Nitin K. Chaudhari

Homogeneous Deposition of Platinum Nanoparticles on Carbon Black for Proton Exchange Membrane Fuel Cell

A simple and efficient approach has been developed for synthesis of carbon-supported Pt nanoparticles (NPs) that combines homogeneous deposition (HD) of Pt complex species through a gradual increase of pH realized by in situ hydrolysis of urea and subsequent uniform reduction by ethylene glycol (EG) in a polyol process, giving control over the size and dispersion of Pt NPs. With increasing amount of urea in the starting Pt salt aqueous solution, the size of Pt complex species decreases and so does that of the metallic Pt NPs. The decrease in size of the Pt species is likely attributable to two determining factors: the steric contraction effect and the electrostatic charge effect. The excellent electrocatalysis ability of the Pt catalysts produced by HD-EG is demonstrated through the determination of electrochemical surface area and fuel-cell polarization performance. The Pt NPs deposited on Vulcan XC-72 (VC) carbon black by the HD-EG strategy show smaller size with more uniform dispersion, higher Pt utilization efficiency, and considerably improved fuel-cell polarization performance compared with the Pt NPs prepared by conventional sodium borohydride reduction or by a microwave-assisted polyol approach. Particularly important and significant is that this HD-EG method is very efficient for the synthesis of high Pt loading catalysts with tunable NP size and uniform particle dispersion. A high metal loading catalyst such as Pt(60 wt %)/VC fabricated by the HD-EG method outperforms ones with mid-to-low metal loadings (i.e., 40 and 20 wt %), even at a very low catalyst loading of 0.2 mg of Pt cm(-2) at the cathode, which is for the first time reported for the VC-supported Pt catalysts.

Incorporating hierarchical nanostructured carbon counter electrode into metal-free organic dye-sensitized solar cell.

Hierarchical nanostructured carbon with a hollow macroporous core of ca. 60 nm in diameter in combination with mesoporous shell of ca. 30 nm in thickness has been explored as counter electrode in metal-free organic dye-sensitized solar cell. Compared with other porous carbon counterparts such as activated carbon and ordered mesoporous carbon CMK-3 and Pt counter electrode, the superior structural characteristics including large specific surface area and mesoporous volume and particularly the unique hierarchical core/shell nanostructure along with 3D large interconnected interstitial volume guarantee fast mass transport in hollow macroporous core/mesoporous shell carbon (HCMSC), and enable HCMSC to have highly enhanced catalytic activity toward the reduction of I(3)(-), and accordingly considerably improved photovoltaic performance. HCMSC exhibits a V(oc) of 0.74 V, which is 20 mV higher than that (i.e., 0.72 V) of Pt. In addition, it also demonstrates a fill factor of 0.67 and an energy conversion efficiency of 7.56%, which are markedly higher than those of its carbon counterparts and comparable to that of Pt (i.e., fill factor of 0.70 and conversion efficiency of 7.79%). Furthermore, HCMSC possesses excellent chemical stability in the liquid electrolyte containing I(-)/I(3)(-) redox couples, namely, after 60 days of aging, ca. 87% of its initial efficiency is still achieved by the solar cell based on HCMSC counter electrode.

Heteroatom-doped highly porous carbon from human urine

Human urine, otherwise potentially polluting waste, is an universal unused resource in organic form disposed by the human body. We present for the first time “proof of concept” of a convenient, perhaps economically beneficial, and innovative template-free route to synthesize highly porous carbon containing heteroatoms such as N, S, Si, and P from human urine waste as a single precursor for carbon and multiple heteroatoms. High porosity is created through removal of inherently-present salt particles in as-prepared “Urine Carbon” (URC), and multiple heteroatoms are naturally doped into the carbon, making it unnecessary to employ troublesome expensive pore-generating templates as well as extra costly heteroatom-containing organic precursors. Additionally, isolation of rock salts is an extra bonus of present work. The technique is simple, but successful, offering naturally doped conductive hierarchical porous URC, which leads to superior electrocatalytic ORR activity comparable to state of the art Pt/C catalyst along with much improved durability and methanol tolerance, demonstrating that the URC can be a promising alternative to costly Pt-based electrocatalyst for ORR. The ORR activity can be addressed in terms of heteroatom doping, surface properties and electrical conductivity of the carbon framework.

Cube‐like α‐Fe2O3 Supported on Ordered Multimodal Porous Carbon as High Performance Electrode Material for Supercapacitors

Well-dispersed cube-like iron oxide (α-Fe2O3) nanoparticles (NPs) supported on ordered multimodal porous carbon (OMPC) are synthesized for the first time by a facile and efficient glycine-assisted hydrothermal route. The effect of OPMC support on growth and formation mechanism of the Fe2O3 NPs is discussed. OMPC as a supporting material plays a pivotal role of controlling the shape, size, and dispersion of the Fe2O3 NPs. As-synthesized α-Fe2O3/OMPC composites reveal significant improvement in the performance as electrode material for supercapacitors. Compared to the bare Fe2O3 and OMPC, the composite exhibits excellent cycling stability, rate capability, and enhanced specific capacitances of 294 F g(-1) at 1.5 A g(-1), which is twice that of OMPC (145 F g(-1)) and about four times higher than that of bare Fe2O3 (85 F g(-1)). The improved electrochemical performance of the composite can be attributed to the well-defined structure, high conductivity, and hierarchical porosity of OMPC as well as the unique α-Fe2O3 NPs with cube-like morphology well-anchored on the OMPC support, which makes the composite a promising candidate for supercapacitors.

