Gopinathan M. Anilkumar

Self-Organized Macroporous Carbon Structure Derived from Phenolic Resin via Spray Pyrolysis for High-Performance Electrocatalyst

The synthesis and evaluation of porous carbon derived from phenolic resin using a fast and facile spray pyrolysis method has been studied for use as a new electrocatalyst support material. By adding polystyrene latex nanoparticles as a template to the phenolic resin precursor, self-organized macroporous carbon structure was first developed. The mass ratio of phenolic resin to PSL at 0.625 gave the optimum porous morphology. Pt nanoparticles (∼20 wt %) were grown on the carbon surface using a standard industrial impregnation method. Well-dispersed Pt nanoparticles of average size 3.91 nm were observed on the surface of porous carbon particles. The high catalytic performance of porous Pt/C electrocatalyst was confirmed by the high mass activity and electrochemically active surface area, which were 450.81 mA mg(-1)-Pt and 81.78 m(2) g(-1)-Pt, respectively. The porous Pt/C catalyst obtains two times higher mass activity than that of the commercial Pt/C catalyst and performs excellent durability under acid conditions.

Aerosol synthesis of self-organized nanostructured hollow and porous carbon particles using a dual polymer system.

A facile method for designing and synthesizing nanostructured carbon particles via ultrasonic spray pyrolysis of a self-organized dual polymer system comprising phenolic resin and charged polystyrene latex is reported. The method produces either hollow carbon particles, whose CO2 adsorption capacity is 3.0 mmol g(-1), or porous carbon particles whose CO2 adsorption capacity is 4.8 mmol g(-1), although the two particle types had similar diameters of about 360 nm. We investigate how the zeta potential of the polystyrene latex particles, and the resulting electrostatic interaction with the negatively charged phenolic resin, influences the particle morphology, pore structure, and CO2 adsorption capacity.

One-Dimensional Assembly of Conductive and Capacitive Metal Oxide Electrodes for High-Performance Asymmetric Supercapacitors

A one-dimensional morphology comprising nanograins of two metal oxides, one with higher electrical conductivity (CuO) and the other with higher charge storability (Co3O4), is developed by electrospinning technique. The CuO-Co3O4 nanocomposite nanowires thus formed show high specific capacitance, high rate capability, and high cycling stability compared to their single-component nanowire counterparts when used as a supercapacitor electrode. Practical symmetric (SSCs) and asymmetric (ASCs) supercapacitors are fabricated using commercial activated carbon, CuO, Co3O4, and CuO-Co3O4 composite nanowires, and their properties are compared. A high energy density of ∼44 Wh kg-1 at a power density of 14 kW kg-1 is achieved in CuO-Co3O4 ASCs employing aqueous alkaline electrolytes, enabling them to store high energy at a faster rate. The current methodology of hybrid nanowires of various functional materials could be applied to extend the performance limit of diverse electrical and electrochemical devices.

Hydrophobic and Metallophobic Surfaces: Highly Stable Non-wetting Inorganic Surfaces Based on Lanthanum Phosphate Nanorods.

Metal oxides, in general, are known to exhibit significant wettability towards water molecules because of the high feasibility of synergetic hydrogen-bonding interactions possible at the solid-water interface. Here we show that the nano sized phosphates of rare earth materials (Rare Earth Phosphates, REPs), LaPO4 in particular, exhibit without any chemical modification, unique combination of intrinsic properties including remarkable hydrophobicity that could be retained even after exposure to extreme temperatures and harsh hydrothermal conditions. Transparent nanocoatings of LaPO4 as well as mixture of other REPs on glass surfaces are shown to display notable hydrophobicity with water contact angle (WCA) value of 120° while sintered and polished monoliths manifested WCA greater than 105°. Significantly, these materials in the form of coatings and monoliths also exhibit complete non-wettability and inertness towards molten metals like Ag, Zn, and Al well above their melting points. These properties, coupled with their excellent chemical and thermal stability, ease of processing, machinability and their versatile photo-physical and emission properties, render LaPO4 and other REP ceramics utility in diverse applications.

Aniosotropically Organized LDH on PVDF: A Geometrically Templated Electrospun Substrate for Advanced Anion Conducting Membranes

A bioinspired geometric templating of an electrospun PVDF substrate with hexagonal platelets of Mg-Al layered double hydroxide (LDH), an intrinsic anion conductor, is presented. The distinctive morphology restructures the internal pore geometry and modulates the dynamic wetting profile of PVDF, transforming it into a highly functional substrate for SAFC anion conducting membranes. The membrane fabricated with PVDF-LDH substrate exhibited exceptionally high durability (>140 °C), high anionic conductivity, ion exchange capacity (IEC), restricted swelling, and improved tensile strength, overcoming critical challenges associated with PVDF electrospun substrates and validating its immense potential as a high-temperature-stable and durable substrate for advanced fuel cell membrane applications.

