally studied for selective, high sensitive and ultra-low level detection of ammonia. Fast responding, high sensitive, large area patternable FG based sensor platform demonstrated here can open new avenues for the development of point-of-care devices and clinical sensors.

Temperature assisted shear exfoliation of layered crystals for the large-scale synthesis of catalytically active luminescent quantum dots

Edge state manipulations of transition metal dichalcogenides of ultra-small sizes are receiving tremendous scientific interest due to their applications in electronics, optoelectronics and energy conversion technologies. Here, we report a novel single step route for the large-scale production of luminescent quantum dots (QDs) of layered materials using a temperature assisted shear exfoliation method. The syntheses of molybdenum disulfide (MoS2) and tungsten disulfide (WS2) QDs are demonstrated, and enhanced hydrogen evolution reaction catalytic activities of QDs in comparison to their bulk and layered counterparts are demonstrated. This synthesis strategy is generalized to other layered structures such as graphite, leading to a bulk production of luminescent monodispersed QDs, enabling their status to the technology readiness level 9.

Transparent flexible lithium ion conducting solid polymer electrolyte

Recent safety threats concerning conventional liquid electrolyte-based Li-ion batteries invoke the search for high ionic conductivity solid electrolytes (SEs) for solid state batteries. Here, the development of a multifunctional polymer SE (ionic conductivity ∼0.03 mS cm−1) is demonstrated and this SE is endowed with other exotic properties such as high Li-ion transport number (∼0.69) with large electrochemical window (2–5 V), high mechanical robustness and flexibility (Youngs modulus ∼1 MPa), visible light transparency (∼85%), and hydrophobicity (contact angle > 100°). Here poly(ethylene oxide) (PEO) and polydimethylsiloxane (PDMS) based polymer complex serves as the Li-ion transport membrane, and lithium perchlorate (LiClO4) as the Li source. The ‘salting in’ phenomenon, induced by the ClO4−–PEO interactions, modifies the crystalline melting temperature of PEO leading to the amorphization of the PEO–PDMS matrix and hence to a high Li-ion conductivity by microstructure modifications. This transparent and flexible SE is shown for its applicability in flexible symmetric capacitors and Li-ion cells without the use of liquid electrolyte interfaces.

Single step, bulk synthesis of engineered MoS2 quantum dots for multifunctional electrocatalysis

Bi- or tri- functional catalysts based on atomic layers are receiving tremendous scientific attention due to their importance in various energy technologies. Recent studies on molybdenum disulphide (MoS2) nanosheets revealed that controlling the edge states and doping/modifying with suitable elements are highly important in tuning the catalytic activities of MoS2. Here we report a bulk, single step method to synthesize metal modified MoS2 quantum dots (QDs). Three elements, namely Fe, Mg and Li, are chosen to study the effects of dopants in the catalytic activities of MoS2. Fe and Mg are found to act like dopants in the MoS2 lattice forming respective doped MoS2 QDs, while Li formed an intercalated MoS2 QD. The efficacy and tunability of these luminescent doped QDs towards various electrocatalytic activities (hydrogen evolution reaction, oxygen evolution reaction and oxygen reduction action) are reported here.

Non-Precious Metal/Metal Oxides and Nitrogen-Doped Reduced Graphene Oxide based Alkaline Water-Electrolysis Cell

The development of strategies for water‐electrolysis half‐cell‐reaction catalysts without the use of precious metals/metal oxides and the synergistic compilation of catalysts for the full‐cell fabrication are receiving tremendous scientific attention. Here, alkaline water‐electrolysis full cells are developed with novel spongy catalysts for both anode and cathode reactions, such as Co3O4 nitrogen‐doped reduced graphene oxide (Co3O4/NrGO) composite sponge for oxygen evolution reaction (OER) and nickel nitrogen‐doped reduced graphene oxide (NiNrGO) for hydrogen evolution reaction (HER). The performance of the developed OER catalyst, Co3O4/NrGO, is compared with that of the commercial one (IrO2) in alkaline medium with a common benchmark cathode catalyst (Pt) and an augmented full‐cell performance is shown from this novel combination (320 mAcm−2 at an operating voltage of 1.9 V for Co3O4/NrGO, with 199 mA cm−2 for IrO2). A water‐electrolysis full cell is developed without the use of HER catalyst Pt, but rather using a porous spongy catalyst, NiNrGO, having a low operating potential with a high stability (270 mA cm−2 at an operating voltage of 1.9 V with a stability tested for more than 9 h). This work opens up the possibilities of designing lightweight water‐electrolysis cells without the use of commercial benchmark precious‐metal catalysts.