Peroxidase mimic activity of hematite iron oxides (α-Fe2O3) with different nanostructures

Enzyme mimics have garnered considerable attention as they can overcome some serious disadvantages associated with the natural enzymes. In recently developed sphere and rod shaped iron oxide peroxidase mimic nanoparticles, the influence of physical parameters such as shape, size and surface area on the catalytic performance was not clearly demonstrated. In order to better understand the influence of physical parameters on the enzyme mimic activity of iron oxide nanoparticles, the present study was initiated using three different shaped hematiteα-Fe2O3 nanostructures, particularly hexagonal prism, cube-like and rods as model systems. A comparative account of kinetic parameters (Km, Vmax and Kcat) of the peroxidase mimic activity by the various α-Fe2O3 nanostructures indicated that the enzymatic potential of these nanoparticles increased from hexagonal prism to rods, via cube-like, suggesting that one-dimensional particles act as a more efficient enzyme mimic system compared to their multi-dimensional counterparts. Surface area is likely to be a key physical aspect responsible for the enzyme mimic activity. Interestingly, however, particles with lower surface area showed better catalytic performance in the case of one-dimensional rod structure. Upon further analysis of the one-dimensional rods, additional physical properties such as porosity and pore shape also seem to have a significant contribution to their catalytic activity.

Easy synthesis and characterization of single-crystalline hexagonal prism-shaped hematite α-Fe2O3 in aqueous media

A simple, mild and environmentally friendly one-pot aqueous synthesis route using urea devoid of surfactant and chelating agents is demonstrated for the first time to fabricate high yield crystalline uniform hexagonal prism-shaped weakly magnetic α-Fe2O3nanocrystals. As synthesized α-Fe2O3nanocrystals show ferromagnetic behavior with coercivity values of 0.8 and 0.2 T at 5 and 300 K, respectively. The urea and reaction temperature plays a crucial role, regulating the morphology and the size.

MXene: An emerging two-dimensional material for future energy conversion and storage applications

The development of two-dimensional (2D) high-performance electrode materials is the key to new advances in the fields of energy conversion and storage. MXenes, a new intriguing family of 2D transition metal carbides, nitrides, and carbonitrides, have recently received considerable attention due to their unique combination of properties such as high electrical conductivity, hydrophilic nature, excellent thermal stability, large interlayer spacing, easily tunable structure, and high surface area. In this review, we discuss how 2D MXenes have emerged as efficient and economical nanomaterials for future energy applications. We highlight the promising potential of these materials in energy conversion and storage applications, such as water electrolyzers, lithium ion batteries, and supercapacitors. Finally, we present an outlook of the future development of MXenes for sustainable energy technologies.

Solvent controlled synthesis of new hematite superstructures with large coercive values

Various morphologies of hematite (α-Fe2O3) superstructures such as grape, cube, dumbbell, and microsphere shapes have been reproducibly obtained by a caffeine-assisted environmentally benign one-step hydrothermal synthesis route in the presence of different solvents. The hematite superstructures are formed by self-assembled aggregation of smaller particles of a few nanometres. It is demonstrated that systematic control over the studied experimental conditions (caffeine, solvents, concentration, reaction time, etc.) efficiently alters the structural and magnetic properties of the iron oxide nanostructures. In particular, the solvent plays a key role for overall architecture of the oxide particles under different polar conditions. Magnetic hysteresis measurements reveal that the shape of nanostructures has a remarkable effect on the magnetic properties at room temperature. Interestingly, the coercive values are much higher at room temperature than those at lower temperature for the α-Fe2O3 superstructures prepared in this work.

Urine to highly porous heteroatom-doped carbons for supercapacitor: A value added journey for human waste

Obtaining functionalized carbonaceous materials, with well-developed pores and doped heteroatoms, from waste precursors using environmentally friendly processes has always been of great interest. Herein, a simple template-free approach is devised to obtain porous and heteroatom-doped carbon, by using the most abundant human waste, “urine”. Removal of inherent mineral salts from the urine carbon (URC) makes it to possess large quantity of pores. Synergetic effect of the heteroatom doping and surface properties of the URC is exploited by carrying out energy storage application for the first time. Suitable heteroatom content and porous structure can enhance the pseudo-capacitance and electric double layer capacitance, eventually generating superior capacitance from the URC. The optimal carbon electrode obtained particularly at 900 °C (URC-900) possesses high BET surface area (1040.5 m2g−1), good conductivity, and efficient heteroatom doping of N, S, and P, illustrating high specific capacitance of 166 Fg−1 at 0.5 Ag−1 for three-electrode system in inorganic electrolyte. Moreover, the URC-900 delivers outstanding cycling stability with only 1.7% capacitance decay over 5,000 cycles at 5 Ag−1. Present work suggests an economical approach based on easily available raw waste material, which can be utilized for large-scale production of new age multi-functional carbon nanomaterials for various energy applications.

Correction: MXene: an emerging two-dimensional material for future energy conversion and storage applications

Correction for ʻMXene: an emerging two-dimensional material for future energy conversion and storage applicationsʼ by Nitin K. Chaudhari et al., J. Mater. Chem. A, 2017, 5, 24564–24579.