Morphologically and compositionally tuned lithium silicate nanorods as high-performance carbon dioxide sorbents

The effective capturing of carbon dioxide using regenerable high capacity sorbents is a prerequisite for industrial applications aiming at CO2 capture and sequestration. The removal of CO2 directly from chemical reaction environments at high temperature is a less energy intensive method of its separation with the added benefit of improved efficiency in equilibrium limited reactions. However, the separation of CO2 at the typical reaction temperatures of 573–1073 K is a challenging task due to the non-availability of absorbents with kinetics comparable to reaction rates. Moreover their poor durability due to sintering and particle growth on prolonged use at high temperature is also an impediment to their practical application. Herein, we demonstrate the development of an efficient CO2 absorbent material, made of Li4SiO4 nanorods, with ultrafast sorption kinetics as well as remarkable durability. These nanorods enabled easier surface reaction with CO2 due to shorter diffusion pathways for lithium from the bulk to the surface of the rods permitting extremely fast absorption of CO2. Furthermore, the compositional tuning of the materials helped to realize absorbents with extraordinary CO2 absorption rates of 0.72 wt% s−1 at 100% CO2/923 K. The exceptional performance of these absorbents at lower temperatures (573–823 K) as well as lower CO2 pressures (0.15 atm) demonstrates their potential in practical CO2 separation applications.

Mg–Al layered double hydroxides: a correlation between synthesis-structure and ionic conductivity

Mg–Al based layered double hydroxide (LDH) samples with distinct morphology and crystallinity were synthesized by controlling urea assisted homogeneous precipitation conditions. The obtained samples were characterized with XRD, TG-DTA, FESEM, CHN and XPS analysis and compared with the ionic conductivity values measured at 80 °C under various humidity conditions. The results revealed that LDH particles with small size and low crystallinity were able to adsorb more water resulting in high ionic conductivity. In contrast, LDH particles with large size and high crystallinity showed low ionic conductivity. However, delamination of such highly crystalline LDH particles was found to be an extremely effective method to increase the ionic conductivity.

Zn2+ substitution effects in layered double hydroxide (Mg(1−x)Znx)2Al: textural properties, water content and ionic conductivity

Recently, layered double hydroxides (LDHs) have been studied as anion conductors for fuel cell applications because of their anion exchange properties and better thermal stability (up to 150 °C) than those of anion exchange polymers. However, the conductivity of the LDHs is very low, under 10−3 S cm−1 at room temperature, and the mechanism of anion conduction has not been explained clearly. In the present study, we investigate the physical properties of LDHs affecting anion conductivity by synthesizing trimetallic LDHs, (Mg(1−x)Znx)2Al–CO32− with different ratios of Mg2+ and Zn2+. The amount of anion in these LDHs and the particle size were kept the same in all LDHs by controlling the amount of Al3+ and the synthesis methods, respectively. The LDHs synthesized were characterized using techniques such as XRD, ICP-AES, TEM, zeta-potential measurements, XPS and TG and also by measuring the adsorbed water content in a range of temperatures and humidities. The ratio of Zn2+ to divalent metal in the LDH framework affected the interlayer distance and the water content. Among the series of LDHs of (Mg(1−x)Znx)2Al–CO32−, the ones with a Zn2+ : divalent metal ratio of around 0.5 presented the largest interlayer distance, the largest amount of adsorbed water and the highest ion conductivity. Interestingly, the anion conductivity showed a good correlation with the interlayer distance and the adsorbed water content. The anion conductivity increased as the interlayer distance increased and also as the amount of adsorbed water increased. These results imply that the anion conduction may occur primarily in the interlayer space and the adsorbed water assists the anion conduction.

Direct synthesis of a carbon nanotube interpenetrated doped porous carbon alloy as a durable Pt-free electrocatalyst for the oxygen reduction reaction in an alkaline medium

Direct synthesis of highly durable carbon nanotube interpenetrated porous carbon alloy electrocatalysts for the oxygen reduction reaction (ORR) from a single precursor, trimetallic zeolitic imidazole framework (t-ZIF), is reported. The use of a single precursor improves the uniform distribution of active reaction centres which is crucial for ORR catalysts. The t-ZIF has Fe, Co and Zn metal centres and 2-methylimidazole as a ligand. Carbonisation of the t-ZIF under an inert atmosphere produces nitrogen and Fe/Co–Nx doped carbon/carbon nanotubes alloyed with metal/metal oxide particles encased inside the carbon structures (FeCo-NCZ). The presence of Zn in the t-ZIF induces porosity in carbon during the carbonisation process. The peculiar morphology with a reasonably high surface area provides efficient mass transport and interpenetrated carbon nanotube assisted fast electron transport in the catalyst. X-ray photoelectron spectroscopy reveals that FeCo-NCZ is enriched with different possible active reaction centres such as pyridinic, graphitic and Fe/Co–Nx type nitrogen coordination on the catalyst surface. The ORR activity of FeCo-NCZ in oxygen saturated 0.1 M KOH was comparable to/higher than that of the reference Pt/C catalyst. The displayed onset potential (1.04 V vs. the RHE) and half-wave potential (0.91 V vs. the RHE) of FeCo-NCZ are more positive compared to those of Pt/C and other control-samples. It is noteworthy that the dioxygen reduction kinetics of FeCo-NCZ are comparable to those of Pt/C as evident from the Tafel slope and oxygen reduction follows a four electron pathway. More interestingly, FeCo-NCZ shows better fuel tolerance and electrochemical stability even at 60 °C compared to Pt/C under alkaline conditions.