R. Fernandes

Hybrid Perovskite Quantum Nanostructures Synthesized by Electrospray Antisolvent–Solvent Extraction and Intercalation

Perovskites based on organometal lead halides have attracted great deal of scientific attention recently in the context of solar cells and optoelectronic devices due to their unique and tunable electronic and optical properties. Herein, we show that the use of electrospray technique in conjunction with the antisolvent-solvent extraction leads to novel low-dimensional quantum structures (especially 2-D nanosheets) of CH3NH3PbI3- and CH3NH3PbBr3-based layered perovskites with unusual luminescence properties. We also show that the optical bandgaps and emission characteristics of these colloidal nanomaterials can be tuned over a broad range of visible spectral region by compositional tailoring of mixed-halide (I- and Br-based) perovskites.

NiS1.97: A New Efficient Water Oxidation Catalyst for Photoelectrochemical Hydrogen Generation.

NiS1.97, a sulfur-deficient dichalcogenide, in nanoscale form, is shown to be a unique and efficient photoelectrochemical (PEC) catalyst for H2 generation by water splitting. Phase pure NiS1.97 nanomaterial is obtained by converting nickel oxide into sulfide by controlled sulfurization method, which is otherwise difficult to establish. The defect states (sulfur vacancies) in this material increase the carrier density and in turn lead to favorable band line-up with respect to redox potential of water, rendering it to be an effective photoelectrochemical catalyst. The material exhibits a remarkable PEC performance of 1.25 mA/cm(2) vs NHE at 0.68 V in neutral pH, which is almost 1000 times superior as compared with that of the stoichiometric phase of NiS2. The latter is well-known to be a cocatalyst but not as a primary PEC catalyst.

Natural-gel derived, N-doped, ordered and interconnected 1D nanocarbon threads as efficient supercapacitor electrode materials†

A natural hydrogel has been successfully templated into a nitrogen doped interconnected 1D nanostructure by a hard templating method using an SBA-15 template. With urea as the nitrogen doping agent a high nitrogen percentage of 7.0 at% was achieved. Urea was seen to play a role in increasing the order and compactness of the final carbon product. By snipping the carbon into nano 1D threads a fairly high surface area up to 837 m2 g−1 was achieved with a high density of mesopores characterized by a pore size of 4–5 nm and a pore volume of 0.87–0.89 cm3 g−1. The mesoporous architecture was channel type with an average width of ∼4 nm. With these characteristics the material represents an architecture that is adequate for high power supercapacitor electrode applications. Indeed, it was seen to deliver a capacity of 285 F g−1 at a current density of 1 A g−1 with only a small percentage loss in this initial capacitance value at a higher current density of 10 A g−1 (210 F g−1). These values suggest a high capacity retention of 74% up to 10 A g−1 and 62% capacitance retention (176 F g−1) at an extremely high current density of 40 A g−1. The cycling stability of the material is also commendable as 96% capacity retention is recorded after 2000 charging–discharging cycles implemented at a high current density of 10 A g−1.

Harvesting Clean Energy Through H2 Production Using Cobalt-Boride-Based Nanocatalyst

Increase in the energy requirement and emission of greenhouse gases have been a growing concern. Hydrogen is recognized as a clean fuel and a promising solution for energy storage. At present, hydrogen required for fuel cell (FC) is mostly produced at industrial scales using the steam reforming of natural gas. These industries possibly leave CO and CO2 into the atmosphere, which are the major known reasons for the devastating climate changes witnessed today. Moreover, improper separation of these carbon contaminants from H2, especially CO (even at ppm level), affects the performance of FC by catalyst poisoning. “Hydrolysis of chemical hydrides” and “electrochemical water splitting,” through renewable energy sources, are considered as the cleanest and simplest techniques to produce FC grade H2 for onboard and off-board applications, respectively. Herein, the role of low-cost cobalt-boride (Co-B)-based nanocatalysts for both these applications is summarized.