Sundaram Chandrasekaran

Highly-ordered maghemite/reduced graphene oxide nanocomposites for high-performance photoelectrochemical water splitting

Highly ordered γ-Fe2O3/reduced graphene oxide (RGO) was synthesized via a facile solution technique combined with calcination at various temperatures. The maghemite iron oxide structure was obtained on the GO surface and improved crystallinity of γ-Fe2O3 was observed as the calcination temperature increased. The prepared highly ordered maghemite structure on RGO exhibited an excellent water splitting performance under UV light (∼360 nm) illumination. The photocurrent density of RGO/γ-Fe2O3 calcined at 500 °C was 6.74 mA cm−2 vs. RHE and a high incident photon to current conversion efficiency (IPCE) of 4.7%, was achieved. This photocurrent density and the IPCE values are 3.7 times and 4 times higher than that of pristine iron oxide, respectively.

Comparative supercapacitance performance of CuO nanostructures for energy storage device applications

In the present study, three different morphologies of copper oxide (CuO) nanostructures; bud-, flower- and plate-shaped CuO structures were synthesized by a simple chemical method. Binder-included pseudocapacitor electrodes were prepared using bud- and flower-shaped CuO structures whereas, directly grown CuO-nanoplates on Ni foam were used as a binder-free electrode in a three-electrode setup for electrochemical studies. Remarkably, the binder-free CuO nanoplates electrode exhibited excellent specific capacitance of 536 F g−1 at a current density of 2 A g−1, whereas the binder-included electrodes of bud- and flower-shaped CuO exhibited 230 F g−1 and 296 F g−1, respectively, at a current density of 0.7 A g−1 in a 6 M KOH electrolyte. The cycling retention test and charge/discharge stability for the binder-free CuO nanoplates electrode showed 94% capacity retention after 2000 cycles and capacitance loss of only 11.3% over ∼1000 cycles at a current density of 4 A g−1 from charge/discharge measurements. Also, the binder-free CuO electrode showed higher energy and power densities of 29.4 W h kg−1 and 12.7 W kg−1, respectively, at 1.96 A g−1 in an asymmetrical device, when compared to the binder-included electrode of flower-shaped CuO.

High performance bifunctional electrocatalytic activity of a reduced graphene oxide–molybdenum oxide hybrid catalyst

The advances in cost effective, highly active and stable electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) remain the major issues for the commercialization of metal air-batteries and alkaline fuel cells. In this aspect, a facile hydrothermal route was developed to prepare nonprecious metal electrocatalysts including pristine MoO3 rods, nanospheres, and their hybrids with reduced graphene oxide (rGO). This is the first report of the use of rGO coupled with hexagonal MoO3 nanocrystals that act as both ORR and OER catalysts. The rGO–MoO3 sphere hybrid catalyst exhibited excellent catalytic activity toward both the ORR and OER compared to pristine MoO3 rods, MoO3 spheres and rGO–MoO3 rods. In addition, the rGO–MoO3 nanosphere hybrid exhibited excellent catalytic activity, long-term durability, and CO tolerance compared to a high quality commercial Pt/C catalyst. This makes the GMS hybrid composite a highly promising candidate for high-performance non-precious metal-based bi-functional electrocatalysts with low cost and high efficiency for electrochemical energy conversion. The enhanced activity of the rGO–MoO3 nanosphere hybrid is due mainly to the enhanced structural openness in the tunnel structure of the hexagonal MoO3 when it is coupled with rGO.

Advanced Nano-Structured Materials for Photocatalytic Water Splitting

The production of oxygen and hydrogen from solar water splitting has been considered to be an ultimate solution for energy and environmental issues, and over the past few years, nano-sized semiconducting metal oxides alone and with graphene have been shown to have great promise for use in photocatalytic water splitting. It is challenging to find ideal materials for photoelectrochemical water splitting, and these have limited commercial applicability due to critical factors, including their physico-chemical properties, the rate of charge-carrier recombination and limited light absorption. This review article discusses these main features, and recent research progress and major factors affect the performance of the water splitting reaction. The mechanism behind these interactions in transition metal oxides and graphene based nano-structured semiconductors upon illumination has been discussed in detail, and such characteristics are relevant to the design of materials with a superior photocatalytic response towards UV and visible light.